Improved biocompatibility of silicone rubber by removal of surface entrapped air nuclei

Control of Blood Coagulation by Hemocompatible Material Surfaces-A Review

Hemocompatibility of biomaterials in contact with the blood of patients is a prerequisite for the short- and long-term applications of medical devices such as cardiovascular stents, artificial heart valves, ventricular assist devices, catheters, blood linings and extracorporeal devices such as artificial kidneys (hemodialysis), extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass. Although lower blood compatibility of materials and devices can be handled with systemic anticoagulation, its side effects, such as an increased bleeding risk, make materials that have a better hemocompatibility highly desirable, particularly in long-term applications. This review provides a short overview on the basic mechanisms of blood coagulation including plasmatic coagulation and blood platelets, as well as the activation of the complement system. Furthermore, a survey on concepts for tailoring the blood response of biomaterials to improve the hemocompatibility of medical devices is given which covers different approaches that either inhibit interaction of material surfaces with blood components completely or control the response of the coagulation system, blood platelets and leukocytes.

Subclinical Infection of the Silicone Breast Implant Surface as a Possible Cause of Capsular Contracture

In order to reexamine the possible association between bacterial presence and capsular contracture, 55 silicone devices (mammary implants or tissue expanders) were cultured at the time of their removal from 40 patients. Special culture techniques were used in an attempt to recover bacteria adhering to the smooth-surfaced implant and encased in glycocalyx biofilm. Bacteria were detected on 56% (15 of 27) of implants surrounded by contracted capsules and on 18% (5 of 28) of those without capsular contracture (p < 0.05). Only three implants tested positive using routine plating techniques. The predominant isolate was Staphylococcus epidermidis. The concept that capsular contracture is associated with subclinical infection of silicone implants is supported by this study. With changes in the microbiological technique, bacterial recovery and growth occurs at a frequency greater than previously thought.

Macrophage behavior on surface-modified polyurethanes

Adherent macrophages and foreign body giant cells (FBGCs) are known to release degradative molecules that can be detrimental to the long-term biostability of polyurethanes. The modification of polyurethanes using surface modifying endgroups (SMEs) and/or the incorporation of silicone into the polyurethane soft segments may alter macrophage adhesion, fusion and apoptosis resulting in improved long-term biostability. An in vitro study of macrophage adhesion, fusion and apoptosis was performed on polyurethanes modified with fluorocarbon SMEs, polyethylene oxide (PEO) SMEs, or poly(dimethylsiloxane) (PDMS) co-soft segment and SMEs. The fluorocarbon SME and PEO SME modifications were shown to have no effect on macrophage adhesion and activity, while silicone modification had varied effects. Macrophages were capable of adapting to the surface and adhering in a similar manner to the silicone-modified and unmodified polyurethanes. In the absence of IL-4, macrophage fusion was comparable on the modified and unmodified polyurethanes, while macrophage apoptosis was promoted on the silicone modified surfaces. In contrast, when exposed to IL-4, a cytokine known to induce FBGC formation, silicone modification resulted in more macrophage fusion to form foreign body giant cells. In conclusion, fluorocarbon SME and PEO SME modification does not affect macrophage adhesion, fusion and apoptosis, while silicone modification is capable of mediating macrophage fusion and apoptosis. Silicone modification may be utilized to direct the fate of adherent macrophages towards FBGC formation or cell death through apoptosis.

Biostability and macrophage-mediated foreign body reaction of silicone-modified polyurethanes

In this study, the effect of soft segment chemistry on the phase morphology and in vivo response of commercial-grade poly(ether urethane) (PEU), silicone-modified PEU (PEU-S), poly(carbonate urethane) (PCU), and silicone-modified PCU (PCU-S) elastomers were examined. Silicone-modified polyurethanes were developed to combine the biostability of silicone with the mechanical properties of PEUs. Results from the infrared spectroscopy confirmed the presence of silicone at the surface of the PEU-S and PCU-S films. Atomic force microscopy phase imaging indicated that the overall two-phase morphology of PEUs, necessary for its thermoplastic elastomeric properties, was not disrupted by the silicone modification. After material characterization, the in vivo foreign body response and biostability of the polyurethanes were studied using a subcutaneous cage implant protocol. The results from the cage implant study indicated that monocytes adhere, differentiate to macrophages which fuse to form foreign body giant cells on all of the polyurethanes. However, the silicone-modified surfaces promoted apoptosis of adherent macrophages at 4 days and high levels of macrophage fusion after 21 days. These results confirm that the surface of a biomaterial may influence the induction of apoptosis of adherent macrophages in vivo and are consistent with previous cell culture studies of these materials. This study validates the use of our standard cell culture protocol to predict in vivo behavior and further supports the hypothesis that interleukin-4 is the primary mediator of macrophage fusion and foreign body giant cell formation in vivo. The impact of these findings on the biostability of polyurethanes is the subject of current investigations. Attenuated total reflectance-Fourier transform infrared analysis of explanted specimens provided evidence of chain scission and crosslinking at the surface of all of the polyurethanes. The silicone modification did not fully inhibit the oxidative biodegradation of the polyether or polycarbonate soft segments; however, the rate of chain scission of PEU-S and PCU-S seemed to be slower than the control polyurethanes. To verify this finding and to quantify the rate of chain scission in order to predict long-term biostability, an in vitro environment that simulated the microenvironment at the adherent cell-material interface was used to accelerate the biodegradation of the polyurethanes. Polyurethane films were treated in vitro for up to 36 days in 20% hydrogen peroxide/0.1M cobalt chloride solution at 37 degrees Celsius. Characterization with attenuated total reflectance-Fourier transform infrared and scanning electron microscopy showed soft segment and hard segment degradation consistent with the chemical changes observed after long-term in vivo treatment. The biostability ranking of these four materials based on rate of chain scission and surface pitting was as follows: PEU < PEU-S PCU < PCU-S. The silicone modification increased the biostability of the PEU and PCU elastomers while maintaining the thermoplastic elastomeric properties.

Investigation of the activation of a human serum complement protein, C3, by orthopedic prosthetic particulates

Myriad molecular, cellular, and physiological processes underlie the inflammatory and osteolytic processes induced by particles of biomaterials resulting from the wear of implants such as total joint replacement prostheses. The objective this study was to investigate the role that the complement system may be playing in these phenomena. The aim was to evaluate the degree to which particles of selected orthopaedic materials--high density and ultrahigh molecular weight polyethylene, polymethylmethacrylate, and commercially pure titanium--cause the elevation of a key complement molecule, C3a, in an in vitro assay that directly measured the concentration of C3a. The results demonstrated that HDPE particles, at high concentration, are capable of causing the elevation of C3a in the in vitro assay. This finding is discussed in the context of other work and the mechanics of the complement system as it may affect the osteolytic process.

Characterization and protein-adsorption behavior of deposited organic thin film onto titanium by plasma polymerization with hexamethyldisiloxane

Plasma polymerized hexamethyldisiloxane (HMDSO) thin film was deposited onto titanium using a radio-frequency apparatus for the surface modification of titanium. A titanium disk was first polished using colloidal silica at pH=9.8. Plasma-polymerized HMDSO films were firmly attached to the titanium by heating the titanium to a temperature of approximately 250 degrees C. The thickness of the deposited film was 0.07-0.35mum after 10-60min of plasma polymerization. The contact angle with respect to double distilled water significantly increased after HMDSO coating. X-ray photoelectron spectroscopy revealed that the deposited thin film consisted of Si, C, and O atoms. No Ti peaks were observed on the deposited surface. The deposited HMDSO film was stable during 2-weeks immersion in phosphate buffer saline solution. Fourier transform reflection-absorption spectroscopy showed the formation of Si-H, Si-C, C-H, and Cz.dbnd6;O bonds in addition to Si-O-Si bonds. Quartz crystal microbalance-dissipation measurement demonstrated that the deposition of HMDSO thin films on titanium has a benefit for fibronectin adsorption at the early stage. In conclusion, plasma polymerization is a promising technique for the surface modification of titanium. HMDSO-coated titanium has potential application as a dental implant material.

Blood compatibility of titanium oxides with various crystal structure and element doping

BACKGROUND

Titanium oxides are known to be good hemocompatible, therefore they are suggested as coatings for blood contacting implants. But little is known about the influence of physical characteristics like crystal structure, roughness and electronic state on the activation of blood platelets and the blood clotting cascade.

METHODS

Titanium oxide films were produced by metal plasma deposition and implantation in the form of rutile, crystalline and nanocrystalline anatase + brookite and amorphous TiO2. The redox potential was reduced by implantation of chromium ions, the Fermi level of the semiconductive oxide was shifted by ion implantation of the electron donor phosphorous. Hemocompatibility was determined by measuring the adhesion of blood platelets, their P-selectine expression, and of the blood clotting time on these samples.

RESULTS

The crystalline titanium oxides had a slightly higher activation of the clotting cascade but lower platelet adhesion than nanocrystalline and amorphous titanium oxides. The surface roughness below 50 nm had no obvious effect. Both, implantation of phosphorous or chromium ions, strongly reduced the activation of the clotting cascade, but only the phosphorous implanted surface also showed a reduced platelet activation, whereas platelet adhesion and activation was strongly increased on the chromium implanted surfaces.

CONCLUSION

Phosphorous doping of rutile TiO2 can increase its hemocompatibility, both concerning blood platelets and blood clotting cascade, but the biochemical mechanism has to be worked out.

In situ complement activation by polyethylene wear debris

A frequent long-term complication of total joint arthroplasty is aseptic loosening, the end result of wear debris accumulation, synovitis, and osteolysis about the implant-bone or cement-bone interface. Complement, an effector system in plasma, synovial fluid, and tissue, has powerful chemotactic, inflammatory, and osteoclast-activating potentials. This study explored the complement-activating ability of polyethylene, a material used in joint implants. In vitro hemolytic assays using sheep red blood cells (E(sh)), human serum, and particulate polyethylene suggested alternative pathway complement activation, as well as polyethylene adsorption of activated complement components. These results were confirmed by enzyme-linked immunosorbent assay (ELISA) quantification of activated complement factors Bb and C3b. In situ double antibody immunoperoxidase staining for factors Bb, C3a, iC3b, and SC5-9 in synovial tissue from revision hip specimens showed localized alternative pathway activation and component adsorption. These results introduce a likely role for complement activation in particle-mediated recruitment, proliferation, and activation of macrophages during early events in osteolysis and implant loosening.

Complement activation by angiographic catheters in vitro

PURPOSE

Four different polymers used in commercial angiographic catheters were compared in vitro with respect to their ability to activate the complement system.

MATERIALS AND METHODS

Commercially available angiographic catheters made from one of the following plastics were used: polyamide, polyethylene, polyurethane, and polytetrafluoroethylene. Silicone-coated latex urinary catheters served as the reference standard. Each catheter was cut into 20-mm segments, immersed in a polypropylene tube containing fresh serum from a volunteer donor, and incubated at 37 degrees C. Samples were drawn at 15 minutes, 1 hour, and 6 hours; C3 activation products (C3AP) and the terminal complement complex (TCC) content were estimated with enzyme immunoassays.

RESULTS

By 1 hour, a significant increase in C3AP and TCC concentrations was observed with all angiographic catheters relative to controls (P < .01-.001). The time-concentration plots for both C3AP and TCC were steepest for polyamide. C3AP concentrations relative to controls were significantly higher with exposure to polyamide compared with polyurethane at 1 hour (P < .01), and with both polyethylene and polyurethane at 6 hours (P < .01). Polytetrafluoroethylene induced larger amounts of C3AP formation by 6 hours than polyethylene and polyurethane (P < .05). However, polytetrafluoroethylene was associated with the lowest relative median concentrations of TCC; the difference with polyamide was significant at 6 hours (P < .001). As with C3AP, differences in TCC generation between polyethylene and polyurethane were marginal at all observation points (P > .05).

CONCLUSIONS

All the polymers tested activated the complement system. Activation was most prominent with exposure to polyamide and least marked with polyurethane.

Subclinical infection of the silicone breast implant surface as a possible cause of capsular contracture

In order to reexamine the possible association between bacterial presence and capsular contracture, 55 silicone devices (mammary implants or tissue expanders) were cultured at the time of their removal from 40 patients. Special culture techniques were used in an attempt to recover bacteria adhering to the smooth-surfaced implant and encased in glycocalyx biofilm. Bacteria were detected on 56% (15 of 27) of implants surrounded by contracted capsules and on 18% (5 of 28) of those without capsular contracture (p less than 0.05). Only three implants tested positive using routine plating techniques. The predominant isolate was Staphylococcus epidermidis. The concept that capsular contracture is associated with subclinical infection of silicone implants is supported by this study. With changes in the microbiological technique, bacterial recovery and growth occurs at a frequency greater than previously thought.