Fibrocartilages in the body, including the temporomandibular joint (TMJ) disc and knee meniscus, lack intrinsic healing capacity following trauma or disease. Current treatments only address the symptoms of fibrocartilage damage and do nothing to prevent further degradation of the joint. A tissue engineered replacement, with biochemical and biomechanical properties approaching those of native tissue, could provide a solution. This thesis investigates two components critical to the generation of a tissue engineered TMJ disc: 1) characterization of the native disc to identify a suitable animal model and create design parameters, and 2) development of approaches to use human embryonic stem cells (hESCs) in fibrocartilage tissue engineering. The first step to achieving this goal was to identify an animal model for the human TMJ disc based on quantitative biochemical and biomechanical properties. To this end, rabbit, goat, pig, cow, and human discs were analyzed, and the pig disc was shown to possess properties most similar to the human. The next step was to further characterize the pig TMJ, as many aspects of the joint were still poorly understood. Though the TMJ disc is anchored to the surrounding bony tissue on all sides by discal attachments, little was known about their properties. Biochemical and histological analysis was performed on these attachments and indicated that they are similar to the disc but possess distinct regional matrix content related to joint biomechanics. Finally, though the contribution of collagen to the mechanical properties of the TMJ disc was well characterized, the contribution of the glycosaminoglycans (GAGs) was unknown. By removing sulfated GAGs with chondroitinase ABC, it was found that these molecules contribute to the viscoelastic compressive properties of the disc, but only in regions with the highest native GAG content. The second aspect of this thesis involved producing fibrocartilage tissue from hESCs. The pluripotency and unlimited self-renewal of these cells makes them ideally suited for producing fibrocartilages that contain a spectrum of matrix components. This work began by investigating what factors are necessary for fibrochondrogenic differentiation of hESCs in embryoid bodies (EBs). Growth factors and co-cultures with primary fibrochondrocytes were both shown to be potent modulators of fibrochondrogenesis, although differentiation of hESCs consistently produced a heterogeneous cell population. To purify populations of fibrochondrocytes differentiated form hESCs, two inexpensive and novel techniques were investigated. First, density gradient separation was the first technique attempted. This technique was able to isolate distinct subpopulations of cells, some of which were mechanically similar to native chondrocytes. Second, a chondrogenic tuning technique was applied to differentiated hESCs. Following fibrochondrogenesis in EBs, cells were expanded in monolayer in chondrocyte specific media before being used for tissue engineering. Chondrogenic tuning produced several distinct cell populations during expansion, and, as a result, a spectrum of different cartilaginous tissues was achieved for tissue engineering. Three of the cell populations produced tissues similar to the native TMJ disc, outer meniscus, and inner meniscus. Overall, this thesis identified an animal model for TMJ characterization and in vivo studies, furthered understanding of structure-function relationships of the TMJ disc and its attachments, and developed a technique for producing a spectrum of engineered fibrocartilages from hESCs.

This study investigates the effect on: 1) the bulk surface; and 2) the three-dimensional non-woven microfabric scaffolds of poly(N-isopropylacylamide)-CNT-polyaniline on growth and viability of  mice fibroblast cells L929. The poly(N-isopropylacylamide)-CNT-polyaniline was prepared using coupling chemistry and electrospinning was then used for the fabrication of responsive, nonwoven microfabric scaffolds. The electrospun microfabrics were assembled in regular three-dimensional scaffolds with OD: 400-500 mm; L: 6-20 cm. Mice fibroblast cells L929 were seeded on the both poly(N-isopropylacylamide)-CNT-polyaniline bulk surface as well as non-woven microfabric scaffolds. Excellent cell proliferation and viability was observed on poly(N-isopropylacylamide)-CNT-polyaniline non-woven microfabric matrices in compare to poly(N-isopropylacylamide)-CNT-polyaniline bulk and commercially available Matrigel™ even with a range of cell lines up to 168 h. Temperature dependent cells detachment behaviour was observed on the poly(N-isopropylacylamide)-CNT-polyaniline scaffolds by varying incubation at below lower critical solution temperature (LCST) of poly(N-isopropylacylamide). The results suggest that poly(N-isopropylacylamide)-CNT-polyaniline non-woven microfabrics could be used as a smart matrices for applications in tissue engineering. / European Commission FP7 (PIIF-GA-2009-254955), JSPS, JST-CREST and MEXT

The growing incidences of coronary artery bypass graft surgeries have triggered a need to engineer a viable small diameter blood vessel substitute. An ideal tissue engineered vascular graft should mimic the microenvironment of a native blood vessel, while providing the adequate compliance post-implantation. Current vascular graft technologies lack the ability to promote vascular ECM deposition, leading to a compliance mismatch and ultimately, graft failure. Hence, in order to engineer suitable vascular grafts, this thesis describes the synthesis and characterization of novel elastin mimetic peptides, EM-19 and EM-23, capable of promoting vascular ECM deposition within a poly(ethylene glycol) diacrylate (PEG-DA) hydrogel. By combining the material properties of a synthetic and bio-inspired polymer, a suitable microenvironment for cell growth and ECM deposition can be engineered, leading to improved compliance. As such, characterization of EM-19 and EM-23 was conducted in human vascular smooth muscle cell (SMC) cultures, and the peptides self-assembled with a growing elastic matrix. After grafting the peptides onto the surface of PEG-DA hydrogels, EM-23 increased SMC adhesion by 6000% over PEG-RGDS hydrogels, which have been the gold standard of cell adhesive PEG scaffolds. Moreover, EM-23 grafted surfaces were able to promote elastin deposition that was comparable to tissue cultured polystyrene (TCPS) surface even though TCPS had roughly 4.5 times more SMCs adhered. Once translated to a 3D model, EM-23 also stimulated increased elastin deposition and improved the mechanical strength of the scaffold over time. Moreover, degradation studies suggested that EM-23 may serve as a template that not only promotes ECM deposition, but also allows ECM remodeling over time. The characterization studies in this thesis suggest that this peptide is an extremely promising candidate for improving vascular ECM deposition within a synthetic substrate, and that it may be beneficial to incorporate EM-23 within polymeric scaffolds to engineer compliant vascular grafts.

Three-dimensional (3D) tissue models have significantly improved our understanding of structure/function relationships and promise to lead to new advances in regenerative medicine. However, despite the expanding diversity of 3D tissue fabrication methods, in vitro approaches for functional assessments have been relatively limited. Herein, we describe the guidance of primary endothelial cells (ECs) in an agarose hydrogel scaffold that is chemically patterned with an immobilized concentration gradient of vascular endothelial growth factor 165 (VEGF165) using multiphoton laser patterning of VEGF165. This is the first demonstration of this patterning technology to immobilize proteins; and the first demonstration of immobilized VEGF165 to guide endothelial cell growth and differentiation in 3D environments. It is particularly compelling that this 3D hydrogels provide an excellent biomimetic environment for stem cell niche, thereby offering a new approach to study stem cell biology. In this thesis, we focused on the retinal stem cell niche, investigating cellular interactions between retinal stem and progenitor cells (RSPCs) and endothelial cells (ECs). By using this 3D in vitro model, we demonstrated the synergistic interactions between RSPCs and ECs wherein RSPCs migrated into 3D gels only in the presence of ECs and RSPCs stabilized EC tubular-like formations. Moreover, we characterized the contact-mediated effects of ECs on RSPC fate in terms of proliferation and differentiation.

Embryonic stem cells (ESC) constitute a promising source of cells for cardiac transplantation strategies. However, complexities associated with in vivo studies have made it difficult to develop a thorough understanding of cell integration. We have engineered an in vitro system that recapitulates the native cardiac environment using 300μm thick collagen scaffolds seeded with neonatal cardiomyocytes (CM) and electrical field stimulation. The injection of undifferentiated ESC served as a baseline to assess the validity of studying cell transplantation in this model. Yfp-ESC survived and proliferated over several days in model tissue. ESC were not observed to significantly differentiate into the cardiac lineage, and did not integrate with the cardiac cell population. While the injection of ESC improved cardiac cell number, tissue functional properties were hindered. The methods developed herein can be readily adapted to study ESC derived progenitor and differentiated cells, to elucidate the optimal cell state for ESC-mediated cell therapy.

This thesis presents a microfluidic strategy for the in-flow definition of a 3D soft material with a tunable and perfusable microstructure. The strategy was enabled by a microfluidic device containing up to fifteen layers that were individually patterned in polydimethylsiloxane (PDMS). Each layer contained an array of ten to thirty equidistantly spaced microchannels. Two miscible fluids (aqueous solutions of alginate and CaCl2) were used as working fluids and were introduced into the device via separate inlets and distributed on chip to form a complex fluid at the exit. The fluid microstructure was tuned by altering the flow rates of the working fluids. Upon solidification of alginate in the presence of calcium chloride, the created microstructure was retained and a soft material with a tunable microstructure was formed. The produced material was subsequently perfused using the same microfluidic architecture. The demonstrated strategy potentially offers applications in materials science and regenerative medicine.

This thesis presents a microfluidic strategy for the in-flow definition of a 3D soft material with a tunable and perfusable microstructure. The strategy was enabled by a microfluidic device containing up to fifteen layers that were individually patterned in polydimethylsiloxane (PDMS). Each layer contained an array of ten to thirty equidistantly spaced microchannels. Two miscible fluids (aqueous solutions of alginate and CaCl2) were used as working fluids and were introduced into the device via separate inlets and distributed on chip to form a complex fluid at the exit. The fluid microstructure was tuned by altering the flow rates of the working fluids. Upon solidification of alginate in the presence of calcium chloride, the created microstructure was retained and a soft material with a tunable microstructure was formed. The produced material was subsequently perfused using the same microfluidic architecture. The demonstrated strategy potentially offers applications in materials science and regenerative medicine.

Cornea is the transparent outermost layer of the eye. It is a thin (500 &micro / m) multilayer tissue which performes around 75% of the total refraction in the eye. It also protects the inner layers against any type of damage. Since it is avascular, the three cellular layers of cornea always need transport of nutrients and other materials in and out of the tissue via diffusion. Any change in shape, transparency or thickness of cornea, or physical damages and infections, may cause serious defects. The conventional methods are satisfactory in the treatment of mild injuries but severe cases require the substitution of the tissue with an equivalent. Keratoprosthesis and donor corneas that are used as replacements do not completely meet requirements. Tissue engineering can be an alternative method for preparing a biocompatible and stable cornea equivalent. The ability to choose from a variety of materials and the ability to incorporate bioactive agents allow the researchers to tailor make the construct. The structure needs to be seeded with the patient&rsquo / s own cells and cultured in vitro to yield an optimal corneal replacement. In this study a novel, split thickness cornea replacement is proposed to substitute the two upper cellular layers (epithelium and stroma) of the native cornea. The design includes a chondroitin sulfate impregnated collagen type I (isolated from rat tail) foam (CSXLF) produced by lyophilization carrying electrospun fibers of the same polymer collected directly on top of the foam, forming the bilayer structure (Fo-Fi). The fiber layer was intended to separate the epithelium and the stroma of the reconstructed cornea yet to allow material transfer in between. The foam layer (bottom) was crosslinked by N-ethyl-N-[3-dimethylaminopropyl] carbodiimide (EDC), and N-hydroxy succinimide and after fiber deposition the bilayer was further stabilized with physical crosslinking (DHT method). The physical characterization of the foam showed that their pore sizes (10-200 &micro / m) and porosities (around 70%) were well within the desired range for typical tissue engineering applications. The cell free wet thicknesses of both single and bilayer constructs were close to that of the native stroma and light transmittance through these scaffolds was quite high (around 82% in the 500-700 nm range). The scaffolds were also tested for their stability and shown to be suitable for in vitro testing. In vitro studies were performed using retinal pigment epithelial cells (RPE, D407 cell line) and isolated human corneal keratocytes (HK) to reconstruct the epithelium and the stroma, respectively. Three types of constructs were prepared / only HK seeded Fo-Fi constructs, RPE-HK seeded CSXLFs, and RPE-HK seeded Fo-Fi constructs. All were shown to support cell attachment and promoted cell proliferation as was shown by the cells that covered the inner and outer spaces of the scaffolds. The fiber layer prevented the mixing of the two cell types, without hindering material exchange between them. Moreover, when co-cultured for 14 days, the keratocytes started to deposit collagen type I, a specific marker of these cells. In contrast, ECM deposition could not be observed in the single type cell seeded samples. The co-cultured bilayer construct was tested for suturability at the end of 31 days of in vitro incubation and it was shown that it could be successfully sutured without any major tears. Under the light of these results it was concluded that both the single layer and the bilayer constructs show promise for use as split thickness cornea replacements.

Cornea is the most exterior, avascular and transparent layer of the eye and is about 500 &micro / m in thick. It protects the eye from external objects and it is the main optical element of the eye refracting 70 % of the incoming light. After cataract, corneal diseases and wounds are the second leading cause of the blindness that affects more than 4 million people worldwide. For the highly damaged corneas where the corrections with spectacles or contact lenses cannot be achieved, tissue replacement is the only choice, and is done by cornea transplantation or keratoprostheses. However, due to limited number of donor corneas and the risk of infections during transplantation, and development of glaucoma, necrosis and other complications caused by the keratoprostheses, prevent them from meeting expectations. Tissue engineering is a promising field which emerged from biomaterials science and aims to replace, restore or improve the function of the diseased or injured tissues. In this method, after the production of an ideal scaffold that mimics the natural human tissue, cells of the host are isolated, increased in number, and seeded on the scaffold developed to serve as the microenvironment of the cells. In the current study a 3D corneal stroma replacement was designed to mimic the native stroma. It consisted of 4 films of patterned collagen or collagen blended with Elastin Like Recombinamer (ELR) stacked on top of each other and then crosslinked by dehydrothermal (DHT) treatment. The characterization of the films showed that the pattern fidelity was good and they did not deteriorate after crosslinking. Enzymatic and in situ degradation studies showed that the DHT treatment at 150 oC for 24 h (DHT150) was the optimum condition. The transparency of all the films was quite high where uncrosslinked (UXL) films and DHT150 Col:ELR films yielded the best results. The individual films and 3D construct of 4 stacked films were seeded with isolated human corneal keratocytes (HK) and cultured for 21 days. Cells attached and proliferated well on the single Col and Col:ELR films. However, the proliferation was higher on Col multilayer constructs than their Col:ELR counterparts. Cells were aligned along the patterns of the films while no significant alignment was observed for the cells on unpatterned films. Ultimate tensile strength (UTS) and Young&rsquo / s Modulus (E) of Col and Col:ELR films were significantly lower after a 30 day culture than that of unseeded films of Day 1. Transparency of the seeded Col:ELR films was superior to Col films over a 30 days test and quite close to the transmittance of the native human cornea. It was concluded that the Col and Col:ELR patterned films and their 3D constructs have a significant potential for use as a corneal stroma equivalent.

Three-dimensional (3D) tissue models have significantly improved our understanding of structure/function relationships and promise to lead to new advances in regenerative medicine. However, despite the expanding diversity of 3D tissue fabrication methods, in vitro approaches for functional assessments have been relatively limited. Herein, we describe the guidance of primary endothelial cells (ECs) in an agarose hydrogel scaffold that is chemically patterned with an immobilized concentration gradient of vascular endothelial growth factor 165 (VEGF165) using multiphoton laser patterning of VEGF165. This is the first demonstration of this patterning technology to immobilize proteins; and the first demonstration of immobilized VEGF165 to guide endothelial cell growth and differentiation in 3D environments. It is particularly compelling that this 3D hydrogels provide an excellent biomimetic environment for stem cell niche, thereby offering a new approach to study stem cell biology. In this thesis, we focused on the retinal stem cell niche, investigating cellular interactions between retinal stem and progenitor cells (RSPCs) and endothelial cells (ECs). By using this 3D in vitro model, we demonstrated the synergistic interactions between RSPCs and ECs wherein RSPCs migrated into 3D gels only in the presence of ECs and RSPCs stabilized EC tubular-like formations. Moreover, we characterized the contact-mediated effects of ECs on RSPC fate in terms of proliferation and differentiation.