Thomas Yong

Electrospun Nanofibers: Solving Global Issues

Energy and environment will head the list of top global issues facing society for the next 50 years. Nanotechnology is responding to these challenges by designing and fabricating functional nanofibers optimized for energy and environmental applications. The route toward these nano-objects is based primarily on electrospinning: a highly versatile method that allows the fabrication of continuous fibers with diameters down to a few nanometers. The mechanism responsible for the fiber formation mainly includes the Taylor Cone theory and flight-instability theory, which can be predicted theoretically and controlled experimentally. Moreover, the electrospinning has been applied to natural polymers, synthetic polymers, ceramics, and carbon. Fibers with complex architectures, such as ribbon fiber, porous fiber, core-shell fiber, or hollow fiber, can be produced by special electrospinning methods. It is also possible to produce nanofibrous membranes with designed aggregate structure including alignment, patterning, and two-dimensional nanonets. Finally, the brief analysis of nanofibers used for advanced energy and environmental applications in the past decade indicates that their impact has been realized well and is encouraging, and will continually represent a key technology to ensure sustainable energy and preserve our environment for the future.

Enhancement of neurite outgrowth using nano-structured scaffolds coupled with laminin

Cell interactions with scaffolds are important for cell and tissue development in the process of repairing and regeneration of damaged tissue. Scaffolds that mimic extracellular matrix (ECM) surface topography, mechanical stiffness, and chemical composition will be advantageous to promote enhanced cell interactions. Electrospinning can easily produce nano-structured synthetic polymer mats with architecture that structurally resembles the ECM of tissue. Although electrospinning can produce sub-micron fibrous scaffolds, modification of electrospun scaffolds with bioactive molecules is beneficial as this can create an environment that consists of biochemical cues to further promote cell adhesion, proliferation and differentiation. Incorporation of laminin, a neurite promoting ECM protein, onto the nanofibers is an alternative to further mimic the biochemical properties of the nervous tissue to create a biomimetic scaffold. In this study, we investigated the feasibility to functionalize scaffolds by coupling laminin onto poly(L-lactic acid) (PLLA) nanofibers. Laminin was successfully added to nanofibers using covalent binding, physical adsorption or blended electrospinning procedures. PC12 cell viability and neurite outgrowth assays confirmed that the functionalized nanofibers were able to enhance axonal extensions. Significantly, compared to covalent immobilization and physical adsorption, blended electrospinning of laminin and synthetic polymer is a facile and efficient method to modify nanofibers for the fabrication of a biomimetic scaffold. Using these functionalization techniques, nanofibers can be effectively modified with laminin for potential use in peripheral nerve regeneration applications.

In vivo study of novel nanofibrous intra-luminal guidance channels to promote nerve regeneration

A novel nanofibrous construct for promoting peripheral nerve repair was fabricated and tested in a rat sciatic nerve defect model. The conduit is made out of bilayered nanofibrous membranes with the nanofibers longitudinally aligned in the lumen and randomly oriented on the outer surface. The intra-luminal guidance channel is made out of aligned nanofibrous yarns. In addition, biomolecules such as laminin and nerve growth factor were incorporated in the nanofibrous nerve construct to determine their efficacy in in vivo nerve regeneration. Muscle reinnervation, withdrawal reflex latency, histological, axon density and electrophysiology tests were carried out to compare the efficacy of nanofibrous constructs with an autograft. Our study showed mixed results when comparing the artificial constructs with an autograft. In some cases, the nanofibrous conduit with aligned nanofibrous yarn as an intra-luminal guidance channel performs better than the autograft in muscle reinnervation and withdrawal reflex latency tests. However, the axon density count is highest in the autograft at mid-graft. Functional recovery was improved with the use of the nerve construct which suggested that this nerve implant has the potential for clinical usage in reconstructing peripheral nerve defects.

Distinctive Degradation Behaviors of Electrospun Polyglycolide, Poly(dl-Lactide-co-Glycolide), and Poly(l-Lactide-co-ɛ-Caprolactone) Nanofibers Cultured With/Without Porcine Smooth Muscle Cells

Biodegradable nanofibers have become a popular candidate for tissue engineering scaffolds because of their biomimetic structure that physically resembles the extracellular matrix. For certain tissue regeneration applications, prolonged in vitro culture time for cellular reorganization and tissue remodeling may be required. Therefore, extensive understanding of cellular effects on scaffold degradation is needed. There are only few studies on the degradation of nanofibers, and also the studies on degradation throughout cell culture are rare. In this study, polyglycolide (PGA), poly(DL-lactide-co-glycolide) (PLGA) and poly(L-lactide-co-epsilon-caprolactone) [P(LLA-CL)] were electrospun into nanofibrous meshes. The nanofibers were cultured with porcine smooth muscle cells for up to 3 months to evaluate their degradation behavior and cellular response. The results showed that the degradation rates are in the order of PGA >> PLGA > P(LLA-CL). PGA nanofibers degraded in 3 weeks and supported cell growth only in the first few days. PLGA nanofiber scaffolds facilitated cell growth during the first 30 days after seeding, but cell growth was slow thereafter. P(LLA-CL) nanofibers facilitated long-term (1-3 months) cell growth. mRNA quantification using real-time polymerase chain reaction revealed that some smooth muscle cell markers (alpha-actinin and calponin) and extracellular matrix genes (collagen and integrin) seemed to be downregulated with increased cell culture time. Cell culture significantly increased the degradation rate of PGA nanofibers, whereas the effect on PLGA and P(LLA-CL) nanofibers was limited. We found that the molecular weight of P(LLA-CL) and PLGA nanofibers decreased linearly for up to 100 days. Half lives of PLGA and P(LLA-CL) nanofibers were shown to be 80 and 110 days, respectively. In summary, this is the first study to our knowledge to evaluate long-term polymeric nanofiber degradation in vitro with cell culture. Cell culture accelerated the nanofibrous scaffold degradation to a limited extent. P(LLA-CL) nanofibers could be a good choice as scaffolds for long-term smooth muscle cell culture.

Nanofibres and their Influence on Cells for Tissue Regeneration

Synthetic polymer and biopolymer nanofibres can be fabricated through self-assembly, phase separation, electrospinning, and mechanical methods. These novel functional biocompatible polymers are very promising for a variety of future biomedical applications. There are many characteristics of nanofibres that would potentially influence cell growth and proliferation. As such, many studies have been carried out to elucidate the cell–nanofibre interaction with the purpose of optimizing the matrix for cell growth and tissue regeneration. In this Review, we present current literatures and our research on the interactions between cells and nanofibres, and the potentials of nanofibre scaffolds for biomedical applications.

Recent Advances In Tissue Engineering Applications Of Electrospun Nanofibers

that information on circul ating low molecular weight peptides can be correlated to certain disease states. Exploitation of the uni fo m1, small pores and surface functi onali za tion propertie enabled by porou silicon particles to extract and enabl e analys is of these peptides as suggested by Liotta et al (to diagnose the early stages of disease by analys i of the low molecular weight proteome using porous silicon particulates) is, in our opinion, feas ible and potentially quite powerful. Recent research on the penetration, loading, and adsorption of proteins into porous silicon, the use of porous silicon as a size-exclusion matrix for resolving protein sizes, and exceptional capacity to tune the pore size indi cate the potential for clinical use of porous silicon in proteomics. . . Furthermore, novel, contro llably dual-s ided, symmetric hydrophobi c and hydrophilic particul ates of porous _s ilicon have been conceived and are being fabri cated (see Figure 3 for an SEM image of the porous silicon surface) . They are prepared from a polysilicon precursor and are precisely size monodisperse on the sca le of one micron (d iameter and thickness). These particulates may enable unidirectional fl ow of transported drugs, proteins/peptides, nucleic ac ids, etc. They may also fac ilitate controllably different intraparti cle surface chemistries, and therefore potenti ally di fferent types of antibodie , proteins, etc., present on the same particle.