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.

Gelatin, a denatured form of collagen, is an attractive biomaterial for biotechnology. In particular, gelatin particles have been noted due to their attractive properties as drug carriers. The drug release from gelatin particles can be easily controlled by the crosslinking degree of gelatin molecule, responding to the purpose of the research. The gelatin particles capable of drug release are effective in wound healing, drug screening models. For example, a sustained release of growth factors for tissue regeneration at the injured sites can heal a wound. In the case of the drug screening model, a tissue-like model composed of cells with high activity by the sustained release of drug or growth factor provides reliable results of drug effects. Gelatin particles are effective in drug delivery and the culture of spheroids or cell sheets because the particles prevent hypoxia-derived cell death. This review introduces recent research on gelatin microparticles-based strategies for regenerative therapy and drug screening models.

The objective of this study is to design a co-culture system of cancer cells and three-dimensional (3D) mesenchymal stem cells (MSC) aggregates for the in vitro evaluation of cancer invasion. First, the MSC of an immunosuppressive phenotype (MSC2) were prepared by the MSC stimulation of polyriboinosinic polyribocytidylic acid. By simple mixing MSC2 and gelatin hydrogel microspheres (GM) in a U-bottomed well of 96 well plates which had been pre-coated with poly (vinyl alcohol), 3D MSC2 aggregates incorporating GM were obtained. The amount of chemokine (C–C motif) ligand 5 (CCL5) secreted from the MSC2 aggregates incorporating GM. Finally, an invasion assay was performed to evaluate the cancer invasion rate by co-cultured cancer cells and the 3D MSC2 incorporating GM. The amount of CCL5 secreted for the 3D MSC2 aggregates incorporating GM was significantly higher than that of two-dimensional (2D) MSC, 2D MSC2, and 3D MSC aggregates incorporating GM. When MDA-MB-231 human breast cancer cells were co-cultured with the 3D MSC2 aggregates incorporating GM, the invasion rate of cancer cells was significantly high compared with that of 2D MSC or 2D MSC2 and 3D MSC aggregates incorporating GM. In addition, high secretion of matrix metalloproteinase-2 was observed for the 3D MSC2 aggregates/cancer cells system. It is concluded that the co-culture system of 3D MSC2 aggregates incorporating GM and cancer cells is promising to evaluate the invasion of cancer cells in vitro.

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). 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. 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. 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.

Background: We have previously reported engineered macrophages (MacTriggers) that can accelerate the release of tumor necrosis factor-α in response to M2 polarization. MacTriggers are characterized by two original characteristics of macrophages: (1) migration to tumors; and (2) polarization to the M2 phenotype in tumors. Intravenously administered MacTriggers efficiently accumulated in the tumors and induced tumor-specific inflammation. This study reports a novel methodology for enhancing the anti-tumor effects of immune checkpoint inhibitors (ICIs). Results: In this study, we newly found that the intravenously administered MacTriggers in BALB/c mouse models upregulated the expression levels of immune checkpoint proteins, such as programmed cell death (PD)-1 in CD8⁺ T cells and PD-ligand 1 (PD-L1) in cancer cells and macrophages. Consequently, in two ICI-resistant tumor-inoculated mouse models, the combined administration of MacTrigger and anti-PD-1 antibody (aPD-1) synergistically inhibited tumor growth, whereas monotherapy with aPD-1 did not exhibit anti-tumor effects. This synergistic effect was mainly from aPD-1 enhancing the tumor-attacking ability of CD8⁺ T cells, which could infiltrate into the tumors following MacTrigger treatment. Importantly, no side effects were observed in normal tissues, particularly in the liver and spleen, indicating that the MacTriggers did not enhance the aPD-1 reactivity in normal tissues. This specificity was from the MacTriggers not polarizing to the M2 phenotype in normal tissues, thereby avoiding inflammation and increased PD-1/PD-L1 expression. MacTriggers could enhance aPD-1 reactivity only in tumors following tumor-specific inflammation induction. Conclusions: Our findings suggest that the MacTrigger and aPD-1 combination therapy is a novel approach for potentially overcoming the current low ICI response rates while avoiding side effects.