Cryopreservation of Fibroblasts Immobilized Within a Porous Scaffold: Effects of Preculture and Collagen Coating of Scaffold on Performance of Three-Dimensional Cryopreservation

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.

Trehalose glycopolymers for cryopreservation of tissue-engineered constructs

The development of an effective cryopreservation method to achieve off-the-shelf and bioactive tissue-engineered constructs (TECs) is important to meet the requirements for clinical applications. The trehalose, a non-permeable cryoprotectant (CPA), has difficulty in penetrating the plasma membranes of mammalian cells and has only been used in combination with other cell penetrating CPA (such as DMSO) to cryopreserve mammalian cells. However, the inherent cytotoxicity of DMSO results in increasing risks with respect to cryopreserved cells. Therefore, in this study, permeable trehalose glycopolymers were synthesised for cryopreservation of TECs. The trehalose glycopolymers exhibited good ice inhibiting activities and biocompatibilities. Furthermore, the viability and function of TECs after cryopreservation with 5.0 wt% S2 were similar to those of the non-cryopreserved TECs. We developed an effective preservation strategy for the off-the-shelf availability of TECs.

Cryopreservable arrays of paper-based 3D tumor models for high throughput drug screening

Three-dimensional (3D) tumor models have gained increased attention in life-science applications as they better represent physiological conditions of in vivo tumor microenvironments, and thus, possess big potential for guiding drug screening studies. Although various techniques proved effective in growing cancer cells in 3D, their procedures are typically complex, time consuming, and expensive. Here, we present a versatile, robust, and cost-effective method that utilizes a paper platform to create cryopreservable high throughput arrays of 3D tumor models. In the approach, we use custom 3D printed masks along with simple chemistry modifications to engineer highly localized hydrophilic 'virtual microwells', or microspots, on paper for 3D cell aggregation, surrounded by hydrophobic barriers that prevent inter-microspot mixing. The method supports the formation and cryopreservation of 3D tumor arrays for extended periods of storage time. Using MCF-7 and MDA-MB-231 breast cancer cell lines, we show that the cryopreservable arrays of paper-based 3D models are effective in studying tumor response to cisplatin drug treatment, while replicating key characteristics of the in vivo tumors that are absent in conventional 2D cultures. This technology offers a low cost, easy, and fast experimental procedure, and allows for 3D tumor arrays to be cryopreserved and thawed for on-demand use. This could potentially provide unparalleled advantages to the fields of tissue engineering and personalized medicine.

Effects of mouse fetal liver cell culture density on hematopoietic cell expansion in three-dimensional cocultures with stromal cells

OBJECTIVE

An effective ex vivo expansion system of primitive hematopoietic cells (HCs) is required for wider application of hematopoietic stem cell transplantation. In this study, we examined effects of culture density on mouse fetal liver cells (FLCs) used as an HC source for the expansion of primitive HCs in three-dimensional (3D) cocultures with two kinds of mouse stromal cell lines (OP9 or C3H10T1/2).

MATERIALS AND METHODS

FLCs were seeded at different densities (1, 2, and 10 × 10⁷ cells/cm³) into porous polymer scaffolds with or without stromal cell layers and HCs were expanded in the cultures for 2 weeks without exogenous cytokines.

RESULTS

Differential effects of culture density on HC expansion were observed between cocultures and solitary FLC controls. In stromal cell cocultures, high expansion of HCs was achieved when FLCs were seeded at low densities. In contrast, the expansion in the controls was enhanced with increasing culture densities. With respect to expansion of primitive HCs existing in the FLCs, cocultures with C3H10T1/2 cells were superior to those with OP9 cells with a 29.3-fold expansion for c-kit⁺ hematopoietic progenitor cells and 8.3-fold expansion for CD34⁺ hematopoietic stem cells. In the controls, HC expansion was lower than in any cocultures, demonstrating the advantages of coculturing for HC expansion.

CONCLUSION

Stromal cell lines are useful in expanding primitive HCs derived from FLCs in 3D cocultures. Culture density is a pivotal factor for the effective expansion of primitive HCs and this effect differs by culture condition.

A Method to Efficiently Cryopreserve Mammalian Cells on Paper Platforms

This protocol describes a simple method to cryopreserve mammalian cells within filter papers as an alternative to conventional slow-freezing approach. The method involves treating paper fibers with fibronectin, using low concentrations of the cryoprotectant dimethyl sulfoxide (DMSO), and slow freezing cells to -80 °C at a 1 °C min^-1 rate. In our method, the biocompatibility, large surface area, 3D porosity and fiber flexibility of the paper, in combination with the fibronectin treatment, yield recovery of cells comparable to conventional approaches, with no additional fine-tuning to freezing and thawing procedures. We expect that the paper-based cryopreservation method will bring several advantages to the field of preserving mammalian cells, including accommodation of a higher number of cells within a unit volume and no cell loss after release. The method requires a minimal storage space, where paper platforms with large areas can be rolled and/or folded and stored in stocks, and allows for efficient transportation/distribution of cells in an on-demand manner. Moreover, an additional feature of this method includes the formation and cryopreservation of cellular spheroids and 3D cell cultures.

Expansion of mouse primitive hematopoietic cells in three-dimensional cultures on chemically fixed stromal cell layers

To establish a practical and convenient method to expand hematopoietic cells (HCs), we applied chemically-fixed stromal cell layers formed within three-dimensional (3D) scaffolds to feeder of HC cultures. The HCs were expanded using two successive cultures. First, stromal cells were cultured within porous polymer scaffolds and formed tissue-engineered constructs (TECs); the scaffolds containing stromal cells, were fixed using aldehyde (formaldehyde or glutaraldehyde) or organic solvents (acetone, methanol or ethanol). Second, mouse fetal liver cells (FLCs), as a source of HCs, were cultured on the TECs for 2 weeks, and the effects of fixative solutions on expansion of primitive HCs (c-kit⁺ and CD34⁺ cells) were examined. In the cultures on aldehyde-fixed TECs, primitive HCs were expanded 2.5- to 5.1-fold in the cultures on TECs fixed with glutaraldehyde, whereas no expansions were detected in those fixed with formaldehyde. However, we achieved expansion of primitive HCs > fivefold in the cultures using TECs fixed with organic solvents. Among these solvents, the highest expansions-of roughly tenfold-were obtained using acetone fixation. Ethanol-fixed TECs also supported the expansion of the primitive HCs well (6.6- to 8.0-fold). In addition to these sufficient expansions, the procedure and storage of fixed TECs is fairly easy. Thus, HC expansion on chemically-fixed TECs may be a practical method for expanding primitive HCs.

Growth and albumin secretion of mouse fetal liver cells cryopreserved within porous polymer scaffolds as a viable cell source for bioartificial livers

To clinically apply bioartificial livers (BALs), an effective liver cell cryopreservation method is required for a stable cell supply. In this study, we performed tissue-engineered construct (TEC) cryopreservation of fetal liver cells (FLCs) in which FLCs cultured within a porous polymer scaffold were cryopreserved. Growth and albumin secretion in TEC-cryopreserved FLCs after thawing were compared to freshly isolated FLCs (control experiments). The effect of preculture duration prior to cryopreservation (0-3 weeks) on these functions was also examined. In the three-dimensional cultures, the TEC-cryopreserved FLCs with preculturing showed constant growth, and this growth was comparable to controls. On the contrary, the TEC-cryopreserved FLCs without preculturing did not proliferate after thawing. Albumin secretion of TEC-cryopreserved FLCs with preculturing rapidly increased up to day 12 and high secretory activity comparable to controls was maintained thereafter in FLCs with 1- or 2-week preculturing, suggesting this as an appropriate preculture duration. Compared to conventionally cryopreserved FLCs, growth and albumin secretion in the TEC-cryopreserved FLCs were significantly higher, indicating their usefulness as a potent cell source for BALs.

Effect of 'in air' freezing on post-thaw recovery of Callithrix jacchus mesenchymal stromal cells and properties of 3D collagen-hydroxyapatite scaffolds

Through enabling an efficient supply of cells and tissues in the health sector on demand, cryopreservation is increasingly becoming one of the mainstream technologies in rapid translation and commercialization of regenerative medicine research. Cryopreservation of tissue-engineered constructs (TECs) is an emerging trend that requires the development of practically competitive biobanking technologies. In our previous studies, we demonstrated that conventional slow-freezing using dimethyl sulfoxide (Me₂SO) does not provide sufficient protection of mesenchymal stromal cells (MSCs) frozen in 3D collagen-hydroxyapatite scaffolds. After simple modifications to a cryopreservation protocol, we report on significantly improved cryopreservation of TECs. Porous 3D scaffolds were fabricated using freeze-drying of a mineralized collagen suspension and following chemical crosslinking. Amnion-derived MSCs from common marmoset monkey Callithrix jacchus were seeded onto scaffolds in static conditions. Cell-seeded scaffolds were subjected to 24 h pre-treatment with 100 mM sucrose and slow freezing in 10% Me₂SO/20% FBS alone or supplemented with 300 mM sucrose. Scaffolds were frozen 'in air' and thawed using a two-step procedure. Diverse analytical methods were used for the interpretation of cryopreservation outcome for both cell-seeded and cell-free scaffolds. In both groups, cells exhibited their typical shape and well-preserved cell-cell and cell-matrix contacts after thawing. Moreover, viability test 24 h post-thaw demonstrated that application of sucrose in the cryoprotective solution preserves a significantly greater portion of sucrose-pretreated cells (more than 80%) in comparison to Me₂SO alone (60%). No differences in overall protein structure and porosity of frozen scaffolds were revealed whereas their compressive stress was lower than in the control group. In conclusion, this approach holds promise for the cryopreservation of 'ready-to-use' TECs.

Paper-Based Cell Cryopreservation

The continuous development of simple and practical cell cryopreservation methods is of great importance to a variety of sectors, especially when considering the efficient short- and long-term storage of cells and their transportation. Although the overall success of such methods has been increased in recent years, there is still need for a unified platform that is highly suitable for efficient cryogenic storage of cells in addition to their easy-to-manage retrieval. Here, a paper-based cell cryopreservation method as an alternative to conventional cryopreservation methods is presented. The method is space-saving, cost-effective, simple and easy to manage, and requires no additional fine-tuning to conventional freezing and thawing procedures to yield comparable recovery of viable cells. It is shown that treating papers with fibronectin solution enhances the release of viable cells post thawing as compared to untreated paper platforms. Additionally, upon release, the remaining cells within the paper lead to the formation and growth of spheroid-like structures. Moreover, it is demonstrated that the developed method works with paper-based 3D cultures, where preformed 3D cultures can be efficiently cryopreserved.

Fabrication of sponge-forming microneedle patch for rapidly sampling interstitial fluid for analysis

Microneedle (MN) patch has been used for collecting dermal interstitial fluid (ISF) containing biomarkers from patients with safety, pain-free and easy-to-use manner. However, long sampling time for biomarkers analysis still poses a significant challenge. Here, we describe a new sponge-forming MN patch consisting of polyvinyl formal (PVF) for rapidly extracting ISF from skin. Owing to the supreme water affinity of PVF, this MN patch can extract 1.6 mg ISF in 1 min without the assistance of extra devices, which remarkably facilitates timely analysis. The MN patch had preserved structural integrity in the swelling hydrated state without leaving residues in skin after usage, and the treated skin recovered within 8 h. More importantly, the extracted ISF can be efficiently recovered from the MN patch by simple centrifugation for the subsequent offline analysis of biomarkers such as glucose and cholesterol. Our results reveal that the new sponge-forming MN patch holds considerable promise for minimally invasive sampling ISF for biomarkers detection in real-life situations.

Expansion of mouse hematopoietic stem/progenitor cells in three-dimensional cocultures on growth-suppressed stromal cell layer

With the aim of establishing an effective method to expand hematopoietic stem/progenitor cells for application in hematopoietic stem cell transplantation, we performed ex vivo expansion of hematopoietic stem/progenitor cells derived from mouse fetal liver cells in three-dimensional cocultures with stromal cells. In these cocultures, stromal cells were first cultured within three-dimensional scaffolds to form stromal layers and then fetal liver cells containing hematopoietic cells were seeded on these scaffolds to expand the hematopoietic cells over the 2 weeks of coculture in a serum-containing medium without the addition of cytokines. Prior to coculture, stromal cell growth was suppressed by treatment with the DNA synthesis inhibitor mitomycin C, and its effect on hematopoietic stem/progenitor cell expansion was compared with that in control cocultures in which fetal liver cells were cocultured with three-dimensional freeze-thawed stromal cells. After coculture with mitomycin C-treated stromal cells, we achieved a several-fold expansion of the primitive hematopoietic cells (c-kit⁺ hematopoietic progenitor cells >7.8-fold, and CD34⁺ hematopoietic stem/progenitor cells >3.5-fold). Compared with control cocultures, expansion of hematopoietic stem/progenitor cells tended to be lower, although that of hematopoietic progenitor cells was comparable. Thus, our results suggest that three-dimensional freeze-thawed stromal cells have higher potential to expand hematopoietic stem/progenitor cells compared with mitomycin C-treated stromal cells.

Fabrication of poly(vinyl alcohol)-Carrageenan scaffolds for cryopreservation: Effect of composition on cell viability

The present investigation reports the fabrication of three dimensional (3D), interconnected, highly porous, biodegradable scaffolds using freeze-gelation technique. The hydrogels prepared with different ratios (5:5, 6:4, 7:3, 8:2 and 9:1) of poly(vinyl alcohol) (PVA) and Carrageenan (Car) was lyophilized to obtain their respective scaffolds. The PVA-Car scaffolds were further characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The prepared scaffolds were found to be biodegradable and highly compatible with hemoglobin. Further, normal keratinocyte (HaCaT) and osteosarcoma (Saos-2) cells seeded on PVA-Car scaffolds were cryopreserved for 15days and their viability was checked at regular interval of 3days (0, 3, 6, 9, 12, 15 days) through MTT assay and fluorescence microscopy. Overall, the collective results indicate the scaffold constructs with 7:3 and 8:2 PVA-Car ratios possess ideal characteristics for tissue engineering applications and for long term cryopreservation of cells.

Expansion of mouse hematopoietic progenitor cells in three-dimensional cocultures on frozen-thawed stromal cell layers formed within porous scaffolds

To establish a highly efficient method of ex vivo expansion of hematopoietic cells (HCs), three-dimensional (3D) cocultures of HCs and stromal cell lines were performed using porous polymer scaffolds. Hematopoietic cells derived from mouse fetal livers were expanded by two successive cultures without the use of exogenous cytokines, namely, 3D cultures of stromal cells (DAS 104-8 cell line) to form stromal layers within the scaffolds, and, subsequently, by cocultures of the HCs on the stromal cell layers for 2 weeks. To expand the HCs more conveniently, in some experiments the stromal layers formed within the scaffolds were frozen (3D freezing) before the cocultures, then stored and applied to the cocultures after thawing. When the HCs were cocultured on the stromal layers of the DAS 104-8 cells, primitive HCs (c-kit(+) and CD34(+) cells) were expanded several fold during the cocultures. In contrast, the expansion of these primitive HCs was remarkably enhanced in the cocultures using the 3D frozen-thawed DAS 104-8 stromal layers (c-kit(+) cells > fifteenfold and CD34(+) cells > thirtyfold), and these expansions were significantly higher than those without the 3D freezing. The expansions enhanced by cocultures on the 3D frozen-thawed stromal layers were also observed in the cocultures with another stromal cell line (DAS 104-4). Because 3D frozen-thawed stromal cell lines are easy to handle, 3D coculture of HCs on frozen-thawed stromal cell lines may be an effective and convenient method for expanding primitive HCs.

Cryopreservation of cell/scaffold tissue-engineered constructs

The aim of this work was to study the effect of cryopreservation over the functionality of tissue-engineered constructs, analyzing the survival and viability of cells seeded, cultured, and cryopreserved onto 3D scaffolds. Further, it also evaluated the effect of cryopreservation over the properties of the scaffold material itself since these are critical for the engineering of most tissues and in particular, tissues such as bone. For this purpose, porous scaffolds, namely fiber meshes based on a starch and poly(caprolactone) blend were seeded with goat bone marrow stem cells (GBMSCs) and cryopreserved for 7 days. Discs of the same material seeded with GBMSCs were also used as controls. After this period, these samples were analyzed and compared to samples collected before the cryopreservation process. The obtained results demonstrate that it is possible to maintain cell viability and scaffolds properties upon cryopreservation of tissue-engineered constructs based on starch scaffolds and goat bone marrow mesenchymal cells using standard cryopreservation methods. In addition, the outcomes of this study suggest that the greater porosity and interconnectivity of scaffolds favor the retention of cellular content and cellular viability during cryopreservation processes, when compared with nonporous discs. These findings indicate that it might be possible to prepare off-the-shelf engineered tissue substitutes and preserve them to be immediately available upon request for patients' needs.

Three-dimensional culture of mouse bone marrow cells on stroma formed within a porous scaffold: influence of scaffold shape and cryopreservation of the stromal layer on expansion of haematopoietic progenitor cells

This study's primary goal was to develop an effective ex vivo expansion method for haematopoietic cells. 3D culture of mouse bone marrow cells was performed in porous scaffolds using a sheet or cube shape. Bone marrow cells were cultured on bone marrow-derived stromal layers formed within the scaffolds and the effect of scaffold shape on the expansion of haematopoietic cells was examined. In some experiments, stromal layers within cubic scaffolds were frozen and then used to culture bone marrow cells after thawing. Results show that after comparison, total cell density and expansion of haematopoietic cells were greater in cultures using the cubic scaffold, suggesting that it was superior to the sheet-like scaffold for expanding haematopoietic cells. When cryopreserved stroma was used, it effectively supported the expansion of haematopoietic cells, and a greater expansion of haematopoietic cells [(erythroid and haematopoietic progenitor cells (HPCs)] was achieved than in cultures with stromal cells that had not been cryopreserved. Expansion of cells using cryopreserved stroma had several other advantages such as a shorter culture period than the conventional method, a stable supply of stromal cells, and ease of handling and scaling up. As a result, this is an attractive method for ex vivo expansion of haematopoietic stem cells (HSCs) and HPCs for clinical use.

Artificial organs 2010: a year in review

In this Editor's Review, articles published in 2010 are organized by category and briefly summarized. As the official journal of The International Federation for Artificial Organs, The International Faculty for Artificial Organs, and the International Society for Rotary Blood Pumps, Artificial Organs continues in the original mission of its founders "to foster communications in the field of artificial organs on an international level."Artificial Organs continues to publish developments and clinical applications of artificial organ technologies in this broad and expanding field of organ Replacement, Recovery, and Regeneration from all over the world. We take this time also to express our gratitude to our authors for offering their work to this journal. We offer our very special thanks to our reviewers who give so generously of time and expertise to review, critique, and especially provide such meaningful suggestions to the author's work whether eventually accepted or rejected and especially to those whose native tongue is not English. Without these excellent and dedicated reviewers the quality expected from such a journal could not be possible. We also express our special thanks to our Publisher, Wiley-Blackwell, for their expert attention and support in the production and marketing of Artificial Organs. In this Editor's Review, that historically has been widely received by our readership, we aim to provide a brief reflection of the currently available worldwide knowledge that is intended to advance and better human life while providing insight for continued application of technologies and methods of organ Replacement, Recovery, and Regeneration. We look forward to recording further advances in the coming years.