Biodegradable pH-Dependent Thermo-Sensitive Hydrogels for Oral Insulin Delivery

Angle-independent pH-sensitive composites with natural gyroid structure

pH sensor is an important and practical device with a wide application in environmental protection field and biomedical industries. An efficient way to enhance the practicability of intelligent polymer composed pH sensor is to subtilize the three-dimensional microstructure of the materials, adding measurable features to visualize the output signal. In this work, C. rubi wing scales were combined with pH-responsive smart polymer polymethylacrylic acid (PMAA) through polymerization to achieve a colour-tunable pH sensor with nature gyroid structure. Morphology and reflection characteristics of the novel composites, named G-PMAA, are carefully investigated and compared with the original biotemplate, C. rubi wing scales. The most remarkable property of G-PMAA is a single-value corresponding relationship between pH value and the reflection peak wavelength (λmax), with a colour distinction degree of 18 nm/pH, ensuring the accuracy and authenticity of the output. The pH sensor reported here is totally reversible, which is able to show the same results after several detection circles. Besides, G-PMAA is proved to be not influenced by the detection angle, which makes it a promising pH sensor with superb sensitivity, stability, and angle-independence.

Oxidation- and thermo-responsive poly(N-isopropylacrylamide-co-2-hydroxyethyl acrylate) hydrogels cross-linked via diselenides for controlled drug delivery

A novel diselenide crosslinked poly(NIPAM-co-HEA) hydrogel was successfully synthesized, which exhibits a dual-stimuli-responsive drug release behaviors,i.e., thermo-induced slow sustained release and oxidation-induced quick burst release.

pH- and thermo-responsive poly(N-isopropylacrylamide-co-acrylic acid derivative) copolymers and hydrogels with LCST dependent on pH and alkyl side groups

A series of pH- and temperature-responsive poly(N-isopropylacrylamide-co-acrylic acid derivative) (P(NIPAM-co-AAD)) copolymers and hydrogels were prepared. The lower critical solution temperatures (LCSTs) of the copolymers exhibited a dependence on both pH and the hydrophobicity of the AAD unit. The influence of pH and temperature on the equilibrium swelling ratio of the hydrogels was investigated. The hydrogels displayed a unique thermo-induced swelling-deswelling transition that can be self-regulated to occur at above or below the physiological temperature in response to the environmental pH. Scanning electron microscopic (SEM) analysis revealed porous sponge-like microstructures of the hydrogels. Insulin was loaded into the hydrogels as a model protein, and the in vitro release profiles indicated that the loaded protein could be protected within the hydrogels in an acidic environment and selectively released in neutral medium. MTT assay proved that both the copolymers and hydrogels are nontoxic. After oral administration of the insulin-loaded hydrogels to streptozotocin-induced diabetic rats at 60 IU per kg, the fasting plasma glucose level was reduced continuously to 72.1% within 6 h. The bioavailability of hydrogel-encapsulated insulin via the oral administration to healthy rabbits reached 5.24%, which is much higher than that of pure insulin solution given orally. These results showed that the smart copolymers and hydrogels may hold great promise for pH-triggered drug delivery systems.

Polymeric hydrogels for oral insulin delivery

The search for an effective and reliable oral insulin delivery system has been a major challenge facing pharmaceutical scientists for over many decades. Even though innumerable carrier systems that protect insulin from degradation in the GIT with improved membrane permeability and biological activity have been developed, yet a clinically acceptable device is not available for human application. Efforts in this direction are continuing at an accelerated speed. One of the preferred systems widely explored is based on polymeric hydrogels that protect insulin from enzymatic degradation in acidic stomach and delivers effectively in the intestine. Swelling and deswelling mechanisms of the hydrogel under varying pH conditions of the body control the release of insulin. The micro and nanoparticle (NP) hydrogel devices based on biopolymers have been widely explored, but their applications in human insulin therapy are still far from satisfactory. The present review highlights the recent findings on hydrogel-based devices for oral delivery of insulin. Literature data are critically assessed and results from different laboratories are compared.