UNDERSTANDING AND ADVANCING SHAPE MEMORY IN SEMI-CRYSTALLINE POLYMER NETWORKS

Semi-crystalline polymer networks are widely used as shape memory materials, given that there are two distinctive networks each in charge of a distinctive shape: a chemical network dictating the as-prepared primary shape, and a crystalline scaffold fixing the programmed secondary shape. The two networks are under constant competition, and delicate balance is required to achieve desirable shape memory pathways. One-way irreversible shape memory can be easily realized by fixing the secondary shape upon cooling and recovering back to the primary shape upon complete removal of crystals. However, to achieve two-way reversible shape memory is very challenging for most semi-crystalline elastomers. We have discovered and established a universal mechanism of reversible shape memory in conventional semi-crystalline elastomers. This mechanism relies on a new partial melting procedure and self-seeding crystallization. At partial melting state, the molten network strands are confined by both the chemical crosslinks and the remaining crystals. Upon cooling, the molten strands undergo self-seeding crystallization, readily restoring the secondary shape. This mechanism can be potentially applied to any types of semi-crystalline elastomers. It enables a novel two-way reversible, free-standing, multiple-times and reprogrammable shape shifting pathway of the conventional irreversible semi-crystalline elastomers. We have further investigated the effect of various chemical network topologies on reversible shape memory performance. We optimized the reversibility, the repeatability, and durability over time. It is shown that only with sufficient chemical crosslinks (crosslinking densities), would there be enough network confinements to ensure a two-way reversible shape memory behavior. We have explored new applications using this new mechanism in semi-crystalline elastomers, including a dynamic optical grating. With the primary shape being a flat surface, we programmed grating structure as the secondary shape on the surface. Therefore by applying partial melting and reversible shape memory protocol, we realized a reversible change in grating’s height, which result in a reversible change in diffraction intensity. The optical reversibility is sufficiently high (>95%), and can be repeated for many cycles (>10). So far, most semi-crystalline shape memory elastomers consist of linear network strands. However, there is an intrinsic lower modulus limit for essentially all linear networks, which is on the order of 105 Pa. To break this lower boundary, and to better mimic soft biological tissues which are usually on the order of 103 Pa, we adopt a new network architecture: bottlebrush network. The resulting modulus change of the semi-crystalline bottlebrush network is unprecedentedly high, covering from GPa at crystalline state, all the way down to kPa or ever lower at amorphous state (six orders of magnitude change). At the rigid state, the material is easy to handle and sharp to penetrate; at the soft state, the material is tunable to mimic the exact modulus of surrounding tissues, even for soft tissues such as brain. We are targeting at two practical applications, brain implant and microneedles drug delivery. In all, semi-crystalline polymer networks show great potential as a versatile shape memory material, which can incorporate both one-way irreversible and two-way reversible shape shifting at the same time. In terms of application, it brings significance in fields such as robotics, actuators, dynamic surface and optics. Also, with the help of bottlebrush network architecture, the semi-crystalline elastomers can possess huge modulus change, which provides a promising candidate for bio-medical implants.Doctor of Philosoph

Social Preference Deficits in Juvenile Zebrafish Induced by Early Chronic Exposure to Sodium Valproate

Prenatal exposure to sodium valproate (VPA), a widely used anti-epileptic drug, is related to a series of dysfunctions, such as deficits in language and communication. Clinical and animal studies have indicated that the effects of VPA are related to the concentration and to the exposure window, while the neurobehavioral effects of VPA have received limited research attention. In the current study, to analyze the neurobehavioral effects of VPA, zebrafish at 24 hours post-fertilization (hpf) were treated with early chronic exposure to 20 μM VPA for 7 hours per day for 6 days or with early acute exposure to 100 μM VPA for 7 hours. A battery of behavioral screenings was conducted at 1 month of age to investigate social preference, locomotor activity, anxiety and behavioral response to light change. A social preference deficit was only observed in animals with chronic VPA exposure. Acute VPA exposure induced a change in the locomotor activity, while chronic VPA exposure did not affect locomotor activity. Neither exposure procedure influenced anxiety or the behavioral response to light change. These results suggested that VPA has the potential to affect some behaviors in zebrafish, such as social behavior and the locomotor activity, and that the effects were closely related to the concentration and the exposure window. Additionally, social preference seemed to be independent from other simple behaviors

Programming temporal shapeshifting

Shapeshifting enables a wide range of engineering and biomedical applications, but until now transformations have required external triggers. This prerequisite limits viability in closed or inert systems and puts forward the challenge of developing materials with intrinsically encoded shape evolution. Herein we demonstrate programmable shape-memory materials that perform a sequence of encoded actuations under constant environment conditions without using an external trigger. We employ dual network hydrogels: in the first network, covalent crosslinks are introduced for elastic energy storage, and in the second one, temporary hydrogen-bonds regulate the energy release rate. Through strain-induced and time-dependent reorganization of the reversible hydrogen-bonds, this dual network allows for encoding both the rate and pathway of shape transformations on timescales from seconds to hours. This generic mechanism for programming trigger-free shapeshifting opens new ways to design autonomous actuators, drug-release systems and active implants

Screening and Stability Evaluation of Angiotensin Converting Enzyme Inhibitory Peptides from Bangia fusco-purpurea

In this study, peptide fractions (F1-F4) with different molecular masses were obtained from Bangia fusco-purpurea through enzymatic hydrolysis and ultrafiltration. F2, with molecular masses of 800–2 000 Da, exhibited the highest in vitro angiotensin-converting enzyme (ACE) inhibitory activity as determined by high performance liquid chromatography (HPLC). The amino acid sequence of F2 was identified through liquid chromatography-tandem mass spectrometry (LC-MS/MS) and de novo sequencing using PEAKS Studio software. Six ACE inhibitory peptides that stably bind to ACE were selected through molecular docking. The predicted peptides were synthesized by solid-phase synthesis and their in vitro ACE inhibitory activity was verified. Among them, L1 (LVLLFLFGE) showed the highest ACE inhibitory activity with a half maximal inhibitory concentration (IC50) value of 14.22 μg/mL. Molecular docking results indicated that the inhibition of ACE by L1 was mainly attributed to its ability to form hydrogen bond interactions with the active site of ACE. Finally, the effects of temperature, pH, metal ions, light exposure, and simulated gastrointestinal digestion on the stability of L1 were investigated. The results revealed that L1 was highly stable to heat and ionic strength. However, its activity gradually decreased at pH > 2, and was affected by ultraviolet treatment. The ACE inhibitory activity of L1 decreased after simulated gastric and intestinal digestion, but was still significant

Bottlebrush Elastomers: A New Platform for Freestanding Electroactuation

Freestanding, single-component dielectric actuators are designed based on bottlebrush elastomers that enable giant reversible strokes at relatively low electric fields and altogether avoid preactuation mechanical manipulation. This materials design platform allows for independent tuning of actuator rigidity and elasticity over broad ranges without changing chemical composition, which opens new opportunities in soft-matter robotics

Green synthesis and characterizations of silver nanoparticles with enhanced antibacterial properties by secondary metabolites of Bacillus subtilis (SDUM301120)

Silver nanoparticles (AgNPs) have been exploited for their broad-spectrum antibacterial effects and their vast applications, which are generating interest of researchers towards green synthesis of AgNPs. In this paper, we describe a novel biosynthesis of AgNPs employing secondary metabolites of Bacillus subtilis (SDUM301120). The mean particle diameter of AgNPs was calculated by the high-resolution transmission electron microscope (HRTEM). HRTEM analysis revealed the particle was spherical and distributed in the range of 2–26 nm. Crystal nature of the nanoparticles in the face-centered cubic structure was confirmed by the peaks in the X-ray diffraction pattern corresponding to (111), (200), (220), and (311) planes. The formation of the reduced AgNPs was monitored by UV–VIS spectrophotometer analysis which displayed a peak in the region of 430–460 nm. We investigated the antibacterial activity of AgNPs against Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 29213, Vibrio Parahaemolyticus ATCC 17802T, and Acinetobacter baumanni ATCC 19606T. The results show that AgNPs with enhanced antibacterial properties have significant antimicrobial effects compared with pure AgNPs, antibacterial substances (lipopeptide), and the mixture of lipopeptide and pure AgNPs. The bacteriostatic experiments compared with antibiotics showed that the obtained AgNPs had a promising future in the bacterial infections

A Cationic Octanuclear Zirconium Peroxide Ring with Unusual Thermal Stability

Studies about the reaction of ZrIV ions with peroxides and the properties of the resulting zirconium peroxide clusters are significant for understanding zirconium chemistry in the nuclear fuel cycle and the advancement of less explored Group IV metal oxo clusters. Herein, an octanuclear zirconium peroxide cluster, designated as Zr8, was synthesized and characterized by using multiple techniques. Crystallographic analysis revealed that Zr8 has a ringlike structure and unusual positive charges, while tetravalent metal oxo clusters are mostly neutral. In situ variable-temperature Raman spectra indicated that Zr8 has unexpected thermal stability, which may be related to the strong interaction between ZrIV ions and peroxide groups. Small-angle X-ray scattering data showed that Zr8 self-assembled in the reactant solution prior to crystallization. In short, Zr8 expands the limited family of zirconium peroxide clusters and enriches the properties of metal peroxides

Tissue‐Adaptive Materials with Independently Regulated Modulus and Transition Temperature

International audienceThe ability of living species to transition between rigid and flexible shapes represents one of their survival mechanisms, which has been adopted by various human technologies. Such transition is especially desired in medical devices as rigidity facilitates the implantation process, while flexibility and softness favor biocompatibility with surrounding tissue. Traditional thermoplastics cannot match soft tissue mechanics, while gels leach into the body and alter their properties over time. Here, a single-component system with an unprecedented drop of Young's modulus by up to six orders of magnitude from the GPa to kPa level at a controlled temperature within 28-43 °C is demonstrated. This approach is based on brush-like polymer networks with crystallizable side chains, e.g., poly(valerolactone), affording independent control of melting temperature and Young's modulus by concurrently altering side chain length and crosslink density. Softening down to the tissue level at the physiological temperature allows the design of tissue-adaptive implants that can be inserted as rigid devices followed by matching the surrounding tissue mechanics at body temperature. This transition also enables thermally triggered release of embedded drugs for anti-inflammatory treatment

Advancing Reversible Shape Memory by Tuning the Polymer Network Architecture

Because of counteraction of a chemical network and a crystalline scaffold, semicrystalline polymer networks exhibit a peculiar behaviorreversible shape memory (RSM), which occurs naturally without applying any external force and particular structural design. There are three RSM properties: (i) range of reversible strain, (ii) rate of strain recovery, and (iii) decay of reversibility with time, which can be improved by tuning the architecture of the polymer network. Different types of poly­(octylene adipate) networks were synthesized, allowing for control of cross-link density and network topology, including randomly cross-linked network by free-radical polymerization, thiol–ene clicked network with enhanced mesh uniformity, and loose network with deliberately incorporated dangling chains. It is shown that the RSM properties are controlled by average cross-link density and crystal size, whereas topology of a network greatly affects its extensibility. We have achieved 80% maximum reversible range, 15% minimal decrease in reversibility, and fast strain recovery rate up to 0.05 K^–1, i.e., ca. 5% per 10 s at a cooling rate of 5 K/min

Universal Coatings Based on Zwitterionic–Dopamine Copolymer Microgels

Multifunctional coatings that adhere to chemically distinct substrates are vital in many industries, including automotive, aerospace, shipbuilding, construction, petrochemical, biomedical, and pharmaceutical. We design well-defined, nearly monodisperse microgels that integrate hydrophobic dopamine methacrylamide monomers and hydrophilic zwitterionic monomers. The dopamine functionalities operate as both intraparticle cross-linkers and interfacial binders, respectively providing mechanical strength of the coatings and their strong adhesion to different substrates. In tandem, the zwitterionic moieties enable surface hydration to empower antifouling and antifogging properties. Drop-casting of microgel suspensions in ambient as well as humid environments facilitates rapid film formation and tunable roughness through regulation of cross-linking density and deposition conditions