Hyaline cartilage is composed of chondrocytes and proteoglycans, interpenetrating a collagenous fibrillar network. A few current repair strategies (ie: Matrix Autologous Chondrocyte Implantation) are based on this architecture and involve the culture of chondrocytes in a biocompatible matrix prior to implantation. A common strategy to produce fibrillar polymeric networks for tissue engineering is electrospinning. However, a characteristic property of electrospun scaffolds, despite the broad range of fibers that can be obtained, is a very compact architecture. As a result, when an electrospun membrane is seeded with cells, they fail to infiltrate it.
Several techniques have been described in the literature to increase its porosity and allow the creation of reinforced cellular structures. A promising technique is the so-called cryo-electrospinning. As opposed to conventional electrospinning, the collecting drum is kept at subzero temperatures throughout the process. While polymer fibers are being collected onto the mandrel, ice crystals are being deposited. The resulting membrane is immediately placed under vacuum to sublimate the ice crystals, leaving void spaces behind. By using this technique, the porosity of electrospun scaffolds can be increased up to 99.5%.
Figure 1 | Cross-section of an electrospun membrane with a conventional setup (left) and a cryo-electrospinning setup.
The resulting scaffold can serve multiple purposes. A homogenous hydrogel/nanofiber composite can be made, reinforcing a mechanically weak hydrogel and allowing their survival in an in vivo environment. The scaffolds also allow the preparation of cell-seeded structures, in a tunable manner. Finally, the cryo-electrospun membrane can be functionalized and used as a drug reservoir for sustained drug delivery. With our approach, we mimic the structure of native cartilage by combining three key components: hydrogel, polymeric network and cells.