EFFECT OF SURFACE PLASMA TREATMENT ON THE CHEMICAL, PHYSICAL, MORPHOLOGICAL, AND MECHANICAL-PROPERTIES OF TOTALLY ABSORBABLE BONE INTERNAL-FIXATION DEVICES

The purpose of this work was threefold: to enhance the adhesion betwee n the reinforced absorbable calcium phosphate (Cap) fibers and the abs orbable polyglycolide acid (PGA) matrix, to improve the hydrolytic deg radation of the CaP fibers, and preliminarily to evaluate the cytotoxi city of the plasma treated surface of CaP fibers. A CH4 plasma treatme nt was used to achieve these goals. The microbond method was used to e valuate the effects of the plasma treatment on the interfacial shear s trength between the PGA matrix and CaP fibers. The treatment increased the mean interfacial shear strength of the CaP/PGA composite system b y 30%. AFM data showed that CH4-treated CaP fibers had considerable mi croscopic surface roughness, which facilitated mechanical interlocking between the reinforced CaP fibers and PGA matrix. The untreated and p lasma-treated fibers were also subjected to in vitro hydrolytic degrad ation in a phosphate buffer solution of pH 7.44 at 37 degrees C for up to 15 h. CH4 plasma treatment resulted in a considerable lower polar term of the surface energy and a significantly higher disperse term in water media. This change in the proportion of surface energy terms ma y reduce the capillary wicking phenomena of water through the CaP fibe r/PGA matrix interface. The CaP fiber dissolution studies revealed tha t both CH4 and Parylene plasma polymer coatings appeared to reduce the solubility of CaP fibers, and that the magnitude of reduction was hig her in an acidic than a physiologic pH environment. A preliminary cyto toxicity test revealed that both CH4 and Parylene plasma-treated CaP f ibers were noncytotoxic. Additional research should be done to determi ne the optimum plasma conditions and the possible use of other plasma gases to improve the interfacial shear stress of the composite and the dissolution properties of CaP fibers. (C) 1994 John Wiley and Sons, I nc.