Tissue engineered vascular grafts (TEVGs) are biodegradable scaffolds intended to replace autologous and synthetic grafts that suffer from suboptimal performance. The majority of TEVG approaches require the incorporation of therapeutic cells to prevent acute thrombosis and promote endogenous cell infiltration followed by tissue remodelling. This project sought to investigate a novel autologous cell source for TEVGs: liposuction aspirate fluid (LAF). LAF would represent a significant advancement as an autologous cell base for TEVGs as LAF requires minimal manipulation, therefore bypassing numerous regulatory issues and presenting with low processing costs. The viability of LAF to act as a cell source for TEVGs was to be investigated by (1) characterisation of LAF cells, (2) modification of the scaffold to best promote positive vascular remodelling, (3) in vivo assessment of the LAF functionalised TEVGs in a small animal model, and (4) scaling of the technology for assessment in a large animal model.
New knowledge generated at the beginning of this action has meant that revisions to objectives 1 and 2 were required. Work conducted by the secondment host lab (Vorp Lab) immediately prior to the commencement of this action identified that adipose stem cells (the primary therapeutic cell found in LAF) derived from elderly and/or diabetic patients are not capable of acting as an effective therapeutic base for TEVGs as they have reduced anti-thrombotic and cell-signalling capabilities. As these patient groups represent the vast majority of patients requiring TEVGs, an autologous cell based approach for TEVGs is not a viable option. These points are addressed in our review article. A further obstacle encountered was the difficulty in obtaining quality PEUU scaffolds. For this reason, an alternate scaffold type has been investigated. Specifically, Bombex mori silk. The action has therefore revised the first 2 objectives of the action to investigate (1) an alternative method of scaffold fabrication and (2) the use of allogeneic adipose derived mesenchymal stem cells (ADMSCs) and their secreted extracellular vesicles (EVs) as a therapeutic base for TEVGs. Furthermore, objective 4 has been abbreviated due to the prohibitive cost of acquiring and maintaining large animals. This study therefore reduced the number of large animal implants from 8 to 1.
Objective 1 (Revised): Design a silk based scaffold for use as a TEVG that can be fabricated in-house in a repeatable manner. This work has been completed and a silk based scaffold has been developed in collaboration with Prof Biman Mandal of the Indian Institute of Technology Guwahati.
Objective 2 (Revised): Investigate the viability of employing commercially available ADMSCs and ADMSC derived EVs as a therapeutic base for TEVGs via in vitro cell-based assays. This work has been completed and demonstrated the positive therapeutic effects of administering ADMSC conditioned media or EVs to the vascular cells necessary for TEVG remodelling.
Objective 3: In vivo assessment of a novel functionalised TEVG in a small animal model. Specifically, incorporate ADMSCs and ADMSC-EVs into the silk based scaffold and perform an in vivo assessment of remodelling in an aortic interposition murine model. This work has been completed and demonstrated that incorporating EVs into silk based scaffolds improves graft patency and remodeling compared to blank and ADMSC seeded scaffolds.
Objective 4 (Abbreviated): Scale the technology to a size appropriate for use in humans and perform an in vivo assessment of the functionalised scaffolds in a large animal model. The technology to incorporate cells into silk based scaffolds has been successfully scaled and allows for even seeding of a human sized scaffold. An ADMSC seeded scaffold was implanted as a carotid interposition graft in a sheep for 10 weeks. The graft remained patent and demonstrated positive matrix remodelling.
