A phosphate glass reinforced composite acrylamide gradient scaffold for osteochondral interface regeneration

Abstract

The bone-cartilage interface is defined by a unique arrangement of cells and tissue matrix. Injury to the interface can contribute to the development of arthritic joint disease. Attempts to repair osteochondral damage through clinical trials have generated mixed outcomes. Tissue engineering offers the potential of integrated scaffold design with multiregional architecture to assist in tissue regeneration, such as the bone-cartilage interface. Challenges remain in joining distinct materials in a single scaffold mass while maintaining integrity and avoiding delamination. The aim of the current work is to examine the possibility of joining two closely related acrylamide derivatives such as, poly n-isopropyl acrylamide (pNIPAM) and poly n‑tert‑butyl acrylamide (pNTBAM). The target is to produce a single scaffold unit with distinct architectural regions in the favour of regenerating the osteochondral interface. Longitudinal phosphate glass fibres (PGFs) with the formula 50P₂O₅.30CaO.20Na₂O were incorporated to provide additional bioactivity by degradation to release ions such as calcium and phosphate which are considered valuable to assist the mineralization process. Polymers were prepared via atom transfer radical polymerization (ATRP) and solutions cast to ensure the integration of polymers chains. Scaffold was characterized using scanning electron microscope (SEM) and Fourier transform infra-red (FTIR) techniques. The PGF mass degradation pattern was inspected using micro computed tomography (µCT). Biological assessment of primary human osteoblasts (hOBs) and primary human chondrocytes (hCHs) upon scaffolds was performed using alizarin red and colorimetric calcium assay for mineralization assessment; alcian blue staining and dimethyl-methylene blue (DMMB) assay for glycosaminoglycans (GAGs); immunostaining and enzyme-linked immunosorbent assay (ELISA) to detect functional proteins expression by cells such as collagen I, II, and annexin A2. FTIR analysis revealed an intact unit with gradual transformation from pNIPAM to pNTBAM. SEM images showed three distinct architectural regions with mean pore diameter of 54.5 µm (pNIPAM), 16.5 µm (pNTBAM) and 118 µm at the mixed interface. Osteogenic and mineralization potential by cells was observed upon the entire scaffold's regions. Chondrogenic activity was relevant on the pNTBAM side of the scaffold only with minimal evidence in the pNIPAM region. PGFs increased mineralization potential of both hOBs and hCHs, evidenced by elevated collagens I, X, and annexin A2 with reduction of collagen II in PGFs scaffolds. In conclusion, pNIPAM and pNTBAM integration created a multiregional scaffold with distinct architectural regions. Differential chondrogenic, osteogenic, and mineralized cell performance, in addition to the impact of PGF, suggests a potential role for phosphate glass-incorporated, acrylamide-derivative scaffolds in osteochondral interface regeneration.