Nanocrystalline spherical hydroxyapatite granules for bone repair: in vitro evaluation with osteoblast-like cells and osteoclasts

Abstract

Conventionally sintered hydroxyapatite-based materials for bone repair show poor resorbability due to the loss of nanocrystallinity. The present study describes a method to establish nanocrystalline hydroxyapatite granules. The material was prepared by ionotropic gelation of an alginate sol containing hydroxyapatite (HA) powder. Subsequent thermal elimination of alginate at 650 °C yielded non-sintered, but unexpectedly stable hydroxyapatite granules. By adding stearic acid as an organic filler to the alginate/HA suspension, the granules exhibited macropores after thermal treatment. A third type of material was achieved by additional coating of the granules with silica particles. Microstructure and specific surface area of the different materials were characterized in comparison to the already established granular calcium phosphate material Cerasorb M(®). Cytocompatibility and potential for bone regeneration of the materials was evaluated by in vitro examinations with osteosarcoma cells and osteoclasts. Osteoblast-like SaOS-2 cells proliferated on all examined materials and showed the typical increase of alkaline phosphatase (ALP) activity during cultivation. Expression of bone-related genes coding for ALP, osteonectin, osteopontin, osteocalcin and bone sialoprotein II on the materials was proven by RT-PCR. Human monocytes were seeded onto the different granules and osteoclastogenesis was examined by activity measurement of tartrate-specific acid phosphatase (TRAP). Gene expression analysis after 23 days of cultivation revealed an increased expression of osteoclast-related genes TRAP, vitronectin receptor and cathepsin K, which was on the same level for all examined materials. These results indicate, that the nanocrystalline granular materials are of clinical interest, especially for bone regeneration.

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications

“…However, at 4 weeks, progressive mineralization of the bone around the coated implant was observed, along with gradual resorption of the CaP coating. In another study [415], cellular and genetic characterization of nanocrystalline spherical HAp granules prepared by wet chemistry indicated that they may be attractive for bone repair.…”

Hydroxyapatite-based materials of marine origin: A bioactivity and sintering study

“…The use of SaOs-2 cells is a well-accepted method to test in vitro hydroxyapatite cytotoxicity [3,4]. The results of the tests for both samples CB and CBCa calcined at 1100 and 1200°C are shown in Fig.…”

Structure control of hydroxyapatite ceramics via an electric field assisted freeze casting method

“…To overcome this, HA scaffold with spherical pores was prepared by Monmaturapoj et al [11]. Unfortunately, the pores of the HA scaffolds with single spherical pores were poorly connected, limiting the growth and reproduction of bone cells [12].…”