Nanostructuring of Biomaterials—A Pathway to Bone Grafting Substitute

Abstract

Background: The bone substitute NanoBone® consists of nanocrystalline hydroxyapatite embedded in a highly porous matrix of silica gel. It promotes the healing of bone defects and is degraded by osteoclasts during bone remodeling. The present study investigates the interactions of NanoBone® with bone tissue. Methods: Granules of NanoBone® were implanted in defects of critical size in the mandible of minipigs. Samples were taken after 5 and 10 weeks and demineralized. The composition of the implanted granules was analyzed by means of transmission and scanning electron microscopy and EDX. Enzymeand immunohistochemistry was used to investigate organic components of NanoBone® granules that arised after implantation in the host. Results: EDX demonstrated that 5 weeks after implantation the silica gel was degraded and replaced by an organic matrix. Ultrastructurally, the matrix appeared amorphous with only single collagen fibrillae. PAS-staining indicated the presence of carbohydrates. Immunohistochemically, the bone proteins osteopontin, osteocalcin and BMP-2 were found as constituents of the new matrix. Alkalic phosphatase activity was located in osteoblasts and newly formed bone on NanoBone® and focally in particles. Osteoclasts with ruffled borders, sealing zones, and acid phosphatase activity were situated in resorption lacunae at granule surfaces not covered by new bone. Conclusions:In vivo, the silica gel of NanoBone® is replaced by bone matrix glycoproteins with known functions in attraction, adhesion, and differentation of bone cells as osteoblasts and osteoclasts. We assume that the deposition of these molecules supports the early phase of NanoBone® degradation by osteoclasts and promotes the production of new bone tissue.

A preliminary study in osteoinduction by a nano-crystalline hydroxyapatite in the mini pig.

“…These findings show that after subcutaneous implantation of the ncHAdesmal osteogenesis occurs as is the case for heterotopic osteoinduction by demineralized bone or calcium phosphate ceramics [17,28]. According to recent findings from previous animal experiments and human testing [13,20,29], multinucleated osteoclasts were identified as cells populating implanted ncHA granules and also participating in remodeling the newly formed bone. These findings in the ectopic implantation situation support the view that this biomaterial is specifically degradaded by osteoclasts and that it is later integrated into the physiological remodeling processes of the host organism [13].…”

“…Histological and immunohistochemical findings obtained after implantation in mini pig jaws and findings in bone biopsies taken from patients after implementation for jaw augmentation revealed its osteoconductive nature and early remodeling in the host [11,13,20]. The appearance of osteoblast precursor cells and the upregulation of BMP-2 also indicated probable osteoinductive features [13,20]. To evaluate the osteoinductive capacities of the material, it was tested after ectopic subcutaneous and intramuscular implantation in the mini pig.…”

“…Furthermore, the early and late stages of osteogenesis in bone substitutes like cell or vessel invasion depend on the micro and macro porosities of the material [26,27]. Recent investigations into osteogenesis after augmentation by using the ncHA biomaterial in animals and humans have demonstrated that the different porosity dimensions ranging between μm and mm may promote these processes [11][12][13]20].…”

“…After fixation, specimens were decalcified in neutral 10% ethylene diamine tetra-acetic acid (EDTA) and processed for paraffin histology as recently described [20]. Selected sections were stained with H.E.…”

Biomaterials Applicable for Alveolar Sockets Preservation: In Vivo and In Vitro Studies

“…Another bone graft material consisting of nanocrystalline hydroxyapatite embedded in a porous silica gel matrix, Nanobone ® was implanted in the mandible of minipigs. It was shown that Nanobone ® is able to stimulate the differentiation of bone cells into osteoblasts and osteoclasts, because osteocalcin, alkaline phosphatase, osteopontin and BMP-2 were located in newly formed bone and focally in particles (Gerber et al 2006). Furthermore, the matrix of all Nanobone ® granules showed very strong immunoreactivity of osteocalcin and alkaline phosphatase in human jaw bone augmented with Nanobone ® (Gotz et al 2008).…”