Over one million meniscal surgeries are performed in the United States every year, where the most common treatment option following a meniscal tear is a partial meniscectomy. Meniscal tissue removal, however, results in a proportional increase in contact stresses on the tibial plateau and predisposes the patient to osteoarthritis. As with other dense fibrous connective tissues, the intrinsic healing of the meniscus is severely limited due to poor vascularity and hypocellularity. Previous research indicates that the high extracellular matrix (ECM) density in the mature meniscus serves as a physical hurdle to cell migration and proliferation, ultimately limiting endogenous repair. To address this limitation, we have developed electrospun fibrous scaffolds to locally deliver collagenase, a matrix-degrading enzyme, in combination with platelet-derived growth factor-AB (PDGF-AB), a known chemokine, to enhance cell mobility and recruitment, respectively, to the wound interface.
Fibrous scaffolds were synthesized via the simultaneous electrospinning of poly(ε-caprolactone) (PCL) for scaffold stability, poly(ethylene oxide) (PEO) for quick release (~hours) of collagenase, and hydroxyethyl methacrylate functionalized hyaluronic acid (HA) for moderate release (~days to weeks) of PDGF-AB onto a common collecting mandrel. Individual fiber components were successfully visualized using encapsulated fluorescent dyes for each fiber component. After electrospinning, scaffolds were evaluated in vitro to determine scaffold stability, biomolecule release profiles, and released biomolecule activity. As expected, the PEO fiber fraction completely dissolved in vitro within 24 hours, with a majority of the loaded collagenase, approximately 60%, released within one hour. In order to delay the initial release of collagenase to less than 20% within the first hour, an extra PCL-only layer was electrospun before and after electrospinning the other fiber fractions. The in vitro protease activity of the released samples was confirmed using a matrix metalloprotease-sensitive fluorogenic peptide substrate. Furthermore, a two-week in vivo subcutaneous rat model, in which fibrous samples were sandwiched between two pieces of bovine meniscal tissue, indicated that the delivery of collagenase from tri-component fibrous scaffolds promoted increased cellularity at the wound interface. Preliminary results investigating PDGF-AB release from the HA fiber fraction show controlled release over approximately two weeks, with ongoing work evaluating PDGF-AB bioactivity. The combined delivery of collagenase and PDGF-AB from electrospun fibrous scaffolds is a promising approach to promote tissue integration at the site of a meniscal tear, where the release profile of both biomolecules can be controlled individually. Ongoing work is evaluating the effect of dual biomolecule delivery on cellular mobility and migration to the repair site in vivo.