Regulating Electrostatic Interactions toward Thermoresponsive Hydrogels with Low Critical Solution Temperature.

Low critical solution temperature (LCST) of commonly used thermoresponsive polymers in water is basically dominated by hydrophobic interactions. Herein, a novel thermoresponsive system based on electrostatic interactions is reported. By simply loading aluminum chloride (AlCl3 ) into non-responsive poly(2-hydroxyethyl acrylate) (PHEA) hydrogels, PHEA-Al gels turn to have reversible thermoresponsive behavior between transparent and opaque without any volume change. Further investigations by changing metal ion-polymer compositions unravel the necessity of specific electrostatic interactions, namely, cation-dipole bonding interactions between hydroxy groups and trivalent metal ions. The thermoresponsive hydrogel demonstrates high transparency (≈95%), excellent luminous modulation capability (>98%), and cyclic reliability, suggesting great potential as an energy-saving material. Although LCST control by salt addition is widely known, salt-induced expression of thermoresponsiveness has barely been discussed before. This design provides a new approach of easy fabrication, low cost, and scalability to develop stimuli-responsive materials.

High transparency, water vapor barrier and antibacterial properties of chitosan/carboxymethyl glucan/poly(vinyl alcohol)/nanoparticles encapsulating citral composite film for fruit packaging.

Utilizing antibacterial packaging material is an effective approach to delay fruit rotting and spoilage thereby minimizing financial losses and reducing health harm. However, the barrier and mechanical properties of biodegradable antibacterial packaging materials are barely compatible with transparency. Herein, antimicrobial nanoparticles encapsulating citral (ANPs) were first prepared by emulsification under the stabilization of oxidized dextran (ODE) and ethylene diamine. Then, composite films with high transparency, good water vapor barrier, and mechanical and antibacterial properties for fruits packaging were prepared from chitosan (CS), carboxymethyl-glucan (CMG), poly(vinyl alcohol) (PVA), and ANPs by solvent casting strategy. The synergistic effects of electrostatic interaction and hydrogen bonding could regulate crystalline architecture, generating high transparency of the composite films (90 %). The mechanical properties of the composite film are improved with elongation at break up to 167 % and stress up to 32 MPa. The water vapor barrier property of the film is appropriate to the packed fruit for less weight loss and firmness remaining. Simultaneously, the addition of ANPs endowed the film with excellent antimicrobial and UV-barrier capabilities to reduce fruit mildew, thereby extending the shelf life of fruits. More importantly, the composite polymer solution could be sprayed or dipped directly on fruits as a coating for food storage to improve food shelf life, substantially expanding its ease of use and scope of use.

High-Sensitivity Flexible Sensor Based on Biomimetic Strain-Stiffening Hydrogel.

Recently, flexible wearable and implantable electronic devices have attracted enormous interest in biomedical applications. However, current bioelectronic systems have not solved the problem of mechanical mismatch of tissue-electrode interfaces. Therefore, the biomimetic hydrogel with tissue-like mechanical properties is highly desirable for flexible electronic devices. Herein, we propose a strategy to fabricate a biomimetic hydrogel with strain-stiffening property via regional chain entanglements. The strain-stiffening property of the biomimetic hydrogel is realized by embedding highly swollen poly(acrylate sodium) microgels to act as the microregions of dense entanglement in the soft polyacrylamide matrix. In addition, poly(acrylate sodium) microgels can release Na+ ions, endowing hydrogel with electrical signals to serve as strain sensors for detecting different human movements. The resultant sensors own a low Young's modulus (22.61-112.45 kPa), high nominal tensile strength (0.99 MPa), and high sensitivity with a gauge factor up to 6.77 at strain of 300%. Based on its simple manufacture process, well mechanical matching suitability, and high sensitivity, the as-prepared sensor might have great potential for a wide range of large-scale applications such as wearable and implantable electronic devices.

Mussel-Inspired Epoxy Bioadhesive with Enhanced Interfacial Interactions for Wound Repair.

The balance between high mechanical properties and strong adhesion strength is crucial in designing and preparing a bio-based hydrogel adhesive for wound closure. Although the adhesion performance of bioadhesives has been remarkably improved by modification with catechol groups, their mechanical properties are yet to meet the biomedical requirements. In this study, mussel-inspired epoxy bioadhesives (CSD-PEG) were synthesized based on catechol-modified chitosan oligosaccharide (CSD) and polyethylene glycol diglycidyl ether (PEGDGE) through nucleophilic substitution. Notably, the CSD-PEG adhesive showed high mechanical and adhesion strengths, which were up to 50.7 kPa and 136.7 kPa, respectively. It was confirmed that a certain amount of the epoxy and catechol groups provided multiple interfacial interactions among the adhesives, substrates, and polymer chains for enhancing the performance of adhesives. The adhesives showed good binding and repairing effects for wound closure and favorable biocompatibility in vivo. The prepared CSD-PEG adhesives are expected to be a promising candidate for surgical tissue repair, wound closure, and tissue engineering fields. STATEMENT OF SIGNIFICANCE: Current reported adhesives composed of biopolymers generally suffer from poor mechanical properties or weak tissue adhesiveness. Therefore, to achieve simultaneously high mechanical and adhesion properties in a bio-based adhesive for wound closure is a big challenge. In this study, mussel-inspired adhesive hydrogels (CSD-PEG) were prepared based on catechol-modified chitosan oligosaccharide (CSD) and polyethylene glycol diglycidyl ether (PEGDGE). The tensile strength and adhesive strength of CSD-PEG on porcine skin reached 50.7 kPa and 136.7 kPa, respectively, which were higher than those for most reported biopolymeric adhesives, mainly due to the multiple interfacial interactions between the catechol and epoxy groups. The CSD-PEG bioadhesives also showed good binding and repairing effects for wound closure and tissue regeneration in vivo.

Photo-cross-linking induces size change and stealth properties of water-dispersible cinnamic acid derivative nanoparticles.

Hydrophilic poly(ethylene glycol) (PEG) was grafted onto poly(4-cinnamic acid)-co-poly(3,4-cinnamic acid) (PCA) by Michael addition. The chemical structures of the PCA-graft-PEG (PCA-PEG) copolymers were confirmed by FT-IR and (1)H NMR measurements. The PCA-PEG nanoparticles were self-assembled by the solvent mixing method, in which additional water was dropped into a DMSO solution of the copolymer. The diameter of the PCA-PEG nanoparticles was below 100 nm, and decreased to about 30 nm upon increasing the composition ratio and molecular weight of PEG. The PCA-PEG nanoparticles showed [2 + 2] cyclobutane formation (cross-linking) following UV irradiation at λ > 280 nm. Moreover, the photo-cross-linking induced size decrement of the nanoparticles depending on the grafting degree and molecular weight of PEG. The amount of protein adsorption onto the surface of the nanoparticles was less than 30 ng/cm(2), due to the high density of PEG chains on their corona layers. Furthermore, photo-cross-linking induced a significant decrement in protein adsorption, due to an increase in PEG chain density triggered by the size decrement of the nanoparticles. These water-dispersible and photoresponsive nanoparticles would be useful as novel, functional carriers for drug delivery systems and biological diagnosis.

Supramolecular micellar drug delivery system based on multi-arm block copolymer for highly effective encapsulation and sustained-release chemotherapy.

Poly(phosphoester)-based biomaterials have great potential in drug delivery systems (DDSs) because of their multifunctional adjustability, stealth effect, excellent biodegradability, and biocompatibility. To further increase the drug loading efficiency (DLE) and sustained release ability, a multi-arm block copolymer, poly(amido amine)-b-poly(2-butenyl phospholane)-b-poly(2-methoxy phospholane) conjugated with folic acid (abbreviated as PAMAM-PBEP-PMP-FA), was designed and prepared. Compared to the traditional linear copolymers, this multi-arm phosphoester block copolymer integrates a balanced combination of unique features. As an advanced DDS, the PAMAM-PBEP-PMP-FA based supramolecular micelle provides good architectural stability, low protein adsorption, extremely high DLE, and sustained drug release for chemotherapy and abundant surface chemistry for target engineering. Benefitting from these novel functions, the supramolecular micellar drug delivery system exhibits great performances both in in vitro and in vivo evaluations. Doxorubicin (DOX)-loaded supramolecular micelles PAMAM-PBEP-PMP-FA/DOX are fast taken up by HepG2 cells and inhibit the tumor growth effectively in HepG2-tumor-bearing nude mice without obvious system toxicity. This work not only suggests a targeted sustained release DDS for effective chemotherapy but also enlightens, through a delicate design at the molecular scale, the brilliance of multifunctional PPE-based nanomaterials towards versatile bio-applications.

Fabrication of polydopamine nanoparticles knotted alginate scaffolds and their properties.

Polydopamine (PDA) can greatly affect polymer's properties, due to the chemical and physical interactions between the polymers and PDA. In this study, PDA was demonstrated to adjust the pore structures and increase the mechanical properties of alginate hydrogel-based cartilage tissue scaffolds. Dopamine modified alginate (Alg-DA) was firstly synthesized by modification of Alg with DA. Alg-DA interacted with preprepared PDA nanoparticles and further crosslinked with calcium ions (Ca2+ ) to form the hydrogel scaffold (Alg-DA/PDA). The Alg-DA/PDA scaffold combined multiple advantageous features, including continuous pore structure, high level of porosity, well mechanical properties, good biocompatibility and appropriate cycle life of degradation. Moreover, it could provide an optimized forming environment for hydroxyapatite (HAp) by mineralization process, thus accelerating cartilage repair. The improved performances were mainly ascribed to physical enhancement of the PDA nanoparticles and crosslinking points among the polymers and catechol groups in DA. These findings might offer a guideline for fabricating robust biocompatible cartilage tissue scaffold. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 3255-3266, 2018.

Fabrication of dopamine modified polylactide-poly(ethylene glycol) scaffolds with adjustable properties.

Bio-based polymers have been widely used to be as scaffolds for repairing the bone defects. However, the polymer scaffolds are generally lack of bioactivity and cell recognition site. Seeking effective ways to improve the bioactivity and interaction between materials and tissue or cells is clinically important for long-term performance of bone repair materials. In this work, polylactide-b-poly(ethylene glycol)-b-polylactide (PLA-PEG-PLA, PLEL) tri-block copolymers were firstly synthesized by ring-opening polymerization of lactide using PEG with various molecular weights. Inspired by excellent adhesion of dopamine (DA), a facile and effective method was developed to fabricate polydopamine (PDA) and polydopamine/nano-hydroxyapatite (PDA/n-HA) modified PLEL scaffolds by deposition of PDA and PDA/n-HA coating. The surface structure, degradation rates and mineralization of the modified PLEL scaffolds were investigated, and obviously improved after immobilization of PDA and PDA/n-HA coatings. Moreover, the biocompatible results showed a significant increase in cells viability and adhesion. Therefore, the surface modification with PDA and PDA/n-HA could not only adjust the properties of scaffolds, but also reinforce the interfacial adhesion between the PLEL and cells.

Preparation and properties of thermoplastic poly(caprolactone) composites containing high amount of esterified starch without plasticizer.

Based on stearyl chloride and native starch, esterified starch were prepared and the chemical structure was characterized by (1)H NMR and FTIR. It was found that stearyl chloride was an efficient agent to fabricate esterified starch with high degree of substitution (DS). During the melt blending of esterified starch (80 wt%) and poly(caprolactone) (PCL, 20 wt%), it was shown the torque of PCL/esterified starch was much lower than that of PCL/native starch without any plasticizer, and further decreased with increasing DS. Compared with PCL/native starch, the tensile properties of PCL/esterified starch composites were significantly enhanced. The tensile strength and elongation at break were increased from 2.7 MPa to 56% for PCL/native starch composites to 9.1 MPa and 626% for PCL/esterified starch ones with DS of 1.50, respectively. SEM observation revealed the esterified starch particles in matrix became smaller and more uniform. In addition, the water resistance and hydrophobic character of PCL/esterified starch composites were improved. PCL composites containing 80 wt% esterified starch with favorable mechanical properties would have great potential applications in broad areas.

[Study on synthesis and photoluminescence of the complexes of rare earth Eu(III) with 4-vinyl pyridine copolymer].

Rare earth (Eu)-polymer ternary complexes were synthesized using copolymer of 4-vinyl pyridine-methyl acrylate as ligand, and using phen and bipy as coordination ligand. The compositions of the complexes were characterized by FTIR and elemental analysis. The photophysical process of photoluminescence of the complexes were characterized by FTIR and elemental analysis. The photophysical process of photoluminescence of the complexes was discussed more fully by UV spectra and fluorescence spectra. The experiment result shows that the copolymer of 4-vinyl pyridine can coordinate into rare ions directly by nitrogen atom in the pyridine ring. When small ligand reacts with coordination, the fluorescence intensity of the complexes increases greatly because of stronger intermolecular energy transfer.

Photo-tunable protein release from biodegradable nanoparticles composed of cinnamic acid derivatives.

A novel functional biodegradable copolymer was prepared by grafting dithiothreitiol (DTT) into poly(3,4-dihydroxycinnamic acid)-co-poly(4-hydroxycinnamic acid) (PCA) by the Michael addition. The PCA-graft-DTT (PCA-DTT) nanoparticles were self-assembled by mixing a DMSO solution of PCA-DTT copolymer and distilled water. The diameter of the PCA-DTT nanoparticles was below 100nm, and increased to about 300nm upon increasing the composition ratio of DTT. The PCA-DTT nanoparticles were crosslinked via [2+2] cyclobutane formation of the cinnamate groups by UV irradiation at λ>280nm. Moreover, a variable size decrement of the nanoparticles after UV crosslinking was observed, depending on the grafting degree of DTT. A model protein, bovine serum albumin (BSA), was successfully encapsulated into the PCA-DTT nanoparticles during the self-assembling process. The protein release behavior was influenced by the grafting degree of DTT and the pH of the buffer. Moreover, the photo-crosslinking of the nanoparticles induced a significant acceleration in the release rate due to shrinkage of the nanoparticles. These biodegradable and photo-responsive nanoparticles possessing photo-tunable release properties would be useful as novel and functional carriers for drug delivery systems.

Unique size-change behavior of photo-crosslinked cinnamic acid derivative nanoparticles during hydrolytic degradation.

A unique size change of photo-crosslinkable poly[(3,4-dihydroxycinnamic acid)-co-(4-hydroxycinnamic acid)] nanoparticles was observed during hydrolytic degradation depending on the crosslinking degree. The diameter of uncrosslinked nanoparticles decreased from 850 to 300 nm during hydrolysis, whereas that of 75% crosslinked nanoparticles increased from 700 to 950 nm. The diameter changes of crosslinked nanoparticles during hydrolysis might be induced by swelling of the crosslinked networks depending on the crosslinking degree. Moreover, the diameter of the uncrosslinked nanoparticle recovered by additional UV irradiation during hydrolysis. These results suggested that the diameter of the nanoparticles could be controlled even during hydrolysis by UV irradiation.

Synthesis and properties of coumaric acid derivative homo-polymers.

Poly(4-hydroxycinnamic acid) (P4HCA), poly(3-hydroxycinnamic acid) (P3HCA), poly(3-methoxy-4-hydroxycinnamic acid) (PMHCA) and poly(3,4-dihydroxycinnamic acid) (PDHCA) were synthesized by the thermal poly-condensation of the corresponding monomers, which are lignin precursors, coumaric acid derivatives consisting of cinnamoyl groups and different position and number of OH groups. The solubility of the homo-polymers in organic solvents decreased in the order of P3HCA > PDHCA > P4HCA > PMHCA. The wide angle X-ray diffraction (WAXD) results indicated that P4HCA or PMHCA with p-OH group had higher crystallinity, in contrast to P3HCA or PDHCA with m-OH group which had lower crystallinity. Crossed-polarizing microscopy suggested that P4HCA had the nematic liquid crystal properties at 220 degrees C and PDHCA showed birefringence properties at 200 degrees C. In cell-adhesion tests, PDHCA showed the highest cell adhesion (ca. 70%), whereas P3HCA, P4HCA and PMHCA had 50, 18 and 10% cell adhesion, respectively. The coumaric acid derivative homo-polymers can be useful as cell adhesion controllable thermotropic polymers for biomedical and environmental fields.

Particulation of hyperbranched aromatic biopolyesters self-organized by solvent transformation in ionic liquids.

Hyperbranched copolymers were prepared by the heat transesterification of 4-hydroxycinnamic acid (4HCA) and 3,4-dihydroxycinnamic acid (DHCA) with a high 4HCA composition dissolved in trifluoroacetic acid (TFA). The nanoparticles were formed after two homogeneous copolymer solutions were mixed in DMF and TFA, which are both good solvents for the copolymer P(4HCA-co-DHCA). We confirmed that the driving force for particulation was solvent interactions that produce ion pairs, which elevate the polarity of the solvent too much to solubilize the copolymers.