Biopolymer-based functional inks for the preparation of artificial cartilage via bioprinting technology

Abstract

We present bioinks based on biopolymers from the native extracellular matrix, namely gelatin and chondroitin sulfate, which are suitable for bioprinting technology applying living mammalian cells. The bioinks can be crosslinked due to chemical modification of the biopolymers with methacrylic functions. Such insoluble hydrogels with tunable physico-chemical propertie are able to closely mimic the native extracellular matrix of biological tissues (ECM). Highly methacrylated gelatin (GM10) resulted in solutions with low viscosities (e.g. 15 wt%: 6.7 ± 1.0 mPa s at 37 °C) within the inkjet-printable range and crosslinked hydrogels with high mechanical strength. Less methacrylated gelatin (GM2) was proper for preparation of soft hydrogels and highly viscous bioinks for pneumatic dispensing technology (e.g. 15 wt%: 39.3 ± 3.6 mPa s at 37 °C). By additional acetylation of GM2 (GM2A8) the solution viscosity could be significantly lowered (e.g. 15 wt%: η = 5.2 ± 0.5 mPa s, 37 °C) and, thus, inkjet-printable bioinks with low crosslinking capacity were also gained. Consequently, a versatile bioink system for bioprinting technology was created. by adjustable twofold modification of gelatin with photochemically reactive and inert groups. Introduction of an additional methacrylated component of the ECM, methacrylated chondroitin sulfate (CSM), further tuned the chemical and physical properties of bioink and hydrogels. GM(A)-CSM hybrid hydrogels possessed for example significantly higher swellability than pure GM(A) hydrogels of the same mass fraction. CSM also influenced bioink viscosity: For unmodified gelatin and gelatin with low degree of modification CSM induced a decrease in bioink viscosity (e.g. 15 wt% GM2: 39.3 ± 3.6 mPa s versus 14 wt% GM2 + 1 wt% CSM: 32.9 ± 6.5 mPa s). In contrast to this, addition of CSM to bioinks made of gelatins with high degree of modification, GM2A8 or GM10, induced an increase in solution viscosity (e.g. 15 wt% GM2A8: 5.2 ± 0.5 mPa s versus 14 wt% GM2A8 + 1 wt% CSM: 6.5 ± 1.0 mPa s). The developed bioinks were proven to be suitable for bioprinting with viable mammalian cells, in this case porcine articular chondrocytes, and for fabrication of tissue models with intrinsic structure. Thus, biomaterials presented in this study can be used for biofabrication of artificial three-dimensional tissues with biomimetic organization, such as articular cartilage with its hierarchical structure.