In the field of tissue engineering, electrospun nanofibers gained notoriety for their capability to mimic the extracellular matrix of native tissues and organs. However, few reports have been published that detail methods of producing electrospun nanofibrous materials with macroscopic three-dimensional complexity. There is a potential method of incorporating the benefits of electrospun nanofibers into prefabricated tissue engineering scaffolds in the form of a thin coating.
Nanofibers of poly-L-lactic acid (PLLA) were applied successfully to tissue engineering scaffolds composed of polycaprolactone/poly-L-lactic acid (PCL/PLLA, 75/25) or sterile, human allograft bone by a modified electrospinning method. The electrospun PLLA nanofibers conform to the shape of the scaffolds, resulting in a thin layer of nanofibers over all the surfaces of the material. These scaffolds were then wrapped with human periosteal tissue and implanted in athymic (nude) mice. The mice, then, acted as bioreactors for growing and developing over various time periods the engineered electrospun PLLA nanofiber-coated constructs. Specimens containing PCL/PLLA as the underlying scaffold material were implanted for 10 weeks in vivo and specimens containing allograft bone as scaffolds were implanted for 20 and 40 weeks. Harvested specimens were analyzed using histochemical and immunohistochemical methods to examine proliferation of cells, growth of new tissue, presence of mineral within the tissue, and presence of osterix, a bone-specific transcription factor necessary for osteoblast differentiation.
Mineralized tissue was present in the electrospun PLLA nanofiber-coated PCL/PLLA constructs wrapped with periosteum after 10 weeks of implantation in vivo. Hematoxylin and eosin stains showed presumably new layers of tissue present between the layers of electrospun nanofibers and the underlying allograft bone in the allograft bone scaffolds coated with PLLA and then wrapped with human periosteal tissue. Osterix was identified by immunohistochemical staining and thereby verified presence of osteoblasts and preosteoblasts within the periosteal tissue and the electrospun PLLA nanofiber layers after 10, 20, and 40 weeks of implantation in vivo. The summary of these novel results suggests that electrospinning nanofibers such as PLLA on polymeric scaffolds or allograft bone can enhance tissue ingrowth from a periosteal wrap over such scaffolds or allografts for wider applications in bone tissue engineering.