Transparent Hydroxyapatite Obtained through Spark Plasma Sintering: Optical and Mechanical Properties

Abstract

Transparent bioceramics have great potential for applications in the biomedical field as they facilitate direct observation of the interactions at biomaterial – cell / tissue interfaces. Thus far, sintering of transparent hydroxyapatite (HA) usually involves application of extraordinarily high pressure and / or long duration. This study attempts to fabricate transparent HA by a direct and fast Spark Plasma Sintering (SPS) process using three different types of raw powder: micro-spheres (MS), nanorods (NR) and nanospheres (NS). The optical and mechanical properties of the sintered pellets were examined and compared. The highest total forward transmittance (TFT) showed by sintered MS pellet (~2 mm thick) was 85% in the visible spectrum, whereas sintered NR and NS pellets were either translucent or opaque. Although lowest degree of transparency was observed for NS pellets, they demonstrated highest Young’s modulus (E), hardness (H) and fracture toughness (KIC). The eminent KIC of NS pellets benefited mainly from its self-toughened microstructure.

Spark Plasma Sintering of Highly Transparent Hydroxyapatite Ceramics

“…and 88% at 400, 600 and 800 nm, respectively. Compared to the theoretical transmission, the present one is lower by less than 1% at > 800 nm, and is comparable to that of Li and Khor 13) . Their HA ceramics, however, were sintered at higher temperatures (1100°C), Byung-Nam KIM, Naohiro HORIUCHI, Apurv DASH, Young-Wook KIM, Koji MORITA, Hidehiro YOSHIDA, Ji-Guang LI and Yoshio SAKKA so that the grain size (> 411 nm) is considerably larger than that of the present one (120 nm).…”

“…Their HA ceramics, however, were sintered at higher temperatures (1100°C), Byung-Nam KIM, Naohiro HORIUCHI, Apurv DASH, Young-Wook KIM, Koji MORITA, Hidehiro YOSHIDA, Ji-Guang LI and Yoshio SAKKA so that the grain size (> 411 nm) is considerably larger than that of the present one (120 nm). Though the total forward transmission for the HA ceramics of Li and Khor 13) is comparable to the present transmission, their in-line transmission would be lower than our results due to the larger grains. The HA-100 ceramics show slightly lower transmission than the LM-HA ceramics in the visible wavelengths, but at > 800 nm, show the transmission (> 88%) almost identical to that of LM-HA.…”

“…Transparent HA ceramics with fine and dense microstructures have been achieved through hot isostatic pressing (HIP) [5][6][7] , microwave sintering 8) and spark plasma sintering (SPS) 2,[9][10][11][12][13] . Transparent HA ceramics allows the direct observation of living cells.…”

Bioceramic-based composites reinforced with carbonaceous nanomaterials

“…The HA powders were sintered by SPS, with the sintering program schematically shown in Fig. 5.1a [289]. Briefly, 0.6 g of raw powders was compacted at the designated temperature (900/950/1000/1050/1100 °C ) for 3 min in a graphite die with an inner diameter of ~10 mm.…”

“…The properties of sintered HA compacts is affected by the properties of starting powder as well as processing parameters, as both can affect its microstructure. Additionally, major differences in the structural, mechanical, and biological properties of sintered samples can be caused by markedly diverse stability and sinterability of different starting HA powders [239,289,290]. However, there have been insufficient studies which examined the influence of HA raw powder on the properties of sintered pellets [291,292].…”