collagen, gelatin, elastin, silk, poly(l-lactic acid) (plla), ploy(glycolic acid) (pga), poly(ԑ-caprolactone) (pcl), and poly(lactic-co-glycolic) acid (plga). the morphology of fibers fabricated through electrospinning varies with the solution properties of the polymer, hydrostatic pressure, temperature, and humidity. nanofiber electrospinning can create loosely connected porous nanofiber mats, which can be fabricated with varying patterns for varying applications. electrospinning nanofibers limits the three-dimensional capabilities of the nano-scaffold, which decreases cell differentiation and gene expressions. three-dimensional electrospun scaffolds have been created by stacking multiple layers and then seeding cells within the scaffold. fabrications with the new advancement in nanotechnologies, there are many methods of fabrication that improve upon the methods previously mentioned . to appropriately emulate the complexity of native tissue and extracellular matrix(ecm) architecture, the adoption of nanotechnology becomes an integral part of scaffold implant production. airbrush in 1936, norton patented the first blow spinning device, most recently in 2015 research was published describing a device with concentric nozzles where a polymer solution was inserted into a stream of flowing gas in order to form nano-fibers from polymers like polystyrene. the new developments lead to the technique of airbrushing for nano-scaffold fabrication. airbrushing is a technique for fiber fabrication that involves two parallel concentric fluid streams; a polymer dissolved in a volatile solvent and a pressurized gas that flows around the polymer solution, generating fibers that are deposited in the direction of gas flow. this method is more favored compared to electrospinning due to the fact that it is less expensive and is easier to interface. this method has the ability to deposit conformal fibers onto both planar and non-planar substrates with a deposition rate that is relatively ten times faster than electrospinning. just like commercial airbrushes the nanofibrous airbrush technique can be used to “paint” nanofibers onto a more extensive range of targets and for the carrier solvent to evaporate quickly before the polymer fibers deposit on the collection surface. although acute exposure to high concentrations of a solvent such as acetone may be toxic, studies have shown that sbs from acetone directly onto cells did not affect viability, resulting in preventing issue of biocompatibility. complication of the airbrush technique arises when formation of fiber mats with the local fiber bundles, this is induced by the morphological differences in fibers and crystalline structures. phase separation in 1999, researchers(need to identify) pioneered a method creating nano-fibrous polyester based scaffolds with high porosity and sub-micron fibers dimensions through the method of phase separation. phase separation, also called as phase inversion, is a technique that has been employed to generate porous polymers scaffolds by promoting the separation of a polymeric solution into two phases: a polymer-rich phase and a polymer-poor phase. polymer solution is driven to separate in phases through cooling or non-solvent exchange, in a way that the polymer is not thermodynamically miscible anymore and forms polymer-rich domains within the solvent. next, the solvent is extracted and the scaffold is frozen to maintain the structure. lastly, lyophilization forms a fibrous scaffold with diameters between 50 and 500 nm(nanometers) and able to exhibit 98.5% porosity. again this method of fabrication is used to create nano-fibrous scaffolds out of aliphatic polyesters. solvents that are used include thf( developing the best results), dmf, thf/methanol, thf/acetone, dioxane/methodal, dioxane/h2o, and dioxane/acetone). phase separation approximates more to conventional foams with larger pore sizes, implying that this method would be prone to cell infiltration, making it favorable for tissue engineering.. phase separation can also lead to smaller pores being produced, however there is difficulty to control the diameter of fibrous due to the fact that the initial polymer concentration does not lead to larger fiber diameters in phase separated scaffolds. this method of fabrication promotes cell growth, proliferation and differentiation, making it suitable to be used as tissues for artificial organs, neural networks, bioreactors, cell sources and drug delivery systems. step techniques “spinneret based turntable engineered parameters” or step technique has been required for nanofiber networks with controllable fiber diameters, controllable spacing, and for the orientation of individual fibers. during this technique micro/nano fibers are pulled from the pendant solution droplet and allows for a collection of highly aligned fibers of uniform dimensions on the substrate. it promotes control of the dimensions of the fibers deposited in the aligned configurations, thus creating a platform for the investigation of cellular dynamics and cellular adhesion on scaffolds. the technique allows precise spacing and orientation of fibers into planar or non-planar structures using a wide spectrum of polymers. however, there is a difficulty in obtaining fibers smaller than 100 nm and as well as limitation to viscoelastic materials used in the step technique. nano-fibrous scaffolds, created from step techniques, have the ability to be used for a wide range of applications in tissue engineering applications bone scaffolds by 2012 the us over half a million people receive bone defect repairs yearly with an estimated cost of $2.5 million and has doubled in recent years. in the us, bone is one of the most transplanted tissues and the increasing demand of bone grafts and substitutes was estimated to be 3.3 billion of revenue. investments in research in tissue engineering solutions have had a massive market especially for bone. as a scaffolding tissue, bone is responsible for support, protection, load bearing and hematopoietic functions. for small defects the human bone has the ability to continuously remodel and rebuild upon itself. however, large scale defects, inflammations caused by accidents, infections and tumors make it difficult for the bone to heal, requiring external interventions. the growing shortage of donors, rejection of transplants, and mechanical failure have made it difficult to have lasting solutions. advancements in nanotechnology have enabled the applications for 3d printing in tissue engineering for the development of bone scaffolds. bone scaffolds are typically made of porous biodegradable materials that provide the mechanical support during repair regeneration of damaged and diseased bone. the design of the scaffolds presents a surface that promotes cell attachments, growth, and differentiation, while providing a porous network for tissue growth. for bone scaffold continuous ingrowth of bone tissue, interconnected porosity is important as it can allow nutrients and molecules to transport to inner parts of scaffold to facilitate cell ingrowth, vascularization, as well as waste material removal. the 3d bioprinting method has been used to fabricate more ideal structural scaffolds with better control of pore morphology, pore size and porosity. 3d printing can be essential to bone scaffolds as it takes into account the high degree of porosity together with high mechanical strength, which is critical for the bone scaffold to perform. heart muscle scaffolds cardiac muscle, on the other hand, has an elastic modulus of only around 10 mpa, 3 orders of magnitude smaller than bone. however, it experiences constant cyclic loading as the heart pumps. this means that the scaffold must be both tough and elastic, a property achieved using polymeric materials. spinal cord engineering spinal cord injury can be seriously detrimental to normal form and function in the human body, often leading to major loss of motor and sensory function that can even affect the whole of the body below the injury level. the number of global spinal cord injury cases rose to 27.04 million in 2016 where each patient can cost the economy from $1–5 million for a given case. as a result, there is a significant need for novel solutions to address the issue. novel biomaterial and tissue engineering strategies have been developed recently to address the need, mainly centering around formulating nanoscaffolds that fill the gap created in the injury site and that foster a pro-regenerative environment that help to facilitate restoration of the spinal cord structure and function. this is achieved through physically connecting the exposed areas in the spinal cord via scaffold as well as providing a favorable environment for regenerative cell types such as mesenchymal stem cells and schwann cells and for promoting axon restoration and remyelination. olfactory ensheathing cells, stem cells, and other neural progenitor cells play a large part in creating a stimulating environment for regenerative purposes. in order to make these nanoscaffolds, both natural and synthetic polymers are used in their synthesis. for natural polymers, hyaluronic acid and collagen are two of the major candidates used in industry today. hyaluronic acid is a major component of the extracellular matrix and has variable properties depending on its molecular weight, which is useful in compensating for properties necessary for a good scaffold. collagen is also a major component of the extracellular matrix, most importantly in central nervous tissue where it has good histocompatibility and supports adhesion and growth.