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.

Inhibition of macrophage development and foreign body giant cell formation by hydrophilic interpenetrating polymer network.

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.

Adherent endotoxin mediates biological responses of titanium particles without stimulating their phagocytosis.

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.

Adhesion behavior of monocytes, macrophages, and foreign body giant cells on poly (N-isopropylacrylamide) temperature-responsive surfaces.

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 degrees C, or contract (dehydrate), creating a hydrophobic surface at 37 degrees 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.