Search

The ability of monocytes to adhere, differentiate into macrophages, and fuse to form foreign body giant cells (FBGCs) on an implanted material surface is a critical step toward biomaterial degradation. Novel homogeneous surfaces were utilized to mediate adhesion. These surfaces consisted of N-(2 aminoethyl)-3-aminopropyltrimethoxysilane (EDS) and an interpenetrating polymer network (IPN) of polyacrylamide and poly(ethylene glycol). These surfaces were designed to control cell adhesion and morphology and mediate cell differentiation, activation, metabolic ability, and apoptosis, resulting in a reduced or controlled inflammatory response. The EDS surface promotes cell adhesion and the IPN minimizes protein adsorption and subsequent cell adhesion. Both surfaces had similar cellular adhesion rates at each respective time point. However, the adherent macrophage morphology was similar at 2 h and day 3, and at days 7 and 10 adherent macrophages on the EDS surface formed FBGCs (46% at day 7 and 40% at day 10). Adherent cells on the IPN surface did not form FBGCs but instead formed monocyte aggregates (73% of adherent cells formed aggregates at day 7 and 63% at day 10). It is indicated that the two surface chemistries differentially controlled monocyte differentiation into macrophages and subsequent macrophage fusion to form FBGCs.

Cell adhesion and maturation can be affected by the protein adsorption profile on the surface of an implanted biomaterial. In this study we have investigated how surface chemistry and adsorbed proteins can modulate monocyte and macrophage adhesion, IL-13-induced foreign-body giant cell formation, and apoptosis in vitro. Compared to a dimethylsilane-modified surface (DM), a surface modified with RGD peptides had no effect on adhesion density, foreign-body giant cell (FBGC) formation, or apoptosis in nondepleted serum conditions. The depletion of specific adhesive proteins affected adhesion, FBGC formation, and apo- ptosis. While the depletion of fibronectin and vitronectin had no overall effect compared to nondepleted serum conditions, the depletion of IgG from serum caused a significant decrease in initial adherent cell density [1000 +/- 200 compared to 2460 +/- 590 (p = 0.02)], a significant decrease in FBGC formation [2% compared to 17% (p = 0.02)], and a significant increase in the level of apoptosis [57% compared to 32% (p = 0.01)] on DM. The lowered initial adherent cell density on DM was not observed on the RGD surface, indicating that the RGD surface promotes increased initial adhesion. However, the RGD surface does not affect FBGC formation (i.e., macrophage fusion) or levels of apoptosis, which remained comparable to those on the DM surfaces at days 7 and 10.

Monocyte and macrophage adhesion and foreign body giant cell (FBGC) formation has been observed on surfaces with a wide range of properties. In this study we have utilized novel, temperature-responsive surfaces (TRS) with dynamic surface properties to investigate inflammatory cell adhesion behavior. With temperature changes, grafted chains of poly-N-isopropylacrylamide pass through their lower critical solution temperature (LCST) and can either extend (hydrate), creating a hydrophilic surface at 20°C, or contract (dehydrate), creating a hydrophobic surface at 37°C. Isolated human monocytes and monocyte-derived macrophages were able to adhere, spread, and form FBGC on the hydrophobic surface. Decreasing the temperature below the lower critical solution temperature induced a change in the surface wettability, creating a hydrophilic surface, that induced a differential detachment of adherent cells that decreased with time, ranging from 98% after 2 h of culture to 30% at day 10. These detached cells remained viable, and were recultured onto TCPS for 3, 7, and 10 days. These novel surfaces allow investigation of the adhesive behavior of adherent inflammatory cells in a temporal manner, and the effects of surface conformation and wettability changes on cell adhesion and detachment. © 2001 Wiley Periodicals, Inc. J Biomed Mater Res 59: 136–143, 2002

Poly(etherurethane urea) (PEUU) elastomers, with their broad range of mechanical properties and high biocompatibility, are used clinically for medical applications. However, the possibility exists for the ether soft segment of PEUU to degrade in long-term uses. To retard degradation, antioxidants that scavenge reactive oxygen intermediates are added. In this study, we incorporated dehydroepiandrosterone (DHEA), which functions by the alternate mechanism of modulating or down-regulating adherent macrophage activity, to retard the biodegradation of PEUUs. Biocompatibility of PEUU samples containing 1% DHEA, 5% DHEA, and 5% vitamin E (α-tocopherol) by weight were studied in vivo and in vitro. The biocompatibility was initially evaluated by examination of the inflammatory cellular exudate. Compared to PEUU without additives and PEUU with 5% vitamin E, the addition of 5% DHEA to PEUU caused a decrease in the total leukocyte exudate concentration at 4 days. The addition of 5% DHEA also caused lower macrophage adhesion and FBGC formation compared to the other materials at 7 days. Despite these short-term effects, the biocompatibility at later time points (14, 21, and 70 days) was similar for all materials. Transmission infrared analysis of the materials revealed that more than 70% of the DHEA had leached out of the samples by 3 days implantation. Furthermore, through attenuated total reflectance Fourier transform analysis and scanning electron microscopy, it was determined that unlike vitamin E, DHEA did not enhance long-term PEUU biostability. The effect of DHEA on inflammatory cell activity appeared to be dose dependent, with improved biocompatibility in vivo for higher loading levels of DHEA, but the overall effect was limited owing to the rapid diffusion of the water-soluble DHEA from the PEUU. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 192–201, 1998.

This paper summarizes our recent efforts to better understand the effects of antioxidants, the effects of strain-state, mechanistic studies of soft segment cleavage by reactive oxygen radicals, and the effects of different soft segment chemistries on the biostability/biodegradation of polyether polyurethanes (PEUUs). In vivo cage implant system studies and in vitro cobalt ion/hydrogen peroxide studies have been carried out on PEUUs and the polymers have been analysed by attenuated total reflectance and Fourier transform infrared (ATR-FTIR) spectroscopy, and scanning electron microscopic (SEM) characterization of the PEUU surfaces. The natural antioxidant, vitamin E, has been shown to inhibit biodegradation and enhance biostability of PEUUs. Studies of the effect of stress state on PEUU biodegradation demonstrate that stress can inhibit biodegradation. While polyether soft segments may be cleaved by the presence of reactive oxygen radicals, the presence of oxygen has a profound effect in accelerating biodegradation. The biodegradation of polyurethanes may be inhibited by substituting different chemistries such as polydimethylsiloxanes, polycarbonates, and hydrocarbon soft segments for the polyether soft segments. To safely utilize polyurethanes in long-term biomedical devices, the biodegradation mechanisms of polyurethane elastomers must be fully understood and subsequently prevented. © 1998 SCI.

Modified segmented polyurethanes were examined for biostability and biocompatibility using an in vivo cage implant system for time intervals of 1, 2, 3, 5, and 10 weeks. Two types of materials were used: polyether polyurethanes and polycarbonate polyurethanes. Two unmodified polyether polyurethanes (PEUU A' and SPU-PRM), one PDMS endcapped polyether polyurethane (SPU-S), and two polycarbonate polyurethanes (SPU-PCU and SPU-C) were investigated in this study. Techniques used to characterize untreated materials were dynamic water contact angle, stress-strain analysis, and gel permeation chromatography. Cellular response was measured by exudate analysis and by macrophage and foreign body giant cell (FBGC) densities. Material characterization, postimplantation, was done by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) in order to quantify biodegradation and scanning electron microscopy (SEM) to qualitatively describe the cellular response and biodegradation. The exudate analysis showed that the acute and chronic inflammatory responses for all materials were similar. Lower FBGC densities and cell coverage on SPU-S were attributed to the hydrophobic surface provided by the PDMS endgroups. The polycarbonate polyurethanes did not show any significant differences in cell coverage or FBGC densities even though the macrophage densities were slightly lower compared to polyether polyurethanes. By 10 weeks, biodegradation in the case of PEUU A' and SPU-PRM was extensive as compared to SPU-S because the PDMS endcaps of SPU-S provided a shield against the oxygen radicals secreted by macrophages and FBGCs and lowered the rate of biodegradation. In the case of polycarbonate polyurethanes, the oxidative stability of the carbonate linkage lowered the rate of biodegradation tremendously as compared to the polyether polyurethanes (including SPU-S). The minor amount of biodegradation seen in polycarbonate polyurethanes at 10 weeks was attributed to hydrolysis of the carbonate linkage.

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.

Aseptic loosening of orthopaedic implants is thought to be primarily due to stimulation of cytokine production by wear particles from the implants. The cytokines increase osteoclast differentiation, leading to osteolysis and implant loosening. Accumulating evidence indicates that adherent endotoxin mediates the biological responses induced by the wear particles. One mechanism by which adherent endotoxin may act is by increasing phagocytosis of the wear particles. To test this hypothesis, the effect of adherent endotoxin on phagocytosis of titanium particles was determined. First, we developed reliable confocal and fluorescence microscopy methods to examine both the attachment and internalization steps of phagocytosis. Use of these methods showed that adherent endotoxin does not detectably alter the rate or the extent of phagocytosis of titanium particles by RAW 264.7 cells. Despite this lack of an effect on phagocytosis, adherent endotoxin dramatically increases the ability of RAW 264.7 cells to produce TNF-alpha and induce osteoclast differentiation. Thus, adherent endotoxin mediates these biological responses by a mechanism that does not rely on increased phagocytosis. These results also demonstrate that phagocytosis is not sufficient to induce cytokine production and osteoclast differentiation but do not rule out the possibility that phagocytosis is required for induction of these responses by titanium particles with adherent endotoxin.