"The field of biofabrication is continually growing due to the increasing life expectancy of humans. The most promising technique in this field is 3D bioprinting, nevertheless, there are still several limitations like low resolution, the challenging printing of hollow tubular structures with low wall thickness due to high shear rates, and low cell alignment. 4D biofabrication is a technique where the fourth dimension is introduced by using smart materials, that are capable to undergo shape transformation after the addition of certain stimuli. The fourth dimension offers advantages such as hollow structure fabrication, various shape formations, and preservation of 2D patterns in the 3D structure. Based on the design using 4D biofabrication it is possible to fabricate highly complex structures with specific/ uniaxial cell alignment that resembles blood vessels, muscle tissues, lungs, etc.
Electrospinning allows the formation of highly aligned fibers in the sub-micron/micron range, that mimics natural fibers in the extracellular matrix. Fibrous electrospun mono-, bi-, and multi-layers by addition of stimuli like temperature and/or aqueous media, can transform into a tubular structure.
We have designed various fibrous shape-morphing systems that can be used as autografts for nerve, blood vessel, and muscle tissue regeneration. The extra high porosity of fibrous shape-morphing materials not only allows fast actuation rates (10s ) but as well supports good nutrition and waste product exchange [1-3]. Designed bilayers have a good degradation rate, showing 70 % mass loss after one-month real-time degradation without losing the stability of sell-rolled construct . Cell types such as fibroblasts, skeletal muscle cells, and nerve cells have shown high viability and good proliferation. The use of conductive particles in fibrous shape-morphing monolayer showed improved differentiation of nerve cells. Overall fibrous shape-morphing systems have shown promising results for muscle, nerve, and blood vessel regeneration.
 Apsite, I; Stoychev, G; Zhang, W; Jehnichen, D; Xie, J; Ionov, L. Biomacromolecules., 2017, 18, 3178
 Apsite, I.; Uribe, J. M.; Posada, A. F.; Rosenfeldt, S.; Salehi, S.; Ionov, L., 4D biofabrication of skeletal muscle microtissues. Biofabrication 2019, 12 (1), 015016.
 Apsite, I.; Constante, G.; Dulle, M.; Vogt, L.; Caspari, A.; Boccaccini, A. R.; Synytska, A.; Salehi, S.; Ionov, L., 4D Biofabrication of fibrous artificial nerve graft for neuron regeneration. Biofabrication 2020, 12 (3), 035027."