Physicochemical Properties of Two Poly-L-Lactic Acid Injectable Implants: Potential Impact on Their Biological Properties

This study evaluated the thermal properties, crystallinity, particle size, morphology, and in vivo local inflammation and persistence of two poly-L-lactic acid (PLLA) injectable implants, Sculptra® (PLLA-SCA) and GANA V® (PLLA-GA). PLLA-SCA and PLLA-GA underwent differential scanning calorimetry and X-ray powder diffraction to evaluate their thermal properties and degree of crystallinity. X-ray powder diffraction spectra displayed a sharper, more intense peak for PLLA-GA than PLLA-SCA, with smaller peaks on either side of the main peak of PLLA-GA but not PLLA-SCA. Differential scanning calorimetry thermograms indicated three thermal events for both PLLA-SCA and PLLA-GA. For PLLA-SCA, the first two events occurred between 65 °C and 90 °C, and the third event occurred at 165 °C. For PLLA-GA all three events occurred between 156 °C and 169 °C. Heating samples to 120 °C and cooling to room temperature prior to differential scanning calorimetry resulted in no thermal events being observed between 65–90 °C with either product, while three events were observed with PLLA-GA and one event with PLLA-SCA between 156 °C and 169 °C. The median volume distribution diameter was 46.4 µm for PLLA-SCA and 31.7 µm for PLLA-GA. Scanning electron microscopy showed PLLA-GA particles were irregular in shape, had no sharp edges and had a wrinkled and crimped surface, while PLLA-SCA particles displayed plate-like shapes and had smoother surfaces. In vivo inflammatory reactivity scores indicated a slight reaction for PLLA-SCA at all time points (3.7 ± 1.1, 6.1 ± 1.6, 5.7 ± 1.2 and 6.2 ± 1.2 at 2, 12, 26 and 52 weeks, respectively), while for PLLA-GA, a moderate reaction was observed at 12 and 26 weeks (2.9 ± 1.5, 10.1 ± 1.0, 9.4 ± 0.7 and 7.1 ± 1.3 at 2, 12, 26 and 52 weeks, respectively). PLLA-SCA and PLLA-GA had similar persistence scores at 2, 12 and 26 weeks, while at 52 weeks the score was markedly higher for PLLA-SCA versus PLLA-GA (1.9 ± 0.2 versus 0.7 ± 0.2). In conclusion, PLLA-SCA is more amorphous than PLLA-GA. The single melting point of PLLA-SCA contrasts with the broader spectrum of melting points for PLLA-GA suggests a more homogenous formulation of PLLA-SCA. This, and its less crystalline structure, result in the slower degradation rate and more sustained biological response of PLLA-SCA compared with PLLA-GA. The physiochemical properties of PLLAs affect the biological response in clinical practice and should be taken into consideration when selecting a PLLA treatment for aesthetic use.