Controlling the interfacial behaviour of colloidal microgel systems

Hydrophobically modified colloidal microgel particles were prepared by a surfactant-free emulsion polymerization of N-isopropylacrylamide (NIPAM) with more hydrophobic vinyl ether/ester/silane co-monomers (10 % total mass monomer). Most of the resultant dispersions were novel co-polymer microgels and all exhibited a thermo-sensitive volume phase transition. Key properties of the microgels, i.e. size, electrophoretic mobility and volume phase transition temperature (VPTT), were determined by dynamic light scattering (DLS), laser Doppler electrophoresis, UV-visible spectrophotometry and scanning electron microscopy. The influence of co-monomer incorporation, e.g. structure and relative hydrophobicity, upon the physicochemical properties of the microgel was examined. Hydrophobic modification strongly influenced size, slightly altered electrophoretic mobility and left the VPTT relatively unaffected. The interfacial properties of the microgels were studied by tensiometry. Substantial reductions in the surface tension of water were observed for all microgels, close in magnitude to that achieved by the surfactant sodium dodecyl sulphate, but at a far lower concentration. The effect was influenced by a complex combination of parameters including size, charge, conformation, co-monomer type, temperature and solvent quality. A DLS study of the swelling response of microgels in the presence of less polar co-solvents (shortchain alcohols) found that hydrophobic modification altered alcohol-induced de-swelling/ re-entrant swelling behaviour and particle-dispersant interactions. Furthermore, the characteristic temperature-driven volume collapse above the VPTT was overcome by alcohol addition. Finally, the stability and heteroflocculation of anionic/cationic mixtures of poly(NIPAM) microgels was studied by DLS and UV-visible spectrophotometry as a function of dispersion temperature, pH and electrolyte concentration. Electrolytes of increasing cation valency (NaCl, MgCl2, LaCl3) were used to reduce the particle Debye length. Conditions conducive to preserving stability or encouraging flocculation were identified and related to the complex balance of particle interactions. It is anticipated that the results of these investigations may support future development of microgels with applications relating to more hydrophobic environments and materials

Multi-responsive microencapsulated nanogels for the oral delivery of small interfering RNA

Multi-responsive, anionic poly(methacrylic acid-co-N-vinyl-2-pyrrolidone) microscale hydrogels (microgels) encapsulating polycationic nanoscale hydrogels (nanogels) were synthesized with either degradable or nondegradable crosslinks. The pH-responsive volume phase transition of these formulations was consistent with the pH transition experienced during intestinal delivery, as the hydrogels swelled at pH values greater than pH 5. The physicochemical characteristics of the nondegradable formulations were evaluated by microscopy, potentiometric titration, Fourier transform infrared spectroscopy, and thermal gravimetric analysis. The nondegradable formulations successfully loaded and released a model protein in physiological buffers, but the ability of the microgels to release the nanogels upon exposure to intestinal conditions was inadequate. Therefore, microgels containing enzyme-degradable oligopeptide crosslinks were synthesized then characterized using Fourier transform infrared spectroscopy, electron microscopy, confocal microscopy, and ImageStream flow cytometry. Degradation of the microgels upon incubation in trypsin solutions, simulated gastric fluid, or simulated intestinal fluid was evaluated by measuring the change in relative turbidity over time. Microgels were degraded specifically by the enzyme trypsin, and the rate of degradation was dependent upon the microgel to trypsin concentration ratio; for all ratios tested, degradation was complete within 4 hours. The cytocompatibility of the enzyme-degraded microgels encapsulating nanogels was evaluated in both a human and a murine cell line; at microgel concentrations less than 0.4 mg/ml the cell viability was greater than 90%. Confocal microscopy was used to obtain Z-stack images of the cells following incubation with the microgels, confirming that nanogels were released from the degraded microgels and subsequently inteRNAlized by RAW 264.7 murine macrophage cells. The microencapsulated nanogels were able to load siRNA via electrostatic complexation with loading efficiencies ranging from 60-80%. Incubation of loaded microgels in simulated intestinal fluid with reduced trypsin concentrations or in rat intestinal fluid resulted in successful degradation of the microgel matrix and release of a detectable amount of viable siRNA. The degraded microgels with nanogels transfected the two different cell lines with up to 20% silencing efficiency. Though the knockdown efficiency is not as high as that of nanogels alone, the microgel results are consistent and reproducible across two cell lines.Chemical Engineerin

Complexation of DNA with Thermoresponsive Charged Microgels: Role of Swelling State and Electrostatics

This research was funded by projects RTI2018-101309-B-C21 and PID2020-631-116615RA-I00, funded by MCIN/AEI/10.13039/501100011033 and by "ERDF A way of making Europe" and by project PY20_00138, funded by Consejeria de Transformacion Economica, Industria, Conocimiento y Universidades (PAIDI2020).Micro- and nanogels are being increasingly used to encapsulate bioactive compounds. Their soft structure allows large loading capacity while their stimuli responsiveness makes them extremely versatile. In this work, the complexation of DNA with thermoresponsive microgels is presented. To this end, PEGylated charged microgels based on poly-N-isopropylacrylamide have been synthesized, allowing one to explore the electrostatics of the complexation. Cationic microgels complexate spontaneously by electrostatic attraction to oppositely charged DNA as demonstrated by electrophoretic mobility of the complexes. Then, Langmuir monolayers reveal an increased interaction of DNA with swollen microgels (20 degrees C). Anionic microgels require the presence of multivalent cations (Ca2+) to promote the complexation, overcoming the electrostatic repulsion with negatively charged DNA. Then again, Langmuir monolayers evidence their complexation at the surface. However, the presence of Ca2+ seems to induce profound changes in the interaction and surface conformation of anionic microgels. These alterations are further explored by measuring adsorbed films with the pendant drop technique. Conformational changes induced by Ca2+ on the structure of the microgel can ultimately affect the complexation with DNA and should be considered in the design. The combination of microstructural and surface properties for microgels offers a new perspective into complexation of DNA with soft particles with biomedical applications.MCIN/AEI RTI2018-101309-B-C21 PID2020-631-116615RA-I00Consejeria de Transformacion Economica, Industria, Conocimiento y Universidades PY20_0013

DEVELOPMENT OF NOVEL TEMPERATURE RESPONSIVE POLYMERIC SORBENTS AND THEIR APPLICATIONS IN WATER REMEDIATION

Water remediation utilizing sorption has found strong interest due to its inexpensiveness, universal nature and ease of operation. In particular, thermo-responsive sorbents consisting of N-isopropylacrylamide (NIPAAm) offer significant potential as “smart” and advanced materials to remove multiple aqueous pollutants. NIPAAm exhibits excellent thermo-responsiveness, which senses the external temperature variation and changes its swelling and sorption behaviors in a sharp and rapid manner. At the beginning of this work, an extensive review of literature has been compiled to provide a summary of NIPAAm-based thermo-responsive sorbents in water/wastewater remediation applications. Initially, we developed a novel approach to synthesize and characterize NIPAAm copolymeric hydrogels. Four different polyphenolic crosslinkers including curcumin multiacrylate (CMA), quercetin multiacrylate (QMA), 4,4’-dihydroxybiphenyl diacrylate (44BDA) and chrysin multiacrylate (ChryMA) were successfully incorporated into crosslinked hydrogels. Their temperature responsiveness and lower critical solution temperature (LCST) were characterized using swelling studies and differential scanning calorimetry (DSC). Increasing the crosslinker content resulted in a significant decrease in the swelling ratio and LCST, which was due to the increased crosslinking and hydrophobicity introduced by the polyphenolic crosslinkers. We also demonstrated the application of two sets of aforementioned crosslinked hydrogels (NIPAAm-co-CMA and NIPAAm-co-44BDA) as effective gel sorbents to capture phenol as a model contaminant. Temperature-dependent sorption was evaluated through a binding study of phenol at 10°C and 50°C. Significant enhancement in the sorption was observed at 50°C, and this can be attributed to the phase transition induced hydrophobic interactions between the copolymer gel and phenol. Moreover, the obtained hydrogels possessed facile and efficient regeneration ability in water at 10°C, without requiring harsh solvent treatment or high energy input. Building on the sorption behavior observed with crosslinked NIPAAm hydrogels, we extended the investigation to linear copolymer systems, and these were demonstrated as a temperature responsive flocculants. Here, NIPAAm copolymers consisting of 2-phenylphenol monoacrylate (2PPMA) were successfully developed as smart flocculants to remove metal oxide nanoparticles (e.g., Fe3O4, CeO2, TiO2). The incorporation of 2PPMA enhanced the flocculation at temperatures above the LCST (e.g., 50°C), which was due to the combined hydrophobicity of 2PPMA and NIPAAm. Overall, NIPAAm-based sorbents have a variety of applications in aqueous pollutant removal and are a promising class of materials for cost-effective water remediation technology

Hydrogels for delivery of therapeutic compounds

In some aspects, methacrylate co-polymers crosslinked with an enzymatically cleavable peptide linker are provided and may be used for the oral delivery of a therapeutic. The peptide linker may be cleavable by an enzyme in the small intestine and may allow for the delivery of a therapeutic protein or nucleic acid to the small intestine. Also provided are methods of using the polymers for the treatment of a disease.Board of Regents, University of Texas Syste

Microgel particles stabilised high internal phase emulsions for applications in tissue engineering

Tissue engineering using polymeric scaffolds to support cell growth and tissue regeneration is currently under development as a promising solution to tissue loss or organ failure. This thesis focuses on fabricating multifunctional scaffolds for tissue engineering using emulsion templating. Poly(N-isopropylacrylamide-co-acrylic acid) [poly(NIPAAm-co-AA)] microgel particles were found capable of stabilising both w/o and o/w high internal phase emulsions (HIPEs), depending on the temperature, pH and salt concentration. PolyHIPEs were prepared by photo-polymerisation of both HIPEs containing monomers in the continuous phase and exhibited pore structures with sizes of a few hundred micrometers. For oil-soluble monomers, e.g., divinylbenzene (DVB), microgel particles stabilised w/o HIPEs were obtained at 40 °C using a microgel suspension (0.4 wt %) in 1 mM KCl solution at pH 4. For water-soluble monomers, e.g., potassium acrylate (KAA), the crosslinker content was found crucial to the formation of an open porous structure in poly(KAA) HIPEs. It was shown by cryo-scanning electron microscopy that the interconnections were not generated upon polymerisation but during solvent extraction. Highly interconnected poly(KAA) HIPEs prepared using 80 vol % internal phase possessed a low density of ca. 0.03 g/cm3 and a porosity up to 97~98%. By using active ingredient (A.I.) loaded microgel particles as emulsifiers, polyHIPEs with delivery functionality were developed. The emulsifying ability of A.I. loaded microgels was found to be dependent on A.I.-microgel interactions. Paracetamol drug loaded microgel particles resulted in stable o/w HIPEs at either low (400 rpm) or high stirring speed (1000 rpm) and hence polyHIPEs with tunable morphologies after polymerisation. Microgel particles stabilised o/w HIPEs were also used to fabricate macroporous dextran and dextran-co-polyNIPAAm. The pH of the aqueous phase was found crucial to HIPE stability and pH 6.8 resulted in stable HIPEs without coalescence and macropores with narrow pore size distribution after freeze-drying. By thermostating HIPEs prior to freezing or by varying dextran concentration, the morphology of macroporous dextran was tunable. Macroporous dextran-co-polyNIPAAm could potentially be used as a multiply responsive scaffold. Besides the stimuli-responsiveness of microgel particles, polyNIPAAm segments of the copolymers enabled scaffold integrity in water at physiological temperature. Microgel particles stabilised HIPEs were established as a truly versatile template to fabricate macroporous polymers for potential applications as tissue engineering scaffolds.Imperial Users Onl

Development and characterization of microencapsulated nanoparticle systems for oral vaccination by protein-antigens

A composite platform strategy for oral vaccination with subunit antigens was developed to improve i) ease of administration and distribution; and ii) induction of mucosal immunity. The platform is referred to as Polyanhdyride-Releasing MicroParticle Technology, or PROMPT. In its core, polyanhydride nanoparticles based on 1,6-bis-(p-carboxyphenoxy)hexane (CPH) and sebacic acid (SA) served simultaneously as adjuvant and delivery vehicle of subunit antigens, while microencapsulation by pH-responsive polymers based on poly(ethylene glycol) (PEG) and poly(methacrylic acid) (PMAA) enabled targeted intestinal delivery of the nanoparticle payload. PROMPT formulations were synthesized by pH-mediated self-assembly to encapsulate nanoparticles. The reversible pH-responsive transition of these formulations coincided with the pH transition experienced during intestinal delivery, such that particles dissociated to release nanoparticles above pH 5. The physicochemical characteristics of the composite microgels were evaluated by Fourier transform infrared spectroscopy, electron microscopy, and confocal microscopy. PROMPT formulations demonstrated pH-dependent burst release of the encapsulated model antigen, ovalbumin, and then sustained release thereafter in both neutral pH and simulated gastrointestinal conditions. The biocompatibility and immunostimulatory capabilities of PROMPT formulations were evaluated in relevant cell lines to identify lead candidates for in vivo immunization experiments. PROMPT composite formulations demonstrated greater than 85% viability at microgel concentrations less than 1mg/mL, as indicated by cellular proliferation and membrane integrity. PROMPT microgels also demonstrated the ability to activate bone marrow-derived dendritic cells in vitro by stimulating cell surface marker expression and cytokine secretion. Finally, the ability of lead formulations to elicit immune responses was assessed in vivo by administering PROMPT formulations to BALB/c mice by oral gavage. PROMPT formulations induced measurable ovalbumin-specific IgA and IgG in mucosal fluids and blood serum, respectively, while soluble antigen and nanoparticles alone did not. This work shows that microencapsulation of nanoparticles for oral vaccine administration is a promising platform for developing safe, effective subunit-based vaccines.Biomedical Engineerin