Dual Extrusion Patterning Drives Tissue Development Aesthetics and Shape Retention in 3D Printed Nipple-Areola Constructs.

Breast cancer and its most radical treatment, the mastectomy, significantly impose both physical transformations and emotional pain in thousands of women across the globe. Restoring the natural appearance of a nipple-areola complex directly on the reconstructed breast represents an important psychological healing experience for these women and remains an unresolved clinical challenge, as current restorative techniques render a flattened disfigured skin tab within a single year. To provide a long-term solution for nipple reconstruction, this work presents 3D printed hybrid scaffolds composed of complementary biodegradable gelatin methacrylate and synthetic non-degradable poly(ethylene) glycol hydrogels to foster the regeneration of a viable nipple-areola complex. In vitro results showcased the robust structural capacity and long-term shape retention of the nipple projection amidst internal fibroblastic contraction, while in vivo subcutaneous implantation of the 3D printed nipple-areola demonstrated minimal fibrotic encapsulation, neovascularization, and the formation of healthy granulation tissue. Envisioned as subdermal implants, these nipple-areola bioprinted regenerative grafts have the potential to transform the appearance of the newly reconstructed breast, reduce subsequent surgical intervention, and revolutionize breast reconstruction practices.

Liposomal SDF-1 Alpha Delivery in Nanocomposite Hydrogels Promotes Macrophage Phenotype Changes and Skin Tissue Regeneration.

Skin regeneration in chronic wounds is often delayed due to persistent inflammation induced by underlying conditions such as diabetes. This effect is mediated, in part, by macrophages present in the wound, which can be stimulated to adopt either pro- or anti-inflammatory phenotypes depending on the status of the local microenvironment. In this work, the prohealing chemokine stromal cell-derived factor-1 alpha (SDF-1α) is controllably released from a hydrogel-based biomaterial to promote skin tissue regeneration and wound closure. This innovative nanocomposite hydrogel system releases liposomal stromal cell-derived factor-1 alpha (lipoSDF) as a new treatment approach for dorsal full-thickness skin wounds in wild-type and diabetic mice. Using this strategy, the recruitment and polarization of macrophages primarily of the anti-inflammatory phenotype were observed, along with a decreased amount of open wound surface area in diabetic mice after 28 days. This was accompanied by histological observations of increased epidermal stratification and dermal angiogenesis. These findings represent an important step of investigation distinctive in its field for developing immunomodulatory biomaterials that are able to influence macrophage phenotype and promote healing as hydrogel-based wound dressings.

Fabrication of centimeter-sized 3D constructs with patterned endothelial cells through assembly of cell-laden microbeads as a potential bone graft.

Modular tissue engineering is a promising biofabrication strategy to create engineered bone grafts in a bottom-up manner, in which cell-laden micro-modules are prepared as basic building blocks to assemble macroscopic tissues via different integrating mechanisms. In this study, we prepared collagen microbeads loaded with human bone marrow derived mesenchymal stem cells (BMSCs) using a microfluidic approach. The cell-laden microbeads were characterized for size change, cell activity, osteogenesis, as well as their self-assembly properties to generate centimeter-sized constructs. Moreover, using the cell-laden beads as a supporting medium, induced pluripotent stem cell-derived endothelial cells (iPSC-EC) were patterned inside bead aggregates through extrusion-based 3D printing. This fabrication approach that combines modular tissue engineering and supports 3D printing has the potential to create 3D engineered bone grafts with a pre-existing, customized vasculature.

A liposome/gelatin methacrylate nanocomposite hydrogel system for delivery of stromal cell-derived factor-1α and stimulation of cell migration.

Chronic, non-healing skin and soft tissue wounds are susceptible to infection, difficult to treat clinically, and can severely reduce a patient's quality of life. A key aspect of this issue is the impaired recruitment of mesenchymal stem cells (MSCs), which secrete regenerative cytokines and modulate the phenotypes of other effector cells that promote healing. We have engineered a therapeutic delivery system that can controllably release the pro-healing chemokine stromal cell derived factor-1α (SDF-1α) to induce the migration of MSCs. In order to protect the protein cargo from hydrolytic degradation and control its release, we have loaded SDF-1α in anionic liposomes (lipoSDF) and embedded them in gelatin methacrylate (GelMA) to form a nanocomposite hydrogel. In this study, we quantify the release of SDF-1α from our hydrogel system and measure the induced migration of MSCs in vitro via a transwell assay. Lastly, we evaluate the ability of this system to activate intracellular signaling in MSCs by using Western blots to probe for the phosphorylation of key proteins in the mTOR pathway. To our knowledge, this is the first study to report the delivery of liposomal SDF-1α using a nanocomposite approach. The results of this study expand on our current understanding of factors that can be modified to affect MSC behavior and phenotype. Furthermore, our findings contribute to the development of new hydrogel-based therapeutic delivery strategies for clinical wound healing applications. STATEMENT OF SIGNIFICANCE: Chronic, non-healing wounds promote an inflammatory environment that inhibits the migration of mesenchymal stem cells (MSCs), which secrete pro-healing and regenerative cytokines. The goal of this project is to apply principles of tissue engineering to achieve controllable release of the pro-healing chemokine SDF-1α to modulate the intracellular signaling and migratory behavior of MSCs. In this work, we introduce a nanocomposite strategy to tailor the release of SDF-1α using a liposome/gelatin methacrylate hydrogel approach. We are the first group to report the delivery of liposomal SDF-1α using this strategy. Our findings aim to further elucidate the role of MSCs in directing wound healing and guide the development of immunomodulatory and therapeutic delivery strategies for clinical wound healing applications.

Current and Future Perspectives on Skin Tissue Engineering: Key Features of Biomedical Research, Translational Assessment, and Clinical Application.

The skin is responsible for several important physiological functions and has enormous clinical significance in wound healing. Tissue engineered substitutes may be used in patients suffering from skin injuries to support regeneration of the epidermis, dermis, or both. Skin substitutes are also gaining traction in the cosmetics and pharmaceutical industries as alternatives to animal models for product testing. Recent biomedical advances, ranging from cellular-level therapies such as mesenchymal stem cell or growth factor delivery, to large-scale biofabrication techniques including 3D printing, have enabled the implementation of unique strategies and novel biomaterials to recapitulate the biological, architectural, and functional complexity of native skin. This progress report highlights some of the latest approaches to skin regeneration and biofabrication using tissue engineering techniques. Current challenges in fabricating multilayered skin are addressed, and perspectives on efforts and strategies to meet those limitations are provided. Commercially available skin substitute technologies are also examined, and strategies to recapitulate native physiology, the role of regulatory agencies in supporting translation, as well as current clinical needs, are reviewed. By considering each of these perspectives while moving from bench to bedside, tissue engineering may be leveraged to create improved skin substitutes for both in vitro testing and clinical applications.