Electrospun nanofibers represent a class of versatile scaffolds for tissue engineering applications owing to their ability to mimic the nanoscale features of the native extracellular matrix (ECM). In addition, nanofibers produced by electrospinning can be readily collected as uniaxially aligned assemblies to recapitulate the architecture of the ECM in tissues with anisotropic characteristics, such as tendon-to-bone insertions, tendons, and nerves. This dissertation focuses on the design, fabrication, functionalization, and assessment of various types of scaffolds consisting of aligned nanofibers, which can be used to augment regeneration in tissues with anisotropic structures. Briefly, for tendon-to-bone insertion repair, I assessed the capability of aligned nanofibers with a gradient in mineral content to induce spatially graded osteogenesis of adipose-derived mesenchymal stem cells (ASCs). I also developed an alternative approach to the production of a gradient in the density of osteoblasts. The graded pattern of osteoblasts generated using both approaches could mimic their distribution in the native tendon-to-bone insertion. To further enhance the stiffness of the scaffolds, a new solution was developed to coat the scaffold with a thicker mineral layer. In a third project, a novel method of generating crimp in aligned nanofibers was developed. A solvent plasticizer was employed to release the residual stress retained in the nanofibers during electrospinning, which led to the generation of crimp. Finally, the outgrowth of neurites derived from embryoid bodies (EBs) was studied using aligned nanofibers as the substrates. Depending on the strength of adhesion between nanofibers and neurites, two patterns of outgrowth--parallel and perpendicular (to the alignment)--were observed. Maturation of neurons derived from dissociated EBs was also investigated, as characterized by their extracellular action potential and the ability to form neuromuscular junctions with co-cultured muscle cells.

Thesis(Ph.D.)--Case Western Reserve University, 2010 / Title from PDF (viewed on 2009-12-22) Department of Macromolecular Science and Engineering Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: hydroxyapatite; electrospinning; scaffold. Includes bibliographical references (leaf 86).

Hydroxyapatite (HA) is the principal inorganic phase in bone. Synthetic hydroxyapatite particles, films, coatings, fibers and porous skeletons are used extensively in various biomedical applications. In this contribution, sol-gel processing and electrospinning have been used to develop a technique to produce fibrous structures. Poly(vinyl alcohol) (PVA) with an average molecular weight (MW) between 40,500 g/mol and 155,000 g/mol was electrospun with a calcium phosphate based sol. The sol was prepared by reacting triethyl phosphite and calcium nitrate and was directly added to an aqueous solution of PVA. This mixture was electrospun at a voltage of 20 - 30 kV. The results indicate that the sol particles were distributed uniformly within the PVA fibers. This electrospun structure was calcined at 600oC for 6 hr to obtain a residual inorganic, sub-micron fibrous network. The fibrous structure after electrospinning is retained after calcination. A variety of structures including solid fibers, micro-porous fibers and interconnected networks could be obtained after calcination. A bead-on-string structure was obtained after electrospinning for MW = 40,500 g/mol. X-Ray diffraction of this fibrous structure indicated that it consisted predominantly of hydroxyapatite with an average crystal size of almost 10-30 nm. The final morphologies of the ceramic fibers were found to depend on polymer molecular weight and sol volume fraction. Average fiber diameters were on the order of 200 nm and 800 nm for molecular weight of 67,500 g/mol and 155,000 g/mol, respectively. By judiciously controlling these material and process variables, non-woven mats of sub-micron fibers with varying degrees of interconnectivity and porosity have been produced. Such novel structures can be useful in drug delivery, tissue engineering and related biomedical applications.

Bioengineered skin is a promising treatment for chronic skin wounds because of its ability to promptly promote wound healing at the injury site and to restore the skin’s epidermal and dermal structures and functions. Despite some level of clinical success, commercially available bioengineered skin substitutes are still limited by a high incidence of infection, a lack of mechanical integrity, and a slow rate of tissue ingrowth from the surrounding wound margin. To address these challenges, we propose to engineer novel polymer composite matrices for dermal regeneration. These matrices consist of two different electrospun polymer layers which create a composite matrix made up of a highly porous three-dimensional fibrous network. Each composite matrix contains a biodegradable electrospun “dermal” layer which acts as a scaffold for dermal cell ingrowth and tissue regeneration and a non-degradable electrospun “epidermal” layer that serves as a provisional barrier to protect the wound from environmental insult. To evaluate the success of our designs, we performed quantitative analyses of the physical properties of our electrospun scaffolds including fiber diameter and angle analyses and mechanical properties. We found our electrospun scaffolds are comprised of a random network of fibers ranging from approximately 0.2 – 5µm in diameter. They exhibit several mechanical properties that are similar to those measured in native skin tissue, including tangent elastic modulus and strain at failure. We have also found the proposed nanofibrous scaffolds to be capable of supporting normal human fibroblast attachment and migration. Our scaffolds show similar attachment to tissue culture polystyrene controls and better attachment than collagen-GAG sponge controls. The dermal layer of our scaffolds show fibroblast outgrowth rates between 185 - 206µm/day, which is similar to rates observed by others in collagen-GAG sponges and wounds. The promising findings from these in vitro studies warrant that our novel electrospun dermal regeneration matrix be further developed.

Bioengineered skin is a promising treatment for chronic skin wounds because of its ability to promptly promote wound healing at the injury site and to restore the skin’s epidermal and dermal structures and functions. Despite some level of clinical success, commercially available bioengineered skin substitutes are still limited by a high incidence of infection, a lack of mechanical integrity, and a slow rate of tissue ingrowth from the surrounding wound margin. To address these challenges, we propose to engineer novel polymer composite matrices for dermal regeneration. These matrices consist of two different electrospun polymer layers which create a composite matrix made up of a highly porous three-dimensional fibrous network. Each composite matrix contains a biodegradable electrospun “dermal” layer which acts as a scaffold for dermal cell ingrowth and tissue regeneration and a non-degradable electrospun “epidermal” layer that serves as a provisional barrier to protect the wound from environmental insult. To evaluate the success of our designs, we performed quantitative analyses of the physical properties of our electrospun scaffolds including fiber diameter and angle analyses and mechanical properties. We found our electrospun scaffolds are comprised of a random network of fibers ranging from approximately 0.2 – 5µm in diameter. They exhibit several mechanical properties that are similar to those measured in native skin tissue, including tangent elastic modulus and strain at failure. We have also found the proposed nanofibrous scaffolds to be capable of supporting normal human fibroblast attachment and migration. Our scaffolds show similar attachment to tissue culture polystyrene controls and better attachment than collagen-GAG sponge controls. The dermal layer of our scaffolds show fibroblast outgrowth rates between 185 - 206µm/day, which is similar to rates observed by others in collagen-GAG sponges and wounds. The promising findings from these in vitro studies warrant that our novel electrospun dermal regeneration matrix be further developed.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 313-357). Also available online.

Thesis(Ph.D.)--Case Western Reserve University, 2010 / Title from PDF (viewed on 2009-12-30) Department of Chemical Engineering Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Schwann cell-seeded guidance channels have been exploited to bridge and guide axonal re-growth across gaps in lesioned nerves. Mis-orientation of Schwann cells in the channels can however distort axonal growth within the lesion. We therefore propose to orient the growth of Schwann cells on aligned nanofibers such that axonal growth can be guided along the designated direction towards the target. Chitosan was the choice scaffold material given its biocompatibility and the tunable susceptibility to biodegradation. To be suitable for electrospinning, chitosan was dissolved in trifluoroacetic acid/methylene chloride solution. By replacing the grounded plate collector of the conventional electrospinning setup with parallel collector plates placed 1.6 cm apart, the positively charged chitosan fibersbecame alternately attracted to the parallel plates and ended up uniaxially aligned as fiber suspension across the plates. Stability of the chitosan fibers in aqueous, physiological environment was achieved with the use of sodium carbonate to neutralize residual acidity in the chitosan fiber preparation. Schwann cells seeded onto these stabilized aligned chitosan nanofibers aligned uniaxially with the chitosan nanofibers. In addition, by seeding dissociated cells of dorsal root ganglia (DRG, E14/15 rats) onto the uniaxially aligned nanofibers, both neurons and Schwann cells were aligned with uniaxial arrangement of nanofibers, and the Schwann cells showed myelination ofthe axons. A model of the chitosan nerve conduit was constructed with a core nanofiberbundle, and seeding of Schwann cells. Thesein vitro results provide proof-of-principle for pursuing improvement in post-traumatic recovery from nerve injury with use of uniaxially aligned chitosan nanofibers in Schwann cell-seeded nerve guidance channels. / published_or_final_version / Biochemistry / Master / Master of Philosophy