Graduate Studies


First Advisor

Dr. Ali Tamayol

Second Advisor

Dr. Michael Sealy

Third Advisor

Dr. Ruiguo Yang

Date of this Version



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Mechanical Engineering and Applied Mechanics, Under the Supervision of Professor Ali Tamayol. Lincoln, Nebraska: July, 2019

Copyright 2019 Carina S. Russell


Tissue engineered scaffolds, reconstructive surgery, and bracing remain inadequate for the treatment of skeletal muscle defects, especially for volumetric muscle loss (VML). Skeletal muscle defects in VML varies on a case-by-case basis, most often in irregular and unpredictable geometries. Three-dimensional (3D) printing has emerged as one strategy that enables the fabrication of scaffolds that match the geometry of the defect site. However, with traditional 3D printing the time and facilities needed for imaging the defect site, post-processing to render computer-aided models, and printing a suitable scaffold prevent immediate reconstructive interventions post-traumatic injuries. In addition, the proper implantation of hydrogel-based scaffolds, which have generated promising results in vitro, is a significant challenge. To overcome these challenges, a new treatment paradigm is proposed in which adhesive gelatin-based hydrogels are printed directly into the defect area and photocrosslinked in situ. The overarching objective was to determine the proper gelatin methacryloyl (GelMA) concentration that exhibited the correct mechanical and physiochemical attributes to facilitate myogenesis. The printability was optimized to ensure continuous fiber deposition and that no back pressure build up from the nozzle could adversely affect the printing of complex structures. The adhesiveness of the bioink hydrogel to the skeletal muscles was assessed ex vivo to confirm that the hydrogel scaffold could adhere to skeletal muscle directly at a defect site. Cellular morphology and the promotion of myogenesis was inspected by staining. The suitability of the in situ bioprinted GelMA hydrogel scaffolds was successfully assessed in vitro for the encapsulation and delivery of skeletal muscle myoblasts. In addition, acellular gelatin-based hydrogel scaffolds were bioprinted in vivo onto a critical VML injury of 11-week old C57/Bl6 mice to examine inflammation, fibrosis formation, rupturing at the scaffold-muscle interface and promotion of remnant skeletal muscle hypertrophy. The developed portable bioprinter capable of 3D in situ printing of adhesive scaffolds successfully demonstrated precise filling of complex skeletal muscle tissue defects.

Advisor: Ali Tamayol