Biodegradable, pH-responsive hydrogel networks composed of poly(methacrylic acid) crosslinked with varying mol percentages of polycaprolactone diacrylate were synthesized. These materials were characterized using NMR and FTIR. The equilibrium and dynamic swelling properties of these pH-responsive materials were studied. Also, the materials’ degradation was characterized using swelling studies and gel permeation chromatography. Methods were developed to incorporate these novel hydrogels as sensing components in silicon-based microsensors. Extremely thin layers of hydrogels were prepared by photopolymerizion atop silicon microcantilever arrays that served to transduce the pH-responsive volume change of the material into an optical signal. Organosilane chemistry allowed covalent adhesion of the hydrogel to the silicon beam. As the hydrogel swelled, the stress generated at the surface between the hydrogel and the silicon caused a beam deflection downward. The resulting sensor demonstrated a maximum sensitivity of 1nm/4.5E-5 pH unit. Sensors were tested in protein-rich solutions to mimic biological conditions and found to retain their high sensitivity. The existing theory was evaluated and developed to predict deflection of these composite cantilever beams. Another type of hydrogel-based microsensor was fabricated utilizing porous silicon rugate filters as transducers. Porous silicon rugate filters are garnering increased attention as components of in vivo biosensors due to their ability for remote readout through tissue. Here, the biodegradable, pH-responsive hydrogel was polymerized within the pores of a porous silicon rugate filter to generate a novel, completely degradable sensor. Silicon was electrochemically etched in hydrofluoric acid to generate the porous silicon rugate filter with its reflectance peak in the near infrared region. Poly(methacrylic acid) crosslinked with polycaprolactone diacrylate was polymerized within the pores using UV free radical photopolymerization. The reflectance peak of this sensor varied linearly with pH in the region pH 2.2 to 8.8. This work shows promise towards utilizing porous silicon rugate filters as transducers for environmentally responsive hydrogels for biosensing applications. / text

My MSc project aims at developing pH-responsive molecular tweezers for drug delivery applications. The project began with the synthesis of our 2nd generation tweezer, whose main objective was to improve our previous model, 1st generation tweezer, which contained a pH-responsive triad spacer and two naphthalene walls known to interact with hydrophobic drugs such as Mitoxantrone®. The naphthalene interaction sites were successfully modified to contain oligoethylene glycol chains to improve their water-solubility, in anticipation for more accurate measurements of pKa and binding constants in aqueous media. However, all attempts to convert such naphthalene derivatives into their corresponding boronic acid or ester through standard protocols (halogen-lithium exchange, palladium catalyzed borylation) failed. Without the required boronic acid/ester, the final Suzuki-Miyaura coupling with the di-bromo triad spacer was not achieved. Synthesis of the 3rd generation tweezer, which was modified to contain theophylline as the new interaction sites, was then attempted. The half-tweezer was successfully synthesized via copper (II) catalyzed coupling of theophylline with the 5-bromo-4-methoxyphenyl boronic acid. However, all attempts to convert it into the required boronic acid/ ester for the final Suzuki- Miyaura coupling reaction with 2,6-dibromopyridine failed. We then focused our attention on the conversion of the triad spacer into its corresponding diboronic acid. The synthesis of the triad diboronic acid was a success, however, the final copper (II) catalyzed reaction with theophylline to form the tweezer only yielded the mono-coupled product. Lastly, our 4th generation tweezer was engineered to avoid the synthetic difficulties encountered in the boronic acid/ ester synthesis stage. Using the commercially available 5-formyl-2-methoxyphenylboronic acid and o-phenylenediamine, we successfully synthesized a benzimidazole-derived “half tweezer” through ring condensation reaction. Alkylation of this half-tweezer was also successfully achieved, although purification of the alkylated product was not optimized. Using this crude product, we carried out the final tweezer reaction via Suzuki- Miyaura coupling with 2,6-dibromopyridine under microwave irradiation. 1H NMR results show formation of new species that is believed to be the 4th generation tweezer (although the presence of impurities made integration of the signals unreliable). Much work is needed in the purification of the alkylated half tweezer boronic acid in order to avoid complicated mixtures in the final tweezer reaction. / Thesis (Master, Chemistry) -- Queen's University, 2011-10-06 00:29:04.248

A scalable method for the synthesis of polyethylene terephthalamide microcapsules grafted with polyacrylic acid to enable pH responsiveness has been developed. Microcapsules were produced by interfacial polymerisation of an oil-in-water emulsion in a 2 L batch reactor and subsequently circulated through an external loop reactor for UV irradiative surface grafting. Ungrafted microcapsule samples yielded 1.0 - 1.2 g desiccated capsules per experiment. Initial production trials were subject to severe agglomeration, observed during dialysis of the microcapsules with 30 % (v/v) ethanol solution. Lowering of the terephthaloyl dichloride monomer concentration, to 0.2 mol L⁻¹ in the chloroform / cyclohexane (3 : 1) organic solution, alleviated this unwanted agglomeration. Laser diffraction particle size analysis revealed microcapsules were produced with a 51 µm average diameter. A purpose built external loop irradiation reactor was used to facilitate graft polymerisation of acrylic acid on the microcapsules, using 254 nm UV light at 19 mW cm⁻². Characterisation of the external loop flow regime showed a mild deviation from ideal plug flow, with a vessel dispersion number of 0.014 and a Reynolds number of 1310. Confirmation of monomer polymerisation was ascertained by back titration and Fourier transform infrared spectroscopy. No distinction between homopolymer and grafted polyacrylic acid could be made by these characterisation methods. A Taguchi analysis on variables influencing grafting revealed high temperature to contribute most significantly to graft yield, followed by a long irradiation period. The development of a packed column pulse response method for testing pH response showed a high repeatability. However, release profile testing of a microcapsule slurry with an observed graft yield of 1.13 mmol g⁻¹ did not provide a definitive pH-based release of mPEG 5000 or PEGylated TAMRA dye. Determination of acrylic acid polymerisation kinetics following UV irradiation of the microcapsules is required for future optimisation of a functional graft yield.

No description available.

Polymer carriers composed of poly(methacrylic acid – grafted – ethylene glycol) (P(MAA-g-EG)) hydrogels modified with poly(butyl acrylate) (PBA) to form IPNs or photopolymerized in the presence of poly(methyl methacrylate) (PMMA) nanoparticles were investigated for their use in the oral delivery of therapeutic agents for cancer treatment. The P(MAA-g-EG) hydrogel provided pH-responsive and hydrophilic properties while PBA or PMMA polymers provided hydrophobic properties. An inulin- doxorubicin conjugate was also synthesized to provide local, direct targeting for the treatment of colon cancer. The pH-responsive behavior of these polymer systems was investigated using equilibrium and dynamic swelling experiments. In gastric conditions (low pH) all materials were in a collapsed state and in intestinal conditions (neutral pH) these material were swollen. The equilibrium swelling ratios decreased with increasing hydrophobic content for both IPNs and compositions of P(MAA-g-EG) containing nanoparticles. The loading efficiencies of doxorubicin, a chemotherapeutic drug, were as high as 56% for IPNs and the IPN structure and hydrophobicity influenced the loading efficiency values. The loading efficiency of doxorubicin using P(MAA-g-EG) containing nanoparticles was as high as 64% and increased with increasing weight percent of PMMA nanoparticles in the P(MAA-g-EG) hydrogel. In gastric conditions (low pH), IPNs released a majority of the encapsulated doxorubicin (up to 70%) as compared to the P(MAA-g-EG) containing nanoparticles (up to 27%). P(MAA-g-EG) containing nanoparticles was used to load and release the inulin-doxorubicin conjugate. Loading efficiency was 54% and release profiles behaved similarly as doxorubicin. Both polymer systems were biocompatible with Caco-2, HT29-MTX, and SW620 cell models over concentration ranging from 1 mg/mL to 5 mg/mL and exposure times lasting from 2 hr to 24 hr. The 75/25 IPN exhibited the highest degree of mucoadhesion and the P(MAA-g-EG)-5.0NP the lowest. Using the same cell lines and cytotoxicity assays, the inulin-doxorubicin conjugate was determined to be more toxic than free doxorubicin at equal doxorubicin concentrations. Doxorobuicin and inulin-doxorubicin conjugate were tested for transport across Caco-2/HT29-MTX cell monolayers with and without the presence of unmodified P(MAA-g-EG) or P(MAA-g-EG)-5.0NP microparticles. The presence of the microparticles did not increase transport across the cell monolayer which is advantageous for local, direct delivery to the colon. / text

This thesis presents an investigation of pH-responsive, redox-sensitive poly(MMA-co- MAA) and poly(EA-co-MAA) hollow particles for the repair of load-bearing soft tissues, such as articular cartilage and the intervertebral disc. Hollow particles continue to attract major interest due to their numerous potential applications. The new method for hollow particle preparation presented in this thesis does not require the use of a colloidal template and is well suited for scaling up. Hollow particles were formed using linear poly(MMA-co-MAA) and poly(EA-co-MAA) aliphatic copolymers synthesised using free-radical chain copolymerisation performed in solution. These copolymers were dissolved in dichloromethane using methanol as a cosolvent and emulsified in water. Diffusion of the methanol into the aqueous phase prompts precipitation of the copolymer at the droplet/water interface. The more hydrophobic copolymers containing less MAA showed improved morphology compared to copolymers containing more MAA. Also, poly(EA-co-MAA) hollow particles had a more spherical morphology than poly(MMA-co-MAA) hollow particles with equivalent MAA contents. This was attributed to the lower Tg of the EA structural monomer, which resulted in more flexible particle shells. Unusually, during potentiometric titration of uncrosslinked hollow particles, the pH of the system decreased with increasing neutralisation. This behaviour is thought to be due to the unfolding of copolymer chains, exposing shielded carboxyl groups. The random structure of the copolymers is believed to be necessary for this behaviour. Crosslinked particles became swollen when the pH was increased using buffers. Concentrated dispersions formed self supporting gels, due to steric confinement, at 5 wt.%. The crosslinking process was performed by functionalising with cystamine using carbodiimide chemistry. This introduced disulphide crosslinks; which could be cleaved under reducing conditions at high pH, dissolving the gels. This ability to reduce the hollow particle shells to their constituent linear copolymer chains gives potential for natural removal from the body via extraction by the renal system. pH-triggered loading and release of a hydrophilic dye using crosslinked hollow particles was demonstrated. The similarity of the particle formation process to traditional solvent evaporation also allowed the loading of a hydrophobic dye. However, these particles were not crosslinked so release following swelling could not be investigated. Cystamine-crosslinked systems suffered from degradation due to thiol-disulphide exchange at high pH (~ pH 8). Crosslinking of one system was performed using 2-amino ethyl methacrylate (AEM). This introduced covalent, vinyl intra-shell crosslinking; which did not break down at high pH. Additional AEM was also used to allow inter-particle UVcrosslinking to form doubly crosslinked (DX) hollow-particle hydrogels. These gels did not re-disperse in buffer. To our knowledge, this is the first example of a covalent hydrogel formed from pH-responsive hollow particles. The DX gels offer improved mechanical properties compared to the singly crosslinked, physical gels. Freeze-dried samples of all of the gels produced during this study showed highly porous structures when observed using SEM. The rapid diffusion of FITC-dextran through a sample of DX gel indicates that these pores were interconnected. This is beneficial as it encourages tissue ingrowth, in addition to allowing the rapid diffusion of nutrients, oxygen and cell waste in vivo.

This thesis presents an investigation of cationic microgels based on poly(N-vinylformamide-co-glycidyl methacrylate) (PNVF-GMA) and poly(N-vinylformamide-co-2-(N-vinylformamido) ethyl ether) (PNVF-NVEE). They arestudied in the context of future heteroaggregated doubly crosslinked (DX) microgelsfor damaged heart tissue repair. The microgel particles were synthesised fromPNVF-GMA, which is also a water swellable microgel. The PNVF-GMA particleshad a core-shell structure in which PNVF provides the core and PGMA creates thecross-linked shell. The morphology of particles is that of a “cane-ball” like shape. There are interconnected ridges, and this unusual morphology can be controlled bythe weight fraction of GMA used during preparation. The hydrolysed PNVF-GMA(H-PNVF-GMA) particles were both positively and negatively charged. Moreover,charge patch aggregation occurred at low ionic strength. However, these microgelswere colloidally unstable after water rinsing due to shell fragmentation. PNVF microgel particles containing (N-Vinylformamido) ethyl ether (NVEE) as acrosslinking agent were also studied to avoid the fragmentation of the particles. Thismicrogel was hydrolysed in alkali conditions to provide poly(vinylamine-co-bis(ethyl vinylamine) ether) (PVAM-BEVAME), which contains primary aminegroups. It is proposed from the data presented that the content of hydrolysis was veryhigh and the particles were stable after hydrolysis owing to the stability of etherlinkage in NVEE. These microgels were able to swell upon decreasing pH. ThePVAM-BEVAME microgel with 9 mol% of BEVAME was then used to formdoubly crosslinked (DX) microgel. To form the inter-particles crosslinking, the vinylgroups were included by functionalisation using glycidyl methacrylate (GMA)monomer. The vinyl groups of neighbouring particles were linked together via freeradical reaction. The DX microgel formed under physiological temperature andshowed extensive porosity. These DX microgels had good mechanical propertiesconfirmed by high storage modulus (G’). Moreover, the precursor gels wereinjectable which is favourable for future biomaterial applications. The study providesa new family of cationic microgel that may be suitable for a future heteroaggregatedDX microgel for heart tissue repair.

No description available.

In the recent years, development of various organic and inorganic nano-sized systems has gained great interests especially for cancer diagnosis and treatment and intense researches are carried out in this area. Regarding to the recent trends for drug delivery system design, the novel approaches for drug carriers are mainly based on development of smart and nano-size drug carriers which are targeted to cancer cells. Hence, for an effective tumor-targeted delivery device, besides its chemical structure further criteria such as detection of tumor site and sensitivity to the higher temperature and lower pH of the tumor compare to rest of the body gains importance. The aim of this study is to design and prepare polysebacic anhydride (PSA) based nanocapsules (NCs) loaded with Doxorubicin (DOX) which is an anti cancer drug. In order to obtain an intelligent delivery system, drug-loaded nanocapsules were coated with pH sensitive poly (L-histidine). PSA nano-carriers were firstly loaded with DOX and then in order to introduce pH sensitivity, they were coated with poly (L-histidine). PLH-coated NCs were modified with polyethylene glycol (PEG) to prevent their macrophage uptake. Drug release profile from this system was examined in two different buffer solutions prepared as acidic (pH 4) and physiological (pH 7.4) media. The physical and chemical properties of the nano particles were characterized by Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), ultraviolet and visible absorption spectroscopy (UV-VIS), and scanning electron microscopy (SEM). In vitro studies of the prepared nanocapsules were performed on MDA-MB-231 breast cancer cells by using WST Kit 8 cell viability test. In order to obtained results, pH sensitive nanocapsules with size 230 nm exhibited cellular uptake and promising intracellular release of drug.

Advances in medical treatment are leading away from generalized care towards intelligent systems or devices which can sense and respond to their environment. With these devices, the burden of monitoring and dosing for treatment can be removed from the doctor (or the patient) and be placed on the device itself. Implicit closed-loop control systems will allow the device to respond to its environment and release therapeutic agent in response to a specific stimulus. Environmentally responsive hydrogels show great promise in being incorporated in such an intelligent device, such as pH-responsive hydrogels which can swell and deswell in response to changes in the pH of the media. Thus, pH changes can be exploited for controlled and intelligent drug delivery when used in combination with these pH-responsive hydrogels. In this work, heterogeneous, thermal-redox initiated free-radical polymerizations were developed to synthesize novel pH-responsive hydrogels, microparticles, and nanogels. The specific disease of interest was type I diabetes, which requires daily doses of insulin both at a basal amount and either a postprandial or preprandial bolus in order to maintain blood glucose levels within safe limits. To allow pH-responsive hydrogels to be sensitive to glucose, glucose oxidase was incorporated which oxidizes glucose to gluconic acid. A novel inverse-emulsion polymerization method was developed for the synthesis of poly[2-(diethylaminoethyl methacrylate)-grafted-polyethylene glycol monoethyl ether monomethacrylate] (P(DEAEM-g-PEGMMA)) nanogels (100-400 nm) for intelligent insulin delivery. The new polymerization method allowed the incorporation of hydrophilic components, such as glucose oxidase and catalase, as well as PEG surface tethers of lengths 400 Da up to 2000 Da. Surface tethers successfully decreased the surface charge of the nanogels. Insulin loading and release was determined for microparticles which were able to imbibe substantial amounts of insulin from solution when swollen, entrap the insulin when collapsed, and then release the insulin in response to either a pH or glucose stimulus. / text