Polymeric biomaterials polyethylene

Based on their behavior in living tissue, polymeric biomaterials can be divided into two groups biostable and biodegradable. Biostable polymers are used when permanent aids are needed, e.g., as prostheses [13]. Biostable polymers, typically polyethylene and poly(methyl methacrylate), should be physiologically inert in tissue conditions and maintain their mechanical properties for decades [11]. 

The first implanted synthetic polymeric biomaterial appears to be PMMA, which was used as a hip prosthesis in 1947 (see USP XVIII, The Pharmacopia of the USA, (18th Revision), US Pharmacopoeial Convention, Inc., Rockville, MD, 1 September 1980). Polyethylene, and then other polymers, were used as implants in the middle ear in the early 1950s, yielding good initial results, but local inflammation limited the use of these materials. 

Hydrophilic coatings have also been popular because of their low interfacial tension in biological environments [Hoffman, 1981]. Hydrogels as well as various combinations of hydrophilic and hydrophobic monomers have been studied on the premise that there will be an optimum polar-dispersion force ratio which could be matched on the surfaces of the most passivating proteins. The passive surface may induce less clot formation. Polyethylene oxide coated surfaces have been found to resist protein adsorption and cell adhesion and have therefore been proposed as potential blood compatible coatings [Lee et al., 1990a]. General physical and chemical methods to modify the surfaces of polymeric biomaterials are listed in Table 40.7 [Ratner et al., 1996]. 

Another ophthalmologic application of polymeric biomaterials is the development of ocular prosthesis and biologically inspired compound eyes [197,198]. Such prostheses, commonly fabricated from porous polyethylene, are designed to serve as nonfunctional artificial substitutes for enucleated eyeballs [199]. 

N.P. Desai and J. A. Hubbell. Solution technique to incorporate polyethylene oxide and other water soluble polymers into the surfaces of polymeric biomaterials. Biomaterials 12 144-153 (1991). 

Archambault JG, Brash JL. Protein repellent polyurethane-urea surfaces by chemical grafting of hydroxyl-terminated poly(ethylene oxide) effects of protein size and charge. Colloids SutfB Biointerfaces 2004 33 111-20. http //dx.doi.Org/10.1016/j.colsurfb.2003.09.004. Desai NP, Hubbell JA. Solution technique to incorporate polyethylene oxide and other water-soluble polymers into surfaces of polymeric biomaterials. Biomaterials 1991 12 144-53. 

Bajpai, A.K. Blood protein adsorption onto a polymeric biomaterial of polyethylene glycol and poly[(2-hydroxyethyl methacrylate)-co-acrylonitiile] and evaluation of in vitro blood compatibility. Polym. Int. 54(2), 304-315 (2005)... 

Hatakeyama H, Kikuchi A, Yamato M et al (2007) Patterned biofunctional designs of thermo-responsive surfaces for spatiotemporally controlled cell adhesion, growth, and thermally induced detachment. Biomaterials 28 3632-3643 Hem DL, Hubbell JA (1998) Incorporation of adhesion peptides into nonadhesive hydrogels useful for tissue resurfacing. J Biomed Mater Res 39 266-276 Huang J, Wang XL, Chen XZ et al (2003) Temperature-sensitive membranes prepared by the plasma-induced graft polymerization of N-isopropylacrylamide into porous polyethylene membranes. J Appl Polym Sci 89 3180-3187... 

Among the many classes of polymeric materials now available for use as biomaterials, non-degradable, hydrophobic polymers are the most widely used. Silicone, polyethylene, polyurethanes, PMMA, and EVAc account for the majority of polymeric materials currently used in clinical applications. Consider, for example, the medical applications listed in Table A.l most of these applications require a polymer that does not change substantially during the period of use. This chapter describes some of the most commonly used non-degradable polymers that are used as biomaterials, with an emphasis on their use in drug delivery systems. 

Low-density polyethylene (LDPE) is commonly used biomaterial which possesses fairly good grafting reactivity compared to other common polymeric materials. A number of plasma modification and plasma polymerization systems have been employed in order to incorporated oxygen-containing functional groups onto polyethylene surfaces for biomaterial applications. i Tiie aim of this work was to introduce acidic sulfur-containing functional groups onto LDPE surfaces by plasma treatment and to assess the potential blood compatibility of the modified materials. 

Clearly, a need exists to develop an optimum polymer/bone interface which will provide a direct, stable, permanent fixation in hard tissue for both present and future polymeric components in orthopaedic prostheses. This need provided a strong incentive to pursue the present study on surface activation and to investigate the development of methods of creating hydroxyapatite-like surfaces on polyethylene, the currently used orthopaedic polymer. The surface activation entailed the selective surface phosphonylation of polymeric films made of polyethylene and nylon-12. Nylon-12 was chosen as a representative heterochain polymer whose chain structure closely resembles polyethylene and yet contains hydrolyzable functionalities similar to those of nylon-6, a widely used biomaterial. To study the biocompatibility of a typical new surface, the current study also involved the interaction of a modified polyethylene film with fibroblasts and hydroxyapatite salt solution. 

Polymeric materials that have been used in the cardiovascular system include polytetrafluorethy-lene, polyethylene terephthalate, polyurethane, polyvinyl chloride, etc. Textiles bas on polytetra-fluorethylene and polyethylene terephthalate are us extensively as fabrics for repair of vasculature and larger-vessel replacement (greater than 6 mm in diameter). Stent-grafts are hybrid stent grafts placed by catheter to treat aortic aneurysms nonsurgically and are fabricated of the same metallic alloys used in stents and textiles similar to those used in vascular grafts. Table 14.1 lists many of the biomaterials currently used in the cardiovascular system. 

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