As reported previously, a porous composite of uncalcined hydroxyapatite (u-HA) and poly-DL-lactide (PDLLA) showed excellent osteoconductivity and biodegradability as a bone substitute in rabbit model. In this study, to investigate the usefulness of this composite as a scaffold loaded with cells, we estimated whether this material showed osteogenesis on implantation to extraosseous site. On loading with syngeneic bone marrow cells and implantation into rat dorsal subcutaneous tissue, osteogenesis with enchondral ossification was seen both on and in the material at 3 weeks after implantation. The osteogenesis in the u-HA/PDLLA had progressed, and newly formed bone tissue was found in the material by 6 weeks. To investigate the osteoinductive properties of the material, we implanted this porous composite material into extraosseous canine dorsal muscle. At 8 weeks, osteogenesis was seen in the pores of the material. Newly formed bone could be observed adjacent to the material. In addition, cuboidal osteoblasts adjacent to the newly formed bone were evident. Neither cartilage nor chondrocytes were found. These results might indicate that the material induced osteogenesis by intramembranous ossification. Conversely, similar porous PDLLA did not induce osteogenesis during the observation period. Therefore, porous HA/PDLLA, which has osteoconductive and osteoinductive properties, might be a useful material for use as a bone substitute and cellular scaffold.

No abstract

We used a novel composite fibre-precipitation method to create bioactive and bioresorbable cellular cubic composites containing calcium phosphate (CaP) particles (unsintered and uncalcined hydroxyapatite (u-HA), a-tricalcium phosphate, b-tricalcium phosphate, tetracalcium phosphate, dicalcium phosphate dihydrate, dicalcium phosphate anhydrate or octacalcium phosphate) in a poly-D/L-lactide matrix. The CaP particles occupied greater than or equal to 70 wt% (greater than or equal to 50 vol%) fractions within the composites. The porosities of the cellular cubic composites were greater than or equal to 70% and interconnective pores accounted for greater than or equal to 70% of these values. In vitro changes in the cellular geometries and physical properties of the composites were evaluated over time. The Alamar Blue assay was used to measure osteoblast proliferation, while the alkaline phosphatase assay was used to measure osteoblast differentiation. Cellular cubic C-u-HA70, which contained 70 wt% u-HA particles in a 30 wt% poly-D/L-lactide matrix, showed the greatest three-dimensional cell affinity among the materials tested. This composite had similar compressive strength and cellular geometry to cancellous bone, could be modified intraoperatively (by trimming or heating) and was able to form corticocancellous bone-like hybrids. The osteoinductivity of C-u-HA70, independent of biological growth factors, was confirmed by implantation into the back muscles of beagles. Our results demonstrated that C-u-HA70 has the potential as a cell scaffold or temporary hard-tissue substitute for clinical use in bone reconstruction.

Currently, the most commonly used bioresorbable scaffold is made of beta-tricalcium phosphate (β-TCP); it is hoped that scaffolds made of a mixture of hydroxyapatite (HA) and poly-D/L-lactide (PDLLA) will be able to act as novel bioresorbable scaffolds. The aim of this study was to evaluate the utility of a HA/PDLLA scaffold compared to β-TCP, at a loading site. Dogs underwent surgery to replace a section of tibial bone with a bioresorbable scaffold. After the follow-up period, the scaffold was subjected to histological analysis. The HA/PDLLA scaffold showed similar bone formation and superior cell and tissue infiltration compared to the β-TCP scaffold, as seen after Villanueva Goldner staining. Moreover, silver staining and immunohistochemistry for Von Willebrand factor and cathepsin K demonstrated better cell infiltration in the HA/PDLLA scaffold. The fibrous tissue and cells that had infiltrated into the HA/PDLLA scaffold tested positive for collagen type I and RUNX2, respectively, indicating that the tissue and cells that had infiltrated into the HA/PDLLA scaffold had the potential to differentiate into bone. The HA/PDLLA scaffold is therefore likely to find clinical application as a new bioresorbable scaffold.

We had investigated the biocompatibility, osteoconductivity, and biodegradability of a porous composite of hydroxyapatite (HA) and poly-DL-lactide (PDLLA) implanted into rabbit femoral condyles. It showed excellent osteoconductivity and biodegradability as a bone substitute. Newly formed bones were remodeled, and materials were resorbed almost completely at 78weeks after implantation. In consideration of its biocompatibility and degradability, we investigated its potential for use as a cellular scaffold and evaluated its osteoinductive property. On implantation to the rat dorsal subcutaneous tissue loaded with syngeneic bone marrow cells, osteogenesis with enchondral ossification was seen both on and in the material at 3 weeks after implantation. This osteogenesis in the HA/PDLLA tended to get mature and newly formed bone tissues were found in the material by 6weeks. To investigate the osteoinductive property material itself has, we attempted to implant this porous composite material to extra-osseous canine dorsal muscle. At 2months, osteogenesis was seen in the pores of the material. It indicated the material induced osteogenesis with intramembranous ossification process. Therefore, HA/PDLLA might be a desirable material for bone substitutes and cellar scaffolds with osteoconductive and osteoinductive property.