Injectable dense collagen gel scaffolds with predictable microstructure via aspiration-ejection

by Neysan Kamranpour

Institution: McGill University
Department: Department of Mining and Materials
Degree: M. Eng.
Year: 2015
Keywords: Engineering - Materials Science
Record ID: 2057933
Full text PDF: http://digitool.library.mcgill.ca/thesisfile130360.pdf


Injectable dense collagen gel (I-DC) scaffolds were produced via a gel aspiration-ejection (GAE) process with the intent of producing synthetic tissue grafts that are easily delivered into a patient, and attain a more relevant tissue-like microstructure. An automated GAE system was developed that applies a vacuum to generate a pressure differential to aspirate precursor highly hydrated collagen (HHC) hydrogels gel out of a mold and into a capillary of predetermined diameter. Upon reversal of the pressure, I-DC gels of controlled collagen fibrillar densities (CFDs) and microstructures can be controllably ejected. The GAE system is designed to reduce user fatigue and provide precise control to controllably deliver the scaffold. Characterization experiments were conducted to determine the versatility and reproducibility of the I-DC processing technique. It was shown that consistent CFDs of I-DC gels were produced by controlling the aspiration needle diameter (gauge sizes 8-14) and the properties of the HHC precursor material (collagen concentration and/or mold geometry). Microstructural analysis with Scanning Electron Microscopy and Non-linear Laser Scanning Microscopy quantitatively and qualitatively determined the microstructural changes imparted onto an I-DC gel compared to a dense collagen (DC) gel scaffold prepared using the Plastic Compression (PC) method, previously developed. It was determined that the dispersion of collagen fibrils was significantly reduced in the I-DC gels compared to that in DC gel due to a two-dimensional compaction process.Tensile mechanical tests were conducted to determine the effect of CFD and microstructure on the macroscopic mechanical properties of the I-DC gels. There were significant increases in I-DC gel apparent modulus and ultimate tensile strength with CFD.I-DC gels were finally seeded with mesenchymal stem cells and cultured in osteogenic and non-osteogenic media. Cell proliferation and differentiation experiments showed that cells survived the processing conditions and successfully proliferated along the altered microstructure. Furthermore, cells cultured in the osteogenic media differentiated and survived where nutrients were available, and those cultured in the non-osteogenic media continued to proliferate throughout the thickness of the gel. There was a greater extent of osteoblastic differentiation of cells when seeded in I-DC gels that provided a synergistic combination of increased fibrillar alignment and physiologically relevant CFD. Les échafaudages de gel collagène dense injectable (I-DC) sont produits grâce à un procédé d'aspiration-éjection du gel (GAE) dans le but d'obtenir des greffes de tissus facilement administrables au patient; celles-ci présentent une microstructure de type tissulaire plus pertinente. On a développé un système automatisé de GAE qui crée un vide pour générer un différentiel de pression, aspirant le précurseur hydraté d'hydrogel (HHC) hors du moule et le transférant dans un capillaire au diamètre prédéterminé. Lorsque la pression est…