Abstract
Two-photon polymerization (2PP) is a high-resolution 3D-printing technology with a very rapidly expanding field of applications, including tissue engineering (TE). In this field, 2PP offers unprecedented possibilities for systematic studies of both cell–cell and cell–material interactions in 3D. For TE applications, the reliable production of biodegradable micro-scaffolds in porous, complex architectures is essential. However, the number of biodegradable materials that support the required level of spatial resolution is very limited, being a major bottleneck for the use of 2PP in the TE field.Herein, we introduce a hexa-functional urethane-based biodegradable precursor that overcomes the limitations associated with the high-resolution printing of current biodegradable precursors. The precursor is a telechelic urethane-based poly-ε-caprolactone (PCL) possessing three acrylate functionalities at each polymer end group which enables the reliable production of complex architectures owing to its superior physical properties as compared to the traditional di-acrylate terminated analogs. The newly developed hexa-functional telechelic urethane-based PCL reveals enhanced crosslinking kinetics and one order of magnitude higher Young’s modulus compared to the di-functional precursor (57.8 versus 6.3 MPa), providing an efficient and solvent-free 2PP processing at fast scanning speeds of up to 100 mm s−1 with unprecedented feature resolutions (143 ± 18 nm at 100 mm s−1 scanning speed). The crosslinked hexa-functional polymer combines strength and flexibility owing to the segregation between its hard polyacrylate and soft PCL segments, which makes it suitable for biological systems in contrast to the highly crosslinked and rigid structures typically manufactured by 2PP. Furthermore, it revealed lower degradation rate compared to its di-functional analog, which can be considered as an advantage in terms of biocompatibility due to the slower formation of acidic degradation products. Extracts of the developed polymers did not show a cytotoxic effect on the L929 fibroblasts as confirmed via ISO 10993-5 standard protocol. The presented precursor design constitutes a simple and effective approach that can be easily translated towards other biodegradable polymers for the manufacturing of biodegradable constructs with nano-scale precision, offering for the first time to use the true capabilities of 2PP for TE applications with the use of synthetic biodegradable polymers.
Highlights
Two-photon polymerization (2PP) [1], sometimes referred to as multiphoton lithography, is a nano- and microfabrication technology with a rapidly growing field of explored applications ranging from the manufacturing of microlenses [2,3], photonic crystals [4,5], to micromechanical and microfluidic devices [6,7,8]
A slightly higher molar mass was observed for UPCL-6 (11,300 g molÀ1) compared to UPCL-2 (9020 g molÀ1), while both of them had an at least 3 times higher molar mass compared to the starting product PCLdiol
Chromatograms of UPCL-2 and UPCL-6, which correspond with the unreacted end-capping agents and/or the adducts formed by the reaction of IPDI with the end-capping agents
Summary
Two-photon polymerization (2PP) [1], sometimes referred to as multiphoton lithography, is a nano- and microfabrication technology with a rapidly growing field of explored applications ranging from the manufacturing of microlenses [2,3], photonic crystals [4,5], to micromechanical and microfluidic devices [6,7,8]. Its main advantage compared to available additive manufacturing (AM) methods is the capability to produce complex threedimensional (3D) structures at a resolution of a few hundred nanometers [11]. This is achieved via two-photon absorption, a nonlinear process, which allows the highly localized deposition of light into a photosensitive resin. There is no need to add material in a layer-by-layer fashion, which is typically the case in conventional AM-technologies [1]
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