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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]

In this article, we demonstrate a method for inducing reversible crystal-to-crystal transitions in binary mixtures of soft colloidal particles. Through a controlled decrease of salinity and increasingly dominating electrostatic interactions, a single sample is shown to reversibly organize into entropic crystals, electrostatic attraction-dominated crystals, or aggregated gels, which we quantify using microscopy and image analysis. We furthermore analyze crystalline structures with bond order analysis to discern between two crystal phases. We observe the different phases using a sample holder geometry that allows both in situ salinity control and imaging through confocal laser scanning microscopy and apply a synthesis method producing particles with high resolvability in microscopy with control over particle size. The particle softness provides for an enhanced crystallization speed, while altering the re-entrant melting behavior as compared to hard sphere systems. This work thus provides several tools for use in the reproducible manufacture and analysis of binary colloidal crystals.

In this work, amyloid fibrils are used as a template for the preparation of long silica fibers, with a variety of aspect ratios and surface roughness. Starting with β-lactoglobulin fibrils with typical diameters of about 20 nm and a length of several micrometers, two different strategies are followed to grow silica: either in water at acidic pH values, or in ethanol-water mixtures under Stöber conditions and an excellent control of both the thickness and the roughness of the silica layer has been achieved. Silica nanofibers with a thickness ranging from a few nanometers to hundreds of nanometers are prepared. As an application, the rough silica nanotubes are used to create superhydrophobic surfaces by mimicking the structure of the lotus leaf. The papillary structure of the lotus leaf is replicated by depositing 10 μm colloidal particles in either a single colloidal crystal, or in a binary colloidal crystal made with smaller sub-micrometer particles. Then, silica nanofibers are deposited on the binary colloidal crystal surfaces through a layer-by-layer deposition procedure to replicate the nanoscale roughness provided by wax nanotubes. Upon hydrophobization of the silica nanotubes, the final surfaces are highly superhydrophobic, with a water contact angle of 165.5°., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Micro- and nanotopographies can interfere with bacteria attachment, however, the interplay existing between surface chemistry and topography remains unclear. Here, self-assembled spherical micrometer- silica and nanometer poly(methyl methacrylate) (PMMA)-sized particles are used to make binary colloidal crystal (BCC) topographical patterns to study bacterial attachment. A uniform surface chemistry of allylamine plasma polymer (AAMpp) is coated on the top of the BCCs to study only the topography effects. The uncoated and coated BCCs are exposed to Pseudomonas aeruginosa, and the surfaces and bacteria are characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and fluorescence microscopy. It is found that bacteria attachment to the uncoated BCCs is delayed and individual cells are attracted to the small particle regions of the patterns. Surprisingly, this phenomenon is also observed for the AAMpp-coated BCCs, with bacteria attaching to the small particle regions of the pattern, in stark contrast to uniform flat films of AAMpp that are highly adhesive toward P. aeruginosa. Also, the overall levels of bacterial attachment are significantly reduced by the BCC patterns compared to controls. Thus, there is a trade-off that exists between chemistry and topography that can be exploited to delay the onset of P. aeruginosa biofilm formation on surfaces., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The ability of bacteria to form biofilms and the emergence of antibiotic-resistant strains have prompted the need to develop the next generation of antibacterial coatings. Antimicrobial peptides (AMPs) are showing promise as molecules that can address these issues, especially if used when immobilized as a surface coating. We present a method that explores how surface patterns together with the selective immobilization of an AMP called PuroA (FPVTWRWWKWWKG-NH 2 ) can be used to both kill bacteria and also as a tool to study bacterial attachment mechanisms. Surface patterning is achieved using stabilized self-assembled binary colloidal crystal (BCC) layers, allowing selective PuroA immobilization to carboxylated particles using N-(3-dimethylaminopropyl)-N'-ethyl carbodiimide (EDC) hydrochloride/N-hydroxysuccinimide (NHS) coupling chemistry. Covalent immobilization of PuroA was compared with physical adsorption (i.e., without the addition of EDC/NHS). The AMP-functionalized colloids and BCC layers were characterized by X-ray photoelectron spectroscopy, ζ potentials, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Surface antimicrobial activity was assessed by viability assays using Escherichia coli. MALDI-TOF MS analysis revealed that although not all of PuroA was successfully covalently immobilized, a relatively low density of PuroA (1.93 × 10 13 molecules/cm 2 and 7.14 × 10 12 molecules/cm 2 for covalent and physical immobilization, respectively) was found to be sufficient at significantly decreasing the viability of E. coli by 70% when compared to that of control samples. The findings provide a proof of concept that BCC layers are a suitable platform for the patterned immobilization of AMPs and the importance of ascertaining the success of small-molecule grafting reactions using surface-MALDI, something that is often assumed to be successful in the field.

A new surface based on self-assembly of two colloids into well-defined nanostructures, so-called binary colloidal crystals (BCCs), was fabricated for stem cell culture. The facile fabrication process are able to cover large surface areas (>3 cm-diameter, i.e. > 7 cm(2)) with ordered surface nanotopographies that is often a challenge particularly in biomaterials science. From our library, four different combinations of BCCs were selected using mixtures of silica, polystyrene and poly(methyl methacrylate) particles with sizes in the range from 100 nm to 5 μm. Cell spreading, proliferation, and surface-induced lineage commitment of human adipose-derived stem cells (hADSCs) was studied using quantitative real time polymerase chain reaction (qRT-PCR) and immunostaining. The results showed that BCCs induced osteo- and chondro- but not adipo-gene expression in the absence of induction medium suggesting that the osteochondral lineage can be stimulated by the BCCs. When applying induction media, higher osteo- and chondro-gene expression on BCCs was found compared with tissue culture polystyrene (TCPS) and flat silica (Si) controls, respectively. Colony forming of chondrogenic hADSCs was found on BCCs and TCPS but not Si controls, suggesting that the differentiation of stem cells is surface-dependent. BCCs provide access to complex nanotopographies and chemistries, which can find applications in cell culture and regenerative medicine.