4. Collagen membranes: Porcine or bovine – artificially or naturally cross-linked – pericardium, dermis or peritoneum?
The use of resorbable collagen barrier membranes of type I & III fibrillar collagen in guided tissue and bone regeneration techniques has been widely published and cited and is now common.
Barrier membranes have been implanted using various animal models and different physiological compartments and their healing characteristics analysed at different points after placement (e.g. see ROTHAMEL et al., 2012; GHANAATI et al., 2012; van LEEUWEN et al., 2012; MOSES et al., 2008; SCHWARZ et al., 2008; TAL et al., 2008, ZUBERY et al., 2007; SCHWARZ et al., 2006a; ROTHAMEL et al., 2005; von ARX et al., 2005; ZHAO et al., 2000; SIMION et al., 1996).
The results from these studies, which are not uniform in some regards, are discussed by the authors in terms of the different membrane characteristics. One approach in this discussion is the question of which species and from which source tissue the collagen was harvested. The correlation with the cross-linking of the collagen is also critical, with native or no additional cross-linking and artificially inserted cross-links between the protein chains in the collagens being differentiated (e.g. see ROTHAMEL et al., 2012; MOURA et al., 2012; BEHRING et al., 2008; ZHENG et al., 2005; ÜNSAL et al., 1997).
Resorbable barrier membranes produced from type I & III collagen from porcine or bovine tissue are the most common type of xenogeneic collagens for use in GBR techniques (BUNYARATAVEJ & WANG, 2001).
A comparison of the cytotoxicity of bovine and porcine collagen membranes prepared using the same parameters on human mononuclear cells in cell culture showed differences in the cell viability that were ultimately attributed to the different xenogeneic origin of the collagen membranes being investigated. The physical and chemical properties of the membranes that were investigated were not described further (MOURA et al., 2012).
JARDELINO et al. (2010) processed porcine peritoneum using mechanical debridement, chemical treatment, lyophilisation and sterilisation among other methods. The experimental membranes prepared in this manner were implanted subcutaneously in mice.
The results presented indicated that the membranes were biocompatible and had been biodegraded after 3 weeks.
ÜNSAL et al. reported in 1997 about the different resorption behaviour and tissue reactions triggered by different human barrier membranes in a subcutaneous placement model in rats. The three human membranes investigated were prepared from different tissues using the same processes. From the resorption kinetics observed, conclusions can be drawn about the origin of the tissue and the resultant properties of the barrier membrane. Porcine collagen membranes showed temporal differences in their biodegradation pattern, regardless of the type of cross-linking. Native cross-linked membranes degrade faster than chemically cross-linked membranes. It could also be demonstrated that the time required for the biodegra- dation increased with the degree of cross-linking. The degree of tissue degradation was inversely proportional to the longer breakdown period, decreasing over time (SCHWARZ et al., 2006a; ROTHAMEL et al., 2005). Different temporal biodegradation patterns that are dependent on the source tissue and the preparation process were also detected for porcine collagen membranes (e.g. see ROTHAMEL et al., 2012; GHANAATI et al., 2012 and personal communication).
In the opinion of the author, the factors ‘source tissue’ and ‘preparation process’ cannot be separated in the studies cited. If and whether factors such as species, source tissue, cross-linking characteristics and preparation process are critical for the biodegradation time or what influence the individual factors have must be investigated in further studies.