Additive manufacturing or, as also called, three-dimensional (3D) printing is considered as a game-changer in replacing traditional processing methods in numerous applications; yet, it has one intrinsic potential weakness related to bonding of layers formed during the printing process. Prior to finding solutions for improvement, a thorough quantitative understanding of the mechanical properties of the interface is needed. Here, a quantitative analysis of the nanomechanical properties in 3D printed photopolymers formed by digital light processing (DLP) stereolithography (SLA) is shown. Mapping of the contact Young’s modulus across the layered structure is performed by atomic force microscopy (AFM) with a submicrometer resolution. The peakforce quantitative nanomechanical mapping (PF-QNM) mode was employed in the AFM experiments. The layered specimens were obtained from an acrylate-based resin (PR48, Autodesk), containing also a light-absorbing dye. We observed local depressions with values up to 30% of the maximum stiffness at the interface between the consecutively deposited layers, indicating local depletion of molecular cross-link density. The thickness values of the interfacial layers were approximately 11 μm, which corresponds to ∼22% of the total layer thickness (50 μm). We attribute this to heterogeneities of the photopolymerization reaction, related to (1) atmospheric oxygen inhibition and (2) molecular diffusion across the interface. Additionally, a pronounced stiffness decay was observed across each individual layer with a skewed profile. This behavior was rationalized by a spatial variation of the polymer cross-link density related to the variations of light absorption within the layers. This is caused by the presence of light absorbers in the printed material, resulting in a spatial decay of light intensity during photopolymerization.

The introduction of two-photon polymerization (2PP) to the field of tissue engineering and regenerative medicine (TERM) has led to great expectations for the production of scaffolds with an unprecedented degree of complexity and tailorable architecture. Unfortunately, resolution and size are usually mutually exclusive when using 2PP, resulting in a lack of highly-detailed scaffolds with a relevant size for clinical application. Through the combination of using a highly reactive photopolymer and optimizing key printing parameters, we propose for the first time a biodegradable and biocompatible poly(trimethylene-carbonate) (PTMC)-based scaffold of large size (18 × 18 × 0.9 mm) with a volume of 292 mm3 produced using 2PP. This increase in size results in a significant volumetric increase by almost an order of magnitude compared to previously available large-scale structures (Stichel 2010 J. Laser Micro./Nanoeng. 5 209–12). The structure’s detailed design resulted in a highly porous scaffold (96%) with excellent cytocompatibility, supporting the attachment, proliferation and differentiation of human adipose-derived mesenchymal stem cells towards their osteogenic and chondrogenic lineages. This work strongly attests that 2PP is becoming a highly suitable technique for producing large-sized scaffolds with a complex architecture. We show as a proof-of-concept that an arrayed design of repetitive units can be produced, but a further perspective will be to print scaffolds with anisotropic features that are more representative of human tissues.

We extend the Liouville-type theorems of Gilbarg and Weinberger and of Koch, Nadirashvili, Seregin and Sverák valid for the stationary variant of the classical Navier-Stokes equations in 2D to the degenerate power law fluid model.

The growth dynamics for metallic filaments in conductive-bridge resistive-switching random access memory (CBRAM) are studied using the kinetic Monte Carlo (KMC) method. The physical process at the atomistic level is revealed in explaining the experimental observation that filament growth can originate at either the cathode or the anode. The statistical nature of the filament growth is best shown by the random topography of dendrite-like conductive paths obtained. Critical material properties, such as charged-particle mobility in the switching layer of a solid electrolyte or a dielectric, are mapped to KMC model parameters through activation energy, etc. The accuracy of the simulator is established by the good agreement between the simulated forming time and the measured data.