Estradiol-Loaded Poly(ε-caprolactone)/Silk Fibroin Electrospun Microfibers Decrease Osteoclast Activity and Retain Osteoblast Function

Estrogen, a steroid hormone, plays an important role in modulating osteoclast proliferation and development. Estrogen deficiency boosts osteoclast activity, leading to osteoporosis in elderly women. In this study, 17-ß estradiol (E2)-loaded poly(ε-caprolactone) (PCL)/silk fibroin (SF) electrospun microfibers were developed as a proposed localized E2 delivery system to treat osteoporotic fractures. PCL is a synthetic polymer known for its biocompatibility and excellent mechanical properties. The bioactivity of PCL was enhanced by mixing it with a natural SF polymer that has low immunogenicity and inherent bioactivity. Different ratios of PCL/SF blends were electrospun and characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and water contact angle measurement. PCL and SF at a ratio of 50:50 (PCL50/SF50) augmented cell proliferation of murine preosteoblast MC3T3-E1 cells and murine preosteoclast RAW 264.7 cells. Hence, PCL50/SF50 was selected and mixed with three concentrations of E2 to produce electrospun fiber mesh (0.1% E2@PCL/SF, 1% E2@PCL/SF, and 5% E2@PCL/SF). Sustained release of E2 was obtained for about 3 weeks at higher E2 concentration 5% E2@PCL/SF. An E2-loaded PCL50/SF50 elecrospun microfiber (1% E2@PCL/SF and 5% E2@PCL/SF) reduced tartrate-resistant acid phosphate activity, total DNA, and multinucleated cell formation of osteoclasts. On the other hand, the alkaline phosphatase activity and collagen I expression of osteoblasts were retained on all E2-loaded electrospun microfibers. The E2@PCL/SF system shows potential to be used for localized E2 delivery for the treatment of osteoporotic fractures.