Fabrication of robust superhydrophobic magnetic multifunctional coatings and liquid marbles

To obtain durable and multi-function superhydrophobic surfaces, we reported a facial method to prepare a multifunctional suspension (γ-Fe₂O₃@SiO₂@PDMS suspension) named as FSP suspension, in which γ-Fe₂O₃ was coated by the silica shell and PDMS was used as the outer layer. Superhydrophobic magnetic polyurethane (SMPU) sponge was prepared by immersing the polyurethane (PU) sponge into the FSP suspension, exhibiting the superior ability to absorb oil. In addition, it could also move directionally by the attraction of magnets and absorb the oil along the fixed path. The heated superhydrophobic magnetic stainless steel (H-SMSS) mesh was acquired by spraying FSP suspension onto the stainless steel mesh and then heating at 400 °C, which demonstrated superior superhydrophobicity and resistance to abrasion and chemical corrosion. Besides, the H-SMSS mesh displayed excellent flux and efficiency to separate the oil/water mixture. Rolling droplets on FSP particles, the superhydrophobic magnetic liquid marbles (SMLMs) were fabricated, in which liquids with different volumes were encapsulated and transported directionally. Further, it was convenient to inject liquid into the SMLM and withdraw liquid from it. Thus, the prepared FSP suspension has promising applications in constructing large-area, robust, and multifunctional surfaces and microreactors.

Visible Light Assisted Organosilane Assembly on Mesoporous Silicon Films and Particles

Porous silicon (PSi) is a versatile matrix with tailorable surface reactivity, which allows the processing of a range of multifunctional films and particles. The biomedical applications of PSi often require a surface capping with organic functionalities. This work shows that visible light can be used to catalyze the assembly of organosilanes on the PSi, as demonstrated with two organosilanes: aminopropyl-triethoxy-silane and perfluorodecyl-triethoxy-silane. We studied the process related to PSi films (PSiFs), which were characterized by X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (ToF-SIMS) and field emission scanning electron microscopy (FESEM) before and after a plasma patterning process. The analyses confirmed the surface oxidation and the anchorage of the organosilane backbone. We further highlighted the surface analytical potential of ¹³C, ¹⁹F and ²⁹Si solid-state NMR (SS-NMR) as compared to Fourier transformed infrared spectroscopy (FTIR) in the characterization of functionalized PSi particles (PSiPs). The reduced invasiveness of the organosilanization regarding the PSiPs morphology was confirmed using transmission electron microscopy (TEM) and FESEM. Relevantly, the results obtained on PSiPs complemented those obtained on PSiFs. SS-NMR suggests a number of siloxane bonds between the organosilane and the PSiPs, which does not reach levels of maximum heterogeneous condensation, while ToF-SIMS suggested a certain degree of organosilane polymerization. Additionally, differences among the carbons in the organic (non-hydrolyzable) functionalizing groups are identified, especially in the case of the perfluorodecyl group. The spectroscopic characterization was used to propose a mechanism for the visible light activation of the organosilane assembly, which is based on the initial photoactivated oxidation of the PSi matrix.

Liquid marble containing degradable polyperoxides for adhesion force-changeable pressure-sensitive adhesives

Non-stick liquid marbles containing a sticky polyperoxide ​provide a strong stick and dismantlability depending on external stimuli.

Liquid marble and water droplet interactions and stability

The interactions between two individual water droplets were investigated in air using a combination of coalescence rig and high speed video camera. This combination allows the visualization of droplet coalescence dynamics with millisecond resolution which provides information on droplet stability. Bare water droplets coalesced rapidly upon contact, while droplet stability was achieved by coating the droplets with polystyrene particles carrying pH-responsive poly[2-(diethylamino)ethyl methacrylate] hairs (PDEA-PS particles) to form liquid marbles. The asymmetric interaction of a water droplet (pH 3 or 10) armoured with the PDEA-PS particles (liquid marble) with a bare droplet at pH 3 exhibited intermediate stability with coalescence observed following an induction time. The induction time was longer for the pH 10 liquid marble, where the PDEA-PS particles have a hydrophobic surface, than in the case of a pH 3 liquid marble, where the PDEA-PS particles have a hydrophilic surface. Furthermore, film formation of PDEA-PS particles on the liquid marble surface with toluene vapour confirmed capsule formation which prevented coalescence with the neighbouring water droplet instead wetting the capsule upon contact within 3 milliseconds. This study illuminates the stability of individual particle-stabilized droplets and has potential impact on processes and formulations which involve their interaction.

Physicochemical properties affect the synthesis, controlled delivery, degradation and pharmacokinetics of inorganic nanoporous materials

Controlling size, shape and uniformity of porous constructs remains a major focus of the development of porous materials. Over the past two decades, we have seen significant developments in the fabrication of new, porous-ordered structures using a wide range of materials, resulting in properties well beyond their traditional use. Porous materials have been considered appealing, due to attractive properties such as pore size length, morphology and surface chemistry. Furthermore, their utilization within the life sciences and medicine has resulted in significant developments in pharmaceutics and medical diagnosis. This article focuses on various classes of porous materials, providing an overview of principle concepts with regard to design and fabrication, surface chemistry and loading and release kinetics. Furthermore, predictions from a multiscale mathematical model revealed the role pore length and diameter could have on payload release kinetics.

Liquid marbles as a micro-reactor for efficient radical alternating copolymerization of diene monomer and oxygen

Liquid marbles are a novel micro-reactor to efficiently synthesize polyperoxides by the radical alternating copolymerization of the 1,3-diene with oxygen.

Microcapsules fabricated from liquid marbles stabilized with latex particles

Millimeter- and centimeter-sized "liquid marbles" were readily prepared by rolling water droplets on a powder bed of dried submicrometer-sized polystyrene latex particles carrying poly[2-(diethylamino)ethyl methacrylate] hairs (PDEA-PS). Scanning electron microscopy studies indicated that flocs of the PDEA-PS particles were adsorbed at the surface of these water droplets, leading to stable spherical liquid marbles. The liquid marbles were deformed as a result of water evaporation to adopt a deflated spherical geometry, and the rate of water evaporation decreased with increasing atmospheric relative humidity. Conversely, liquid marbles formed using saturated aqueous LiCl solution led to atmospheric water absorption by the liquid marbles and a consequent mass increase. The liquid marbles can be transformed into polymeric capsules containing water by exposure to solvent vapor: the PDEA-PS particles were plasticized with the solvent vapor to form a polymer film at the air-water interface of the liquid marbles. The polymeric capsules with aqueous volumes of 250 μL or less kept their oblate ellipsoid/near spherical shape even after complete water evaporation, which confirmed that a rigid polymeric capsule was successfully formed. Both the rate of water evaporation from the pure water liquid marbles and the rate of water adsorption into the aqueous LiCl liquid marbles were reduced with an increase of solvent vapor treatment time. This suggests that the number and size of pores within the polymer particles/flocs on the liquid marble surface decreased due to film formation during exposure to organic solvent vapor. In addition, organic-inorganic composite capsules and colloidal crystal capsules were fabricated from liquid marbles containing aqueous SiO2 dispersions.

Co-delivery of a hydrophobic small molecule and a hydrophilic peptide by porous silicon nanoparticles

Nanoparticulate drug delivery systems offer remarkable opportunities for clinical treatment. However, there are several challenges when they are employed to deliver multiple cargos/payloads, particularly concerning the synchronous delivery of small molecular weight drugs and relatively larger peptides. Since porous silicon (PSi) nanoparticles (NPs) can easily contain high payloads of drugs with various properties, we evaluated their carrier potential in multi-drug delivery for co-loading of the hydrophobic drug indomethacin and the hydrophilic human peptide YY3-36 (PYY3-36). Sequential loading of these two drugs into the PSi NPs enhanced the drug release rate of each drug and also their amount permeated across Caco-2 and Caco-2/HT29 cell monolayers. Regardless of the loading approach used, dual or single, the drug permeation profiles were in good correlation with their drug release behaviour. Furthermore, the permeation studies indicated the critical role of the mucus intestinal layer and the paracellular resistance in the permeation of the therapeutic compounds across the intestinal wall. Loading with PYY3-36 also greatly improved the cytocompatibility of the PSi NPs. Conformational analysis indicated that the PYY3-36 could still display biological activity after release from the PSi NPs and permeation across the intestinal cell monolayers. These results are the first demonstration of the promising potential of PSi NPs for simultaneous multi-drug delivery of both hydrophobic and hydrophilic compounds.

Selective functionalization of the internal and the external surfaces of mesoporous silicon by liquid masking

A general approach for selective, differential functionalization of the interior and exterior surfaces of mesoporous Si is reported. The method employs two immiscible liquids, one inert and the other chemically reactive with the porous Si nanostructure. First, a porous Si sample is prepared by electrochemical etch and then it is mildly oxidized, which places a thin layer of silicon oxide at the surface. The inner pore walls of the partially oxidized porous Si film are then infiltrated with an inert liquid (octane). The sample is then immersed in aqueous solution containing hydrogen fluoride (HF), which serves as the reactive liquid. The hydrophobic phase is retained in the interior of the porous nanostructure, and HF(aq) attacks only the exposed surfaces of the oxidized porous Si sample, generating a hydrophobic, hydrogen-terminated (Si-H) outer layer. The reaction is self-limiting due to the immiscibility of octane and water, and the extent of penetration of the Si-H surface into the porous layer is dependent on the time of exposure to HF(aq). The Si-H surface can then be modified by thermal hydrosilylation (1-dodecene or 10-bromo-1-decene) in a subsequent step, resulting in a bifunctional porous Si film containing hydrophobic pore entrances to hydrophilic inner pores. The hydrophobic dodecyl species at the mouths of the pores is found to form a barrier for molecular transport; it decreases the rate of leaching (into water) of a rhodamine test molecule that is preloaded into the sample by >8 fold.

Tailored porous silicon microparticles: fabrication and properties

The use of mesoporous silicon particles for drug delivery has been widely explored thanks to their biodegradability and biocompatibility. The ability to tailor the physicochemical properties of porous silicon at the micro- and nanoscale confers versatility to this material. A method for the fabrication of highly reproducible, monodisperse, mesoporous silicon particles with controlled physical characteristics through electrochemical etching of patterned silicon trenches is presented. The particle size is tailored in the micrometer range and pore size in the nanometer range, the shape from tubular to discoidal to hemispherical, and the porosity from 46 to over 80%. In addition, the properties of the porous matrix are correlated with the loading of model nanoparticles (quantum dots) and their three-dimensional arrangement within the matrix is observed by transmission electron microscopy tomography. The methods developed in this study provide effective means to fabricate mesoporous silicon particles according to the principles of rational design for therapeutic vectors and to characterize the distribution of nanoparticles within the porous matrix.

Cellular association and assembly of a multistage delivery system

The realization that blood-borne delivery systems must overcome a multiplicity of biological barriers has led to the fabrication of a multistage delivery system (MDS) designed to temporally release successive stages of particles or agents to conquer sequential barriers, with the goal of enhancing delivery of therapeutic and diagnostic agents to the target site. In its simplest form, the MDS comprises stage-one porous silicon microparticles that function as carriers of second-stage nanoparticles. Cellular uptake of nontargeted discoidal silicon microparticles by macrophages is confirmed by electron and atomic force microscopy (AFM). Using superparamagnetic iron oxide nanoparticles (SPIONs) as a model of secondary nanoparticles, successful loading of the porous matrix of silicon microparticles is achieved, and retention of the nanoparticles is enhanced by aminosilylation of the loaded microparticles with 3-aminopropyltriethoxysilane. The impact of silane concentration and reaction time on the nature of the silane polymer on porous silicon is investigated by AFM and X-ray photoelectron microscopy. Tissue samples from mice intravenously administered the MDS support co-localization of silicon microparticles and SPIONs across various tissues with enhanced SPION release in spleen, compared to liver and lungs, and enhanced retention of SPIONs following silane capping of the MDS. Phantom models of the SPION-loaded MDS display negative contrast in magnetic resonance images. In addition to forming a cap over the silicon pores, the silane polymer provides free amines for antibody conjugation to the microparticles, with both VEGFR-2- and PECAM-specific antibodies leading to enhanced endothelial association. This study demonstrates the assembly and cellular association of a multiparticle delivery system that is biomolecularly targeted and has potential for applications in biological imaging.

Porous silicon in drug delivery devices and materials

Porous Si exhibits a number of properties that make it an attractive material for controlled drug delivery applications: The electrochemical synthesis allows construction of tailored pore sizes and volumes that are controllable from the scale of microns to nanometers; a number of convenient chemistries exist for the modification of porous Si surfaces that can be used to control the amount, identity, and in vivo release rate of drug payloads and the resorption rate of the porous host matrix; the material can be used as a template for organic and biopolymers, to prepare composites with a designed nanostructure; and finally, the optical properties of photonic structures prepared from this material provide a self-reporting feature that can be monitored in vivo. This paper reviews the preparation, chemistry, and properties of electrochemically prepared porous Si or SiO2 hosts relevant to drug delivery applications.