Understanding the Role of Soluble Inorganic Ions on the Cytocompatibility and Biodegradation of Bioceramic Biodegradable Coatings and Resorbable Calcium Phosphate

Biodegradable scaffolds have been researched extensively over the years due to their promise in regenerative medicine and tissue engineering. Several biodegradable biopolymers, bioceramics, and bioresorbable metals have been the focus of research. The degradation rates of these biodegradable scaffolds have a strong influence on the structural integrity, cytocompatibility, and overall biocompatibility of the scaffold. During degradation, it is imperative that the scaffold not elicit any local or systemic toxicity caused by the biodegradation products, in particular, the dissolved ions released from the scaffold. Thus, recent work has focused on implementing methods to alter the degradation rates of various biodegradable scaffolds demonstrating their safety and efficacy while also evaluating their overall effect on in-vitro cytocompatibility. Current research is targeted at understanding the degradation of ion substituted resorbable calcium phosphate (CaP) bone cement and inorganic ion containing coatings on bioresorbable magnesium alloys. The objective of this research is to understand the influence of soluble ions on 1) the corrosion resistance and degradation of a micro-arc oxidized (MAO) ceramic coating on lithium-aluminum-and zinc (LAZ) and lithium-zinc (LZ) Mg based alloys and 2) the cementing reaction and dissolution of a strontium (Sr) substituted dicalcium phosphate dihydrate (DCPD) and amorphous calcium phosphate (ACP) based bone cement. The degradation and dissolution rates of the two systems serves to understand the effect of soluble ions on the in-vitro cytocompatibility of the scaffolds. Results indicate that the increased corrosion resistance and associated decrease in release of Mg, Li, and Zn ions of MAO coated LAZ631 enables direct cell seeding and proliferation of MC3T3 preosteoblasts. Additionally, 10 and 15 mol% substitution of Sr2+ in the DCPD-ACP based cements allows the formation of a highly porous cement comprising Sr containing hydroxyapatite (HAp), the mineralized matrix of natural bone. The Sr substituted HAp cement formed following the final setting reaction facilitates a constant Sr2+ release over a 21-day period promoting increased cytocompatibility of MC3T3 preosteoblasts determined by Live/dead staining and MTT assay conducted at days 1 and 4 of culture in the growth media. Results show the potential of these bioresorbable scaffolds for future investigations in tissue engineering and regenerative medicine