A novel approach for the cryodesiccated preservation of tissue-engineered skin substitutes with trehalose

Speeding up the Production of Clinical-Grade Skin Substitutes Using Off-the-shelf Decellularized Self-Assembled Dermal Matrices

Patients with deep and extensive wounds need urgent skin coverage to re-establish the cutaneous barrier that prevents life-threatening infections and dehydration. However, the current clinically-available skin substitutes intended for permanent coverage are limited in number, and a trade-off between production time and quality must be made. Here, we report the use of decellularized self-assembled dermal matrices to reduce by half the manufacturing process time of clinical-grade skin substitutes. These decellularized matrices can be stored for over 18 months and recellularized with patients' cells in order to generate skin substitutes that show outstanding histological and mechanical properties in vitro. Once grafted in mice, these substitutes persist over weeks with high graft take, few contraction events, and high stem cell content. These next-generation skin substitutes constitute a substantial advancement in the treatment of major burn patients, combining, for the first time, high functionality, rapid manufacturability and easy handling for surgeons and healthcare practitioners. Future clinical trials will be conducted to assess the advantages of these substitutes over existing treatments. STATEMENT OF SIGNIFICANCE: The number of patients in need for organ transplantation is ever-growing and there is a shortage in tissue and organ donors. In this study, we show for the first time that we can preserve decellularized self-assembled tissues and keep them in storage. Then, in only three weeks we can use them to produce bilayered skin substitutes that have properties very close to those of the native human skin. These findings therefore represent a major step forward in the field of tissue engineering and organ transplantation, paving the way toward a universal off-the-shelf biomaterial for tissue reconstruction and surgery that will be beneficial for many clinicians and patients.

The Stimulation of Macrophages by Systematical Administration of GM-CSF Can Accelerate Adult Wound Healing Process

Skin wound repair remains a major challenge in clinical care, and various strategies have been employed to improve the repair process. Recently, it has been reported that macrophages are important for the regeneration of various tissues and organs. However, their influence on wound repair is unclear. Here, we aimed to explore whether macrophages would participate in the wound healing process and to explore new possibilities of treatment for skin defects. We firstly created a mouse full-thickness skin defect model to observe the distribution of macrophages in the regenerating tissue and then detected the influence of macrophages on skin defect repair in both macrophage-depletion and macrophage-mobilization models. We found that the number of macrophages increased significantly after skin defect and persisted during the process of wound repair. The regeneration process was significantly prolonged in macrophage-depleted animals. RT-qPCR and ELISA assays further demonstrated that the expression of growth factors was perturbed in the regenerating tissue. The activation of macrophages by granulocyte-macrophage colony-stimulating factor (GM-CSF) injection could significantly improve wound healing, accompanied with an upregulation of the expression of various growth factors. In conclusion, the current study demonstrated that macrophages are critical for skin regeneration and that GM-CSF exhibited therapeutic potential for wound healing.

Accelerating cryoprotectant diffusion kinetics improves cryopreservation of pancreatic islets

Cryopreservation offers the potential to increase the availability of pancreatic islets for treatment of diabetic patients. However, current protocols, which use dimethyl sulfoxide (DMSO), lead to poor cryosurvival of islets. We demonstrate that equilibration of mouse islets with small molecules in aqueous solutions can be accelerated from > 24 to 6 h by increasing incubation temperature to 37 °C. We utilize this finding to demonstrate that current viability staining protocols are inaccurate and to develop a novel cryopreservation method combining DMSO with trehalose pre-incubation to achieve improved cryosurvival. This protocol resulted in improved ATP/ADP ratios and peptide secretion from β-cells, preserved cAMP response, and a gene expression profile consistent with improved cryoprotection. Our findings have potential to increase the availability of islets for transplantation and to inform the design of cryopreservation protocols for other multicellular aggregates, including organoids and bioengineered tissues.

Human Amniotic Membrane: A review on tissue engineering, application, and storage

Human amniotic membrane (hAM) has been employed as scaffolding material in a wide range of tissue engineering applications, especially as a skin dressing and as a graft for corneal treatment, due to the structure of the extracellular matrix and excellent biological properties that enhance both wound healing and tissue regeneration. This review highlights recent work and current knowledge on the application of native hAM, and/or production of hAM-based tissue-engineered products to create scaffolds mimicking the structure of the native membrane to enhance the hAM performance. Moreover, an overview is presented on the available (cryo) preservation techniques for storage of native hAM and tissue-engineered products that are necessary to maintain biological functions such as angiogenesis, anti-inflammation, antifibrotic and antibacterial activity.

Stabilizing Enzymes within Polymersomes by Coencapsulation of Trehalose

Enzymes are essential biocatalysts and very attractive as therapeutics. However, their functionality is strictly related to their stability, which is significantly affected by the environmental changes occurring during their usage or long-term storage. Therefore, maintaining the activity of enzymes is essential when they are exposed to high temperature during usage or when they are stored for extended periods of time. Here, we stabilize and protect enzymes by coencapsulating them with trehalose into polymersomes. The anhydrobiotic disaccharide preserved up to about 81% of the enzyme's original activity when laccase/trehalose-loaded nanoreactors were kept desiccated for 2 months at room temperature and 75% of its activity when heated at 50 °C for 3 weeks. Moreover, the applicability of laccase/trehalose-loaded nanoreactors as catalysts for bleaching of the textile dyes orange G, toluidine blue O, and indigo was proven. Our results demonstrate the advantages of coencapsulating trehalose within polymersomes to stabilize enzymes in dehydrated state for extended periods of time, preserving their activity even when heated to elevated temperature.

Endogenous viable cells in lyopreserved amnion retain differentiation potential and anti-fibrotic activity in vitro

Human amniotic membrane (AM) has intrinsic anti-inflammatory, anti-fibrotic and antimicrobial properties. Tissue preservation methods have helped to overcome the short shelf life of fresh AM allowing "on demand" use of AM grafts. Cryopreserved AM that retains all native tissue components, including viable cells, has clinical benefits in treating chronic wounds. However, cryopreservation requires ultra-low temperature storage, limiting the use of cryopreserved products. To overcome this limitation, a new lyopreservation method has been developed for ambient storage of living tissues. The goal of this study was to investigate the viability and functionality of AM cells following lyopreservation. Fresh AM and devitalized lyopreserved AM (DLAM) served as positive and negative controls, respectively. Using live/dead staining, we confirmed the presence of living cells in viable lyopreserved AM (VLAM) and showed that these cells persisted up to 21 days in culture medium. The functionality of cells in VLAM was assessed by their differentiation potential and anti-fibrotic activity in vitro. With osteogenic induction, cells in VLAM deposited calcium within the membrane, a marker of osteogenic cells, in a time-dependent manner. The migration of human lung fibrotic fibroblasts in a scratch wound assay was reduced significantly in the presence of VLAM-derived conditioned medium. Quantitative PCR analyses indicated that VLAM reduced the expression of pro-fibrotic factors such as type I collagen and increased the expression of anti-fibrotic factors such as hepatocyte growth factor and anti-fibrotic microRNA in fibrotic fibroblasts. Taken together, these results demonstrate that endogenous cells in VLAM remain viable and functional post-lyophilization. STATEMENT OF SIGNIFICANCE: This study, for the first time, provides direct evidence showing that tissue viability and functional cells can be preserved by lyophilization. Similar to fresh amniotic membrane (AM), viable lyopreserved AM (VLAM) retains viable cells for extended periods of time. More importantly, these cells are functional and maintain their osteogenic differentiation potential and anti-fibrotic activity. Our results confirmed that the novel lyophilization method preserves tissue viability.

Approaches to cutaneous wound healing: basics and future directions

The skin provides essential functions, such as thermoregulation, hydration, excretion and synthesis of vitamin D. Major disruptions of the skin cause impairment of critical functions, resulting in high morbidity and death, or leave one with life-changing cosmetic damage. Due to the complexity of the skin, diverse approaches are needed, including both traditional and advanced, to improve cutaneous wound healing. Cutaneous wounds undergo four phases of healing. Traditional management, including skin grafts and wound dressings, is still commonly used in current practice but in combination with newer technology, such as using engineered skin substitutes in skin grafts or combining traditional cotton gauze with anti-bacterial nanoparticles. Various upcoming methods, such as vacuum-assisted wound closure, engineered skin substitutes, stem cell therapy, growth factors and cytokine therapy, have emerged in recent years and are being used to assist wound healing, or even to replace traditional methods. However, many of these methods still lack assessment by large-scale studies and/or extensive application. Conceptual changes, for example, precision medicine and the rapid advancement of science and technology, such as RNA interference and 3D printing, offer tremendous potential. In this review, we focus on the basics of wound treatment and summarize recent developments involving both traditional and hi-tech therapeutic methods that lead to both rapid healing and better cosmetic results. Future studies should explore a more cost-effective, convenient and efficient approach to cutaneous wound healing. Graphical abstract Combination of various materials to create advanced wound dressings.

Properties of viable lyopreserved amnion are equivalent to viable cryopreserved amnion with the convenience of ambient storage

Human amniotic membrane (AM) has a long history of clinical use for wound treatment. AM serves as a wound protective barrier maintaining proper moisture. AM is anti-inflammatory, anti-microbial and antifibrotic, and supports angiogenesis, granulation tissue formation and wound re-epithelialization. These properties of AM are attributed to its native extracellular matrix, growth factors, and endogenous cells including mesenchymal stem cells. Advances in tissue preservation have helped to overcome the short shelf life of fresh AM and led to the development of AM products for clinical use. Viable cryopreserved amnion (VCAM), which retains all native components of fresh AM, has shown positive outcomes in clinical trials for wound management. However, cryopreservation requires ultra-low temperature storage and shipment that limits widespread use of VCAM. We have developed a lyopreservation technique to allow for ambient storage of living tissues. Here, we compared the structural, molecular, and functional properties of a viable lyopreserved human amniotic membrane (VLAM) with properties of VCAM using in vitro and in vivo wound models. We found that the structure, growth factors, and cell viability of VLAM is similar to that of VCAM and fresh AM. Both, VCAM and VLAM inhibited TNF-α secretion and upregulated VEGF expression in vitro under conditions designed to mimic inflammation and hypoxia in a wound microenvironment, and resulted in wound closure in a diabetic mouse chronic wound model. Taken together, these data demonstrate that VLAM structural and functional properties are equivalent to VCAM but without the constraints of ultra-low temperature storage.

Effects of Water on Structure and Dynamics of Trehalose Glasses at Low Water Contents and its Relationship to Preservation Outcomes

Dry preservation of biologics in sugar glasses is regarded as a promising alternative to conventional cryopreservation. Evidence from various studies has suggested that there is a critical range of water content beyond which the viability of preserved biologics can be greatly compromised. In this study the viability of T-cells was determined as a function of end water content after microwave-assisted drying in trehalose solutions. Hydrogen-bonding and clustering phenomena in trehalose solutions of the same moisture content were also evaluated using molecular dynamics simulation. Post-rehydration viability decreased dramatically within the range of 0.1-1 gH2O/gdw. Molecular modeling revealed that as the water content approached 0.1 gH2O/gdw the matrix formed a large interconnected trehalose skeleton with a minimal number of bound water molecules scattered in the bulk. The diffusion coefficients of trehalose oxygen atoms most distant from the glycosidic linkage fluctuated around 7.5 × 10(-14) m(2)/s within the range of 0.02-0.1 gH2O/gdw and increased again to ~1.13 × 10(-13) m(2)/s at 0.01 gH2O/gdw and below due to the loss of water in the free volume between trehalose molecules. These insights can guide the optimal selection of final moisture contents to advance dry preservation methods.