SummaryA brief discussion is presented of some of the problems and artifacts inherent in the testing of soft tissue reactions to artificial implants. The process of inflammation and wound healing is presented. The various factors affecting the foreign body reaction (chemical, mechanical, geometrical, and others) are discussed. The cellular components of the foreign body reaction are described and the sequential cellular changes that may occur as a result of implanting an artificial device are examined. The foreign body reaction should be considered as a chronic inflammatory response.
We have previously shown that the adsorption of model proteins at model interfaces can be quantitatively understood via a careful consideration of the proteins' three dimensional structure and its stability. Using computer molecular graphics, dynamic surface tension, fluorescence probes and labels, and solution denaturation data, we can relate the chemical and structural properties of proteins to their interface behavior. We have developed a novel means to present these data and correlations in a simple radial plot (the "Tatra" plot). We are now extending these approaches to complex multi-domain proteins. Albumin consists of three large domains with differences in electrostatic nature, charge-pH characteristics, and denaturability. The interfacial activity of albumin is due, at least in part, to the interfacial activity of its constituent domains. Consideration of the structure and interfacial activity of the various domains permits new and more precise hypotheses to be developed, with which new and better experiments can be designed. Such hypotheses allow one to evaluate and compare adsorption data, including kinetics and isotherms, adsorbed layer thickness, refractive index, multilayer formation, etc. We feel strongly that each different protein is a unique molecular personality, which must be understood and considered if we are to more fully understand and apply the interfacial behavior of complex proteins. Expanded treatments of these topics are available in References 1-4. PRINCIPLES OF PROTEIN ADSORPTIONThe principles of protein adsorption have been presented in a number of monographs, review papers, and conference proceedings [l -81.The arrival of protein at the interface is assumed to be driven solely by diffusion processes, which are dependent on bulk concentration and diffusion coefficient. That results in a collision frequency[9]. The particular surface chemistry of the protein and of the surface dictates the residence time due to the initial interaction energy. The surface dynamics, or denaturability, of the protein itself, together with the residence time, probably controls the surface denaturability of the protein. The protein tends to denature with time at the interface. With increasing residence time, denaturation reaches a maximum. With increasing denaturation, the interaction energy in the adsorbed state is increased, and the probability for desorption, or the rate of desorption, is decreased.The reality of the process of course is that proteins are not homogeneous particles. Not all collisions are equally effective in adsorption, and different protein "surfaces," or faces, result in different interaction energies with the protein, and therefore different tendencies for surface denaturation. We attempt to illustrate this in Figure 1, in which the protein is shown as having four "faces:" a hydrophobic face, a positively charged face, a negatively charged face, and a neutral hydrophilic face. Although all collisions are equally probable, it is only those collisions which result in interaction ener...
The morphology and microheterogeneous composition of polymeric surfaces partially determines their adsorption and absorption characteristics. The surface structure, often significantly different from that of the bulk, is influenced by the environment, and especially by the interfacial energetics of the surrounding medium. These effects result in dynamic properties with relaxation times that affect the sorptive properties of the materials. Microheterogeneity on surfaces has been shown to have significant effects on the biological interactions between synthetic materials and proteins and/or cells; however, the in situ surface character, which determines the blood compatibility of biomedical copolymers, has only recently come under investigation. The objective of this paper is to present a perspective view of several methods for the characterization of microheterogeneity of dynamic surfaces in an aqueous-or fluid-phase environment. This work focuses on the investigation of the dynamic properties of microheterogeneous biomedical polyurethanes, and on the characterization of these surfaces with novel spectroscopic, surface energetic, and surface imaging techniques. Contact angle, infrared spectroscopy, and inverse chromatography are used to characterize the surface reorientation and heterogeneous microphase nature of polyurethane surfaces. The polyurethanes studied are shown to have a multicomponent surface with detectable hard-segment domains. The chemical structure of the copolymers suggests that the material is composed of domains 150 A in diameter. Evidence of these domains at the surface is presented. We have observed that the concentration of hard-segment surface groups, identified by the aromatic groups in the hard segment, varies as a function of polymer composition. The composition of surface hard segment is minimized with increasing phase purity, indicating the significance of morphology in determining surface composition of these polyurethanes and the ability of the surface to reorient in response to their environment. We have observed polyurethane surface structural rearrangements induced by hydration of the polymer film. These infrared and contact angle data indicate reorientation of the surface phase structure to enhance the surface concentration of the more polar phase in an aqueous environment. From these studies, structural models of selected polyurethane surfaces have been presented and additional analytical methods sensitive to in situ surface morphology have been proposed.
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