Controlled Hydration, Transition, and Drug Release Realized by Adjusting Layer Thickness in Alginate-Ca2+/poly(N-isopropylacrylamide) Interpenetrating Polymeric Network Hydrogels on Cotton Fabrics

The controlled hydration, transition, and drug release are realized by adjusting layer thickness in thermoresponsive interpenetrating polymeric network (IPN) hydrogels on cotton fabrics. IPN hydrogels are synthesized by sodium alginate (SA) and poly(N-isopropylacrylamide) (PNIPAM) with a ratio of 1:5/% (w/v). The cotton-fabric-supported IPN hydrogels with a thickness of 1000 μm exhibit a transition temperature (TT) at 35.2 °C. When the hydrogel thicknesses are thinned to 500 and 250 μm, the TTs are reduced to 34.8 and 34.1 °C, respectively. Interestingly, the morphology of IPN hydrogels switches from a well-defined honeycomb-like network structure (1000 μm) to a densely packed layer structure (250 μm). The thinner layers not only present a smaller extent of hydration and collapse but also require longer time to reach an equilibrium state, which can be attributed to the more pronounced hindrance of the chain rearrangement by the cotton fabrics. To address the influence of layer thickness on the drug release, we compare the release rate and cumulative release percentage of the test drugs tetracycline hydrochloride (TCH) and levofloxacin hydrochloride (LH) between pure IPN hydrogels and cotton-fabric-supported IPN hydrogels (250, 500, and 1000 μm) at 25 °C (below the TT) and 37 °C (above the TT). Because of the compressive stress from the collapsed hydrogels, a higher release is observed in both hydrogels when the temperature is above TT. The cotton fabric induces a slower and less prominent drug release in IPN hydrogels. Thus, combining the obtained correlation between the transition and hydrogels layer thickness, the drug release in cotton-fabric-supported IPN hydrogels can be regulated by the layer thickness, which appears especially suitable for a controlled release in wound dressing applications.

Demonstration of thermo-sensitive tetra-gel with implication for facile and versatile platform for a new class of smart gels

A tertiary branched poly(N-isopropylacrylamide) with controlled molecular weight, distribution and the end amino-functionalization (tetra-PNIPAAm-NH₂) was studied for the ability to form a gel via in situ chain-end reaction with a counterpart tertiary branched poly(ethyleneglycol) bearing N-hydroxysuccinimide end groups (tetra-PEG-NHS), a well-documented class of building block to yield the tetra-gel. Some of these polymers, both comparable and distinct (relative to the counterpart) extended chain length pairs, provided a self-standing and macroscopically homogeneous gel, which was capable of undergoing thermo-sensitive and reversible change in hydration in line with the nature of PNIPAAm. Phantom network model based calculation indicated that a half molar fraction of the polymer chains in the network remained unreacted, revealing further room for optimizing the reaction condition. Since such tetra-PNIPAAm based motif can be readily tailored to a variety of other physicochemical stimuli-responsive analogues, our finding may give important insight into a platform for 'smart' tetra-gels with exceptional mechanical properties and potentially highly controllable molecular cut-off capability.

Hydrogel-Coated Near Infrared Absorbing Nanoshells as Light-Responsive Drug Delivery Vehicles

Nanoparticle drug delivery carriers that can modulate drug release based on an exogenous signal, such as light, are of great interest, especially for improving cancer therapy. A light-activated delivery vehicle was fabricated by synthesizing a thin, thermally responsive poly(N-isopropylacrylamide-co-acrylamide) hydrogel coating directly onto the surfaces of individual near-infrared (NIR) absorbing gold-silica nanoshells. This hydrogel was designed to be in a swollen state under physiological conditions and expel large amounts of water, along with any entrapped drug, at elevated temperatures. The required temperature change can be achieved via NIR absorption by the nanoshell, allowing the hydrogel phase change to be triggered by light, which was observed by monitoring changes in particle sizes as water was expelled from the hydrogel network. The phase change was reversible and repeatable. As a model drug, the chemotherapeutic doxorubicin was loaded into this delivery vehicle, and rapid release of doxorubicin occurred upon NIR exposure. Further, colon carcinoma cells exposed to the irradiated platform displayed nearly 3 times as much doxorubicin uptake as cells exposed to nonirradiated particles or free drug, which in turn resulted in a higher loss of cell viability. We hypothesize these effects are because the NIR-mediated heating results in a transient increase in cell membrane permeability, thus aiding in cellular uptake of the drug.

Release of anti-inflammatory peptides from thermosensitive nanoparticles with degradable cross-links suppresses pro-inflammatory cytokine production

Pro-inflammatory cytokines tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6) are mediators in the development of many inflammatory diseases. To demonstrate that macrophages take up and respond to thermosensitive nanoparticle drug carriers, we synthesized PEGylated poly(N-isopropylacrylamide-2-acrylamido-2-methyl-1-propanesulfonate) particles cross-linked with degradable disulfide (N,N'-bis(acryloyl)cystamine) (NGPEGSS). An anti-inflammatory peptide (KAFAK) was loaded and released from the thermosensitive nanoparticles and shown to suppress levels of TNF-α and IL-6 production in macrophages. Cellular uptake of fluorescent, thermosensitive, and degradable nanoparticles and therapeutic efficacy of free KAFAK peptide compared to that of KAFAK loaded in PEGylated degradable thermosensitive nanoparticles were examined. The data suggests that the degradable, thermosensitive nanoparticles loaded with KAFAK may be an effective tool to treat inflammatory diseases.

Concentration and Preservation of Very Low Abundance Biomarkers in Urine, such as Human Growth Hormone (hGH), by Cibacron Blue F3G-A Loaded Hydrogel Particles

Urine is a potential source of diagnostic biomarkers for detection of diseases, and is a very attractive means of non-invasive biospecimen collection. Nonetheless, proteomic measurement in urine is very challenging because diagnostic biomarkers exist in very low concentration (usually below the sensitivity of common immunoassays) and may be subject to rapid degradation. Hydrogel nanoparticles functionalized with Cibacron Blue F3G-A (CB) have been applied to address these challenges for urine biomarker measurement. We chose one of the most difficult low abundance, but medically relevant, hormones in the urine: human growth hormone (hGH). The normal range of hGH in serum is 1 to 10 ng/mL but the urine concentration is suspected to be a thousand times less, well below the detection limit (50 pg/mL) of sensitive clinical hGH immunoassays. We demonstrate that CB particles can capture, preserve and concentrate hGH in urine at physiological salt and urea concentrations, so that hGH can be measured in the linear range of a clinical immunometric assay. Recombinant and cadaveric hGH were captured from synthetic and human urine, concentrated and measured with an Immulite chemiluminescent immunoassay. Values of hGH less than 0.05 ng/mL (the Immulite detection limit) were concentrated to 2 ng/mL, with a urine volume of 1 mL. Dose response studies using 10 mL of urine demonstrated that the concentration of hGH in the particle eluate was linearly dependent on the concentration of hGH in the starting solution, and that all hGH was removed from solution. Thus if the starting urine volume is 100 mL, the detection limit will be 0.1 pg/mL. Urine from a healthy donor whose serum hGH concentration was 1.34 ng/mL was studied in order detect endogenous hGH. Starting from a volume of 33 mL, the particle eluate had an hGH concentration of 58 pg/mL, giving an estimated initial concentration of hGH in urine of 0.175 pg/mL. The nanotechnology described here appears to have the desired precision, accuracy and sensitivity to support large scale clinical studies of urine hGH levels.