To overcome the problem caused by the lability of the Au–S bond, we demonstrate the first use of Mn2(CO)10 for visible-light-induced surface grafting polymerization on Au surfaces in this paper. The visible-light-induced surface grafting of poly(N-isopropylacrylamide) (PNIPAAm) has the features of a “controlled” polymerization, which is characterized by a linear relationship between the thickness of the grafting layer and the monomer concentration. Ellipsometry indicated the formation of PNIPAAm films of up to ∼200 nm in thickness after only 10 min of polymerization at room temperature, demonstrating that this is a very fast process in comparison with traditional grafting polymerization techniques. Moreover, to demonstrate the potential applications of our approach, different substrates grafted by PNIPAAm and the covalent immobilization of a range of polymers on Au surfaces were also demonstrated. Considering the advantages of simplicity, efficiency, and mild reaction conditions as well as the ability of catecholic derivatives to bind to a large variety of substrates, this visible-light-induced grafting method is expected to be useful in designing functional interfaces.

Thrombus formation remains a serious problem in developing blood compatible materials. Despite continuous, intensive efforts over many years to prepare surfaces that prevent clotting, such surfaces have not been achieved; indeed it seems that surface-induced clotting is inevitable. An alternative approach is to accept that clotting will occur and to design surfaces so that small, nascent clots will be lysed before they can cause harm. The generation of plasmin, as in the fibrinolytic system, may be adopted for this purpose. The vascular endothelium (the inner surface of intact blood vessels) releases nitric oxide (NO) on a continuous basis. NO protects against platelet activation and aggregation, and also has an anti-proliferative effect on smooth muscle cells (SMCs). Based on these two important functions of the vascular system, the approach of constructing a fibrinolytic surface that generates NO is developed in the present work. Poly(oligo(ethylene glycol) methyl ether methacrylate-co-6-amino-2-(2-methacylamido)-hexanoic acid) (poly(OEGMA-co-LysMA)) was attached to a vinyl-functionalized polyurethane (PU) surface by graft polymerization giving a surface (PU-POL) with protein-resistant properties (via poly(OEGMA)) and clot lysing properties (via poly(LysMA)). Selenocystamine, which catalyzes S-nitrosothiol decomposition to generate NO in the vasculature, was then immobilized on the PU-POL surface via covalent attachment. A dual functioning surface with fibrinolytic activity (lysis of nascent clots) and NO releasing ability (inhibition of platelet adhesion and SMC adhesion as well as proliferation) was thereby constructed.

AbstractChemical modification of surfaces is recognized as efficient strategies to prevent bacterial contamination and the associated infection. Herein, a novel ionic liquid derivative 1-(((4-benzoylbenzoyl)oxy)methyl)-3-methyl-1H-imidazol-3-ium bromide (BMI) containing benzophenone moieties is developed to act as both a photoreactive cross-linker and an antibacterial agent. BMI can rapidly and efficiently form a “smart” antibacterial film on a variety of substrate surfaces in 2 min under mild UV irradiation. The modified surfaces show highly antibacterial activity, achieving more than 99% bacterial killing efficiency against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli using live/dead staining methods. In addition, the BMI-modified surfaces can release ≈97% of the killed bacteria via ion-exchange of hexametaphosphate (PP6−) anions and can regenerate bactericidal properties over three cycles. Moreover, in vitro cytocompatibility tests indicate that the BMI-modified surfaces have good biocompatibility. Thus, it can be concluded that cross-linked BMI layers provide a practical and convenient approach for the fabrication of “smart” antibacterial surfaces.

Mimicking natural fibrinolytic mechanisms that covalently bind lysine-ligands (free ε-amino and carboxylic groups) onto biomaterial surfaces is an attractive strategy to prevent clot formation on blood contact materials. However, the modification process is typically complicated and limited due to the diversity of biomaterials. Herein, we describe a simple, substrate-independent protocol to prepare a lysine-ligand functionalized layer on biomaterial surfaces. This approach is based on the adsorption and cross-linking of aldehyde-functionalized poly(N-(2,2-dimethoxyethyl)methacrylamide) (APDMEA) and amino-functionalized polymethacryloyl-L-lysine (APMLys) on a variety of substrates, such as polyurethane (PU), polydimethylsiloxane (PDMS), polyvinylchloride (PVC), stainless steel (SS) and cellulose acetate (CA). The lysine-ligand functionalized layer on substrates highly enhanced the specific adsorption of plasminogen from plasma and showed good chemical stability and excellent biocompatibility with L929 cells using the MTT assay. Moreover, for example, after the adsorbed plasminogen was activated and converted into plasmin, the fibrinolytic functionalization of CA was demonstrated using a modified plasma recalcification assay. Collectively, considering the advantages of simplicity, environmental friendliness and substrate-independence, the present study might therefore represent a general approach for the construction of a biointerface with fibrinolytic activity.

Tailoring the surface properties of poly(dimethylsiloxane) (PDMS) is essential for the advancement of its applications. However, the modification process is usually complicated and limited due to the chemical inertness of the surfaces of PDMS. Here, we report for the first time, a facile and versatile method for the functional surface modification of PDMS via visible light-induced grafting polymerization at room temperature. This modification is readily achieved in two steps: (1) covalently integrating alkyl bromine into the PDMS networks using a simple mixing procedure and (2) visible light-induced surface grafting polymerization using Mn2(CO)10. We have demonstrated that the PDMS surface can be functionalized with a wide variety of polymers via covalent grafting, such as poly(trifluoroethyl methacrylate) (PTFEMA), poly(N-isopropylacrylamide) (PNIPAAm), poly(acrylic acid) (PAA) and poly(vinyl acetate) (PVAc). As an example, after the grafted PVAc was transformed into its hydrophilic analogue poly(vinyl alcohol) (PVA), anti-biofouling functionalization of PDMS was obtained. The anti-biofouling properties of the functionalized PDMS were demonstrated using cell adhesion and bacterial adhesion tests. Moreover, the grafting kinetics of PVAc showed that this process was fast and efficient.

A simple and versatile method for the preparation of surfaces to control bacterial adhesion is described. Substrates were first treated with two catechol-based polymerization initiators, one for thermal initiation and one for visible-light photoinitiation. Graft polymerization in sequence of dimethylaminoethyl methacrylate (DMAEMA) and 3-acrylamidebenzene boronic acid (BA) from the surface-bound initiators to form mixed polymer brushes on the substrate was then carried out. The PDMAEMA grafts were thermally initiated and the PBA grafts were visible-light-photoinitiated. Gold, poly(vinyl chloride) (PVC), and poly(dimethylsiloxane) (PDMS) were used as model substrates. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), and ellipsometry analysis confirmed the successful grafting of PDMAEMA/PBA mixed brushes. We demonstrated that the resulting surfaces showed charge-reversal properties in response to change of pH. The transition in surface charge at a specific pH allowed the surface to be reversibly switched from bacteria-adhesive to bacteria-resistant. At pH 4.5, below the isoelectric points (IEP, pH 5.3) of the mixed brushes, the surfaces are positively charged and the negatively charged Gram-positive S. aureus adheres at high density (2.6 × 106 cells/cm2) due to attractive electrostatic interactions. Subsequently, upon increasing the pH to 9.0 to give negatively charged polymer brush surface, ∼90% of the adherent bacteria are released from the surface, presumably due to repulsive electrostatic interactions. This approach provides a simple method for the preparation of surfaces on which bacterial adhesion can be controlled and is applicable to a wide variety of substrates.

Controlling the interface of biomaterials that take advantage of the natural fibrinolytic or clot-dissolving capacity of the body is attractive for preventing clot formation on an implanted biomaterial. Here, we engineer the interface of a biopolymer electrospun fiber mat with a serine protease of the tissue plasminogen activator (t-PA), aiming to simulate fibrinolytic functions of the body. The method is based on the one-step electrospinning aqueous solution of poly(vinyl alcohol) (PVA) and lysine ligand-modified PVA (PVA–Lys), in which the ε-amino and carboxyl groups of the lysine ligands were free. These electrospun mats showed good resistance to non-specific protein adsorption of fibrinogen and excellent biocompatibility with L929 cells using the MTT assay. A highly specific tethering of t-PA was facilitated by the lysine-functionalized surface through molecular recognition of t-PA to the lysine ligands. Moreover, the t-PA anchorage to the PVA/PVA–Lys mats can be easily released by plasminogen displacement when exposed to plasma, and can efficiently lyse the formed-clot in an in vitro plasma assay. In particular, the quantities of t-PA tethered on the mats could easily be regulated by simply varying the blend ratio of PVA and PVA–Lys in the electrospinning process. Collectively, considering the advantages of simplicity, controllability and biocompatibility, this approach is expected to be useful for the construction of a biointerface for blood-contacting devices.

A simple approach has been developed to functionalize various substrates, such as gold and polyvinylchloride, with dopamine methacrylamide—a molecule with adhesive properties that mimic those of mussels—to produce a versatile and general platform for subsequent surface modification. With active double bonds on the surface, various polymers, such as poly([2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (PMEDSAH) and poly(N-vinylpyrrolidone) (PVP), can be grafted by conventional radical polymerization. Double bond surface functionalization and subsequent polymer grafting have been verified by static water contact angle, Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. Protein adsorption assays showed that the polymer-modified substrates have good protein-resistant properties. Considering the advantages of facility, versatility and substrate-independence, this method should be useful in designing functional interfaces for bioengineering applications.

To overcome the problem caused by the lability of the Au–S bond, we demonstrate the first use of Mn2(CO)10 for visible-light-induced surface grafting polymerization on Au surfaces in this paper. The visible-light-induced surface grafting of poly(N-isopropylacrylamide) (PNIPAAm) has the features of a “controlled” polymerization, which is characterized by a linear relationship between the thickness of the grafting layer and the monomer concentration. Ellipsometry indicated the formation of PNIPAAm films of up to ∼200 nm in thickness after only 10 min of polymerization at room temperature, demonstrating that this is a very fast process in comparison with traditional grafting polymerization techniques. Moreover, to demonstrate the potential applications of our approach, different substrates grafted by PNIPAAm and the covalent immobilization of a range of polymers on Au surfaces were also demonstrated. Considering the advantages of simplicity, efficiency, and mild reaction conditions as well as the ability of catecholic derivatives to bind to a large variety of substrates, this visible-light-induced grafting method is expected to be useful in designing functional interfaces.

Hydrogen sulfide (H2S) is accepted as a third “gasotransmitter’’ of human physiology and pathology but remains difficult to study, in large part because of the lack of methods for the selective monitoring of this small signaling molecule in live biological specimens. We now report a new reaction-based polymeric fluorescent sensor for selective imaging of H2S in living cells. A novel functional monomer, 2-allyl-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinoline-6-sulfonyl azide (AISA) was firstly synthesized and copolymerized with styrene to obtain a polymeric fluorescent sensor material. AISA and poly(styrene-co-AISA) (PSAISA) showed a fast turn-on fluorescence signal enhancement and a high selectivity for hydrogen sulfide (H2S) over other biologically relevant species including HSO3−, SO42−, S2O32− and cysteine. Furthermore, upon reaction with H2S, PSAISA gave a strong spectral response changing from colorless to bright yellow. FT-IR and 1H NMR data confirmed that the fluorescence enhancement of PSAISA was caused by the reduction of sulfonyl azide to sulfonamide in the presence of H2S. This property was successfully used to image H2S in living cells, thus demonstrating the potential of this material in biosensor applications.

Novel antifouling (AF)/fouling release (FR) surfaces based on poly(N-vinylpyrrolidone) (PVP)-grafted poly(dimethylsiloxane) (PDMS) have been developed using surface-initiated atom transfer radical polymerization of N-vinylpyrrolidone (NVP). Grafting was verified by several analytical techniques including attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and water contact angle measurements. The PVP-grafted PDMS surfaces showed excellent protein resistance and very low cell adhesion and bacterial adhesion even after storage in ambient conditions for 30 days. Scanning electron microscopy and atomic force microscopy revealed that the grafted PVP layers formed regular domain-like microtopographic structures. Moreover, the size of the domains could be tuned by varying the surface mass density of the PVP. The combination of tunable microtopography and AF properties on the same surface provides a novel approach for the preparation of AF/FR surfaces having long-term stability.

A method was developed to modify silicon surfaces with good protein resistance and specific cell attachment. A silicon surface was initially deposited using a block copolymer of N-vinylpyrrolidone (NVP) and 2-hydroxyethyl methacrylate (HEMA) (PVP-b-PHEMA) film through surface-initiated atom transfer radical polymerization and then further immobilized using a short arginine-glycine-aspartate (RGD) peptide. Our results demonstrate that the RGD-modified surfaces (Si-RGD) can suppress non-specific adsorption of proteins and induce the adhesion of L929 cells. The Si-RGD surface exhibited higher cell proliferation rates than the unmodified silicon surface. This research established a simple method for the fabrication of dual-functional silicon surface that combines antifouling and cell attachment promotion.

The present work aimed to study the interaction between plasma proteins and PVP-modified surfaces under more complex protein conditions. In the competitive adsorption of fibrinogen (Fg) and human serum albumin (HSA), the modified surfaces showed preferential adsorption of HSA. In 100% plasma, the amount of Fg adsorbed onto PVP-modified surfaces was as low as 10 ng/cm2, suggesting the excellent protein resistance properties of the modified surfaces. In addition, immunoblots of proteins eluted from the modified surfaces after plasma contact confirmed that PVP-modified surfaces can repel most plasma proteins, especially proteins that play important roles in the process of blood coagulation.

Well-controlled polymerization of N-vinylpyrrolidone (NVP) on Au surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP) was carried out at room temperature by a silanization method. Initial attempts to graft poly(N-vinylpyrrolidone) (PVP) layers from initiators attached to alkanethiol monolayers yielded PVP films with thicknesses less than 5 nm. The combined factors of the difficulty in the controllable polymerization of NVP and the instability of alkanethiol monolayers led to the difficulty in the controlled polymerization of NVP on Au surfaces. Therefore, the silanization method was employed to form an adhesion layer for initiator attachment. This method allowed well-defined ATRP polymerization to occur on Au surfaces. Water contact angle, X-ray photoelectron spectroscopy (XPS), and reflectance Fourier transform infrared (reflectance FTIR) spectroscopy were used to characterize the modified surfaces. The PVP-modified gold surface remained stable at 130 °C for 3 h, showing excellent thermal stability. Thus, postfunctionalization of polymer brushes at elevated temperatures is made possible. The silanization method was also applied to modify SPR chips and showed potential applications in biosensors and biochips.

Thrombus formation remains a serious problem in developing blood compatible materials. Despite continuous, intensive efforts over many years to prepare surfaces that prevent clotting, such surfaces have not been achieved; indeed it seems that surface-induced clotting is inevitable. An alternative approach is to accept that clotting will occur and to design surfaces so that small, nascent clots will be lysed before they can cause harm. The generation of plasmin, as in the fibrinolytic system, may be adopted for this purpose. The vascular endothelium (the inner surface of intact blood vessels) releases nitric oxide (NO) on a continuous basis. NO protects against platelet activation and aggregation, and also has an anti-proliferative effect on smooth muscle cells (SMCs). Based on these two important functions of the vascular system, the approach of constructing a fibrinolytic surface that generates NO is developed in the present work. Poly(oligo(ethylene glycol) methyl ether methacrylate-co-6-amino-2-(2-methacylamido)-hexanoic acid) (poly(OEGMA-co-LysMA)) was attached to a vinyl-functionalized polyurethane (PU) surface by graft polymerization giving a surface (PU-POL) with protein-resistant properties (via poly(OEGMA)) and clot lysing properties (via poly(LysMA)). Selenocystamine, which catalyzes S-nitrosothiol decomposition to generate NO in the vasculature, was then immobilized on the PU-POL surface via covalent attachment. A dual functioning surface with fibrinolytic activity (lysis of nascent clots) and NO releasing ability (inhibition of platelet adhesion and SMC adhesion as well as proliferation) was thereby constructed.

Mimicking natural fibrinolytic mechanisms that covalently bind lysine-ligands (free ε-amino and carboxylic groups) onto biomaterial surfaces is an attractive strategy to prevent clot formation on blood contact materials. However, the modification process is typically complicated and limited due to the diversity of biomaterials. Herein, we describe a simple, substrate-independent protocol to prepare a lysine-ligand functionalized layer on biomaterial surfaces. This approach is based on the adsorption and cross-linking of aldehyde-functionalized poly(N-(2,2-dimethoxyethyl)methacrylamide) (APDMEA) and amino-functionalized polymethacryloyl-L-lysine (APMLys) on a variety of substrates, such as polyurethane (PU), polydimethylsiloxane (PDMS), polyvinylchloride (PVC), stainless steel (SS) and cellulose acetate (CA). The lysine-ligand functionalized layer on substrates highly enhanced the specific adsorption of plasminogen from plasma and showed good chemical stability and excellent biocompatibility with L929 cells using the MTT assay. Moreover, for example, after the adsorbed plasminogen was activated and converted into plasmin, the fibrinolytic functionalization of CA was demonstrated using a modified plasma recalcification assay. Collectively, considering the advantages of simplicity, environmental friendliness and substrate-independence, the present study might therefore represent a general approach for the construction of a biointerface with fibrinolytic activity.

Tailoring the surface properties of poly(dimethylsiloxane) (PDMS) is essential for the advancement of its applications. However, the modification process is usually complicated and limited due to the chemical inertness of the surfaces of PDMS. Here, we report for the first time, a facile and versatile method for the functional surface modification of PDMS via visible light-induced grafting polymerization at room temperature. This modification is readily achieved in two steps: (1) covalently integrating alkyl bromine into the PDMS networks using a simple mixing procedure and (2) visible light-induced surface grafting polymerization using Mn2(CO)10. We have demonstrated that the PDMS surface can be functionalized with a wide variety of polymers via covalent grafting, such as poly(trifluoroethyl methacrylate) (PTFEMA), poly(N-isopropylacrylamide) (PNIPAAm), poly(acrylic acid) (PAA) and poly(vinyl acetate) (PVAc). As an example, after the grafted PVAc was transformed into its hydrophilic analogue poly(vinyl alcohol) (PVA), anti-biofouling functionalization of PDMS was obtained. The anti-biofouling properties of the functionalized PDMS were demonstrated using cell adhesion and bacterial adhesion tests. Moreover, the grafting kinetics of PVAc showed that this process was fast and efficient.

Controlling the interface of biomaterials that take advantage of the natural fibrinolytic or clot-dissolving capacity of the body is attractive for preventing clot formation on an implanted biomaterial. Here, we engineer the interface of a biopolymer electrospun fiber mat with a serine protease of the tissue plasminogen activator (t-PA), aiming to simulate fibrinolytic functions of the body. The method is based on the one-step electrospinning aqueous solution of poly(vinyl alcohol) (PVA) and lysine ligand-modified PVA (PVA–Lys), in which the ε-amino and carboxyl groups of the lysine ligands were free. These electrospun mats showed good resistance to non-specific protein adsorption of fibrinogen and excellent biocompatibility with L929 cells using the MTT assay. A highly specific tethering of t-PA was facilitated by the lysine-functionalized surface through molecular recognition of t-PA to the lysine ligands. Moreover, the t-PA anchorage to the PVA/PVA–Lys mats can be easily released by plasminogen displacement when exposed to plasma, and can efficiently lyse the formed-clot in an in vitro plasma assay. In particular, the quantities of t-PA tethered on the mats could easily be regulated by simply varying the blend ratio of PVA and PVA–Lys in the electrospinning process. Collectively, considering the advantages of simplicity, controllability and biocompatibility, this approach is expected to be useful for the construction of a biointerface for blood-contacting devices.

The development of a smart antibacterial surface that can both kill attached live bacteria and release dead bacteria is reported. The surface consists of counterion-responsive poly(cationic liquid) brushes of poly(1-(2-methacryloyloxyhexyl)-3-methylimidazolium bromide) (PIL(Br)), the properties of which can be switched repeatedly between bacterial killing and bacterial release. Upon counter-anion exchange of PIL(Br) chains using lithium bis(trifluoromethanesulfonyl) amide (LiTf2N) to yield PIL(Tf2N), the wettability of the surface changes from hydrophilic (water contact angle ∼52°) to hydrophobic (∼97°). The PIL(Br) chains adopt an extended conformation with bactericidal properties. Counter-anion switching to PIL(Tf2N) gives a collapsed chain conformation allowing the release of killed bacteria. The switchable killing and releasing actions of the surface were maintained over three cycles. Thus it is concluded that PIL(Br) layers provide a viable approach for the fabrication of “smart” antibacterial surfaces.