Dual-function injectable angiogenic biomaterial for the repair of brain tissue following stroke.

Stroke is the primary cause of disability due to the brain's limited ability to regenerate damaged tissue. After stroke, an increased inflammatory and immune response coupled with severely limited angiogenesis and neuronal growth results in a stroke cavity devoid of normal brain tissue. In the adult, therapeutic angiogenic materials have been used to repair ischaemic tissues through the formation of vascular networks. However, whether a therapeutic angiogenic material can regenerate brain tissue and promote neural repair is poorly understood. Here we show that the delivery of an engineered immune-modulating angiogenic biomaterial directly to the stroke cavity promotes tissue formation de novo, and results in axonal networks along thee generated blood vessels. This regenerated tissue produces functional recovery through the established axonal networks. Thus, this biomaterials approach generates a vascularized network of regenerated functional neuronal connections within previously dead tissue and lays the groundwork for the use of angiogenic materials to repair other neurologically diseased tissues.

Utilizing cell-matrix interactions to modulate gene transfer to stem cells inside hyaluronic acid hydrogels.

The effective delivery of DNA locally would increase the applicability of gene therapy in tissue regeneration, where diseased tissue is to be repaired in situ. One promising approach is to use hydrogel scaffolds to encapsulate and deliver plasmid DNA in the form of nanoparticles to the diseased tissue, so that cells infiltrating the scaffold are transfected to induce regeneration. This study focuses on the design of a DNA nanoparticle-loaded hydrogel scaffold. In particular, this study focuses on understanding how cell-matrix interactions affect gene transfer to adult stem cells cultured inside matrix metalloproteinase (MMP) degradable hyaluronic acid (HA) hydrogel scaffolds. HA was cross-linked to form a hydrogel material using a MMP degradable peptide and Michael addition chemistry. Gene transfer inside these hydrogel materials was assessed as a function of polyplex nitrogen to phosphate ratio (N/P = 5 to 12), matrix stiffness (100-1700 Pa), RGD (Arg-Gly-Asp) concentration (10-400 µM), and RGD presentation (0.2-4.7 RGDs per HA molecule). All variables were found to affect gene transfer to mouse mensenchymal stem cells culture inside the DNA loaded hydrogels. As expected, higher N/P ratios lead to higher gene transfer efficiency but also higher toxicity; softer hydrogels resulted in higher transgene expression than stiffer hydrogels, and an intermediate RGD concentration and RGD clustering resulted in higher transgene expression. We believe that the knowledge gained through this in vitro model can be utilized to design better scaffold-mediated gene delivery for local gene therapy.

Directing three-dimensional multicellular morphogenesis by self-organization of vascular mesenchymal cells in hyaluronic acid hydrogels.

BACKGROUND: Physical scaffolds are useful for supporting cells to form three-dimensional (3D) tissue. However, it is non-trivial to develop a scheme that can robustly guide cells to self-organize into a tissue with the desired 3D spatial structures. To achieve this goal, the rational regulation of cellular self-organization in 3D extracellular matrix (ECM) such as hydrogel is needed. RESULTS: In this study, we integrated the Turing reaction-diffusion mechanism with the self-organization process of cells and produced multicellular 3D structures with the desired configurations in a rational manner. By optimizing the components of the hydrogel and applying exogenous morphogens, a variety of multicellular 3D architectures composed of multipotent vascular mesenchymal cells (VMCs) were formed inside hyaluronic acid (HA) hydrogels. These 3D architectures could mimic the features of trabecular bones and multicellular nodules. Based on the Turing reaction-diffusion instability of morphogens and cells, a theoretical model was proposed to predict the variations observed in 3D multicellular structures in response to exogenous factors. It enabled the feasibility to obtain diverse types of 3D multicellular structures by addition of Noggin and/or BMP2. CONCLUSIONS: The morphological consistency between the simulation prediction and experimental results probably revealed a Turing-type mechanism underlying the 3D self-organization of VMCs in HA hydrogels. Our study has provided new ways to create a variety of self-organized 3D multicellular architectures for regenerating biomaterial and tissues in a Turing mechanism-based approach.

Three dimensional tubular structure self-assembled by vascular mesenchymal cells at stiffness interfaces of hydrogels.

In this study, we report a rational and robust methodology to construct three dimensional (3D) tubular-structures solely by self-assembly of vascular mesenchymal cells (VMCs). Using the cell-laden hyaluronic acid hydrogel surrounded by cell-free gel with a higher stiffness, VMCs spontaneously migrated across the interface and assembled into 3D tubes, which composes of numerous cells. Based on turing instability which describes the reaction-diffusion processes of inhibitors and activators, this result of 3D tubular structure formation agrees with theoretical predictions from simulations of the reaction-diffusion of morphogens and cells under the initial conditions of patterned cell-laden hydrogel. We showed that this combination of theoretical prediction and experiments is able to produce multi-cellular 3D tubes with desired dimensions and determinate orientation in hydrogel mimicking the 3D features of tubular tissue. This work provides a reliable methodology for creating tubular structures with controllable sizes inside the 3D hydrogel through multi-cellular self-organization.

The spreading, migration and proliferation of mouse mesenchymal stem cells cultured inside hyaluronic acid hydrogels.

Synthetic hydrogel scaffolds that can be used as culture systems that mimic the natural stem cell niche are of increased importance for stem cell biology and regenerative medicine. These artificial niches can be utilized to control the stem cell fate and will have potential applications for expanding/differentiating stem cells in vitro, delivering stem cells in vivo, as well as making tissue constructs. In this study, we synthesized hyaluronic acid (HA) hydrogels that could be degraded through a combination of cell-released enzymes and used them to culture mouse mesenchymal stem cells (mMSC). To form the hydrogels, HA was modified to contain acrylate groups and crosslinked through Michael addition chemistry using non-degradable, plasmin degradable or matrix metalloproteinase (MMP) degradable crosslinkers. Using this hydrogel we found that mMSC proliferation occurred in the absence of cell spreading, that mMSCs could only spread when both RGD and MMP degradation sites were present in the hydrogel and that mMSCs in hydrogels with high density of RGD (1000 µm) spread and migrated faster and more extensively than in hydrogels with low density of RGD (100 µm).