3D polymeric scaffolds towards biomedical applications

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI--COLUMBIA AT REQUEST OF AUTHOR.] How can research on mechanical engineering and materials science contribute to human health? The fabrication of biomedical scaffolds could be a good entry point. Scaffolds are broadly applied in biomedical fields with multiple functions, such as repair, replacement, and stimulation and monitoring when they are integrated with electronic/optoelectronic devices. Besides biocompatible, the scaffolds should be soft and in form of three-dimensional (3D) structures in order to mechanically and geometrically match the natural tissues and organs. Polymers are the most promising candidate materials for the scaffold fabrication. Compared to metals and ceramics, substantial polymers have biocompatibility and all of them have low Young's modulus and high processability. Benefiting from the high processability, a variety of approaches can be used to shape polymeric scaffolds with 3D architectures. The major three approaches are flexibility, stress induced assembly, and printing. However, none of them is flawless: (1) For flexibility, the scaffolds that integrated with electronic devices have large thickness which exponentially lower the flexibility. (2) For stress-induced assembly, the assembly operation requires complicated actuation equipment and the assembled scaffolds are usually tethered on cumbersome elastomeric substrates. (3) For printing, few of scaffolds fabricated by emerging 4D printing technologies are responsive to biocompatible stimuli. This dissertation aims at addressing these three problems. First, a new device structure, i.e., lateral electrode, is proposed to reduce the thickness and then improve the flexibility of the scaffolds with electronics, which is validated by fabricating flexible photodetectors on polyimide substrates. The photodetectors have excellent flexibility and can be bent to 3D structures. Second, a new stress-induced assembly strategy, i.e., responsive buckling, is developed in which the elastomeric substrates are replaced with deft responsive polymeric substrates. Various 3D polymeric scaffolds either with or without electronic devices are assembled when the substrates are exposed to external stimuli without manual intervention. This strategy is first verified by an acetone responsive organogel and then developed toward biomedical applications by using a body temperature responsive hydrogel. Third, a new shape memory polymer, i.e., poly (glycerol dodecanoate) acrylate (PGDA), whose transition temperature is in the range of 20-37 [degrees]C, is exploited for 4D printing of scaffolds. Because of the propriate transition temperature, the shape memory process of the scaffolds can be completed by using room temperature and body temperature as stimuli, which are harmless for human body. Moreover, a variety of delicate 3D structures including an artery-like tube are printed.