nano-scaffold nano-scaffold nano-scaffolding or nanoscaffolding is a medical process used to regrow tissue and bone, including limbs and organs. the nano-scaffold is a three-dimensional structure composed of polymer fibers very small that are scaled from a nanometer (10−9 m) scale. developed by the american military, the medical technology uses a microscopic apparatus made of fine polymer fibers called a scaffold. damaged cells grip to the scaffold and begin to rebuild missing bone and tissue through tiny holes in the scaffold. as tissue grows, the scaffold is absorbed into the body and disappears completely. nano-scaffolding has also been used to regrow burned skin. the process cannot grow complex organs like hearts. historically, research on nano-scaffolds dates back to at least the late 1980s when simon showed that electrospinning could be used to produced nano- and submicron-scale polymeric fibrous scaffolds specifically intended for use as in vitro cell and tissue substrates. this early use of electrospun fibrous lattices for cell culture and tissue engineering showed that various cell types would adhere to and proliferate upon polycarbonate fibers. it was noted that as opposed to the flattened morphology typically seen in 2d culture, cells grown on the electrospun fibers exhibited a more rounded 3-dimensional morphology generally observed of tissues in vivo. mechanism of tissue regeneration using nanoscaffolds nano-scaffolding is very small, 100 times smaller than the human hair and is built out of biodegradable fibers. the use of this scaffolding allows more effective use of stem cells and quicker regeneration. electrospun nanofibers are prepared using microscopic tubes that range between 100 and 200 nanometers in diameter. these entangle with each other in the form of a web as they're produced. electrospinning allows the construction of these webs to be controlled in the sense of the tube's diameter, thickness, and the material being used. nano-scaffolding is placed into the body at the site where the regeneration process will occur. once injected, stem cells are added to the scaffolding. stem cells that are attached to a scaffold are shown to be more successful in adapting to their environment and performing the task of regeneration. the nerve ends in the body will attach to the scaffolding by weaving in-between the openings. this will cause them to act as a bridge to connect severed sections. over time the scaffolding will dissolve and safely exit the body leaving healthy nerves in its place. this technology is the combination of stem cell research and nanotechnology. the ability to be able to repair damaged nerves is the greatest challenge and prize for many researchers as well as a huge step for the medical field. this would allow doctors to repair nerves damaged in an extreme accident, like third degree burns. the technology however, is still in its infancy and is still not capable of regenerating complex organs like a heart, although it can already be used to create skin, bone and nails. nano scaffolding has been shown to be four to seven times more effective in keeping the stem cells alive in the body, which would allow them to perform their job more effectively. this technology can be used to save limbs that would otherwise need amputation. nanoscaffolding provides a large surface area for the material being produced, along with changeable chemical and physical properties. this allows them to be applicable in many different types of technological fields. background tissue engineering tissue engineering consists of the use of cells, scaffolds, and varying tissue architecture techniques to restore, replace, and regenerate damaged body tissue. tissue engineering consists of the use of cells, scaffolds, and varying tissue architecture techniques to restore, replace, and regenerate damaged body tissue. the goal of tissue engineering is to restore, replace, or regenerate damaged body tissue. nano-scaffolds along with cells and growth factor signals are utilized in tissue engineering applications. tissue engineering applications are designed to overcome hurdles associated with allotransplantation, which include unavailable donors, complex surgeries, and postoperative care. in 2015, the tissue engineering global market was estimated at $23 billion, and expected to reach $94.2 billion by 2022. the anticipation of fast growth was due to an increase in bone and joint disorders, with musculoskeletal regenerative medicines comprising 26.4% of the regenerative medicine market. extracellular matrix most human cells within tissues anchor to the solid extracellular matrix (ecm). ecm components vary between various types of body tissues. the ecm acts as a natural "scaffolding". the ecm has five major function: provide cellular support and microenvironment necessary to enable cell growth, migration, and signal response. provide tissue mechanical properties, such as rigidity and elasticity. these properties vary to provide for specific tissue functions. provide bioactive regulators to trigger cell responses. provide a reservoir for cellular growth factors to enhance cell responses. provide a degradable physical environment to accommodate ecm remodeling in response to developmental, physiological, and pathological inputs during tissue processes. the goal of the nano-scaffold is to mimic the ecm functions to encourage tissue restoration, replacement, and regeneration. both ecm variations between tissue types and the complexity of the ecm make nano-scaffold mimicry difficult. nano-scaffold in order to mimic the ecm, the nano-scaffold follows four main features and functions: architecture: must provide empty space for new tissue to form. nano-scaffold biomaterials must be porous to allow for nutrient transportation to the tissue within the construct. however, despite the porous architecture, the nano-scaffold must be mechanically strong enough to withstand physiological loads. cyto- and tissue compatibility: nano-scaffolds must support cell attachment, growth, and differentiation prior to implantation in vitro and after in vivo implantation. bioactivity: biomaterials within the nano-scaffold must facilitate and regulate cell and tissue activity, as in natural host tissue. mechanical property: must provide shape and stability to the damaged tissue. the mechanical properties of the nano-scaffold determine cell differentiation, morphology, and characteristics due to the cell ability to sense substrate stiffness. approach there are four major nano-scaffolding approaches, which include pre-made porous scaffolds for cell seeding, decellularized ecm from allogeneic or xenogeneic tissues for cell seeding, cell sheets with self-secreted ecm, and cell encapsulation in a self-assembled hydrogel matrix. each approach contains varying materials, fabrication methods, and resulting mechanical properties. in addition to these four approaches, metallic nano-particles have been researched to enhance the mechanical properties of nano-scaffolds. nanofiber electrospinning is another fabrication method for nano-scaffolding. pre-made porous scaffolds for cell seeding a wide array of nano-scaffold biomaterials have been used for pre-made porous scaffolds for cell seeding. these biomaterials can be classified as either natural or synthetic. natural biomaterials are obtained from natural sources, which include but are not limited to, ecm from allografts or xenografts, calcium phosphates, and organic polymers, such as proteins, polysaccharides, lipids, and polynucleotides. natural biomaterials increase nano-scaffold biocompatibility, but limit physical and mechanical stability. natural biomaterials risk a negative immune response in the implantation host due to the allogeneic or xenogeneic source. synthetic biomaterials can be subclassified as organic or inorganic. compared to natural, synthetic biomaterials are more easily tailored to varying tissue hardness, and therefore are applicable to a wider variety of tissues. synthetic biomaterials are less biocompatible and result in decreased cell attachment and growth. surface and bulk properties can be altered within a synthetic biomaterials in an attempt to increase the biocompatibility of a surface. various fabrication techniques have been employed to fabricate a porous scaffold, such as porogens within biomaterials, solid free-form or rapid prototyping, and utilizing woven or non-woven fibers. to employ porogens in the nano-scaffold biomaterial, solid materials in solids or dissolved in solvents are combined with the porogen. porogens include carbon dioxide, water, and paraffin. one the biomaterial is fabricated, the porogens are removed with methods such as sublimation, evaporation, and melting. therefore, when the porogens are removed the porous scaffold is left behind with pores. to fabricate with solid free-form or rapid prototyping, methods such as laser sintering, stereolithography, and 3d printing have been utilized. these methods use light or heat transfer to bond or crosslink the biomaterial being used. cross-linking provides enhanced material strength. the fabrication technique utilizing woven and non-woven fiber structures provides a porous structure when the fibers are bonded with thermal energy. electrospinning is utilized via application of high voltages in a polymer solution. a spinning fiber jet is formed when the electrostatic forces surpass the forces within the polymer solution. the pre-made porous scaffolding method allows for a defined structure formation. with fabricating allowing an intricate structure formation, the nano-scaffolds utilizing this method can be tuned to resemble specific tissue ecms. decellularized ecm from allogeneic and xenogeneic tissues for cell seeding decellularized ecm from allogeneic and xenogeneic tissues have been utilized in tissue engineering for heart valves, vessels, nerves, tendons, and ligaments. to utilize the ecm from allogeneic or xenogeneic tissues the cellular antigens must be removed due to implant recipient immune response. decellularization is conducted with a combination of physical, chemical, and enzymatic processes. freeze-thaw cycles or ionic solutions have been utilized to lyse cell membranes. trypsin/edta treatments are then utilized to separate ecm cellular components. detergents solubilize and remove cell cytoplasm's and nuclei. the decellularized ecm with preserved growth factors is utilized as the nano-scaffold. decellularized ecm nano-scaffolding provides mechanical properties closer to natural values than other methods due to utilizing a natural ecm structure. cell sheets with self-secreted ecm in the cell sheet approach, cells are utilized to secrete an ecm for scaffolding. cells are cultured until confluence on a thermo-responsive polymer. hydrophobicity is thermally-regulated repeatedly to detach multiple cell sheet layers. loading capabilities of this approach are limited due to the use of thin cell sheets. cell sheets with self-secreted ecm provide a high cell density and tight cell association within the nano-scaffold. the hydrogel structure consists of cross-linked hydrophilic polymer chains. cell encapsulation in a self-assembled hydrogel matrix the hydrogel structure consists of cross-linked hydrophilic polymer chains. a semi-permeable membrane or a homogeneous solid mass encapsulate cells. natural and synthetic hydrogels are used to encapsulate the cells. algae and sodium alginate provide a commonly used source for polysaccharides. other natural biomaterials utilized include agarose and chitosan. synthetic biomaterials include poly(ethylene glycol) (peg) and polyvinyl alcohol (pva). prior to initiation, the biomaterials exist as a liquid monomer. the biomaterials are mixed with cells. once initiated by ph, temperature, ionic strength, or light control, the biomaterials self-assembles into a solid polymer meshwork. since the cells are mixed before initiation, this allows for the fabrication of the nano-scaffold construct, and cell seeding in one step. this method contains low mechanical properties due to the highly moldable structure of the nano-scaffold and is not ideal for load-bearing applications. metallic nano-scaffolds metallic nanoparticles within polymers increase mechanical strength and biocompatibility of nano-scaffolds. copper, gold, iron oxide, platinum, palladium, strontium, titanium, zinc, and their oxides have been utilized in bone tissue regenerative applications. these nano-particles have been incorporated within polymers such as poly (lactic-co-glycolic acid) (plda), poly (l-lactic acid) (plla), poly (caprolactone (pcl), collagen, hyaluronic acid, silk, alginate, and fibrin. copper nanoparticles within nano-scaffolding enhances antioxidant and anti-diabetic activities. copper nanoparticles within nano-scaffolding can stimulate angiogenesis, cell migration, and proliferation of endothelial cells. gold nanoparticles within nano-scaffolding induces osteogenic differentiation due to signal transduction from mechanical stimuli. platinum nanoparticles and palladium nanoparticles within nano-scaffolding reduces oxidative stresses which decreases disease progression. silver nanoparticles within nano-scaffolding are antimicrobial and aid in preventing postoperative pathogenic infections. silver nanoparticles within nano-scaffolding have been used to develop microbe resistant coating. titanium nanoparticles within nano-scaffolding are highly porous, which is ideal for cell proliferation. zinc nanoparticles within nano-scaffolding decrease the number of reactive oxygen species, which are associated with failure of implants due to bacterial infection. nano-fiber electrospinning electrospinning systems consist of high voltage power, material delivery, and fiber collection units. the high voltages produce charged polymer solution, which exits from the delivery unit in a jet form. the jet of polymer solution is elongated and the solvent either evaporates or solidifies. fibers are then collected in the collection unit. flat plated are utilized to randomly collect the fibers. rotors are utilized to rotate the collector to collect aligned fibers. concentric collectors are utilized to collect the fibers in a disc, drum, or cone shape. compared to random fibers, aligned fibers enhance integrin signaling pathways, and contain anisotropic properties similar to ecms characterized by high degrees of orientation. fibers may be fabricated from natural and synthetic polymers, including