Bone defects caused by various aetiologies, such as trauma, tumours, infection and congenital deformities, together with articular cartilage defects and osteochondral complex defects caused by trauma and degenerative diseases, are common clinical diseases that significantly affect the patient’s quality of life. Repair and regenerating these defects in bone and cartilage is a considerable challenge for clinicians.

There has been significant progress in the development of tissue engineering over the past two decades, which has brought new hope for the regenerative treatment of bone and cartilage defects. Conventional tissue engineering techniques mainly include the injection of a cell suspension and the transplantation of scaffolds seeded with cells. However, several problems remain to be solved.

With the injection of a cell suspension, locating the injected suspension and controlling the shape and size of the cell suspension after injection is difficult. The number of cells that can be delivered by one injection is quite limited, and the cells are easily lost after injection. Additionally, a uniform distribution of the injected suspension is difficult to achieve. Thus far, the cell injection technique cannot meet the requirements for regenerating tissue morphology and function.

An ideal biodegradable scaffold material that can efficiently promote cell adhesion, proliferation and extracellular matrix (ECM) secretion with suitable mechanical properties is still being sought by researchers. Existing scaffold materials usually have several limitations, such as insufficient biological activity, unstable degradation rate and immunogenicity, resulting in immune responses and inflammation after transplantation. Cell–material interactions are usually uncontrollable and may result in high cell mortality.

Cell–cell interactions and ECM formation contribute to maintaining tissue stability. Conventional tissue engineering techniques for harvesting cells by trypsin digestion damage cell–cell interactions, cell–ECM interactions and cell membrane proteins, resulting in decreased cell adhesion and proliferation.

To overcome the shortcomings of conventional tissue engineering technology, cell sheet technology, an alternative approach, has gradually attracted the attention of researchers in recent years. Cell sheet technology was developed based on a novel technique for culturing and harvesting cells using temperatureresponsive culture dishes, which was first reported in 1990. The hydrophilic and hydrophobic properties of the temperature sensitive material poly(N-isopropylacrylamide) (PIPAAm) could be altered by changing the temperature, resulting in control over cell attachment and detachment. Cell sheet technology can be used to harvest cells without utilising proteolytic enzymes, such as trypsin, or chelating agents, such as ethylenediaminetetraacetic acid. Thus the cell–cell junctions, ECM and cell sheet structure are effectively preserved, allowing the constructed tissue to have a high cell density and a uniform cell distribution and thus to mimic native tissue more closely.

In addition, cell sheets are prepared by the formation of cell–cell junctions and the secretion of ECM and are free from the limitations of scaffold materials, such as the immune and inflammatory reactions caused by scaffold implantation, tissue collapse caused by a fast degradation rate and compromised tissue formation caused by a slow degradation rate.

The application of this technology in bone and cartilage regeneration has been widely studied. On the one hand, cell sheets can be used without scaffolds for bone and cartilage regeneration; thus they more closely mimic native tissue and avoid the limitations and potential problems of scaffolds. On the other hand, cell sheets can also be used in combination with various scaffolds and may be a better choice than traditional scaffolds seeded with cell suspensions because cell sheets can effectively preserve cell–cell junctions and ECM. Several widely used cell sheet preparation systems, including traditional methods, and recent improvements in these methods, as well as their advantages and shortcomings, will be reviewed.

In this paper just published in International Journal of Oral Science by researchers of Shanghai Jiao Tong University School of Medicine recent advances in the application of cell sheet technology for the repair and regeneration of bone and cartilage defects are reviewed and the key limitations of cell sheet applications in bone and cartilage regeneration, along with directions for future research, are discussed.

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