New Biodegradable Thermogelling Copolymers Having Very Low Gelation Concentrations

New biodegradable multiblock amphiphilic and thermosensitive poly(ether ester urethane)s consisting of poly[(R)-3-hydroxybutyrate] (PHB), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) blocks were synthesized, and their aqueous solutions were found to undergo a reversible sol−gel transition upon temperature change at very low copolymer concentrations. The multiblock poly(ether ester urethane)s were synthesized from diols of PHB, PEG, and PPG using 1,6-hexamethylene diisocyanate as a coupling reagent. The chemical structures and molecular characteristics of the copolymers were studied by GPC, 1H NMR, 13C NMR, and FTIR. The thermal stability of the poly(PEG/PPG/PHB urethane)s was studied by thermogravimetry analysis (TGA), and the PHB contents were calculated based on the thermal degradation profile. The results were in good agreement with those obtained from the 1H NMR measurements. The poly(PEG/PPG/ PHB urethane)s presented better thermal stability than the PHB precursors. The water soluble poly(ether ester urethane)s had very low critical micellization concentration (CMC). Aqueous solutions of the new poly(ether ester urethane)s underwent a sol−gel−sol transition as the temperature increased from 4 to 80 °C, and showed a very low critical gelation concentration (CGC) ranging from 2 to 5 wt %. As a result of its multiblock architecture, a novel associated micelle packing model can be proposed for the sol−gel transition for the copolymer gels of this system. The new material is thought to be a promising candidate for injectable drug systems that can be formulated at low temperatures and forms a gel depot in situ upon subcutaneous injection

Control of PLA Stereoisomers-Based Polyurethane Elastomers as Highly Efficient Shape Memory Materials

Poly­(lactic acid) (PLA) has received increasing attention in the development of shape memory polymers (SMPs) due to its excellent physical properties and good biocompatibility. However, the intrinsically increased crystallinity of PLA at higher deformation ratios still remains a significant challenge, which remarkably restricts the chain mobility and reduces shape recovery efficiency. Being different from other types of biodegradable polymers, the diverse isomeric forms of PLA have provided great opportunities for modulation of PLA toward a favorable property by incorporating different PLA stereoisomers in one macromolecular architecture. In this paper, we report a completely amorphous PLA poly­(ester urethane) elastomer that exhibits excellent shape fixity (>99%) and shape recovery (>99%) in a time frame of seconds. By means of adjusting the stereoisomeric ratios and control over architecture, the resultant poly­(PLLA/PDLLA urethane)­s (PLDU) elastomers show a single glass transition temperature (<i>T</i>_g), as the only thermal event, in the range of 38–46 °C in a predictable manner. The elastic moduli of PLDU elastomers display a 100-fold loss during the sharp transition from a glassy to a rubbery state with temperature alternation across their corresponding <i>T</i>_g, indicating a successful manipulation of the thermo-mechanical properties by temperature as required in thermally induced SMPs. In addition, all samples display a typical elastomeric behavior with elongation at break (ε_b) greater than 400%. The effect of the stereoisomer content on the tensile modulus and elastic mechanical behavior were also systematically investigated. Together with the prominent degradation property, the new PLDU elastomers developed in this study show great potential for biomedical applications as shape memory implants

Synthesis of Novel Biodegradable Thermoresponsive Triblock Copolymers Based on Poly[(<i>R</i>)-3-hydroxybutyrate] and Poly(<i>N</i>-isopropylacrylamide) and Their Formation of Thermoresponsive Micelles

Novel thermoresponsive amphiphilic triblock copolymers with two hydrophilic poly(N-isopropylacrylamide) blocks flanking a central hydrophobic poly[(R)-3-hydroxybutyrate] block were synthesized by atom transfer radical polymerization. The copolymers were characterized by gel permeation chromatography (GPC) and 1H and 13C NMR spectroscopy. The thermal stability of the copolymer was investigated by thermogravimetric analysis (TGA), and crystallization behavior was studied by differential scanning calorimetry (DSC). The water-soluble copolymers formed core−corona-type micelle aggregates in water. The critical micelle concentrations of the triblock copolymers were in the range of 1.5 to 41.1 mg/L, and the partition coefficients were in the range of (1.64−20.42) × 105. Transmission electron microscopy showed that the self-assembled micelle aggregates had well-defined spherical shape. The temperature sensitivity of the micelles was demonstrated by the phase transition of a 0.5 mg/mL aqueous polymer solution at the lower critical solution temperature (LCST). Preliminary cytotoxicity studies showed that these micelles were nontoxic and could be potential candidates for the encapsulation and release of therapeutic drugs in the biological system

Micellized α‑Cyclodextrin-Based Supramolecular Hydrogel Exhibiting pH-Responsive Sustained Release and Corresponding Oscillatory Shear Behavior Analysis

The fabrication of supramolecular hydrogels from micellized PLLA/DMAEMA/PEGMA polymers with α-CD has been explored to design injectable gel formulations for sustained drug release. The tricomponent hydrogels (5% w/v)/α-CD (10% w/v) were able to sustain protein (BSA and lysozyme) release for 60–120 h at different pH conditions (pH 3, 7 and 10). In-depth rheological analysis highlighted the role of pH in tuning hydrogel behavior upon shear at microscopic level affecting protein release profiles. Protein release involved complex interactions within the network (isoelectric point and diffusion coefficient of the protein, p<i>K</i>_a of DMAEMA, and pore size of the hydrogel). Lissajous–Bowditch curves explained the microstructural response to increasing strain which weakened the supramolecular association and collapsed the formation of the porous hydrogel. Power Law was adopted to represent both transport mechanism and drug release phenomena. The release mechanism resulted from a combination of erosion- and diffusion-controlled release (non-Fickian and super case II)

Purification and Characterization of a Vaterite-Inducing Peptide, Pelovaterin, from the Eggshells of <i>Pelodiscus </i><i>s</i><i>inensis</i> (Chinese Soft-Shelled Turtle)

Proteins play a crucial role in the biomineralization of hard tissues such as eggshells. We report here the purification, characterization, and in vitro mineralization studies of a peptide, pelovaterin, extracted from eggshells of a soft-shelled turtle. It is a glycine-rich peptide with 42 amino acid residues and three disulfide bonds. When tested in vitro, the peptide induced the formation of a metastable vaterite phase. The floret-shaped morphology formed at a lower concentration (∼1 μM) was transformed into spherical particles at higher concentrations (>500 μM). The solution properties of the peptide are investigated by circular dichroism (CD), fluorescence emission spectroscopy, and dynamic light scattering (DLS) experiments. The conformation of pelovaterin changed from an unordered state at a low concentration to a β-sheet structure at high concentrations. Fluorescence emission studies indicated that the quantum yield is significantly decreased at higher concentrations, accompanied by a blue shift in the emission maximum. At higher concentrations a red-edge excitation shift was observed, indicating the restricted mobility of the peptide. On the basis of these observations, we discuss the presence of a peptide concentration-dependent monomer−multimer equilibrium in solution and its role in controlling the nucleation, growth, and morphology of CaCO3 crystals. This is the first peptide known to induce the nucleation and stabilization of the vaterite phase in solution

Additive Manufacturing of Thermoelectrics: Emerging Trends and Outlook

Additive manufacturing (AM) has progressed rapidly in recent years, thanks to its versatility in printing complex and intricate shapes. Very recently, it has also been making inroads into functional and energy materials. On the other hand, thermoelectrics is a relatively mature field, with well-established understanding and design, especially on the materials level. However, complexities in device fabrication and scalability issues have greatly hindered thermoelectric (TE) applications. In this Focus Review, we discuss the advent of AM as a timely and important tool not only to overcome the scalability issues but also to achieve shape intricacies and conformability for flexible and wearable applications. In particular, direct ink writing (DIW), a subset under materials extrusion methods, holds great promise as a versatile fabrication technique for integrated TE devices. More importantly, we discuss the great promise of “engineered nanostructuring” using DIW as a new paradigm to improve TE performance beyond intrinsic properties

Autonomous Chitosan-Based Self-Healing Hydrogel Formed through Noncovalent Interactions

A facile strategy was developed for the formation of an autonomous chitosan-based self-healing hydrogel. This hydrogel was fabricated using in situ free radical polymerization of acrylic acid (AA) and acrylamide (AM) in the presence of chitosan in dilute acetic acid aqueous solution under mild conditions. The in situ formed hydrogel is mainly composed of chitosan graft copolymers (CS-g-P­(AM-r-AA)) and a small amount of nongrafted copolymers (P­(AM-r-AA)), which interact with each other through a combination of multiple noncovalent interactions, including the interchain electrostatic complexation between −[AA]– segments and positively charged amino groups of chitosan, the H-bonding between −[AM]– segments, and the H-bonding between −[AM]– segments and the chitosan backbone. Owing to the cooperation of these noncovalent interactions and the reversible nature of the noncovalent network structure, the obtained hydrogel exhibits rapid network recovery, high stretchability, and efficient autonomous self-healing properties. The hydrogel can also dissolve completely in dilute acidic aqueous solution under mild conditions, visibly reflecting the unique network feature of this self-healing hydrogel system

‘Living’ Controlled <i>in Situ</i> Gelling Systems: Thiol−Disulfide Exchange Method toward Tailor-Made Biodegradable Hydrogels

A ‘living’ controlled hydrogel formation method was first reported to create loose and compact in situ biodegradable hydrogels. The method executed under mild reaction conditions can conveniently tailor the hydrogel properties, and it has the potential to develop into a powerful tool for the design, synthesis, and self-assembly of novel tailor-made biomaterials and drug delivery systems

Pseudo-Block Copolymer Based on Star-Shaped Poly(<i>N</i>-isopropylacrylamide) with a β-Cyclodextrin Core and Guest-Bearing PEG: Controlling Thermoresponsivity through Supramolecular Self-Assembly

Pseudo-Block Copolymer Based on Star-Shaped Poly(N-isopropylacrylamide) with a β-Cyclodextrin Core and Guest-Bearing PEG: Controlling Thermoresponsivity through Supramolecular Self-Assembl

Table_1_Self-Healable, Fast Responsive Poly(ω-Pentadecalactone) Thermogelling System for Effective Liver Cancer Therapy.DOCX

A polyurethane based thermogelling system comprising poly(ω-pentadecalactone) (PPDL), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG), termed as PDEP, was synthesized. The incorporation of PPDL lowers critical micelle concentration (CMC) as well as critical gelation concentration (CGC) of the novel copolymers compared to commercial Pluronic® F127. The thermogels showed excellent thermal stability at high temperature up to 80°C, fast response to temperature change in a time frame of less than second, as well as remarkable self-healing properties after being broken at high strain. In vitro drug release studies using docetaxel (DTX) and cell uptake studies using doxorubicin (DOX) show high potential of the hydrogel as drug reservoir for sustainable release profile of payloads, while the in vivo anti-tumor evaluation using mice model of hepatocellular carcinoma further demonstrated the significant inhibition on the growth of tumor. Together with its excellent biocompatibility in different organs, the novel PDPE thermogelling copolymers reported in this work could potentially be utilized as in situ-forming hydrogels for liver cancer therapy.</p