3D Bioprinting of Dermal Scaffolds for Full-Thickness Skin Tissue Regeneration

Academic Background

The skin, being the largest organ of the human body, plays a crucial role in defending against external environmental damage and preventing microbial invasion. However, when the skin suffers extensive damage, its self-repair capabilities are limited, often leading to issues such as scar formation and inflammatory responses, which affect the normal morphology and function of the skin. Traditional skin substitutes, such as films, hydrogels, and nanofiber membranes, can accelerate wound healing but fail to fully replicate the microenvironment of healthy skin, resulting in differences in morphology and function compared to normal skin. In recent years, three-dimensional (3D) bioprinting technology has emerged as a research hotspot in the field of skin tissue engineering due to its ability to precisely control the deposition of biomaterials and cells, enabling the construction of complex 3D structures.

This study aims to develop a novel bioink using Digital Light Processing (DLP) technology to print skin scaffolds with antibacterial, anti-inflammatory, and cell proliferation-promoting functions, thereby accelerating the healing process of full-thickness skin defects.

Source of the Paper

This paper was co-authored by Lu Han, Zixian Liu, Meng Li, Zhizhong Shen, Jianming Wang, and Shengbo Sang from institutions such as Taiyuan University of Technology, Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering, and General Hospital of Tisco. The paper was published online on December 27, 2024, in the journal Bio-design and Manufacturing, with the DOI 10.1631/bdm.2400058.

Research Process and Results

1. Preparation and Characterization of Bioink

This study developed a composite bioink composed of methacrylated gelatin (GelMA) and chitosan oligosaccharide (COS). GelMA is a photocrosslinkable hydrogel with excellent biocompatibility and adjustable physicochemical properties, while COS possesses antibacterial, anti-inflammatory, and cell proliferation-promoting functions. The researchers first synthesized GelMA and mixed it with different concentrations of COS to prepare four bioinks with varying ratios (G10C0, G10C1, G10C3, G10C6).

Through Fourier Transform Infrared Spectroscopy (FTIR) analysis, the researchers confirmed the chemical structure of the GelMA/COS hydrogel and found that as the COS concentration increased, the crosslinking density of the hydrogel decreased, leading to enhanced water absorption capacity and degradation rate. Additionally, compression tests showed that the introduction of COS improved the elasticity of the hydrogel but reduced its compressive modulus. Scanning Electron Microscopy (SEM) observations revealed that the hydrogel had a porous and interconnected microstructure, with pore size decreasing and porosity increasing as the COS concentration increased.

2. Antibacterial Performance Testing

To evaluate the antibacterial properties of the GelMA/COS hydrogel, the researchers conducted surface antibacterial experiments using Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) as typical Gram-positive and Gram-negative bacteria, respectively. The results showed that as the COS concentration increased, the inhibition rates of the hydrogel against both bacteria gradually increased, reaching up to 94% and 95%, respectively. This indicates that COS can bind to the negatively charged groups on bacterial cell membranes, disrupting their structure and exerting antibacterial effects.

3. Cytocompatibility Study

The researchers seeded Human Dermal Fibroblasts (HDFs) into the GelMA/COS hydrogel to evaluate cell proliferation, viability, and morphology. The CCK-8 assay showed that as the COS concentration increased, the proliferation capacity of HDFs significantly improved. Live/dead staining experiments demonstrated high cell viability in all hydrogels, with good cell morphology. Immunofluorescence staining and quantitative real-time PCR (qPCR) analysis further indicated that the addition of COS suppressed the expression of fibrosis-related genes (such as collagen I, collagen III, and fibronectin I), thereby reducing scar formation.

4. DLP Printing of Skin Scaffolds

The researchers used a DLP printer to print the G10C1 bioink into a grid-like structure, constructing a cell-laden skin scaffold. SEM observations revealed that the scaffold had a uniformly distributed porous structure, promoting cell migration and nutrient exchange. Live/dead staining and immunofluorescence staining results showed high cell viability after printing, with HDFs growing along the scaffold pores and secreting extracellular matrix (ECM) proteins.

5. In Vivo Experiments

To assess the wound healing efficacy of the skin scaffold, the researchers created a full-thickness skin defect model on the backs of nude mice and implanted the cell-laden scaffold into the wounds. The results demonstrated that the cell-laden scaffold significantly accelerated wound closure, reduced inflammatory responses, and promoted angiogenesis. Histological analysis showed more organized collagen deposition and less scar formation in the scaffold group. Immunohistochemical staining further confirmed lower expression of inflammatory factors (such as TNF-α) and higher expression of angiogenesis markers (such as CD31 and α-SMA) in the scaffold group.

Conclusions and Significance

This study successfully developed a composite bioink based on GelMA/COS and rapidly constructed a cell-laden skin scaffold using DLP technology. The scaffold exhibited excellent water absorption, degradation, mechanical properties, and cytocompatibility, along with significant antibacterial activity. In vivo experiments demonstrated that the scaffold accelerated wound closure, reduced inflammation, promoted angiogenesis, and improved wound healing.

The scientific value of this study lies in providing a novel bioink formulation and 3D printing technology that can precisely mimic the structure and function of natural skin, offering new insights for the treatment of full-thickness skin defects. Its application value lies in the scaffold’s ease of manufacturing, excellent biocompatibility, and antibacterial properties, making it a promising candidate for clinical skin tissue regeneration.

Research Highlights

1. Novel Bioink: The GelMA/COS composite bioink exhibits excellent biocompatibility, antibacterial properties, and adjustable physicochemical characteristics.
2. DLP Printing Technology: High-resolution, high-cell-viability 3D printing was achieved using DLP technology, enabling the construction of skin scaffolds with complex structures.
3. In Vivo Validation: The scaffold’s significant effects on accelerating wound healing, reducing inflammation, and promoting angiogenesis were validated in a nude mouse model.

Additional Valuable Information

A limitation of this study is that while promising results were obtained in the nude mouse model, significant differences exist between wound healing processes in mice and humans. Therefore, future studies should further validate its applicability and regenerative effects in larger animal models, such as pigs.