New bioink to mimic human skin constructs using 3D bioprinting

Engineered skin tissues have versatile applications in clinical settings, such as skin substitution and advanced wound dressings, as well as in pre-clinical scenarios to test new drugs, disease modelling, and cosmetic studies. An ideal engineered skin tissue should be easy to prepare, resistant to mechanical shear forces, and conducive for cell adhesion and growth, in both the epidermal and dermal compartments. It must strike a balance between elasticity and mechanical stability while providing a suitable cell microenvironment to support the different compartments of the human skin.  

Recently, researchers led by Elena Martínez, head of the Biomimetic Systems for Cell Engineering group at IBEC, have published the work “Mimicking human skin constructs using norbornene-pullulan-based hydrogels” on the International Journal of Bioprinting, that will help addressing and solving these issues. Concretely, they introduced a novel photocrosslinkable bioink designed for engineering human skin constructs, based on thiol-norbornene-pullulan (N-PLN) formulations combined with various crosslinkers.  

This new bioink was effectively used in a customized direct laser writing setup to mimic epithelized dermal skin constructs. The dermal compartment was formed by photocrosslinking a pre-gel solution containing human fibroblasts, while the epidermal compartment was developed by seeding human keratinocytes on the fibroblast-laden hydrogels. Using visible light, 2.5 mm³ cell-laden hydrogels could be printed in just 10 seconds. The thiol-ene photocrosslinking chemistry employed here created a well-defined extracellular matrix with orthogonal crosslinks, maintaining high cellular viability rates for encapsulated fibroblasts.  

This study proposes a promising strategy for developing an epithelized dermal human skin model using a custom-made 3D light-based bioprinting system and novel N-PLN polymers. The hydrogels formed after brief exposure to low-dose visible light exhibit the physicochemical properties necessary to support excellent cell viability, proliferation, matrix protein secretion, and elongation, which are crucial for cellular network formation. Additionally, the fibroblast-laden hydrogels support the culture of keratinocytes, enabling the formation of epithelized dermal constructs. 

This method represents an optimistic starting point for developing photocrosslinkable hydrogel-based human skin constructs using thiol-ene norbornene chemistry, paving the way for the creation of complex in vitro models of human tissues. By combining visible light photopolymerization with N-PLN-based materials, this approach represents an alternative method for developing ready-to-use skin models that are easy, fast, reproducible, and cost-effective, which could be particularly beneficial for pre-clinical in vitro assays in cosmetic and pharmaceutical research.