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Surface coatings are critical in biomaterials and biomedical devices. Chemical vapor deposition (CVD) is a well-known technology for the generation of thin films on a surface. However, the granular structures produced using CVD are rare. Recently, we used PPX-C, an excellent insulating material, for granular structure coating using CVD. Colloidal self-assembly is also a well-established method to generate granular structures named colloidal self-assembled patterns (cSAPs). In this study, we combined these two technologies to generate hierarchical granular structures and tested the biophysical effect of these hybrid surfaces on human bone marrow mesenchymal stem cells (hBMSCs). Two CVD-derived granular structures were made using water or glycerin droplets (i.e., CVD or GlyCVD surfaces). Water drops generate porous particles, while glycerin drops generate core–shell particles on the surface. These particles were dispersed randomly on the surface with sizes ranging from 1 to 20 μm. These CVD surfaces were hydrophobic (WCA ~ 80–110 degrees). On the other hand, a binary colloidal crystal (BCC), one type of cSAPs, composed of 5 μm Si and 400 nm carboxylated polystyrene (PSC) particles, had a close-packed structure and a hydrophilic surface (WCA ~ 45 degrees). The hybrid surfaces (i.e., CVD-BCC and GlyCVD-BCC) were smooth (Ra ~ 1.1–1.5 μm) and hydrophilic (WCA ~ 50 degrees), indicating a large surface coverage of BCC dominating the surface property. The hybrid surfaces were expected to be slightly negatively charged due to naturally charged CVD particles and negatively charged BCC particles. Cell adhesion was reduced on the hybrid surfaces, leading to an aggregated cell morphology, without reducing cell activity, compared to the flat control after 5 days. qPCR analysis showed that gene expression of type II collagen (COL2) was highly expressed on the GlyCVD-BCC without chemical induction after 3 and 14 days compared to the flat control. This proof-of-concept study demonstrates the potential of combining two technologies to make hybrid structures that can modulate stem cell attachment and differentiation. [ABSTRACT FROM AUTHOR]

[Display omitted] The colloidal epitaxy utilizing a patterned substrate is used to fabricate colloidal crystals of the same structure and lattice spacing with the substrate, which is an effective technique for creating desired nanoscale architectures. However, this technique has been mainly limited to a single-component system. The colloidal epitaxy is versatile if multicomponent colloidal crystals can be produced, which is inspired by our previous study regarding binary colloidal crystals (b-CCs) fabricated at the edge of single-component crystals. We have examined various particle size combinations of binary colloidal mixture and substrates for heteroepitaxial growth of b-CCs. Colloidal crystallization was achieved through depletion attraction induced by added polymers. We demonstrated heteroepitaxial growth of b-CCs on the foreign colloidal crystals as the substrate. Under depletion attraction, deviation from equilibrium interparticle distance because of lattice mismatch between the substrate and epitaxial layers induces strain energy among the particles, yielding the b-CCs to attain minimum strain energy. Various types of b-CCs are created by adjusting the particle size ratio and polymer concentration. The heteroepitaxial growth technique enables the fabrication of complex multicomponent colloidal crystals that greatly facilitate versatile applications of the colloidal crystals. [ABSTRACT FROM AUTHOR]

In this paper, we consider numerical approximations for the two-component PFC models for binary colloidal crystals. In addition to the Cahn–Hilliard type two-component PFC model that is commonly used for considering mass conservation, we also derived a new Allen–Cahn type two-component PFC model by using the L 2 -gradient flow and add two nonlocal Lagrange multipliers to the system to conserve the mass for each component. For these two types of two-component PFC models, the stabilized scalar auxiliary variable (SAV) approach is adopted to develop efficient, decoupled, second-order accurate, and linear numerical schemes, where a new SAV is introduced to reformulate the models, and two extra linear stabilization terms are added to improve the stability and keep the required accuracy thus allowing large time steps. These schemes are unconditionally energy stable, mass conservative and require solving only four linear equations with constant coefficients at each time step. Numerical examples are performed to demonstrate the accuracy and energy stability of the proposed schemes, and numerous 2D and 3D simulations are also presented to show a variety of complex binary ordered patterns of phase transformation. [ABSTRACT FROM AUTHOR]

Self-assembly of two types of particles into the binary colloidal crystals (BCCs) leads to the peculiar features which the monocomponent colloidal crystals do not possess. However, the self-assembly methods of the BCCs are still limited. A facile, cost-effective and controllable approach was presented to fabricate the BCCs by directly dripping silica particle suspensions containing water and ethanol into the monodisperse polytetrafluoroethylene (PTFE) colloidal solutions. The BCCs composed of the silica and PTFE particles were formed at the air-liquid interface and picked up using the target substrates, followed by the corrosion of silica particles. Using this strategy, various ordered porous PTFE films including homo-pore-size mono/multilayer and hetero-pore-size bilayer films were prepared. The chemical composition of the porous films was well controlled. The dissolution of ethanol resulted in the interfacial tension gradient, and thus the Marangoni convection and the relative movement of the liquid and the particles emerged. The silica particles were trapped at the air-liquid interface and the PTFE particles filled the interstitial spaces between the silica particles. After the porous films were sintered at temperatures above the melting point of PTFE, the PTFE particles were transformed into nanofibers, leading to the transferability, excellent superhydrophobicity and environmental durability. [ABSTRACT FROM AUTHOR]

Surface topography can have significant impact on the cell fate decisions of stem cells. Construction of a biomaterial that can mimic the physiological microenvironment can be used to enhance the maintenance or differentiation of stem cells. Here, we manufacture two surfaces with monolayer binary colloidal crystals (BCCs) having different topographies, Si2PM and Si5PM, and examined their effect on maintenance and differentiation of human embryonic stem cells (hESCs). Our results demonstrated that BCCs can be coupled with vitronectin to maintain pluripotency of hESCs during culture, and with a gelatin coating to improve early definitive endoderm differentiation of hESCs using an embryonic body assay (i.e., FOXA2 up-regulation). BCCs can be used as novel cell culture substrates to support stem cell maintenance and differentiation. [ABSTRACT FROM AUTHOR]

Binary colloidal crystals (BCCs) possess great potentials in tuning material and optical properties. In this paper, the combination of interface transferred method and spin-coating method is used to fabricate BCCs with different patterns via controlling the size ratio of small (S) to large (L) colloidal spheres and the spin speeds. It is found that BCCs formed LS 2 , LS 4 and LS 6 by changing the size ratio. In addition, there are some new and complicated structures, such as LS 12 , Janus arrays, formed at the low spin speed. This simple assembly method has potential to allow for the creation of optical metmaterials and the plasmonic structures with chiral optical properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • A PS bCCs-based MIM SERS substrate is fabricated. • The bCCs nanostructure provides rich hot spots and stability for the SERS substrates. • The MIM structure substrates could enhance the SERS performance further. • The PS bCCs-based MIM SERS substrates exhibit outstanding SERS activity. Surface-enhanced Raman scattering (SERS) is a powerful molecular vibrational spectrum characterization method, and has shown promising applications in surface science, life science, environmental monitoring, etc. Developing new simple processes to fabricate low-cost substrates is an essential prerequisite to promote and strengthen the practical application of the SERS technique. For this purpose, the present work reports on the development of a metal/insulator/metal (MIM) structure combined with polystyrene (PS) binary colloidal crystals (bCCs) based on nanosphere self-assembly and electron-beam evaporation technologies. The PS bCCs are used to form a dielectric layer sandwiched between a bottom Ag reflection layer and an upper Ag shell layer. Compared with single-sized colloidal spheres, the PS bCCs exhibit considerably richer morphologies and structures. In addition, the closely packed Ag shell arrays enhance the density of electromagnetic field "hot spots" thus increasing the SERS activity. The PS bCCs-based MIM substrate could achieve an enhancement factor (EF) of 1.10 × 108 and an ultralow detection limit for the Rhodamine 6G (R6G) molecule of about 10−14 M. The results demonstrate that the proposed substrates with a facile fabrication strategy, low cost, large area and high sensitivity have high potential applications of SERS sensors for bio- and chemical molecular analysis. [ABSTRACT FROM AUTHOR]

Abstract: Monodispersed silica particles with bimodal size distribution were successfully prepared through adding an ethanol (EtOH) solution containing tetraethylorthosilicate (TEOS) dropwise into an ammonia EtOH solution at a constant low rate. The effects of the reaction parameters such as ammonia/ethanol ratio, feeding rate of TEOS solution, reaction temperature, and time on the size and size distribution of the as-obtained particles were investigated. Based on these phenomena, a modified LaMer model of nucleation and growth mechanism was proposed to reasonably explain the formation of the as-obtained silica particles with bimodal size distribution. The as-prepared monodispersed silica particles with bimodal size distribution can be directly fabricated into binary colloidal crystals with small particles surrounding large particles by evaporation–induced cooperative self–assembly. This suggests that the method reported here provides a straightforward and effective route to the in situ fabrication of novel binary colloidal crystals and their replicated patterns in one reaction system. [Copyright &y& Elsevier]

Abstract: We report an improved convective self-assembly method for the fabrication of highly ordered, crack-free binary colloidal crystals (BCCs) and the associated inverse structures in large domains at length scales of several centimeters. With this method, BCCs can be fabricated in a non-close packed pattern and binary inverse opal films can be obtained over a centimeter scale. The presence of tetraethyl orthosilicate (TEOS) sol in the self-assembly system was found to play a significant role in the resultant structures. The pseudostop band positions are adjustable via varying the number ratio of small to large polystyrene (PS) spheres. At a given TEOS-to-PS ratio, the binary inverse opal film thickness was controllable by varying the colloidal volume fraction with an upper thickness threshold (>16 layers). [Copyright &y& Elsevier]

Abstract: Theoretical and experimental investigations have demonstrated that full bandgaps are not easy to achieve in the face-centered cubic (fcc) unary and binary structures; even for unary inverse opals with high refractive index network, the bandgaps are not as large as 1D or 2D structures. In this work, we simulated the bandgap of a binary inverse opal, which is over 16% larger than that of a unary inverse crystal. Two kinds of binary colloidal crystals and their inverse structures have been fabricated by a horizontal deposition method. [Copyright &y& Elsevier]

• Different surface topographies were prepared using BCC fabrication. • ESCs showed different population growth patterns on different topographies. • BCCs (COM1 & COM2) showed a better support for stemness of ESCs compared to TCPs. Understanding the interactions of stem cells with surface topography can give us an invaluable tool in controlling stemness and fate of stem cells for further use in biomedical applications. In this study, we have fabricated topographical features using a class of cell culture substrates called binary colloidal crystals (BCCs), that are made by self-assembly of mixtures of spherical micron sized silica (Si) and nanometer sized polystyrene (PS) or poly (methyl methacrylate) (PMMA) particles. The substrates formed are arrays of ordered, hexagonally packed large Si particles inter-dispersed with the PS particles that are stabilized by gentle heating, which melts the PS or PMMA forming substrates suitable for cell culture. BCC substrates were used for culture of mouse embryonic stem cells (mESCs). Compared to tissue culture plates, COM1 (Si5-PMMA0.4), COM2 (Si5-PS0.4) and COM4 (Si2-PSC0.22) have shown to provide a better support for mESC proliferation in the presence of the cytokine leukemia inhibitory factor (LIF). The behavior of mESCs with the BCCs in presence and absence of LIF, was further explored and it was found that interaction of mESCs with the culture substrate can be controlled by tuning surface topography and roughness, which is determined by the size and type of particles used in making BCCs. Furthermore, it was shown that limiting cell-surface interactions and controlling colony shape can promote stemness maintenance on COM1 and COM2 substrates as indicated by better proliferation and higher expression of pluripotency genes including Nanog both in presence and in absence of LIF. Together with higher expression of GATA6 gene, it can be stated that these surfaces can be used for endodermic priming of mESCs. Therefore, we believe that these surfaces, especially COM1 and COM2 surfaces can be beneficial as stem cell culture systems for further use in biomedical research. [ABSTRACT FROM AUTHOR]