Layer‐by‐Layer Growth of Multicomponent Colloidal Crystals Over Large Areas

Self‐assembly of different sized colloidal particles into multicomponent crystals results in novel material properties compared to the properties of the individual components alone. The formation of binary and, for the first time, ternary colloidal crystals through a simple and inexpensive confined‐area evaporation‐induced layer‐by‐layer (LBL) assembly method is reported. The proposed method produces high quality multicomponent colloidal crystal films over a broad range of particle size‐ratios and large surface areas (cm²) from silica/polystyrene colloidal suspensions of low concentration. By adjusting the size‐ratio and concentration of the colloidal particles, complex crystals of tunable stoichiometries are fabricated and their structural characteristics are further confirmed with reported crystal analogues. In addition, complex structures form as a result of the interplay of the template layer effect, the surface forces exerted by the meniscus of the drying liquid, the space filling principle, and entropic forces. Thus, this LBL approach is a versatile way to grow colloidal crystals with binary, ternary, or more complex structures.     

The adsorption characteristics of osteopontin on hydroxyapatite and gold

The adsorption of osteopontin on hydroxyapatite (HA) and reference gold (Au) surfaces was studied at different protein bulk concentrations over the temperature range 295-317 K, using quartz crystal microbalance with dissipation (QCM-D) and X-ray photoelectron spectroscopy (XPS). The QCM-D protein adsorption studies were complemented with polyclonal antibodies to examine the availability of protein sequences on the resulting protein layer. The QCM-D and XPS results show that the osteopontin surface mass uptake is larger on Au as compared to HA surfaces within the range of experimental conditions examined (protein bulk concentrations and temperature range), in accordance with the formation of a more compact protein film on Au. The specific antibody binding to the resulting adsorbed osteopontin layer as measured by QCM-D further confirms that the protein packing and conformational/orientational changes occurring during OPN adsorption on Au and HA are different, since fewer antibodies are observed to bind per OPN molecule on Au as compared to HA. The adsorption process on the respective surfaces was modeled using both the Langmuir and Hill adsorption isotherms, and from these isotherm curves, the Gibbs free energy, ?G, of the osteopontin adsorption was determined. The estimated ?G values indicate that the osteopontin molecules have a high affinity towards Au, while a lower affinity is observed between osteopontin and HA. By examining the changes in ?G as a function of temperature, we additionally find that the osteopontin adsorption on HA and Au is endothermic and driven by an increase in entropy.     

Electrostatic and capillary force directed tunable 3D binary micro- and nanoparticle assemblies on surfaces

We report a simple, rapid and cost-effective method based on evaporation induced assembly to grow 3D binary colloidal assemblies on a hydrophobic/hydrophilic substrate by simple drop casting. The evaporation of a mixed colloidal drop results in ring-like or uniform area deposition depending on the concentration of particles, and thus assembly occurs at the periphery of a ring or uniformly all over the drop area. Binary colloidal assemblies of different crystal structure are successfully prepared over a wide range of size ratios (γ = small/large) from 0.06 to 0.30 by tuning the γ of the micro- and nanoparticles used during assembly. The growth mechanism of 3D binary colloidal assemblies is investigated and it is found that electrostatic forces facilitate assembly formation until the end of the evaporation process, with capillary forces also playing a role. In addition, the effects of solvent type, humidity, and salt concentration on crystal formation and ordering behaviour are also examined. Furthermore, long range, highly ordered binary colloidal assemblies can be fabricated by the choice of a low conducting solvent combined with evaporation induced assembly.     

3D Biomaterial Microarrays for Regenerative Medicine: Current State‐of‐the‐Art,Emerging Directions and Future Trends

Three dimensional (3D) biomaterial microarrays hold enormous promise for regenerative medicine because of their ability to accelerate the design and fabrication of biomimetic materials. Such tissue‐like biomaterials can provide an appropriate microenvironment for stimulating and controlling stem cell differentiation into tissue‐specific lineages. The use of 3D biomaterial microarrays can, if optimized correctly, result in a more than 1000‐fold reduction in biomaterials and cells consumption when engineering optimal materials combinations, which makes these miniaturized systems very attractive for tissue engineering and drug screening applications.     

Immobilisation of living bacteria for AFM imaging under physiological conditions

Atomic force microscopy (AFM) holds great potential for studying the nanoscale surface structures of living cells, and to measure their interactions with abiotic surfaces, other cells, or specific biomolecules. However, the application of AFM in microbiology is challenging due to the difficulty of immobilising bacterial cells to a flat surface without changing the cell surface properties or cell viability. We have performed an extensive and thorough study of how to functionalise surfaces in order to immobilise living bacteria for AFM studies in liquid environments. Our aim was to develop a scheme which allows bacterial cells to be immobilised to a flat surface with sufficient strength to avoid detachment during the AFM scanning, and without affecting cell surface chemistry, structure, and viability. We compare and evaluate published methods, and present a new, reproducible, and generally applicable scheme for immobilising bacteria cells for an AFM imaging.     

Nanoreinforced Hydrogels for Tissue Engineering: Biomaterials that are Compatible with Load‐Bearing and Electroactive Tissues

Given their highly porous nature and excellent water retention, hydrogel‐based biomaterials can mimic critical properties of the native cellular environment. However, their potential to emulate the electromechanical milieu of native tissues or conform well with the curved topology of human organs needs to be further explored to address a broad range of physiological demands of the body. In this regard, the incorporation of nanomaterials within hydrogels has shown great promise, as a simple one‐step approach, to generate multifunctional scaffolds with previously unattainable biological, mechanical, and electrical properties. Here, recent advances in the fabrication and application of nanocomposite hydrogels in tissue engineering applications are described, with specific attention toward skeletal and electroactive tissues, such as cardiac, nerve, bone, cartilage, and skeletal muscle. Additionally, some potential uses of nanoreinforced hydrogels within the emerging disciplines of cyborganics, bionics, and soft biorobotics are highlighted.     

An investigation of the reasons for non-compliance with FAR regulations in Tehran

The majority of the Tehran metropolitan region’s problems are associated with building contraventions, which intensified after migration from other parts of the country to the region increased. This migration coincided with a boom in the construction sector and an increase in density selling by the Tehran municipality.     

A Combinatorial Library of Micro‐Topographies and Chemical Compositions for Tailored Surface Wettability

Surface modification of topography and chemistry in order to achieve a specific water contact angle (CA) has been explored by using a novel combinatorial screening platform. The screening arrays consisted of 507 distinct combinations of micro‐topographies and chemical compositions. By performing chemical modifications with 1H, 1H, 2H, 2H perfluoroethyltriethoxy‐silane (PFS) and n‐octadecyltriethoxysilane (ODS) on standard silicon wafers it was possible to include both superhydrophobic and very hydrophilic pad arrays in the same screening platform. Surfaces modified with PFS were more hydrophobic than surfaces modified with ODS, while the unmodified silicon surfaces were hydrophilic. For the PFS modified surfaces the largest CAs were achieved with a small pillar size of X = 1 µm and an intermediate inter‐pillar gap size of Y = 4 µm with superhydrophobic CAs over 170°. Surface analysis with X‐ray photoelectron spectroscopy (XPS) revealed that CF₃ groups were present at the surface, contributing to the superhydrophobic effect. The ODS modified surfaces had intermediate wettabilities with CAs between 100 and 150°, which were dependent on the pillar size, the inter‐pillar gap size, and the specific pillar pattern. The unmodified silicon topographical surfaces were very hydrophilic with CAs below 20° independent of specific topography. With this approach we have managed to fabricate 507 distinct surface areas covering a range of wettabilities, which is useful when screening these effects in several different applications. The measured CAs did not follow the simple Wenzel model. Furthermore, the adaptation of the Cassie model introduces Φ_s, the fraction of solid surface in contact with the liquid, which is difficult to estimate, thereby emphasizing the need for an experimental determination.