Acellular Gellan-gum based bilayered structures for the regeneration of osteochondral defects: a preclinical study

In orthopaedics, treatment of osteochondral (OC) defects remains a clinical challenge. Autologous osteochondral mosaicplasty has been used for OC treatments although with donor site morbidity present. Engineering a structure capable of mimicking different tissues (cartilage-subchondral bone) could be an approach to regenerate OC defects. We have been proposing bilayered structures to regenerate osteochondral defects [1]. This study investigates the pre-clinical performance of bilayered hydrogels and spongy-like hydrogels in in vivo models, in subcutaneous and orthotopic models. Bilayered structures were produced from Low Acyl Gellan-Gum (LAGG) from Sigma-Aldrich, USA. Cartilage-like layers made of 2wt%LAGG. Bone-like layers made of 2wt%LAGG with hydroxyapatite incorporation (20% and 30%) (w/v). Hydrogels and spongy-like were subcutaneouly implanted in mice to evaluate the inflammatory response and OC defects were induced in rabbit knee to create a critical size defect:4mm diameter and 5mm depth), then hydrogels and sponges were implanted. Hydrogels were injected allowing in situ crosslinking and spongy-like were pre-formed by freeze-drying. Subcutaneous implantation (2 weeks) and critical size OC defect (4 weeks) studies were performed. Cellular behavior and inflammatory responses were assessed by histology staining and biochemical function and matrix deposition by immunohistochemistry. Both OC structures stability and new cartilage and bone formation were evaluated by vivo-computed-tomography (Scanco 80). No acute inflammatory response was showed. New tissue formation and integration in adjacent tissues were observed. A novel strategy for regeneration ofOC defects can be designed encompassing both, hydrogels and spongy-like structures and cellular approaches.