Collagen plays a central role as a biomaterial and as a scaffold in the regenerative tissue replacement strategies. Surgeries of load bearing tissues such as tendons and ligaments are occurring by hundreds of thousands annually and existing synthetic analogs of collagen have extremely poor biomechanical properties in comparison to the tissues they are targeted to replace. This shortcoming is due, in part, to the lack of orientation in hierarchical orders above the level of fibers.
This project will improve the strength and viscoelasticity of synthetic collagenous constructs to match those of natural counterparts by: a) an unconventional electrochemical process to attain an unprecedented level of molecular alignment and molecular packing density persistent across all levels of structural hierarchies, and, 2) the control of interfibrillar attachment by use of a biomimetic decorin-like linkage molecule. Phase 1 of proposed studies will optimize the mechanical strength and stiffness of the construct by elucidating the mechanisms by which collagen solutions achieve long-range order under the effect of weak currents applied directly to the solutions. The effects of electric current amplitude and collagen concentration on the hierarchical organization of collagen will be investigated to optimize the synthesis process. The strength of resulting oriented collagen gels will be improved by identifying the appropriate type and concentration of crosslinking amongst glutaraldehyde, genipin, nordihydroguaiaretic acid (NDGA) or ribose. Phase 2 will modulate the viscoelastic properties of oriented and crosslinked gels by decorin mimics consisting of dermatan sulfate attached to peptide motifs which selectively bind to type I collagen molecules. Mechanical properties of resulting synthetic constructs will be assessed at the bundle and the fiber levels by macroscale mechanical tests and atomic force microscopy, respectively, and compared to those of rat tendon, a reference natural tissue. The third phase is going to assess the phenotypic and genotypic response of tendon fibroblasts seeded in three-dimensional networks of the oriented collagenous construct in vitro, and, by assessing the non-enzymatic and enzymatic degradation rates of constructs in vitro.
The project will include the outreach component of familiarizing the minority middle-school student population with the emerging field of biomedical engineering. This aim will be attained by a summer activity during which students will conduct hands-on projects in the area of biomedical engineering through coordination with the Minority Engineering Program at Purdue University. Broader impacts will be further strengthened by creation of a laboratory module in an undergraduate biomechanics/biomaterials laboratory by incorporating outcomes of the proposed research and by way of accommodating 9 undergraduates for summer research during the course of the project through Summer Undergraduate Fellowship program (SURF) at Purdue.
In the overall, the proposed study will develop a novel fabrication process towards the design of a new biomaterial which may play a key role in creating strategies towards replacement of tissues such as tendons, ligaments, skin, cornea and vascular walls.
Collagen is a molecule that is one of the basic building blocks of tissues that make up bones, ligaments and tendons. Akin to a brick assembly resulting in a wall, assembly of collagen molecules results in load bearing tissues. Surgeries of load bearing tissues such as tendons and ligaments occur by hundreds of thousands annually and mechanically robust biomaterials are needed for their repair. Collagen that is reconstituted in the lab generally has poor biomechanical properties in comparison to the tissues it is targeted to replace. The collagen fibrils are disordered in such weak collagen gels. Providing uniform alignment and close packing of molecules and fibrils would provide a collagen-based biomaterial that is stronger. Activities: The major intellectual merit of the project was to improve the strength and viscoelasticity of synthetic collagen biomaterial to match those of natural counterparts by: a) a process which involves application of electric currents to collagen solutions to induce a high level of molecular alignment and packing density, and, 2) the control of interfibrillar attachment by use of a biomimetic molecule which emulates a naturally occurring molecule called as decorin. The studies optimized the mechanical strength and stiffness of the construct by controlling the crosslinking conditions and by incorporation of the decorin-mimic. Mechanical properties of resulting constructs were assessed at the macroscale and at molecular scale by mechanical tests and atomic force microscopy, respectively, and compared to those of rat tendon, a reference natural tissue. Tendon fibroblasts and mesenchymal stem cells were seeded on the material and their responses were assessed. A biophysical molecular model was established to explain the mobility of collagen molecules under the effect of electrical current. Outcomes: One Ph.D. dissertation, five peer-reviewed manuscripts and five conference abstracts resulted from this project. Broader Impact: Male and female undergraduates were continually involved in project activities throughout the project period. The key deliverable was the obtainment of a collagen-based biomaterial in thread form which had mechanical properties matching those of the tendons. It was also shown that the incorporation of the decorin mimic had a profound effect on the viscoelastic behavior of the material. Cell assays indicated that the material is receptive to cell migration. Finally, the biophysical model demonstrated that the electrical forces generated by the electric current were sufficient to mobilize the molecules in the viscous environment in which they reside. Overall, the proposed study developed a novel fabrication process towards the design of a new biomaterial that may play a key role in creating strategies towards replacement of tissues such as tendons, ligaments, skin, cornea and vascular walls.
