Porous polymer films templated by marangoni flow-induced water droplet arrays

Harnessing Polyhydroxyalkanoates and Pressurized Gyration for Hard and Soft Tissue Engineering

Organ dysfunction is a major cause of morbidity and mortality. Transplantation is typically the only definitive cure, challenged by the lack of sufficient donor organs. Tissue engineering encompasses the development of biomaterial scaffolds to support cell attachment, proliferation, and differentiation, leading to tissue regeneration. For efficient clinical translation, the forming technology utilized must be suitable for mass production. Herein, uniaxial polyhydroxyalkanoate scaffolds manufactured by pressurized gyration, a hybrid scalable spinning technique, are successfully used in bone, nerve, and cardiovascular applications. Chorioallantoic membrane and in vivo studies provided evidence of vascularization, collagen deposition, and cellular invasion for bone tissue engineering. Highly efficient axonal outgrowth was observed in dorsal root ganglion-based 3D ex vivo models. Human induced pluripotent stem cell derived cardiomyocytes exhibited a mature cardiomyocyte phenotype with optimal calcium handling. This study confirms that engineered polyhydroxyalkanoate-based gyrospun fibers provide an exciting and unique toolbox for the development of scalable scaffolds for both hard and soft tissue regeneration.

Gradient Porous Structure Templated by Breath Figure Method

Surfaces with gradient topography are important in various fields but are difficult to fabricate. Herein, we report a facile and robust way to fabricate a surface with gradient topography of porous structure, in one direction, based on the breath figure (BF) method for the first time. The influencing factors including relative humidity (RH), sample immersion time, and solvent composition, affecting the speed, time, and model of the droplet growth, respectively, were investigated to control gradient BF pores with different ranges of pore sizes. Applying appropriate parameters, gradient BF pores with a diameter difference over 400% were prepared on one sample. The mechanism of gradient duration of solvent evaporation at different regions of a sample for fabricating gradient pores was proposed and experimentally verified with recording optical and thermographic changes of the sample in the BF procedure. This new method provides a novel site for gradient topography fabrication.

Liquid Spreading Induced by In Situ Generation of Metallic Nanoparticles

Spreading or pinning of a liquid drop on a solid substrate is determined by the surface energy of solid and liquid, topography of substrate surface, and different external forces like electric field, magnetic field, and vibration. Here we present a novel mechanism of depinning, driven by in situ generation of a species following reaction between a constituent of the droplet and one in the substrate. In particular, fluoro-carbon (FC) functionalized agarose and pHEMA gels are used as the substrates; the substrate is soaked with chloroauric acid. A drop of poly(dimethylsiloxane) (PDMS) mixed with the cross-linking agent is dispensed on it. The drop does not spread in absence of the salt, but as the salt concentration increases, the spreading diameter increases with decrease in the contact angle. The Si-H group, present as a constituent in the cross-linking agent, reduces the salt, leading to in situ generation of gold nanoparticles, that mitigates the pinning effect of the drop and the drop spreads.

Binary breath figures for straightforward and controllable self-assembly of microspherical caps

The intense interest surrounding asymmetrical microparticles originates from their unique anisotropic properties and promising applications. In this work, direct self-assembly of polymeric microspherical caps without the assistance of any additives has been achieved by using low-surface-tension methanol (MeOH) and high-surface-tension water as binary breath figures (BFs). With the evaporation of polystyrene (PS) solution containing low-boiling-point solvent in the binary vapors, the formed MeOH BFs could quickly diffuse into solution, while water BFs tended to remain at the solution surface. This led to the formation of a gradient nonsolvent layer at the vapor/solution interface, which induced the formation of nuclei and guided further asymmetrical growth of polymer particles. After the spontaneous removal of MeOH, water and residual solvent by evaporation, polymeric microspherical caps were left on the substrate. Through controlling the proportion of water introduced by adjusting the ratios of MeOH and water, polymeric microspherical caps with a range of controllable shapes (divided at different positions of a sphere) were successfully obtained. The formation mechanism was explained based on the difference of vapor pressure, surface tension and miscibility between the employed solvents and nonsolvents. A solvent possessing a high vapor pressure, low surface tension and good miscibility with MeOH contributed to the formation of microspherical caps. This flexible, green and straightforward technique is a nondestructive strategy, and avoids complicated work on design, preparation and removal of hard templates and additives.

Breath Figure Micromolding Approach for Regulating the Microstructures of Polymeric Films for Triboelectric Nanogenerators

A triboelectric nanogenerator (TENG) is an innovative kind of energy harvester recently developed on the basis of organic materials for converting mechanical energy into electricity through the combined use of the triboelectric effect and electrostatic induction. Polymeric materials and their microstructures play key roles in the generation, accumulation, and retainment of triboelectric charges, which decisively determines the final electric performance of TENGs. Herein we report a simple and efficient breath figure (BF) micromolding approach to rapidly regulate the surface microstructures of polymeric films for the assembly of TENGs. Honeycomb porous films with adjustable pore size and dimensional architectures were first prepared by the BF technique through simply adjusting the concentration of the polymer solution. They were then used as negative molds for straightforward synthesis of polydimethylsiloxane (PDMS) films with different microlens arrays (MLAs) and lens sizes, which were further assembled for TENGs to investigate the influence of film microstructures. All MLA-based TENGs were found to have an obviously enhanced electric performance in comparison with a flat-PDMS-film-based TENG. Specifically, up to 3 times improvement in the electric performance can be achieved by the MLA-based TENG with optimal surface microstructures over flat-PDMS-film-based TENG under the same triggering conditions. A MLA-based TENG was further successfully used to harvest the waste mechanical energy generated by different human body motions, including finger tapping, hand clapping, and walking with a frequency ranging from 0.5 to 5.5 Hz.

Porous Polymeric Films from Microbubbles Generated Using a T-Junction Microfluidic Device

In this work, a simple microfluidic junction with a T geometry and coarse (200 μm diameter) capillaries was used to generate monodisperse microbubbles with an alginate polymer shell. Subsequently, these bubbles were used to prepare porous alginate films with good control over the pore structure. The lack of pore size, shape, and surface control in scalable forming of polymeric films is a major application-limiting drawback at present. Controlling the thinning process of the shell of the bubbles to tune the surface of the resulting structures was also explored. Films were prepared with nanopatterned surfaces by controlling the thinning of the bubble shell, with the aid of surfactants, to induce efficient bursting (fragmentation) of bubbles to generate nanodroplets, which become embedded within the film surface. This novel feature greatly expands and enhances the use of hydrophilic polymers in a wide range of biomedical applications, particularly in drug delivery and tissue engineering, such as studying cellular responses to different morphological surfaces.

A rapid one-step fabrication of patternable superhydrophobic surfaces driven by Marangoni instability

We present a facile and inexpensive approach without any fluorinated chemistry to create superhydrophobic surface with exceptional liquid repellency, transportation of oil, selective capture of oil, optical bar code, and self-cleaning. Here we show experimentally that the control of evaporation is important and can be used to form superhydrophobic surface driven by Marangoni instability: the method involves in-situ photopolymerization in the presence of a volatile solvent and porous PDMS cover to afford superhydrophobic surfaces with the desired combination of micro- and nanoscale roughness. The porous PDMS cover significantly affects Marangoni convection of coating fluid, inducing composition gradients at the same time. In addition, the change of concentration of ethanol is able to produce versatile surfaces from hydrophilic to superhydrophobic and as a consequence to determine contact angles as well as roughness factors. In conclusion, the control of evaporation under the polymerization provides a convenient parameter to fabricate the superhydrophobic surface, without application of fluorinated chemistry and the elegant nanofabrication technique.

Multiple interfaces in self-assembled breath figures

Progress in the breath figure method is reviewed by emphasizing the role of the multiple interfaces and the applications of honeycomb films in separation, biocatalysis, biosensing, templating, stimuli-responsive surfaces and adhesive surfaces.

Non-close-packed pore arrays through one-step breath figure self-assembly and reversal

Non-close-packed breath figure arrays were observed to form at the periphery of close-packed arrays. We propose a mechanism for their formation and show a proof-of-concept that these non-close-packed pore arrays are formed due to a reversal of breath figure formation, and hence introduce a novel route to the self-assembly of such non-close-packed structures.

Solventless fabrication of porous-on-porous materials

Here we fabricate patterned porous polymer membranes on porous substrates by a combination of physical masking and chemical vapor deposition. This all-dry technique eliminates solvent-related issues and allows for the fabrication of hierarchical porous-on-porous structures with a wide range of chemical compositions and shapes. The porous polymer membranes are made by operating at unconventional processing conditions to simultaneously deposit and polymerize monomer. The solid monomer serves as a porogen and creates microstructures around which polymer forms. Membranes with thicknesses ranging from a few hundred micrometers to a millimeter are fabricated on porous paper substrates. The resolution of the patterning process and the structure of the resulting membranes are analyzed as a function of the deposition time. It was found that the patterned membranes exhibit a tapered structure and the dimensions are in good agreement with the dimensions of the mask. One potential application of these patterned polymer membranes is demonstrated for the selective separation of analytes for diagnostic applications on paper-based microfluidic devices. The ability to pattern porous-on-porous structures can be useful for the development of hierarchical membranes for water purification and gas separation, and for sensing, patterned tissue scaffolding, and other lab-on-a-chip applications.

Concentration polarization effect at the deposition of charged Langmuir monolayers

The review summarizes the results of the recent studies of the electrokinetic relaxation process within the meniscus region during the deposition of charged Langmuir monolayers. Such electrokinetic relaxation is the consequence of the initial misbalance of partial ion fluxes within a small region near the contact line, where the diffuse parts of electric double layers, formed at the monolayer and the substrate surface, overlap. The concentration polarization within the solution near the three-phase contact line should lead to long-term relaxations of the meniscus after beginning and stopping the deposition process, to changes of the ionic composition within the deposited films, to change of the interaction of the monolayer with the substrate, and to dependence of the maximum deposition rate on the subphase composition.

Directing the formation of nanostructured rings via local oxidation

We provide compelling evidence that ring formation in solutions of thiol-passivated Au nanoparticles is driven by breath figure dynamics. A method for the controlled placement of rings of nanoparticles on a solid substrate, which exploits variations in substrate wettability to fix the positions of the submicrometer water droplets formed in the breath figure process, has been developed. This is achieved by heterogeneously patterning hydrogen-terminated silicon substrates with oxide regions that act as adsorption sites for the droplets. The droplets in turn template the formation of thiol-passivated Au nanoparticle rings during spin-casting from volatile solvents.