Surface properties and hemocompatibility of alkyl-siloxane monolayers supported on silicone rubber: effect of alkyl chain length and ionic functionality

Modifications of Textile Materials with Functional Silanes, Liquid Silicone Softeners, and Silicone Rubbers-A Review

General information concerning different kinds of chemical additives used in the textile industry has been described in this paper. The properties and applications of organofunctional silanes and polysiloxanes (silicones) for chemical and physical modifications of textile materials have been reviewed, with a focus on silicone softeners, silane, and silicones-based superhydrophobic finishes and coatings on textiles composed of silicone elastomers and rubbers. The properties of textile materials modified with silanes and silicones and their practical and potential applications, mainly in the textile industry, have been discussed.

Surface Modification of Decellularized Heart Valve by the POSS-PEG Hybrid Hydrogel to Prepare a Composite Scaffold Material with Anticalcification Potential

Tissue-engineered heart valves (TEHVs) are the most promising replacement for heart valve transplantation. Decellularized heart valve (DHV) is one of the most common scaffold materials for TEHVs. In actual clinical applications, the most widely used method for treating DHV is cross-linking it with glutaraldehyde, but this method could cause serious problems such as calcification. In this study, we introduced polyhedral oligomeric silsesquioxane (POSS) nanoparticles into a poly(ethylene glycol) (PEG) hydrogel to prepare a POSS-PEG hybrid hydrogel, and then coated them on the surface of DHV to prepare the composite scaffold. The chemical structures, microscopic morphologies, cell compatibilities, blood compatibilities, and anticalcification properties were further investigated. Experimental results showed that the composite scaffold had good blood compatibility and excellent cell compatibility and could promote cell adhesion and proliferation. In vivo and in vitro anticalcification experiments showed that the introduction of POSS nanoparticles could reduce the degree of calcification significantly and the composite scaffold had obvious anticalcification ability. The DHV surface-coated with the POSS-PEG hybrid hydrogel is an alternative scaffold material with anticalcification potential for an artificial heart valve, which provides an idea for the preparation of TEHVs.

Biocompatibility Computation of Muscle Cells on Polyhedral Oligomeric Silsesquioxane-Grafted Polyurethane Nanomatrix

This study was performed to appraise the biocompatibility of polyhedral oligomeric silsesquioxane (POSS)-grafted polyurethane (PU) nanocomposites as potential materials for muscle tissue renewal. POSS nanoparticles demonstrate effectual nucleation and cause noteworthy enhancement in mechanical and thermal steadiness as well as biocompatibility of resultant composites. Electrospun, well-aligned, POSS-grafted PU nanofibers were prepared. Physicochemical investigation was conducted using several experimental techniques, including scanning electron microscopy, energy dispersive X-ray spectroscopy, electron probe microanalysis, Fourier transform infrared spectroscopy, and X-ray diffraction pattern. Adding POSS molecules to PU did not influence the processability and morphology of the nanocomposite; however, we observed an obvious mean reduction in fiber diameter, which amplified specific areas of the POSS-grafted PU. Prospective biomedical uses of nanocomposite were also appraised for myoblast cell differentiation in vitro. Little is known about C2C12 cellular responses to PU, and there is no information regarding their interaction with POSS-grafted PU. The antimicrobial potential, anchorage, proliferation, communication, and differentiation of C2C12 on PU and POSS-grafted PU were investigated in this study. In conclusion, preliminary nanocomposites depicted superior cell adhesion due to the elevated free energy of POSS molecules and anti-inflammatory potential. These nanofibers were non-hazardous, and, as such, biomimetic scaffolds show high potential for cellular studies and muscle regeneration.

Anticalcification Potential of POSS-PEG Hybrid Hydrogel as a Scaffold Material for the Development of Synthetic Heart Valve Leaflets

Calcification of bioprosthetics is a primary challenge in the field of artificial heart valves and a main reason for biological heart valve prostheses failure. Recent advances in nanomaterial science have promoted the development of polymers with advantageous properties that are likely suitable for artificial heart valves. In this work, we developed a nanocomposite polymeric biomaterial POSS-PEG (polyhedral oligomeric silsesquioxane-polyethylene glycol) hybrid hydrogel, which not only has improved mechanical and surface properties but also excellent biocompatibility. The results of atomic force microscopy and in vivo animal experiments indicated that the content of POSS in the PEG matrix plays an important role on the surface and contributes to its biological properties, compared to the decellularized porcine aortic valve scaffold. Additionally, this modification leads to enhanced protection of the hydrogel from thrombosis. Furthermore, the introduction of POSS nanoparticles also gives the hydrogel a better calcification resistance efficacy, which was confirmed through in vitro tests and animal experiments. These findings indicate that POSS-PEG hybrid hydrogel is a potential material for functional heart valve prosthetics, and the use of POSS nanocomposites in artificial valves may offer potential long-term performance and durability advantages.

Direct Synthesis of Peptide-Containing Silicones: A New Way to Bioactive Materials

A simple and efficient way to synthesize peptide-containing silicone materials is described. Silicone oils containing a chosen ratio of bioactive peptide sequences were prepared by acid-catalyzed copolymerization of dichlorodimethylsilane, hybrid dichloromethyl peptidosilane, and Si(vinyl)- or SiH-functionalized monomers. Functionalized silicone oils were first obtained and then, after hydrosilylation cross-linking, bioactive polydimethylsiloxane (PDMS)-based materials were straightforwardly obtained. The introduction of an antibacterial peptide yielded PDMS materials showing activity against Staphylococcus aureus. PDMS containing RGD ligands showed improved cell-adhesion properties. This generic method was fully compatible with the stability of peptides and thus opened the way to the synthesis of a wide range of biologically active silicones.

Sulfur and nitrogen containing plasma polymers reduces bacterial attachment and growth

Role of sulfur (S) and nitrogen (N) groups in promoting cell adhesion or commonly known as biocompatibility, is well established, but their role in reducing bacterial attachment and growth is less explored or not well-understood. Natural sulfur-based compounds, i.e. sulfide, sulfoxide and sulfinic groups, have shown to inhibit bacterial adhesion and biofilm formation. Hence, we mimicked these surfaces by plasma polymerizing thiophene (ppT) and air-plasma treating this ppT to achieve coatings with S of similar oxidation states as natural compounds (ppT-air). In addition, the effects of these N and S groups from ppT-air were also compared with the biocompatible amine-amide from n-heptylamine plasma polymer. Crystal violet assay and live and dead fluorescence staining of E. coli and S. aureus showed that all the N and S coated surfaces generated, including ppHA, ppT and ppT-air, produced similarly potent, growth reduction of both bacteria by approximately 65% at 72 h compared to untreated glass control. The ability of osteogenic differentiation in Wharton's jelly mesenchymal stem cells (WJ-MSCs) were also used to test the cell biocompatibility of these surfaces. Alkaline phosphatase assay and scanning electron microscopy imaging of these WJ-MSCs growths indicated that ppHA, and ppT-air were cell-friendly surfaces, with ppHA showing the highest osteogenic activity. In summary, the N and S containing surfaces could reduce bacteria growth while promoting mammalian cell growth, thus serve as potential candidate surfaces to be explored further for biomaterial applications.

Octadecyl Chains Immobilized onto Hyaluronic Acid Coatings by Thiol-ene "Click Chemistry" Increase the Surface Antimicrobial Properties and Prevent Platelet Adhesion and Activation to Polyurethane

Infection and thrombus formation are still the biggest challenges for the success of blood contact medical devices. This work aims the development of an antimicrobial and hemocompatible biomaterial coating through which selective binding of albumin (passivant protein) from the bloodstream is promoted and, thus, adsorption of other proteins responsible for bacterial adhesion and thrombus formation can be prevented. Polyurethane (PU) films were coated with hyaluronic acid, an antifouling agent, that was previously modified with thiol groups (HA-SH), using polydopamine as the binding agent. Octadecyl acrylate (C18) was used to attract albumin since it resembles the circulating free fatty acids and albumin is a fatty acid transporter. Thiol-ene "click chemistry" was explored for C18 immobilization on HA-SH through a covalent bond between the thiol groups from the HA and the alkene groups from the C18 chains. Surfaces were prepared with different C18 concentrations (0, 5, 10, and 20%) and successful immobilization was demonstrated by scanning electron microscopy (SEM), water contact angle determinations, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The ability of surfaces to bind albumin selectively was determined by quartz crystal microbalance with dissipation (QCM-D). Albumin adsorption increased in response to the hydrophobic nature of the surfaces, which augmented with C18 saturation. HA-SH coating reduced albumin adsorption to PU. C18 immobilized onto HA-SH at 5% promoted selective binding of albumin, decreased Staphylococcus aureus adhesion and prevented platelet adhesion and activation to PU in the presence of human plasma. C18/HA-SH coating was established as an innovative and promising strategy to improve the antimicrobial properties and hemocompatibility of any blood contact medical device.

A Biodesigned Nanocomposite Biomaterial for Auricular Cartilage Reconstruction

Current biomaterials for auricular replacement are associated with high rates of infection and extrusion. The development of new auricular biomaterials that mimic the mechanical properties of native tissue and promote desirable cellular interactions may prevent implant failure. A porous 3D nanocomposite scaffold (NS) based on POSS-PCU (polyhedral oligomeric silsesquioxane nanocage into polycarbonate based urea-urethane) is developed with an elastic modulus similar to native ear. In vitro biological interactions on this NS reveal greater protein adsorption, increased fibroblast adhesion, proliferation, and collagen production compared with Medpor (the current synthetic auricular implant). In vivo, the POSS-PCU with larger pores (NS2; 150-250 μm) have greater tissue ingrowth (≈5.8× and ≈1.4 × increase) than the POSS-PCU with smaller pores (NS1; 100-50 μm) and when compared to Medpor (>100 μm). The NS2 with the larger pores demonstrates a reduced fibrotic encapsulation compared with NS1 and Medpor (≈4.1× and ≈1.6×, respectively; P < 0.05). Porosity also influences the amount of neovascularization within the implants, with no blood vessel observed in NS1 (12 weeks postimplantation). The lack of chronic inflammatory response for all materials may indicate that the elastic modulus and pore size of the implant scaffold could be important design considerations for influencing fibrotic responses to auricular and other soft tissue implants.

POSS–PU electrospinning nanofibers membrane with enhanced blood compatibility

The addition of POSS results in (a) platelet adsorption amount of electrospun fibers membrane decreased (b) protein adsorption of electrospun fibers membrane decreased (c) the growth of bacteria was inhibited.

Small-molecule axon-polarization studies enabled by a shear-free microfluidic gradient generator

A deep understanding of the mechanisms behind neurite polarization and axon path-finding is important for interpreting how the human body guides neurite growth during development and response to injury. Further, it is of great clinical importance to identify diffusible chemical cues that promote neurite regeneration for nervous tissue repair. Despite the fast development of various types of concentration gradient generators, it has been challenging to fabricate neuron-friendly (i.e. shear-free and biocompatible for neuron growth and maturation) devices to create stable gradients, particularly for fast diffusing small molecules, which typically require high flow and shear rates. Here we present a finite element analysis for a polydimethylsiloxane/polyethylene glycol diacrylate (PDMS/PEG-DA) based gradient generator, describe the microfabrication process, and validate its use for neuronal axon polarization studies. This device provides a totally shear-free, biocompatible microenvironment with a linear and stable concentration gradient of small molecules such as forskolin. The gradient profile in this device can be customized by changing the composition or width of the PEG-DA barriers during direct UV photo-patterning within a permanently bonded PDMS device. Primary rat cortical neurons (embryonic E18) exposed to soluble forskolin gradients for 72 h exhibited statistically significant polarization and guidance of their axons. This device provides a useful platform for both chemotaxis and directional guidance studies, particularly for shear sensitive and non-adhesive cell cultures, while allowing fast new device design prototyping at a low cost.

Bioactive technologies for hemocompatibility

The contact of any biomaterial with blood gives rise to multiple pathophysiologic defensive mechanisms such as activation of the coagulation cascade, platelet adhesion and activation of the complement system and leukocytes. The reduction of these events is of crucial importance for the successful clinical performance of a cardiovascular device. This can be achieved by improving the hemocompatibility of the device materials or by pharmacologic inhibition of the key enzymes responsible for the activation of the cascade reactions, or a combination of both. Different strategies have been developed during the last 20 years, and this article attempts to review the most significant, by dividing them into three main categories: bioinert or biopassive, biomimetic and bioactive strategies. With regard to bioactive strategies, particular attention is given to heparin immobilization and recent related technologies. References from both scientific literature and commercial sites are provided. Future development and studies are suggested.

Osteoblastic cells culture on electrospun poly(ε-caprolacton) scaffolds incorporating amphiphilic PEG-POSS telechelic

In this work, novel poly(ε-caprolactone) (PCL) fibrous membranes incorporating amphiphilic polyhedral oligosilsesquioxane (POSS) telechelic (PEG-POSS telechelic) were prepared via electrospinning. The unique microstructure, morphology, thermal stability of the resulting PCL/PEG-POSS telechelic electrospun nanowebs were investigated by X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis, respectively. The addition of amphiphilic PEG-POSS telechelic strongly influenced the fiber diameters, microstructures of the resultant PCL/PEG-POSS telechelic nanofibers, compared to pure PCL nanofibers. The potential biomedical applications of such PEG-POSS telechelic nanowebs as a scaffolding material were also evaluated in vitro using mouse osteoblast-like MC3T3-E1 cells. The cell adhesion, spreading, and interaction behavior of pure PCL and PCL/PEG-POSS telechelic fibrous membranes were explored. It was found that electrospun PCL fibrous membranes incorporating amphiphilic PEG-POSS telechelic showed higher initial cell attachment than pure PCL due to the higher surface free energy of POSS siloxanes. Moreover, the obtained PCL/PEG-POSS telechelic fibrous scaffolds were found to be nontoxic and to maintain the good adhesion ratio between cells and surface (about ~93 %) after cell culturing for 24 h.

Combining dynamic stretch and tunable stiffness to probe cell mechanobiology in vitro

Cells have the ability to actively sense their mechanical environment and respond to both substrate stiffness and stretch by altering their adhesion, proliferation, locomotion, morphology, and synthetic profile. In order to elucidate the interrelated effects of different mechanical stimuli on cell phenotype in vitro, we have developed a method for culturing mammalian cells in a two-dimensional environment at a wide range of combined levels of substrate stiffness and dynamic stretch. Polyacrylamide gels were covalently bonded to flexible silicone culture plates and coated with monomeric collagen for cell adhesion. Substrate stiffness was adjusted from relatively soft (G′ = 0.3 kPa) to stiff (G′ = 50 kPa) by altering the ratio of acrylamide to bis-acrylamide, and the silicone membranes were stretched over circular loading posts by applying vacuum pressure to impart near-uniform stretch, as confirmed by strain field analysis. As a demonstration of the system, porcine aortic valve interstitial cells (VIC) and human mesenchymal stem cells (hMSC) were plated on soft and stiff substrates either statically cultured or exposed to 10% equibiaxial or pure uniaxial stretch at 1Hz for 6 hours. In all cases, cell attachment and cell viability were high. On soft substrates, VICs cultured statically exhibit a small rounded morphology, significantly smaller than on stiff substrates (p<0.05). Following equibiaxial cyclic stretch, VICs spread to the extent of cells cultured on stiff substrates, but did not reorient in response to uniaxial stretch to the extent of cells stretched on stiff substrates. hMSCs exhibited a less pronounced response than VICs, likely due to a lower stiffness threshold for spreading on static gels. These preliminary data demonstrate that inhibition of spreading due to a lack of matrix stiffness surrounding a cell may be overcome by externally applied stretch suggesting similar mechanotransduction mechanisms for sensing stiffness and stretch.

Cardiovascular application of polyhedral oligomeric silsesquioxane nanomaterials: a glimpse into prospective horizons

Revolutionary advances in nanotechnology propose novel materials with superior properties for biomedical application. One of the most promising nanomaterials for biomedical application is polyhedral oligomeric silsesquioxane (POSS), an amazing nanocage consisting of an inner inorganic framework of silicon and oxygen atoms and an outer shell of organic groups. The unique properties of this nanoparticle has led to the development of a wide range of nanostructured copolymers with significantly enhanced properties including improved mechanical, chemical, and physical characteristics. Since POSS nanomaterials are highly biocompatible, biomedical application of POSS nanostructures has been intensely explored. One of the most promising areas of application of POSS nanomaterials is the development of cardiovascular implants. The incorporation of POSS into biocompatible polymers has resulted in advanced nanocomposite materials with improved hemocompatibility, antithrombogenicity, enhanced mechanical and surface properties, calcification resistance, and reduced inflammatory response, which make these materials the material of choice for cardiovascular implants. These highly versatile POSS derivatives have opened new horizons to the field of cardiovascular implant. Currently, application of POSS containing polymers in the development of new generation cardiovascular implants including heart valve prostheses, bypass grafts, and coronary stents is under intensive investigation, with encouraging outcomes.

Synthesis and characterization of surface-grafted polyacrylamide brushes and their inhibition of microbial adhesion

A method is presented to prevent microbial adhesion to solid surfaces exploiting the unique properties of polymer brushes. Polyacrylamide (PAAm) brushes were grown from silicon wafers by atom transfer radical polymerization (ATRP) using a three-step reaction procedure consisting of immobilization of a coupling agent gamma-aminopropyltriethoxysilane, anchoring of an ATRP initiator 4-(chloromethyl)benzoyl chloride, and controlled radical polymerization of acrylamide. The surfaces were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, ellipsometry, and contact-angle measurements. The calculated grafting density pointed to the presence of a dense and homogeneous polymer brush. Initial deposition rates, adhesion after 4 h, and detachment of two bacterial strains (Staphylococcus aureus ATCC 12600 and Streptococcus salivarius GB 24/9) and one yeast strain (Candida albicans GB 1/2) to both PAAm-coated and untreated silicon surfaces were investigated in a parallel plate flow chamber. A high reduction (70-92%) in microbial adhesion to the surface-grafted PAAm brush was observed, as compared with untreated silicon surfaces. Application of the proposed grafting method to silicone rubbers may offer great potential to prevent biomaterials-centered infection of implants.

Surface characterization and platelet compatibility evaluation of the binary mixed self-assembled monolayers

This report describes a technique that used mixed self-assembled monolayer (SAM) as a model surface to evaluate the effect of steric hindrance on the SAM packing quality and its platelet compatibility. Two series of binary mixed SAMs were formed by mixing the bulky terminated alkanethiol (HS(CH2)10PO3H2) with a smaller terminated one (HS(CH2)9CH3 and HS(CH2)11OH) respectively. Surface characterization results showed the hydrophilicity on these two series of mixed SAMs changed with the solution mole fraction of PO3H2 terminated thiol, chi(PO3H2,soln), and reached to a nearly constant value as chi(PO3H2,soln) was 0.6 for PO3H2+CH3 SAM and 0.4 for PO3H2+OH SAM. This finding should be due to the gradual saturation of surface PO3H2 functionality on these mixed SAMs. The XPS analysis indicated the addition of the CH3 and OH terminated thiol could reduce the steric hindrance effect of PO3H2 functionality on monolayer formation and, henceforth, improve the SAM packing quality. In vitro platelet adhesion assay revealed the platelet compatibility on the PO3H2+OH SAMs was better than that on the PO3H2+CH3 and the pure PO3H2 ones. Moreover, the PO3H2+OH SAM with a low chi(PO3H2,soln) value exhibited the least platelet activating property of these two mixed SAM systems. These findings suggested that material's surface wettability and surface charge density should act collectively in affecting its platelet compatibility.

Nanocomposite Containing Bioactive Peptides Promote Endothelialisation by Circulating Progenitor Cells: An In vitro Evaluation

OBJECTIVE

The formation of an endothelial cell layer on the luminal surface of cardiovascular devices, especially bypass grafts, is an important attribute in order to improve their patency. Endothelial progenitor cells (EPCs) have a potential role in the endothelialisation of bypass grafts. We hypothesised that a novel approach to improve endothelialisation of bypass grafts by EPCs would be the creation on the graft lumen of a microenvironment that supports EPC adhesion and differentiation.

METHODS

A new generation of nanocomposite based on silsesquioxane in the form of polyhedral oligomeric silsesquioxane (POSS) nanocages which incorporate bioactive peptides (RGD) was made into sheets. Peripheral blood mononuclear cells (PBMCs) containing EPCs isolated from six consenting young, healthy, adult volunteers were then plated both on (1) sheets of the nanocomposite with the bioactive peptide, (2) sheets of the nanocomposite without the bioactive peptide, (3) culture dishes as control and then cultured in presence of vascular endothelial growth factor (VEGF). Confirmation of endothelial and EPCs markers was carried out using fluorescence-activated cell sorter (FACS) analysis, reverse transcription polymerase chain reaction (RT-PCR) and immunostaining.

RESULTS

One to two percent of PBMCs expressed CD34 as determined by FACS analysis. Cells were demonstrated to express mRNA for the EPC markers CD34, platelet-endothelial cell adhesion molecule-1 (CD31), CD133 and vascular endothelial growth factor receptor-2(FlK-1/KDR). Endothelial cell-colony forming units were formed between day 5 and day 7 after plating. Colonies were confirmed to be endothelial like cells by immunostaining. There were significantly greater numbers of EPC colonies on the bioactive nanocomposites as compared to the nanocomposite alone and the uncoated dishes.

CONCLUSION

We report a new nanocomposite based biomaterial that has been demonstrated, in vitro, to promote endothelialisation from PBMCs containing EPCs.

Mycobacterium marinum biofilm formation reveals cording morphology

Abstract The emergence of the nontuberculosis mycobacteria (NTM) as clinically relevant pathogens has warranted the study of these ubiquitous organisms in the context of their likely environmental niche, the biofilm. We assayed the NTM bacterium Mycobacterium marinum strain 1218R, a fish outbreak isolate, for biofilm formation on different surfaces over time using three different methods. Using the MBEC system, biofilm development occurred continually over the 14-day culture period reaching a mature or stable biofilm state after 7 days postinoculation. Quantification of M. marinum biofilm formation on high-density polyethylene (HDPE), polycarbonate (PC) and silicon (Si) coupons over a 14-day period was evaluated using a continuous flow reactor system. M. marinum developed biofilms on all of the surfaces tested. However, substantially more biofilm accumulated on the silicon than on the other substrates (Si>HDPE>PC) under the same growth conditions indicating that silicon was the most effective substratum studied for the generation of M. marinum biofilms and suggesting a correlation between surface hydrophobicity and attachment. Finally, confocal laser scanning microscopy was used to visualize M. marinum biofilm development in situ over time and revealed an unusual biofilm ultrastructure. Large cell clusters attached to the surface grew in parallel sinuous arrays of cells that formed large cords.

The antithrombogenic potential of a polyhedral oligomeric silsesquioxane (POSS) nanocomposite

We have developed a nanocomposite using a silica nanocomposite polyhedral oligomeric silsesquioxane (POSS) and poly(carbonate-urea)urethane (PCU) for potential use in cardiovascular bypass grafts and the microvascular component of artificial capillary beds. In this study, we sought to compare its antithrombogenicity to that of conventional polymers used in vascular bypass grafts so as to improve upon current patency rates, particularly in the microvascular setting. Using atomic force microscopy (AFM) and transmission electron microscopy (TEM), surface topography and composition were studied, respectively. The ability of the nanocomposite surface to repel both proteins and platelets in vitro was assessed using thromboelastography (TEG), fibrinogen ELISA assays, antifactor Xa assays, scanning electron microscopy (SEM), and platelet adsorption tests. TEG analysis showed a significant decrease in clot strength (one-way ANOVA, p < 0.001) and increase in clot lysis (one-way ANOVA, p < 0.0001) on the nanocomposite when compared to both poly(tetrafluoroethylene) (PTFE) and PCU. ELISA assays indicate lower adsorption of fibrinogen to the nanocomposite compared to PTFE (one-way ANOVA, p < 0.01). Interestingly, increasing the concentration of POSS nanocages within these polymers was shown to proportionately inhibit factor X activity. Platelet adsorption at 120 min was also lower compared to PTFE and PCU (two-way ANOVA, p < 0.05). SEM images showed a "speckled" morphologic pattern with Cooper grades I platelet adsorption morphology on the nanocomposite compared to PTFE with grade IV morphology. On the basis of these results, we concluded that POSS nanocomposites possess greater thromboresistance than PTFE and PCU, making it an ideal material for the construction of both bypass grafts and microvessels.

In vitro hemocompatibility of self-assembled monolayers displaying various functional groups

Self-assembled monolayers (SAMs) of alkanethiols with various terminating groups (-OH, -CH3, -COOH) and binary mixtures of these alkanethiols were studied with respect to their hemocompatibility in vitro by means of freshly taken human whole blood. The set of smooth monomolecular films with graded surface characteristics was applied to scrutinize hypotheses on the impact of surface chemical-physical properties on distinct blood activation cascades, i.e. to analyze -OH surface groups vs. complement activation, acidic surface sites vs. contact activation/coagulation and surface hydrophobicity vs. thrombogenicity. Blood and model surfaces were analyzed after incubation for the related hemocompatibility parameters. Our results show that the adhesion of leukocytes is abolished on a -CH3 surface and greatly enhanced on surfaces with -OH groups. The opposite was detected for the adhesion of platelets. A strong correlation between the activation of the complement system and the adhesion of leukocytes with the content of -OH groups could be observed. The contact activation for hydrophilic surfaces was found to scale with the amount of acidic surface sites. However, the coagulation and platelet activation did not simply correlate with any surface property and were therefore concluded to be determined by a superposition of contact activation and platelet adhesion.

In vitro stability study of organosilane self-assemble monolayers and multilayers

The stability of self-assembled monolayers (SAMs) and multilayers formed on silicon surface by amino-terminated silanes and SAMs formed by alkyl and glycidyl terminated silanes were investigated in vitro with saline solution at 37 degrees C for up to 10 days. FTIR and XPS results indicated that amino-terminated SAMs and multilayers are very unstable if the alkyl chain is short ((CH2)3), while stable if the alkyl chain is long ((CH2)11). On the other hand, alkyl-terminated SAMs are very stable regardless of the alkyl chain length, and glycidyl terminated SAM retained approximately 77% of the organosilane molecules after 10 days. Hydrogen bonding between the organosilane monomer and silicon surface and among the organosilane monomers is believed to contribute to the instability of the SAM and multilayer formed by amino-terminated silane with a short alkyl chain ((CH2)3). Therefore, the widely used (3-aminopropyl) trimethoxysilane (APTMS) SAM and multilayer may not be suitable for implantable biomedical applications.

Polyhedral oligomeric silsesquioxane nanocomposites: the next generation material for biomedical applications

The unique properties of nanocomposites have seen them creating the next revolution in materials science. Their quantal properties as a result of their size have given them unique physical characteristics, previously not possible because of classical physical laws. There is now evidence that these may also extend into the world of biology and medicine. In this Account, we look at the birth of a new generation of silica nanocomposites using polyhedral oligomeric silsesquioxanes, a promising nanoscale silica particle with particular use in cardiovascular interventional devices.

In vitro haemocompatibility and stability of two types of heparin-immobilized silicon surfaces

Heparin was covalently immobilized onto a silicon surface by two different methods, carbodiimide-based immobilization and photo-immobilization. In the former method, a (3-aminopropyl) trimethoxysilane (APTMS) self-assembled monolayer (SAM) or multilayer was first coated onto the silicon surface as the bridging layer, and heparin was then attached to the surface in the presence of water-soluble carbodiimide. In the latter method, an octadecyltrichlorosilane (OTS) SAM was coated on the silicon surface as the bridging layer, and heparin was modified by attaching photosensitive aryl azide groups. Upon UV illumination, the modified heparin was then covalently immobilized onto the surface. The hydrophilicity of the silicon surface changed after each coating step, and heparin aggregates on APTMS SAM and OTS SAM were observed by atomic force microscopy (AFM). In vitro haemocompatibility assays demonstrated that the deposition of APTMS SAM, APTMS multilayer and OTS SAM enhanced the silicon's haemocompatibility, which was further enhanced by the heparin immobilization. There is no evident distinction regarding the haemocompatibility between the heparin-immobilized surfaces by both methods. However, heparin on silicon with APTMS SAM and multilayer as the bridging layers is very unstable when tested in vitro with a saline solution at 37 degrees C, due to the instability of APTMS SAM and multilayer on silicon. Meanwhile, photo-immobilized heparin on silicon with OTS SAM as the bridging layer showed superb stability.

Poly(dimethylsiloxane) thin films as biocompatible coatings for microfluidic devices: cell culture and flow studies with glial cells

Oxygen plasma treatment of poly(dimethylsiloxane) (PDMS) thin films produced a hydrophilic surface that was biocompatible and resistant to biofouling in microfluidic studies. Thin film coatings of PDMS were previously developed to provide protection for semiconductor-based microoptical devices from rapid degradation by biofluids. However, the hydrophobic surface of native PDMS induced rapid clogging of microfluidic channels with glial cells. To evaluate the various issues of surface hydrophobicity and chemistry on material biocompatibility, we tested both native and oxidized PDMS (ox-PDMS) coatings as well as bare silicon and hydrophobic alkane and hydrophilic oligoethylene glycol silane monolayer coated under both cell culture and microfluidic studies. For the culture studies, the observed trend was that the hydrophilic surfaces supported cell adhesion and growth, whereas the hydrophobic ones were inhibitive. However, for the fluidic studies, a glass-silicon microfluidic device coated with the hydrophilic ox-PDMS had an unperturbed flow rate over 14 min of operation, whereas the uncoated device suffered a loss in rate of 12%, and the native PDMS coating showed a loss of nearly 40%. Possible protein modification of the surfaces from the culture medium also were examined with adsorbed films of albumin, collagen, and fibrinogen to evaluate their effect on cell adhesion.

Platelet adhesion and protein adsorption on silicone rubber surface by ozone-induced grafted polymerization with carboxybetaine monomer

Platelet adhesion and protein adsorption on the silicone rubber film grafted with N,N'-dimethyl-N-methacryloyloxyethyl-N-(2-carboxyethyl) ammonium (DMMCA) was studied. The grafting was carried out by means of ozone-induced method and was confirmed by ATR-FTIR and XPS investigations. The grafted films possessed relatively hydrophilic surface revealed by contact angle measurement. The blood compatibility of the grafted film was evaluated in vitro by platelet adhesion in platelet-rich plasma (PRP) and protein absorption in bovine fibrinogen (BFG) using silicone film as the reference. No substantial platelet adhesion was observed for the grafted films incubated in PRP for 60 and 180 min. The protein absorption was also significantly reduced after incubated in bovine fibrinogen for 60 min. Both the results indicated that the blood compatibility of silicone rubber was greatly improved by ozone-induced grafting of carboxybetaine zwitterionic polymer onto its surface.

Reduced adherence ofCandida to silane-treated silicone rubber

Silicone rubber is widely used in the construction of medical devices that can provide an essential role in the treatment of human illness. However, subsequent microbial colonization of silicone rubber can result in clinical infection or device failure. The objective of this study was to determine the effectiveness of a novel silane-treated silicone rubber in inhibiting microbial adherence and material penetration. Test material was prepared by a combination of argon plasma discharge treatment and fluorinated silane coupling. Chemicophysical changes were then confirmed by X-ray photoelectron spectroscopy, contact-angle measurement, and atomic force microscopy. Two separate adherence assays and a material penetration assay assessed the performance of the new material against four strains of Candida species. Results showed a significant reduction (p < 0.01) of Candida albicans GDH 2346 adherence to silane-treated silicone compared with untreated controls. This reduction was still evident after the incorporation of saliva into the assay. Adherence inhibition also occurred with Candida tropicalis MMU and Candida krusei NCYC, although this was assay dependent. Reduced penetration of silane-treated silicone by Candida was evident when compared to untreated controls, plaster-processed silicone, and acrylic-processed silicone. To summarize, a novel silicone rubber material is described that inhibits both candidal adherence and material penetration. The clinical benefit and performance of this material remains to be determined.

Synthesis, permeability and biocompatibility of tricomponent membranes containing polyethylene glycol, polydimethylsiloxane and polypentamethylcyclopentasiloxane domains

The synthesis of "smart" tricomponent amphiphilic membranes containing poly(ethylene glycol) (PEG), polydimethylsiloxane (PDMS) and polypentamethylcyclopentasiloxane (PD(5)) domains is described. Contact angle hysteresis indicates that in air, the surfaces of such PEG/PD(5)/PDMS membranes are enriched by the hydrophobic components, PDMS and PD(5), while in water, the surfaces are rich in the hydrophilic PEG. The oxygen permeability of a series of membranes with varying M(c,hydrophilic) (M(n,PEG)=4600, 10,000 and 20,000 g/mol) and varying PEG/PD(5)/PDMS compositions was studied. Oxygen permeability increased with the amount of PDMS in the membrane. The molecular weight cut-off (MWCO) ranges and permeability coefficients of insulin through a series of PEG/PD(5)/PDMS(=29/14/57) membranes with varying M(c,hydrophilic) were determined. Insulin permeability is directly related to M(c,hydrophilic) of the membrane. MWCO studies show that the membranes are semipermeable to, i.e., allow the transport of smaller proteins such as insulin (M(n)=5733 g/mol, R(s)=1.34 nm) and cytochrome c (M(n)=12,400 g/mol, R(s)=1.63 nm), but are barriers to larger proteins such as albumin (M(n)=66,000 g/mol, R(s)=3.62 nm). Implantation of representative membranes in rats showed them to be biocompatible. According to these studies, PEG/PD(5)/PDMS membranes may be suitable for biological applications, e.g., immunoisolation of cells.

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.

GRGDSP peptide-bound silicone membranes withstand mechanical flexing in vitro and display enhanced fibroblast adhesion

Mechanobiological studies of cardiac tissue require devices that allow forces to be exerted on cells in vitro. Silicone elastomer is often used in these devices because it is flexible and transparent, permitting optical imaging of the cells. However, native untreated silicone is hydrophobic and is unsuitable for cell culture. Peptides covalently bound to silicone surfaces are examined here for the enhancement of cellular adhesion during in vitro dynamic flexing. A procedure is described for the chemical modification of medical grade silicone membranes with covalently bound GRGDSP peptides. The conditions for mechanical studies of cardiac cell cultures are then duplicated and it is demonstrated that the peptide layers survive 48 h of mechanical flexing in vitro. Specifically, mechanical flexing in vitro of the 30 pmol/cm2 peptide-modified silicone membranes has no significant effect on the amount of peptides that remains bound to the surface. Cardiac fibroblasts display enhanced adhesion to these peptide-bound silicone membranes for at least 24 h of growth, compared with native silicone or tissue culture polystyrene. The effects of serum versus serum-free media on fibroblast growth are also examined.

Argon microwave plasma treatment and subsequent hydrosilylation grafting as a way to obtain silicone biomaterials with well-defined surface structures

A method of grafting well-defined and hydrolytically stable surface structures onto cross-linked poly(dimethylsiloxane) (PDMS) has been developed. In the first step, argon microwave plasma was used to introduce Si-H groups onto the surface. In the second step, allyltetrafluoroethyl ether was grafted to these Si-H groups using a platinum-catalyzed hydrosilylation reaction. The influences of the plasma parameters of power, pressure, and treatment time on the surface composition, both before and after the hydrosilylation step, were investigated by X-ray photoelectron spectroscopy and contact angle measurements. It was found that the pressure had little influence on the results, whereas the power and treatment time determined the rate of change in surface composition during the plasma treatment. The graft yield reached a plateau value corresponding to about 5% grafted molecules in the analyzed surface region. Hydrosilylation grafting of PDMS is a promising method to obtain biomaterials with hydrolytically stable structures covalently bound to the surface.

Synthesis and Surface Properties of Environmentally Responsive Segmented Polyurethanes

Polyurethanes, containing well-defined assemblies of perfluoro-polyether (PFPE or hexafluoropropene oxide oligomer), polydimethylsiloxane (PDMS), and polyethylene glycol (PEG) segments, exhibit oleophobic, hydrophobic, and hydrophilic properties in response to the polarity of the contacting medium. These polymers were prepared by reacting hydroxy(polyethyleneoxy)-propylether-terminated PDMS block copolymer (HO-PEG-PDMS-PEG-OH) with 4,4'-methylene-bis(phenylene isocyanate) (MDI) in the presence of dibutyltin dilaurate catalyst, followed by reaction with 1,2-diol functional PFPE and chain extension with 2,2,3,3-tetrafluoro-1,4-butanediol (FB). The oleophobic and hydrophobic properties of the segmented polyurethanes (SPU) are due to the segregation of PFPE segments at the polymer-air interface. Wettability studies revealed that the same surface becomes hydrophilic, presumably due to the segregation of the PEG segments at the polymer-water interface. This hydrophobic-to-hydrophilic transformation of the surface prevails not only when the polymer is in contact with liquid water but with water vapor as well. The understanding of the reconstruction mechanism of this novel family of SPU surfaces would furnish valuable information for various applications where dynamic transformation of surface activity is desired.

In vitro and in vivo antimicrobial activity of covalently coupled quaternary ammonium silane coatings on silicone rubber

Biomaterial-centered infection is a dreaded complication associated with the use of biomedical implants. In this paper, the antimicrobial activity of silicone rubber with a covalently coupled 3-(trimethoxysilyl)-propyldimethyloctadecylammonium chloride (QAS) coating was studied in vitro and in vivo. Gram-positive Staphylococcus aureus ATCC 12600, Staphylococcus epidermidis HBH, 102, and Gram-negative Esherichia coli O2K2 and Pseudomonas aeruginos AK1 were seeded on silicone rubber with and without QAS-coating, in the absence or presence of adsorbed human plasma proteins. The viability of the adherent bacteria was determined using a live/dead fluorescent stain and a confocal laser scanning microscope. The coating reduced the viability of adherent staphylococci from 90% to 0%), and of Gram-negative bacteria from 90% to 25% while the presencc of adsorbed plasma proteins had little influence. The biomaterials were also subcutaneously implanted in rats for 3 or 7 days, while pre- or postoperatively seeded with S. aureus ATCC 12600. Preoperative seeding resulted in infection of 7 out of 8 silicone rubber implants against 1 out of 8 QAS-coated silicone rubber implants. Postoperative seeding resulted in similar infection incidences on both implant types, but the numbers of adhering bacteria were 70% lower on QAS-coated silicone rubber. In conclusion, QAS-coated silicone rubber shows antimicrobial properties against adhering bacteria, both in vitro and in vivo.