4D printing of biodegradable elastomers with tailorable thermal response at physiological temperature.

4D printing has a great potential for the manufacturing of soft robotics and medical devices. The alliance of digital light processing (DLP) 3D printing and novel shape-memory photopolymers allows for the fabrication of smart 4D-printed medical devices in high resolution and with tailorable functionalities. However, most of the reported 4D-printed materials are nondegradable, which limits their clinical applications. On the other hand, 4D printing of biodegradable shape-memory elastomers is highly challenging, especially when transition points close to physiological temperature and shape fixation under ambient conditions are required. Here, we report the 4D printing of biodegradable shape-memory elastomers with tailorable transition points covering physiological temperature, by using poly(D,L-lactide-co-trimethylene carbonate) methacrylates at various monomer feed ratios. After the programming step, the high-resolution DLP printed stents preserved their folded shape at room temperature, and showed efficient shape recovery at 37 °C. The materials were cytocompatible and readily degradable under physiological conditions. Furthermore, drug-loaded devices with tuneable release kinetics were realized by DLP-printing with resins containing polymers and levofloxacin or nintedanib. This study offers a new perspective for the development of next-generation 4D-printed medical devices.

Composites reinforced via mechanical interlocking of surface-roughened microplatelets within ductile and brittle matrices.

Load-bearing reinforcing elements in a continuous matrix allow for improved mechanical properties and can reduce the weight of structural composites. As the mechanical performance of composite systems are heavily affected by the interfacial properties, tailoring the interactions between matrices and reinforcing elements is a crucial problem. Recently, several studies using bio-inspired model systems suggested that interfacial mechanical interlocking is an efficient mechanism for energy dissipation in platelet-reinforced composites. While cheap and effective solutions are available at the macroscale, the modification of surface topography in micron-sized reinforcing elements still represents a challenging task. Here, we report a simple method to create nanoasperities with tailored sizes and densities on the surface of alumina platelets and investigate their micromechanical effect on the energy dissipation mechanisms of nacre-like materials. Composites reinforced with roughened platelets exhibit improved mechanical properties for both organic ductile epoxy and inorganic brittle cement matrices. Mechanical interlocking increases the modulus of toughness (area under the stress-strain curve) by 110% and 56% in epoxy and cement matrices, respectively, as compared to those reinforced with flat platelets. This interlocking mechanism can potentially lead to a significant reduction in the weight of mechanical components while retaining the structural performance required in the application field.

Monodisperse functional colloidosomes with tailored nanoparticle shells.

We report the assembly of monodisperse colloidosomes containing a wide range of functional nanoparticles in the outer shell using a double emulsion templating method in a microfluidic device. By selecting nanoparticles of specific functionalities, hollow capsules with inert, magnetic, photocatalytic, and potentially biocompatible and piezoelectric shells are easily obtained. Proper control over the surface chemistry of the nanoparticles forming the shell and of the liquid interfaces involved is key to enable the assembly of colloidosomes using this double emulsification route.

Fatigue of zirconia and dental bridge geometry: Design implications.

UNLABELLED: Zirconia is currently used as a framework material for posterior all-ceramic bridges. While the majority of research efforts have focused on the microstructure and corresponding mechanical properties of this material, clinical fractures appear to be largely associated with the appliance geometry. OBJECTIVE: The objective of this study was to estimate the maximum stress concentration posed by the connector geometry and to provide adjusted estimates of the minimum connector diameter that is required for achieving 20 years of function. METHODS: A simple quantitative description of the connector geometry in an all-ceramic 4-unit bridge design is used with published stress concentration factor charts to estimate the degree of stress concentration and the maximum stress. RESULTS: The magnitude of stress concentration estimated for clinically relevant connector geometries ranges from 2 to 3. Using previously published recommendations for connector designs, adjusted estimates for the minimum connector diameter required to achieve 20 years of clinical function are presented. SIGNIFICANCE: To prevent clinical fractures the minimum connector diameter in multi-unit bridges designs must account for the loads incurred during function and the extent of stress concentration posed by the connector geometry.

In vitro lifetime of dental ceramics under cyclic loading in water.

All-ceramic dental restorations exhibit enhanced esthetics and biocompatibility as compared to traditional metal-based prosthesis. However, long-term fatigue and subcritical crack growth in the presence of water and cyclic loading can decrease the strength of ceramic components over time. We investigated the cyclic fatigue in water of three dental materials currently used as frameworks in all-ceramic restorations: a 3 mol%-yttria partially stabilized zirconia (3Y-TZP, Cercon, Degudent GmbH), a Al(2)O(3)-ZrO(2)-Glass composite (Inceram-Zirconia, Vita Zahnfabrik GmbH) and a Li(2)O.2SiO(2) glass ceramic (Empress 2, Ivoclar Vivadent AG). Fatigue and fast fracture tests were performed to determine the Weibull distribution of lifetime and initial mechanical strength for each framework component. In spite of its noticeable susceptibility to fatigue in water, the 3Y-TZP material was found to be particularly suitable for the preparation of posterior all-ceramic bridges due to its high initial mechanical strength. Guidelines are provided for the selection of materials and the design of all-ceramic posterior bridges exhibiting lifetime longer than 20 years under severe wet and cyclic loading conditions.

Change of zeta potential of biocompatible colloidal oxide particles upon adsorption of bovine serum albumin and lysozyme.

The amounts of negatively charged bovine serum albumin and positively charged lysozyme adsorbed on alumina, silica, titania, and zirconia particles (diameters 73 to 271 nm) in aqueous suspensions are measured. The adsorbed proteins change the zeta potentials and the isoelectric points (IEP) of the oxide particles. The added to adsorbed protein ratios at pH 7.5 are compared with the protein treated particle zeta potentials. It is found that the amounts of adsorbed proteins on the alumina, silica, and titania (but not on the zirconia) particle surfaces are highly correlated with the zeta potential. For the slightly less hydrophilic zirconia particles high amounts of protein adsorption are observed even under repulsive electrostatic conditions. One reason could be that the hydrophobic effect plays a more important role for zirconia than electrostatic interaction.