The ultimate goal of this study is to regenerate lost dental pulp and dentin via stem/progenitor cell-based approaches and tissue engineering technologies. In this study, we tested the possibility of regenerating vascularized human dental pulp in emptied root canal space and producing new dentin on existing dentinal walls using a stem/progenitor cell-mediated approach with a human root fragment and an immunocompromised mouse model. Stem/progenitor cells from apical papilla and dental pulp stem cells were isolated, characterized, seeded onto synthetic scaffolds consisting of poly-D,L-lactide/glycolide, inserted into the tooth fragments, and transplanted into mice. Our results showed that the root canal space was filled entirely by a pulp-like tissue with well-established vascularity. In addition, a continuous layer of dentin-like tissue was deposited onto the canal dentinal wall. This dentin-like structure appeared to be produced by a layer of newly formed odontoblast-like cells expressing dentin sialophosphoprotein, bone sialoprotein, alkaline phosphatase, and CD105. The cells in regenerated pulp-like tissue reacted positively to anti-human mitochondria antibodies, indicating their human origin. This study provides the first evidence showing that pulp-like tissue can be regenerated de novo in emptied root canal space by stem cells from apical papilla and dental pulp stem cells that give rise to odontoblast-like cells producing dentin-like tissue on existing dentinal walls.

We have proposed engineering tissues by the incorporation and sustained release of plasmids encoding tissue-inductive proteins from polymer matrices. Matrices of poly(lactide-co-glycolide) (PLG) were loaded with plasmid, which was subsequently released over a period ranging from days to a month in vitro. Sustained delivery of plasmid DNA from matrices led to the transfection of large numbers of cells. Furthermore, in vivo delivery of a plasmid encoding platelet-derived growth factor enhanced matrix deposition and blood vessel formation in the developing tissue. This contrasts with direct injection of the plasmid, which did not significantly affect tissue formation. This method of DNA delivery may find utility in tissue engineering and gene therapy applications.

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Regenerative medicine aims to create functional tissue replacements, typically through creating a controlled environment that promotes and directs the differentiation of stem or progenitor cells, either endogenous or transplanted. Scaffolds serve a central role in many strategies by providing the means to control the local environment. Gene delivery from the scaffold represents a versatile approach to manipulating the local environment for directing cell function. Research at the interface of biomaterials, gene therapy, and drug delivery has identified several design parameters for the vector and the biomaterial scaffold that must be satisfied. Progress has been made towards achieving gene delivery within a tissue engineering scaffold, though the design principles for the materials and vectors that produce efficient delivery require further development. Nevertheless, these advances in obtaining transgene expression with the scaffold have created opportunities to develop greater control of either delivery or expression and to identify the best practices for promoting tissue formation. Strategies to achieve controlled localized expression within the tissue engineering scaffold will have broad application to the regeneration of many tissues, with great promise for clinical therapies.