Islet cell spheroids produced by a thermally sensitive scaffold: a new diabetes treatment.

The primary issues in treating type 1 diabetes mellitus (T1DM) through the transplantation of healthy islets or islet ß-cells are graft rejection and a lack of available donors. Currently, the majority of approaches use cell encapsulation technology and transplant replacement cells that can release insulin to address transplant rejection and donor shortages. However, existing encapsulation materials merely serve as carriers for islet cell growth. A new treatment approach for T1DM could be developed by creating a smart responsive material that encourages the formation of islet cell spheroids to replicate their 3D connections in vivo and controls the release of insulin aggregates. In this study, we used microfluidics to create thermally sensitive porous scaffolds made of poly(N-isopropyl acrylamide)/graphene oxide (PNIPAM/GO). The material was carefully shrunk under near-infrared light, enriched with mouse insulinoma pancreatic ß cells (ß-TC-6 cells), encapsulated, and cultivated to form 3D cell spheroids. The controlled contraction of the thermally responsive porous scaffold regulated insulin release from the spheroids, demonstrated using the glucose-stimulated insulin release assay (GSIS), enzyme-linked immunosorbent assay (ELISA), and immunofluorescence assay. Eventually, implantation of the spheroids into C57BL/6 N diabetic mice enhanced the therapeutic effect, potentially offering a novel approach to the management of T1DM.

Thermo-Responsive Polymer-siRNA Conjugates Enabling Artificial Control of Gene Silencing around Body Temperature.

PURPOSE: Controlling small interfering RNA (siRNA) activity by external stimuli is useful to exert a selective therapeutic effect at the target site. This study aims to develop a technology to control siRNA activity in a thermo-responsive manner, which can be utilized even at temperatures close to body temperature. METHODS: siRNA was conjugated with a thermo-responsive copolymer that was synthesized by copolymerization of N-isopropylacrylamide (NIPAAm) and hydrophilic N,N-dimethylacrylamide (DMAA) to permit thermally controlled interaction between siRNA and an intracellular gene silencing-related protein by utilizing the coil-to-globule phase transition of the copolymer. The composition of the copolymer was fine-tuned to obtain lower critical solution temperature (LCST) around body temperature, and the phase transition behavior was evaluated. The cellular uptake and gene silencing efficiency of the copolymer-siRNA conjugates were then investigated in cultured cells. RESULTS: The siRNA conjugated with the copolymer with LCST of 38.0°C exhibited ~ 11.5 nm of the hydrodynamic diameter at 37°C and ~ 9.8 nm of the diameter at 41°C, indicating the coil-globule transition above the LCST. In line with this LCST behavior, its cellular uptake and gene silencing efficiency were enhanced when the temperature was increased from 37°C to 41°C. CONCLUSION: By fine-tuning the LCST behavior of the copolymer that was conjugated with siRNA, siRNA activity could be controlled in a thermo-responsive manner around the body temperature. This technique may offer a promising approach to induce therapeutic effects of siRNA selectively in the target site even in the in vivo conditions.

One-Step Preparation of Thermo-Responsive Poly(N-isopropylacrylamide)-Based Block Copolymer Nanoparticles by Aqueous Photoinitiated Polymerization-Induced Self-Assembly.

Poly(N-isopropylacrylamide) (PNIPAM) is an important thermo-responsive polymer that finds applications in many areas. However, the preparation of PNIPAM-based block copolymer nanoparticles with higher-order morphologies at high solids is challenging. Herein, aqueous photoinitiated polymerization-induced self-assembly (photo-PISA) of N-isopropylacrylamide (NIPAM) using an asymmetrical cross-linker is developed for one-step preparation of PNIPAM-based block copolymer nanoparticles with various morphologies (spheres, worms, and vesicles). It is demonstrated that reaction temperature has a great effect on both polymerization kinetics and morphologies of block copolymer nanoparticles. Reversible addition-fragmentation chain transfer (RAFT) reactive groups embedded inside the PNIPAM core provide a landscape for further functionalization. PNIPAM-based block copolymer nanoparticles with different surface properties are prepared by seeded photo-PISA at room temperature. Finally, these block copolymer nanoparticles are also used as additives to tune mechanical properties of hydrogels via covalent cross-linking.

Synthesis and Self-Assembly of Thermoresponsive Biohybrid Graft Copolymers Based on a Combination of Passerini Multicomponent Reaction and Molecular Recognition.

Amphiphilic graft copolymers exhibit fascinating self-assembly behaviors. Their molecular architectures significantly affect the morphology and functionality of the self-assemblies. Considering the potential application of amphiphilic graft copolymers in the fabrication of nanocarriers, it is essential to synthesize well-defined graft copolymers with desired functional groups. Herein, the Passerini reaction and molecular recognition are introduced to the synthesis of functional thermoresponsive graft copolymers. A bifunctional monomer 2-((adamantan-1-yl)amino)-1-(4-((2-bromo-2-methylpropanoyl)oxy)phenyl)-2-oxoethyl methacrylate (ABMA) with a bromo group for atom transfer radical polymerization (ATRP) and an adamantyl group for molecular recognition is synthesized through the Passerini reaction. The graft copolymers are prepared by reversible addition-fragmentation transfer (RAFT) copolymerization of ABMA and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) followed by RAFT end group removal and ATRP of di(ethylene glycol)methyl ether methacrylate (DEGMA) initiated by the ABMA units. The graft copolymer P(OEGMA-co-ABMA)-g-PDEGMA can be functionalized with ß-cyclodextrin modified peptides, affording a thermoresponsive biohybrid graft copolymer. At a temperature above its lower critical solution temperature, the biohybrid graft copolymer self-assembles into peptide-modified polymersomes.

An Artificial Phase-Transitional Underwater Bioglue with Robust and Switchable Adhesion Performance.

Complex coacervation enables important wet adhesion processes in natural and artificial systems. However, existed synthetic coacervate adhesives show limited wet adhesion properties, non-thermoresponsiveness, and inferior biodegradability, greatly hampering their translations. Herein, by harnessing supramolecular assembly and rational protein design, we present a temperature-sensitive wet bioadhesive fabricated through recombinant protein and surfactant. Mechanical performance of the bioglue system is actively tunable with thermal triggers. In cold condition, adhesion strength of the bioadhesive was only about 50 kPa. By increasing temperature, the strength presented up to 600 kPa, which is remarkably stronger than other biological counterparts. This is probably due to the thermally triggered phase transition of the engineered protein and the formation of coacervate, thus leading to the enhanced wet adhesion bonding.

Thermally Induced Reversible Self-Assembly of Apoferritin-Block Copolymer Complexes.

Protein cages are interesting building blocks for functional supramolecular assemblies. A multi-responsive system composed of apoferritin and thermo-responsive block copolymers complexed through electrostatic interactions is described here. The polymers are linear chains with cationic and thermo-responsive blocks, and both diblock and triblock copolymers are studied. The apoferritin can be reversibly assembled and disassembled in aqueous solutions by altering the temperature and electrolyte concentration of the solutions. The control over the conditions is straightforward and all the components can be recovered, offering a potential alternative for systems requiring chemical or genetic modification of proteins.

Mineralized Supramolecular Hydrogels Bearing Tunable Thermo-Responsiveness.

Although a variety of biomimetic mineralized materials have been created in the lab, the vast majority of these manmade examples lack response to external stimuli. Here, mineralized supramolecular hydrogels with on-demand thermo-responsiveness that are formed by a simple, physical crosslinking between amorphous CaCO3 (ACC) nanoparticles and poly(acrylic acid) (PAA) are reported. Upon the addition of Na2 CO3 solution into a mixture composed of PAA and CaCl2 , amorphous ACC nanoparticles are formed in situ and simultaneously crosslinked by PAA chains, giving rise to the mineralized hydrogels. Interestingly, upon tuning the content of the formed ACC, hydrogels with different types of thermo-responsiveness can be easily obtained, and the transparencies of the resulting hydrogels are dramatically changed during the temperature-driven phase transitions. As an application, these thermo-responsive mineralized hydrogels are used to control the exposure of UV light, which is successfully applied to switch fluorescent signals in response to temperature.

LCST phase behavior of benzo-21-crown-7 with different alkyl chains.

The introduction of hydrophobic units into crown ethers can dramatically decrease the critical transition temperature of LCST and realize macroscopic phase separation at low to moderate temperature and concentration. Minor modifications in the chemical structure of crown ethers (benzo-21-crown-7, B21C7s) can effectively control the thermo-responsive properties.

Ion Selectivity in Nonpolymeric Thermosensitive Systems Induced by Water-Attenuated Supramolecular Recognition.

The chemistry of aqueous salt solutions is rich with ambiguities, especially in stimuli-responsive supramolecular systems. Rational use of ion specificity to design supramolecular responsive materials, however, remains a challenging task. In this work, a low-molecular-weight supramolecular system was developed that was used to reveal the underlying systematic relationship between ions, water, and solutes. By utilizing these water-attenuated supramolecular forces (with Ka only ca. 30 m-1 ), an alternative concept for fabricating an aqueous responsive system in ionic medium was demonstrated. This work not only provides mechanistic insight into the underdeveloped role of topology in ion specificity upon noncharged polar surfaces, but also demonstrates the feasibility of utilizing weak supramolecular approaches to control the thermoresponsiveness.

Development and evaluation of locust bean gum based in situ gel for ocular delivery of ofloxacin for treatment of bacterial keratitis.

One of the drawbacks of conventional ocular dosage forms is their short residence time in the eye. To address this, we propose an ocular in situ gel that adheres to the eye surface for a prolonged period. Locust bean gum (LBG), a galactomannan polysaccharide, exhibits the desired characteristics to serve as a drug carrier for ocular application. However, the gum has not yet been investigated for ocular drug delivery. In this work, we have developed an LBG based in situ gel loaded with ofloxacin and evaluated its drug delivery efficacy through in vitro and ex vivo tests. To confer temperature sensitivity, LBG was grafted with N-isopropyl acrylamide (NIPAAm), and a series of solutions were made with ofloxacin (0.03 % w/v). The solution turned into a gel when the temperature was raised to 37 °C. The safety and efficacy of the developed in situ gels were validated through experiments on rat eyes infected with clinical strains of bacteria. The developed keratitis was completely healed indicating that the grafted LBG can be used as a potential candidate for the development of ocular in situ gel.

Bio-Inspired Double-Layered Hydrogel Robot with Fast Response via Thermo-Responsive Effect.

Bio-inspired hydrogel robots have become promising due to their advantage of the interaction safety and comfort between robots and humans, while current hydrogel robots mainly focus on underwater movement due to the hydration-dehydration process of thermo-responsive hydrogels, which greatly limits their practical applications. To expand the motion of the thermo-responsive hydrogel robot to the ground, we constructed a hydrogel robot inspired by a caterpillar, which has an anisotropic double-layered structure by the interfacial diffusion polymerization method. Adding PVA and SA to PNIPAm will cause different conformation transitions. Therefore, sticking the two layers of hydrogel together will form a double-layer anisotropic structure. The ultra-high hydrophilicity of PVA and SA significantly reduces the contact angle of the hydrogel from 53.1° to about 10° and reduces its hydration time. The responsive time for bending 30° of the hydrogel robot has been greatly reduced from 1 h to half an hour through the enhancement of photo-thermal conversion and thermal conductivity via the addition of Fe3O4 nanoparticles. As a result, the fabricated hydrogel robot can achieve a high moving speed of 54.5 mm·h-1 on the ground. Additionally, the fabricated hydrogel has excellent mechanical strength and can endure significant flexibility tests. This work may pave the road for the development of soft robots and expand their applications in industry.

Controlled Amphiphilicity and Thermo-Responsiveness of Functional Copolymers Based on Oligo(Ethylene Glycol) Methyl Ether Methacrylates.

In this work, comb homopolymers as well as comb-type copolymers of thermo-responsive oligo(ethylene glycol methyl ether methacrylate)s, OEGMAs, with various chain lengths (DEGMA, PEGMA500, and PEGMA950 containing 2, 9, or 19 repeating ethylene glycol units, respectively) were synthesized through free radical (co)polymerization. For the copolymers, either the functional hydrophobic glycidyl methacrylate (GMA) or the inert hydrophilic N,N-dimethylacrylamide (DMAM) were selected as comonomers. The self-assembly and thermo-responsive behavior of the products was investigated through Nile Red fluorescence probing, turbidimetry, and dynamic light scattering (DLS). Interestingly, it was found that all OEGMA-based homopolymers exhibit a tendency to self-organize in aqueous media, in addition to thermo-responsiveness. The critical aggregation concentration (CAC) increases with the number of repeating ethylene oxide units in the OEGMA macromonomers (CAC was found to be 0.003, 0.01, and 0.03% w/v for the homopolymers PDEGMA, PPEGMA500, and PPEGMA950, respectively). Moreover, the CAC of the copolymers in aqueous media is highly affected by the incorporation of hydrophobic GMA or hydrophilic DMAM units, leading to lower or higher values, respectively. Thus, the CAC decreases down to 0.003% w/v for the GMA-richest copolymer of PEGMA950, whereas CAC increases up to 0.01% w/v for the DMAM-richest copolymer of DEGMA. Turbidimetry and DLS studies proved that the thermo-sensitivity of the polymers is governed by several parameters such as the number of repeating ethylene glycol groups in the side chains of the OEGMAs, the molar percentage of the hydrophobic or hydrophilic comonomers, along with the addition of salts in the aqueous polymer solutions. Thus, the cloud point of the homopolymer PDEGMA was found at 23 °C and it increases to 33.5 °C for the DMAM-richest copolymer of DEGMA. Lastly, the formation of a hydrogel upon heating aqueous mixtures of the GMA-comprising copolymers with silica nanoparticles overnight is strong evidence of the functional character of these polymers.

Elastin-like polypeptide-based micelles as a promising platform in nanomedicine.

New and improved nanomaterials are constantly being developed for biomedical purposes. Nanomaterials based on elastin-like polypeptides (ELPs) have increasingly shown potential over the past two decades. These polymers are artificial proteins of which the design is based on human tropoelastin. Due to this similarity, ELP-based nanomaterials are biodegradable and therefore well suited to drug delivery. The assembly of ELP molecules into nanoparticles spontaneously occurs at temperatures above a transition temperature (Tt). The ELP sequence influences both the Tt and the physicochemical properties of the assembled nanomaterial. Nanoparticles with desired properties can hence be designed by choosing the appropriate sequence. A promising class of ELP nanoparticles are micelles assembled from amphiphilic ELP diblock copolymers. Such micelles are generally uniform and well defined. Furthermore, site-specific attachment of cargo to the hydrophobic block results in micelles with the cargo shielded inside their core, while conjugation to the hydrophilic block causes the cargo to reside in the corona where it is available for interactions. Such control over particle design is one of the main contributing factors for the potential of ELP-based micelles as a drug delivery system. Additionally, the micelles are easily loaded with protein or peptide-based cargo by expressing it as a fusion protein. Small molecule drugs and other cargo types can be either covalently conjugated to ELP domains or physically entrapped inside the micelle core. This review aims to give an overview of ELP-based micelles and their applications in nanomedicine.

Thermo-responsive behavior and gelation of curdlan alkyl-ethers prepared by homogeneous reaction.

To resolve the major obstacles of poor water solubility and few functional derivatives in the practical utilization of curdlan, we prepared highly soluble and thermal-responsively alkylated curdlan with different degrees of substitution (DS) via homogeneous reaction. The properties of these derivatives were investigated by rheology, inline attenuated total reflective-Fourier transform infrared spectroscopy, Raman and fluorescence spectroscopy, micro-differential scanning calorimetry, dynamic light scattering, and in vitro cytotoxicity assay. The newly developed methylated and ethylated curdlan can form thermal reversible heat-set hydrogels accompanied by volume shrinkage due to syneresis. Their gelation temperatures depend strongly on the DS, size of hydrophobic groups, and the order of the Hofmeister series salts added. Experimental results indicated that the gel network was induced by the enhanced hydrophobic interaction among macromolecular chains and weakened hydrogen bonding between the polymer and water on heating, leading to phase separation and gelation.

Mechanically Tunable Hydrogels with Self-Healing and Shape Memory Capabilities from Thermo-Responsive Amino Acid-Derived Vinyl Polymers.

In this study, we report the fabrication and characterization of self-healing and shape-memorable hydrogels, the mechanical properties of which can be tuned via post-polymerization crosslinking. These hydrogels were constructed from a thermo-responsive poly(N-acryloyl glycinamide) (NAGAm) copolymer containing N-acryloyl serine methyl ester (NASMe) units (5 mol%) that were readily synthesized via conventional radical copolymerization. This transparent and free-standing hydrogel is produced via multiple hydrogen bonds between PNAGAm chains by simply dissolving the polymer in water at a high temperature (~90 °C) and then cooling it. This hydrogel exhibited moldability and self-healing properties. The post-polymerization crosslinking of the amino acid-derived vinyl copolymer network with glutaraldehyde, which acts as a crosslinker between the hydroxy groups of the NASMe units, tuned mechanical properties such as viscoelasticity and tensile strength. The optimal crosslinker concentration efficiently improved the viscoelasticity. Moreover, these hydrogels exhibited shape fixation (~60%)/memory (~100%) behavior owing to the reversible thermo-responsiveness (upper critical solution temperature-type) of the PNAGAm units. Our multifunctional hydrogel, with moldable, self-healing, mechanical tunability via post-polymerization crosslinking, and shape-memorable properties, has considerable potential for applications in engineering and biomedical materials.

Biomimetic Gradient Hydrogel Actuators with Ultrafast Thermo-Responsiveness and High Strength.

Most current hydrogel actuators suffer from either poor mechanical properties or limited responsiveness. Also, the widely used thermo-responsive poly-(N-isopropylacrylamide) (PNIPAM) homopolymer hydrogels have a slow response rate. Thus, it remains a challenge to fabricate thermo-responsive hydrogel actuators with both excellent mechanical and responsive properties. Herein, ultrafast thermo-responsive VSNPs-P(NIPAM-co-AA) hydrogels containing multivalent vinyl functionalized silica nanoparticles (VSNPs) are fabricated. The ultrafast thermo-responsiveness is due to the mobile polymer chains grafted from the surfaces of the VSNPs, which can facilitate hydrophobic aggregation, inducing the phase transition and generating water transport channels for quick water expulsion. In addition, the copolymerization of NIPAM with acrylic acid (AA) decreases the transition temperature of the thermo-responsive PNIPAM-based hydrogels, contributing to ultrafast thermo-responsive shrinking behavior with a large volume change of as high as 72.5%. Moreover, inspired by nature, intelligent hydrogel actuators with gradient structure can be facilely prepared through self-healing between the ultrafast thermo-responsive VSNPs-P(NIPAM-co-AA) hydrogel layers and high-strength VSNPs-PAA-Fe3+ multibond network (MBN) hydrogel layers. The obtained well-integrated gradient hydrogel actuators show ultrafast thermo-responsive performance within only 9 s in 60 °C water, as well as high strength, and can be used for more practical applications as intelligent soft actuators or artificial robots.

Self-assembled Fluorescent Nanoparticles with Tunable LCST Behavior in Water.

The development of stimuli-responsive fluorescent materials in water based on organic molecule has drawn significant interest. Herein, we designed and synthesized an amphiphilic molecule M containing a fixed tetraphenylethylene moiety (FTPE) as hydrophobic part and tri(ethylene glycol) (TEG) chains as hydrophilic part. Notably, the FTPE moiety is aggregation-induced emission (AIE) active, while the TEG chains are thermo-responsive. M can self-assemble into fluorescent nanoparticles (NPs) in water, which showed lower critical solution temperature (LCST) behavior. Moreover, its clouding point can be reversibly tuned upon the concentration variation. Interestingly, the NPs can be acted as a fluorescence thermometer in aqueous media owing to their unique AIE and LCST behaviors. Our work herein not only provides an integration strategy to construct stimuli-responsive fluorescent materials but also shows great potential in biological applications including bioimaging and biosensors.

Smart and eco-friendly N-isopropylacrylamide and cellulose hydrogels as a safe dual-drug local cancer therapy approach.

Local cancer treatment by in situ injections of thermo-responsive hydrogels (HG) offers several advantages over conventional systemic anti-cancer treatments. In this work, a biodegradable and multicompartmental HG composed of N-isopropylacrylamide, cellulose, citric acid, and ceric ammonium nitrate was developed for the controlled release of hydrophilic (doxorubicin) and hydrophobic (niclosamide) drugs. The formulation presented ideal properties regarding thermo-responsiveness, rheological behavior, drug release profile, biocompatibility, and biological activity in colon and ovarian cancer cells. Cellulose was found to retard drugs release rate, being only 4 % of doxorubicin and 30 % of niclosamide released after 1 week. This low release was sufficient to cause cell death in both cell lines. Moreover, HG demonstrated a proper injectability, in situ prevalence, and safety profile in vivo. Overall, the HG properties, together with its natural and eco-friendly composition, create a safe and efficient platform for the local treatment of non-resectable tumors or tumors requiring pre-surgical adjuvant therapy.

Dual pH-/thermo-responsive chitosan-based hydrogels prepared using "click" chemistry for colon-targeted drug delivery applications.

A dual pH-/thermo-responsive hydrogel was designed based on a polyelectrolyte complex of polyacrylic acid (PAA) and norbornene-functionalized chitosan (CsNb), which was synergized with chemical crosslinking using bistetrazine-poly(N-isopropyl acrylamide) (bisTz-PNIPAM). The thermo-responsive polymeric crosslinker, bisTz-PNIPAM, was synthesized via reversible addition-fragmentation transfer polymerization of NIPAM. FTIR, XRD, rheological and morphological analyses demonstrated the successful formation of the polyelectrolyte network. The highly porous structure generated through the in-situ "click" reaction between Tz and Nb resulted in a higher drug loading (29.35 %). The hydrogel (COOH/NH2 mole ratio of 3:1) exhibited limited drug release (8.5 %) of 5-ASA at a pH of 2.2, but it provided an almost complete release (92 %) at pH 7.4 and 37 °C within 48 h due to the pH responsiveness of PAA, hydrogel porosity, and shrinkage behavior of PNIPAM. The hydrogels were biodegradable and non-toxic against human fibroblast cells, suggesting their considerable potential for a colon-targeted drug delivery system.