The goal of this project is to develop novel synthetic scaffolds that not only recapitulate the ECM environment structurally and mechanically but also integrate bioactive signaling motifs to promote cell adhesion, proliferation and differentiation. This award has enabled the development of three types of novel materials that are mechanically robust and biologically active.

 The first type of material is PCL-derived random copolymers containing cyclic ketals and readily accessible crosslinking moieties (ECT2-AC). UV-initiated radical polymerization of ECT2-AC resulted in a crosslinked network that is cytocompatible, mechanically compliant and exhibit unique shape memory properties. cultured mesenchymal stem cells. The crosslinkable polyester copolymers can be potentially used as tissue engineering scaffolds and minimally invasive medical devices.

Separately, we have demonstrated the efficient synthesis of ultrahigh molecular weight multiblock copolymers via interfacial bioorthogonal polymerization employing the rapid cycloaddition of s-tetrazines (Tz) with strained trans-cyclooctenes (TCO). The step growth polymerization is controlled by the diffusion of the monomeric species. Using simple equipment and without additional processing steps, robust micron-diameter polymer fibers were directly pulled from the oil/water interface using tetrazine and trans-cyclooctene-functionalized monomeric building blocks. Monomers with unprotected peptide side chains are fully compatible with the polymerization, and the resulting polymers mimic fibrous proteins found in the extracellular matrix, providing guidance cues for cell attachment and elongation.

 We have also produced water soluble, covalently crosslinkable copolymers with a multivalent presentation of peptidic signals. The PAA-based bioactive and chemically reactive polymers were synthesized via atom transfer radical polymerization, followed by post-polymerization polymer modification. The resultant peptide-conjugated, chemically crosslinkable copolymer was mixed with thiolated hyaluronic acid (HA-SH) to form a macroscopic hydrogel with tunable ligand density/clustering and matrix stiffness. LNCaP prostate cancer cells encapsulated in HA-PolyRGD gels as dispersed single cells formed multicellular tumoroids and interact with the matrix through integrin binding with the multivalent RGD. Such an interaction increased cellular metabolism, promoted the development of larger tumoroids and enhanced the expression of E-cadherin and integrins.

By serendipity, we discovered that the alteration of the fiber diameter of electrospun scaffold create enough disturbances in epithelial organization and scattering. PCL-based scaffolds with an average fiber diameter of 0.5 µm and 5 µm were produced via electrospinning. Cell-adhesive peptide motifs were conjugated to the fiber surface to facilitate cell attachment. Madin-Darby Canine Kidney (MDCK) cells grown on these substrates showed distinct phenotypes. On 0.5 µm substrates, cells grew as compact colonies with an epithelial phenotype. On 5 µm scaffolds, cells were more individually dispersed and appeared more fibroblastic. Upon addition of hepatocyte growth factor (HGF), an EMT inducer, cells grown on the 0.5 µm scaffold underwent pronounced scattering, as evidenced by the alteration of cell morphology, localization of focal adhesion complex, weakening of cell-cell adhesion, and upregulation of mesenchymal markers. By contrast, HGF did not induce a pronounced scattering of MDCK cells cultured on the 5.0 µm scaffold. This result underscores the importance of physical properties of the native ECM is defining tissue morphogenesis and disease progression.

In summary, our innovation has led to the development of novel biomimetic polymers, gels and fibrous scaffolds. These materials provide a powerful platform for engineering replacement tissues or tissue models. Our work has been summarized in various publications (11 total) in scientific journals. This award has provided partial support for 2 postdoctoral researcher (one female), 6 PhD students (3 female) and 2 undergraduate students (1 female, 1 underrepresented minority). Discoveries made from this project have been integrated in multiple hands-on lab demonstrations to K-12 students. Results collected from this project have also been incorporated in graduate/senior undergraduate level biomaterials courses at the University of Delaware.

Last Modified: 09/29/2016
Modified by: Xinqiao Jia