Biology of Resorbable Bone Substitutes: CaP-Based and Polymers

Resorbable bone substitutes of different origins are standardly applied in clinical practice. In addition to natural-based materials derived from both human donors (allografts) and animals (xenografts), synthetic or alloplastic materials, mostly based on calcium phosphates, are clinically applied. Polymer-based materials for 3D-printing of individualized implants have been gaining focus for several years. The principle behind the application of resorbable bone substitutes is called “creeping substitution.” Thus, a resorbable bone substitute should optimally combine the processes of bone regeneration and material resorption to result in restitutio ad integrum. In this context, the analysis of bone growth and of degradation mechanisms is of special interest. Most bone substitute materials induce an inflammatory tissue reaction cascade involving different cell types, such as macrophages and multinucleated giant cells, which perform the degradation of materials. Tissue regeneration and the inflammatory tissue response are coupled via different molecules. Thus, understanding the biological and molecular mechanisms of different bone substitute materials and those of newly developed materials is important for the development of bone substitutes. In this chapter, we present different preclinical in vitro and in vivo methods, as well as methods for the analysis of clinical biopsies, which allow for the examination of the bone regeneration process and degradation mechanisms of resorbable bone substitutes.