Study On Synthesis And Prooerties Of Phenylboronic Acid-based Hydrogels And Copolymers For Glucose Sensing And Insulin Delivery

Stimuli-responsive polymers that undergo physicochemical property changes in response to external stimuli can provide both a functional and structural basis for sensors and self-regulated systems.For example,the response of smart polymers to the fluctuation in the concentration of specific biomolecules,which can mimic biofeedback systems in response to chemical stimuli can provide several attractive platforms for biomedical applications.Phenylboronic acid(PBA)is considered as artificial mimic of lectin due to its ability to bind strongly to 1,2-or 1,3-cis-diols such as glucose to form cyclic esters via reversible covalent interactions.This tight binding tolerates PBA to function as a glucose recognition moiety for glucose sensing and smart insulin regulatory systems.Unlike glucose oxidase(GOx)and lectin concanavalin A(Con A),which are susceptible to environmental changes and unstable on storage,usage and sterilization,PBA is an enzyme and protein-free material.Although it is less specific to glucose,nevertheless it is reliable,stable for a long time and less sensitive to protein denaturation.Bring together all these characteristics offers bright prospects to accomplish new glucose sensors and closed-loop insulin delivery systems.Accordingly,different forms of copolymers-bearing PBA have been synthesized to serve in glucose sensing and glucose-induced insulin delivery systems.Among them,gels-bearing PBA are considered excellent platforms for insulin regulatory systems due to their biocompatibility and microporous structure.In hydrogels-bearing PBA,the PBA moiety endows the hydrogel the reversible volumetric change in response to glucose,while the hydrogel provides the tunable pore size that can accumulate insulin and release it in response to glucose and/or other stimuli.Random copolymers are other important platform due to their easy synthesis and characterization.Hence,copolymer self-assemblies are an attractive approach for smart delivery systems.They can be functionalized with recognition moieties and their morphologies and sizes can be tuned by external stimuli such as glucose.However,PBA-based gels and copolymers are still at a distance from being clinically applicable under physiologically relevant conditions due to their high pKa values,low biodegradability,low volumetric change,slow response rate and insufficient structural integrity particularly for implantable and injectable platforms.In this thesis,w'e synthesized different PBA-based gels and copolymers,studied their glucose-sensing properties and/or glucose-induced insulin delivery behavior.1)Different glucose-responsive nanostructured hydrogels(NSGs)were synthesized using activated nanogels(ANGs)as nano-crosslinkers.The ANGs(P(NIPAM-co-MBA)s)were prepared via precipitation polymerization of N-isopropylacrylamide(NIPAM)and N.'N methylenebisacrylamide(MBA).The corresponding NSGs were synthesized using 3-acrylamidophenylboronic acid(AAPBA)and NIPAM as monomers and the pre-synthesized ANG as nano-crosslinker via redox-initiated free radical polymerization.The structure,morphology and hydrodynamic diameter of the synthesized ANGs were examined by fourier transforms infrared(FTIR),transmission electron microscope(TEM)and dynamic light scattering(DLS),respectively.The interior morphology of NSGs was tested using scanning electron microscope(SEM).The swelling behavior of NSGs was examined as a function of glucose and temperature.The prepared NSGs showed glucose-responsiveness in a remarkable concentration-dependent manner and exhibited high elasticity upon compression,slicing,and resisted high level of deformation such as bending,twisting and stretching.2)Different glucose-responsive nanogels of N-isopropylacrylamide(NIPAM)and 4-(1,6-dioxo-2,5-diaza-7-oxamyl)phenylboronic acid(DDOPBA)were synthesized using dextran-grafted maleic acid(Dex-MA)as a crosslinker.The formed nanogels(P(NIPAM-co-Dex-co-DDOPBA)s)were verified by 1H NMR,TEM,DLS and X-ray photoelectron spectroscopy(XPS).The incorporation of DDOPBA and the usage of Dex-MA endowed the prepared nanogels high sensitivity towards glucose at physiological pH and temperature.The nanogels were loaded with insulin and the in vitro release profiles showed an increment in the triggered amount of insulin when more glucose was existed in the release medium.It was concluded that these nanogels could be suitable for insulin delivery systems as their response to glucose alterations occurred at pH 7.4 and temperature 37 ?.3)Different glucose-responsive hydrogels of poly(acrylamide-co-poly(ethylene glycol)diacrylate-co-3-acrylamido phenylboronic acid-co-chitosan grafted maleic acid)(P(AM-co-PEGDA-co-AAPBA-co-CSMA)s)were synthesized using poly(ethylene glycol)diacrylate(PEGDA)as a crosslinker.The structure and morphology of the hydrogels,named as CSPBA were studied by FTIR and SEM,while the mchanical properties were tested using dynamic mechanical analysis(DMA)and universal testing machine.The hydrogels shrinked at low glucose concentration due to the 2:1 boronate-glucose binding,and swelled at high glucose concentration because of 1:1 boronate-glucose complexation.Both binding mechanisms are useful for glucose sensing and insulin delivery.The integration of CSMA into hydrogel's network not only enhanced the response to glucose at physiological pH,but also improved the mechanical properties and increased the encapsulation efficiency.These CSPBA may find potential as implantable hydrogels in applications where continuous glucose monitoring and controlled release is beneficial.4)Four glucose-responsive copolymers(GRCPs)of poly(acrylamide-co-dimethylamino ethyl methacrylate-co-3-acrylamidophenylboronic acid)s(P(AM-co-DMAMEA-co-AAPBA)s)were synthesized and characterized by 1H NMR and FTIR.The morphology of the prepared copolymers was examined using TEM.The cloud point was located using UV-vis spectroscopy.The copolymers showed a good response to glucose concentration under physiological conditions.Alizarin red S was loaded into copolymer and a remarkable increase in their fluorescent intensity was achieved when glucose was added.The results proved that though a rational design the response to glucose can be achieved under physiological pH and temperature.These copolymers have the potential to serve in insulin delivery systems.