Cryogelation of molecularly imprinted nanoparticles: A macroporous structure as affinity chromatography column for removal of β-blockers from complex samples.

We report one-step microfluidic synthesis and characterization of novel Janus microhydrogels composed entirely of the same base material, N-isopropylacrylamide (NIPAAm). The microhydrogels were fabricated by the microfluidic generation of Janus monomer microdroplets based on separation of a supersaturated aqueous NIPAAm solution into NIPAAm-rich and -poor phases followed by UV irradiation. The resulting Janus microhydrogels exhibited tunable anisotropic thermo-responsive behavior and organophilic/hydrophilic loading capability.

One-step microfluidic synthesis of Janus microhydrogels with anisotropic thermo-responsive behavior and organophilic/hydrophilic loading capability.

Poly(vinyl alcohol) (PVA) is an attractive polymer for various applications based on membranes. To increase water resistance, PVA material has to be adequately crosslinked. However, crosslinking behavior on the whole PVA membrane generally leads to obviously increased brittleness and deteriorated transparency. In the present research, a kind of glutaraldehyde crosslinked PVA membrane with gradient structure has been successfully designed and prepared by the casting membrane of pure PVA aqueous solution and the following surface post-crosslinking processes. The method can endow the PVA membrane with the gradiently decreased crosslinking degree from the surface to inside. Such gradient cross-linked PVA membrane not only keeps good flexibility and transparency, but also possesses satisfactory water-proof property. The structure and properties of the prepared the gradient acetalized PVA (GAPVA) membranes were analyzed and characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscope (SEM), tensile measurement, water resistance test and transparency observation, etc. Compared with pure PVA membrane and uniform acetalized PVA (UAPVA) one, such GAPVA membrane displays excellent performance including good water resistance, transparency and mechanical properties, much higher than those of UAPVA membrane.

Preparation and properties of glutaraldehyde crosslinked poly(vinyl alcohol) membrane with gradient structure

Composite cryogels containing porous adsorbent particles were prepared under cryogelation conditions. The composites with immobilized concanavalin A (Con A) were used for capturing glycoproteins. Adsorbent particles were introduced into the structure in order to improve the capacity and to facilitate the handling of the particles. The monolithic composite cryogels were produced from suspensions of polyvinyl alcohol particles and porous adsorbent particles and cross-linked under acidic conditions at sub-zero temperature. The cryogels were epoxy activated and Con A was immobilized as an affinity ligand. Binding and elution of horseradish peroxidase (HRP) was studied in batch experiment and in a chromatographic setup. Increasing adsorbent concentration in composite cryogels will increase ligand density, which therefore enhances the amount of bound HRP from 0.98 till 2.9 (milligram enzyme per milliliter of gel) in the chromatographic system. The material was evaluated in 10 cycles for binding and elution of HRP.

Composite cryogel with immobilized concanavalin A for affinity chromatography of glycoproteins

Materials having the ability to hold water within the voids of acrylic-based polymeric chain are special class materials used for biomedical applications. In the present review, the different therapeutic applications such as drug diffusivity, tissue engineering, gene delivery and pharmaceutical applications of various poly (acrylic acid) hydrogels and nanohydrogels are discussed. Several techniques for the preparation of different nanohydrogels are compared. The Fourier Transform Infrared, X-ray diffraction, Scanning electron microscopy, 1H-NMR and X-ray photoelectron spectroscopy are discussed for the characterization of nanohydrogels. The swelling, mechanical, and rheological properties of nanohydrogels are also described. The combined accounts of preparation, characterization and properties of nanohydrogels along with the description of various biomedical applications may explore an emerging idea in the area of material sciences.

Biomedical applications of acrylic-based nanohydrogels

Drug stability and sustained release issues are important areas in drug-delivery research. The sustained release of proteins can be achieved by their encapsulation with a hydrophobic polymer, but this requires the proteins to be protected from the harsh processing environments of organic solvents and mechanical force. Preencapsulation with poly(vinyl alcohol) (PVA) using a freeze/thaw method has been shown to allow successful protection and sustained release. This study examined the effects of freezing/thawing on PVA encapsulation in the preparation of PVA-PLGA composite particles. Freezing/thawing slightly improved the crystalline peaks and the heat of fusion of PVA, but more distinct differences were observed when the properties of the surface layers were probed by AFM. The hardness of particles’ surfaces increased with increasing number of freezing/thawing cycles, whereas the adhesion force with an AFM cantilever tip decreased. The mean particle size and entrapment efficiency decreased. These results suggest that surface hardening is the major mechanism responsible for the sustained release characteristics.

Freezing/thawing processing of PVA in the preparation of structured microspheres for protein drug delivery

Recently, anisometric structures, which are popular in nature but uncommon in artificial materials, have been actively investigated for the development of novel materials designed for sensors, optical systems, scaffolds, etc. In this study we investigated the hypothesis that the symmetry of two-compartment hydrogels influences their temperature responsive behavior and drug diffusivity. Composite hydrogels with isometric and anisometric compartments were prepared using poly(N-isopropylacrylamide), poly(acrylamide), and nanoclay. The anisometric hydrogel showed a markedly smaller volume transition and equilibrium swelling ratio than its isometric counterpart, possibly because of more restriction from the two-compartment structure. Furthermore, water retention and the release of cilostazol were significantly sustained in the case of the anisometric hydrogel. By incorporating Ag nanoparticles into one compartment, an IR responsive transition was achieved, which showed the consistent effect of the anisometric structure. Finite element analysis further confirmed the difference found in the experimental results by presenting a prevailing von Mises stress in the anisometric case. This study provides a novel engineering strategy for hydrogel properties and a fundamental understanding valuable for designing anisometric hydrogel materials.

Anisometric nanocomposite hydrogels with temperature responsive compartments

Vascular embolization is a minimally invasive nonsurgical technique obstructing a blood vessel by lodgment of embolic materials to treat cancers and vascular lesions. In this paper, we have carried out a parametric study of generation of monodisperse clay–poly(N-isopropylacrylamide) (clay–PNIPAAm) embolic microspheres of which size is comparable to a blood vessel (about 400 µm). To achieve monodisperse water-phase clay/NIPAAm microdroplets, we have designed and fabricated a poly(dimethylsiloxane) (PDMS) hydrodynamic focusing microfluidic device (HFMD) for the generation of microdroplets with the affinity of continuous oil-phase fluid to the hydrophobic PDMS taken into account. We have investigated the influence of process-related flow conditions on the microdroplet generation to determine a proper processing window for obtaining monodisperse microdroplets with the fabricated HFMD. A parametric study of generation of monodisperse microdroplets was carried out by changing volumetric flow rates of two immiscible fluids within the determined processing window. For the suggested condition, the fabricated clay–PNIPAAm microspheres of about 400 µm in diameter showed an extremely narrow size distribution with a coefficient of variation of 0.41%. We have also showed the floatability of the fabricated clay–PNIPAAm microspheres in saline and the smooth passage of the microspheres through a commercially available microcatheter as in vitro characterization for embolization.

Effect of Flow Rates on Generation of Monodisperse Clay--Poly(N-isopropylacrylamide) Embolic Microspheres Using Hydrodynamic Focusing Microfluidic Device

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Freezing/thawing processing of PVA in the preparation of structured microspheres for protein drug delivery

Anisometric nanocomposite hydrogels with temperature responsive compartments

Effect of Flow Rates on Generation of Monodisperse Clay--Poly(N-isopropylacrylamide) Embolic Microspheres Using Hydrodynamic Focusing Microfluidic Device