Angiogenic and anti-microbial supports for pulp regeneration

Project Summary: The dental pulp is the vital microenvironment in the tooth, harboring blood vessels and nerves, not to mention odontoblasts that interface with the dentinal tubules. Trauma or bacterial infection may inflame the dental pulp, creating extreme pain. Extirpating the inflamed pulp (and potentially replacing it with inert materials) ameliorates the pain, but the procedure leaves a devitalized tooth. An alternative is possible in juvenile patients, called over-instrumentation (OI). During OI, the pulpal chamber is exposed to the peripheral circulation post-pulpectomy. As long as the apical papilla is intact, some tissue regeneration takes place in the pulpal canal subsequently — although the disorganized tissue does not mimic native soft tissue. In adults in particular, OI results in non-functional pulpal ossification. Another concern in endodontic procedures is occurrence/recurrence of colonization by oral bacteria. Such infections may prolong and exacerbate pulpal inflammation. A material- based formulation is proposed that can (a) promote vascularized soft-tissue regeneration in the pulp, while (b) resisting bacterial infection. Our strategy rests on self-assembling peptide hydrogels — a class of supramolecular materials that can be injected in vivo while keeping their gel-like properties. The materials consist of canonical amino acids and are biocompatible. Such materials need to provide both mechanical support and biological cues for tissue ingrowth. Somewhat counter-intuitively, a self-assembling peptide hydrogel, without added growth factors or exogenous cells, demonstrated formation of vascularized soft-tissue in a canine pulpectomy model in 28 days. In a separate study, a different cationic amphiphilic hydrogel belonging to the same platform, showed efficacy in inhibiting bacterial growth via membrane permeabilization. In this proposal, a combinatorial treatment modality will be tested for its effectiveness in achieving the dual goals described above. A mechanistic puzzle that these projects would help solve is the lineage/source of infiltrating cells and evolution of the cellular milieu in the pulpal canal after pulpectomy and implantation of soft biomimetic hydrogels. Characterization of the long- term maturation of the vascularized soft tissue promoted by such hydrogels is another target. The multi- disciplinary project proposed in this Bioengineering Research Grant application would bring together a chemist and bioengineer (PI V.A.K., an early-stage investigator), a specialist in oral bacterial colonies (co-I C.C.), and an endodontist (co-I E.S.), to solve an enduring challenge: regenerating biomimetic vascularized soft tissue post- pulpectomy. In vitro mechanistic analyses, in vivo characterization of infiltrating cells, and histologic/radiographic identification of long-term evolution of the pulpal soft tissue and the pulp-dentin complex would build on published studies and extensive preliminary data. Even if the proposed experiments are only partially successful, we would learn about tissue-material interaction in the context of dental pulp. Success of the aims would produce compelling data for a cell-free, growth-factor-free, off-the-shelf material formulation ideal for application in endodontic settings and improve clinical outcomes in millions of patients needing pulpectomy.