The possibility of long-term cryopreservation of cultured dermal substitute

Specifics of Cryopreservation of Hydrogel Biopolymer Scaffolds with Encapsulated Mesenchymal Stem Cells

The demand for regenerative medicine products is growing rapidly in clinical practice. Unfortunately, their use has certain limitations. One of these, which significantly constrains the widespread distribution and commercialization of such materials, is their short life span. For products containing suspensions of cells, this issue can be solved by using cryopreservation. However, this approach is rarely used for multicomponent tissue-engineered products due to the complexity of selecting appropriate cryopreservation protocols and the lack of established criteria for assessing the quality of such products once defrosted. Our research is aimed at developing a cryopreservation protocol for an original hydrogel scaffold with encapsulated MSCs and developing a set of criteria for assessing the quality of their functional activity in vitro. The scaffolds were frozen using two alternative types of cryocontainers and stored at either -40 °C or -80 °C. After cryopreservation, the external state of the scaffolds was evaluated in addition to recording the cell viability, visible changes during subsequent cultivation, and any alterations in proliferative and secretory activity. These observations were compared to those of scaffolds cultivated without cryopreservation. It was shown that cryopreservation at -80 °C in an appropriate type of cryocontainer was optimal for the hydrogels/adipose-derived stem cells (ASCs) tested if it provided a smooth temperature decrease during freezing over a period of at least three hours until the target values of the cryopreservation temperature regimen were reached. It was shown that evaluating a set of indicators, including the viability, the morphology, and the proliferative and secretory activity of the cells, enables the characterization of the quality of a tissue-engineered construct after its withdrawal from cryopreservation, as well as indicating the effectiveness of the cryopreservation protocol.

Freezing biological organisms for biomedical applications

Biological organisms play important roles in human health, either in a commensal or pathogenic manner. Harnessing inactivated organisms or living organisms is a promising way to treat diseases. As two types of freezing, cryoablation makes it simple to inactivate organisms that must be in a non-pathogenic state when needed, while cryopreservation is a facile way to address the problem of long-term storage challenged by living organism-based therapy. In this review, we present the latest studies of freezing biological organisms for biomedical applications. To begin with, the freezing strategies of cryoablation and cryopreservation, as well as their corresponding technical essentials, are illustrated. Besides, biomedical applications of freezing biological organisms are presented, including transplantation, tissue regeneration, anti-infection therapy, and anti-tumor therapy. The challenges and prospects of freezing living organisms for biomedical applications are well discussed. We believe that the freezing method will provide a potential direction for the standardization and commercialization of inactivated or living organism-based therapeutic systems, and promote the clinical application of organism-based therapy.

Cryopreservation of Tissue-Engineered Scaffold-Based Constructs: from Concept to Reality

Creation of scaffold-based tissue-engineered constructs (SB TECs) is costly and requires coordinated qualified efforts. Cryopreservation enables longer shelf-life for SB TECs while enormously enhancing their availability as medical products. Regenerative treatment with cryopreserved SB TECs prepared in advance (possibly prêt-à-porter) can be started straight away on demand. Animal studies and clinical trials indicate similar levels of safety for cryopreserved and freshly prepared SB TECs. Although cryopreservation of such constructs is more difficult than that of cell suspensions or tissues, years of research have proved the principal possibility of using ready-to-transplant SB TECs after prolonged cryostorage. Cryopreservation efficiency depends not only on the sheer viability of adherent cells on scaffolds after thawing, but largely on the retention of proliferative and functional properties by the cells, as well as physical and mechanical properties by the scaffolds. Cryopreservation protocols require careful optimization, as their efficiency depends on multiple parameters including cryosensitivity of cells, chemistry and architecture of scaffolds, conditions of cell culture before freezing, cryoprotectant formulations, etc. In this review we discuss recent achievements in SB TEC cryopreservation as a major boost for the field of tissue engineering and biobanking.

Evolution of Biological Bandages as First Cover for Burn Patients

Significance: Cutaneous wound regeneration is vital to keep skin functions and for large wounds, to maintain human survival. In a deep burn, the ability of the skin to heal is compromised due to the damage of vasculature and resident cells, hindering a coordinated response in the regeneration process. Temporal skin substitutes used as first cover can play a major role in skin regeneration as they allow a rapid wound covering that, in turn, can significantly reduce infection risk, rate of secondary corrective surgeries, and indirectly hospitalization time and costs. Recent Advances: Skin was one of the first tissues to be bioengineered providing thus a skin equivalent; however, what is the current status subsequent to 40 years of tissue engineering? We review the classic paradigms of biological skin substitutes used as first cover and evaluate recent discoveries and clinical approaches adapted for burn injuries cover, with an emphasis on innovative cell-based approaches. Critical Issues: Cell-based first covers offer promising perspectives as they can have an active function in wound healing, such as faster healing minimizing scar formation and prepared wound bed for subsequent grafting. However, cell-based therapies encounter some limitations due to regulatory hurdles, as they are considered as "Advanced Therapy Medicinal Products," which imposes the same industry-destined good manufacturing practices as for pharmaceutical products and biological drug development. Future Directions: Further improvements in clinical outcome can be expected principally with the use of cell-based therapies; however, hospital exemptions are necessary to assure accessibility to the patient and safety without hindering advances in therapies.

Cell therapy for severe burn wound healing

Cell therapy has emerged as an important component of life-saving procedures in treating burns. Over past decades, advances in stem cells and regenerative medicine have offered exciting opportunities of developing cell-based alternatives and demonstrated the potential and feasibility of various stem cells for burn wound healing. However, there are still scientific and technical issues that should be resolved to facilitate the full potential of the cellular devices. More evidence from large, randomly controlled trials is also needed to understand the clinical impact of cell therapy in burns. This article aims to provide an up-to-date review of the research development and clinical applications of cell therapies in burn wound healing and skin regeneration.

Skin substitutes based on allogenic fibroblasts or keratinocytes for chronic wounds not responding to conventional therapy: a retrospective observational study

Chronic wounds are an expression of underlying complex pathologies and have a high incidence. Skin substitutes may represent an alternative approach to treat chronic ulcers. The aim of this retrospective observational study was to evaluate the wound reduction using skin substitutes based on allogenic fibroblasts or keratinocytes in 30 patients not responding to conventional therapy. Wound bed was prepared, then keratinocytes on Laserskin(®) to treat superficial wounds or fibroblasts on Hyalograft 3D(R) to treat deep leg ulcers were applied, and finally wounds were treated with a secondary dressing composed of nanocrystalline silver. Once a week constructs were removed and new bioengineered products were applied, as well as nanocrystalline silver medication. In none of the cases under examination did any complications arise relating to the treatment. We also achieved a reduction in wound dimension and exudates, and an increase in wound bed score. Postoperative assessment shows a degree of healing that is statistically higher in the group treated with keratinocytes as compared with the fibroblast group. This retrospective study improves our understanding and defines the clinical indications for the various uses of the two types of skin substitutes.

Thermomechanical analysis of freezing-induced cell-fluid-matrix interactions in engineered tissues

Successful cryopreservation of functional engineered tissues (ETs) is significant to tissue engineering and regenerative medicine, but it is extremely challenging to develop a successful protocol because the effects of cryopreservation parameters on the post-thaw functionality of ETs are not well understood. Particularly, the effects on the microstructure of their extracellular matrix (ECM) have not been well studied, which determines many functional properties of the ETs. In this study, we investigated the effects of two key cryopreservation parameters--(i) freezing temperature and corresponding cooling rate; and (ii) the concentration of cryoprotective agent (CPA) on the ECM microstructure as well as the cellular viability. Using dermal equivalent as a model ET and DMSO as a model CPA, freezing-induced spatiotemporal deformation and post-thaw ECM microstructure of ETs was characterized while varying the freezing temperature and DMSO concentrations. The spatial distribution of cellular viability and the cellular actin cytoskeleton was also examined. The results showed that the tissue dilatation increased significantly with reduced freezing temperature (i.e., rapid freezing). A maximum limit of tissue deformation was observed for preservation of ECM microstructure, cell viability and cell-matrix adhesion. The dilatation decreased with the use of DMSO, and a freezing temperature dependent threshold concentration of DMSO was observed. The threshold DMSO concentration increased with lowering freezing temperature. In addition, an analysis was performed to delineate thermodynamic and mechanical components of freezing-induced tissue deformation. The results are discussed to establish a mechanistic understanding of freezing-induced cell-fluid-matrix interaction and phase change behavior within ETs in order to improve cryopreservation of ETs.

Potential of a cryopreserved cultured dermal substitute composed of hyaluronic acid and collagen to release angiogenic cytokine

An allogeneic cultured dermal substitute (CDS) was prepared by culturing fibroblasts on a spongy matrix of hyaluronic acid (HA) and collagen (Col), which was then cryopreserved. This cryopreserved allogeneic CDS (CDS-1; cryopreserved for 1 month, CDS-6; cryopreserved for 6 months) was thawed and re-cultured for a period of 7 days to investigate the potential of the CDS for wound treatment. The cell metabolic activity in the CDS and their cytokine production were measured using an MTT assay and ELISA. Fibroblast metabolic activity in each CDS-1 and CDS-6 immediately after thawing and following 3 and 7 days of re- cultivation was 56, 67 and 93%, and 49, 64 and 86%, respectively, of that before cryopreservation. The amount of vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) released from the CDS-1 on days 1, 3 and 7 of re-cultivation after thawing was 8, 44 and 92% (VEGF) and 3, 7 and 28% (HGF), respectively, of that before cryopreservation. The amount of VEGF and HGF released from the CDS-6 on days 1, 3 and 7 of re-cultivation after thawing was 9, 32 and 45% (VEGF) and 6, 10 and 27% (HGF), respectively, of that before cryopreservation. These findings showed that the potential of the CDS was restored to some extent over the first 3 days of re-cultivation after thawing. The potential of the CDS for wound treatment was then evaluated using a wound surface model, in which the each CDS-1 and CDS-6 that was re-cultured for 3 days after thawing was elevated at the air/culture medium interface, and a wound dressing was placed on top, and then cultured for 5 days. Two different types of wound dressing were tested. Fibroblasts in the CDS in Group II (placing a wound dressing with EGF) released increased amount of VEGF and HGF compared with that in Group I (placing a wound dressing without EGF). These findings suggest that re-culture of the CDS for 3 days following thawing results in a CDS with improved wound healing potential and that an EGF-incorporating wound dressing is useful as a top dressing for the CDS.

Clinical trial of allogeneic cultured dermal substitutes for intractable skin ulcers

The effect of allogeneic cultured dermal substitute (CDS) on wound healing was evaluated in 9 intractable skin ulcers in 5 patients who had failed to improve despite conventional topical treatment with basic fibroblast growth factor (bFGF) for more than 2 months. In general, the topical application of bFGF is effective in facilitating wound healing. However, skin regeneration was very slow in the present 9 cases. In this study, to improve the condition of these wounds, allogeneic CDS was applied once a week for 2 months. The wound healing process was evaluated, focusing on the reduction ratio of wound size through the granulation tissue formation associated with epithelialization. In all 9 cases, the wound size was successfully decreased after the application of CDS, and ulcers were completely resurfaced in 2 cases. In all cases, except the 2 cases showing complete wound closure, the mean wound size decreased to 33.3% of the original size, i.e., a mean reduction ratio of 33.3%. The present results indicate that allogeneic CDS can promote wound healing of intractable skin ulcers that fail to improve despite treatment with bFGF.

Effects of freezing-induced cell-fluid-matrix interactions on the cells and extracellular matrix of engineered tissues

The two most significant challenges for successful cryopreservation of engineered tissues (ETs) are preserving tissue functionality and controlling highly tissue-type dependent preservation outcomes. In order to address these challenges, freezing-induced cell-fluid-matrix interactions should be understood, which determine the post-thaw cell viability and extracellular matrix (ECM) microstructure. However, the current understanding of this tissue-level biophysical interaction is still limited. In this study, freezing-induced cell-fluid-matrix interactions and their impact on the cells and ECM microstructure of ETs were investigated using dermal equivalents as a model ET. The dermal equivalents were constructed by seeding human dermal fibroblasts in type I collagen matrices with varying cell seeding density and collagen concentration. While these dermal equivalents underwent an identical freeze/thaw condition, their spatiotemporal deformation during freezing, post-thaw ECM microstructure, and cellular level cryoresponse were characterized. The results showed that the extent and characteristics of freezing-induced deformation were significantly different among the experimental groups, and the ETs with denser ECM microstructure experienced a larger deformation. The magnitude of the deformation was well correlated to the post-thaw ECM structure, suggesting that the freezing-induced deformation is a good indicator of post-thaw ECM structure. A significant difference in the extent of cellular injury was also noted among the experimental groups, and it depended on the extent of freezing-induced deformation of the ETs and the initial cytoskeleton organization. These results suggest that the cells have been subjected to mechanical insult due to the freezing-induced deformation as well as thermal insult. These findings provide insight on tissue-type dependent cryopreservation outcomes, and can help to design and modify cryopreservation protocols for new types of tissues from a pre-developed cryopreservation protocol.

Development of a wound dressing composed of hyaluronic acid and collagen sponge with epidermal growth factor

This study was designed to investigate the effect of a wound dressing composed of hyaluronic acid (HA) and collagen (Col) sponge containing epidermal growth factor (EGF) on various parameters of wound healing in vitro and in vivo. High-molecular-weight (HMW) HA solution, hydrolyzed low-molecular-weight (LMW) HA solution and heat-denatured Col solution were mixed, followed by freeze-drying to obtain a spongy sheet. Cross-linkage between Col molecules was induced by UV irradiation to the spongy sheet (Type-I dressing). In a similar manner, a spongy sheet containing EGF was prepared (Type-II dressing). The efficacy of these products was firstly evaluated in vitro. Fibroblast proliferation was assessed in culture medium in the presence or absence of a piece of each wound dressing. EGF stimulated cell proliferation after UV irradiation and dry sterilization at 110°C for 1 h. In the second experiment, fibroblasts-embedded Col gels were elevated to the air-liquid interface to create a wound surface model, on which wound dressings were placed and cultured for 1 week. Cell proliferation and the production of vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) were investigated. With Type-II dressings, the amounts of VEGF and HGF released from fibroblasts in the Col gel were significantly increased compared with Type-I dressing. Next, the efficacy of these products was evaluated in vivo using Sprague-Dawley (SD) rats. Wound conditions after 1 and 2 weeks of treatment with the wound dressings were evaluated based on the gross and histological appearances. Type-II dressings promoted a decrease in wound size, re-epithelialization and granulation tissue formation associated with angiogenesis. These findings indicate that the combination of HA, Col and EGF promotes wound healing by stimulating fibroblast function.

A case of lower-extremity deep burn wounds with periosteal necrosis successfully treated by use of allogenic cultured dermal substitute

In patients with burns, bone exposure accompanies serious problems which occasionally lead to amputation. We present a case of an 82-year-old woman who sustained 22% of total body surface area flame burns on her bilateral lower extremities with bone exposure. Despite fascial excision and mesh skin graft, muscles, bones, and tendons were widely exposed on her right leg. The wound was infected by methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. To promote wound healing, we applied an allogeneic cultured dermal substitute (CDS) to the wound surface once weekly, resulting in healthy granulation except for the exposed bone area of the right anterior tibia. We then shaved the cortex of the exposed bone surface until bone marrow bleeding, and grafted mesh skin in combination with CDS. Finally, all wounds healed without osteomyelitis. The use of CDS to treat deep burns exposing bone surface may expand reconstructive options for extremities that otherwise might have been amputated.

Cryopreserved tissue engineered mucosa

Single cells suspensions used for grafting in the clinical setting may be reliably cryopreserved by established protocols. However, for tissue engineered constructs which now also get used as grafts in the clinic such established protocols and assays which indicate graft viability and their function as graft do not exist. a) The purpose was to develop a cryoprotocol and an animal model to test the efficacy of tissue engineered to act as graft after cryopreservation. b) Therefore, tissue engineered mucosa grafts consisting of keratinocytes and fibroblasts grown in a collagen sponge were cryopreserved and grafted in the nude rat to test its efficacy to function as mucosa graft. At different points after cryopreservation the mucosa was grafted into the nude rats. Healing of grafts was allowed for one or three weeks. c) Sufficient cells survived the cryopreservation allowing for the development of epithelial-fibroblast tissue in the collagen sponge. After three weeks of healing the formation of mucosa tissue was more complete and more collagen sponge had disappeared. d) The nude rat model is suitable to assess the efficacy of tissue engineered mucosa to function as graft after cryopreservation. The formation of human epithelial-fibroblast tissue in vivo has to be interpreted as proof of principle that the approach of cryopreservation of tissue engineered grafts is working.

Standardization for mass production of allogeneic cultured dermal substitute by measuring the amount of VEGF, bFGF, HGF, TGF-beta, and IL-8

Fibroblasts were isolated from a piece of donated skin measuring about 1 x 1 cm and were proliferated over nine successive cultivations. Fibroblasts obtained from the fourth cultivation were cryopreserved in 10 cryotubes as master cells. Fibroblasts obtained from the fifth to ninth cultivations were cryopreserved in 49 cryotubes in total as working cells. At the end of each procedure in the fourth to eighth cultivations, about three-quarters of the proliferated fibroblasts were cryopreserved, and the remaining one-quarter were proliferated in the next cultivation. All fibroblasts obtained from the ninth (final) procedure were cryopreserved as the last working cells. Two cryotubes of the last cryopreserved working cells (ninth cultivation) were thawed and proliferated. Cultured dermal substitute (CDS) was prepared by performing ten successive cultivations. After each cultivation, about three-quarters of the resulting fibroblasts were used to prepare CDS, and the remaining one-quarter were proliferated in the next cultivation for 1 week. Finally, all fibroblasts produced by the tenth (final) procedure were used to prepare CDS. In each of the first to ninth cultivations for CDS preparation, the density of fibroblasts remained relatively constant, and the levels of cytokines, i.e., vascular endothelial growth factor, basic fibroblast growth factor, hepatocyte growth factor, transforming growth factor-beta 1, and interleukin-8 released from CDS remained relatively constant. In total, 47 sheets of CDS measuring 10 x 10 cm were prepared. The present findings indicate that about 1000 sheets of CDS measuring 10 x 10 cm can be prepared using all the working cells prepared from a piece of donated skin measuring 1 x 1 cm.

Comparative evaluation of re-epithelialization promoted by fresh or cryopreserved cultured dermal substitute

Allogeneic cultured dermal substitute (CDS) was prepared by plating cultured fibroblasts on a two-layered spongy matrix of hyaluronic acid and atelocollagen, followed by culturing for 1 week. The resulting fresh CDS was then cryopreserved in a freezer at -152 degrees C in accordance with conventional procedures. Fresh CDS was rinsed thoroughly with lactated Ringer's solution to remove fetal bovine serum (FBS) and was then used in the clinical study, whereas cryopreserved CDS was thawed and then rinsed with lactated Ringer's solution to remove cryoprotectant and FBS. The present study was designed to compare the efficacy of fresh and cryopreserved CDS in promoting reepithelialization at donor sites leaving behind split-thickness skin autografts. Fourteen donor sites were used for this comparative study. There were no differences in the period of complete re-epithelialization between the fresh and cryopreserved CDS. The results of this comparative study thus suggest that cryopreserved CDS is able to maintain the same level of potency to promote re-epithelialization as fresh CDS. This indicates that, although the release of growth factors is suppressed to some extent during the course of cryopreserving, thawing, and rinsing procedures, it is still sufficient to promote re-epithelialization.

Clinical trial of allogeneic cultured dermal substitutes for intractable skin ulcers of the lower leg

The efficacy of allogeneic cultured dermal substitute (CDS) on wound healing was evaluated in six patients with intractable skin ulcers on the lower extremities. Allogeneic CDS was repeatedly applied to wounds at intervals of 4-7 days to prepare a wound bed acceptable for skin grafting or to induce resurfacing through the granulation tissue formation associated with epithelialization. In one patient with a leg ulcer, the wound size decreased to 32% of the original size within 10 weeks and skin grafting was conducted. In the other five patients with leg, ankle, or foot ulcers, the wound size decreased to 9%-25% of the original size within 6 weeks.

Cryopreserved human adipogenic-differentiated pre-adipocytes: a potential new source for adipose tissue regeneration

BACKGROUND

Previously, we have shown that in vitro adipogenic differentiation of pre-adipocytes before implantation can enhance in vivo adipose tissue formation. For large-scale adipose tissue engineering or repeat procedures, cryopreservation of fat grafts has been commonly used in recent years. However, the feasibility of cryopreservation of adipogenic differentiated pre-adipocytes has not been investigated.

METHODS

To examine the impact of cryopreservation on the adipogenic functions of adipogenic-differentiated pre-adipocytes, freeze-thawed adipocytes were compared with fresh differentiated adipocytes in vitro and in vivo. Adipogenic function was assessed by Oil red O staining, ELISA analysis of leptin secretion and RT-PCR of adipogenic-related genes. After transplantation, adipose tissue formation was assessed by histomorphologic and volumetric analysis.

RESULTS

Freeze-thawed adipocytes constantly showed typical adipogenic functions in terms of lipid content, leptin secretion and adipogenic gene expression, as well as good viability. Importantly, implants derived from freeze-thawed adipocytes were successfully developed to adipose tissue and newly formed adipose tissues were similar to those developed from fresh differentiated adipocytes, based on histomorphologic and volumetric analysis. In addition, CD34-positive endothelial cells were detected in implants. These results demonstrate that the specific characters of adipogenic-differentiated pre-adipocytes are successfully conserved after cryopreservation without any significant alteration.

DISCUSSION

Cryopreservation of adipogenic-differentiated pre-adipocytes is a feasible method and extends their clinical use in adipose tissue-engineering applications and transplantation.