A Review on Stimuli-Actuated 3D Micro/Nanostructures for Tissue Engineering and the Potential of Laser-DirectWriting via Two-Photon Polymerization for Structure Fabrication

In this review, we present the most recent and relevant research that has been done
regarding the fabrication of 3D micro/nanostructures for tissue engineering applications. First, we
make an overview of 3D micro/nanostructures that act as backbone constructs where the seeded cells
can attach, proliferate and differentiate towards the formation of new tissue. Then, we describe the
fabrication of 3D micro/nanostructures that are able to control the cellular processes leading to faster
tissue regeneration, by actuation using topographical, mechanical, chemical, electric or magnetic
stimuli. An in-depth analysis of the actuation of the 3D micro/nanostructures using each of the
above-mentioned stimuli for controlling the behavior of the seeded cells is provided. For each type
of stimulus, a particular recent application is presented and discussed, such as controlling the cell
proliferation and avoiding the formation of a necrotic core (topographic stimulation), controlling the
cell adhesion (nanostructuring), supporting the cell differentiation via nuclei deformation (mechanical
stimulation), improving the osteogenesis (chemical and magnetic stimulation), controlled drug delivery
systems (electric stimulation) and fastening tissue formation (magnetic stimulation). The
existing techniques used for the fabrication of such stimuli-actuated 3D micro/nanostructures, are
briefly summarized. Special attention is dedicated to structures’ fabrication using laser-assisted
technologies. The performances of stimuli-actuated 3D micro/nanostructures fabricated by laser direct
writing via two-photon polymerization are particularly emphasized.