Bone grafts are crucial for the treatment of bone defects caused by tumor excision. The gold standard is autograft but their availability is limited. Allografts are an alternative, but there is a risk of rejection by the immune system. The tissue engineering field is trying to develop vascularized bone grafts, using innovative biomaterials for surgery applications. While the gold standard in bone graft in dentistry is the use of decellularized bovine bone particles (Bio-Oss®), our work has produced a polysaccharide-based composite matrix (composed of PUllulan, DextraNand particles of HydroxyApatite (PUDNHA), as a new scaffold for promoting bone formation and vascularization of the tissue. In the context of bone tissue regeneration, the function of osteoblast and endothelial cells has been extensively studied, while the impact of osteocytes has been regarded as secondary. Nonetheless, the osteocytes represent 90–95% of bone cells and are responsible for orchestration of bone remodeling.

Here, we propose an original method to analyze the interaction between bone and biomaterials, after in vivo implantation of the matrix PUDNHA in an experimental sheep model. Our objectives are to analyze the network established by osteocytes in the newly formed tissue induced by the matrix, as well as their interactions with the blood vessels.

Sheep have been implanted with the Bio-Oss® or the PUDNHA using the sinus lift technique. After 3 (3M) and 6 months (6M), the animals were euthanazied and the explants were fixed, analyzed by X-ray, embedded in Methylmetacrylate/Buthylmetacrylate and analyzed histologically by Trichrome staining. Thereafter, the samples (n=3/group) were polished using different sand papers. A final polish was realized using a 1µm Diamond polishing compound. The blocks were incubated 10 or 30s with 37% phosphoric acid to remove the mineral on the surface, then dipped in 2.6% sodium hypochlorite to remove the collagen. The samples were air dried overnight, metallized with Gold palladium the following day, before being imaged with a SEM.

As expected, PUDNHA activates bone regeneration in this sinus lift model after 3M and 6M. X-ray analysis and histological data revealed more bone regeneration at 6M versus 3M in both groups. With this acid eching technique, we were able to visualize the interface of bone with the biomaterials. This treatment coupled with SEM analysis, confirmed the increase of bone formation with time of implantation in both groups. In addition, SEM images revealed that osteocyte alignment and their network were different in the new regenerated bone compared to the host bone. Moreover, images showed the direct contact of the osteocytes with the blood vessels formed in the new regenerated bone.

This acid eching technique can be useful in the field of biomaterials to see the relationship between cells, blood vessels and the material implanted and understand how the new bone is forming around the different biomaterials.

Purpose of the study: The osteoconductive properties of hydroxyapatite surfacing improves the biointegration of orthopedic implants. Current high- and low-temperature resurfacing techniques have several drawbacks, particularly concerning the control of phases. The «low-temperature nanocrystalline apatite resurfacing technique using amorphous phosphate» was developed to avoid this type of inconvenience. The purpose of this study was to examine the biocompatibility of resurfacings produced with this patented technique and to compare biological efficacy with that of the reference technique of plasma torch resurfacing.

Material and methods: The cytocompatibility tests included cell proliferation and attachment tests using human osteoprogenesis cells, and phenotypic characterization of phosphatase alkaline (PAL) and pro-collagen (type I) activity. Biocompatibility studies were performed. Cylinders of natural titanium or titanium resurfaced with the plasma method and the low-temperature method (single layer, bilayer) were implanted in 16 rabbits in condylar and tibial sites. Histological examinations without decalcification were performed one and three months after implantation (n=8 for each time and condition). The implant-quantity of bone in contact ratio was determined by histomorphometry. Scan electron microscopy was used to ascertain the persistence of the resurfacing.

Results: The cell attachment rate of 30–40% confirmed earlier results. The cells grew, and preserved and maintained their differentiation properties (PAL activity at 7, 14 and 21 days). The histological results revealed that all types of resurfacing were well tolerated. HIstomorphometry confirmed the influence of the implantation site on the tissue reaction. One month after implantation, the low-temperature amorphous resurfacing appeared to produce a better result with an optimal ratio for the bilayer in the tibial site and an optimal ratio for the monolayer in the condylar site. The trend was the same three months after implantation, but was less pronounced compared with the plasma torch resurfacing. Paradoxically, the absence of treatment produced a very satisfactory ratio at the condylar level. Scan electron microscopy demonstrated rapid resorption of amorphous resurfacing unlike plasma torch resurfacing with was detectable three months after implantation.

Discussion and conclusion: The different performance levels of bilayer and single-layer resurfacings depending on the implantation site might be explained by the cortical or cancellous nature of the neighboring bone. Low-temperature resurfacing would be more appropriate for implants inserted into cortical bone. In vivo, this resurfacing is resorbed but appears to enable, like the plasma process, the formation of peri-implant bone formation. It offers the advantage of enabling incorporation of compounds of interest (antibiotics, growth factors).