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 (M.Sc.Eng.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / The electrospinning process can produce submicron fibers for a variety of applications since a wide range of polymers can be used. For many advanced applications, achieving the desired fiber diameter, maximizing productivity, and achieving high yield are important production objectives. This thesis addresses several important areas needed to develop a general electrospinning control approach that aids in achieving those objectives including: developing a correlation between process conditions to fiber diameter, developing a method to determine an operating regime that meets manufacture objective, identification of process dynamics needed to develop a realtime control system, and insight into the role that relative humidity (RH) has on the process physics. A primary requirement for developing a general electrospinning control approach is to develop a correlation that maps measurable process parameters to the resulting fiber diameter, since electrospun nanofibers can not be observed in real time. Building on Yans identification of a fiber diameter correlation based on measuring the processes straight jet diameter and the ambient relative humidity for Polyethylene oxide (PEO)/water solutions, this thesis extends that work for a different polymer (Poly(vinylpyrrolidone) (PVP)) using three non-aqueous solvents. A correlation of process measurements to fiber diameter is developed, which is useful for both determining the operating regime (specification of voltage, flow rate and RH that meets the manufacturing objectives) as well as real-time control system design. An interpretation of experimental results also provides insight into the multiple roles that RH has on the electrospinning process physics in terms of the effective electric field that determines the upper jet geometry and current; the total solvent evaporation rate; and the impact of the electric stretching forces in the bending region A generalized operating regime determination strategy is presented that obtains the desired fiber diameter with maximum production rate. In addition, the process dynamics characteristics and how they scale with different operating conditions are identified, which is needed to develop real-time control algorithm. The process dynamics of PVP/alcohol solutions are shown to be similar to those of PEO/water solutions, and are determined by the Taylor cone volume dynamics. / 2031-01-01

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