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Carbon Materials in the Treatment of Soft and Hard Tissue Injuries

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Carbon Materials in the Treatment of Soft and Hard Tissue Injuries EuropeanM. Blazewicz Cells and Materials V ol. 2. 2001 (pages 21-29) Carbon DOI: materials 10.22203/eCM.v002a03 in the treatment of soft and hard ISSN tissue 1473-2262 injuries CARBON MATERIALS IN THE TREATMENT OF SOFT AND HARD TISSUE INJURIES M. Blazewicz Department of Special Ceramics, University of Mining and Metallurgy, al. Mickiewicza 30, 30-059 Cracow, Poland Abstract Introduction Carbon-based implant materials are of interest because Over the past twenty-five years various carbon materials they are well accepted by the biological environment. have been investigated in many areas of medicine (Bohem, Carbon fibrous materials developed in the Department of 1966; Arru et al., 1987; Jockish et al., 1992; Vallana et Special Ceramics of the University of Mining and Metal- al., 1993; Blazewicz et al., 1994; Carranza-Bencano et lurgy in Cracow were tested in in vivo studies to deter- al., 2000). The large range of papers presented in scien- mine their influence on the living body. For comparative tific journals is related to the spectacular chemical and purposes, different carbon fibers were prepared and sub- physical properties of carbon materials. Carbon occurs in jected to different surface modifications. Carbon materi- different lattice forms, from amorphous through interme- als prepared in the form of braids were implanted in subcu- diate to crystalline, e.g., hexagonal or regular lattice dia- taneous tissue of rabbits and into skeletal muscle of rats. mond. The broad range of applications of carbon materi- Carbon fabrics were examined as scaffolds in reconstruc- als in medicine is also the outcome of many preparation tion of bone defects. methods. Carbon implant materials can be produced by The present study examined the synthesis-structure- pyrolysis of solid, liquid and gaseous carbon precursors. property relationships of fibrous carbon samples with re- The pyrolysis method applied to carbon compounds al- spect to the tissue response. It was shown that the tissue lows the production of carbon of different structure and response depends on the form of the material form, the microstructure in the form of thin films or thick layers, degree of order of the crystallites, the surface state and solid pyrolytic carbon, powders and in the form of fibers microstructural parameters. Carbon fibers with higher (Pampuch et al., 1988). The different forms of carbon crystallinity and a better-organized graphite structure were that have received attention are artificial graphites, glass- assimilated by the body with more difficulty and small like carbon, carbon fibers, pyrolytic carbon and vapor- particles coming from these materials were found in the grown carbon coatings. Among pure forms of carbon, the regional lymph nodes. Low- carbonized carbon fibers pyrolytic carbons and carbon coatings on various substrates (small crystallite size) underwent partial fragmentation have found clinical applications in the cardiovascular, and reacted with the biological environment by being orthopedic and dental areas as well as in long-term tran- gradually resorbed in the implantation site. The presence scutaneous applications (Bokros et al., 1972; Buttazzoni, of acidic groups on the surface of the carbon fibers en- 1987; Feng and Andrade, 1994; Louis and Dabadie, 1996; hanced phagocytosis of the carbon material by De Santis et al., 2000). macrophages. Depending on the surface state of carbon Carbon fibers represent transition graphite structures fibers different rates of bone wound healing were observed. obtained mainly by a carbonization process of organic fibers. The process makes it possible to retain the fibrous Key Words: Carbon implants, carbon fibers, surface form of the precursor. However, the carbon atom arrange- modification, tissue response, in vivo study. ment is similar to that in graphite. The major difference between the structure of graphite and carbon fibers is that, at the atom level, the degree of structural ordering in the carbon fibers is present only in the basal planes. The physi- cal and chemical properties of carbon fibers are also de- termined by their microstructure. This is particularly im- portant in the case of carbon fibers used in medicine. The Address for correspondence: size of coherent crystallites in carbon fiber lattice, corre- M. Blazewicz sponding to the crystallite thickness (La) and crystallite Department of Special Ceramics, height (Lc) is of decisive importance for, e.g., fiber resist- University of Mining and Metallurgy, ance to oxidation and, in a biological environment, may al. Mickiewicza 30, influence the interaction between the fiber and the envi- 30-059 Cracow, ronment (Blazewicz et al., 1991). Poland One of the earliest medical uses of carbon fibers was E-mail: [email protected] replacement or repair of ligaments and tendons (Forster 21 M. Blazewicz Carbon materials in the treatment of soft and hard tissue injuries et al., 1978; Miller, 1984; Jenkins, 1985). Most of the form of unwoven fabric were used as scaffolds in recon- studies on carbon fibrous implants confirm that carbon struction of experimentally prepared bone defects. fibers do not inhibit tissue growth, and thus can act as a scaffold for tissue proliferation (Forster et al., 1978; Becker Materials and Methods et al., 1996). Controversy surrounds the mechanism of the disintegration and removal of the implanted carbon Carbon fibrous implants prepared in the laboratory were fibers. A histological study showed that the carbon fibers used in this study. Polyacrylonitrile precursor (PAN) with gradually broke down and migrated into the nearest lymph co-monomer (6 wt% methyl acrylate and 1 wt% itaconic nodes with no apparent detrimental effect (Becker et al., acid) was used to prepare carbon fibers. 1996). In all instances the carbon fibers acted as a scaf- The yarns of PAN fibers containing 300 filaments of fold that allowed the regeneration of tendon and ligament. 13-14 mm diameter were transformed into braids and In contrast to these investigations, Morris et al. (1990) unwoven fabrics. These two types of carbon precursors showed that fragmentation of fibers did not occur and were subjected to thermal processing, first in air atmos- implant debris was not found in the regional nodes. Moreo- phere (stabilization step) and then in pure argon (car- ver, carbon fibers induced significantly more tissue in- bonization) (Blazewicz et al., 1989). The physical and growth than polypropylene mesh at 6 to 12 months chemical properties of carbon implants obtained by car- postoperatively. A probable elimination mechanism by bonization were modified by means of different techniques erosion of carbon particles and their retention in the fi- including high temperature treatment, oxidative surface brous capsule surrounding the implant was suggested by treatment and vapor-grown carbon coating. More et al. (1988). Although the results of most investi- Temperature treatment gations of carbon fibers in vivo were evaluated as good, Two kinds of carbon braids were heat-treated at dif- several authors were skeptical as to the superiority of car- ferent final temperatures in an argon atmosphere, namely bon fibrous implants over other prosthetic materials at 1200°C and at 2700°C. The structural parameters of (Strover and Firer, 1985; Alexander et al., 1987). these carbon samples are presented in Table 1. The struc- In a review by Christel et al. (1991) carbon fibers were tural parameters of carbon fibers obtained at 2700°C and considered to be a good candidate biomaterial for total their other technical data (Young ‘s modulus, tensile hip replacement and internal fixation in the form of com- strength, strain to failure, elemental composition) are typi- posites. In spite of controversial results with carbon fibers cal for technical carbon fibers used in many areas in lei- used for replacement and reconstruction of ligaments and sure products and industrial developments, particularly tendons, several other clinical studies were undertaken. in aerospace materials (Donnet and Bansal, 1986). Carbon fibers were studied as construction material in Oxidative surface treatment keratoprosthesis (Kain, 1990), and their use in the repair Carbon braids obtained at 1200ºC were subjected to of joint surfaces and as scaffolds (Robinson et al., 1993; further surface modification by means of oxidative treat- Brittberg et al., 1994) as well as in bone defect treatment ment. The samples of carbon braids were oxidized in (Abusafieh et al., 1997; Lewandowska et al., 1999) was boiling nitric acid for 30 minutes. The amount of acidic considered. and basic groups on the fiber surface was determined by The different results obtained in evaluating carbon neutralization with 0.01 N NaOH and 0.01N HCl solu- fibers as a biomaterial can probably be explained by the tions, respectively. The method of identification of chemi- use of different types of carbon fibers of different physi- cal surface groups on carbon materials has been described cal, structural and chemical properties, resulting from by Bohem (1966) and Bohem (1994). The chemical char- many technological parameters. Most of the papers con- acteristics of the samples before and after modification cerning examinations of carbon fibers for medical pur- are summarized in Table 2. poses describe neither the type of carbon fibers used nor Vapor-grown coating their fundamental properties determining their behavior This technique was applied to carbon unwoven fab- in a biological environment. rics. The samples of carbon fabrics were
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