Co-reporter:S. O. Dozie-Nwachukwu;J. D. Obayemi
Journal of Materials Science: Materials in Medicine 2017 Volume 28( Issue 9) pp:143
Publication Date(Web):17 August 2017
DOI:10.1007/s10856-017-5943-2
This paper explores the adhesion of biosynthesized gold nanoparticles (AuNPs) and gold (Au) nanoparticle/prodigiosin (PG) drug nanoparticles to breast cancer cells (MDA-MB-231 cells). The AuNPs were synthesized in a record time (less than 30 s) from Nauclea latifolia leaf extracts, while the PG was produced via bacterial synthesis with Serratia marcescens sp. The size distributions and shapes of the resulting AuNPs were characterized using transmission electron microscopy (TEM), while the resulting hydrodynamic diameters and polydispersity indices were studied using dynamic light scattering (DLS). Atomic Force Microscopy (AFM) was used to study the adhesion between the synthesized gold nanoparticles (AuNPs)/LHRH-conjugated AuNPs and triple negative breast cancer cells (MDA-MB-231 cells), as well as the adhesion between LHRH-conjugated AuNP/PG drug and MDA-MB-231 breast cancer cells. The adhesion forces between LHRH-conjugated AuNPs and breast cancer cells are shown to be five times greater than those between AuNPs and normal breast cells. The increase in adhesion is shown to be due to the over-expression of LHRH receptors on the surfaces of MDA-MB-231 breast cancer cells, which was revealed by confocal immuno-fluorescence microscopy. The implications of the results are then discussed for the selective and specific targeting and treatment of triple negative breast cancer.
Co-reporter:Y. Danyuo;O. E. Oberaifo;J. D. Obayemi
Journal of Materials Science: Materials in Medicine 2017 Volume 28( Issue 4) pp:
Publication Date(Web):
DOI:10.1007/s10856-017-5866-y
Co-reporter:Y. Danyuo;O. E. Oberaifo;J. D. Obayemi
Journal of Materials Science: Materials in Medicine 2017 Volume 28( Issue 4) pp:
Publication Date(Web):
DOI:10.1007/s10856-017-5866-y
Co-reporter:Y. Danyuo;O. E. Oberaifo;J. D. Obayemi
Journal of Materials Science: Materials in Medicine 2017 Volume 28( Issue 4) pp:61
Publication Date(Web):01 March 2017
DOI:10.1007/s10856-017-5866-y
The kinetics of degradation and sustained cancer drugs (paclitaxel (PT) and prodigiosin (PG)) release are presented for minirods (each with diameter of ~5 and ~6 mm thick). Drug release and degradation mechanisms were studied from solvent-casted cancer drug-based minirods under in vitro conditions in phosphate buffer solution (PBS) at a pH of 7.4. The immersed minirods were mechanically agitated at 60 revolutions per minute (rpm) under incubation at 37 °C throughout the period of the study. The kinetics of drug release was studied using ultraviolet visible spectrometry (UV-Vis). This was used to determine the amount of drug released at 535 nm for poly(lactic-co-glycolic acid) loaded with prodigiosin (PLGA-PG) samples, and at 210 nm, for paclitaxel-loaded samples (PLGA-PT). The degradation characteristics of PLGA-PG and PLGA-PT are elucidated using optical microscope as well as scanning electron microscope (SEM). Statistical analysis of drug release and degradation mechanisms of PLGA-based minirods were performed. The implications of the results are discussed for potential applications in implantable/degradable structures for multi-pulse cancer drug delivery.
Co-reporter:Y. Danyuo;O. E. Oberaifo;J. D. Obayemi
Journal of Materials Science: Materials in Medicine 2017 Volume 28( Issue 4) pp:61
Publication Date(Web):01 March 2017
DOI:10.1007/s10856-017-5866-y
The kinetics of degradation and sustained cancer drugs (paclitaxel (PT) and prodigiosin (PG)) release are presented for minirods (each with diameter of ~5 and ~6 mm thick). Drug release and degradation mechanisms were studied from solvent-casted cancer drug-based minirods under in vitro conditions in phosphate buffer solution (PBS) at a pH of 7.4. The immersed minirods were mechanically agitated at 60 revolutions per minute (rpm) under incubation at 37 °C throughout the period of the study. The kinetics of drug release was studied using ultraviolet visible spectrometry (UV-Vis). This was used to determine the amount of drug released at 535 nm for poly(lactic-co-glycolic acid) loaded with prodigiosin (PLGA-PG) samples, and at 210 nm, for paclitaxel-loaded samples (PLGA-PT). The degradation characteristics of PLGA-PG and PLGA-PT are elucidated using optical microscope as well as scanning electron microscope (SEM). Statistical analysis of drug release and degradation mechanisms of PLGA-based minirods were performed. The implications of the results are discussed for potential applications in implantable/degradable structures for multi-pulse cancer drug delivery.
Co-reporter:John D. Obayemi, Jingjie Hu, Vanessa O. Uzonwanne, Olushola S. Odusanya, Karen Malatesta, Nicolas Anuku, Winston O. Soboyejo
Journal of the Mechanical Behavior of Biomedical Materials 2017 Volume 68(Volume 68) pp:
Publication Date(Web):1 April 2017
DOI:10.1016/j.jmbbm.2017.02.004
•Ligand-conjugation of biosynthesized magnetite nanoparticles (BMNPs).•Overexpression of LHRH and EPhA2 receptors on the surfaces of breast cancer.•Adhesion forces of Ligand-conjugated BMNPs and CMNPs nanoparticles to breast cancer.•Insights for potential screening of breast cancer ligands for specific targeting.This paper presents the results of an experimental study of the adhesion forces between components of model conjugated magnetite nanoparticle systems for improved selectivity in the specific targeting of triple negative breast cancer. Adhesion forces between chemically synthesized magnetite nanoparticles (CMNPs), biosynthesized magnetite nanoparticles (BMNPs), as well as their conjugated systems and triple negative breast cancer cells (MDA-MB-231) or normal breast cells (MCF 10A) are elucidated at a nanoscale. In all cases, the BMNPs had higher adhesion forces (to breast cancer cells and normal breast cells) than CMNPs. The adhesion of LHRH-conjugated BMNPs or BSA-conjugated BMNPs to cancer cells is shown to be about 6 times to that of normal breast cells. The increase in adhesion forces between luteinizing hormone-releasing hormone, LHRH- or EphA2, a breast specific antibody(BSA)-conjugated BMNPs to breast cancer cells is attributed to van der Waals interactions between the peptides/antibodies from the conjugated nanoparticles and the over-expressed receptors (revealed using immunofluorescence staining) on the surfaces of the breast cancer. The implications of the results are discussed for the selectivity and specificity of breast cancer targeting by ligand-conjugated BMNPs.Download high-res image (134KB)Download full-size image
Co-reporter:S.O. Dozie-Nwachukwu, Y. Danyuo, J.D. Obayemi, O.S. Odusanya, K. Malatesta, W.O. Soboyejo
Materials Science and Engineering: C 2017 Volume 71() pp:268-278
Publication Date(Web):1 February 2017
DOI:10.1016/j.msec.2016.09.078
•Prodigiosin of ~ 92.8% purity was extracted from locally isolated Serratia marcescens.•This approach reduces the cost and ensure availability of drugs for cancer treatment.•High encapsulation efficiency which increased with increasing drug:polymer ratio•The percentage yield was generally poor due to the recovery process.•Prodigiosin greatly reduced the viability of the breast cancer cell line (MDA-MB-231).The encapsulation of drugs in polymeric materials has brought opportunities to the targeted delivery of chemotherapeutic agents. These polymeric delivery systems are capable of maximizing the therapeutic activity, as well as reducing the side effects of anti-cancer agents. Prodigiosin, a secondary metabolite extracted from the bacteria, Serratia marcescens, exhibits anti-cancer properties. Prodigiosin-loaded chitosan microspheres were prepared via water-in-oil (w/o) emulsion technique, using glutaraldehyde as a cross-linker. The morphologies of the microspheres were studied using scanning electron microscopy. The average sizes of the microspheres were between 40 μm and 60 μm, while the percentage yields ranged from 42 ± 2% to 55.5 ± 3%. The resulting encapsulation efficiencies were between 66.7 ± 3% and 90 ± 4%. The in-vitro drug release from the microspheres was characterized by zeroth order, first order and Higuchi and Korsmeyer-Peppas models.
Co-reporter:E. K. Arthur;E. Ampaw;M. G. Zebaze Kana;A. R. Adetunji
Waste and Biomass Valorization 2016 Volume 7( Issue 3) pp:603-614
Publication Date(Web):2016 June
DOI:10.1007/s12649-016-9479-3
This paper presents the results of an experimental study of the effects of biocyaniding with dried cassava leaves obtained from Manihot spp. with BaCO3 energizer. These are processed and used for the surface hardening of AISI 8620 steel. The case microstructures associated with carbo-nitriding are elucidated along with the effects of bio-cyaniding on the microstructure, microhardness and wear properties of the carbo-nitrided surfaces. The bio-processed waste (B-PW) was diffused (by heat treatment) into the surfaces of AISI 8620 steel using four different powder sizes (212, 300, 600 and 850 µm) and four different temperatures (750, 800, 850 and 900 °C). The resulting microstructures and micro-hardness profiles were then characterized along with the pin-on-disk wear behavior of the “case microstructures” that were formed. Superficial hardness and wear resistance were observed to increase with increasing particle size of B-PW and increasing pack cyaniding temperature. Finally, the wear mechanisms were also investigated by using scanning electron observations of the worn surfaces of the disks. The implications of the results are discussed for value addition to cassava waste.
Co-reporter:Y. Danyuo, S. Dozie-Nwachukwu, J.D. Obayemi, C.J. Ani, O.S. Odusanya, Y. Oni, N. Anuku, K. Malatesta, W.O. Soboyejo
Materials Science and Engineering: C 2016 Volume 59() pp:19-29
Publication Date(Web):1 February 2016
DOI:10.1016/j.msec.2015.09.090
•Polymerization of PNIPA-based hydrogels for biomedical applications.•Biosynthesis of prodigiosin by Serratia marcescens (SM) subsp. marcescens.•Mechanisms of drug diffusion and the swelling characteristics of PNIPA-based gels.•Statistical analysis of gel swelling behaviors•HPLC analysis of prodigiosin extracted.We present the results of swelling experiments on poly(N-isopropylacrylamide) P(NIPA)-based hydrogels. The swelling characteristics of P(NIPA)-based homo-polymer and P(NIPA)-based co-polymers with Acrylamide (AM) and Butyl Methacrylate (BMA), were studied using weight gain experiments. The swelling due to the uptake of biosynthesized cancer drug, prodigiosin (PG), was compared to swelling in controlled environments (distilled water (DW), paclitaxel™ (PT) and bromophenol blue (BB)). PG was synthesized with Serratia marcescens (SM) subsp. marcescens bacteria. The mechanisms of drug diffusion and swelling of P(NIPA)-based hydrogels are also elucidated along with characterizing the heterogeneous porous structure of the P(NIPA)-based hydrogels. High Performance Liquefied Chromatography (HPLC) analysis revealed the purity of the biosynthesized prodigiosin to be 92.8%. PG was then absorbed by P(NIPA)-based hydrogels at temperatures between 28–48 °C. This is a temperature range that might be encountered during the implantation of biomedical devices for localized cancer treatment via drug delivery and hyperthermia. The results obtained are shown to provide insights for the design of implantable biomedical devices for the localized treatment of breast cancer.
Co-reporter:J.D. Obayemi, Y. Danyuo, S. Dozie-Nwachukwu, O.S. Odusanya, N. Anuku, K. Malatesta, W. Yu, K.E. Uhrich, W.O. Soboyejo
Materials Science and Engineering: C 2016 Volume 66() pp:51-65
Publication Date(Web):1 September 2016
DOI:10.1016/j.msec.2016.04.071
•New insights into the controlled release of prodigiosin (PG) anticancer drug from PLGA microspheres•Understanding of the kinetics of PG release and the degradation mechanisms of PG-loaded PLGA microspheres•New insights into the effects of processing parameters on drug microspheres formation.•New insights into the lowering of cell viability (breast cancer cells) by PG released from PG-loaded PLGA microspheres•Understanding the morphologies and physicochemical properties of PG and PT-loaded microspheres and their release ratesThis paper presents the synthesis and physicochemical characterization of biodegradable poly (d,l-lactide-co-glycolide) (PLGA)-based microparticles that are loaded with bacterial-synthesized prodigiosin drug obtained from Serratia marcescens subsp. Marcescens bacteria for controlled anticancer drug delivery. The micron-sized particles were loaded with anticancer drugs [prodigiosin (PG) and paclitaxel (PTX) control] using a single-emulsion solvent evaporation technique. The encapsulation was done in the presence of PLGA (as a polymer matrix) and poly-(vinyl alcohol) (PVA) (as an emulsifier). The effects of processing conditions (on the particle size and morphology) are investigated along with the drug release kinetics and drug-loaded microparticle degradation kinetics. The localization and apoptosis induction by prodigiosin in breast cancer cells is also elucidated along with the reduction in cell viability due to prodigiosin release. The implication of this study is for the potential application of prodigiosin PLGA-loaded microparticles for controlled delivery of cancer drug and treatment to prevent the regrowth or locoregional recurrence, following surgical resection of triple negative breast tumor.
Co-reporter:Jing Du, Xinrui Niu, Wole Soboyejo
Journal of the Mechanical Behavior of Biomedical Materials 2015 Volume 46() pp:41-48
Publication Date(Web):June 2015
DOI:10.1016/j.jmbbm.2015.01.019
•Creep tests in individual layers in bio-inspired dental multilayers.•Measured creep rates well predicted by Prony series.•Creep behavior of bio-inspired dental multilayers predicted by finite element models.•Critical loads under Hertzian contact predicted using slow crack growth and creep models.•Predictions of critical loads shown to be consistent with measured loading rates.Ceramic crown structures under occlusal contact are often idealized as flat multilayered structures that are deformed under Hertzian contact loading. Previous models treated each layer as linear elastic materials and resulted in differences between the measured and predicted critical loads. This paper examines the combined effects of creep (in the adhesive and substrate layers) and creep-assisted slow crack growth (in the ceramic layer) on the contact-induced deformation of bio-inspired, functionally graded multilayer (FGM) structures and the conventional tri-layers. The time-dependent moduli of each of the layers were determined from constant load creep tests. The resulting modulus–time characteristics were modeled using Prony series. These were then incorporated into a finite element model for the computation of stress distributions in the sub-surface regions of the top ceramic layer, in which sub-surface radial cracks, are observed as the clinical failure mode. The time-dependent stresses are incorporated into a slow crack growth (SCG) model that is used to predict the critical loads of the dental multilayers under Hertzian contact loading. The predicted loading rate dependence of the critical loads is shown to be consistent with experimental results. The implications of the results are then discussed for the design of robust dental multilayers.
Co-reporter:Kwabena Kan-Dapaah, Nima Rahbar, Abdullahi Tahlil, David Crosson, Nan Yao, Wole Soboyejo
Journal of the Mechanical Behavior of Biomedical Materials 2015 Volume 49() pp:118-128
Publication Date(Web):September 2015
DOI:10.1016/j.jmbbm.2015.04.023
•Magnetic nanoparticle (γ-Fe2O3) filled poly-dimethylsiloxane nanocomposites were fabricated using soft lithography method.•Their mechanical and hyperthermic properties were studied as a function of the weight fraction of γ-Fe2O3.•Increasing weight fraction of γ-Fe2O3 increases Young’s modulus but decreases strength.•Heat generation within alternating magnetic field increases with weight fraction of γ-Fe2O3.•These enhanced properties can be exploited for the development of biomedical devices such as lab-on chip and hyperthermic thermoseeds/probes.An understanding of the properties of multifunctional materials is important for the design of devices for biomedical applications. In this paper, a combination of experiments and models was used to study the mechanical and hyperthermic properties of magnetic nanoparticles (MNP)-filled PDMS composites for biomedical applications. These are studied as a function of the weight of MNP, γ-Fe2O3. The results showed the effects on mechanical behavior, and specific losses in a magnetic field. The measured Young’s moduli are in good agreement with the moduli predicted from the Bergström–Boybce model. Specific losses calculated from magnetic measurements are used to predict the thermal dose under in-vivo conditions. The implications of the results were discussed for potential applications in biomedical devicesGraphcal abstract
Co-reporter:E.K. Arthur, E. Ampaw, M.G. Zebaze Kana, K.J. Akinluwade, A.R. Adetunji, O.O. Adewoye, W.O. Soboyejo
Materials Science and Engineering: A 2015 Volume 644() pp:347-357
Publication Date(Web):17 September 2015
DOI:10.1016/j.msea.2015.07.040
This paper explores the indentation size effect (ISE) in pack carbo-nitrided AISI 8620 steel surfaces. The surfaces of the AISI 8620 steel samples were pack carbo-nitrided at 900 °C using cyanide-containing dried cassava leaves (bio-processed waste). This was achieved by quenching in different pH levels of cyanide-based bio-processed solution (BPS). Nanoindentation was carried out (using a Berkovich tip) on the surface modified steels. This was used to measure the hardness and reduced elastic moduli of the quenched-carbonitrided and the as-received steel surfaces. The surface-modified steel was shown to have higher hardness than the as-received steel. The hardness was also found to depend strongly on the indentation size. The paper also considers the potential contributions from microstructure, geometrically necessary dislocations (GNDs) and C/N diffusion on the measured hardness values. However, the measured ISEs are attributed largely to the role of GNDs that are modeled using the Nix and Gao mechanism-based strain gradient plasticity model. The implications of the results are then discussed for the design of hard carbo-nitrided steel surfaces.
Co-reporter:J.D. Obayemi, S. Dozie-Nwachukwu, Y. Danyuo, O.S. Odusanya, N. Anuku, K. Malatesta, W.O. Soboyejo
Materials Science and Engineering: C 2015 Volume 46() pp:482-496
Publication Date(Web):1 January 2015
DOI:10.1016/j.msec.2014.10.081
•Biosynthesis of MNPs with clinically relevant sizes between 10 and 60 nm.•New insights into the effects of pH and processing time on nanoparticle shapes and sizes.•Successful conjugation of biosynthesized magnetite nanoparticles to LHRH ligands.•Conjugated BMNPs that are monodispersed with potential biomedical relevance.•Magnetic properties of biosynthesized MNPs suggest potential for MRI enhancement.This paper presents the results of an experimental study of the biosynthesis of magnetite nanoparticles (BMNPs) with particle sizes between 10 nm and 60 nm. The biocompatible magnetic nanoparticles are produced from Magnetospirillum magneticum (M.M.) bacteria that respond to magnetic fields. M.M. bacteria were cultured and used to synthesize magnetite nanoparticles. This was done in an enriched magnetic spirillum growth medium (EMSGM) at different pH levels. The nanoparticle concentrations were characterized with UV–Visible (UV–Vis) spectroscopy, while the particle shapes were elucidated via transmission electron microscopy (TEM). The structure of the particles was studied using X-ray diffraction (XRD), while the hydrodynamic radii, particle size distributions and polydispersity of the nanoparticles were characterized using dynamic light scattering (DLS). Carbodiimide reduction was also used to functionalize the BMNPs with a molecular recognition unit (luteinizing hormone releasing hormone, LHRH) that attaches specifically to receptors that are over-expressed on the surfaces of most breast cancer cell types. The resulting nanoparticles were examined using Fourier Transform Infrared (FTIR) spectroscopy and quantitative image analysis. The implications of the results are then discussed for the potential development of magnetic nanoparticles for the specific targeting and treatment of breast cancer.
Co-reporter:S. T. Azeko;G. A. Etuk-Udo;O. S. Odusanya;K. Malatesta
Waste and Biomass Valorization 2015 Volume 6( Issue 6) pp:1047-1057
Publication Date(Web):2015 December
DOI:10.1007/s12649-015-9421-0
This paper presents the results of an experimental study of the bacterial-mediated biodegradation of linear low density polyethylene (LLDPE) by Serratia marcescens subsp. marcescens (S. marcescens marcescens) bacterium without prior exposure of the LLDPE to thermo-oxidative aging. Degradation promoted by supernatant from S. marcescens marcescens was also studied, and compared to that promoted by direct exposure to S. marcescens marcescens cells. The results show that the cell-free extracts degrade LLDPE faster than the S. marcescens marcescens. The mechanisms of degradation are also elucidated via Scanning Electron Microscopy, Differential Scanning Calorimetry and Fourier Transform Infra-Red Spectroscopy. These methods show that the S. marcescens marcescens and its supernatant both degrade LLDPE. There was also an increase in the concentrations of the carbonyl groups (new peaks) after the microbial degradation of LLDPE. The degradation process results in the formation and growth of microvoids. The latter are also found to coalesce to form larger defects with increasing exposure to supernatant/cell-free extracts or S. marcescens marcescens.
Co-reporter:Y. Danyuo, J.D. Obayemi, S. Dozie-Nwachukwu, C.J. Ani, O.S. Odusanya, Y. Oni, N. Anuku, K. Malatesta, W.O. Soboyejo
Materials Science and Engineering: C 2014 Volume 42() pp:734-745
Publication Date(Web):1 September 2014
DOI:10.1016/j.msec.2014.06.008
•Fabricated thermo-sensitive hydrogels for localized drug release from an implantable biomedical device.•Determined the cancer drug diffusion mechanisms of PNIPA-co-AM copolymer hydrogel.•Encapsulated PNIPA-based hydrogels in PDMS capsules for controlled drug delivery.•Established the kinetics of drug release from gels and channels in an implantable biomedical device.•Demonstrated the potential for the controlled release of prodigiosin (PG) as an anticancer drug.This paper presents an implantable encapsulated structure that can deliver localized heating (hyperthermia) and controlled concentrations of prodigiosin (a cancer drug) synthesized by bacteria (Serratia marcesce (subsp. marcescens)). Prototypical Poly-di-methyl-siloxane (PDMS) packages, containing well-controlled micro-channels and drug storage compartments, were fabricated along with a drug-storing polymer produced by free radical polymerization of Poly(N-isopropylacrylamide)(PNIPA) co-monomers of Acrylamide (AM) and Butyl-methacrylate (BMA). The mechanisms of drug diffusion of PNIPA-base gels were elucidated. Scanning Electron Microscopy (SEM) was also used to study the heterogeneous porous structure of the PNIPA-based gels. The release exponents, n, of the gels were found to between 0.5 and 0.7. This is in the range expected for Fickian (n = 0.5). Deviation from Fickian diffusion was also observed (n > 0.5) diffusion. The gel diffusion coefficients were shown to vary between 2.1 × 10− 12 m2/s and 4.8 × 10− 6 m2/s. The implications of the results are then discussed for the localized treatment of cancer via hyperthermia and the controlled delivery of prodigiosin from encapsulated PNIPA-based devices.
Co-reporter:J. Du, X. Niu, N. Rahbar, W. Soboyejo
Acta Biomaterialia 2013 Volume 9(Issue 2) pp:5273-5279
Publication Date(Web):February 2013
DOI:10.1016/j.actbio.2012.08.034
Abstract
The ceramic crown structures under occlusal contact are idealized as flat multilayered structures that are deformed under Hertzian contact loading. Those multilayers consist of a crown-like ceramic top layer, an adhesive layer and the dentin-like substrate. Bio-inspired design of the adhesive layer proposed functionally graded multilayers (FGM) that mimic the dentin–enamel junction in natural teeth. This paper examines the effects of FGM layer architecture on the contact-induced deformation of bio-inspired dental multilayers. Finite element modeling was used to explore the effects of thickness and architecture on the contact-induced stresses that are induced in bio-inspired dental multilayers. A layered nanocomposite structure was then fabricated by the sequential rolling of micro-scale nanocomposite materials with local moduli that increase from the side near the soft dentin-like polymer composite foundation to the side near the top ceramic layer. The loading rate dependence of the critical failure loads is shown to be well predicted by a slow crack growth model, which integrates the actual mechanical properties that are obtained from nanoindentation experiments.
Co-reporter:T. Tan, J. Meng, N. Rahbar, H. Li, G. Papandreou, C.A. Maryanoff, W.O. Soboyejo
Materials Science and Engineering: C 2012 Volume 32(Issue 3) pp:550-557
Publication Date(Web):1 April 2012
DOI:10.1016/j.msec.2011.12.008
Parylene can be coated on stainless steel substrates with and without γ-methacryloxypropyltrimethoxysilane (γ-MPS) as an adhesion promoter. In order to study the effects of silane (γ-MPS) on the adhesion and mixed-mode interfacial fracture performance between parylene C and 316L stainless steel, this paper presents the results of a combined experimental and theoretical approach. Atomic force microscopy (AFM) was used to obtain pull-off forces between parylene coated AFM tips with or without γ-MPS and 316L substrates. A combination of adhesion theories and fracture mechanics models was then used to obtain estimates of the fracture energy release rates over a wide range of mode mixities between pure mode I and pure mode II. The trends in the estimates were shown to be in good agreement with experimental measurements of interfacial fracture toughness obtained from Brazil nut tests coated with parylene C in the presence or absence of γ-MPS over the same range of mode mixities. The study determined that the contribution of silane to the adhesion of parylene C to 316L steel was modest.Highlights► An integrated experimental and modeling approach was applied to characterize effects of silane on interfacial fracture behavior of a parylene film over a stainless steel substrate. ► AFM measurements were obtained for the adhesion of parylene over stainless steel in the presence and absence wiht γ-methacryloxypropyltrimethoxysilane(γ-MPS). ► Brazil nut test was also used to measure interfacial fracture energy release rates over a wide range of mode mixities. ► Good agreement was achieved between these measurements and predictions from both zone and row fracture mechanics models.
Co-reporter:C. Theriault, E. Paetzell, R. Chandrasekar, C. Barkey, Y. Oni, W.O. Soboyejo
Materials Science and Engineering: C 2012 Volume 32(Issue 8) pp:2242-2249
Publication Date(Web):1 December 2012
DOI:10.1016/j.msec.2012.06.010
This paper presents an implantable biomedical device for the localized killing of cancer cells through hyperthermia. Heating, accomplished via resistive heating, is modeled using numerical heat transfer techniques, which are tested under experimental conditions. The effect of temperature in the therapeutic domain of 37 to 45 °C as studied on breast cancer cell line MDA-MB-231 is also reported. The results show the predicted temperature variations are consistent with temperature measurements obtained from the experimental set-ups. The paper also examines the effects of isothermal heating on the cell morphology. Isothermal heating is shown to cause significant physical changes in the cell cytoskeleton. Finally, the paper explores the effects of hyperthermia on cell growth and cell death under isothermal and cyclic conditions. The underlying effects of heat shock protein expression are elucidated before discussing the implications of the results for cancer treatment via localized hyperthermia.Highlights► An implantable device uses resistive heating to deliver localized hyperthermia. ► Controlled, cyclic hyperthermia is achieved using a biomedical device. ► Isothermal heating causes morphological, physical changes in the cell cytoskeleton. ► After 5 days of cyclic heat treatment, MDA-MB-231 cells undergo cell cycle arrest.
Co-reporter:Y. Oni, W.O. Soboyejo
Materials Science and Engineering: C 2012 Volume 32(Issue 1) pp:24-30
Publication Date(Web):1 January 2012
DOI:10.1016/j.msec.2011.09.006
This paper presents the results of an experimental study of the swelling and diffusion of poly(N-iso-propyl-acrylamide) PNIPA-based gels with the potential for applications in bio-micro-electro-mechanical systems (BioMEMS) for localized cancer treatment that involves both chemotherapy and hyperthermia. The swelling due to the uptake of water, rhodamine dye and the cancer drug, paclitaxel, are studied using weight gain experiments that are conducted over a range of temperatures in which hyperthermia can occur during drug delivery. The release of rhodamine dye and paclitaxel is also elucidated by considering their diffusion through the gels. The underlying mechanisms of diffusion and swelling are discussed over a temperature range in which synergistic cancer treatment can be effected by the combined use of hyperthermia and chemotherapy.Highlights► Characterized the swelling and diffusion of PNIPA-based gels. ► Swelling ratio increased with temperature. ► Swelling ratio was more pronounced at transition temperature of each gel. ► Swelling and Diffusion release were found to be mostly non-Fickian. ► Results provide useful insights into drug loading for drug delivery devices.
Co-reporter:I. Yakub, J. Du, W.O. Soboyejo
Materials Science and Engineering: A 2012 Volume 558() pp:21-29
Publication Date(Web):15 December 2012
DOI:10.1016/j.msea.2012.07.038
Porous ceramics with three different porosities were fabricated by the sintering of redart clay and woodchips (sawdust). The latter was used as the pore-forming agent in porous ceramic water. The porosity, pore size and density of the materials were characterized using Mercury Intrusion Porosimetry and Helium Pyncnometer technique, while the structure and chemistry of the materials were elucidated via X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM) and energy dispersive X-ray spectroscopy (EDX). The compressive strength of the porous clay ceramics were found to exhibit a downward trend with increasing porosity. Due to the anisotropic nature of the porous material, two types of specimen (T- and S-Type) were fabricated for the measurement of flexural strength, fracture toughness and resistance-curve behavior under three point bending. The observed crack-tip shielding/toughening mechanism was then modeled using fracture mechanics concepts. The measured mechanical/physical properties, such as: elastic modulus, density and porosity, were then incorporated into finite element models for the computation of stress distributions due to hydrostatic pressures exerted on the porous clay ceramics by the water in filter with different geometries and supporting configurations. The implications of the results are discussed for potential scale-up and design of a mechanically robust porous ceramic for water filtration.
Co-reporter:T. Tan, N. Rahbar, S.M. Allameh, S. Kwofie, D. Dissmore, K. Ghavami, W.O. Soboyejo
Acta Biomaterialia 2011 Volume 7(Issue 10) pp:3796-3803
Publication Date(Web):October 2011
DOI:10.1016/j.actbio.2011.06.008
Abstract
This paper presents the results of a series of multi-scale experiments and numerical models concerning the mechanical properties of moso culm functionally graded bamboo structures. On the nano- and microscales, nanoindentation techniques are used to study the local variations in the Young’s moduli of moso culm bamboo cross-sections. These are then incorporated into finite element models in which the actual variations in Young’s moduli are used to model the deformation and fracture of bamboo during fracture toughness experiments. Similarly, the measured gradations in moduli are incorporated into crack bridging models that predict the toughening observed during resistance curve tests. The implications of the results are discussed for the bio-inspired design of structures that mimic the layered, functionally graded structure of bamboo.
Co-reporter:Y. Oni, C. Theriault, A.V. Hoek, W.O. Soboyejo
Materials Science and Engineering: C 2011 Volume 31(Issue 2) pp:67-76
Publication Date(Web):12 March 2011
DOI:10.1016/j.msec.2010.07.016
This paper presents the results of an experimental study of the effects of temperature on the diffusion from poly(N-isopropylacrylamide) (PNIPA)-based gels with hydrophilic (acrylamide) or hydrophobic (butyl methacrylate) co-monomers. The elutions of rhodamine dye and cancer drug, paclitaxel™ are studied over a range of temperatures in which localized chemotherapy can be combined with hyperthermia (37–45 °C). Dye and drug release from the gels is shown to be well described by monolithic and membrane diffusion models. The current work introduces a multi-modal device that can potentially kill cancer cells by chemotherapy and hyperthermia. A clear advantage over prior devices is the ability to combine these two therapeutic interventions in one device. The implications of the results are discussed for the development of thermosensitive drug eluting Bio-Micro-Electro-Mechanical Systems (BioMEMS) devices that can treat cancer locally via the combined effects of chemotherapy and hyperthermia.
Co-reporter:Ting Tan, Nima Rahbar, Andrea Buono, George Wheeler, Wole Soboyejo
Materials Science and Engineering: A 2011 528(10–11) pp: 3697-3704
Publication Date(Web):
DOI:10.1016/j.msea.2011.01.001
Co-reporter:G. Fu, W.O. Soboyejo
Materials Science and Engineering: C 2010 30(1) pp: 8-13
Publication Date(Web):
DOI:10.1016/j.msec.2009.07.017
Co-reporter:Jianbo Chen, Emily Paetzell, Jikou Zhou, Lauren Lyons, Wole Soboyejo
Materials Science and Engineering: C 2010 30(5) pp: 647-656
Publication Date(Web):
DOI:10.1016/j.msec.2010.01.005
Co-reporter:Xinrui Niu, Nima Rahbar, Stephen Farias, Wole Soboyejo
Journal of the Mechanical Behavior of Biomedical Materials 2009 Volume 2(Issue 6) pp:596-602
Publication Date(Web):December 2009
DOI:10.1016/j.jmbbm.2008.10.009
This paper combines experiments, simulations and analytical modeling that are inspired by the stress reductions associated with the functionally graded structures of the dentin–enamel-junctions (DEJs) in natural teeth. Unlike conventional crown structures in which ceramic crowns are bonded to the bottom layer with an adhesive layer, real teeth do not have a distinct “adhesive layer” between the enamel and the dentin layers. Instead, there is a graded transition from enamel to dentin within a ∼10 to 100 μm thick regime that is called the Dentin Enamel Junction (DEJ). In this paper, a micro-scale, bio-inspired functionally graded structure is used to bond the top ceramic layer (zirconia) to a dentin-like ceramic-filled polymer substrate. The bio-inspired functionally graded material (FGM) is shown to exhibit higher critical loads over a wide range of loading rates. The measured critical loads are predicted using a rate dependent slow crack growth (RDEASCG) model. The implications of the results are then discussed for the design of bio-inspired dental multilayers.
Co-reporter:C. Milburn, J. Chen, Y. Cao, G.M. Oparinde, M.O. Adeoye, A. Beye, W.O. Soboyejo
Materials Science and Engineering: C 2009 29(1) pp: 306-314
Publication Date(Web):
DOI:10.1016/j.msec.2008.07.003
Co-reporter:A.Y. Fasasi, S. Mwenifumbo, N. Rahbar, J. Chen, M. Li, A.C. Beye, C.B. Arnold, W.O. Soboyejo
Materials Science and Engineering: C 2009 29(1) pp: 5-13
Publication Date(Web):
DOI:10.1016/j.msec.2008.05.002
Co-reporter:G. Fu, C. Milburn, S. Mwenifumbo, Y. Cao, G.M. Oparinde, M.O. Adeoye, C. Therialt, A.C. Beye, W.O. Soboyejo
Materials Science and Engineering: C 2009 29(4) pp: 1293-1301
Publication Date(Web):
DOI:10.1016/j.msec.2008.10.026
Co-reporter:J. Meng, J. Fan, G. Galiana, R.T. Branca, P.L. Clasen, S. Ma, J. Zhou, C. Leuschner, C.S.S.R. Kumar, J. Hormes, T. Otiti, A.C. Beye, M.P. Harmer, C.J. Kiely, W. Warren, M.P. Haataja, W.O. Soboyejo
Materials Science and Engineering: C 2009 29(4) pp: 1467-1479
Publication Date(Web):
DOI:10.1016/j.msec.2008.09.039
Co-reporter:G. Fu, W.O. Soboyejo
Materials Science and Engineering: C 2009 29(6) pp: 2011-2018
Publication Date(Web):
DOI:10.1016/j.msec.2009.03.017
Co-reporter:Y. Cao, J. Chen, M.O. Adeoye, W.O. Soboyejo
Materials Science and Engineering: C 2009 29(1) pp: 119-125
Publication Date(Web):
DOI:10.1016/j.msec.2008.05.015
Co-reporter:Y. Yang;B. Imasogie;G.J. Fan;Peter K. Liaw
Metallurgical and Materials Transactions A 2008 Volume 39( Issue 5) pp:1145-1156
Publication Date(Web):2008 May
DOI:10.1007/s11661-008-9487-4
This article presents the results of an experimental study of fracture and fatigue in a nanostructured (an average grain size of ∼23 nm) bulk Ni-18 wt pct Fe alloy that was produced using a pulsed electrodeposition technique. The fracture behavior of the alloy is investigated using fracture resistance experiments, while the fatigue behavior is studied in fatigue crack growth experiments. The alloy exhibits limited toughening as the crack initiates at a fracture toughness of about
\( 25\,{\text{MPa}}{\sqrt {\text{m}} } \) and propagates with a slight increase to a plateau value of about \( 30\,{\text{MPa}}{\sqrt {\text{m}} } \). The limited toughening arises from the slight increase in the crack-tip plastic-deformation zone at the early crack growth and ligament bridging due to the microcrack formation ahead of the tip of the main crack. In contrast with a flat fatigue-crack wake, a wavy crack wake was observed under monotonic loading. This trend is attributed to the following: (a) nanovoid coalescence at grain boundaries, (b) microcrack formation by joining nanovoids, and (c) the linking of microcracks with the main crack through the fracture of inclined bridging ligaments. The fractured surface is shown to contain ductile dimple structures with average diameters of ∼100 nm. Focused-ion-beam (FIB) methods are also used to study fatigue-crack growth. These results show that fatigue crack growth occurs by the coalescence of nanovoids that form ahead of the crack tip. The observed mechanisms of fatigue crack growth are shown to be consistent with the results of prior atomistic simulations.
Co-reporter:Y. Yang, N. Yao, B. Imasogie, W.O. Soboyejo
Acta Materialia 2007 Volume 55(Issue 13) pp:4305-4315
Publication Date(Web):August 2007
DOI:10.1016/j.actamat.2007.03.027
Abstract
This paper presents a novel edge-notched microbeam technique for the study of short fatigue crack growth. The technique is used to study submicron and nanoscale fatigue in LIGA Ni thin films with columnar microstructures. The edge-notched microbeams were fabricated within LIGA Ni thin films, using focused ion beam (FIB) techniques. The microbeams were then cyclically deformed to failure at a stress ratio of 0.1. Different slip-band structures were observed below the nanoscale notches. Cyclic deformation resulted in the formation of primary slip bands below the notch. Subsequent crack growth then occurred by the unzipping of fatigue cracks along intersecting slip bands. The effects of the primary slip bands were idealized using dislocation-based models. These were used to estimate the intrinsic fatigue threshold and the fatigue endurance limit. The estimates from the model are shown to be consistent with experimental data from prior stress-life experiments and current/prior fatigue threshold estimates.
Co-reporter:J. Chen;C. Langhammer;S. Mwenifumbo;A. Beye;J.-P. McGovern;M. Li;W. O. Soboyejo
Journal of Biomedical Materials Research Part B: Applied Biomaterials 2007 Volume 82B(Issue 2) pp:360-373
Publication Date(Web):23 JAN 2007
DOI:10.1002/jbm.b.30741
This paper presents the results of an experimental study of the effects of surface texture on the interactions between human osteo-sarcoma (HOS) cells and Ti-6Al-4V. These include the Ti-6Al-4V with polished (smooth); Al2O3 blasted (rough); and laser micro-grooved geometries with controlled spacings and depths. Immuno-fluorescence staining of adhesion proteins (actin and vinculin) was used to study the spreading and adhesion of HOS cells in 2 day culture experiments. Quantitative measures of adhesion were also obtained using an enzymatic detachment assay. The results are discussed within the context of existing theories of cell adhesion. The implications of the results are also examined for the design of textured surfaces in biomedical systems. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007
Co-reporter:S. Levy;M. Van Dalen;S. Agonafer
Journal of Materials Science: Materials in Medicine 2007 Volume 18( Issue 1) pp:89-102
Publication Date(Web):2007 January
DOI:10.1007/s10856-006-0666-9
This paper examines the effects of surface texture (smooth versus rough) on cell/surface interactions on the bioactive glass, 45S5. The cell surface interactions associated with cell spreading are studied using cell culture experiments. Subsequent energy dispersive x-ray spectroscopy is also used to reveal the distributions of calcium, phosphorous, sodium and oxygen on the surfaces of the bioactive glasses. The implications of the results are then discussed for the applications of textured bioactive glasses in medicine.
Co-reporter:Yifang Cao;Randy Bly;Will Moore;Zhan Gao
Journal of Materials Science: Materials in Medicine 2007 Volume 18( Issue 1) pp:103-109
Publication Date(Web):2007 January
DOI:10.1007/s10856-006-0667-8
This paper presents a method for determining the elastic modulus of human osteosarcoma (HOS) cells. The method involves a combination of shear assay experiments and finite element analysis. Following in-situ observations of cell deformation during shear assay experiments, a digital image correlation (DIC) technique was used to determine the local displacement and strain fields. Finite element analysis was then used to determine the Young’s moduli of HOS cells. This involved a match of the maximum shear stresses estimated from the experimental shear assay measurements and those calculated from finite element simulations.
Co-reporter:J. Zhou;J. Mah;P. Shrotriya;C. Mercer
Journal of Materials Science: Materials in Medicine 2007 Volume 18( Issue 1) pp:71-78
Publication Date(Web):2007 January
DOI:10.1007/s10856-006-0664-y
This paper presents the results of a combined experimental and computational study of contact damage in a 3 mole% yttria partially stabilized zirconia (3-YSZ) that is relevant to hip implants and dental restorations. Contact-induced loading in real applications is idealized using Hertzian contact model to explain plasticity phenomena and failure mechanisms observed under monotonic and cyclic loading. Under monotonic loading, the elastic moduli increase with increasing loading levels. Under cyclic loading, the ceramic specimens fail with progressive cone cracking. X-ray analyses reveal that stress-induced phase transformation (from tetragonal to monoclinic phases) occurs under cyclic contact loading above the critical load levels (~8.5 kN). Furthermore, when the cyclic loading level (5.0 kN) is less than a critical load levels (7.5 kN) that is required to induce surface cone cracks, significant plastic damage is observed in the subsurface zone underneath the contact area. These suggest that the cyclic contact loading induce both plastic damage and tetragonalto-monoclinic phase transformation in the 3-YSZ, leading to significant degradation in long-term strength. The implications of the results are discussed for the design of zirconia femoral heads in total hip replacements and zirconia crowns in dental restoration.
Co-reporter:M. Huang;R. Wang;V. Thompson;D. Rekow
Journal of Materials Science: Materials in Medicine 2007 Volume 18( Issue 1) pp:57-64
Publication Date(Web):2007 January
DOI:10.1007/s10856-006-0662-0
This paper considers the use of bioinspired functionally graded structures in the design of dental multi-layers that are more resistant to sub-surface crack nucleation. Unlike existing dental crown restorations that give rise to high stress concentration, the functionally graded layers (between crown materials and the joins that attach them to dentin) are shown to promote significant reductions in stress and improvements in the critical crack size. Special inspiration is drawn from the low stress concentrations associated with the graded distributions in the dentin-enamel-junction (DEJ). The implications of such functionally graded structures are also discussed for the design of dental restorations.
Co-reporter:M. Huang;X. Niu;W. O. Soboyejo
Journal of Materials Science: Materials in Medicine 2007 Volume 18( Issue 1) pp:65-69
Publication Date(Web):2007 January
DOI:10.1007/s10856-006-0663-z
This paper considers foundation and epoxy creep induced loading rate effects on radial cracks in multilayered structures. These include top layers of glass or silicon that are bonded to polycarbonate foundations with epoxy. The creep properties of the epoxy join and the polycarbonate foundation are determined using compression experiments and spring-dashpot models. The measured creep parameters are then incorporated into an analytical mechanics model, and finite element simulations are used to predict the effects of creep on the critical loads for radial cracking at different loading rates. The models suggest that the combined effects of creep and slow crack growth must be considered in the predictions of the critical loads required for radial cracking in the systems containing glass top layers. Since slow crack growth does not occur in silicon, the model considering the creep effect is used to predict the critical loads for radial cracking in the systems containing silicon top layers. In both of the structures, analytical solutions are obtained for bi-layer structures and finite element simulations are used for tri-layer structures. Our results show that the analytical solutions obtained by bi-layer structures provide good estimations for tri-layer structures when the epoxy thickness is less than 100 μm. The predictions obtained for both systems are shown to provide improved predictions by comparing with experimental results reported by Lee et al. [J. Am. Ceram. Soc., 2002, 85(8), 2019–2024]. In both systems, the modeling of join/substrate creep is shown to be important for the accurate prediction of loading rate effects on radial cracking.
Co-reporter:Steven Mwenifumbo;Mingwei Li;Jianbo Chen
Journal of Materials Science: Materials in Medicine 2007 Volume 18( Issue 1) pp:9-23
Publication Date(Web):2007 January
DOI:10.1007/s10856-006-0658-9
This paper examines the effects of nano-scale titanium coatings, and micro-groove/micro-grid patterns on cell/surface interactions on silicon surfaces. The nature of the cellular attachment and adhesion to the coated/uncoated micro-textured surfaces was elucidated by the visualization of the cells and relevant cytoskeletal & focal adhesion proteins through scanning electron microscopy and immunofluorescence staining. Increased cell spreading and proliferation rates are observed on surfaces with 50 nm thick Ti coatings. The micro-groove geometries have been shown to promote contact guidance, which leads to reduced scar tissue formation. In contrast, smooth surfaces result in random cell orientations and the increased possibility of scar tissue formation. Immunofluorescence cell staining experiments also reveal that the actin stress fibers are aligned along the groove dimensions, with discrete focal adhesions occurring along the ridges, within the grooves and at the ends of the cell extensions. The implications of the observed cell/surface interactions are discussed for possible applications of silicon in implantable biomedical systems.
Co-reporter:S. M. Allameh;O. Akogwu;M. Collinson
Journal of Materials Science: Materials in Medicine 2007 Volume 18( Issue 1) pp:39-45
Publication Date(Web):2007 January
DOI:10.1007/s10856-006-0660-2
This paper presents the results of a study of the effect of cyclic loading parameters on the performance of piezo crystals. The output power of the crystals was observed to increase with parameters such as the cyclic frequency and the dynamic load range. However, the output power also decreased with increasing mean load. The efficiency of the crystal was calculated based on the mechanical energy applied to the piezo crystal. The ratio of the electrical output to mechanical energy input was taken as the efficiency of the crystal. This ratio was seen to increase with the cycling frequency, and also with the dynamic load range. However, increasing mean load caused the efficiency to drop significantly. The implications of the results are discussed for possible applications implanted bioMEMS and microelectronics systems.
Co-reporter:Y. Yang;S. Allameh;B. Boyce;K.S. Chan
Metallurgical and Materials Transactions A 2007 Volume 38( Issue 6) pp:1223-1230
Publication Date(Web):2007 June
DOI:10.1007/s11661-007-9147-0
This article presents the results of an experimental study of fracture in LIGA Ni micro-electro-mechanical systems (MEMS) thin films. Microtesting techniques are developed for the study of the J-resistance curve (J-Δa) behavior in compact tension (CT) thin film specimens. In-situ measurements of crack-tip strain are presented together with in-situ and ex-situ microscopic images of crack-tip deformation and fracture mechanisms. Fractographic observation showed a mixture of inclined fracture planes (slant fracture) that are relatively featureless and normal fracture planes that exhibit dimples and microholes resulting from plastic deformation.
Co-reporter:M. Huang, N. Rahbar, R. Wang, V. Thompson, D. Rekow, W.O. Soboyejo
Materials Science and Engineering: A 2007 Volume 464(1–2) pp:315-320
Publication Date(Web):25 August 2007
DOI:10.1016/j.msea.2007.02.058
This paper considers the use of bioinspired functionally graded structures in the design of dental multi-layers that are more resistant to sub-surface crack nucleation. Unlike existing dental crown restorations that give rise to high stress concentration, the functionally graded layers (between crown materials and the joins that attach them to dentin) are shown to promote significant reductions in stress and improvements in the critical crack size. Special inspiration is drawn from the low stress concentrations associated with the graded distributions in the dentin–enamel junction (DEJ). The implications of such functionally graded structures are also discussed for the design of dental restorations.
Co-reporter:Y. Yang, B.I. Imasogie, S.M. Allameh, B. Boyce, K. Lian, J. Lou, W.O. Soboyejo
Materials Science and Engineering: A 2007 Volume 444(1–2) pp:39-50
Publication Date(Web):25 January 2007
DOI:10.1016/j.msea.2006.06.124
This paper presents the results of an experimental study of the mechanisms of fatigue in LIGA Ni micro-electro-mechanical systems (MEMS) thin films with micro-scale columnar and nano-scale equiaxed grains. Stress-life behavior is reported for films with thicknesses of 70 and 270 μm. The stress-life data are compared with previously reported data for Ni MEMS films and bulk Ni. The films with the nano-scale grains (15 nm average grain size) are shown to have higher strength and fatigue resistance (stress-life data) than those with columnar grain structures. The thicker films (with a columnar microstructure) are also shown to have comparable fatigue life to annealed Ni, while the thinner films (with a columnar microstructure) have comparable fatigue life to wrought Ni. The underlying mechanisms of crack nucleation and growth are elucidated via scanning and transmission electron microscopy. These reveal the formation of slip bands and surface oxides and crystallographic surface/sub-surface crack nucleation and growth in the films with the columnar structures. Surface and corner crack nucleations (from pre-existing defects) are observed in the nanostructured films. The implications of the results are discussed for the analyses of fatigue in nickel MEMS structures.
Co-reporter:Timothy J. Baker, Josephat Zimba, Edem T. Akpan, Ishmael Bashir, Conrad T. Watola, Winston O. Soboyejo
Acta Materialia 2006 Volume 54(Issue 10) pp:2665-2675
Publication Date(Web):June 2006
DOI:10.1016/j.actamat.2006.02.009
Abstract
This paper presents the results of a combined experimental and theoretical study of the effects of Na2O addition on the microstructure, viscoelastic toughening and thermal shock resistance of aluminosilicate refractory ceramics. The Na2O was added to change the viscosity–temperature characteristics of the glassy phase and to promote viscoelastic toughening. It was observed that doping of an aluminosilicate with 4–6 wt.% Na2O significantly alters the microstructure, from mullite within a glassy matrix to aluminum oxide laths within a glassy matrix. The glassy matrix is shown to form viscoelastic ligaments. These bridge cracks form and grow during cold shock from elevated temperatures (1100–1400 °C). The viscoelastic bridges have the net effect of shielding the crack tips from transient thermal stresses due to thermal shock. They therefore improve the cold shock resistance of the ceramic. The insights developed from the experiments were used to guide the development of a fracture mechanics model for the prediction of viscoelastic toughening due to crack bridging.
Co-reporter:J. Zhou, M. Huang, F. Sagnang, W.O. Soboyejo
Dental Materials 2006 Volume 22(Issue 6) pp:585-591
Publication Date(Web):June 2006
DOI:10.1016/j.dental.2005.06.007
ObjectivesTo measure the interfacial fracture toughness and investigate failure mechanisms of dental cements bound to soda-lime glasses elastically equivalent to dental ceramics, as loading angle changes from 0 to 20°.MethodsTwo half-circle glass discs received surface treatment were bound using dental cement (3M RelyXTM ARC BLBL) to make Brazil-nut sandwich specimens for interfacial toughness testing. Before bonding the two half-circle glass disks, 8% hydrofluoric acid (HF) was applied on the surfaces to bond for 2 min, washed thoroughly for 1 min under tap water and air dried. The surfaces were further treated using silane primer Monobond-s (Vivadent, Liechtenstein) for 60 s and air dried. Interfacial toughness as a function of mode mixity was measured using an Instron testing machine by changing loading angels from 0 to 20°. The interfacial fracture surfaces were examined using SEM and EDX to determine the failure modes when loading angles change.ResultsInterfacial toughness increases from ∼1 to 8 J/m/m when loading angle increases from 0 to ∼20°. Increasing deformation and fracture in dental cement occur when loading angle increases.SignificancesIncreasing interfacial toughness can be attributed to more deformation and fracture of dental cement when loading angle increases. Brazil-nut sandwich samples are shown to provide a promising alternative method to evaluate bond strength and interfacial failure for dental restoration. Research was supported by NIH (NYU/PHS No. F5262-07).
Co-reporter:Jikou Zhou, Carola Leuschner, Challa Kumar, Josef F. Hormes, Winston O. Soboyejo
Biomaterials 2006 Volume 27(Issue 9) pp:2001-2008
Publication Date(Web):March 2006
DOI:10.1016/j.biomaterials.2005.10.013
In this study, the sub-cellular accumulation of superparamagnetic iron oxide nanoparticles (SPIONs) in breast tumors and peripheral organs were investigated. MNPs were conjugated with luteinizing hormone releasing hormone (LHRH), whose receptors are expressed by most types of breast cancer cells. After the nanoparticles were injected into female nude mice bearing MDA-MB-435S.luc tumors, the mice were sacrificed to collect tumors and peripheral organs for biological and TEM analyses. LHRH conjugated SPIONs (LHRH- SPIONs) were found to accumulate in cancer cells, mainly in the primary tumors and the metastatic lungs, where they aggregated to form clusters. In contrast, most of the unconjugated SPIONs were collected in the liver cells. The results suggest that LHRH- SPIONs can be used to target cancer cells in the primary breast tumors and the lung metastases. TEM is also shown to be a useful tool for the studies of sub-cellular distributions of SPIONs in tumors and tissues.
Co-reporter:J. Lou, P. Shrotriya, S. Allameh, T. Buchheit, W.O. Soboyejo
Materials Science and Engineering: A 2006 Volume 441(1–2) pp:299-307
Publication Date(Web):15 December 2006
DOI:10.1016/j.msea.2006.08.048
This paper presents a recent study of the effects of plasticity strain gradient length scale parameters on plastic deformation. The plasticity length scale parameters are obtained for LIGA Ni MEMS structures plated from sulfamate baths. Micro-tensile experiments were explored in current study to evaluate the basic tensile properties for LIGA Ni MEMS structures at micron scale. The composite length scale parameter [J.S. Stölken, A.G. Evans, Acta Mater. 6 (1998) 5109–5115] was obtained from the micro-bend techniques, and the stretch gradient length scale parameter [J.S. Stölken, A.G. Evans, Acta Mater. 46 (1998) 5109–5115; N.A. Fleck, J.W. Hutchinson, Adv. Appl. Mech. 33 (1997) 295–361; W.D. Nix, H. Gao, J. Mech. Phys. Solids 46 (1998) 411–425; M.R. Begley, J.W. Hutchinson, J. Mech. Phys. Solids 46 (1998) 2049–2068] was extracted from the nano-indentation experiments. A constitutive expression, which is an extension of the traditional J2 theory, was obtained for the LIGA Ni MEMS structures. This constitutive equation can be used for the further modeling of plasticity of LIGA Ni MEMS structures plated under similar conditions. The implications of plasticity length scale parameters are discussed for multi-scale modeling between the micron- and nano-scales.
Co-reporter:F. McBagonluri, E. Akpan, C. Mercer, W. Shen, W.O. Soboyejo
Materials Science and Engineering: A 2005 Volume 405(1–2) pp:111-134
Publication Date(Web):25 September 2005
DOI:10.1016/j.msea.2005.05.097
This paper presents the results of a combined experimental and mechanistic modeling approach to the study of dwell fatigue in Ti-6242. Crack shape evolution, depth and surface crack growth rates are established using beachmarking, acoustic emission and scanning electron microscopy (SEM) techniques. The underlying crack nucleation and fatigue fracture modes are elucidated for three microstructures: equiaxed (microstructure 1), elongated (microstructure 2) and colony (microstructure 3) of Ti-6242. The dominant crack nucleation mode is shown to involve a Stroh-type dislocation mechanism, where sub-surface cracks are characterized by prominent facetted fracture modes in the near-threshold regime. Subsequent fatigue crack growth occurs by fatigue striations and ductile dimples or cleavage-like static modes at higher stress intensity factor ranges. The long crack growth data are similar for both dwell and pure fatigue. However, the dwell fatigue crack growth rates are shown to be much greater than those due to pure fatigue in the short crack growth regime. The differences between the dwell crack growth rates and the pure fatigue crack growth rates in the short regime are attributed to possible creep effects that give rise to a mean stress effect in the case of dwell fatigue. Subsequently, the measured crack growth rates are incorporated into a fracture mechanics framework for the estimation of fatigue life in the three microstructures. The implications of the predictions are discussed for the modeling of dwell fatigue.
Co-reporter:S.M Allameh, J Lou, F Kavishe, T Buchheit, W.O Soboyejo
Materials Science and Engineering: A 2004 Volume 371(1–2) pp:256-266
Publication Date(Web):25 April 2004
DOI:10.1016/j.msea.2003.12.020
This paper presents results of an experimental study of fatigue in LIGA Ni micro-electro-mechanical systems (MEMS)/thin films produced by electroplating from a sulfamate bath at a current density of 50 mA/cm2. Following a brief description of microstructure and micro-tensile properties, the results of stress-life (S-N) experiments are presented for specimens with thicknesses of 70 and 270 μm. Specimens with the thicker cross-sections (270 μm thick) are shown to have comparable fatigue resistance to annealed bulk Ni in the as-plated condition. The thinner specimens (70 μm thick) have comparable fatigue resistance to hardened Ni, and better fatigue resistance than the thicker samples. The underlying fatigue fracture modes are elucidated via scanning electron microscopy. The implications of the results are then discussed for the failure analysis of LIGA Ni MEMS structures.
Co-reporter:J. Zhou, W.O. Soboyejo
Materials Science and Engineering: A 2004 Volume 369(1–2) pp:23-35
Publication Date(Web):25 March 2004
DOI:10.1016/j.msea.2003.08.009
This paper presents the results of an experimental study of the fatigue mechanisms of Duocel® open cell aluminum foams and the effects of heat treatment on foam fatigue behaviour. The macro-/micro-mechanisms of fatigue were studied for the foams in the as-fabricated (F), annealed (O) and T6-strengthened (T6) conditions. The effects of annealing and T6-strengthening on the stress–strain behavior and plastic collapse strengths of foams were introduced before presenting the results of compression–compression fatigue experiments. The formation of localized deformation bands were investigated using an in-situ digital camera. Scanning electron microscopy (SEM) revealed clear evidence of the surface crack nucleation in the individual struts, prior to the abrupt strain jumps. Fractographic analysis of the failed struts also revealed fatigue striations and surface crack nucleation mechanisms in the struts. Finally, a simple compression–compression fatigue mechanism is proposed to link the observed macro- and micro-scale fatigue mechanisms in open cell aluminum foams.
Co-reporter:J Lou, K Bhalerao, A.B.O Soboyejo, W.O Soboyejo
Cement and Concrete Composites 2003 Volume 25(Issue 6) pp:599-605
Publication Date(Web):August 2003
DOI:10.1016/S0958-9465(02)00073-2
This paper examines the effects of mix strength on the fracture initiation and resistance-curve behavior of concrete. The fracture initiation toughness and the resistance-curve behavior are shown to increase with increasing mix strength. However, the extent of stable crack growth is shown to decrease with increasing mix strength. The measured resistance-curve behavior is associated with the beneficial effects of crack-tip shielding due to ligament bridging mechanisms. The observed small- and large-scale bridging phenomena are then modeled using fracture mechanics models. The studies show that the measured resistance-curve behavior is predicted largely by considering the beneficial effects of ligament bridging. Finally, the implications of the results are then discussed for the design of durable concrete structures.
Co-reporter:K Bhalerao, W Shen, A.B.O Soboyejo, W.O Soboyejo
Cement and Concrete Composites 2003 Volume 25(Issue 6) pp:607-615
Publication Date(Web):August 2003
DOI:10.1016/S0958-9465(02)00074-4
This paper presents a probabilistic multiparameter framework for the modeling of fatigue crack growth in three grades of concrete. The framework relies on the use of ranked fatigue crack growth rate data (with specified occurrence probability levels) in the formulation of multiparameter fatigue crack growth expressions. These relate ranked fatigue crack growth rates to crack driving force parameters such as the stress intensity factor range, maximum stress intensity factor, stress ratio and occurrence probability level. A probabilistic framework is then presented for the estimation of material reliability or failure probability due to fatigue crack growth. The probabilistic model is then validated for the available data.
Co-reporter:N. Marcantonio;W. O. Soboyejo;B. Nemetski;J. Ricci;S. Allameh;C. Mercer
Journal of Biomedical Materials Research Part A 2002 Volume 62(Issue 1) pp:56-72
Publication Date(Web):14 JUN 2002
DOI:10.1002/jbm.10221
This paper presents the results of an experimental study of the interactions between MC3T3-E1 (mouse calvarian) cells and textured Ti6Al4V surfaces, including surfaces produced by laser microgrooving; blasting with alumina particles; and polishing. The multiscale interactions between MC3T3-E1 cells and these textured surfaces are studied using a combination of optical scanning transmission electron microscopy and atomic force microscopy. The potential cytotoxic effects of microchemistry on cell–surface interactions also are considered in studies of cell spreading and orientation over 9-day periods. These studies show that cells on microgrooved Ti6Al4V geometries that are 8 or 12 μm deep undergo contact guidance and limited cell spreading. Similar contact guidance is observed on the surfaces of diamond-polished surfaces on which nanoscale grooves are formed due to the scratching that occurs during polishing. In contrast, random cell orientations are observed on alumina-blasted Ti6Al4V surfaces. The possible effects of surface topography are discussed for scar-tissue formation and improved cell–surface integration. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res 62: 56–72, 2002
Co-reporter:S Shademan, W.O Soboyejo
Materials Science and Engineering: A 2002 Volume 335(1–2) pp:116-127
Publication Date(Web):25 September 2002
DOI:10.1016/S0921-5093(01)01934-7
This paper presents the results of an experimental study of the growth of two-dimensional, short fatigue cracks, in Ti–6Al–4V with well-controlled colony microstructures. The underlying crack/microstructure interactions associated with anomalous short fatigue crack growth behavior are elucidated for three colony microstructures with controlled α lath dimensions and β volume fractions. The fatigue fracture modes in the short crack regime are shown to be similar to those in the long crack growth near-threshold regime in the same microstructural conditions. However, unlike long cracks in the near-threshold regime, no evidence of closure contact-induced debris is observed on the fracture surfaces of the short fatigue cracks.
Co-reporter:S.M. Allameh, R.W. Hayes, M. Li, E.A. Loria, D.J. Srolovitz, W.O. Soboyejo
Materials Science and Engineering: A 2002 Volume 328(1–2) pp:122-132
Publication Date(Web):May 2002
DOI:10.1016/S0921-5093(01)01675-6
This paper presents the results of a study of microstructure and mechanical properties (tensile and creep behavior) of a multicomponent body-centered-cubic Nb–35Ti–6Al–5Cr–8V–1W–0.5Mo–0.3Hf–0.5C alloy (compositions quoted in atomic% unless stated otherwise). The double extruded material is shown to have a Van Gogh Sky microstructure that is formed as a result of the combined effects of microsegregation and deformation gradients. The effects of recrystallization heat treatments on microstructure were examined in an effort to produce a fully recrystallized microstructure. The changes in tensile properties and fracture mechanisms at different temperatures (27–704 °C) are discussed for material in fully recrystallized condition. The micromechanisms of creep deformation at 704 °C are also elucidated for the fully recrystallized condition.
Co-reporter:S Shademan, A.B.O Soboyejo, J.F Knott, W.O Soboyejo
Materials Science and Engineering: A 2001 Volume 315(1–2) pp:1-10
Publication Date(Web):30 September 2001
DOI:10.1016/S0921-5093(01)01211-4
A physically-based model is presented for the prediction of fatigue crack growth in Ti–6Al–4V. The model assumes that the crack extension per cycle is directly proportional to the change in the crack-tip opening displacement, during cyclic loading between the maximum and minimum stress intensity factor. The extent of irreversibility is also assumed to exhibit a power law dependence on the effective stress intensity factor range. A simple power law equation is then derived for the prediction of fatigue crack growth as a function of the effective stress intensity factor range. The model is validated for fatigue crack growth in the near-threshold, Paris and high-ΔK regimes. The fatigue crack growth mechanisms associated with the parametric combinations of stress intensity factor ranges and maximum stress intensity factor are then summarized on fatigue mechanism maps. Mechanistically-based fatigue crack growth relationships are thus obtained for the prediction of fatigue crack growth in the near-threshold, Paris and high-ΔK regimes.
Co-reporter:V Sinha, C Mercer, W.O Soboyejo
Materials Science and Engineering: A 2000 Volume 287(Issue 1) pp:30-42
Publication Date(Web):15 July 2000
DOI:10.1016/S0921-5093(00)00817-0
This paper presents the results of a study of the effects of positive stress ratios on the propagation of long and short fatigue cracks in mill annealed Ti–6Al–4V. Differences between the long fatigue crack growth rates at positive stress ratios (R=Kmin/Kmax=0.02–0.8) are attributed largely to the effects of crack closure. Microstructurally short fatigue cracks are shown to grow at stress intensity factor ranges below the long crack fatigue threshold. Anomalously high fatigue crack growth rates and crack retardation are also shown to occur in the short crack regime. Differences between the long and the short crack behavior at low stress ratios are attributed to lower levels of crack closure in the short crack regime.
Co-reporter:M Li, W.O Soboyejo
Materials Science and Engineering: A 1999 Volume 271(1–2) pp:491-495
Publication Date(Web):1 November 1999
DOI:10.1016/S0921-5093(99)00384-6
This paper presents preliminary experimental evidence of synergistic interactions between transformation toughening and crack bridging in an NiAl composite reinforced with 2 mol% yttria partially stabilized zirconia and molybdenum particles. The observed levels of synergy are shown to be consistent with predictions from a theoretical model by Amazigo and Budiansky (J.C. Amazigo, B. Budiansky, J. Mech. Phys. Solids 36 (1988) 581–595.). The implications of the results are also discussed for the potential development of synergistically toughened intermetallic and ceramic composites.
