Inhibition of phase transformation from β- to α-tricalcium phosphate with addition of poly (L-lactic acid) in selective laser sintering

Purpose - The paper aims to fabricate an alpha-tricalcium phosphate (TCP) scaffold with an interconnected porous structure via selective laser sintering (SLS). To inhibit the phase transformation from beta- to alpha-TCP in fabrication process of porous scaffolds, a small amount (1 weight per cent) of poly (L-lactic acid) (PLLA) is added into beta-TCP powder to introduce the transient liquid phase. Design/methodology/approach - The paper opted for the transient liquid phase of melting PLLA to decrease the sintering temperature in SLS. Meanwhile, the densification of beta-TCP is enhanced with a combined effect of the capillary force caused by melting PLLA and the surface energy of beta-TCP particles. Moreover, the PLLA will gradually decompose and completely disappear with laser irradiation. Findings - The testing results show the addition of PLLA enables the scaffolds to achieve a higher beta-TCP content of 77 +/- 1.49 weight per cent compared with the scaffold sintered from beta-TCP powder (60 +/- 1.65 weight per cent), when the laser energy density is 0.4 J/mm(2). The paper provides the mechanism of PLLA inhibition on the phase transformation from beta- to alpha-TCP. And the optimum sintering parameters are obtained based on experimental results, which are used to prepare a TCP scaffold with an interconnected porous structure via SLS. Research limitations/implications - This paper shows that the laser energy density is an important sintering parameter that can provide the means to control the micro-porous structure of the scaffold. If the laser energy density is too low, the densification is not enough. On the other hand, if the laser energy density is too high, the microcracks are observed which are attributed to the volume expansion during the phase transformation from beta- to alpha-TCP. Therefore, the laser energy density must be optimized. Originality/value - The paper provides a feasible method for fabricating TCP artificial bone scaffold with good biological and mechanical properties.