PNIPAAm Hydrogels Research Articles

Hepatic cell-sheet fabrication of differentiated mesenchymal stem cells using decellularized extracellular matrix and thermoresponsive polymer

PurposeLiver tissue engineering via cell sheet technology would open new doors for treatment of patients with liver failure. Decellularized tissues could provide sufficient extracellular matrix (ECM) to support development of hepatocytes in in vivo niches. Besides, with the potential of temperature responsive polymer (pNIPAAm) as an intelligent surface for controlling the attachment/detachment of cell, we set out to generate three in vitro microenvironments models including I: pNIPAAm hydrogel (pN hydrogel), II: decellularized ECM incorporated into pNIPAAm hydrogel (dECM + pN hydrogel) and III: decellularized ECM scaffold (dECM scaffold) to investigate the structural and function cues of hepatocyte-like cells after differentiation of adipose tissue-derived mesenchymal stem cells (AT-MSCs) on the surface of these models. MethoddECM scaffold was obtained after decellularization of rat liver, and its efficiency was analyzed. pN hydrogel and dECM + pN hydrogel (1:3 and 2:3 ratios) of were fabricated, and scaffold architecture was characterized. Each well of culturing plates was coated separately with these three constructs and AT-MSCs were instructed to differentiate into hepatocyte-like cells (HLCs). After recellularization, patterns of differentiation, and expression of hepatogenic markers were investigated via biochemical assays and qRT-PCR at different time points. ResultsMultipotency of AT-MSCs, after their ability for osteogenesis and adipogenesis was documented. Production of dense and intact cell sheets was reported in dECM + pN hydrogel, as opposed to pN hydrogel and dECM scaffold. Also, statistically significant difference of HLCs functionality in dECM + pN hydrogel was confirmed after evaluation of the expression of hepatocyte markers including, alpha-fetoprotein, cytokeratin 18, cytochrome P450-2E1 and phosphoenolpyruvate carboxykinase. ConclusionOur results proved dECM + pN hydrogel were able to preserve hepatocyte function in cell sheets owing to the high level of albumin, urea, hepatogenic markers, and glycogenesis potential of HLCs. Accordingly, dECM incorporated in pN hydrogel could remodel microenvironments to guide the AT-MSCs into conducive differentiation and proliferation to give rise to multilayer sheets of cells in their own ECM.

Novel fluorescent hydrogel for the adsorption and detection of Fe (III)

A novel PNIPAAm-CD hydrogel with good adsorption property and stable fluorescence detection for Fe3+ was prepared by copolymerizing PCDs with NIPAAm monomers. As a fluorescence probe, carbon quantum dots (CDs) were modified by glycidyl methacrylate (GMA) to obtain PCDs, which had double bond and could react with N-isopropyl acrylamide to form hydrogel. The functionalization of the amine groups on the surface of the PCDs enables PNIPAAm-CD hydrogel also exhibits photoluminescence behavior. In addition, the PNIPAAm-CD hydrogels stably shows higher adsorption performance for Fe3+ than the pure PNIPAAm hydrogel. The honeycomb PNIPAAm-CD hydrogel had a good quenching response to metallic iron ions, and the detection limit was as low as 0.27 μM in the range of 1μM～1mM. The results of adsorption isotherms and adsorption kinetics showed that the adsorption procedure of metal ions conforms to the pseudo-second-order model and langmuir model, respectively. The effective detection and the high adsorption of PNIPAAm-CD hydrogel for Fe3+ make it an effective portable platform potential, which has the dual functions of visual detection and adsorption of Fe3+.

Controlled release of anti-cancer drug from the shell and hollow cavities of poly(N-isopropylacrylamide) hydrogel particles synthesized via reversible addition-fragmentation chain transfer polymerization

Temperature-responsive poly(N-isopropylacrylamid) (PNIPAAm) hydrogels with two different crosslinking densities were coated on silica nanoparticles via surface-initiated reversible addition-fragmentation chain transfer network formation method in an inverse emulsion medium. The temperature-responsive hollow hydrogel particles were also prepared by etching of the silica cores using hydrofluoric acid. The hybrid and hollow hydrogel particles were used as doxorubicin (DOX) delivery systems. The synthesis process was evaluated by proton magnetic nuclear resonance and Fourier-transform infrared spectroscopies, thermogravimetric analysis, and scanning and transmission electron microscopies. Dynamic light scattering and turbidimetry by UV–vis spectroscopy were also used to study responsivity of the hybrid and hollow PNIPAAm hydrogels to temperature. Gel collapse temperature (GCT) of the hydrogels was studied using UV transmittance curves. UV transmittance and the GCT value of the hollow hydrogels were higher than the hybrid samples. The hollow hydrogel particles with higher crosslinking density showed higher hydrodynamic diameter (Dh) at temperatures of above the GCT, whereas the hollow cavity and lower crosslinking densities resulted in higher Dh at temperatures below GCT. Release of DOX from the hybrid and hollow hydrogel particles with two different crosslinking densities was investigated by using UV–vis spectroscopy at below and above GCT of the hydrogel particles (25 and 45 °C, respectively). The hollow particles with low crosslinking density showed the lowest release percent due to its higher loading capacity. In addition, the DOX release percent was reduced by increasing temperature from 25 to 40 °C.

Thermally reversible shape transformation of nano-patterned PNIPAAm hydrogel

In the field of stimuli-responsive polymer research, poly-N-isopropylacrylamide (PNIPAAm) has been widely studied, because this material has unique properties which respond to temperatures near to that of the human body, approximately 36 °C. In this study, a nano-patterned PNIPAAm hydrogel was prepared using UV-irradiation and soft lithography. Chemical changes in the C–C double bonds of the PNIPAAm hydrogel were confirmed by FT-IR analysis. The thermal properties of the hydrogel were analyzed by differential scanning calorimetry (DSC), which confirmed its low critical solution temperature (LCST). The highest gel content of approximately 46% was achieved at 120 min UV-irradiation. The nano-patterned morphology of the PNIPAAm hydrogel exhibited temperature-dependent reversible shape transformation. This study shows that the reversible shape transformation of the PNIPAAm hydrogel was due to swelling and shrinking.

Synthesis and Evaluation of a Thermoresponsive Degradable Chitosan-Grafted PNIPAAm Hydrogel as a "Smart" Gene Delivery System.

Thermoresponsive hydrogels demonstrate tremendous potential as sustained drug delivery systems. However, progress has been limited as formulation of a stable biodegradable thermosensitive hydrogel remains a significant challenge. In this study, free radical polymerization was exploited to formulate a biodegradable thermosensitive hydrogel characterized by sustained drug release. Highly deacetylated chitosan and N-isopropylacrylamide with distinctive physical properties were employed to achieve a stable, hydrogel network at body temperature. The percentage of chitosan was altered within the copolymer formulations and the subsequent physical properties were characterized using 1H-NMR, FTIR, and TGA. Viscoelastic, swelling, and degradation properties were also interrogated. The thermoresponsive hydrogels were loaded with RALA/pEGFP-N1 nanoparticles and release was examined. There was sustained release of nanoparticles over three weeks and, more importantly, the nucleic acid cargo remained functional and this was confirmed by successful transfection of the NCTC-929 fibroblast cell line. This tailored thermoresponsive hydrogel offers an option for sustained delivery of macromolecules over a prolonged considerable period.

Electro-conductive and temperature-sensitive poly(N-isopropylacrylamide) composite hydrogels with improved mechanical properties

Poly(N-isopropylacrylamide) (PNIPAAm) hydrogel with temperature-sensitive properties can be potentially applied in smart response area. However, poor mechanical and non-conductive characteristic have greatly restricted its widespread application. In this work, PNIPAAm composite hydrogels containing graphene aerogel (GA) and graphene oxide (GO) were prepared via vacuum-assisted backfilling and in-situ polymerization. After an introduction of 0.29 wt% GA and 0.09 wt% GO, the compressive strength and modulus of PNIPAAm hydrogel increase by 100% and 582%, respectively. Moreover, the ternary composite hydrogel has a good electric conductivity, reaching up to 0.52 S/m, due to the electro-conductive network of GA. Combining the good conductivity and itself temperature-sensitive property of PNIPAAm, a smart switch was assembled and could switch off automatically under a high voltage, which has potential applications in sensor area.

UV-Laser Interference Lithography for Local Functionalization of Plasmonic Nanostructures with Responsive Hydrogel.

A novel approach to local functionalization of plasmonic hotspots at gold nanoparticles with biofunctional moieties is reported. It relies on photocrosslinking and attachment of a responsive hydrogel binding matrix by the use of a UV interference field. A thermoresponsive poly(N-isopropylacrylamide)-based (pNIPAAm) hydrogel with photocrosslinkable benzophenone groups and carboxylic groups for its postmodification was employed. UV-laser interference lithography with a phase mask configuration allowed for the generation of a high-contrast interference field that was used for the recording of periodic arrays of pNIPAAm-based hydrogel features with the size as small as 170 nm. These hydrogel arrays were overlaid and attached on the top of periodic arrays of gold nanoparticles, exhibiting a diameter of 130 nm and employed as a three-dimensional binding matrix in a plasmonic biosensor. Such a hybrid material was postmodified with ligand biomolecules and utilized for plasmon-enhanced fluorescence readout of an immunoassay. Additional enhancement of the fluorescence sensor signal by the collapse of the responsive hydrogel binding matrix that compacts the target analyte at the plasmonic hotspot is demonstrated.

Expansion of Ion Effects on Water Induced by a High Hydrophilic Surface of a Polymer Network.

The spatial extent and anion-cation cooperativity of the ion effect on the structure and dynamics of water have long been debated but are still controversial. Previously, we experimentally demonstrated the extensive and cooperative effect of ions on water in a polyamide network by measuring the reflection wavelength (λ) on the ion sensor of poly(N-isopropylacrylamide) (PNIPAAm) hydrogel-immobilized photonic crystals. In the present study, we investigated the influence of the polymer surface on the ion effect by adopting a highly hydrophilic poly(N-isopropylacrylamide-co-N-acryloylaza-18-crown-6) hydrogel as a sensor matrix. In alkaline earth metal salt solutions, the copolymer hydrogel membrane sensor showed the redshift of λ for the specific combination of cations and anions, that is, Ca2+/Cl- and Sr2+/NO3-, which resulted from the concerted binding of ion pairs to the copolymer receptor. In alkali metal salt solutions, the ion sensor showed the blueshift of λ originating from the osmotic dehydration suppressed by the salts. The strength of the ion effect was evaluated by the average osmotic pressure (ΠA) required for the salt-inhibited dehydration in the early stage of hydrogel contraction. From the calculation results of ΠA for the copolymer and PNIPAAm hydrogels, it was found that the high hydrophilic copolymer surface more significantly enhanced the ion effect of structure-making cations (i.e., Li+) compared with borderline (Na+) and structure-breaking (K+ and Cs+) cations. Furthermore, the ion effect exhibited the higher ion cooperativity in combination with chloride anions than with nitrate anions. The enhancement of the long-range cooperative ion effect is derived from the expansion of the interactions between ions, water molecules, and the hydrophilic polymer network.

Visualization and Quantification of Microwaves Using Thermoresponsive Color-Change Hydrogel.

Visualization and quantification of invisible lights, such as microwaves, are significant for their safe use. In general, a sensitizer material combined with a transistor is used as electronic devices for the measurement. Here, we developed a thermoresponsive color-change hydrogel of poly(N-isopropylacrylamide) (PNIPAAm) cross-linked by a layered organic composite based on polydiacetylene (PDA) for visualization and colorimetric quantification of microwaves. The layered PDA in the PNIPAAm hydrogel showed the temperature-dependent gradual color change with heating. Irradiation of microwaves induced the color change of PDA through heating of water in the hydrogel and subsequent volume shrinkage. The color of the gel was applied to visualize the temperature distribution with increasing irradiation time of microwaves. Moreover, the power of the irradiated microwave was quantified by time to the complete color change of the gel. The results indicate that the stimulus conversion process has potentials for development of a variety of imaging and quantification devices based on the layered PDA.

Rapid photothermal actuation of light-addressable, arrayed hydrogel columns in a macroporous silicon membrane

This paper presents rapid photothermal actuation of light-addressable, arrayed hydrogel columns in a macroporous silicon membrane. Au nanorods are incorporated into thermo-responsive p-NIPAAm hydrogel to utilize surface plasmon-induced local heating by near-infrared light. By measuring optical transmission through the fabricated membrane structure with Au nanorod embedded hydrogel, we have demonstrated that photothermal actuation of the hydrogel can be done in two-dimensional, pixel-like configuration with high spatial and temporal resolutions. Benefiting from the hydrogel volume confinement within micron-sized pores, we have achieved sub-second response time of hydrogel photothermal actuation and its repeatable photothermal actuation on highly localized illuminated area. Considering that each hydrogel column is confined within each pore and different wavelengths of light can be used to induce photothermal actuation of hydrogel’s deswelling characteristics by modifying the physical dimensions of Au nanorods, it has a potential for optically-addressable, multiplexed drug release systems with the rapid response time.

Effect of ionomer/multiplet formation on mechanical properties and ascorbic acid release behavior of PNIPAAm hydrogels copolymerized by DMAEMA, DMAPMAAm and MAPTAC

Poly(N-isopropylacrylamide) (PNIPAAm) hydrogels containing N-[3-(N,N-dimethylamino)propyl]methacrylamide (DMAPMAAm), 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and [3-(methacryloylamino)propyl]trimethylammonium chloride (MAPTAC) as cationic monomers were cross-linked with N,N’-methylenebisacrylamide (BIS) and tetraallylammonium bromide (TAB). The swelling degrees, uniaxial compression moduli and L-ascorbic acid (L-AA) releases of these cationic PNIPAAm hydrogels synthesized in 1,4-dioxane were compared with the one prepared in distilled–deionized water (DDW) and in aqueous sodium hydroxide solution (0.1 N NaOH). P(NIPAAm-co-MAPTAC)/BIS and P(NIPAAm-co-DMAEMA)/BIS hydrogels at 37 °C in DDW and at 37 °C/pH 4 exhibited higher gel strengths and compressive moduli than all the others cross-linked and copolymerized with TAB and DMAPMAAm, respectively. All the observations indicated that the physical cross-linking points created by ionomer pairs of MAPTA+Cl− units and the hydrophobic contributions of ester groups in the DMAEMA units might be a reason of their improved mechanical properties in DDW at 37 °C. Further, the charge screening effect of chloride ions in the swelling medium at pH 4 also resulted in the improved compressive moduli compared to the ones in DDW. The water diffusion into/from all the copolymeric PNIPAAm hydrogels during the swelling/deswelling processes at 25 °C/37 °C in DDW and their L-AA releases at 37 °C in DDW also revealed the importance of these ionic and hydrophobic effects. Water transport through the ones cross-linked with TAB was controlled by non-Fickian process due to the repulsive forces between the quaternized ammonium groups on the chemical cross-links while in the case of P(NIPAAm-co-MAPTAC)/BIS, water transport followed Fickian diffusion because the multiplet formations behaved as additional cross-links. Furthermore, P(NIPAAm-co-MAPTAC)/BIS hydrogel due to the ionomer-multiplet transitions at 37 °C in DDW has exhibited less-Fick diffusion that resulted in a lower diffusion coefficient during the release of L-AA as compared to the others.

NIR-induced pH-reversible self-healing monitoring with smartphone by wireless hydrogel sensor

Near infrared (NIR)-induced reversible self-healing hydrogel electronics with pH-dependent controllable properties was designed by employing the pH-driven “blooming-bridged” phenomenon between polydopamine (PDA) and the zwitterionic fluorescent carbon dot (ZFCD). This self-healing hydrogel (PDA@ZFCD-PNIPAAm) was synthesized by incorporating an NIR-responsive PDA-loaded zwitterionic fluorescent carbon dot (PDA@ZFCD) into a thermo-responsive PNIPAAm hydrogel, and further combined with wireless device to monitor self-healing and electronic property of hydrogel. The change in PDA@ZFCD-PNIPAAm hydrogel properties depended on the “blooming-bridged” effect of PDA@ZFCD, which controlled the photothermal release and intermolecular hydrogen bonding of PDA under different pH conditions. At the acidic and basic conditions (blooming-bridged state), PDA@ZFCD-PNIPAAm hydrogel displayed a self-healing behavior under NIR irradiation, which did not occur at a neutral pH (bloomless state) owing to different activation of photothermal heat under NIR irradiation with different hydrogel pore size. This hydrogel also demonstrated different thermal and electronic properties in different pH owing to the “bridged” phenomenon of PDA nanoparticles. Moreover, PDA@ZFCD-PNIPAAm hydrogel indicated reversible fluorescence on/off, self-healing, and electronic properties as the pH conditions changed. In addition, the self-healing phenomenon of hydrogel and the change of its electronic property can be easily monitored in a smartphone as a real-time information via wireless sensor. Therefore, this approach offers new insight on the development of self-healing hydrogels with simple, rapid and real-time monitoring on self-healing behavior, which can be used for future applications of hydrogels.

Dual-Responsive Alginate Hydrogels for Controlled Release of Therapeutics.

In this work, with the drug oxytetracycline (OTC) released, cell cytotoxicity and antimicrobial studies of dual-responsive sodium alginate and N-Isopropylacrylamide hydrogels (SA/pNIPAAm) with enclosed OTC were investigated. The molecular OTC release was explored with different acid-base conditions and temperature conditions. In order to characterize cell cytotoxicity and antimicrobial efficacy, time-dependent OTC release analysis of different acid-base conditions was performed in SA/pNIPAAm hydrogels. OTC@SA/pNIPAAm hydrogels showed excellent time-dependent antimicrobial efficacy, in which the IC50 values were 50.11 μg mL−1, 34.27 μg mL−1, and 22.39 μg mL−1 among three consecutive days, respectively. Meanwhile, the human cells showed excellent viability at the IC50 dosage of OTC@SA/pNIPAAm (50.11 μg mL−1). OTC@SA/pNIPAAm performed in this study indicated that SA/pNIPAAm may serve as drug carriers for sustainable release at a specific concentration and for being employed as substrates for decreasing drug toxicity. Besides, pH-responsive and thermos-responsive SA/pNIPAAm may lead to the better selectivity of drug release in the ideal location or site. Finally, the results demonstrate that the designed, dual-responsive, biocompatible OTC@SA/pNIPAAm hydrogels showed excellent antimicrobial efficacy and may potentially be found to have enormous applicability in the field of pharmaceutics.

Graphene Oxide Nanosheet-Composited Poly(N-isopropylacrylamide) Hydrogel for Cell Sheet Recovery

Cell sheet engineering technique has been applied to treat various tissues without the use of a traditional scaffold. To date, methods for the cell sheet harvesting depend mostly on grafted poly(N-isopropylacrylamide) (pNIPAAm) thin layers, while the native pNIPAAm hydrogel, which possibly presents the easiest way to prepare thermo-responsive materials, is not suitable for the cell sheet harvesting due to its low cell attachment. In this study, the graphene oxide (GO) nanosheet was utilized as an additive to enhance the bio-compatibility of the pNIPAAm hydrogel. Different concentrations of GO nanosheets were added to prepare GO/pNIPAAm composite hydrogels through the in-situ free radical polymerization with polyethylene glycol dimethacrylate (PEGDA) as a cross-linker. The results indicated that the physical properties of the composite hydrogels had little difference with that of the native pNIPAAm hydrogel. However, the cell attachment, proliferation and detachment behaviors on the composite hydrogel surface were greatly enhanced. Monkey fibroblast COS7 cells attached and proliferated better on the GO/pNIPAAm composite hydrogel, while intact COS7 cell sheets could be harvested from the composite hydrogels by simply lowering the temperature. In contrast, the cells appeared as clusters on the native pNIPAAm hydrogel. Furthermore, when HeLa and COS7 cells were seeded successively onto the micropatterned GO/pNIPAAm hydrogel, there could be the formation of a patterned HeLa/COS7 cell layer. The geometrically patterned GO/pNIPAAm hydrogel may provide an easy-to-prepare material for releasing patterned cell sheets compared to the specific cell-adhesive proteins reported to make patterned cell layers.

Tuning of thermoresponsive pNIPAAm hydrogels for the topical retention of controlled release ocular therapeutics.

Low patient compliance and poor bioavailability of ophthalmic medications are the main limitations of topical eye drops. A potential solution to these disadvantages could be provided by thermoresponsive hydrogels, which could be used as the basis for a gelling eye drop for long-term release of therapeutics. We previously reported such a system capable of being retained in the lower fornix of rabbits, continuously releasing an anti-glaucoma drug for one month. Here, we sought to improve the properties of the existing gels as most relevant to patient use without altering the drug release profile. Specifically, we optimized the sol-to-gel transition temperature and de-swelling kinetics of pNIPAAm gels to avoid risk of the gelled drop reverting to liquid during cold or windy weather, and ensure quick gelation upon administration. A reduction of the gel LCST, faster gelation kinetics, and suitable viscosity for the administration as an eye drop were successfully achieved through modification of the poly(ethylene glycol) content in the water phase and its molecular weight. Our data suggest that drug release is not affected by these changes, with representative drug concentration profiles of the previous and new formulations demonstrating comparable anti-glaucoma release kinetics.

Tailored macroporous hydrogel–nanoparticle nanocomposites for monolithic flow-through catalytic reactors

Highly porous poly(N-isopropylacrylamide) PNIPAam hydrogel monoliths with tunable microstructures and comprising gold, silver or palladium nanoparticles, display significant catalytic activity when used in flow-through microreactors.

Bulk poly(N-isopropylacrylamide) (PNIPAAm) thermoresponsive cell culture platform: toward a new horizon in cell sheet engineering.

Although a conventional method of utilizing thermoresponsive grafted poly(N-isopropylacrylamide) (PNIPAAm) enables the harvest of a healthy confluent cell-to-cell junction preserved cell sheet while limiting the use of the trypsin enzyme, the absolute necessity in the delicate control of a sensitive nm-scale PNIPAAm chain length inevitably decelerates the advancement of cell sheet engineering. In this study, we demonstrate, for the first time, a thermoresponsive cell culture platform composed only of a 'bulk' form of a PNIPAAm hydrogel with the Young's modulus being increased up to the MPa scale. The surface roughness of the bulk PNIPAAm hydrogel initially modulated by the cross-linker concentration was altered from the nm- to μm-scale in response to a change in temperature above/below the low critical solution temperature (LCST) of 32 °C. The appropriate control of the surface roughness allowed the stable attachment (above the LCST) and easy detachment (below the LCST) of diverse cells and enabled the harvest of cell sheets composed of cell lines (C2C12 and NIH3T3) or even primary cells (human umbilical vein endothelial cells and keratinocytes). During their incubation at 37 °C, the cell lines were able to be attached on every surface of the prepared PNIPAAm cell culture platforms, whereas the primary cells were found to be only attached on a surface having a roughness below ∼30 nm. Furthermore, in the aspect of cell sheet detachment at the incubation temperature of 20 °C, the cell sheets composed of cell lines were fully detached from the surface of the platform having a roughness of ∼10 μm or higher, while the cell sheets composed of primary cells were entirely detached from the surface with a roughness of ∼19 μm or higher. Based on such behaviors of the diverse cells at a given surface roughness, this study further suggests a universal thermoresponsive cell culture platform which allows the harvest of all types of cells from cell lines to primary cells in a desired shape. Our suggested universal cell culture platform could play a powerful and versatile role in accelerating the advancement of cell sheet engineering.

Sliding Crosslinked Thermoresponsive Materials: Polypseudorotaxanes Made of Poly(N-Isopropylacrylamide) and Acrylamide-γ-Cyclodextrin.

Novel polypseudorotaxanes (PPR) based on poly(N-isopropylacrylamide) (PNIPAAm) and acrylamide-γ-cyclodextrin (AγCD) are successfully synthesized. AγCD gives rise to sliding crosslinking systems and influences the thermoresponsive and swelling behavior of PNIPAAm hydrogels. Namely, their lower critical solution temperature (LCST) can be tuned up to 38°C, thus making the resulting materials of great interest in biomedical applications. Also, AγCD influences the thermal and mechanical properties of hydrogels, by affecting the Tg and E modulus values.

Surfactant-free fabrication of pNIPAAm microgels in microfluidic devices

Conventional pNIPAAm microgel synthesis utilizes surfactants to suspend pre-gel droplets in the immiscible continuous phase due to the slow polymerization required for synthesizing pNIPAAm in aqueous solvent. To improve the fabrication process and to eliminate the effects of surfactant on microgel quality, a surfactant-free and water-free method was developed. Rapid polymerization of high-quality microgels was achieved in a single-channel microfluidic device to help maintain the integrity of gel particles without the addition of surfactants. The droplet generation mechanism and the effect of flow rate of the two in-going immiscible fluid on the geometry of the produced microgels were studied. The produced microgels have low polydispersity with a dispersity index of 6.4%. The pNIPAAm hydrogels fabricated in the DMSO solvent has smaller pore size and more uniform microstructure compared to that synthesized in water. The fabricated pNIPAAm microgels show a sharp volume phase transition at ∼32 °C and high deswelling/swelling rate.

Prevention of allergic inflammation by oral administration of bromelain in a murine asthma model

Thermosensitive materials, such as PNIPAAm, are considered for the development of hydrogels for controlled release, especially for topical use. Bromelain is a set of proteases found in plants (Bromeliceae family) and it is known for having several medical uses, including healing of topical wounds. The combination of PNIPAAm hydrogels and bromelain could result in a potential formulation for topical injuries. In this work, different NIPAAm hydrogels were submitted to swelling tests for 24 h. The selected formulation presented a swelling ratio of 340%, and was used for bromelain loading, reaching up to 30% of protein loading. After loading, hydrogel disks were dried and immersed in phosphate buffer (pH 7.0) for release study. Release studies pointed to an initial burst release, followed by a modified (slower) release, reaching its optimum enzymatic activity release rates at around 60 min in both temperatures (25 °C and 37 °C). Scanning electron microscopy and Fourier transform infrared spectroscopy confirmed bromelain loading through hydrogen bonds, without interfering in intermolecular polymeric chains. Bromelain presence decreased mucoadhesion at 25 °C and increased at 37 °C; it also increases polymers crosslink, without interfering in elastic properties (drilling and resilience). Hydrogels (blank and loaded with bromelain) showed a typical behavior of crosslinked hydrogels at rheology tests, and bromelain increased storage modulus. Both hydrogels showed a significant cell death after 24 h in NIH/3T3 cell line.