Three-dimensional bioprinting of a full-thickness functional skin model using acellular dermal matrix and gelatin methacrylamide bioink.

Treatment of full-thickness skin defects still presents a significant challenge in clinical practice. Three-dimensional (3D) bioprinting technique offers a promising approach for fabricating skin substitutes. However, it is necessary to identify bioinks that have both sufficient mechanical properties and desirable biocompatibilities. In this study, we successfully fabricated acellular dermal matrix (ADM) and gelatin methacrylamide (GelMA) bioinks. The results demonstrated that ADM preserved the main extracellular matrix (ECM) components of the skin and GelMA had tunable mechanical properties. Both bioinks with shear-thinning properties were suitable for 3D bioprinting and GelMA bioink exhibited high printability. Additionally, the results revealed that 20% GelMA with sufficient mechanical properties was suitable to engineer epidermis, 1.5% ADM and 10% GelMA displayed relatively good cytocompatibilities. Here, we proposed a new 3D structure to simulate natural full-thickness skin, which included 20% GelMA with HaCaTs as an epidermal layer, 1.5% ADM with fibroblasts as the dermis, and 10% GelMA mesh with human umbilical vein endothelial cells (HUVECs) as the vascular network and framework. We demonstrated that this 3D bioprinting functional skin model (FSM) could not only promote cell viability and proliferation, but also support epidermis reconstruction in vitro. When transplanted in vivo, the FSM could maintain cell viability for at least 1 week. Furthermore, the FSM promoted wound healing and re-epithelization, stimulated dermal ECM secretion and angiogenesis, and improved wound healing quality. The FSM may provide viable functional skin substitutes for future clinical applications. STATEMENT OF SIGNIFICANCE: We propose a new 3D structure to simulate natural full-thickness skin, which included 20% GelMA with HaCaTs as an epidermal layer, 1.5% ADM with fibroblasts as the dermis, and 10% GelMA mesh with HUVECs as the vascular network. It could not only maintain a moist microenvironment and barrier function, but also recreate the natural skin microenvironment to promote cell viability and proliferation. This may provide viable functional skin substitutes for future clinical applications.

Regeneration of skin appendages and nerves: current status and further challenges.

Tissue-engineered skin (TES), as an analogue of native skin, is promising for wound repair and regeneration. However, a major drawback of TES products is a lack of skin appendages and nerves to enhance skin healing, structural integrity and skin vitality. Skin appendages and nerves are important constituents for fully functional skin. To date, many studies have yielded remarkable results in the field of skin appendages reconstruction and nerve regeneration. However, patients often complain about a loss of skin sensation and even cutaneous chronic pain. Restoration of pain, temperature, and touch perceptions should now be a major challenge to solve in order to improve patients' quality of life. Current strategies to create skin appendages and sensory nerve regeneration are mainly based on different types of seeding cells, scaffold materials, bioactive factors and involved signaling pathways. This article provides a comprehensive overview of different strategies for, and advances in, skin appendages and sensory nerve regeneration, which is an important issue in the field of tissue engineering and regenerative medicine.

Epidemiology of bus fires in mainland China from 2006 to 2015.

OBJECTIVE: This study analyses the epidemiological characteristics of bus fires in mainland China over the past 10 years to develop prevention strategies and emergency procedures for such incidence and the resulting casualties. METHODS: We collected reports on bus fires from the media and news websites and looked up on Medline, PubMed, and Chinese National Knowledge Infrastructure databases for relevant publications in English or Chinese from January 1, 2006 to December 31, 2015. RESULTS: In the past 10 years, there were 382 bus fires in mainland China. The frequency of fires was markedly higher in 2013 and 2014. The vast majority (89.1%) of the fires were caused by spontaneous combustion, followed by arson (5.0%). There were reports of casualties in 41 (10.7%) of the bus fires, including 144 deaths and 567 injuries. The fires leading to casualties resulted from spontaneous combustion in 22 (53.7%) incidents, arson in 12 (29.3%) incidents, and traffic accidents in 7 (17.1%) incidents. Arson caused the most casualties, including 91 deaths and 323 injuries. CONCLUSIONS: This epidemiological study presents characteristic findings related to bus fires in China mainland. The general trend of bus fires showed a gradual increase but with a fluctuation in several years. The regional distribution of bus fires revealed some specific characteristics, and most of bus fires happened in those regions locating in the eastern area of China mainland. The largest number of bus fires were caused by spontaneous combustion. Bus fires caused by arson accounting for only 5% of the total bus fires resulted in the most severe casualties. Most of bus arson occurred in the morning and evening rush hours.

Non-viral gene delivery systems for tissue repair and regeneration.

Critical tissue defects frequently result from trauma, burns, chronic wounds and/or surgery. The ideal treatment for such tissue loss is autografting, but donor sites are often limited. Tissue engineering (TE) is an inspiring alternative for tissue repair and regeneration (TRR). One of the current state-of-the-art methods for TRR is gene therapy. Non-viral gene delivery systems (nVGDS) have great potential for TE and have several advantages over viral delivery including lower immunogenicity and toxicity, better cell specificity, better modifiability, and higher productivity. However, there is no ideal nVGDS for TRR, hence, there is widespread research to improve their properties. This review introduces the basic principles and key aspects of commonly-used nVGDSs. We focus on recent advances in their applications, current challenges, and future directions.