Synthesis and characterization of poly(amino urea urethane)-based block copolymer and its potential application as injectable pH/temperature-sensitive hydrogel for protein carrier

Advances in the stimuli-responsive injectable hydrogel for controlled release of drugs

The stimuli-responsiveness of injectable hydrogel has been drastically developed for the controlled release of drugs and achieved encouraging curative effects in a variety of diseases including wounds, cardiovascular diseases and tumors. The gelation, swelling and degradation of such hydrogels respond to endogenous biochemical factors (such as pH, reactive oxygen species, glutathione, enzymes, glucose) and/or to exogenous physical stimulations (like light, magnetism, electricity and ultrasound), thereby accurately releasing loaded drugs in response to specifically pathological status and as desired for treatment plan and thus improving therapeutic efficacy effectively. In this paper, we give a detailed introduction of recent progresses in responsive injectable hydrogels and focus on the design strategy of various stimuli-sensitivities and their resultant alteration of gel dissociation and drug liberation behaviour. Their application in disease treatment is also discussed. This article is protected by copyright. All rights reserved.

Thiol-Epoxy "Click" Chemistry to Engineer Cytocompatible PEG-Based Hydrogel for siRNA-Mediated Osteogenesis of hMSCs

Thiol-epoxy "click" chemistry is employed for the first time to engineer a new cytocompatible PEG-based hydrogel system in aqueous media with the ability to encapsulate human mesenchymal stem cells (hMSCs) and control their fate for tissue regeneration. Cells were easily encapsulated into the hydrogels and exhibited high cell viability over 4 weeks of culture regardless of the presence of siRNA, complexed with polyethylenimine (PEI) in the form of siRNA/PEI nanocomplexes, indicating the biocompatibility of the developed hydrogel. Loading pro-osteogenic siNoggin in the hydrogel significantly enhanced the osteogenesis of encapsulated hMSCs, demonstrating the potential application of this system in tissue engineering.

Synthesis of an injectable, self-healable and dual responsive hydrogel for drug delivery and 3D cell cultivation

An injectable, self-healable and dual pH and temperature responsive hydrogel was facilely prepared and applied as a potential carrier for drug delivery and cell cultivation.

Thermally-Induced Triple-Shape Hydrogels: Soft Materials Enabling Complex Movements

Shape-memory hydrogels enable directed movements of a specimen in response to temperature, whereby crystallizable switching segments incorporated as side chains resulted in constant degrees of swelling during the shape-memory cycle. Here we report about hydrogels exhibiting a thermally induced triple-shape effect that allows complex movements of soft materials with two almost independent shape changes. Potential applications for those soft triple-shape materials are two-step self-unfolding devices or temperature-sensitive hydrogel actuators, for example, smart valves for flow rate control in aqueous media. Series of hydrogels with two different hydrophobic crystallizable switching segments were prepared. The degrees of swelling of the triple-shape hydrogels were not affected for different shapes or temperatures, which avoided in this way interferences on the shape shifts. During the two-step programming procedure, two distinct shapes can be implemented as reflected by shape fixity ratios of generally >50%. Structural analysis of the switching domains during the triple-shape cycle by means of X-ray scattering indicates that longer side chains gain lower orientation after deformation and that shorter side chains orient perpendicular to the hydrophilic main chain. Furthermore, it is observed that increased orientation of the switching domains is not a key requirement for adequate shape fixity and recovery ratios of the triple-shape effect in hydrogels, thus longer side chains can be utilized as switching segments in other shape-memory hydrogels.

Sulfamethazine-based pH-sensitive hydrogels with potential application for transcatheter arterial chemoembolization therapy

Transcatheter arterial chemoembolization (TACE) is the most common palliative therapy for unresectable hepatocellular carcinoma (HCC). The conventional TACE technique, which employs the Lipiodol® emulsion, has been widely used for human cancer treatments. However, this delivery system seems to be inconsistent and unstable in maintaining a high concentration of drugs at tumor sites. An alternative approach for TACE is loading drugs into a liquid embolic solution that exists as an injectable solution and can exhibit a sol-to-gel phase transition to form a solidified state once delivered to the tumor site. Here, we develop a novel sulfamethazine-based anionic pH-sensitive block copolymer with potential application as a radiopaque embolic material. The copolymer, named PCL-PEG-SM, and comprised of poly(ε-caprolactone), sulfamethazine, and poly(ethylene glycol), was fabricated by free radical polymerization. An aqueous solution of the developed copolymer underwent a sol-to-gel phase transition upon lowering the environmental pH to create a gel region that covered the physiological condition (pH 7.4, 37°C) and the low pH conditions at tumor sites (pH 6.5-7.0, 37°C). The release of doxorubicin (DOX) from DOX-loaded copolymer hydrogels could be sustained for more than 4weeks in vitro, and the released DOX retained its fully bioactivity via inhibition the proliferation of hepatic cancer cells. The radiopaque embolic formulations that were prepared by mixing copolymer solutions at pH 8.0 with Lipiodol®, a long-lasting X-ray contrast agent, could exhibit the gelation inside the tumor after intratumoral injection or intraarterial administration using a VX2 carcinoma hepatic tumor rabbit model. These results suggest that a novel anionic pH-sensitive copolymer has been developed with a potential application as a liquid radiopaque embolic solution for TACE of HCC.

STATE OF SIGNIFICANCE

Transcatheter arterial chemoembolization (TACE) has been widely used as a palliative treatment therapy for unresectable hepatocellular carcinoma (HCC). Conventional TACE technique, which usually employs emulsion of DOX-in-Lipiodol®, followed by an embolic agent, has significant limitation of inconsistency and lack of controlled release ability. To address these limitations of conventional TACE material system, we introduced a novel liquid radiopaque embolic material from our pH-sensitive hydrogel. The material has low viscosity that can be injected via a microcatheter, rather biocompatibility, and drug controlled release ability. Importantly, it can form gel in the tumor as well as tumoral vasculature in response to the lowered pH at the tumor site, which proved the potential for the use to treat HCC by TACE therapy.

Temperature-Responsive Smart Nanocarriers for Delivery Of Therapeutic Agents: Applications and Recent Advances

Smart drug delivery systems (DDSs) have attracted the attention of many scientists, as carriers that can be stimulated by changes in environmental parameters such as temperature, pH, light, electromagnetic fields, mechanical forces, etc. These smart nanocarriers can release their cargo on demand when their target is reached and the stimulus is applied. Using the techniques of nanotechnology, these nanocarriers can be tailored to be target-specific, and exhibit delayed or controlled release of drugs. Temperature-responsive nanocarriers are one of most important groups of smart nanoparticles (NPs) that have been investigated during the past decades. Temperature can either act as an external stimulus when heat is applied from the outside, or can be internal when pathological lesions have a naturally elevated termperature. A low critical solution temperature (LCST) is a special feature of some polymeric materials, and most of the temperature-responsive nanocarriers have been designed based on this feature. In this review, we attempt to summarize recent efforts to prepare innovative temperature-responsive nanocarriers and discuss their novel applications.

Light-triggered RNA release and induction of hMSC osteogenesis via photodegradable, dual-crosslinked hydrogels

AIM

To engineer a photodegradable hydrogel system for actively controlled release of bioactive unmodified RNA at designated time points to induce hMSC osteogenesis.

MATERIALS & METHODS

RNA/polyethylenimine complexes were loaded into dual-crosslinked photodegradable hydrogels to examine the capacity of UV light application to trigger their release. The ability of released RNA to drive hMSC osteogenic differentiation was also investigated.

RESULTS & CONCLUSION

RNA release from photodegradable hydrogels was accelerated upon UV application, which was not observed in non-photodegradable hydrogels. Regardless of the presence of UV light, released siGFP exhibited high bioactivity by silencing GFP expression in HeLa cells. Importantly, siNoggin or miRNA-20a released from the hydrogels induced hMSC osteogenesis. This system provides a potentially valuable physician/patient-controlled 'on-demand' RNA delivery platform for biomedical applications.

Intraarterial gelation of injectable cationic pH/temperature-sensitive radiopaque embolic hydrogels in a rabbit hepatic tumor model and their potential application for liver cancer treatment

Radiopaque embolic solutions employing cationic poly(amino ester urethane)-based copolymers are injected into a rabbit hepatic tumor artery and form hydrogels in response to local temperature and pH for chemoembolization.

A high water-content and high elastic dual-responsive polyurethane hydrogel for drug delivery

Stimuli-responsive hydrogels are soft, biocompatible and smart biomaterials; however, the poor mechanical properties of the hydrogels limit their application. Herein, we prepared a reductant- and light-responsive polyurethane hydrogel which was made of polyethylene glycol, 1,6-diisocyanatohexane, azobenzene, cyclodextrin and disulfide. Attenuated Total Reflectance Infrared Spectra and ¹H NMR were used to characterize the structure of the hydrogel. The hydrogel has a high elasticity (a tensile modulus of 36.5 ± 0.5 kPa and a storage modulus of 52.9 ± 1.2 kPa) at a high water content (91.2 ± 0.4%). Swelling, mechanical and rheological properties of the hydrogel can be tuned by the content of the crosslinker, light and reductant. The hydrogel has low cytotoxicity and it can be used for drug delivery. Ultraviolet irradiation helped to load drugs and the reductant accelerated the drug release. With its high mechanical properties and light- and reductant-responsiveness, the hydrogel is hopefully to be used as a drug carrier.

Nanostructure controlled sustained delivery of human growth hormone using injectable, biodegradable, pH/temperature responsive nanobiohybrid hydrogel

The clinical efficacy of a therapeutic protein, the human growth hormone (hGH), is limited by its short plasma half-life and premature degradation. To overcome this limitation, we proposed a new protein delivery system by the self-assembly and intercalation of a negatively charged hGH onto a positively charged 2D-layered double hydroxide nanoparticle (LDH). The LDH-hGH ionic complex, with an average particle size of approximately 100 nm, retards hGH diffusion. Nanobiohybrid hydrogels (PAEU/LDH-hGH) were prepared by dispersing the LDH-hGH complex into a cationic pH- and temperature-sensitive injectable PAEU copolymer hydrogel to enhance sustained hGH release by dual ionic interactions. Biodegradable copolymer hydrogels comprising poly(β-amino ester urethane) and triblock poly(ε-caprolactone-lactide)-poly(ethylene glycol)-poly-(ε-caprolactone-lactide) (PCLA-PEG-PCLA) were synthesized and characterized. hGH was self-assembled and intercalated onto layered LDH nanoparticles through an anion exchange technique. X-ray diffraction and zeta potential results showed that the LDH-hGH complex was prepared successfully and that the PAEU/LDH-hGH nanobiohybrid hydrogel had a disordered intercalated nanostructure. The biocompatibility of the nanobiohybrid hydrogel was confirmed by an in vitro cytotoxicity test. The in vivo degradation of pure PAEU and its nanobiohybrid hydrogels was investigated and it showed a controlled degradation of the PAEU/LDH nanobiohybrids compared with the pristine PAEU copolymer hydrogel. The LDH-hGH loaded injectable hydrogels suppressed the initial burst release of hGH and extended the release period for 13 days in vitro and 5 days in vivo. The developed nanohybrid hydrogel has the potential for application as a protein carrier to improve patient compliance.

A heparin-mimicking reverse thermal gel for controlled delivery of positively charged proteins

Positively charged therapeutic proteins have been used extensively for biomedical applications. However, the safety and efficacy of proteins are mostly limited by their physical and chemical instability and short half-lives in physiological conditions. To this end, we created a heparin-mimicking sulfonated reverse thermal gel as a novel protein delivery system by sulfonation of a graft copolymer, poly(serinol hexamethylene urea)-co-poly(N-isopropylacylamide), or PSHU-NIPAAm. The net charge of the sulfonated PSHU-NIPAAm was negative due to the presence of sulfonate groups. The sulfonated PSHU-NIPAAm showed a typical temperature-dependent sol-gel phase transition, where polymer solutions turned to a physical gel at around 32°C and maintained gel status at body temperature. Both in vitro cytotoxicity tests using C2C12 myoblast cells and in vivo cytotoxicity tests by subcutaneous injections demonstrated excellent biocompatibility. In vitro release tests using bovine serum albumin revealed that the release from the sulfonated PSHU-NIPAAm was more sustained than that from the plain PSHU-NIPAAm. Furthermore, this sulfonated PSHU-NIPAAm system did not affect protein structure after 70-day observation periods.

Bioactive factor delivery strategies from engineered polymer hydrogels for therapeutic medicine

Polymer hydrogels have been widely explored as therapeutic delivery matrices because of their ability to present sustained, localized and controlled release of bioactive factors. Bioactive factor delivery from injectable biopolymer hydrogels provides a versatile approach to treat a wide variety of diseases, to direct cell function and to enhance tissue regeneration. The innovative development and modification of both natural-(e.g., alginate (ALG), chitosan, hyaluronic acid (HA), gelatin, heparin (HEP), etc.) and synthetic-(e.g., polyesters, polyethyleneimine (PEI), etc.) based polymers has resulted in a variety of approaches to design drug delivery hydrogel systems from which loaded therapeutics are released. This review presents the state-of-the-art in a wide range of hydrogels that are formed though self-assembly of polymers and peptides, chemical crosslinking, ionic crosslinking and biomolecule recognition. Hydrogel design for bioactive factor delivery is the focus of the first section. The second section then thoroughly discusses release strategies of payloads from hydrogels for therapeutic medicine, such as physical incorporation, covalent tethering, affinity interactions, on demand release and/or use of hybrid polymer scaffolds, with an emphasis on the last 5 years.

Controlled release of protein from biodegradable multi-sensitive injectable poly(ether-urethane) hydrogel

The synthesis and characterization of multi-sensitive polymers for use as injectable hydrogels for controlled protein/drug delivery is reported. A series of biodegradable multi-sensitive poly(ether-urethane)s were prepared through a simple one-pot condensation of poly(ethylene glycol), 2,2'-dithiodiethanol, N-methyldiethanolamine, and hexamethylene diisocyanate. The sol-gel phase transition behaviors of the obtained copolymers were investigated. Experimental results showed that the aqueous medium comprising the multi-segment copolymers underwent a sol-to-gel phase transition with increasing temperature and pH. At a certain concentration, the copolymer solution could immediately change to a gel under physiological conditions (37 °C and pH 7.4), indicating their suitability as in situ injectable hydrogels in vivo. Insulin was used as a model protein drug for evaluation of the injectable hydrogels as a site-specific drug delivery system. The controlled release of insulin from the hydrogel devices was demonstrated by degradation of the copolymer, which is modulated via the 2,2'-dithiodiethanol content in the poly(ether-urethane)s. These hydrogels having multi-responsive properties may prove to be promising candidates for injectable and controllable protein drug delivery devices.