Two-Way Reversible Shape Memory Polymers Containing Polydopamine Nanospheres: Light Actuation, Robotic Locomotion, and Artificial Muscles

Two-way reversible shape memory polymers (2W-SMPs), especially those that are light-responsive, are highly desirable for many applications, especially in the biomedical field, because of the convenience of indirect heating. We have designed and prepared a series of light-actuated 2W-SMP composites by incorporating very small amounts of polydopamine (PDA) nanospheres into semicrystalline polymer networks based on biodegradable poly­(ε-caprolactone) copolymers. PDA nanospheres can be well dispersed in chloroform and well mixed with the polymer network. PDA nanospheres manifest good photothermal effect because of their strong absorption of light. The variation in temperature of the polymer composites can be correlated with irradiation time, light intensity, and the content of PDA nanospheres. Equations are developed to fit the temperature changes of the materials as a function of irradiation power and of the PDA particles content for a better understanding of the kinetics of the light-to-heat conversion. These polymer composites show excellent two-way reversible shape memory effects (2W-SMEs) under stress-free condition when the light is switched on and off showing a reversible angle change of 45°. The speed of angle change is larger for polymer composites irradiated with a stronger light or with a higher content of PDA nanospheres. This is the first report on 2W-SMPs using incorporated PDA nanospheres as photothermal fillers. A moving robot is designed based on photoresponsive 2W-SMP composites, which can walk on a track with triangular saw-teeth. This composite is capable of lifting and lowering a weight, acting as artificial muscles, and its actuated stress is much higher than the maximum stress yielded by most mammalian skeletal muscles. The use of biodegradable polyesters and thermal fillers made of a natural compound dopamine makes such composites potentially useful as biomaterials

Two-Way Reversible Shape Memory Polymers Containing Polydopamine Nanospheres: Light Actuation, Robotic Locomotion, and Artificial Muscles

Two-way reversible shape memory polymers (2W-SMPs), especially those that are light-responsive, are highly desirable for many applications, especially in the biomedical field, because of the convenience of indirect heating. We have designed and prepared a series of light-actuated 2W-SMP composites by incorporating very small amounts of polydopamine (PDA) nanospheres into semicrystalline polymer networks based on biodegradable poly­(ε-caprolactone) copolymers. PDA nanospheres can be well dispersed in chloroform and well mixed with the polymer network. PDA nanospheres manifest good photothermal effect because of their strong absorption of light. The variation in temperature of the polymer composites can be correlated with irradiation time, light intensity, and the content of PDA nanospheres. Equations are developed to fit the temperature changes of the materials as a function of irradiation power and of the PDA particles content for a better understanding of the kinetics of the light-to-heat conversion. These polymer composites show excellent two-way reversible shape memory effects (2W-SMEs) under stress-free condition when the light is switched on and off showing a reversible angle change of 45°. The speed of angle change is larger for polymer composites irradiated with a stronger light or with a higher content of PDA nanospheres. This is the first report on 2W-SMPs using incorporated PDA nanospheres as photothermal fillers. A moving robot is designed based on photoresponsive 2W-SMP composites, which can walk on a track with triangular saw-teeth. This composite is capable of lifting and lowering a weight, acting as artificial muscles, and its actuated stress is much higher than the maximum stress yielded by most mammalian skeletal muscles. The use of biodegradable polyesters and thermal fillers made of a natural compound dopamine makes such composites potentially useful as biomaterials

Two-Way Reversible Shape Memory Polymers Containing Polydopamine Nanospheres: Light Actuation, Robotic Locomotion, and Artificial Muscles

Two-way reversible shape memory polymers (2W-SMPs), especially those that are light-responsive, are highly desirable for many applications, especially in the biomedical field, because of the convenience of indirect heating. We have designed and prepared a series of light-actuated 2W-SMP composites by incorporating very small amounts of polydopamine (PDA) nanospheres into semicrystalline polymer networks based on biodegradable poly­(ε-caprolactone) copolymers. PDA nanospheres can be well dispersed in chloroform and well mixed with the polymer network. PDA nanospheres manifest good photothermal effect because of their strong absorption of light. The variation in temperature of the polymer composites can be correlated with irradiation time, light intensity, and the content of PDA nanospheres. Equations are developed to fit the temperature changes of the materials as a function of irradiation power and of the PDA particles content for a better understanding of the kinetics of the light-to-heat conversion. These polymer composites show excellent two-way reversible shape memory effects (2W-SMEs) under stress-free condition when the light is switched on and off showing a reversible angle change of 45°. The speed of angle change is larger for polymer composites irradiated with a stronger light or with a higher content of PDA nanospheres. This is the first report on 2W-SMPs using incorporated PDA nanospheres as photothermal fillers. A moving robot is designed based on photoresponsive 2W-SMP composites, which can walk on a track with triangular saw-teeth. This composite is capable of lifting and lowering a weight, acting as artificial muscles, and its actuated stress is much higher than the maximum stress yielded by most mammalian skeletal muscles. The use of biodegradable polyesters and thermal fillers made of a natural compound dopamine makes such composites potentially useful as biomaterials

Two-Way Reversible Shape Memory Polymers Containing Polydopamine Nanospheres: Light Actuation, Robotic Locomotion, and Artificial Muscles

Two-way reversible shape memory polymers (2W-SMPs), especially those that are light-responsive, are highly desirable for many applications, especially in the biomedical field, because of the convenience of indirect heating. We have designed and prepared a series of light-actuated 2W-SMP composites by incorporating very small amounts of polydopamine (PDA) nanospheres into semicrystalline polymer networks based on biodegradable poly­(ε-caprolactone) copolymers. PDA nanospheres can be well dispersed in chloroform and well mixed with the polymer network. PDA nanospheres manifest good photothermal effect because of their strong absorption of light. The variation in temperature of the polymer composites can be correlated with irradiation time, light intensity, and the content of PDA nanospheres. Equations are developed to fit the temperature changes of the materials as a function of irradiation power and of the PDA particles content for a better understanding of the kinetics of the light-to-heat conversion. These polymer composites show excellent two-way reversible shape memory effects (2W-SMEs) under stress-free condition when the light is switched on and off showing a reversible angle change of 45°. The speed of angle change is larger for polymer composites irradiated with a stronger light or with a higher content of PDA nanospheres. This is the first report on 2W-SMPs using incorporated PDA nanospheres as photothermal fillers. A moving robot is designed based on photoresponsive 2W-SMP composites, which can walk on a track with triangular saw-teeth. This composite is capable of lifting and lowering a weight, acting as artificial muscles, and its actuated stress is much higher than the maximum stress yielded by most mammalian skeletal muscles. The use of biodegradable polyesters and thermal fillers made of a natural compound dopamine makes such composites potentially useful as biomaterials

Core Cross-linked Micelles Made of Glycopolymers Bearing Dopamine and Cholic Acid Pendants

A series of block glycopolymers bearing galactose, dopamine, and cholic acid (CA) pendants have been synthesized by RAFT polymerization. These copolymers can self-assemble into micelles in water. The dopamine moieties, located near the interface of the core and shell of the micelles, can self-polymerize in a weakly basic solution, stabilizing the micelles in both water and organic solvent (DMSO). The cross-linked micelles are smaller in size than the uncross-linked precursors. Introducing more CA groups into the copolymers promotes the self-assembly to form larger aggregates, controls the cross-linking of the stabilized micelles, and facilitates the encapsulation of hydrophobic compounds such as Nile Red (NR). The amount of CA comonomers added also helps to control the cross-linking density, which affects the loading and release of NR. The core cross-linked micelles displayed a slow but sustained NR release and interact effectively with lectin (RCA₁₂₀), demonstrating their potential use as a biocompatible multifunctional platform for targeted release of drugs

Thermoresponsiveness of Copolymers Bearing Cholic Acid Pendants Induced by Complexation with β‑Cyclodextrin

Copolymers of <i>N</i>-alkylacrylamides and methacrylate bearing cholic acid pendant groups were synthesized via radical polymerization. The cholic acid pendant groups of such copolymers can form complexes with β-cyclodextrin, and the effect of complexation on their thermoresponsive properties was studied. The phase transition temperatures (transition from hydrophilic to hydrophobic state) of the copolymers gradually increase with the addition of β-cyclodextrin, due to the complexation of the cholic acid guest with the β-cyclodextrin host. The increase of the phase transition temperature may be reversed by the addition of a competing guest molecule, potassium 1-adamantylcarboxylate. The host–guest complexation provides a straightforward way to vary the thermoresponsive properties of such copolymers

Thermo- and pH-Responsive Copolymers Bearing Cholic Acid and Oligo(ethylene glycol) Pendants: Self-Assembly and pH-Controlled Release

A family of block and random copolymers of norbornene derivatives bearing cholic acid and oligo­(ethylene glycol) pendants were prepared in the presence of Grubbs’ catalyst. The phase transition temperature of the copolymers in aqueous solutions may be tuned by the variation of comonomer ratios and pH values. Both types of copolymers formed micellar nanostructures with a hydrophilic poly­(ethylene glycol) shell and a hydrophobic core containing cholic acid residues. The micellar size increased gradually with increasing pH due to the deprotonation of the carboxylic acid groups. These micelles were capable of encapsulating hydrophobic compounds such as Nile Red (NR). A higher hydrophobicity/hydrophilicity ratio in both copolymers resulted in a higher loading capacity for NR. With similar molecular weights and monomer compositions, the block copolymers showed a higher loading capacity for NR than the random copolymers. The NR-loaded micelles exhibited a pH-triggered release behavior. At pH 7.4 within 96 h, the micelles formed by the block and random of copolymers released 56 and 97% NR, respectively. Therefore, these micelles may have promise for use as therapeutic nanocarriers in drug delivery systems

Self-Healing Supramolecular Hydrogel Made of Polymers Bearing Cholic Acid and β‑Cyclodextrin Pendants

Natural compounds cholic acid and β-cyclodextrin are attached separately as pendant groups in a copolymer with <i>N</i>,<i>N</i>′-dimethylacrylamides. The formation of supramolecular hydrogels is induced by inclusion complex formation between cholic acid and β-cyclodextrin moieties as evidenced by rheological analysis and ¹H NMR spectroscopy. Storage modulus of the hydrogel shows a maximum value when the molar ratio of cholic acid to β-cyclodextrin units is adjusted to 1:1. The concentration of the hydrogel can be as low as 5.5 wt %. Both shear-thickening and shear-thinning have been observed when the shear rate gradually increases from 0.01 to 100 s^–1. The inclusion complexation renders the gel–sol process reversible under heating and cooling cycles. The self-healing of such hydrogels is observed and confirmed by step-strain rheological measurements. The dynamically reversible host–guest complexation provides reasonably good mechanical properties of the cross-linked polymer network. The natural origin of the constituents may make the hydrogels suitable candidates for biomedical applications pending further tests

Two-Step Enzymatic Synthesis of Biocompatible Polymers Made from Cholic Acid

Polyesters are known biodegradable materials that are frequently used for biomedical applications that require biocompatibility. Their synthesis usually requires transition metal catalysts, which may become a source of contamination. In addition, using such compounds translates to extensive purification procedures, which do not agree with green chemistry principles. In addition to being renewable, enzymes such as lipases are milder for biological systems, and were studied for both ring-closure and ring-opening reactions. Here, Candida antarctica lipase B was used in ring-closure, reducing a two-step synthesis to a single step with 58% yield. The bile acid-containing macrocycles were subsequently polymerized with the same enzyme; relatively high molar masses (40 000 g/mol) were obtained. The conditions for the enzymatic ring-closure and ring-opening reactions were established through the reaction of thapsic acid with 1,10-decanediol. The di- and tetralactones afforded semicrystalline polymers with relatively high molar masses. Therefore, lipases were successfully used for both ring-closing reactions and ring-opening polymerizations of large rigid moieties as well as more flexible structures. The use of enzymes for the multistep syntheses shows their utility as a simple and green method for monomer and polymer synthesis with better biocompatibility and tunable properties

CO₂‑Switchable Self-Healing Host–Guest Hydrogels

The use of natural compounds to construct reversible networks is an attractive strategy in biomaterials design. Our design is based on a host–guest pair of natural compounds β-cyclodextrin and cholic acid through the use of a cholic acid dimer tethered with a poly­(ethylene glycol) spacer, which subsequently served as a guest cross-linker to afford a hydrogel with copolymers bearing β-cyclodextrin pendants. The hydrogel after incision self-heals rapidly under ambient atmosphere as observed and confirmed by rheological measurements. To endow the hydrogels with reversibility and responsiveness, the addition of a CO₂-switchable guest of benzimidazole followed by alternating treatments with CO₂ and N₂ leads to a reversible sol–gel transition due to the dynamic complexation between the cholic acid and β-cyclodextrin units. The CO₂ responsiveness and the natural origin of the constituents make these self-healing hydrogels attractive as smart biomaterials