Surface characterization and biological properties study of silicone rubber membrane grafted with phospholipid as biomaterial via plasma induced graft copolymerization

Photoassisted Surface Modification with Zwitterionic Phosphorylcholine Polymers for the Fabrication of Ideal Biointerfaces

Surface modification using zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers is commonly performed to fabricate interfaces that reduce nonspecific fouling by biomolecules and cells. Accordingly, several clinically used devices, such as guide wires, stents, oxygenators, left ventricular assist devices, and microcatheters have been modified using MPC polymers. The specific types of surface modifications vary across substrates and applications. Recently, photoreactions have garnered attention for surface modification due to their stability and tunability. This review highlights various studies that employed photoreactions to modify surfaces using MPC polymers, especially photoinduced graft polymerization of MPC. In addition to antifouling materials, several micromanipulated, long-lasting hydrophilic, and super antiwear surfaces are summarized. Furthermore, several photoreactive MPC polymers that can be used to control interactions between biomolecules and materials are presented along with their potential to form selective recognition surfaces that target biomolecules for biosensors and diagnostic devices.

Paclitaxel-eluting nanofiber-covered self-expanding nonvascular stent for palliative chemotherapy of gastrointestinal cancer and its related stenosis

Self-expanding non-vascular metal stents (SEMS) is now a choice of treatment for tumor-induced obstructive symptoms of gastrointestinal tract. But in-growing tumor causes re-stenosis. Here, we studied a paclitaxel-eluting nanofiber-covered stent for palliative chemotherapy of gastrointestinal cancer and its related stenosis. In vivo and in vitro feasibility of nanofiber-covered nonvascular stent was evaluated in this study. Nanofiber-covered stent released paclitaxel (PTX) in controlled manner for 30 days. PTX-NFM significantly inhibited the growth of CT-26 colon cancer in comparison with PTX injection. PTX maintained higher tumor concentrations over 1.0 μg/ml for more than 14 days without systemic exposure. TUNEL and H&E staining proved locally concentrated PTX induced the higher apoptosis than PTX injection. In this way, PTX-eluting nanofiber-covered stent possibly inhibits in-growth of cancer and extends patency of stent. Clinical feasibility of PTX-eluting nanofiber nonvascular stent for cholangiocarcinoma and gastrointestinal cancers will be investigated in further studies.

A review on the wettability of dental implant surfaces II: Biological and clinical aspects

Dental and orthopedic implants have been under continuous advancement to improve their interactions with bone and ensure a successful outcome for patients. Surface characteristics such as surface topography and surface chemistry can serve as design tools to enhance the biological response around the implant, with in vitro, in vivo and clinical studies confirming their effects. However, the comprehensive design of implants to promote early and long-term osseointegration requires a better understanding of the role of surface wettability and the mechanisms by which it affects the surrounding biological environment. This review provides a general overview of the available information about the contact angle values of experimental and of marketed implant surfaces, some of the techniques used to modify surface wettability of implants, and results from in vitro and clinical studies. We aim to expand the current understanding on the role of wettability of metallic implants at their interface with blood and the biological milieu, as well as with bacteria, and hard and soft tissues.

A general strategy for creating self-defending surfaces for controlled drug production for long periods of time

Infections associated with bacterial adhesion and subsequent biofilm formation constitute a grave medical issue for which conventional antibiotic therapies remain ineffective. Here, we introduce a new strategy employing nanotechnology to create smart surfaces with self-defending properties that result in controlled drug production and controlled release for long periods of time. Self-defending surfaces on solid supports are prepared by immobilizing polymer nanoreactors containing an encapsulated biocatalyst that can convert non-antibiotic substrates to an abiotic drug. For medical applications and biosensing, the immobilization method must fulfill specific criteria, and these were achieved by an immobilization strategy based on Schiff base formation between aldehyde groups on the outer surface of nanoreactors and amino groups on the solid support surface, followed by reductive amination. The resulting self-defending surfaces allow control of drug production at a specific rate for a specific period of time by adding predetermined amounts of substrate to the outer medium, minimization of dosages and therefore systemic toxicity, and limitation of the immune response. Such self-defending surfaces producing drugs offer a versatile strategy for the development of smart surfaces with improved stability and efficacy (by changing the biocatalyst) to serve as biosensors, antifouling surfaces, or smart packages.

Optimized molecular structure of photoreactive biocompatible block copolymers for surface modification of metal substrates

Poly(2-methacryloyloxyethyl phosphorylcholine)-b-poly(2-methacryloyloxyethyl phosphate-co-2-cinnamoyloxyethyl methacrylate) (PMPC-b-P(MPA/CMA)) was prepared by reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization. The block copolymers were coated on stainless steel (SUS316L) and other metal substrates, and then the surface was subsequently irradiated with UV light. The wettability of a specimen surface treated with a block copolymer was improved in comparison with that of an untreated SUS316L plate. From X-ray photoelectron spectroscopy (XPS) data, it was clear that the P(MPA/CMA) block worked as a binding site on the SUS316L surface. The surface density of the block copolymer-immobilized SUS316L surface was influenced by the molecular weight of the PMPC block. The stability of the immobilized layer was improved by UV irradiation, which induced intermolecular dimerization of the CMA. In addition to the SUS316L surface, various other metal surfaces could be modified by surface immobilization of block copolymers. Serum protein adsorption and fibroblast adhesion were effectively reduced by surface immobilization of block copolymers with optimal molecular weight of PMPC block. The nonfouling property was preserved after 1 week of cell cultivation.

The impact of dendrimer-grafted modifications to model silicon surfaces on protein adsorption and bacterial adhesion

In the oral cavity, omnipresent salivary protein films (pellicle) mediate bacterial adhesion and biofilm formation on natural tissues as well as on artificial implant surfaces, which may cause serious infectious diseases like periimplantitis. The purpose of this in vitro study was to investigate the adsorption/desorption behaviour of human saliva on model surfaces grafted with polyamidoamine (PAMAM) dendrimer molecules compared to self-assembled monolayers (SAMs) exhibiting the same terminal functions (-NH(2), -COOH) by two complementary analytical methods. Furthermore, the role of saliva conditioning of PAMAM and analogous SAM modifications on the adhesion of Streptococcus gordonii DL1, an early oral colonizer, was investigated. In contrast to SAMs, PAMAM-grafted surfaces showed reduced streptococcal adherence in the absence of pre-adsorbed saliva similar to the level obtained for poly(ethylene glycol) (PEG) coatings. Moreover, coatings of PAMAM-NH(2) maintained their bacteria-repellent behaviour even after saliva-conditioning. As a general outcome, it was found that lower amounts of protein adsorbed on PAMAM coatings than on analogous SAMs. Since this study demonstrates that covalently bound PAMAM dendrimers can modulate the oral bacterial response, this approach has significant potential for the development of anti-adhesive biomaterial surfaces that are conditioned with proteinaceous films.

Development of robust biocompatible silicone with high resistance to protein adsorption and bacterial adhesion

A new biocompatible silicone comprising a carboxybetaine (CB) ester analogue, 3-methacryloxypropyltris(trimethylsiloxy)silane (TRIS) and an organic silicone macromer (bis-α,ω-(methacryloxypropyl) polydimethylsiloxane) has been developed using photo-polymerisation. Following interfacial hydrolysis of the CB ester, the resulting zwitterionic material became significantly more hydrophilic and exhibited high resistance to both non-specific protein adsorption and bacterial adhesion. Moreover, the stability of these non-fouling properties was dramatically improved by using a slow and controlled rate of ester hydrolysis of the original protective hydrophobic matrix. The subsequent ability to maintain the original optical and mechanical properties of the bare silicone following surface activation makes this material an ideal candidate for preparing contact lenses and other medical devices.

Candida albicans biofilm formation on peptide functionalized polydimethylsiloxane

In order to prevent biofilm formation by Candida albicans, several cationic peptides were covalently bound to polydimethylsiloxane (PDMS). The salivary peptide histatin 5 and two synthetic variants (Dhvar 4 and Dhvar 5) were used to prepare peptide functionalized PDMS using 4-azido-2,3,5,6-tetrafluoro-benzoic acid (AFB) as an interlinkage molecule. In addition, polylysine-, polyarginine-, and polyhistidine-PDMS surfaces were prepared. Dhvar 4 functionalized PDMS yielded the highest reduction of the number of C. albicans biofilm cells in the Modified Robbins Device. Amino acid analysis demonstrated that the amount of peptide immobilized on the modified disks was in the nanomole range. Poly-d-lysine PDMS, in particular the homopeptides with low molecular weight (2500 and 9600) showed the highest activity against C. albicans biofilms, with reductions of 93% and 91%, respectively. The results indicate that the reductions are peptide dependent.

Functionalization of poly(dimethylsiloxane) surfaces with maleic anhydride copolymer films

Combining advantageous bulk properties of polymeric materials with surface-selective chemical conversions is required in numerous advanced technologies. For that aim, we investigate strategies to graft maleic anhydride (MA) copolymer films onto poly(dimethylsiloxane) (PDMS) precoatings. Amino groups allowing the covalent attachment of the MA copolymer films to the PDMS (Sylgard 184) surface were introduced either by low-pressure ammonia plasma treatment, or by attachment of 3-aminopropyltriethoxysilane (APTES) onto air plasma-treated PDMS. The resultant coatings were extensively characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), contact angle measurements, and atomic force microscopy (AFM). The results show that the impact of the plasma treatment on the physical properties on the topmost surface of the PDMS is critically important for the characteristics of the layered coatings.

Surface response of fluorine polymer-incorporated resin composites to cariogenic biofilm adherence

Experimental resin composites with incorporated polytetrafluoroethylene (PTFE) particles were developed, which theoretically could improve the surface properties of the materials, including the inhibition of bacterial adherence. To assess the surface properties in relation to biofilm formation and detachment, 23.1% (wt/wt) linear PTFE particles (FL-30) and cross-linked PTFE particles (FC-30) were incorporated into pure resin composites. Pure PTFE plates and pure resin composites without PTFE (F-0) were used as control specimens. Sucrose-dependent Streptococcus mutans biofilms were formed on the specimen blocks inside an oral biofilm reactor for various time periods and analyzed with or without application of driving forces. In addition, water contact angles and surface roughness were measured. The water contact angles of FL-30 (61.2 degrees ) and FC-30 (65.8 degrees ) were larger than that of F-0 (48.5 degrees ). The largest contact angle (107 degrees ) was detected on pure PTFE plates. However, the surfaces of FL-30, FC-30, and pure PTFE plates were rougher than that of F-0. Although the surface properties of the materials differed in terms of contact angles and roughness, these factors seemed not to affect biofilm formation on the surfaces within 5 h. Pure PTFE plates harbored almost the same amounts of biofilm as F-0. However, when a very strong driving force was applied, it was clear that there were significantly smaller amounts of biofilms retained on pure PTFE plates, which showed contact angles much higher than those of the other materials. Hydrophobicity of the resin composite was improved by incorporation of PTFE fillers. However, surface resistance against biofilm formation was not improved.

Surface modification with well-defined biocompatible triblock copolymers

To improve interfacial phenomena of poly(dimethylsiloxane) (PDMS) as biomaterials, well-defined triblock copolymers were prepared as coating materials by reversible addition-fragmentation chain transfer (RAFT) controlled polymerization. Hydroxy-terminated poly(vinylmethylsiloxane-co-dimethylsiloxane) (HO-PV(l)D(m)MS-OH) was synthesized by ring-opening polymerization. The copolymerization ratio of vinylmethylsiloxane to dimethylsiloxane was 1/9. The molecular weight of HO-PV(l)D(m)MS-OH ranged from (1.43 to 4.44)x10(4), and their molecular weight distribution (M(w)/M(n)) as determined by size-exclusion chromatography equipped with multiangle laser light scattering (SEC-MALS) was 1.16. 4-Cyanopentanoic acid dithiobenzoate was reacted with HO-PV(l)D(m)MS-OH to obtain macromolecular chain transfer agents (macro-CTA). 2-Methacryloyloxyethyl phosphorylcholine (MPC) was polymerized with macro-CTAs. The gel-permeation chromatography (GPC) chart of synthesized polymers was a single peak and M(w)/M(n) was relatively narrow (1.3-1.6). Then the poly(MPC) (PMPC)-PV(l)D(m)MS-PMPC triblock copolymers were synthesized. The molecular weight of PMPC in a triblock copolymer was easily controllable by changing the polymerization time or the composition of the macro-CTA to a monomer in the feed. The synthesized block copolymers were slightly soluble in water and extremely soluble in ethanol and 2-propanol. Surface modification was performed via hydrosilylation. The block copolymer was coated on the PDMS film whose surface was pretreated with poly(hydromethylsiloxane). The surface wettability and lubrication of the PDMS film were effectively improved by immobilization with the block copolymers. In addition, the number of adherent platelets from human platelet-rich plasma (PRP) was dramatically reduced by surface modification. Particularly, the triblock copolymer having a high composition ratio of MPC units to silicone units was effective in improving the surface properties of PDMS. By selective decomposition of the Si-H bond at the surface of the PDMS substrate by irradiation with UV light, the coating region of the triblock copolymer was easily controlled, resulting in the fabrication of micropatterns. On the surface, albumin adsorption was well manipulated.

Improvement of the surface biocompatibility of silicone intraocular lens by the plasma‐induced tethering of phospholipid moieties

To improve the surface biocompatibility of the silicone intraocular lens (IOL), 2-methacryloyloxyethyl phosphorylcholine (MPC) was tethered onto the IOL through air plasma treatment. Chemical changes on the IOL surface were characterized by X-ray photoelectron spectroscopy (XPS) to confirm the covalent binding of MPC. Morphologies of the IOL surfaces were observed by scanning electron microscopy (SEM) to optimize the plasma treatment process. The hydrophilicity and biocompatibility of the control and modified IOLs were compared by the measurements of water contact angle, platelet adhesion, macrophage cell culture, and lens epithelial cell (LEC) attachment. It was found that, after the tethering of MPC, the hydrophilicity of the IOL can be improved significantly and permanently, and the platelet, macrophage, and LEC adhesion on the IOL surface are obviously suppressed, which indicated the enhancement of surface biocompatibility.

Poly(N-acryloylsarcosine methyl ester) Protein-Resistant Surfaces

A new class of protein-resistant film based on N-substituted glycine derivatives is described. Pulsed plasma deposited poly(N-acryloylsarcosine methyl ester) coatings are shown to be resistant toward the adsorption of fibrinogen and lysozyme. Deposition and UV irradiation of the polymer through a masked grid are found to be effective ways for generating negative and positive image protein arrays, respectively, onto a range of different substrate materials.

Enhancing the blood compatibility of ion-selective electrodes

In vivo monitoring of various analytes is important for many bioanalytical and biomedical applications. The crucial challenge in this type of applications is the interaction of the sensor with the host environment, which is qualitatively described by the term biocompatibility. This review discusses recent advances in methods and materials used for the improvement of the biocompatibility of ion-selective electrodes especially as it relates to their interaction with blood components.

Protein repellant silicone surfaces by covalent immobilization of poly(ethylene oxide)

Polydimethylsiloxane elastomers were surface modified with passivating polyethylene oxide (PEO) polymers of different molecular weights, both monofunctional and bifunctional. Following the introduction of Si-H groups on the surfaces by acid-catalyzed equilibration in the presence of polymethylhydrosiloxane, the PEO was linked by platinum-catalyzed hydrosilylation. ATR-FTIR, X-ray photoelectron spectroscopy (XPS) and water contact angle results confirmed that the PEO was successfully grafted to the silicone rubber. Atomic force microscopy and XPS suggested that surface coverage with PEO was very high on the modified surfaces but not complete. The protein-resistant properties of the PEO-modified surfaces were demonstrated by measuring the adsorption of fibrinogen from both buffer and plasma. Fibrinogen adsorption from buffer to the PEO-modified surfaces was reduced by more than 90% compared with controls.

DNA attachment chemistry at the flexible silicone elastomer surface: toward disposable microarrays

This paper describes the preparation and surface characterization of maleimide-activated silicone elastomer (PDMS(MCC)) followed by covalent functionalization using thiol-terminated DNA sequences (primary oligo). The stability of this attachment chemistry was demonstrated by the retention of the primary oligo through the process of hybridization with a labeled complementary DNA sequence. In these studies, the hybridized labeled DNA oligomers were detected using confocal fluorescence microscopy. We have employed a vapor deposition technique in which a plasma-treated silicone elastomer (PDMS(OH)) was exposed to vapors of 3-(aminopropyl)triethoxysilane (APTS) under vacuum, to yield the amine-functionalized silicone elastomer (PDMS(NH)(2)). PDMS(NH)(2) was further coupled with a heterofunctional cross-linker, sulfosuccinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate to obtain PDMS(MCC). The surface functionalities of the elastomers were characterized using contact angle measurements and X-ray photoelectron spectroscopy. Surface-modified silicone elastomers appear to be promising substrates for use as substrates for disposable microarrays.

Silicone elastomers for reduced protein adsorption

Monofunctional poly(ethylene oxide) polymers of molecular weight (MW) 350, 750, and 2000, respectively, were modified with Si(OEt)3 groups. These polymers underwent classic condensation cure with hydroxy-terminated silicone polymers and Si(OEt)4 to give composites with poly(ethylene oxide) (PEO) rich surfaces under aqueous conditions, as shown by contact angle and XPS data. The hydrophobicity of the surfaces was considerably higher in air. The greatest PEO concentration was observed with relatively short chain polymers of MW 350. Silicone polymers bearing short chain PEO chains were also observed to be the most protein rejecting from either buffer (fibrinogen) (90%) or plasma (85%). The silicone/TES-MPEO formulation offers the advantage of a one step/one shot polymerization process that gives materials with a high protein rejection ability than can be cast as films, or molded into complex shapes. Covalently linked PEO films of a variety of chain lengths and total surface coverage can be readily accommodated.

Adhesion of human U937 macrophages to phosphorylcholine-coated surfaces

A new type of amphiphilic phosphorylcholine (PC) polymer was used in this work to develop a cell culture surface that allows the attachment of U937 macrophages. The PC polymer was a random copolymer of N-isopropylacrylamide (45%), N-(phosphorylcholine)-N'-(ethylenedioxy-bis(ethyl)) acrylamide (41%), and the hydrophobic monomer N-(n-octadecyl) acrylamide (14%). Polypropylene (PP) films (1 cm2) were coated with the polymer solution by immersion. U937 macrophage suspensions were applied on PC polymer-coated surfaces and incubated for up to 72 h at 37 degrees C. While U937 cells did not adhere to PP, ammonia, nitrogen, or oxygen plasma-treated surfaces, they attached rapidly on PC-coated surfaces (< 1 h), proliferated, and stayed attached to the modified surface for at least 72 h, suggesting that unique features of the PC polymer, and the U937 macrophages, are responsible for the attachment of these cells. We compared the effect of Co2+ and Cr3+ ions on the expression of bone-resorbing cytokines (TNF-alpha, IL-6, IL-1beta) in U937 macrophages cultured on PC-coated surfaces to the response of U937 macrophages in suspension. Cytokine gene expression was analyzed by reverse transcription polymerase chain reaction (RT-PCR). Addition of Co2+ and Cr3+ ions led to a significant increased expression of TNF-alpha in both cultured and suspension cells. On the other hand, Co2+ and Cr3+ ions had a weak stimulatory effect or no effect on IL-1beta and IL-6, respectively, in both cultured and suspension cells. In conclusion, the use of PC polymer-modified surfaces might offer promising new opportunities for the culture of human U937 cells and may also point to the mechanism by which macrophages interact with lipid bilayers of biological membranes.

Interactions of corneal epithelial cells and surfaces modified with cell adhesion peptide combinations

In order to facilitate the adhesion of corneal epithelial cells to a poly dimethyl siloxane (PDMS) substrate ultimately for the development of a synthetic keratoprosthesis, PDMS surfaces were modified by covalent attachment of combinations of cell adhesion and synergistic peptides derived from laminin and fibronectin. Peptides studied included YIGSR and its synergistic peptide PDSGR from laminin and the fibronectin derived RGDS and PHSRN. Surfaces were modified with combinations of peptides determined by an experimental design. Peptide surface densities, measured using 125-I labeled tyrosine containing analogs, were on the order of pmol/cm2. Surface density varied as a linear function of peptide concentration in the reaction solution, and was different for the different peptides examined. The lowest surface density at all solution fractions was obtained with GYRGDS, while the highest density was consistently obtained with GYPDSGR. These results provide evidence that the surfaces were modified with multiple peptides. Water contact angles and XPS results provided additional evidence for differences in the chemical composition of the various surfaces. Significant differences in the adhesion of human corneal epithelial cells to the modified surfaces were noted. Statistical analysis of the experimental adhesion results suggested that solution concentration YIGSR, RGDS, and PHSRN as well as the interaction effect of YIGSR and PDSGR had a significant effect on cell interactions. Modification with multiple peptides resulted in greater adhesion than modification with single peptides only. Surface modification with a control peptide PPSRN in place of PHSRN resulted in a decrease in cell adhesion in virtually all cases. These results suggest that surface modification with appropriate combinations of cell adhesion peptides and synergistic peptides may result in improved cell surface interactions.

Immobilization of an oxalate-degrading enzyme on silicone elastomer

Urinary biomaterials are compromised by device-related urinary tract infections, bacterial biofilm formation, and biomineral encrustation. In the absence of urinary infection, calcium oxalate is the prevalent encrustation mineral formed. Considering this, a novel approach was taken in the study reported here, in that an oxalate-degrading enzyme, oxalate oxidase (OXO), was immobilized on the surface of silicone elastomer (PDMS), a common urological biomaterial. It was hypothesized that the enzymatic action of OXO could lower urinary oxalate levels near the device surface, thereby preventing calcium oxalate crystal formation. The PDMS surface was functionalized with the use of radio-frequency plasma discharge (RFPD) in the presence of water vapor, then coated with 3-aminopropyltriethoxysilane (AMEO). The resulting aminated surface was covalently coupled with OXO via glutaraldehyde bioconjugation. The ability of the OXO-coated PDMS to prevent calcium oxalate encrustation was evaluated with the use of a modified Robbins device (MRD) encrustation model. RFPD performed on PDMS resulted in an increase in the hydrophilicity of treated surfaces, as measured by contact angle. X-ray photoelectron spectroscopy studies showed increases in elemental oxygen, after water-vapor plasma, and in nitrogen after AMEO derivatization. The immobilized enzyme was shown to retain 47.5% of its specific enzymatic activity as compared to free enzyme. In vitro experiments for 6 days, with the use of a MRD, showed 53% less encrustation deposits on discs coated with OXO than control discs. The results from the current study suggest that PDMS-immobilized oxalate-degrading enzymes are active against calcium oxalate encrustation.

Functionalization of poly-L-lactic-co-ε-caprolactone: effects of surface modification on endothelial cell proliferation and hemocompatibility

A copolymer of L-lactic acid and epsilon-caprolactone (PLLACL) was synthesized with the aim of preparing a bioartificial, small-diameter and partially resorbable vascular graft. The material was submitted to surface functionalizations (i.e. chemical modification by means of hydrolytic 'etching' and plasma discharge) to promote endothelial cell (EC) adhesion and growth avoiding platelet adhesion or coagulation factor absorption. Furthermore, the behaviour of human microvascular endothelial cells (HMVEC) seeded on the untreated and treated copolymer is described, as well as the platelet adhesion and the modifications of coagulation factors determined by the copolymer itself. PLLACL in its native state provided little support for EC adhesion. Improved EC adherence was obtained when functional groups were provided on the polymer surface by surface chemical hydrolysis. HMVEC seeded and cultured on the polymer surface did not show any ultrastructural alteration, thus demonstrating the absence of the polymer cytotoxicity. Moreover, SEM analysis performed on cold plasma modified specimens showed the presence of a subconfluent monolayer of EC, with an elongated spread morphology. Both the untreated and treated copolymers induced only slight variations of platelet number, but determined the activated partial thromboplastin time (APTT) increase, due to factor XI reduction. Finally, a prototype of partially biodegradable vascular prosthesis was prepared with NaOH/HCl-treated copolymer. Pre-cultured HMVEC seeding of the prosthesis by means of a rotation device resulted in an almost completely coverage of the graft inner surface.

Gelatin-glutaraldehyde cross-linking on silicone rubber to increase endothelial cell adhesion and growth

Silicone is a biomaterial that is widely used in many areas because of its high optical clarity, its durability, and the ease with which it can be cast. However, these advantages are counterbalanced by strong hydrophobicity. Gelatin cross-linking has been used as a hydrophilic coating on many biomaterials but not on silicone rubber. In this study, two gelatin glutaraldehyde (GA) cross-linking methods were used to coat a hydrophilic membrane on silicone rubber. In method I, gelatin and GA were mixed in three different proportions (64:1, 128:1, and 256:1) before coating. In method II, a newly formed 5% gelatin membrane was cross-linked with a 2.5% GA solution. All coatings were hydrophilic, as determined from the measurement of contact angle for a drop of water on the surface. Bovine coronary arterial endothelial cells were shown to grow well on the surface modified by method II at 72 h. In method I, the cells grew well for gelatin-GA proportions of 64:1 and 128:1 at 72 h. No cell attachment on untreated silicone rubber was observed by the third d of seeding. The results indicated that both methods of gelatin-GA cross-linking provided a hydrophilic surface on silicone for endothelial cell adhesion and growth in vitro.

A nonthrombogenic gas-permeable membrane composed of a phospholipid polymer skin film adhered to a polyethylene porous membrane

Polymer membranes are widely used in biomedical applications such as hemodialysis, membrane oxygenator, etc. When the membranes come in contact with blood or body fluids, protein adsorption and cell adhesion occur rapidly. Nonspecific protein adsorption and cell adhesion on the membranes induce not only various bio-rejections but also a decrease in their performance. We hypothesized that a blood compatible gas-permeable membrane could be prepared from polyethylene (PE) porous membranes modified with phospholipid polymers. In this study, poly[(2-methacryloyloxyethyl phosphorylcholine) (MPC)-co-dodecyl methacrylate] (PMD) skin film adhered to a PE porous membrane (PMD/PE porous membrane) was prepared. Elution of PMD was not detected meaning that the PMD film did not detach from the PE porous membrane even after soaking in water for more than 6 months. The permeation coefficient of oxygen gas through the PE membrane with the adhered PMD containing more than 0.20 mole fraction of the MPC unit, was the same as that of the original PE porous membrane. The PMD surface effectively reduced biofouling. We concluded that the PMD/PE porous membrane is useful as a novel membrane oxygenator due to its excellent gas-permeability and blood compatibility.

Absorbable sandwich-like membrane for retinal-sheet transplantation

Neural retinal transplantation has great potential for the alleviation of different degenerative and hereditary retinal disorders. However, because of the fragile and soft nature of retina, retinal-sheet transplantation is relatively difficult to achieve. To overcome this difficulty, we developed a technique for lamellar tissue transplantation. Biodegradable gelatin membranes were fabricated into a sandwich and encapsulated retinal grafts for transplantation. Before transplantation, we characterized the in vivo and in vitro properties of such membranes to determine the optimal sterilization procedure, that is, a sterile membrane with suitable degradability and good mechanical properties and without cytotoxicity. Three sterilization methods were conducted, with hydrogen peroxide gas plasma (HPGP), ethylene oxide (EO), and gamma-ray irradiation (gamma). The results were compared with those of a control (no disinfection). Initial studies revealed that the gelatin membranes sterilized with HPGP or EO exhibited retinal pigment epithelium (RPE) cytotoxicity, whereas the membrane sterilized by 16.6-kGy gamma ray irradiation had no RPE cytotoxicity and had enhanced mechanical properties. In the in vivo rabbit study, implanted gelatin membranes demonstrated satisfactory biocompatibility without any inflammation. Transplanted retinal sheets survived well and developed laminar structures. Such a method using gelatin membranes for tissue transportation has great potential for future routine retinal-sheet transplantation.

Hydrogels based on poly(ethylene oxide) and poly(tetramethylene oxide) or poly(dimethyl siloxane): synthesis, characterization, in vitro protein adsorption and platelet adhesion

In vitro protein adsorption, platelet adhesion and activation on new hydrogel surfaces, composed of poly(ethylene oxide) (PEO) and poly(tetramethylene oxide) (PTMO) or poly(dimethyl siloxane) (PDMS), were investigated. By varying PEO length (MW = 2000 or 3400), hydrophobic components (PTMO or PDMS) or polymer topology (block or graft copolymers), various physical hydrogels were produced. Their structures were verified by 1H NMR and ATR-IR and the molecular weights were determined by gel permeation chromatography. The hydrogels were soluble in a variety of organic solvents, while absorbed a significant amount of water with preserved three-dimensional structure by physical crosslinking. The dynamic contact angle measurement revealed that the surface hydrophilicity increased by incorporating longer PEO, PEO grafting, and adopting PDMS as a hydrophobic segment instead of PTMO. It was observed from in vitro protein adsorption study that the hydrogels exhibited significantly lower adsorption of human serum albumin (HSA), human fibrinogen (HFg), and IgG, when compared with Pellethane, a commercial polyurethane taken as a control. The hydrogels were attractive for HSA but not sensitive to HFg and IgG. And more than 65% of the proteins detected on the surfaces of the hydrogels were reversibly detached by being treated with an SDS solution. It was evident that the hydrogels synthesized in this study were much more resistant to platelet adhesion than the control, which might depend on the composition of proteins adsorbed on the surfaces and their degree of denaturation. Among the hydrogels tested, PEO3,4kPDMS exhibited albumin-rich and platelet-resistant surfaces, implying a potential candidate for biomaterial.

Comparison of corneal epithelial cellular growth on synthetic cornea materials

The application of artificial corneas for severely wounded ocular surfaces has always encountered the problem of biocompatibility with corneal epithelial cells (CECs). For the eye to stay healthy, it must continually have a complete sheet of CECs across the artificial corneal surface. Various surface modifications of different polymeric materials have been examined to determine which have the best cellular growth rates. A mathematical model of corneal cell growth profiles on synthetic materials was formulated based upon a linear mitotic growth rate. Experimental data reported for the CEC growth on modified poly(vinyl alcohol), silicone rubber, polystyrene, and polycarbonate was analyzed using the model to estimate the linear mitotic rate constant (k). The model proved to be useful in comparing data from different investigators. Plasma-induced graft copolymerized poly(hydroxyethyl methacrylate) (pHEMA) on silicone rubber provided the best growth rate from this particular set of data.

Phosphorylcholine-based polymers and their use in the prevention of biofouling

This article provides an overview of work carried out on the synthesis and non-fouling properties of phosphorylcholine (PC)-containing polymers. The concept of biomimicry is outlined and the major classes of synthetic PC-based materials described. Studies on the interaction of these materials with various proteins are collated and the mechanism for their protein-resistant nature is discussed. Similarly, cellular interactions are also reviewed, with ex-vivo and in-vivo clinical data provided to demonstrate the usefulness of these materials for improving the properties of medical devices.

Inhibition of fibroblast cell adhesion on substrate by coating with 2-methacryloyloxyethyl phosphorylcholine polymers

Fibroblast adhesion and growth behavior were examined on various polymers coated on a poly(ethylene telephthalate) (PET) substrate. The polymers are poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylatel copolymer (PMB)s with different MPC unit compositions, and poly(2-hydroxyethyl methacrylate). Surface analysis by dynamic contact angle measurement revealed that the mobility of the polymer chain on the PET substrate depended on the MPC unit composition, but there was no significant difference between the PMBs with 3-10 mol% MPC units and poly(HEMA). Fibronectin adsorption on the polymer surface from a cell culture medium was determined by immunoassay. The adsorbed fibronection was evenly distrubuted in every polymer, however, the amount was reduced with an increase in the MPC unit composition in the PMB. This result suggested that the MPC unit could weaken the interaction between the polymer surface and proteins. When fibroblast L-929 cells, were cultured on the polymers, the cells adhered and the number of cells increased on not only the hydrophobic poly(BMA) but also on the hydrophilic poly(HEMA). However, the number of cells that adhered on the PMB surface decreased with an increase in the MPC unit composition. This was a result of the fibronectin adsorption behavior. Thus, it could be concluded that since the PMB could suppress cell adhesion proteins e.g. fibronectin, the PMB showed excellent cell adhesive resistance properties.