Hydroxyapatite scaffolds derived from deer antler: Structure dependence on processing temperature

Abstract

Discarded antlers from deer are proposed as a promising alternative CaP-based bone graft to fulfil specific unsolved clinical requirements, such as osteoinductive properties or an optimal balance in stability/resorbability. Moreover, depending on the location of the bone defect and the type of bone lost (cortical versus cancellous), adequate morphological/mechanical properties for indicated biomaterials are needed. At the present work a detailed study of the physicochemical properties of two bioceramics obtained from the cortical and the trabecular sections of deer antler is presented. The influence of temperature on both bioceramics was also evaluated in depth to guarantee removal of organic material, analyze the compositional changes for high temperatures (up to 1100 °C) and study how their specific morphological features can influence these modifications. Morphological evaluation (SEM, porosity) of both final bioapatites (cortical and trabecular) was assessed, together with composition (ICP-OES, EDS, FT-Raman, XRD, TEM) and mechanical properties (nano-indentation). Optimal temperature for calcination was selected, through a thermogravimetric analysis, to ensure: the removal of organic material and a re-crystallization process (carbonate group decomposition) in both sections. Main contribution of hydroxyapatite (Ca5(PO4)3(OH)) in hexagonal phase was found, structure similar to human bone, with the presence of periclase (MgO). A Ca/P ratio in the same range as porcine and bovine bones, and with trace elements, such as Mg and Na, that play relevant roles in osteogenic metabolism was also detected. The dense and compact structure in cortical section and the spongy-like structure in the trabecular one, with pores >200 μm in diameter occupying a surface of 52 ± 8% were characterized. Related to these morphological properties, the same calcination temperature was proven to yield larger crystals in the trabecular section, given the higher availability of space for the crystal to grow (lower density of material).