Extemporaneous Preparation of Injectable and Enzymatically Degradable 3D Cell Culture Matrices from an Animal-Component-Free Recombinant Protein Based on Human Collagen Type I

Human collagen type I‑based scaffold retains human‑derived fibroblasts in a patient‑derived tumor xenograft mouse model

The present study aimed to investigate the role of a recombinant protein based on human collagen type I (RCPhC1) as a scaffold in maintaining the human tumor microenvironment within a patient-derived tumor xenograft (PDTX) model. RCPhC1, synthesized under animal component-free conditions, was explored for its potential to support the human-specific stroma associated with tumor growth. PDTX models were established using resected colorectal cancer liver metastasis specimens, and stromal cell populations from humans and mice were compared using three scaffolds: No scaffold (control), Matrigel and recombinant human collagen type I, across two passages. Specific antibodies for human Lamin B and mouse Lamin B were used for immunostaining to distinguish between human and mouse cells. Additionally, the impact of each scaffold on the invasive ability of mouse fibroblasts was assessed using an invasion assay. Patient-derived tumor tissues embedded with RCPhC1 hydrogels had significantly more human Lamin B-positive cells and fewer mouse Lamin B cells than those embedded with no scaffolds or Matrigel. The human Lamin B-positive cells in PDTX tumors with RCPhC1 hydrogels were recognized as fibroblasts. Additionally, these hydrogels significantly reduced the invasion of mouse fibroblast cell lines in vitro compared with Matrigel. The present study investigated RCPhC1 hydrogels as a new scaffold material for tumor engraftment in PDTX mouse models, and identified a promising experimental tool for maintaining the tumor microenvironment.

Preclustering Gelatin for Faster-Forming Injectable Hydrogels: A Strategy for Fabricating 3D Hydrogel Scaffolds with Improved Cell Dispersion

Gelatin-based injectable hydrogels capable of encapsulating cells are pivotal in tissue engineering because they can conform to any geometry and exhibit physical properties similar to those of living tissues. However, the slow gelation process observed in these cell-encapsulating hydrogels often causes an uneven dispersion of cells. This study proposes an approach for achieving fast gelation of unmodified gelatin under physiological conditions through gelatin preclustering. By using tetrafunctional succinimidyl-terminated poly(ethylene glycol) as a clustering agent, the gelation process is successfully expedited fivefold without requiring chemical modifications, effectively addressing the associated challenges of uneven cell distribution.

Tissue-Adhesive Hydrogel Spray System for Live Cell Immobilization on Biological Surfaces

Gelatin hydrogels are used as three-dimensional cell scaffolds and can be prepared using various methods. One widely accepted approach involves crosslinking gelatin amino groups with poly(ethylene glycol) (PEG) modified with N-hydroxysuccinimide ester (PEG-NHS). This method enables the encapsulation of live cells within the hydrogels and also facilitates the adhesion of the hydrogel to biological tissues by crosslinking their surface amino groups. Consequently, these hydrogels are valuable tools for immobilizing cells that secrete beneficial substances in vivo. However, the application of gelatin hydrogels is limited due to the requirement for several minutes to solidify under conditions of neutral pH and polymer concentrations suitable for live cells. This limitation makes it impractical for use with biological tissues, which have complex shapes or inclined surfaces, restricting its application to semi-closed spaces. In this study, we propose a tissue-adhesive hydrogel that can be sprayed and immobilized with live cells on biological tissue surfaces. This hydrogel system combines two components: (1) gelatin/PEG-NHS hydrogels and (2) instantaneously solidifying PEG hydrogels. The sprayed hydrogel solidified within 5 s after dispensing while maintaining the adhesive properties of the PEG-NHS component. The resulting hydrogels exhibited protein permeability, and the viability of encapsulated human mesenchymal stem/stromal cells (hMSCs) remained above 90% for at least 7 days. This developed hydrogel system represents a promising approach for immobilizing live cells on tissue surfaces with complex shapes.

Adjustable biodegradability of low-swelling hydrogels prepared from recombinant peptides based on human collagen type 1

An ideal hydrogel for tissue engineering and regenerative therapy is cytocompatible, biocompatible, and has low-swelling characteristics. Recently, a novel low-swelling hydrogel with a homogenous structure was developed by crosslinking a recombinant peptide, modeled on human collagen type 1 (RCPhC1), with a four-arm polyethylene glycol (tetra-PEG). Here, we hypothesized that the biodegradability of the RCPhC1 hydrogel was adjustable by altering its initial polymer concentration. Three types of RCPhC1 hydrogels were prepared using the initial polymer at different concentrations, and their morphology, swelling ratio, collagenase degradability, cytocompatibility, biocompatibility, and biodegradability were compared. The results revealed a low swelling ratio. The higher the concentration of the initial polymer, the longer it took for it to be degraded by collagenase. The average cell viability ratio was over 92% when using the direct contact method, which suggests that the hydrogels have excellent cytocompatibility. No death, tumorigenesis, exposure of the implants, or skin necrosis associated with the subcutaneous implantation of the hydrogels was found in mice in vivo. Moreover, histological evaluation revealed the formation of a thin fibrous capsule, which suggests an acceptable biocompatibility. Furthermore, as hypothesized, it was confirmed that the biodegradability can be adjusted by changing the initial polymer concentration. Collectively, the ability to fine-tune the biodegradability of RCPhC1 hydrogels demonstrates their potential for use in various clinical applications.

On-demand retrieval of cells three-dimensionally seeded in injectable thioester-based hydrogels

Scaffold systems that can easily encapsulate cells and safely retrieve them at the desired time are important for the advancement of cell-based medicine. In this study, we designed and fabricated thioester-based poly(ethylene glycol) (PEG) hydrogels with injectability and on-demand degradability as new scaffold materials for cells. Hydrogels can be formed in situ within minutes via thioester cross-linking between PEG molecules and can be degraded under mild conditions in response to l-cysteine molecules through thiol exchange occurring at the thioester linkage. Various cell experiments, especially with sucrose, which enables the adjustment of the osmotic pressure around the cells, showed that the damage to the cells during encapsulation and degradation was minimal, indicating the capability of on-demand retrieval of intact cells. This hydrogel system is a versatile tool in the field of cell-based research and applications such as tissue regeneration and regenerative medicine.

Human mesenchymal stem/stromal cells can be three-dimensionally encapsulated in hydrogels cross-linked with thioester linkages. Degrading the cell-embedded hydrogels by l-cysteine molecules enables safe on-demand retrieval of the cells.