page_title: Nanofiber
section_title: Tissue engineering
hierarchical_section_title: Nanofiber / Applications / Tissue engineering
caption_attribution_description: English: Woven bone matrix showing collagen fibrils.
context_page_description: Nanofibers are fibers with diameters in the nanometer range. Nanofibers can be generated from different polymers and hence have different physical properties and application potentials. Examples of natural polymers include collagen, cellulose, silk fibroin, keratin, gelatin and polysaccharides such as chitosan and alginate. Examples of synthetic polymers include poly, polycaprolactone, polyurethane, poly, poly, and poly. Polymer chains are connected via covalent bonds. The diameters of nanofibers depend on the type of polymer used and the method of production. All polymer nanofibers are unique for their large surface area-to-volume ratio, high porosity, appreciable mechanical strength, and flexibility in functionalization compared to their microfiber counterparts.
  There exist many different methods to make nanofibers, including drawing, electrospinning, self-assembly, template synthesis, and thermal-induced phase separation.
context_section_description: In tissue engineering, a highly porous artificial extracellular matrix is needed to support and guide cell growth and tissue regeneration. Natural and synthetic biodegradable polymers have been used to create such scaffolds.
  Simon, in a 1988 NIH SBIR grant report, showed that electrospinning could be used to produced nano- and submicron-scale polystyrene and polycarbonate fibrous mats specifically intended for use as in vitro cell substrates. This early use of electrospun fibrous lattices for cell culture and tissue engineering showed that Human Foreskin Fibroblasts (HFF), transformed Human Carcinoma (HEp-2), and Mink Lung Epithelium (MLE) would adhere to and proliferate upon the fibers.
  Nanofiber scaffolds are used in bone tissue engineering to mimic the natural extracellular matrix of the bones.  The bone tissue is arranged either in a compact or trabecular pattern and composed of organized structures that vary in length from the centimeter range all the way to the nanometer scale. Nonmineralized organic component (i.e. type 1 collagen), mineralized inorganic component (i.e. hydroxyapatite), and many other noncollagenous matrix proteins (i.e. glycoproteins and proteoglycans) make up the nanocomposite structure of the bone ECM. The organic collagen fibers and the inorganic mineral salts provide flexibility and toughness, respectively, to ECM.
  Although the bone is a dynamic tissue that can self-heal upon minor injuries, it cannot regenerate after experiencing large defects such as bone tumor resections and severe nonunion fractures because it lacks the appropriate template.  Currently, the standard treatment is autografting which involves obtaining the donor bone from a non-significant and easily accessible site (i.e. iliac crest) in the patient own body and transplanting it into the defective site. Transplantation of autologous bone has the best clinical outcome because it integrates reliably with the host bone and can avoid complications with the immune system. But its use is limited by its short supply and donor site morbidity associated with the harvest procedure. Furthermore, autografted bones are avascular and hence are dependent on diffusion for nutrients, which affects their viability in the host. The grafts can also be resorbed before osteogenesis is complete due to high remodeling rates in the body. Another strategy for treating severe bone damage is allografting which transplants bones harvested from a human cadaver. However, allografts introduce the risk of disease and infection in the host.
  Bone tissue engineering presents a versatile response to treat bone injuries and deformations. Nanofibers produced via electrospinning mimics the architecture and characteristics of natural extracellular matrix particularly well. These scaffolds can be used to deliver bioactive agents that promote tissue regeneration. These bioactive materials should ideally be osteoinductive, osteoconductive, and osseointegratable. Bone substitute materials intended to replace autologous or allogeneic bone consist of bioactive ceramics, bioactive glasses, and biological and synthetic polymers. The basis of bone tissue engineering is that the materials will be resorbed and replaced over time by the body’s own newly regenerated biological tissue.
  Tissue engineering is not only limited to the bone: a large amount of research is devoted to cartilage, ligament, skeletal muscle, skin, blood vessel, and neural tissue engineering as well.
caption: Bone matrix composed of collagen fibrils. Nanofiber scaffolds are able to mimic such structure.
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