Cell-Biomaterial constructs for wound healing and skin regeneration.

Over the years, conventional skin grafts, such as full-thickness, split-thickness, and pre-sterilized grafts from human or animal sources, have been at the forefront of skin wound care. However, these conventional grafts are associated with major challenges, including supply shortage, rejection by the immune system, and disease transmission following transplantation. Due to recent progress in nanotechnology and material sciences, advanced artificial skin grafts-based on the fundamental concepts of tissue engineering-are quickly evolving for wound healing and regeneration applications, mainly because they can be uniquely tailored to meet the requirements of specific injuries. Despite tremendous progress in tissue engineering, many challenges and uncertainties still face skin grafts in vivo, such as how to effectively coordinate the interaction between engineered biomaterials and the immune system to prevent graft rejection. Furthermore, in-depth studies on skin regeneration at the molecular level are still not fully understood; as a consequence, the development of novel biomaterial-based systems that interact with the skin at the core level has also been slow. This review will discuss (1) the biological aspects of wound healing and skin regeneration, (2) important characteristics and functions of biomaterials for skin regeneration applications, and (3) synthesis and applications of common biomaterials for skin regeneration. Finally, the current challenges and future directions of biomaterial-based skin regeneration will be addressed.

Dendritic cell biocompatibility of ether-based urethane films.

The use of synthetic materials for biomedical applications is ever expanding. One of the major requirements for these materials is biocompatibility, which includes prevention of immune system responses. Due to the inherent complexity of their structural composition, the polyurethane (PU) family of polymers is being used in a variety of medical applications, from soft and hard tissue scaffolds to intricate coatings on implantable devices. Herein, we investigated whether two polymer materials, D3 and D7, induced an immune response, measured by their effects on a dendritic cell (DC) line, JAWS II. Using a lactate dehydrogenase cytotoxicity assay and Annexin V/PI staining, we found that the PU materials did not induce cytotoxicity in DC cells. Using confocal microscopy, we also showed that the materials did not induce activation or maturation, as compared to positive controls. This was confirmed by looking at various markers, CD80, CD86, MHC class I, and MHC class II, via flow cytometry. Overall, the results indicated that the investigated PU films are biocompatible in terms of immunotoxicology and immunogenicity and show great promise for use in regenerative medicine.

Graphene-based 2D constructs for enhanced fibroblast support.

Complex skin wounds have always been a significant health and economic problem worldwide due to their elusive and sometimes poor or non-healing conditions. If not well-treated, such wounds may lead to amputation, infections, cancer, or even death. Thus, there is a need to efficiently generate multifunctional skin grafts that address a wide range of skin conditions, including non-healing wounds, and enable the regeneration of new skin tissue. Here, we propose studying pristine graphene and two of its oxygen-functionalized derivatives-high and low-oxygen graphene films-as potential substrates for skin cell proliferation and differentiation. Using BJ cells (human foreskin-derived fibroblasts) to represent basic skin cells, we show that the changes in surface properties of pristine graphene due to oxygen functionalization do not seem to statistically impact the normal proliferation and maturation of skin cells. Our results indicate that the pristine and oxidized graphenes presented relatively low cytotoxicity to BJ fibroblasts and, in fact, support their growth and bioactivity. Therefore, these graphene films could potentially be integrated into more complex skin regenerative systems to support skin regeneration. Because graphene's surface can be relatively easily functionalized with various chemical groups, this finding presents a major opportunity for the development of various composite materials that can act as active components in regenerative applications such as skin regeneration.

Quantification of cellular associated graphene and induced surface receptor responses.

The use of graphene for biomedical and other applications involving humans is growing and shows practical promise. However, quantifying the graphitic nanomaterials that interact with cells and assessing any corresponding cellular response is extremely challenging. Here, we report an effective approach to quantify graphene interacting with single cells that utilizes combined multimodal-Raman and photoacoustic spectroscopy. This approach correlates the spectroscopic signature of graphene with the measurement of its mass using a quartz crystal microbalance resonator. Using this technique, we demonstrate single cell noninvasive quantification and multidimensional mapping of graphene with a detection limit of as low as 200 femtograms. Our investigation also revealed previously unseen graphene-induced changes in surface receptor expression in dendritic cells of the immune system. This tool integrates high-sensitivity real-time detection and monitoring of nanoscale materials inside single cells with the measurement of induced simultaneous biological cell responses, providing a powerful method to study the impact of nanomaterials on living systems and as a result, the toxicology of nanoscale materials.

Modifying Dendritic Cell Activation with Plasmonic Nano Vectors.

Dendritic cells (DCs) can acquire, process, and present antigens to T-cells to induce an immune response. For this reason, targeting cancer antigens to DCs in order to cause an immune response against cancer is an emerging area of nanomedicine that has the potential to redefine the way certain cancers are treated. The use of plasmonically active silver-coated gold nanorods (henceforth referred to as plasmonic nano vectors (PNVs)) as potential carriers for DC tumor vaccines has not been presented before. Effective carriers must be able to be phagocytized by DCs, present low toxicity, and induce the maturation of DCs-an early indication of an immune response. When we treated DCs with the PNVs, we found that the cell viability of DCs was unaffected, up to 200 µg/ml. Additionally, the PNVs associated with the DCs as they were phagocytized and they were found to reside within intracellular compartments such as endosomes. More importantly, the PNVs were able to induce expression of surface markers indicative of DC activation and maturation, i.e. CD40, CD86, and MHC class II. These results provide the first evidence that PNVs are promising carriers for DC-based vaccines and warrant further investigating for clinical use.

The role of surface chemistry in the cytotoxicity profile of graphene.

Graphene and its derivative, because of their unique physical, electrical and chemical properties, are an important class of nanomaterials being proposed as foundational materials in nanomedicine as well as for a variety of industrial applications. A major limitation for graphene, when used in biomedical applications, is its poor solubility due to its rather hydrophobic nature. Therefore, chemical functionalities are commonly introduced to alter both its surface chemistry and biochemical activity. Here, we show that surface chemistry plays a major role in the toxicological profile of the graphene structures. To demonstrate this, we chemically increased the oxidation level of the pristine graphene and compared the corresponding toxicological effects along with those for the graphene oxide. X-ray photoelectron spectroscopy revealed that pristine graphene had the lowest amount of surface oxygen, while graphene oxide had the highest at 2.5% and 31%, respectively. Low and high oxygen functionalized graphene samples were found to have 6.6% and 24% surface oxygen, respectively. Our results showed a dose-dependent trend in the cytotoxicity profile, where pristine graphene was the most cytotoxic, with decreasing toxicity observed with increasing oxygen content. Increased surface oxygen also played a role in nanomaterial dispersion in water or cell culture medium over longer periods. It is likely that higher dispersity might result in graphene entering into cells as individual flakes ~1 nm thick rather than as more cytotoxic aggregates. In conclusion, changes in graphene's surface chemistry resulted in altered solubility and toxicity, suggesting that a generalized toxicity profile would be rather misleading. Copyright © 2016 John Wiley & Sons, Ltd.