Intelligent hydrogel design: Towards more performing hydrogel processing

Despite their highly attractive properties, 3D printing of hydrogel materials can be rather challenging. Herein, we present a novel hydrogel material that can be easily processed into three-dimensional scaffolds using different 3D printing technologies. An acrylate-terminated, urethane-based PEG was prepared by reacting PEG 2000 with isophorone diisocyanate (IPDI) and monoacrylated PEG (336 g/mol) in a 1:2:2 molar ratio (WO 2017/005613 A1). For melt 3D-printing, pure polymer was used (Tm 38°C). For bioprinting, a 50 wt% solution with 3 wt% Laponite was used. Please click Additional Files below to see the full abstract

A semiempirical scaling model for the solid- and liquid-state photopolymerization kinetics of semicrystalline acrylated oligomers

The recent introduction of semicrystalline acrylated oligomers exhibiting fast photoinitiated free radical polymerization in the solid state calls for a deeper understanding of the mechanisms behind the reaction kinetics. The photoinduced polymerization of an acrylated urethane-based poly(ethylene glycol) precursor was studied in detail at temperatures below the melting point using differential photocalorimetry. In isothermal conditions, the exothermal heat flow profile is characterized by an acceleration step followed by a gradual deceleration. In contrast to liquid-state photopolymerization, the well-known gel effect cannot be invoked to account for the reaction acceleration in the crystallized resin. By revisiting the kinetics of free-radical polymerization, it appears that the acceleration results from the buildup of the radical concentration toward steady state in a reaction diffusion driven process. The kinetic behavior is examined in terms of conversion for which any structure-dependent kinetic effect is described by a power-law approximation based on scaling arguments from experimental evidence and polymer physics. This results in a closed-form analytical expression that compares well to experimental data for the photopolymerization kinetics of a semicrystalline acrylated urethane precursor upon adjustment of three parameters. The model is extended to include the additional kinetic complexity for liquid (meth)acrylates and provides a unified approach to free-radical polymerization built on fundamental insights

Printability Evaluation of UV-Curable Aqueous Laponite/Urethane-Based PEG Inks

In the present research, we evaluated the printability of inks that were formulated using an acrylate-endcapped urethane-based poly(ethylene glycol) hydrogel precursor (AUP) and a silicate-based nanoclay Laponite. Flow characterization of the AUP/ Laponite hydrogel inks revealed both yielding and shear thinning behavior, strongly dependent on the concentrations of the AUP and Laponite. In order to have a better insight into printability, the flow behavior along the cross section inside the printing needle was evaluated from the experimental shear flow data. The maximum stress values estimated inside the needle were applied to investigate the structural recovery of the inks using oscillatory rheology. Close analysis of the shear modulus recovery of the AUP/Laponite inks revealed a biexponential behavior, indicating a two-step recovery mechanism. The recovery mechanism is composed of fast and slow recovery steps and it appears that the shape fidelity after ink deposition is primarily controlled by the fast recovery contribution. Optimal printability was achieved for the ink formulation with the shortest characteristic time as well as a high modulus (>500 Pa) compared to the inks which could not be printed into well-defined structures. In the final part, cell interactivity of the three-dimensional (3D)-printed scaffolds was evaluated via live/dead cell assays

Indirect rapid prototyping : opening up unprecedented opportunities in scaffold design and applications

Over the past decades, solid freeform fabrication (SFF) has emerged as the main technology for the production of scaffolds for tissue engineering applications as a result of the architectural versatility. However, certain limitations have also arisen, primarily associated with the available, rather limited range of materials suitable for processing. To overcome these limitations, several research groups have been exploring novel methodologies through which a construct, generated via SFF, is applied as a sacrificial mould for production of the final construct. The technique combines the benefits of SFF techniques in terms of controlled, patient-specific design with a large freedom in material selection associated with conventional scaffold production techniques. Consequently, well-defined 3D scaffolds can be generated in a straightforward manner from previously difficult to print and even "unprintable" materials due to thermomechanical properties that do not match the often strict temperature and pressure requirements for direct rapid prototyping. These include several biomaterials, thermally degradable materials, ceramics and composites. Since it can be combined with conventional pore forming techniques, indirect rapid prototyping (iRP) enables the creation of a hierarchical porosity in the final scaffold with micropores inside the struts. Consequently, scaffolds and implants for applications in both soft and hard tissue regeneration have been reported. In this review, an overview of different iRP strategies and materials are presented from the first reports of the approach at the turn of the century until now

A Semiempirical Scaling Model for the Solid- and Liquid-State Photopolymerization Kinetics of Semicrystalline Acrylated Oligomers

The recent introduction of semicrystalline acrylated oligomers exhibiting fast photoinitiated free radical polymerization in the solid state calls for a deeper understanding of the mechanisms behind the reaction kinetics. The photoinduced polymerization of an acrylated urethane-based poly­(ethylene glycol) precursor was studied in detail at temperatures below the melting point using differential photocalorimetry. In isothermal conditions, the exothermal heat flow profile is characterized by an acceleration step followed by a gradual deceleration. In contrast to liquid-state photopolymerization, the well-known gel effect cannot be invoked to account for the reaction acceleration in the crystallized resin. By revisiting the kinetics of free-radical polymerization, it appears that the acceleration results from the buildup of the radical concentration toward steady state in a reaction–diffusion driven process. The kinetic behavior is examined in terms of conversion for which any structure-dependent kinetic effect is described by a power-law approximation based on scaling arguments from experimental evidence and polymer physics. This results in a closed-form analytical expression that compares well to experimental data for the photopolymerization kinetics of a semicrystalline acrylated urethane precursor upon adjustment of three parameters. The model is extended to include the additional kinetic complexity for liquid (meth)­acrylates and provides a unified approach to free-radical polymerization built on fundamental insights