With the ultimate goal to generate suitable materials for the repair of osteochondral defects, in this work we aimed at developing composite osteochondral scaffolds organized in different integrated layers, with features which are biomimetic for articular cartilage and subchondral bone and can differentially support formation of such tissues.A biologically inspired mineralization process was first developed to nucleate Mg-doped hydroxyapatite crystals on type I collagen fibers during their self assembling. The resulting mineral phase was non-stoichiometric and amorphous, resembling chemico-physical features of newly deposited, natural bone matrix. A graded material was then generated, consisting of (i) a lower layer of the developed biomineralized collagen, corresponding to the subchondral bone, (ii) an upper layer of hyaluronic acid-charged collagen, mimicking the cartilaginous region, and (iii) an intermediate layer of the same nature as the biomineralized collagen, but with a lower extent of mineral, resembling the tidemark. The layers were stacked and freeze-dried, to obtain an integrated, monolithic composite. Culture of the material for 2 weeks after loading with articular chondrocytes yielded cartilaginous tissue formation selectively in the upper layer. Conversely, ectopic implantation in nude mice of the material after loading with bone marrow stromal cells resulted in bone formation which remained confined within the lower layer.In conclusion, we developed a composite material with cues which are biomimetic of an osteochondral tissue and with the capacity to differentially support cartilage and bone tissue generation. The results warrant test of the material as a substitute for the repair of osteochondral lesions in orthotopic animal models.
Response to Reviewer #1:1) results and discussion should be separated We would prefer to maintain Results and Discussion combined, in order to avoid possible redundancies and improve readability.
2) figures should be detailed with arrows and information about specific orientations. Details and arrows have been included in the Figures3) collagen type 1 was used for the creation of the construct -in every layer? Usually collagen type 1 does not play a role in articular cartilage. This should be addressed in the discussion. According to the Reviewer's comment, a rationale for the use of type I collagen has been included in the text, as follows: "Type I collagen was selected for the synthesis of the composite layers, including the cartilaginous one, due to (i) its good physico-chemical stability and processability and (ii) high safety and biocompatibility profile, related to the removal of all Reply Letter to Editor and referee's comments telopeptides, which are potentially responsible for immunological reactions." (Section 2.1, Page 2, 1 st paragraph). Indeed, type II collagen is normally extracted porcine derivative, and is still not available either in bulk for processing or for clinical use. Nowadays there are only few papers on experimental studies desc...
