Tissue engineering via two-photon polymerization
(Attilio Marino) Several biophysical investigations suggest that a peculiar cell behavior can be in vitro resembled by mimicking the corresponding in vivo conditions.  In order to in vitro mimic the 3D natural microenvironment of the bone tissue we prepared, thanks to the slice-by-slice two-photon polymerization (2PP) approach, trabecula-like structures (named ‘‘Osteoprints’’) that resemble the typical microenvironment of trabecular bone cells. 
Particularly, the 3D model of the Osteoprint was obtained from X-ray micro-computed tomography (µ-CT) scans of a human trabecular bone biopsy, taken from the femoral neck (Fig. 1). Osteoprints were subsequently fabricated through 2PP of the biocompatible ceramic photopolymer Ormocomp®, the mechanical properties of which are similar to that of the natural bone. SEM imaging (Fig. 2) of the obtained Osteoprints reveals a shape and size exactly resembling those of the corresponding 3D µ-CT model, thus demonstrating the high resolution and reliability of the 2PP technique.
left: Fig. 1: 3D reconstruction of bone trabeculae obtained by μ-CT scans of a biopsy from the human femoral neck.
right: Fig. 2: SEM imaging of an Osteoprint prepared by slice-by-slice 2PP of the hybrid ceramic Ormocomp® photoresist.
Fig. 3: 3D reconstruction of a bone cell culture on the Osteoprint (in red), highlighting the deposition of several hydroxyapatite nodules (in green).
After an extensive Osteoprint characterization, the adhesion, proliferation and differentiation of SaOS-2 osteoblast-like cells were studied on the obtained scaffolds.
The presence of the Osteoprints was able to deeply affect cell behavior, promoting the cell cycle exit and the osteogenic differentiation. An up-regulation of the genes involved on osteogenesis and an enhancement of the hydroxyapatite nodule production were the major outcomes (Fig. 3).
These results encourage the exploitation of the 2PP for obtaining 3D biomimetic structures, useful for a wide range of in vitro application and even in tissue engineering and regenerative medicine. 
This article was provided by Nanoscribe’s customer, the Italian Institute of Technology, Center for Micro-BioRobotics @SSSA.
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