Enhancing Osteogenesis Differentiation and In Vitro Degradation in Polymer Scaffolds with Spike-like Strontium Carbonate Microrods

Abstract

Poly-(L-lactic-acid) (PLLA) has shown significant promise in the fields of orthopedics and dentistry. However, its lack of inherent osteogenic activity limits its potential for further application in bone repair and fixation. In this study, we synthesized strontium carbonate (SrCO₃) nanoparticles and incorporated them into PLLA to prepare bioactive composite scaffolds using selective laser sintering technology. The synthesized SrCO₃ particles exhibited a unique microrod morphology with spike-like structures. In vitro degradation experiments demonstrated that SrCO₃ effectively neutralized acidic byproducts and promoted the degradation of PLLA in a dose-dependent manner. Furthermore, in vitro cell culture experiments revealed that composite scaffolds containing 1-2 wt % SrCO₃ significantly enhanced the adhesion, proliferation, and osteogenic differentiation of mouse bone marrow mesenchymal stem cells compared to the PLLA scaffolds. This can be attributed to the sustained release of Sr ions from the composite scaffolds. Overall, our study elucidates the positive effects of incorporating SrCO₃ into the PLLA matrix, highlighting its potential as an alternative to the currently used PLLA implants for promoting degradation and facilitating osteogenesis.

1

Low (a) and high (b) magnification SEM images of SrCO₃; TEM image (c), high-resolution TEM image (d), and SAED pattern (e) of SrCO₃; XRD patterns (f) and FTIR spectra (g) of SrCO₃.

2

Weight loss (a) of the PLLA and SrCO₃/PLLA composite scaffolds and the pH changes (b) of five groups of the scaffolds after being soaked in PBS for different times; noncumulative (c) and cumulative (d) release curves of Sr²⁺ from the SrCO₃/PLLA composite scaffolds in PBS. Data are presented as mean ± SD (N = 3).

3

Compressive stress–strain curves (a) and compressive strength and modulus (b) of the PLLA and SrCO₃/PLLA composite scaffolds; the tensile stress–strain curves (c) and tensile strength and modulus (d) of the composite scaffolds; the three-point bending stress–strain curves (e) and bending strength and modulus (f) of the composite scaffolds. Data are presented as mean ± SD (N = 3). *p < 0.05, * *p < 0.01, * **p < 0.001.

4

SEM images of the fracture surface of the PLLA and SrCO₃/PLLA composite scaffolds.

5

(a) Fluorescent staining of the live and dead mBMSCs after culture with different scaffold-conditioned media for 1 and 3 days; (b) CCK-8 results of mBMSCs cultured with different scaffold-conditioned media for 1 and 3 days; (c) SEM images of mBMSCs adhesion after cocultured with different scaffolds for 3 days. Data are presented as mean ± SD (N = 3). *p < 0.05, * *p < 0.01, * **p < 0.001.

6

(a) ALP staining of mBMSCs after coculturing with different scaffolds and their conditioned media for 5 days; (b) Alizarin red staining of mBMSCs after coculturing with different scaffolds and their conditioned media for 14 days.