Osteogenic Potential of Nano-Hydroxyapatite and Strontium-Substituted Nano-Hydroxyapatite

Abstract

Nanohydroxyapatite (nanoHA) is the major mineral component of bone. It is highly biocompatible, osteoconductive, and forms strong bonds with native bone, making it an excellent material for bone regeneration. However, enhanced mechanical properties and biological activity for nanoHA can be achieved through enrichment with strontium ions. Here, nanoHA and nanoHA with a substitution degree of 50 and 100% of calcium with strontium ions (Sr-nanoHA_50 and Sr-nanoHA_100, respectively) were produced via wet chemical precipitation using calcium, strontium, and phosphorous salts as starting materials. The materials were evaluated for their cytotoxicity and osteogenic potential in direct contact with MC3T3-E1 pre-osteoblastic cells. All three nanoHA-based materials were cytocompatible, featured needle-shaped nanocrystals, and had enhanced osteogenic activity in vitro. The Sr-nanoHA_100 indicated a significant increase in the alkaline phosphatase activity at day 14 compared to the control. All three compositions revealed significantly higher calcium and collagen production up to 21 days in culture compared to the control. Gene expression analysis exhibited, for all three nanoHA compositions, a significant upregulation of osteonectin and osteocalcin on day 14 and of osteopontin on day 7 compared to the control. The highest osteocalcin levels were found for both Sr-substituted compounds on day 14. These results demonstrate the great osteoinductive potential of the produced compounds, which can be exploited to treat bone disease.

Evaluation of Remineralisation Potential of an Indigenously Developed Dentifrice – An In Vitro Study

“…It is this partial substitution of strontium ions for calcium ions in the hydroxyapatite matrix that causes an increase in hydroxyapatite's insolubility [24]. Hydroxyapatite with increased lattice dimensions is formed due to the higher atomic radius of strontium compared to calcium [7]. Strontium was doped in different concentrations to hydroxyapatite for this purpose.…”

“…Nanoparticles (NPs) exhibit superior ion release in comparison to microparticles [6]. They also have accelerated absorption rates, extended half-life, increased concentration, and targeted drug delivery [7][8]. Recently, biomimetic remineralization materials have been used to create NPs that can form apatite crystals inside fully demineralized collagen fibres [3].…”

“…Recently, biomimetic remineralization materials have been used to create NPs that can form apatite crystals inside fully demineralized collagen fibres [3]. Nanohydroxyapatite has bioactive properties as osteoconductivity and cytocompatibility as is the major constituent of mineralised tissue of the human body and can be substituted for repair biomimetically [7]. Since the early 1980's field trials of toothpastes containing nano hydroxyapatite have been carried out in Japan, which led to its approval as an anti-caries agent in 1993 [9,10].…”