Physical and chemical factors influencing the porosity of apatite-biopolymer composites

The undamaged structure and functionality of the skeleton are a prerequisite for ensuring the quality of human life. The introduction of the latest treatment methods and prosthetics in traumatic surgery, oncology, cranial surgery, and dentistry form a demand for biomaterials with functionalized properties. The growth of new bone tissue is a cell-regulated process based on creating a specific bone morphology, which combines the organic matrix and its inorganic content. The inorganic component of human bones and teeth is calcium deficiency hydroxyapatite (cdHA), with a molar ratio of Ca/P ranging from 1.5 to 1.67. The combination of cdHA and natural polymers in the material allows the incorporation of proteins and growth factors into the polymer matrix. It promotes biocompatibility and the growth of new bone tissue. This review considers the critical role of the porosity parameter of biomaterials (BM) in their use for bone regeneration. Porosity is an essential characteristic of BM and guarantees the interaction of the material with cells in bone formation, promoting vascularization and the process of biosorption of synthetic graft when it is replaced by newly formed native bone. At the same time, the degree of porosity should correlate with mechanical stability to maintain the structural integrity of BM in the process of hard tissue regeneration. Processes involving cells and proteins during BM implantation with both high (70–80 %) and low (≤ 45 %) degrees of porosity are considered. Data on existing methods of obtaining BM in porous scaffolds are given. The specified degree of porosity is provided by chemical (cross-linking) and physical (sublimation) methods. The effects of pores of different sizes and shapes on bone formation and vascularization are considered. It is shown that porosity is an influential factor influencing the mechanical properties of scaffolds, in particular, the stiffness of BM - a parameter that affects the proliferation of osteoblasts by regulating cell adhesion in the scaffold structure. The influence of the biopolymer component (Sodium Alginate - AN) on the porosity and swelling of hybrid apatite-biopolymer (HA/AN) composites, in which nanometric needle crystallites represent HA, is analyzed in detail.