Purpose

Synthetic polymers such as poly(lactic acid) (PLA) are well suited for preparing patient-specific bone tissue scaffolds by three-dimensional (3D) printing due to their favorable mechanical properties; however, they have limited biological activity. Natural polymers have good bioactivity and provide a better cellular microenvironment for attachment, proliferation, and differentiation, but lack the mechanical strength required as a bone substitute.

Method

In this work, porous PLA scaffolds were prepared by fused filament fabrication. For uniform cell seeding and enhanced cellular function, a silk fibroin-alginate (SF/Alg) blend hydrogel loaded with human mesenchymal cells (hMSCs) was loaded into the pores of the 3D-printed hybrid scaffolds between the struts. The physicochemical properties of the scaffold and the hMSC response were characterized.

Results

The gel-loaded 3D-printed PLA scaffolds were stable over 21 days in an aqueous buffer solution. The compressive strength of the scaffolds was ≈ 10 MPa, which is similar to that of cancellous bone. The proliferation and viability of hMSCs were significantly enhanced when loaded within the SF/Alg hydrogel in the PLA scaffolds than in the neat PLA scaffold. Furthermore, the stem cells in the gel-loaded 3D-printed PLA scaffold showed markedly higher alkaline phosphatase expression and calcium phosphate deposition, which indicates higher osteogenic differentiation with the gels. These observations were corroborated by increased expressions of osteocalcin, RUNX2, and BMP-2.

Conclusion

Thus, the combination of SF/Alg hydrogel loaded with stem cells offers a promising route for enhancing the bioactivity of 3D-printed PLA scaffolds with significant clinical potential for bone tissue engineering.

Lay Summary

Owing to their good mechanical stability, 3D-printed porous scaffolds of thermoplastics such as PLA have been used for bone tissue engineering applications. However, the presence of macro-sized pores leads to low cell attachment efficiency and distribution within the scaffolds, which results in low osteogenic activity. In this work, stem cells were encapsulated within the sonicated silk fibroin and alginate blend hydrogel and embedded within the gaps of 3D-printed PLA struts. This hybrid approach maximizes the cell density and uniform distribution and leverages the mechanical integrity of the 3D-printed PLA scaffold and osteoconductive microenvironment for proliferation and differentiation offered by the silk fibroin and alginate hydrogel. The cell-laden gels loaded within 3D-printed scaffold showed improved proliferation and osteogenic activity of stem cells, which makes the system a promising bone substitute for regeneration or healing.

中文翻译：

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在 3D 打印的多孔聚（乳酸）骨组织支架中嵌入丝素蛋白-海藻酸盐水凝胶增强干细胞功能

目的

聚乳酸 (PLA) 等合成聚合物由于其良好的机械性能，非常适合通过三维 (3D) 打印制备患者特异性骨组织支架；然而，它们的生物活性有限。天然聚合物具有良好的生物活性，可为附着、增殖和分化提供更好的细胞微环境，但缺乏作为骨替代物所需的机械强度。

方法

在这项工作中，多孔 PLA 支架是通过熔丝制造制备的。为了统一细胞接种和增强细胞功能，将载有人间充质细胞 (hMSC) 的丝素蛋白-藻酸盐 (SF/Alg) 混合水凝胶加载到支柱之间的 3D 打印混合支架的孔隙中。表征了支架的物理化学特性和 hMSC 反应。

结果

载有凝胶的 3D 打印 PLA 支架在水性缓冲溶液中稳定超过 21 天。支架的抗压强度≈10 MPa，与松质骨相似。当加载到 PLA 支架中的 SF/Alg 水凝胶中时，hMSC 的增殖和生存能力比在纯 PLA 支架中显着增强。此外，载有凝胶的 3D 打印 PLA 支架中的干细胞显示出显着更高的碱性磷酸酶表达和磷酸钙沉积，这表明凝胶具有更高的成骨分化。骨钙素、RUNX2 和 BMP-2 的表达增加证实了这些观察结果。

结论

因此，载有干细胞的 SF/Alg 水凝胶的组合为增强 3D 打印 PLA 支架的生物活性提供了一条有前途的途径，具有骨组织工程的重要临床潜力。

外行摘要

由于其良好的机械稳定性，3D 打印的热塑性塑料多孔支架（例如 PLA）已被用于骨组织工程应用。然而，大孔的存在导致支架内细胞附着效率和分布低，从而导致成骨活性低。在这项工作中，干细胞被封装在经过超声处理的丝素蛋白和海藻酸盐混合水凝胶中，并嵌入到 3D 打印的 PLA 支柱的间隙中。这种混合方法最大限度地提高了细胞密度和均匀分布，并利用 3D 打印的 PLA 支架和骨传导微环境的机械完整性，以促进丝素蛋白和藻酸盐水凝胶提供的增殖和分化。