The orthopaedic field has been facing challenging difficulties when it comes to regeneration
of grade 4 osteochondral defects (OCD). Autologous osteochondral mosaicplasty has been
used as valid option for OCD treatment. But donor site morbidity remains a big issue with
most used autografts [1]. Our group has been proposed bilayered structures to regenerate
osteochondral defects [2]. The underlying hypothesis of our study was to compare the in vivo
responses of bilayered hydrogels and spongy-like structures applied as 3D implants for OCD
regeneration following an acellular strategy. The subcutaneous inflammatory response was
assessed in mice model and the materials performance for OC regeneration was assessed
in rabbit critical size OCD model (diameter 4 mm and 5 mm depth) for 4 weeks. Cartilage-like
layer was obtained from a 2wt% LAGG and bone-like layer consisted of a 2wt% LAGG
incorporating hydroxyapatite (20-30wt%). While hydrogels were made in situ, the spongy-like
were previous produced by means of freeze-drying and posterior sterilization. Both
approaches were assessed by histology staining, immunohistochemistry and vivo-CT.
Observing the histologic characterization no acute inflammation, no macrophages invasion,
but fibrous capsule formation was observed at both mice implants. OC regeneration
photographic images of the defects sites with implanted structures showed the formation of
tissue surrounding the defect with a bright and natural coloration. The hydrogels formed an
yellowish tissue inside the defect. In the case of empty defects a thin membrane of tissue
was formed. Comparing empty defects and the defects with implanted hydrogels by vivo-CT
is evident that there is hard tissue formation. The sponge-like structures showed higher
formation of soft tissue on the cartilage region of the defect. From histologic studies, it was
possible to observe the invasion of collagen and reabsorption of LAGG in the defects with
implanted structures. Immunohistochemistry showed the formation of collagen type II in all
conditions. The empty defects were fulfilled with this type of collagen, while the defects with
structures avoided the formation of collagen type II in the bone region. Concluding, the
hydrogel reinforcement within spongy-like structures might enhance mechanical properties
and could lead to proper cellular and physiological behavior.
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