Effect of cell seeding methods on the distribution of cells into the gelatin hydrogel nonwoven fabric

Bioactive gelatin-sheets as novel biopapers to support prevascularization organized by laser-assisted bioprinting for bone tissue engineering

Despite significant advances in the management of patients with oral cancer, maxillofacial reconstruction after ablative surgery remains a clinical challenge. In bone tissue engineering, biofabrication strategies have been proposed as promising alternatives to solve issues associated with current therapies and to produce bone substitutes that mimic both the structure and function of native bone. Among them, laser-assisted bioprinting (LAB) has emerged as a relevant biofabrication method to print living cells and biomaterials with micrometric resolution onto a receiving substrate, also called 'biopaper'. Recent studies have demonstrated the benefits of prevascularization using LAB to promote vascularization and bone regeneration, but mechanical and biological optimization of the biopaper are needed. The aim of this study was to apply gelatin-sheet fabrication process to the development of a novel biopaper able to support prevascularization organized by LAB for bone tissue engineering applications. Gelatin-based sheets incorporating bioactive glasses (BGs) were produced using various freezing methods and crosslinking (CL) parameters. The different formulations were characterized in terms of microstructural, physical, mechanical, and biological properties in monoculture and coculture. Based on multi-criteria analysis, a rank scoring method was used to identify the most relevant formulations. The selected biopaper underwent additional characterization regarding its ability to support mineralization and vasculogenesis, its bioactivity potential andin vivodegradability. The biopaper 'Gel5wt% BG1wt%-slow freezing-CL160 °C 24 h' was selected as the best candidate, due to its suitable properties including high porosity (91.69 ± 1.55%), swelling ratio (91.61 ± 0.60%), Young modulus (3.97 × 104± 0.97 × 104Pa) but also its great cytocompatibility, osteogenesis and bioactivity properties. The preorganization of human umbilical vein endothelial cell using LAB onto this new biopaper led to the formation of microvascular networks. This biopaper was also shown to be compatible with 3D-molding and 3D-stacking strategies. This work allowed the development of a novel biopaper adapted to LAB with great potential for vascularized bone biofabrication.

A Gelatin Hydrogel Nonwoven Fabric Enhances Subcutaneous Islet Engraftment in Rats

Although subcutaneous islet transplantation has many advantages, the subcutaneous space is poor in vessels and transplant efficiency is still low in animal models, except in mice. Subcutaneous islet transplantation using a two-step approach has been proposed, in which a favorable cavity is first prepared using various materials, followed by islet transplantation into the preformed cavity. We previously reported the efficacy of pretreatment using gelatin hydrogel nonwoven fabric (GHNF), and the length of the pretreatment period influenced the results in a mouse model. We investigated whether the preimplantation of GHNF could improve the subcutaneous islet transplantation outcomes in a rat model. GHNF sheets sandwiching a silicone spacer (GHNF group) and silicone spacers without GHNF sheets (control group) were implanted into the subcutaneous space of recipients three weeks before islet transplantation, and diabetes was induced seven days before islet transplantation. Syngeneic islets were transplanted into the space where the silicone spacer was removed. Blood glucose levels, glucose tolerance, immunohistochemistry, and neovascularization were evaluated. The GHNF group showed significantly better blood glucose changes than the control group (p < 0.01). The cure rate was significantly higher in the GHNF group (p < 0.05). The number of vWF-positive vessels was significantly higher in the GHNF group (p < 0.01), and lectin angiography showed the same tendency (p < 0.05). The expression of laminin and collagen III around the transplanted islets was also higher in the GHNF group (p < 0.01). GHNF pretreatment was effective in a rat model, and the main mechanisms might be neovascularization and compensation of the extracellular matrices.

Modified gelatin hydrogel nonwoven fabrics (Genocel) as a skin substitute in murine skin defects

Introduction

From previous research, an emerging material composed of gelatin hydrogel nonwoven fabric (Genocel) has shown potential as a skin substitute, by improving neovascularization promotion in the early phase of wound healing. However, Genocel was inferior in terms of granulation formation compared to Pelnac. To solve this problem, we modified the manufacturing process of Genocel to reduce its water content, extend the degradation time (Genocel-L), and evaluate its healing process as a skin substitute.

Methods

Genocel with a low water content (Genocel-L) was prepared and the difference in water content compared to that of the conventional Genocel was confirmed. Degradation tests were performed using collagenase and compared among Genocel-L, Genocel, and Pelnac sheets. In the in vivo study, sheets of Genocel-L or Pelnac were applied to skin defects created on the backs of C57BL/6JJcl mice. On days 7, 14, and 21, the remaining wound area was evaluated and specimens were harvested for Hematoxylin and Eosin, Azan, anti-CD31, CD68, and CD163 staining to assess neoepithelialization, granulation tissue, capillary formation, and macrophage infiltration.

Results

Genocel-L had a lower water content than the conventional Genocel and a slower degradation than Genocel and Pelnac. In the in vivo experiment, no significant differences were observed between Genocel-L and Pelnac in relation to the wound area, neoepithelium length, granulation formation, and the number of newly formed capillaries. The area of newly formed capillaries in the Pelnac group was significantly larger than that in the Genocel-L group on day 21 (p < 0.05). Regarding macrophage infiltration, significantly more M2 macrophages were induced in the Pelnac group on days 14 and 21, and the M2 ratio was larger in the Pelnac group (p < 0.05) during the entire process.

Conclusions

Genocel-L has a lower water content and slower degradation rate than the conventional Genocel. Genocel-L had equivalent efficacy as a skin substitute to Pelnac, and can therefore be considered feasible for use as a skin substitute. However, a manufacturing method that can further modify Genocel-L is required to recover its early angiogenic potential.

Development of gelatin hydrogel nonwoven fabrics (Genocel®) as a novel skin substitute in murine skin defects

Introduction

Genocel is an emerging material, used in cell culture, with high mechanical strength and good cytocompatibility. Based on these characteristics, Genocel is considered a promising skin substitute for wound healing. In this study, we explored the possibility of using Genocel as a skin substitute for murine skin defects and compared it with a conventional skin substitute.

Methods

Sheets of Genocel and Pelnac were applied to skin defects created on the backs of mice. On days 7, 14, and 21, the remaining wound area was evaluated and specimens were harvested for HE, Azan, anti-CD31, CD68, and CD163 staining to assess neoepithelialization, granulation tissue, capillary formation, and macrophage infiltration.

Results

No significant differences in the wound area or neoepithelium length were observed between groups. The number of newly formed capillaries in the Genocel group was significantly higher than that in the Pelnac group on day 7 (p < 0.05). In contrast, granulation tissue formation in the Pelnac group was greater than that in the Genocel group on day 14 (p < 0.05). Regarding macrophage infiltration, the pan-macrophage number, M2 macrophage number, and M2 ratio in the Pelnac group were higher than those in the Genocel group on day 14 (p < 0.05). In other aspects, the two materials displayed comparable behavior.

Conclusions

Genocel can be used as a skin substitute equivalent to the conventional one. In addition, Genocel accelerated capillary formation, which is more appropriate than conventional treatments for chronic skin ulcers, such as diabetic ulcers.

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Gelatin hydrogel nonwoven fabrics, Genocel was used for the first time as a skin substitute for murine skin defects.

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Genocel displayed comparable behavior with Pelnac and accelerated capillary formation in the early phase.

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However, the Pelnac group produced more granulation tissue and more macrophages than the Genocel group on day 14.

Research and Development of Microphysiological Systems in Japan Supported by the AMED-MPS Project

Microphysiological systems (MPS) have been actively developed as a new technology for in vitro toxicity testing platforms in recent years. MPS are culture techniques for the reconstruction of the specific functions of human organs or tissues in a limited space to create miniaturized human test systems. MPS have great promise as next-generation in vitro toxicity assessment systems. Here, I will review the current status of MPS and discuss the requirements that must be met in order for MPS to be implemented in the field of drug discovery, presenting the example of an in vitro cell assay system for drug-induced liver injury, which is the research subject in our laboratory. Projects aimed at the development of MPS were implemented early in Europe and the United States, and the AMED-MPS project was launched in Japan in 2017. The AMED-MPS project involves industry, government, and academia. Researchers in the field of drug discovery in the pharmaceutical industry also participate in the project. Based on the discussions made in the project, I will introduce the requirements that need to be met by liver-MPS as in vitro toxicity test platforms.

Gelatin hydrogel nonwoven fabrics of a cell culture scaffold to formulate 3-dimensional cell constructs

The objective of this study is to evaluate the possibility of gelatin hydrogel nonwoven fabrics (GHNF) of a cell culture scaffold to formulate 3-dimensional (3D) cell construct. The thickness of cell construct is about 1 mm and the cells inside are live and bio-active, irrespective of their internal distribution. The GHNF were prepared by the solution blow method of gelatin, following by dehydrothermal crosslinking. The GHNF showed a mechanical strength strong enough not to allow the shape to deform even in a wet state. The wet GHNF also showed resistance against repeated compression. After human mesenchymal stromal cells (hMSC) were seeded and cultured, the inner distribution in GHNF, the apoptosis, hypoxia inducible factor (HIF)-1α, Ki67, collagen or sulfated glycosaminoglycan (sGAG) secretion of cells were evaluated. The hMSC proliferated inside the GHNF with time while a homogeneous distribution in the number of cells proliferated from the surface to the 1000 μm depth of GHNF was observed. The number of apoptosis and HIF-1α positive cells was significantly low compared with that of polypropylene nonwoven fabrics with the similar fiber diameters and intra-structure. The GHNF were degraded during cell culture, and completely replaced by collagen and sGAG secreted. It is concluded that the GHNF is a promising cell culture scaffold for 3D cell constructs.

Efficient cell transplantation combining injectable hydrogels with control release of growth factors

Introduction

The objective of this study is to investigate the effect of gelatin microspheres incorporating growth factors on the therapeutic efficacy in cell transplantation. The strength of this study is to combine gelatin hydrogel microspheres incorporating basic fibroblast growth factor and platelet growth factor mixture (GM/GF) with bioabsorbable injectable hydrogels (iGel) for transplantation of adipose-derived stem cells (ASCs).

Methods

The rats ASCs suspended in various solutions were transplanted in masseter muscle. Rats were euthanized 2, 7, 14 days after injection for measurement of the number of ASCs retention in the muscle and morphological evaluation of muscle fibers and the inflammation of the injected tissue by histologic and immunofluorescent stain.

Results

Following the injection into the skeletal muscle, the GM/GF allowed the growth factors to release at the injection site over one week. When ASCs were transplanted into skeletal muscle using iGel incorporating GM/GF (iGel+GM/GF), the number of cells grafted was significantly high compared with other control groups. Moreover, for the groups to which GM/GF was added, the cells transplanted survived, and the Myo-D expression of a myoblast marker was observed at the region of cells transplanted.

Conclusions

The growth factors released for a long time likely enhance the proliferative and differentiative capacity of cells. The simple combination with iGel and GM/GF allowed ASCs to enhance their survival at the injected site and consequently achieve improved therapeutic efficacy in cell transplantation.

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The rats adipose-derived stem cells (ASCs) suspended in various solutions were transplanted in masseter muscle.

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The number of cells transplanted using this study's technology was significantly high compared with other control groups.

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For the groups with growth factors, the Myo-D (myoblast marker) expression was observed at the region of cells transplanted.

Biomaterial-Assisted Regenerative Medicine

This review aims to show case recent regenerative medicine based on biomaterial technologies. Regenerative medicine has arousing substantial interest throughout the world, with “The enhancement of cell activity” one of the essential concepts for the development of regenerative medicine. For example, drug research on drug screening is an important field of regenerative medicine, with the purpose of efficient evaluation of drug effects. It is crucial to enhance cell activity in the body for drug research because the difference in cell condition between in vitro and in vivo leads to a gap in drug evaluation. Biomaterial technology is essential for the further development of regenerative medicine because biomaterials effectively support cell culture or cell transplantation with high cell viability or activity. For example, biomaterial-based cell culture and drug screening could obtain information similar to preclinical or clinical studies. In the case of in vivo studies, biomaterials can assist cell activity, such as natural healing potential, leading to efficient tissue repair of damaged tissue. Therefore, regenerative medicine combined with biomaterials has been noted. For the research of biomaterial-based regenerative medicine, the research objective of regenerative medicine should link to the properties of the biomaterial used in the study. This review introduces regenerative medicine with biomaterial.