Promoting Regenerative Tendon Healing Using Materials Design Strategies
Poly(ethylene glycol) (PEG) hydrogels provide biophysical and biochemical cues that promote a regenerative phenotype of tenocytes in vivo. Resident tendon fibroblasts, tenocytes, are isolated from the flexor digitorum longus (FDL) tendon. Tenocytes are then encapsulated into a poly(ethylene glycol) (PEG) hydrogel where biochemical and biophysical cues such as cell adhesive peptide and crosslinker are modulated to alter cell phenotype and function. A design of experiments approach is utilized to identify which combination(s) of cell adhesive peptide, concentration of cell adhesive peptide, and crosslinker promote a regenerative phenotype in vitro. The hydrogels will then be examined in vivo to assess healing outcomes.
Collaborator: Prof. Alayna Loiselle
When a tendon is injured, movement becomes limited and the injury becomes a source of chronic pain. These injuries impact over 15 million people annually, resulting in need for costly medical treatment. Despite medical efforts, healing of injured tendons rarely results in full restoration of function and reinjuries are prominent. Limited restoration of function is attributed to the fibrotic healing of tendon that results in the development of scar tissue at the injury site, rather than regenerative healing that promotes restoration of tendon function. To improve the quality of life after recovery from tendon injury, methods for promoting regenerative healing are critical. In this respect, we are developing regenerative strategies by designing materials encompassing biochemical signaling, mechanical stimulation, and systemically targeted drug delivery.
One route to regenerative tendon healing we are exploring is the integration of biochemical cues in an engineered extracellular matrix (eECM). The tendon has been identified as a heterogeneous tissue where multiple resident tendon cell (tenocyte) subpopulations are present. However, how the tenocyte subpopulation(s) shift the balance from fibrotic healing towards regenerative healing remains unknown. Recent work from our collaborators in the Loiselle lab has established a novel murine model of enhanced tendon healing. Here, we will characterize the enhanced healing milieu to identify divergences from the fibrotic healing environment. This information will then be leveraged to establish success metrics to recapitulate the enhanced healing environment and design criteria for our eECM. This work will improve our understanding of cell-matrix interactions, the spatiomolecular map of enhanced tendon healing, and will establish important in vitro to in vivo success criteria, ultimately leading to improvements in tendon healing.
Poly(ethylene glycol) (PEG) hydrogels that contain an MMP degradable crosslinker support cell spreading. Poly(ethylene glycol) (PEG) is a bioinert material that can be functionalized with norbornene using standard carbodiimide chemistry. Through cysteine thiol-ene reactions, multiple adhesion ligands and crosslinkers can be modulated to understand individual effects and interactions (a). At Day 3 post-encapsulation of 3T3 cells, cell spreading is observed in the matrix metalloproteinase (MMP) cleavable hydrogel but not the non-matrix metalloproteinase cleavable hydrogel (b). Matrix biochemical and biophysical cues interact to alter cell phenotype and function.
Beyond promoting regenerative healing through biochemical signals, we are also exploring the integration of mechanical cues into the eECM. Since their primary function is force transmission from muscle to bone, tendons
undergo large mechanical stresses regularly. It has been previously demonstrated that loading promotes restored function and improves healing in many rehabilitative strategies for injured tendons. Therefore, it is hypothesized that simulating rehabilitative mechanical cues and guiding structurally-relevant orientation of tenocytes from within an eECM will promote higher levels of restored function than a static, isotropic eECM for in vitro regenerative tendon healing models. In this respect, we are designing a hydrogel eECM that promotes anisotropic alignment of tenocytes and stimuli-responsive eECM for on-demand mechanical actuation.