Implants, polymeric fibers

Sutures are the largest group of devices implanted into humans. Sutures are employed to hold together parts of the body generally through the use of fibers. A wide variety of materials are available today, each with known advantages and limitations and all are essentially polymeric. 

Many of the silicone elastomers that are used in biomedical applications are produced by Dow Chemical Corp., under the trade name SILASTIC . For example, a typical medical-grade silicone (like SILASTIC MDX4-4210 Medical grade elastomer) contains, after curing, cross-linked drmethylsiloxane polymer and silica for reinforcement. Silcones are also reinforced with PET (Dacron) fiber meshes for certain biomedical applications. For implantable medical devices, it is important to realize that the cured polymer contains residual catalysts and silicone cross-linkers, which are necessary for the polymerization. 

Yasuda et al. [198-200] studied the effect of plasma treatment on different fibers and fabrics. They used four nonpolymerizing gases helium, air, nitrogen, and tetra-fluoromethane. It was found that in some cases the etching of the fiber was accompanied by the implantation of the specific atoms into its surface. The model studies performed with nylon 6 have shown that plasma treatment, similar to plasma polymerization, may be carried out in the power-deficient range as well as in the gas-deficient range. 

Synthetic pol)mieric materials have been widely used in medical disposable supply, prosthetic materials, dental materials, implants, dressings, extracorporeal devices, encapsulants, polymeric drug delivery systems, tissue engineered products, and orthodoses as that of metal and ceramics substituents [Lee, 1989]. The main advantages of the polymeric biomaterials compared to metal or ceramic materials are ease of manufacturability to produce various shapes (latex, film, sheet, fibers, etc.), ease of secondary processability, reasonable cost, and availability with desired mechanical and physical properties. The required properties of polymeric biomaterials are similar to other biomaterials, that is, biocompatibility, sterilizability, adequate mechanical and physical properties, and manufacturability as given in Table 40.1. 

Bone cements used to fill the void and improve adhesion between implants and the host bone tissue have been reinforced with various fibers to prevent loosening and enhance shear strength. The typical bone cement is PMMA powder mixed with a methacrylate-type monomer that is polymerized during fixation. Low volume fractions of graphite, carbon, and Kevlar fibers have been added to PMMA matrices to increase fatigue life and r uce creep deformation. ... 

No polymeric material is ideally elastic or immune to any change they all degrade irreversibly and at different rates. Tissues, on the other hand, have the ability to repair damage inflicted on them. There is therefore great interest in the development of engineered tissues as implants, both as pure biological products and as composites with fibers. 

In the same way, PLGA enhances the properties of PLA implantable conduits and allows better control over the degradation rate, depending on the ratio of lactide to gly-colide used for the polymerization. The presence of lactic acid first slows ingress of water in fiber. Then, spaces induced by lactic acid ease water penetration into filaments and speed up the erosion process. 

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