Wavelength-Dependent Shaping of Azopolymer Micropillars for Three-Dimensional Structure Control

: Surfaces endowed with three-dimensional (3D) mesostructures, showing features in the nanometer to micrometer range, are critical for applications in several fields of science and technology. Finding a fabrication method that is simultaneously inexpensive, simple, fast, versatile, highly scalable, and capable of producing complex 3D shapes is still a challenge. Herein, we characterize the photoreconfiguration of a micropillar array of an azobenzene-containing polymer at different light wavelengths and demonstrate the tailoring of the surface geometry and its related functionality only using light. By changing the irradiated light wavelength and its polarization, we demonstrate the fabrication of various complex isotropic and anisotropic 3D mesostructures from a single original pristine geometry. Quantitative morphological analyses revealed an interplay between the decay rate of absorbed light intensity, micropillar volume preservation, and the cohesive forces between the azopolymer chains as the origin of distinctive wavelength-dependent 3D structural remorphing. Finally, we show the potentialities of this method in surface engineering by photoreshaping a single original micropillar surface into two sets of different mesostructured surfaces exhibiting tunable hydrophobicity in a wide water contact angle range. Our study opens up a new paradigm for fabricating functional 3D mesostructures in a simple, low-cost, fast, and scalable manner

Diffractive Refractometer Based on Scalar Theory

The measurement of the refractive index typically requires the use of optical ellipsometry which, although potentially very accurate, is extremely sensitive to the structural properties of the sample and its theoretical modeling, and typically requires specialized expertise to obtain reliable output data. Here, we propose a simple diffractive method for the measurement of the refractive index of homogenous solid thin films, which requires only the structuring of the surface of the material to be measured with the profile of a diffraction grating. The refractive index of an exemplary soft-moldable material is successfully estimated over a wide wavelength range by simply incorporating the measured topography and diffraction efficiency of the grating into a convenient scalar theory-based diffraction model. Without the need for specialized expertise and equipment, the method can serve as a simple and widely accessible optical characterization of materials useful in material science and photonics applications

Effectiveness of various sintering aids on the densification and in vitro properties of carbonated hydroxyapatite porous scaffolds produced by foam replication technique

Synthetic carbonated hydroxyapatite (CHA) ceramics are considered as future materials for bone substitutes due to their good bioactivity, biocompatibility and similarity to the inorganic mineralized phase of bone. However, the limited thermal stability of CHA-based materials at elevated temperature remains a critical challenge particularly in producing three-dimensional (3D) porous scaffolds. To address the aforementioned limitation, this paper presents a new approach by incorporating several types of sintering aids, namely Mg(OH)2, Ca(OH)2, NaOH, KOH and K2CO3 into the CHA slurry composition to identify the most effective ones in developing 3D CHA scaffolds. This approach focused on physico-chemical, mechanical and biological characteristics that can be helpful in designing scaffolds for bone tissue engineering. Five compositions of scaffolds were prepared by replication technique, sintered at 800°C and eventually cooled down in wet CO2 atmosphere. Scaffolds prepared with K2CO3 (CHAKC) as sintering aid exhibited optimum interconnected pores with densified struts and the highest compressive strength. Biologically, CHAKC provides the most favorable milieu in supporting apatite formation as well as encouraging better cell attachment and activities. Our findings highlight that the use of K2CO3 had effectively enhanced the architecture and compressive strength of the CHA scaffolds without any toxicity evidence