Hybrid bioengineering of tubular constructs for esophagus by melt-drawing and 3D bioprinting
Tan, Yu Jun
Date of Issue2018-01-16
School of Mechanical and Aerospace Engineering
Tissue engineering (TE) offers an important alternative for surgical replacement of diseased or traumatized esophagus. The TE replacement can replicate the native esophagus in shape and performance. This dissertation describes the fabrication and characterization of two key components in esophageal TE, i.e. the muscle and the epithelium. Two different additive fabrication techniques are investigated due to the inherent diversity in structure of an esophagus. Customizations of dimension and mechanical properties are made possible by the additive fabrication, which are vital factors for implantation across ages and genders. Tubular poly(L-lactide-co-e-caprolactone) (PLC) scaffold is fabricated by a melt-drawing method to mimic the structure of circular muscles. The microfibrous solid scaffold serves as exterior of the TE replacement, which is strong and elastic circumferentially to accommodate bolus. Moreover, it consists of highly aligned microfibers in the circumferential direction with a uniform distribution of fiber diameters, which allows the muscle cells to grow along the fiber alignment direction. The crystallinity of PLC fibers increases with an increasing melt-drawing speed due to the strain-induced crystallization. The modulus and the strength are increased with an increase in crystallinity of the PLC scaffold. Tensile properties of the tubular scaffold are comparable to those of the human esophagus in the circumferential direction, which also can be finetuned by adjusting the melt-drawing fabrication parameters. Furthermore, tubular scaffolds with varying diameters and lengths are fabricated. In addition, 3D bioprinting is employed to regenerate a layer of cell-laden, folded epithelium in a lumen of esophagus. A new bioink using cell-laden microspheres (CLMs) with a thin encapsulation of agarose-collagen blend hydrogel (AC blend hydrogel) is introduced. Highly porous microspheres provide high specific surface areas for anchorage-dependent cells to attach, infiltrate and proliferate before printing. AC blend hydrogel allows a good printability of CLMs, with immediate gelation of the construct upon printing on the chilled build platform. Tightly packed construct is bioprinted with high stacking ability using a micropipette extrusionbased method. The mechanical strength of the bioprinted construct is considerably enhanced when compared to that with just AC blend hydrogel. The bioprinted cells proliferate and maintain high viability for up to 2 weeks. In vitro performance of individual components of a hybrid esophageal TE construct is successfully illustrated. The hybrid bioengineering of muscle cell-seeded exterior tubular scaffold and 3D bioprinted interior folded epithelium in the lumen have taken a great step towards functional esophageal TE.