Co-reporter:Megan J. Neufeld, Alec Lutzke, W. Matthew Jones, and Melissa M. Reynolds
ACS Applied Materials & Interfaces October 18, 2017 Volume 9(Issue 41) pp:35628-35628
Publication Date(Web):October 4, 2017
DOI:10.1021/acsami.7b11846
Cu-BTTri (H3BTTri = 1,3,5-tris[1H-1,2,3-triazol-5-yl]benzene) is a water-stable, copper-based metal–organic framework (MOF) that exhibits the ability to generate therapeutic nitric oxide (NO) from S-nitrosothiols (RSNOs) available within the bloodstream. Immobilization of Cu-BTTri within a polymeric membrane may allow for localized NO generation at the blood–material interface. This work demonstrates that Cu-BTTri can be incorporated within hydrophilic membranes prepared from poly(vinyl alcohol) (PVA), a polymer that has been examined for numerous biomedical applications. Following immobilization, the ability of the MOF to produce NO from the endogenous RSNO S-nitrosoglutathione (GSNO) is not significantly inhibited. Poly(vinyl alcohol) membranes containing dispersions of Cu-BTTri were tested for their ability to promote NO release from a 10 μM initial GSNO concentration at pH 7.4 and 37 °C, and NO production was observed at levels associated with antithrombotic therapeutic effects without significant copper leaching (<1%). Over 3.5 ± 0.4 h, 10 wt % Cu-BTTri/PVA membranes converted 97 ± 6% of GSNO into NO, with a maximum NO flux of 0.20 ± 0.02 nmol·cm–2·min–1. Furthermore, it was observed for the first time that Cu-BTTri is capable of inducing NO production from GSNO under aerobic conditions. At pH 6.0, the NO-forming reaction of 10 wt % Cu-BTTri/PVA membrane was accelerated by 22%, while an opposite effect was observed in the case of aqueous copper(II) chloride. Reduced temperature (20 °C) and the presence of the thiol-blocking reagent N-ethylmaleimide (NEM) impair the NO-forming reaction of Cu-BTTri/PVA with GSNO, with both conditions resulting in a decreased NO yield of 16 ± 1% over 3.5 h. Collectively, these findings suggest that Cu-BTTri/PVA membranes may have therapeutic utility through their ability to generate NO from endogenous substrates. Moreover, this work provides a more comprehensive analysis of the parameters that influence Cu-BTTri efficacy, permitting optimization for potential medical applications.Keywords: biomaterials; nitric oxide; poly(vinyl alcohol); S-nitrosothiols; water-stable metal−organic frameworks;
Co-reporter:Heather N. Rubin and Melissa M. Reynolds
Inorganic Chemistry May 1, 2017 Volume 56(Issue 9) pp:5266-5266
Publication Date(Web):April 13, 2017
DOI:10.1021/acs.inorgchem.7b00373
The overall versatility of a material can be immensely expanded by the ability to controllably tune its hydrophobicity. Herein we took advantage of steric bias to demonstrate that tricarboxylate metal–organic frameworks (MOFs) can undergo covalent postsynthetic modification to confer various degrees of hydrophobicity. MOF copper 2-aminobenzene-1,3,5-tricarboxylate was modified with varying-length aliphatic carbon chains. Unmodified Cu3(NH2BTC)2 degrades in minutes upon contact with water, whereas modification as low as 14% results in powders that show significantly enhanced hydrophobic character with contact angles up to 147°. The modified material is capable of withstanding direct contact with water for 30 min with no visual evidence of altered surface characteristics. A linear relationship was observed between the length of the tethered chain and the water contact angle. These results reveal a predictable method for achieving a range of desirable sorption rates and highly controllable hydrophobic character. This work thereby expands the possibilities of rationally modifying MOFs for a plethora of target-specific applications.
Co-reporter:Alec Lutzke;Jesus B. Tapia;Megan J. Neufeld
ACS Applied Materials & Interfaces February 15, 2017 Volume 9(Issue 6) pp:5139-5148
Publication Date(Web):February 6, 2017
DOI:10.1021/acsami.6b14937
It has been previously demonstrated that copper-based metal–organic frameworks (MOFs) accelerate formation of the therapeutically active molecule nitric oxide (NO) from S-nitrosothiols (RSNOs). Because RSNOs are naturally present in blood, this function is hypothesized to permit the controlled production of NO through use of MOF-based blood-contacting materials. The practical implementation of MOFs in this application typically requires incorporation within a polymer support, yet this immobilization has been shown to impair the ability of the MOF to interact with the NO-forming RSNO substrate. Here, the water-stable, copper-based MOF H3[(Cu4Cl)3-(BTTri)8] (H3BTTri = 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene), or Cu-BTTri, was incorporated within the naturally derived polysaccharide chitosan to form membranes that were evaluated for their ability to enhance NO generation from the RSNO S-nitrosoglutathione (GSNO). This is the first report to evaluate MOF-induced NO release from GSNO, the most abundant small-molecule RSNO. At a 20 μM initial GSNO concentration (pH 7.4 phosphate buffered saline, 37 °C), chitosan/Cu-BTTri membranes induced the release of 97 ± 3% of theoretical NO within approximately 4 h, corresponding to a 65-fold increase over the baseline thermal decomposition of GSNO. Furthermore, incorporation of Cu-BTTri within hydrophilic chitosan did not impair the activity of the MOF, unlike earlier efforts using hydrophobic polyurethane or poly(vinyl chloride). The reuse of the membranes continued to enhance NO production from GSNO in subsequent experiments, suggesting the potential for continued use. Additionally, the major organic product of Cu-BTTri-promoted GSNO decomposition was identified as oxidized glutathione via mass spectrometry, confirming prior hypotheses. Structural analysis by pXRD and assessment of copper leaching by ICP-AES indicated that Cu-BTTri retains crystallinity and exhibits no significant degradation following exposure to GSNO. Taken together, these findings provide insight into the function and utility of polymer/Cu-BTTri systems and may support the development of future MOF-based biomaterials.Keywords: biomaterials; chitosan; metal−organic frameworks; nitric oxide; S-nitrosothiols;
Co-reporter:Bella H. Neufeld;Megan J. Neufeld;Alec Lutzke;Sarah M. Schweickart
Advanced Functional Materials 2017 Volume 27(Issue 34) pp:
Publication Date(Web):2017/09/01
DOI:10.1002/adfm.201702255
An 85% reduction in the bacterial attachment of Pseudomonas aeruginosa is achieved using a water-stable metal–organic framework (MOF) blended with chitosan. These materials demonstrate this reduction in bacterial adhesion in the first 6 h and maintain it over the full 24 h exposure period, a remarkable impediment of biofilm formation to achieve, given the strength of this bacteria strain. The films elicit the same inhibitory effect after a second round of experiments, suggesting reusability of the materials. Characterization of the films by powder X-ray diffraction, attenuated total reflectance-IR, and scanning electron microscopy supports retention of the MOF structure within the chitosan matrix. The extensive control experiments employed in this study isolate the observed biological effects to the synthesized films, and not to possible leachates from the films. This presents the first account of using a water-stable MOF within a polymer as a means to achieve an antibacterial surface by demonstrating an 85% reduction in bacterial attachment of Pseudomonas aeruginosa.
Co-reporter:Jesus B. Tapia;Hailey A. J. Hibbard
Journal of The American Society for Mass Spectrometry 2017 Volume 28( Issue 10) pp:2201-2208
Publication Date(Web):19 June 2017
DOI:10.1007/s13361-017-1717-9
We present the use of a simple, one-pot derivatization to allow the polysaccharide dextran to carry multiple positive charges, shifting its molecular weight distribution to a lower m/z range. We performed this derivatization because molecular weight measurements of polysaccharides by mass spectrometry are challenging because of their lack of readily ionizable groups. The absence of ionizable groups limits proton abstraction and suppresses proton adduction during the ionization process, producing mass spectra with predominantly singly charged metal adduct ions, thereby limiting the detection of large polysaccharides. To address this challenge, we derivatized dextran T1 (approximately 1 kDa) by attaching ethylenediamine, giving dextran readily ionizable, terminal amine functional groups. The attached ethylenediamine groups facilitated proton adduction during the ionization process in positive ion mode. Using the low molecular weight dextran T1, we tracked the number of ethylenediamine attachments by measuring the mass shift from underivatized to derivatized dextran T1. Using electrospray ionization time-of-flight mass spectrometry, we observed derivatized dextran chains ranging from two to nine glucose residues with between one and four attachments/charges. Our success in shifting derivatized dextran T1 toward the low m/z range suggests potential for this derivatization as a viable route for analysis of high molecular weight polysaccharides using electrospray ionization time-of-flight mass spectrometry.
Co-reporter:Alec Lutzke, Jesus B. Tapia, Megan J. Neufeld, and Melissa M. Reynolds
ACS Applied Materials & Interfaces 2017 Volume 9(Issue 3) pp:
Publication Date(Web):January 9, 2017
DOI:10.1021/acsami.6b12888
Nitric oxide (NO) occurs naturally in mammalian biochemistry as a critical signaling molecule and exhibits antithrombotic, antibacterial, and wound-healing properties. NO-forming biodegradable polymers have been utilized in the development of antithrombotic or antibacterial materials for biointerfacial applications, including tissue engineering and the fabrication of erodible coatings for medical devices such as stents. Use of such NO-forming polymers has frequently been constrained by short-term release or limited NO storage capacity and has led to the pursuit of new materials with improved NO release function. Herein, we report the development of an NO-releasing bioerodible coating prepared from poly[bis(3-mercapto-3-methylbut-1-yl glycinyl)phosphazene] (POP-Gly-MMB), a polyphosphazene based on glycine and the naturally occurring tertiary thiol 3-mercapto-3-methylbutan-1-ol (MMB). To evaluate the NO release properties of this material, the thiolated polymer POP-Gly-MMB-SH was applied as a coating to glass substrates and subsequently converted to the NO-forming S-nitrosothiol (RSNO) derivative (POP-Gly-MMB-NO) by immersion in a mixture of tert-butyl nitrite (t-BuONO) and pentane. NO release flux from the coated substrates was determined by chemiluminescence-based NO measurement and was found to remain in a physiologically relevant range for up to 2 weeks (6.5–0.090 nmol of NO·min–1·cm–2) when immersed in pH 7.4 phosphate-buffered saline (PBS) at 37 °C. Furthermore, the coating exhibited an overall NO storage capacity of 0.89 ± 0.09 mmol·g–1 (4.3 ± 0.6 μmol·cm–2). Erosion of POP-Gly-MMB-NO in PBS at 37 °C over 6 weeks results in 14% mass loss, and time-of-flight mass spectrometry (TOF-MS) was used to characterize the organic products of hydrolytic degradation as glycine, MMB, and several related esters. The comparatively long-term NO release and high storage capacity of POP-Gly-MMB-NO coatings suggest potential as a source of therapeutic NO for biomedical applications.Keywords: biodegradation; biomaterials; nitric oxide; polyphosphazenes; S-nitrosothiols;
Co-reporter:Alec Lutzke, Bella H. Neufeld, Megan J. Neufeld and Melissa M. Reynolds
Journal of Materials Chemistry A 2016 vol. 4(Issue 11) pp:1987-1998
Publication Date(Web):26 Feb 2016
DOI:10.1039/C6TB00037A
Nitric oxide (NO) is a unique bioactive molecule that performs multiple physiological functions and has been found to exhibit antithrombotic, antimicrobial, and wound-healing effects as an exogenous therapeutic agent. NO release from polymeric materials intended for use in biomedical applications has been established to reduce their thrombogenicity and decrease the likelihood of infection and inflammation that frequently produce medical complications. As a result, numerous NO-releasing polymers have been developed in an effort to utilize the beneficial properties of NO to improve the performance of implantable materials. The majority of synthetic NO-releasing biodegradable polymers that have been reported to date are polyesters, and there is significant interest in the development of new NO-releasing materials with improved or distinctive physicochemical characteristics. Polyphosphazenes are polymers with inorganic phosphorus–nitrogen backbones, and hydrolytically-sensitive derivatives with organic substituents have been prepared that degrade under physiological conditions. For this reason, biodegradable poly(organophosphazenes) are interesting candidate materials for applications such as tissue engineering, where the addition of NO release capability may be therapeutically useful. Herein, we report the first development and characterization of an NO-releasing poly(organophosphazene) from poly(ethyl S-methylthiocysteinyl-co-ethyl cysteinyl phosphazene) (POP-EtCys-SH). The thiolated polymer was synthesized from the reaction of poly(dichlorophosphazene) with ethyl S-methylthiocysteinate, followed by partial cleavage of the disulfide linkages to form free thiol groups. The conversion of thiol to the NO-releasing S-nitrosothiol functional group with tert-butyl nitrite resulted in a polymer (POP-EtCys-NO) with an average NO content of 0.55 ± 0.04 mmol g−1 that was found to release a total of 0.35 ± 0.02 mmol NO g−1 over 24 h under physiological conditions (37 °C, pH 7.4 phosphate buffered saline). Extracts obtained from both the thiolated and S-nitrosated polymers were not found to significantly impair the viability of human dermal fibroblasts or induce morphological changes, indicating that this cysteine-based polyphosphazene may possess potential utility as an NO-releasing biomaterial.
Co-reporter:Megan J. Neufeld, Brenton R. Ware, Alec Lutzke, Salman R. Khetani, and Melissa M. Reynolds
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 30) pp:19343
Publication Date(Web):July 22, 2016
DOI:10.1021/acsami.6b05948
Metal–organic frameworks (MOFs) have demonstrated promise in biomedical applications as vehicles for drug delivery, as well as for the ability of copper-based MOFs to generate nitric oxide (NO) from endogenous S-nitrosothiols (RSNOs). Because NO is a participant in biological processes where it exhibits anti-inflammatory, antibacterial, and antiplatelet activation properties, it has received significant attention for therapeutic purposes. Previous work has shown that the water-stable MOF H3[(Cu4Cl)3–(BTTri)8] (H3BTTri = 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene), or CuBTTri, produces NO from RSNOs and can be included within a polymeric matrix to form NO-generating materials. While such materials demonstrate potential, the possibility of MOF degradation leading to copper-related toxicity is a concern that must be addressed prior to adapting these materials for biomedical applications. Herein, we present the first cytotoxicity evaluation of an NO-generating CuBTTri/polymer composite material using 3T3-J2 murine embryonic fibroblasts and primary human hepatocytes (PHHs). CuBTTri/polymer films were prepared from plasticized poly(vinyl chloride) (PVC) and characterized via PXRD, ATR-FTIR, and SEM-EDX. Additionally, the ability of the CuBTTri/polymer films to enhance NO generation from S-nitroso-N-acetylpenicillamine (SNAP) was evaluated. Enhanced NO generation in the presence of the CuBTTri/polymer films was observed, with an average NO flux (0.90 ± 0.13 nmol cm–2 min–1) within the range associated with antithrombogenic surfaces. The CuBTTri/polymer films were analyzed for stability in phosphate buffered saline (PBS) and cell culture media under physiological conditions for a 4 week duration. Cumulative copper release in both cell media (0.84 ± 0.21%) and PBS (0.18 ± 0.01%) accounted for less than 1% of theoretical copper present in the films. In vitro cell studies performed with 3T3-J2 fibroblasts and PHHs did not indicate significant toxicity, providing further support for the potential implementation of CuBTTri-based materials in biomedical applications.Keywords: copper toxicity; cytocompatibility; metal−organic frameworks; nitric oxide; primary human hepatocytes
Co-reporter:J. P. Yapor, A. Lutzke, A. Pegalajar-Jurado, B. H. Neufeld, V. B. Damodaran and M. M. Reynolds
Journal of Materials Chemistry A 2015 vol. 3(Issue 48) pp:9233-9241
Publication Date(Web):16 Nov 2015
DOI:10.1039/C5TB01625H
Nitric oxide (NO) is a biologically-active free radical involved in numerous physiological processes such as regulation of vasodilation, promotion of cell proliferation and angiogenesis, and modulation of the inflammatory and immune responses. Furthermore, NO has demonstrated the ability to mitigate the foreign body response that often results in the failure of implanted biomedical devices. Although NO has promising therapeutic value, the short physiological half-life of exogenous NO complicates its effective delivery. For this reason, the development of NO-releasing materials that permit the localized delivery of NO is an advantageous method of utilizing this molecule for biomedical applications. Herein, we report the synthesis and characterization of biodegradable NO-releasing polyesters prepared from citric acid, maleic acid, and 1,8-octanediol. NO release was achieved by incorporation of S-nitrosothiol donor groups through conjugation of cysteamine and ethyl cysteinate to the polyesters, followed by S-nitrosation with tert-butyl nitrite. The extent of NO loading and the release properties under physiological conditions (pH 7.4 PBS, 37 °C) were determined by chemiluminesence-based NO detection. The average total NO content of poly(citric-co-maleic acid-co-1,8-octanediol)-cysteamine was determined to be 0.45 ± 0.07 mol NO g−1 polymer, while the NO content for poly(citric-co-maleic acid-co-1,8-octanediol)-ethyl cysteinate was 0.16 ± 0.04 mol NO g−1 polymer. Continuous NO release under physiological conditions was observed for at least 6 days for the cysteamine analog and 4 days for the ethyl cysteinate analog. Cell viability assays and morphological studies with human dermal fibroblasts indicated an absence of toxic leachates at a cytotoxic level, and suggested that these citrate-based polyesters may be suitable for future biomedical applications.
Co-reporter:Megan J. Neufeld, Jacqueline L. Harding, and Melissa M. Reynolds
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 48) pp:26742
Publication Date(Web):November 23, 2015
DOI:10.1021/acsami.5b08773
Immobilization of metal–organic frameworks (MOFs) onto flexible polymeric substrates as secondary supports expands the versatility of MOFs for surface coatings for the development of functional materials. In this work, we demonstrate the deposition of copper(II) benzene-1,3,5-tricarboxylate (CuBTC) crystals directly onto the surface of carboxyl-functionalized cotton capable of generating the therapeutic bioagent nitric oxide (NO) from endogenous sources. Characterization of the CuBTC-cotton material by XRD, ATR-IR, and UV–vis indicate that CuBTC is successfully immobilized on the cotton fabric. In addition, SEM imaging reveals excellent surface coverage with well-defined CuBTC crystals. Subsequently, the CuBTC-cotton material was evaluated as a supported heterogeneous catalyst for the generation of NO using S-nitrosocysteamine as the substrate. The resulting reactivity is consistent with the activity observed for unsupported CuBTC particles. Overall, this work demonstrates deposition of MOFs onto a flexible polymeric material with excellent coverage as well as catalytic NO release from S-nitrosocysteamine at therapeutic levels.Keywords: catalysis; cotton; hard−soft interfaces; metal−organic frameworks; nitric oxide
Co-reporter:Adoracion Pegalajar-Jurado, Kathryn A. Wold, Jessica M. Joslin, Bella H. Neufeld, Kristin A. Arabea, Lucas A. Suazo, Stephen L. McDaniel, Richard A. Bowen, Melissa M. Reynolds
Journal of Controlled Release 2015 Volume 217() pp:228-234
Publication Date(Web):10 November 2015
DOI:10.1016/j.jconrel.2015.09.015
Health-care associated infections (HAIs) and the increasing number of antibiotic-resistant bacteria strains remain significant public health threats worldwide. Although the number of HAIs has decreased by using improved sterilization protocols, the cost related to HAIs is still quantified in billions of dollars. Furthermore, the development of multi-drug resistant strains is increasing exponentially, demonstrating that current treatments are inefficient. Thus, the quest for new methods to eradicate bacterial infection is increasingly important in antimicrobial, drug delivery and biomaterials research. Herein, the bactericidal activity of a water-soluble NO-releasing polysaccharide derivative was evaluated in nutrient broth media against three bacteria strains that are commonly responsible for HAIs. Data confirmed that this NO-releasing polysaccharide derivative induced an 8-log reduction in bacterial growth after 24 h for Escherichia coli, Acinetobacter baumannii and Staphylococcus aureus. Additionally, the absence of bacteria after 72 h of exposure to NO illustrates the inability of the bacteria to recover and the prevention of biofilm formation. The presented 8-log reduction in bacterial survival after 24 h is among the highest reduction reported for NO delivery systems to date, and reaches the desired standard for industrially-relevant reduction. More specifically, this system represents the only water-soluble antimicrobial to reach such a significant bacterial reduction in nutrient rich media, wherein experimental conditions more closely mimic the in vivo environment than those in previous reports. Furthermore, the absence of bacterial activity after 72 h and the versatility of using a water-soluble compound suggest that this NO-releasing polysaccharide derivative is a promising route for treating HAIs.
Co-reporter:Jacqueline L. Harding;Jarid M. Metz
Advanced Functional Materials 2014 Volume 24( Issue 47) pp:7503-7509
Publication Date(Web):
DOI:10.1002/adfm.201402529
The versatile chemical and physical properties of metal organic frameworks (MOFs) have made them unique platforms for the design of biomimetic catalysts, but with only limited success to date due to instability of the MOFs employed in physiological environments. Herein, the use of Cu(II)1,3,5-Benzene-tris-triazole (CuBTTri) is demonstrated for the catalytic generation of the bioactive agent nitric oxide (NO) from endogenous sources, S-nitrosothiols (RSNOs). CuBTTri exhibits structural integrity in aqueous environments, including phosphate buffered saline (76 h, pH 7.4, 37 °C), cell media used for in vitro testing (76 h, pH 7.4, 37 °C), and fresh citrated whole blood (30 min, pH 7.4, 37 °C). The application of CuBTTri for use in polymeric medical devices is explored through the formation of a composite CuBTTri-poly by blending CuBTTri into biomedical grade polyurethane matrices. Once prepared, the CuBTTri-poly material retains the catalytic function towards the generation of NO with tunable release kinetics proportional to the total content of CuBTTri embedded into the polymeric material with a surface flux corresponding to the therapeutic range of 1–100 nm cm−2 min−1, which is maintained even following exposure to blood.
Co-reporter:Alec Lutzke, Adoracion Pegalajar-Jurado, Bella H. Neufeld and Melissa M. Reynolds
Journal of Materials Chemistry A 2014 vol. 2(Issue 42) pp:7449-7458
Publication Date(Web):19 Sep 2014
DOI:10.1039/C4TB01340A
Nitric oxide (NO)-releasing derivatives of chitin and chitosan were prepared through incorporation of the symmetrical dithiols 1,2-ethanedithiol, 1,3-propanedithiol, and 1,6-hexanedithiol, followed by S-nitrosation with tert-butyl nitrite. The NO loading of the materials and their real-time NO release profiles under physiological conditions (pH 7.4 phosphate buffered saline, 37 °C) were recorded over 24 hours, and in vitro cytotoxicity studies were performed using human dermal fibroblasts (HDF) to assess the suitability of the materials for biomedical applications. Of the six thiolated parent materials, five exhibited cell viability higher than 70% (MTS assay), an outcome that was corroborated by LIVE/DEAD assay. In all cases, HDF morphology was unaffected by the presence of extracts obtained from the thiolated materials.
Co-reporter:Jacqueline L. Harding and Melissa M. Reynolds
Journal of Materials Chemistry A 2014 vol. 2(Issue 17) pp:2530-2536
Publication Date(Web):09 Dec 2013
DOI:10.1039/C3TB21458C
Polyurethane/metal organic framework composite materials were prepared for the generation of the bioregulatory agent, nitric oxide (NO). Extruded tubing was fabricated though a 2-step compounding and extrusion method that yielded a uniform composition of the MOF catalyst in the tubing, where the MOF remained structurally robust during the extrusion process. The resulting MOF embedded polymeric tubing facilitated the generation of NO from bioavailable S-nitrosothiols. The function of the catalyst in the composite material was compared to neat catalysts. The substrate structure was found to have significant influence on the reactivity of the MOF catalyst with NO release times ranging from 1 to 16 h. The dosage of NO could be tuned based on the S-nitrosothiol employed. The ability for sustained NO release from a composite material is a promising approach for long-term biocompatibility.
Co-reporter:Jacqueline L. Harding and Melissa M. Reynolds
Analytical Chemistry 2014 Volume 86(Issue 4) pp:2025
Publication Date(Web):January 20, 2014
DOI:10.1021/ac403174e
Nitric oxide (NO) is an essential messenger in human physiology, mediating cellular processes ranging from proliferation to apoptosis. The effects of NO are concentration dependent, and control over the instantaneous amount of NO available to cells is essential for determining the therapeutic NO dosages for various applications. As such, the development of NO therapeutic materials relies on accurate quantitative NO measurements that provide both total NO release from the NO donor as well as instantaneous NO concentrations. On the basis of the complexity of the cell media environment, inaccurate NO reporting often occurs for in vitro studies. These inaccuracies result from using inert media such as phosphate buffer saline (PBS), failing to account for the reactivity of media components. In this work, we describe a method for directly quantifying the instantaneous and total amounts of NO from commonly used NO donors in commercially available cell media routinely used for endothelial and neural cell lines. A riboflavin–tryptophan complex found in the media was identified as the major scavenger of NO in the cell media and likely reacts with NO via a radical–radical reaction. This finding significantly impacts the amount of available NO. The scavenging effects are concentration dependent on the riboflavin–tryptophan complex and the NO release rate from the NO donor. The results of this study provide insights on the exogenous amounts of NO that are present in cell media and may provide an explanation for differences in NO dosages between buffer experiments and in vitro and in vivo studies.
Co-reporter:J. M. Joslin, B. H. Neufeld and Melissa M. Reynolds
RSC Advances 2014 vol. 4(Issue 79) pp:42039-42043
Publication Date(Web):28 Aug 2014
DOI:10.1039/C4RA04817B
This study marks the first parallel measurements where S-nitrosothiol behaviour is directly correlated to nitric oxide (NO) release for an established polymer system under exposure conditions that are specific to S-nitrosothiol decomposition (i.e. heat, light, pH). These methods are intended to be applied to confirm the NO source in any biomaterial system.
Co-reporter:Jessica M. Joslin, Sarah M. Lantvit, and Melissa M. Reynolds
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 19) pp:9285
Publication Date(Web):August 19, 2013
DOI:10.1021/am402112y
Tygon is a proprietary plasticized poly(vinyl chloride) polymer that is used widely in bioapplications, specifically as extracorporeal circuits. To overcome issues with blood clot formation and infection associated with the failure of these medical devices upon blood contact, we consider a Tygon coating with the ability to release the natural anticlotting and antibiotic agent, nitric oxide (NO), under simulated physiological conditions. These coatings are prepared by incorporating 20 w/w% S-nitrosoglutathione (GSNO) donor into a Tygon matrix. These films release NO on the order of 0.64 ± 0.5 × 10–10 mol NO cm–2 min–1, which mimics the lower end of natural endothelium NO flux. We use a combination of assays to quantify the amount of GSNO that is found intact at different time points throughout the film soak, as well as monitor the total thiol content in the soaking solution due to any analyte that has leached from the polymer film. We find that a burst of GSNO is released from the material surface within 5 min to 1 h of soaking, which only represents 0.25% of the total GSNO contained in the film. After 1 h of film soak, no additional GSNO is detected in the soaking solution. By further considering the total thiol content in solution relative to the intact GSNO, we demonstrate that the amount of GSNO leached from the material into the buffer soaking solution does not contribute significantly to the total NO released from the GSNO-incorporated Tygon film (<10% total NO). Further surface analysis using SEM-EDS traces the elemental S on the material surface, demonstrating that within 5 min −1 h soaking time, 90% of the surface S is removed from the material. Surface wettability and roughness measurements indicate no changes between the GSNO-incorporated films pre- to postsoak that will be significant toward the adsorption of biological components, such as proteins, relative to the presoaked donor-incorporated film. Overall, we demonstrate that, for a 20 w/w% GSNO-incorporated Tygon film, relatively minimal GSNO leaching is experienced, and the lost GSNO is from the material surface. Varying the donor concentration from 5 to 30 w/w% GSNO within the film does not result in significantly different NO release profiles. Additionally, the steady NO flux associated with the system is predominantly due to localized release from the material, and not donor lost to soaking solution. The surface properties of these materials generally imply that they are useful for blood-contacting applications.Keywords: donor leaching; extracorporeal circuit; localized release; nitric oxide; S-nitrosoglutathione; surface analysis; Tygon;
Co-reporter:Sarah M. Lantvit;Brittany J. Barrett
Journal of Biomedical Materials Research Part A 2013 Volume 101( Issue 11) pp:3201-3210
Publication Date(Web):
DOI:10.1002/jbm.a.34627
One mechanism of the failure of blood-contacting devices is clotting. Nitric oxide (NO) releasing materials are seen as a viable solution to the mediation of surface clotting by preventing platelet activation; however, NO's involvement in preventing clot formation extends beyond controlling platelet function. In this study, we evaluate NO's effect on factor XII (fibrinogen) adsorption and activation, which causes the initiation of the intrinsic arm of the coagulation cascade. This is done by utilizing a model plasticized poly(vinyl) chloride (PVC), N-diazeniumdiolate system and looking at the adsorption of fibrinogen, an important clotting protein, to these surfaces. The materials have been prepared in such a way to eliminate changes in surface properties between the control (plasticized PVC) and composite (NO-releasing) materials. This allows us to isolate NO release and determine the effect on the adsorption of fibrinogen, to the material surface. Surprisingly, it was found that an NO releasing material with a surface flux of 17.4 ± 0.5 × 10−10 mol NO cm−2 min−1 showed a significant increase in the amount of fibrinogen adsorbed to the material surface compared to one with a flux of 13.0 ± 1.6 × 10−10 mol NO cm−2 min−1 and the control (2334 ± 496, 226 ± 99, and 103 ±31% fibrinogen adsorbed of control, respectively). This study suggests that NO's role in controlling clotting is extended beyond platelet activation. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A: 3201–3210, 2013.
Co-reporter:Vinod B. Damodaran, Victoria Leszczak, Kathryn A. Wold, Sarah M. Lantvit, Ketul C. Popat and Melissa M. Reynolds
RSC Advances 2013 vol. 3(Issue 46) pp:24406-24414
Publication Date(Web):10 Oct 2013
DOI:10.1039/C3RA45521A
Controlling platelet activation and clotting initiated by cardiovascular interventions remains a major challenge in clinical practice. In this work, the antithrombotic properties of a polysaccharide-based nitric oxide (NO)-releasing dextran derivative are presented. Total platelet adhesion, platelet morphology and whole blood clotting kinetics were used as indicators to evaluate the anticlotting properties of this material. With a total NO delivery of 0.203 ± 0.003 μmol, the NO-releasing dextran derivative (Dex–SNO) mixed with blood plasma demonstrated a significantly lower amount of platelet adhesion and activation onto a surface and reduced whole blood clotting kinetics. Nearly 75% reduction in platelet adhesion and a significant retention of platelet morphology were observed with blood plasma treated with Dex–SNO, suggesting this to be a potential antiplatelet therapeutic agent for preventing thrombosis that does not have an adverse effect on circulating platelets.
Co-reporter:Jessica M. Joslin, Vinod B. Damodaran and Melissa M. Reynolds
RSC Advances 2013 vol. 3(Issue 35) pp:15035-15043
Publication Date(Web):13 Jun 2013
DOI:10.1039/C3RA41988F
The formation of stable nitric oxide (NO) moieties onto polymer substrates is a critical part of NO materials development. Depending upon the polymer functionality, nitrosation of the material can result in a variety of different NO moieties. Toward the ability to selectively load NO in the presence of other reactive sites on a polymer substrate, we investigate how the polymer functionality affects the ability to preferentially form S-nitrosothiol groups over unwanted byproducts, such as N-nitrosamines. Using modified dextran as our model polymer, we demonstrate that N-nitrosamines form on 2° amine sites under S-nitrosation conditions, but are not a significant source of released NO under physiological pH. By tuning the synthetic conditions associated with the polymer synthesis, we demonstrate that by replacing 2° amine sites on the polymer with amide sites, N-nitrosation is effectively eliminated, resulting instead in predominant S-nitrosation. The selectively S-nitrosated materials experience near-complete donor decomposition, giving rise to NO under physiological pH. The ability to tune the availability and reactivity of different functional groups is additionally helpful toward materials synthesis and application in general.
Co-reporter:Jacqueline L. Harding
Journal of the American Chemical Society 2012 Volume 134(Issue 7) pp:3330-3333
Publication Date(Web):January 20, 2012
DOI:10.1021/ja210771m
The use of metal organic frameworks (MOFs) for the catalytic production of nitric oxide (NO) is reported. In this account we demonstrate the use of Cu3(BTC)2 as a catalyst for the generation of NO from the biologically occurring substrate, S-nitrosocysteine (CysNO). The MOF catalyst was evaluated as an NO generator by monitoring the evolution of NO in real time via chemiluminescence. The addition of 2, 10, and 15-fold excess CysNO to MOF-CuII sites and cysteine (CysH) resulted in catalytic turnover of the active sites and nearly 100% theoretical yield of the NO product. Control experiments without the MOF present did not yield appreciable NO generation. In separate studies the MOF was found to be reusable over successive iterations of CysNO additions without loss of activity. Subsequently, the MOF catalyst was confirmed to remain structurally intact by pXRD and ATR-IR following reaction with CysNO and CysH.
Co-reporter:Vinod B. Damodaran, Jessica M. Joslin, Kathryn A. Wold, Sarah M. Lantvit and Melissa M. Reynolds
Journal of Materials Chemistry A 2012 vol. 22(Issue 13) pp:5990-6001
Publication Date(Web):15 Feb 2012
DOI:10.1039/C2JM16554F
A new class of nitric oxide (NO)-releasing biodegradable polymers has been synthesized by derivatizing poly(lactic-co-glycolic-co-hydroxymethyl propionic acid) (PLGH) polymers with structurally unique thiol functionalities followed by nitrosation with t-butyl nitrite to yield pendant S-nitrosothiol moieties. The extent of thiolation was found to be dependent on the thiol moiety itself with the efficiency of incorporation as follows: cysteamine > cysteine > homocysteine. Glutathione and penicillamine were not incorporated to any significant extent. The structure and polymer environment associated with the pendant thiol has been related to the physicochemical properties of the resulting polymers. To quantify the extent of S-nitrosation, chemiluminescence and UV-visible spectroscopy techniques were employed in combination. The cysteamine and homocysteine derivatives were found to have the highest extent of nitrosation at 93 ± 3% and 96 ± 3%, respectively, followed by 43 ± 1% for cysteine. Thermal decomposition led to near-complete recovery of NO based upon the quantification of the RSNO formation for each nitrosated polymer. Our ability to exert control over the thiol structure, extent of incorporation and the subsequent nitrosation is crucial to the resulting range of NO release kinetics that were yielded. The functional utility of these materials is demonstrated in that these non-toxic polymers release NO under physiological conditions, have degradation profiles that are appropriate for tissue scaffolds and can be prepared as electrospun nanofibers, commonly used in tissue and bone regeneration applications.
Co-reporter:Vinod B. Damodaran, Laura W. Place, Matt J. Kipper and Melissa M. Reynolds
Journal of Materials Chemistry A 2012 vol. 22(Issue 43) pp:23038-23048
Publication Date(Web):20 Sep 2012
DOI:10.1039/C2JM34834A
Herein we report the development and evaluation of enzymatically degradable nitric oxide (NO) releasing S-nitrosated dextran thiomers as potent biomedical materials. These materials are characterized by their specificity to release NO under arterial blood conditions, followed by their susceptibility to undergo enzymatic degradation by dextranase. The very specific conjugation chemistries we employed for the thiol incorporation resulted in characteristic stabilization of the resulting S-nitrosothiol moieties, and consequently yielded stable pro-drugs for the storage and controlled delivery of NO. We evaluated the extent of NO loading and release kinetics using multiple and independent analytical techniques, and related these to the structure and environment associated with the thiol moiety incorporated onto the dextran backbone. Finally, the enzymatic degradation kinetics was followed by monitoring the molecular weight profile using gel permeation chromatography, and the results were interpreted using well-established model predictions.
Co-reporter:Jessica M. Joslin and Melissa M. Reynolds
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 2) pp:1126
Publication Date(Web):January 20, 2012
DOI:10.1021/am201807c
An understanding of the nitrosation processes that dictate S-nitrosothiol formation in the presence of a polymer is crucial toward the controlled synthesis of nitric oxide (NO)-releasing materials, an important class of biomaterials that mimic the natural function of cells. Herein, the kinetics of S-nitrosoglutathione (GSNO) formation in the presence of dextran under a variety of nitrosation conditions, including the nitrosating agent and the dextran concentration, are reported. When comparing nitrous acid and t-butyl nitrite as the nitrosating agent, the use of nitrous acid results in 100% nitrosation of the thiol sites within less than a minute and t-butyl nitrite requires more than 5 min to reach completion. This trend establishes nitrous acid as a highly efficient nitrosating agent. In the presence of increasing dextran concentration from 0 w/v% to 10 w/v%, the extent of nitrosation decreases by approximately 5% and 30% using nitrous acid and t-butyl nitrite, respectively. With sufficient reaction time, either reagent leads to 100% nitrosation. This indicates that t-butyl nitrite is the preferred reagent for fine-tuned NO loading of thiol sites as the extent of reaction is greatly impacted by the polymer concentration. Taken together, these studies provide valuable insights regarding the ability to tailor NO storage within biomaterials for use in a wide range of clinical applications.Keywords: biomaterials; dextran; glutathione; nitric oxide loading; nitrosating agent; S-nitrosation;
Co-reporter:Kathryn A. Wold, Vinod B. Damodaran, Lucas A. Suazo, Richard A. Bowen, and Melissa M. Reynolds
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 6) pp:3022
Publication Date(Web):June 4, 2012
DOI:10.1021/am300383w
Many common wound healing aids are created from biodegradable polymeric materials. Often, these materials are unable to induce complete healing in wounds because of their failure to prevent infection and promote cell growth. This study reports the development of therapeutic materials aimed at overcoming these limitations through the release of a naturally occurring antimicrobial agent from a porous, polymeric fiber scaffold. The antimicrobial character was achieved through the release of nitric oxide (NO) while the porous structure was fabricated through electrospinning polymers into nanofibers. Three variations of the polymer poly(lactic-co-glycolic-co-hydroxymethyl propionic acid) (PLGH) modified to include thiol and NO groups were investigated. Fibers of the modified polymers exhibited smooth, bead free morphologies with diameters averaging between 200 and 410 nm. These fibers were deposited in a random manner to create a highly porous fibrous scaffold. The fibers were found to release NO under physiological pH and temperature and have the capacity to release 0.026 to 0.280 mmol NO g–1. The materials maintained their fibrous morphological structure after this exposure to aqueous conditions. The sustained morphological stability of the fiber structure coupled to their extended NO release gives these materials great potential for use in wound healing materials.Keywords: antibacterial; biodegradable; electrospinning; nanofiber; nitric oxide; therapeutic release; wound healing;
Co-reporter:Vinod B. Damodaran and Melissa M. Reynolds
Journal of Materials Chemistry A 2011 vol. 21(Issue 16) pp:5870-5872
Publication Date(Web):15 Mar 2011
DOI:10.1039/C1JM10315F
A biodegradable multiblock polymer containing the S-nitrosothiol moiety was synthesized via a 4 step process using non-aqueous reaction conditions. The structural and morphological properties of the material were characterized via1H NMR, GPC, DSC, TGA, and SAXS. The nitric oxide (NO) storage capacity of the polymer was found to be 0.42 ± 0.01 mmol NO per g polymer using UV spectroscopy, and real-time chemiluminescence measurements demonstrated a controlled and extended NO release profile. The degradation rate of the material was the most rapid during the first week followed by a slower linear release rate. Preliminary biocompatibility testing of the material using ISO protocols indicated no cell lysis in vitro. Taken together, this material has the requisite properties to control initial biological responses and the longevity to provide longer term mechanical support.
Co-reporter:Jacqueline L. Harding, Melissa M. Reynolds
Trends in Biotechnology (March 2014) Volume 32(Issue 3) pp:140-146
Publication Date(Web):1 March 2014
DOI:10.1016/j.tibtech.2013.12.004
•Biofouling as a result of thrombus and bacterial biofilms leads to device rejection.•Ideal devices treat the ailment, minimize adverse effects, and aid in regeneration.•Chemical and surface properties of device materials dictates the biological response.•Material design with passive and active approaches can be used to minimize biofouling.•Material integration with tissues and fluids will lead to device incorporation.When interfaced with the biological environment, biomedical devices are prone to surface biofouling due to adhesion of microbial or thrombotic agents as a result of the foreign body response. Surface biofouling of medical devices occurs as a result of nonspecific adhesion of noxious substrates to the surface. Approaches for biofouling-resistant surfaces can be categorized as either the manipulation of surface chemical functionalities or through the incorporation of regulatory biomolecules. This review summarizes current strategies for creating biofouling-resistant surfaces based on surface hydrophilicity and charge, biomolecule functionalization, and drug elution. Reducing the foreign body response and restoring the function of cells around the device minimizes the risk of device rejection and potentially integrates devices with surrounding tissues and fluids. In addition, we discuss the use of peptides and NO as biomolecules that not only inhibit surface fouling, but also promote the integration of medical devices with the biological environment.
Co-reporter:Jacqueline L. Harding and Melissa M. Reynolds
Journal of Materials Chemistry A 2014 - vol. 2(Issue 17) pp:NaN2536-2536
Publication Date(Web):2013/12/09
DOI:10.1039/C3TB21458C
Polyurethane/metal organic framework composite materials were prepared for the generation of the bioregulatory agent, nitric oxide (NO). Extruded tubing was fabricated though a 2-step compounding and extrusion method that yielded a uniform composition of the MOF catalyst in the tubing, where the MOF remained structurally robust during the extrusion process. The resulting MOF embedded polymeric tubing facilitated the generation of NO from bioavailable S-nitrosothiols. The function of the catalyst in the composite material was compared to neat catalysts. The substrate structure was found to have significant influence on the reactivity of the MOF catalyst with NO release times ranging from 1 to 16 h. The dosage of NO could be tuned based on the S-nitrosothiol employed. The ability for sustained NO release from a composite material is a promising approach for long-term biocompatibility.
Co-reporter:Alec Lutzke, Bella H. Neufeld, Megan J. Neufeld and Melissa M. Reynolds
Journal of Materials Chemistry A 2016 - vol. 4(Issue 11) pp:NaN1998-1998
Publication Date(Web):2016/02/26
DOI:10.1039/C6TB00037A
Nitric oxide (NO) is a unique bioactive molecule that performs multiple physiological functions and has been found to exhibit antithrombotic, antimicrobial, and wound-healing effects as an exogenous therapeutic agent. NO release from polymeric materials intended for use in biomedical applications has been established to reduce their thrombogenicity and decrease the likelihood of infection and inflammation that frequently produce medical complications. As a result, numerous NO-releasing polymers have been developed in an effort to utilize the beneficial properties of NO to improve the performance of implantable materials. The majority of synthetic NO-releasing biodegradable polymers that have been reported to date are polyesters, and there is significant interest in the development of new NO-releasing materials with improved or distinctive physicochemical characteristics. Polyphosphazenes are polymers with inorganic phosphorus–nitrogen backbones, and hydrolytically-sensitive derivatives with organic substituents have been prepared that degrade under physiological conditions. For this reason, biodegradable poly(organophosphazenes) are interesting candidate materials for applications such as tissue engineering, where the addition of NO release capability may be therapeutically useful. Herein, we report the first development and characterization of an NO-releasing poly(organophosphazene) from poly(ethyl S-methylthiocysteinyl-co-ethyl cysteinyl phosphazene) (POP-EtCys-SH). The thiolated polymer was synthesized from the reaction of poly(dichlorophosphazene) with ethyl S-methylthiocysteinate, followed by partial cleavage of the disulfide linkages to form free thiol groups. The conversion of thiol to the NO-releasing S-nitrosothiol functional group with tert-butyl nitrite resulted in a polymer (POP-EtCys-NO) with an average NO content of 0.55 ± 0.04 mmol g−1 that was found to release a total of 0.35 ± 0.02 mmol NO g−1 over 24 h under physiological conditions (37 °C, pH 7.4 phosphate buffered saline). Extracts obtained from both the thiolated and S-nitrosated polymers were not found to significantly impair the viability of human dermal fibroblasts or induce morphological changes, indicating that this cysteine-based polyphosphazene may possess potential utility as an NO-releasing biomaterial.
Co-reporter:Vinod B. Damodaran and Melissa M. Reynolds
Journal of Materials Chemistry A 2011 - vol. 21(Issue 16) pp:NaN5872-5872
Publication Date(Web):2011/03/15
DOI:10.1039/C1JM10315F
A biodegradable multiblock polymer containing the S-nitrosothiol moiety was synthesized via a 4 step process using non-aqueous reaction conditions. The structural and morphological properties of the material were characterized via1H NMR, GPC, DSC, TGA, and SAXS. The nitric oxide (NO) storage capacity of the polymer was found to be 0.42 ± 0.01 mmol NO per g polymer using UV spectroscopy, and real-time chemiluminescence measurements demonstrated a controlled and extended NO release profile. The degradation rate of the material was the most rapid during the first week followed by a slower linear release rate. Preliminary biocompatibility testing of the material using ISO protocols indicated no cell lysis in vitro. Taken together, this material has the requisite properties to control initial biological responses and the longevity to provide longer term mechanical support.
Co-reporter:J. P. Yapor, A. Lutzke, A. Pegalajar-Jurado, B. H. Neufeld, V. B. Damodaran and M. M. Reynolds
Journal of Materials Chemistry A 2015 - vol. 3(Issue 48) pp:NaN9241-9241
Publication Date(Web):2015/11/16
DOI:10.1039/C5TB01625H
Nitric oxide (NO) is a biologically-active free radical involved in numerous physiological processes such as regulation of vasodilation, promotion of cell proliferation and angiogenesis, and modulation of the inflammatory and immune responses. Furthermore, NO has demonstrated the ability to mitigate the foreign body response that often results in the failure of implanted biomedical devices. Although NO has promising therapeutic value, the short physiological half-life of exogenous NO complicates its effective delivery. For this reason, the development of NO-releasing materials that permit the localized delivery of NO is an advantageous method of utilizing this molecule for biomedical applications. Herein, we report the synthesis and characterization of biodegradable NO-releasing polyesters prepared from citric acid, maleic acid, and 1,8-octanediol. NO release was achieved by incorporation of S-nitrosothiol donor groups through conjugation of cysteamine and ethyl cysteinate to the polyesters, followed by S-nitrosation with tert-butyl nitrite. The extent of NO loading and the release properties under physiological conditions (pH 7.4 PBS, 37 °C) were determined by chemiluminesence-based NO detection. The average total NO content of poly(citric-co-maleic acid-co-1,8-octanediol)-cysteamine was determined to be 0.45 ± 0.07 mol NO g−1 polymer, while the NO content for poly(citric-co-maleic acid-co-1,8-octanediol)-ethyl cysteinate was 0.16 ± 0.04 mol NO g−1 polymer. Continuous NO release under physiological conditions was observed for at least 6 days for the cysteamine analog and 4 days for the ethyl cysteinate analog. Cell viability assays and morphological studies with human dermal fibroblasts indicated an absence of toxic leachates at a cytotoxic level, and suggested that these citrate-based polyesters may be suitable for future biomedical applications.
Co-reporter:Alec Lutzke, Adoracion Pegalajar-Jurado, Bella H. Neufeld and Melissa M. Reynolds
Journal of Materials Chemistry A 2014 - vol. 2(Issue 42) pp:NaN7458-7458
Publication Date(Web):2014/09/19
DOI:10.1039/C4TB01340A
Nitric oxide (NO)-releasing derivatives of chitin and chitosan were prepared through incorporation of the symmetrical dithiols 1,2-ethanedithiol, 1,3-propanedithiol, and 1,6-hexanedithiol, followed by S-nitrosation with tert-butyl nitrite. The NO loading of the materials and their real-time NO release profiles under physiological conditions (pH 7.4 phosphate buffered saline, 37 °C) were recorded over 24 hours, and in vitro cytotoxicity studies were performed using human dermal fibroblasts (HDF) to assess the suitability of the materials for biomedical applications. Of the six thiolated parent materials, five exhibited cell viability higher than 70% (MTS assay), an outcome that was corroborated by LIVE/DEAD assay. In all cases, HDF morphology was unaffected by the presence of extracts obtained from the thiolated materials.
Co-reporter:Vinod B. Damodaran, Jessica M. Joslin, Kathryn A. Wold, Sarah M. Lantvit and Melissa M. Reynolds
Journal of Materials Chemistry A 2012 - vol. 22(Issue 13) pp:NaN6001-6001
Publication Date(Web):2012/02/15
DOI:10.1039/C2JM16554F
A new class of nitric oxide (NO)-releasing biodegradable polymers has been synthesized by derivatizing poly(lactic-co-glycolic-co-hydroxymethyl propionic acid) (PLGH) polymers with structurally unique thiol functionalities followed by nitrosation with t-butyl nitrite to yield pendant S-nitrosothiol moieties. The extent of thiolation was found to be dependent on the thiol moiety itself with the efficiency of incorporation as follows: cysteamine > cysteine > homocysteine. Glutathione and penicillamine were not incorporated to any significant extent. The structure and polymer environment associated with the pendant thiol has been related to the physicochemical properties of the resulting polymers. To quantify the extent of S-nitrosation, chemiluminescence and UV-visible spectroscopy techniques were employed in combination. The cysteamine and homocysteine derivatives were found to have the highest extent of nitrosation at 93 ± 3% and 96 ± 3%, respectively, followed by 43 ± 1% for cysteine. Thermal decomposition led to near-complete recovery of NO based upon the quantification of the RSNO formation for each nitrosated polymer. Our ability to exert control over the thiol structure, extent of incorporation and the subsequent nitrosation is crucial to the resulting range of NO release kinetics that were yielded. The functional utility of these materials is demonstrated in that these non-toxic polymers release NO under physiological conditions, have degradation profiles that are appropriate for tissue scaffolds and can be prepared as electrospun nanofibers, commonly used in tissue and bone regeneration applications.
Co-reporter:Vinod B. Damodaran, Laura W. Place, Matt J. Kipper and Melissa M. Reynolds
Journal of Materials Chemistry A 2012 - vol. 22(Issue 43) pp:NaN23048-23048
Publication Date(Web):2012/09/20
DOI:10.1039/C2JM34834A
Herein we report the development and evaluation of enzymatically degradable nitric oxide (NO) releasing S-nitrosated dextran thiomers as potent biomedical materials. These materials are characterized by their specificity to release NO under arterial blood conditions, followed by their susceptibility to undergo enzymatic degradation by dextranase. The very specific conjugation chemistries we employed for the thiol incorporation resulted in characteristic stabilization of the resulting S-nitrosothiol moieties, and consequently yielded stable pro-drugs for the storage and controlled delivery of NO. We evaluated the extent of NO loading and release kinetics using multiple and independent analytical techniques, and related these to the structure and environment associated with the thiol moiety incorporated onto the dextran backbone. Finally, the enzymatic degradation kinetics was followed by monitoring the molecular weight profile using gel permeation chromatography, and the results were interpreted using well-established model predictions.
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