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In the present paper, we report results on the impact of thermal shock cycles on mechanical properties and microstructure of lithium disilicate dental glass-ceramic relevant to the production process. A distinct reduction of the bending strength is observed after suffering more than five thermal shock cycles. The crystal, morphological and atomic structural characteristics before and after the thermal shock were detected by X-ray diffraction, infrared spectroscopy and field-emission scanning electron microscopy. Furthermore, theoretical calculations, based on density functional theory, were performed on models for the distorted and undistorted lithium disilicate crystal lattices. We show that the morphological and mechanical changes can be attributed primarily to the distortion of the Si-O-Si structural unit of the lithium disilicate glass-ceramic.

Inspired by flagellate microorganisms in nature, the microhelix is considered as an ideal model for transportation in fluid environment with low Reynolds number. However, how to promote the swimming and loading capabilities of microhelices with controllable geometries remains challenging. In this study, a novel kind of conical hollow microhelices is proposed and a method is developed to rapidly fabricate these microhelices with controllable parameters by femtosecond vortex beams generated from spatial light modulation along helical scanning. Conical hollow microhelices with designable heights (H = 45-75 µm), diameters (D = 6-18 µm), pitch numbers (Pi = 2-4), taper angles (T = 0.1-0.6 rad), and pitch periods (ΔP = 10-30 µm) are efficiently fabricated. In addition, compared with straight microhelices, the forward swimming capability of conical microhelices increases by 50% and the lateral drift of the conical hollow microhelices is reduced by 70%. Finally, the capabilities of these conical hollow microhelices for nanocargo loading and release by the inner hollow core, as well as transportation of neural stem cells by the outer surface are demonstrated. This work provides new insights into faster and simultaneous transportation of multicargoes for hybrid drug delivery, targeted therapy, and noninvasive surgery in vivo.

In this Letter, parallel writing of silver microwire (AgMW) arrays based on femtosecond laser multiphoton reduction (MPR) is realized by modulating a femtosecond laser beam into a multifoci pattern with a spatial light modulator (SLM). Arbitrarily distributed multifoci are generated with predesigned holograms loaded on a SLM for MPR. The experimental parameters for the desired fabrication of AgMWs with multifoci are systematically investigated and optimized. On this basis, different AgMW patterns are dynamically and simultaneously fabricated by loading different holograms onto a high-frequency refreshed SLM in sequence. The quantity and distribution of multifoci can be controlled dynamically by the SLM in the fabrication process, and even the intensity of individual focus is dynamically modulated by the control of the gray level of holograms. Finally, the potential application of this flexible and rapid AgMW fabrication method in microheater fabrication is demonstrated. The microheaters exhibit a controllable temperature gradient after energized.

Microfabrication by using structured laser beams provides a rapid and facile way for creating some specific microstructures. As an important member in the structured beam category, optical vortices can be easily generated by a helical phase and focused into a geometry-tunable pattern by an objective. In this work, optical vortices with diverse intensity distributions, e.g., different sizes, geometries, and deflection angles, are generated by controlling the phase factors imprinted on optical vortices, including topological charge, fold number, and modulation depth, respectively. The focusing properties of the measured optical vortices in a high numerical aperture laser microfabrication system agree with the theoretical calculation by the Debye vectorial diffraction theory. Three dimensional complex microtubes are rapidly realized by simply scanning the optical vortices along a designed route in a photoresist. With this method, microtubes with controlled diameters, polygonal geometry, winding edges, and ev...

In this Letter, superposed Bessel beams (SBBs) are realized by alternatively imprinting holograms of opposite-order Bessel beams along the radial direction on a spatial light modulator. The propagation invariance and non-rotation properties of SBBs are theoretically predicted and experimentally demonstrated. The focusing property of SBBs with a high numerical aperture (NA) objective is investigated with the Debye vectorial diffraction theory. Near the focal plane, a circularly distributed multiple foci pattern is achieved. The multiple foci generated from SBBs are adopted in a two-photon fabrication system, and micropattern fabrication by a single exposure is demonstrated. Facile fabrication of three-dimensional microstructures with SBBs is realized by dynamically controlling the number of focal spots, and the diameter and rotation of the focal pattern.