RESUMEN
Water-in-oil-in-water (W/O/W) Pickering double emulsions are promising materials for the construction of carriers for water-soluble and oil-soluble molecules or drug delivery systems if the contradictive trade-off between their extreme stability and controlled release properties can be resolved. In this study, biodegradable and biocompatible poly(ethylene glycol)-b-poly(ε-caprolactone-co-δ-valerolactone) (PEG-b-PCVL) diblock copolymers with predesigned hydrophilic to hydrophobic block length ratios and nearly identical ε-caprolactone/δ-valerolactone molar ratio (8/2), were synthesized by ring-opening copolymerization. Then, they self-assembled to create semicrystalline micelles. The melting points of PEG-b-PCVL copolymers and their lyophilized micelles were within a physiological range of temperatures, as determined by differential scanning calorimetry. Water contact angle measurements provided evidence that the surface wettability of PEG-b-PCVL micelles could be tuned by the PCVL block mass fractions or temperature stimulus. Such PEG-b-PCVL micelles were employed as a single particulate stabilizer to develop Pickering double emulsions through a one-step emulsification technique. W/O/W Pickering double emulsions could be generated using relatively hydrophobic PEG-b-PCVL micelles with high mass fractions (exceeding about 89%) of PCVL blocks, and they displayed excellent long-term physical stabilities at room temperature. However, the Pickering double emulsions underwent a rapid microstructural transition into simple oil-in-water Pickering emulsions instead of complete demulsification at elevated temperature (37 °C), which was attributed to the hydrophilicity of micelles enhanced when the core-forming PCVL melted realized by temperature stimulus. Consequently, such W/O/W Pickering double emulsions stabilized solely with semicrystalline PEG-b-PCVL micelles exhibit thermal responsiveness, enabling them to release vitamin B12 encapsulated within the internal aqueous phase rapidly.
Asunto(s)
Micelas , Agua , Emulsiones , Polietilenglicoles/química , Glicol de Etileno , Preparaciones de Acción Retardada , Poliésteres/química , Polímeros/química , Portadores de Fármacos/químicaRESUMEN
Constructing dual or multiple noncovalent crosslinks is highly effective to improve the mechanical and stimuli-responsive properties of supramolecular physical hydrogels, due to the synergistic effects of different noncovalent bonds. Herein, a series of tough physical hydrogels are prepared by solution casting and subsequently swelling the films of poly(ureidopyrimidone methacrylate-co-stearyl acrylate-co-acrylic acid). The hydrophobic interactions between crystallizable alkyl chains and the quadruple hydrogen bonds between ureidopyrimidone (UPy) motifs serve as the dual crosslinks of hydrogels. Synergistic effects between the hydrophobic interactions and hydrogen bonds render the hydrogels excellent mechanical properties, with tensile breaking stress up to 4.6 MPa and breaking strain up to 680%. The UPy motifs promote the crystallization of alkyl chains and the hydrophobic alkyl chains also stabilize UPy-UPy hydrogen bonding. The resultant hydrogels are responsive to multiple external stimuli, such as temperature, pH, and ion; therefore, they show the thermal-induced dual and metal ion-induced triple shape memory behaviors.
Asunto(s)
Reactivos de Enlaces Cruzados/química , Hidrogeles/química , Polímeros/química , Acrilatos/química , Enlace de Hidrógeno , Interacciones Hidrofóbicas e Hidrofílicas , Pirimidinonas/químicaRESUMEN
CBABC-type poly(lactic acid) (PLA)/poly(ethylene glycol) (PEG) pentablock copolymers composed of a central PEG block (A) and enantiomeric poly(l-lactic acid) (PLLA, B), poly(d-lactic acid) (PDLA, C) blocks were synthesized. Such pentablock copolymers form physical hydrogels at high concentrations in an aqueous solution, which stem from the aggregation and physical bridging of copolymer micelles. These gels are thermoresponsive and turn into sols upon heating. Physical gelation, gel-to-sol transition, crystalline state, microstructure, rheological behavior, biodegradation, and drug release behavior of PLA/PEG pentablock copolymers and their gels were investigated; they were also compared with PLA-PEG-PLA triblock copolymers containing the isotactic PLLA or atactic poly(d,l-lactide) (PDLLA) endblocks and PLLA-PEG-PLLA/PDLA-PEG-PDLA enantiomeric mixtures. PLA hydrophobic domains in pentablock copolymer gels changed from a homocrystalline to stereocomplexed structure as the PLLA/PDLA block length ratio approached 1/1. The gel of symmetric pentablock copolymer exhibited a wider gelation region, higher gel-to-sol transition temperature, higher hydrophobic domain crystallinity, larger intermicellar distance, higher storage modulus, and slower degradation and drug release rate compared to those of the asymmetric PLA/PEG pentablock copolymers or triblock copolymers. SAXS results indicated that the PLLA/PDLA blocks stereocomplexation in pentablock copolymers facilitated the intermicellar aggregation and bridging. Cylindrical ordered structures were observed in all the gels formed from the PLA/PEG pentablock and triblock copolymers. The stereocomplexation degree and intermicellar distance of the pentablock copolymer gels increased with heating.
Asunto(s)
Hidrogeles/química , Interacciones Hidrofóbicas e Hidrofílicas , Lactatos/química , Polietilenglicoles/química , Temperatura , Liberación de Fármacos , Reología , Dispersión del Ángulo Pequeño , Estereoisomerismo , Difracción de Rayos XRESUMEN
Poly(ethylene glycol)-b-poly(L-lactic acid)-b-poly(D-lactic acid) (PEG-b-PLLA-b-PDLA) stereoblock copolymers were synthesized by sequential ring-opening polymerization. Their micelle formation, precise micelle structure, biodegradation, and drug release behavior were systematically investigated and compared with the PEG-b-poly(lactic acid) (PEG-b-PLA) diblock copolymers with various PLA stereostructures and PEG-b-PLLA/PEG-b-PDLA enantiomeric mixture. Stereoblock copolymers having comparable PLLA and PDLA block lengths and enantiomerically-mixed copolymers assemble into the stereocomplexed core-shell micelles, while the isotactic and atactic PEG-b-PLA copolymers formed the homocrystalline and amorphous micelles, respectively. The PLA segments in stereoblock copolymer micelles show smaller crystallinity than those in the isotactic and enantiomerically-mixed ones, attributed to the short block length and presence of covalent junction between PLLA and PDLA blocks. As indicated by the synchrotron radiation small-angle X-ray scattering results, the stereoblock copolymer micelles have larger size, micellar aggregation number, core radius, smaller core density, and looser packing of core-forming segments than the isotactic and enantiomerically-mixed copolymer micelles. These unique structural characteristics cause the stereoblock copolymer micelles to possess higher drug loading content, slower degradation, and drug release rates.
Asunto(s)
Sustancias Macromoleculares/química , Micelas , Poliésteres/química , Polietilenglicoles/química , Rastreo Diferencial de Calorimetría , Estructura Molecular , Espectroscopía de Protones por Resonancia Magnética , Dispersión de RadiaciónRESUMEN
Poly(ethylene glycol)-b-poly(ε-caprolactone) diblock copolymers (PEG-b-PCL) with predesigned hydrophilic/hydrophobic block length ratios have been synthesized and self-assembled to form micelles, then used to emulsify medium-chain triglycerides with an aqueous phase. The morphologies and sizes of PEG-b-PCL copolymer micelles have been characterized by transmission electron microscopy and dynamic light scattering. Interfacial tension testing between micellar dispersions and oil, combined with water contact angle measurements, have been performed to assess the ability of these micelles to adjust interfacial tension and micellar hydrophobicity, respectively. Relationship between the wettability of PEG-b-PCL copolymer micelles and their emulsification properties has been proved through phase diagram, optical microscopic observation, droplet sizes evolution and phase separation behavior of Pickering emulsion samples. Results show that both oil-in-water and water-in-oil Pickering emulsions, as well as water-in-oil-in-water (W/O/W) double-Pickering emulsions, may be controllably prepared through one-step homogenization. Double microstructure of W/O/W Pickering emulsion has proved to be extremely stable during long-term storage.
Asunto(s)
Micelas , Polímeros , Emulsiones , Glicoles de Etileno , Poliésteres , PolietilenglicolesRESUMEN
Constructing the spatio-selective crystalline structures has been an effective strategy to diversify the functions and applications of polymers. However, it is still challenging to program the crystalline heterogeneity into commercialized polymers and realize associate functions by a simple yet generalizable method. Herein, we propose a facile approach to fabricate multifunctional materials by programming the spatial distribution of crystal size in semicrystalline polymers. Various crystal size patterns in both plane and depth directions are introduced by the photothermal effect of printed ink and subsequent crystallization at different temperatures, which can be reprogrammed by repeated melting and crystallization. These obtained materials with well-defined crystal size heterogeneities exhibit diverse and regulable optics, mechanical and swelling properties, as manifested in applications including rewritable polymer paper, programmed mechanics, and advanced morphing devices. The light-induced crystal size heterogeneity of polymers has provided insights into developing advanced multifunctional materials.
Asunto(s)
Polímeros , Escritura , Cristalización , Polímeros/químicaRESUMEN
Stereocomplex (SC) crystallization between polymer enantiomers has opened a promising avenue for preparing high-performance materials. However, high-crystallinity SCs are difficult to achieve for high-molecular-weight (HMW) enantiomeric blends of chiral polymers [e.g., poly(lactic acid)]. Despite extensive studies, why HMW enantiomeric blends have difficulty in SC crystallization has not been clarified. Herein, we chose the HMW poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) 1/1 blend as the model system and demonstrated the crucial role of chain entanglement in regulating SC crystallization. PLLA/PDLA blends with various entanglement degrees were prepared by freeze-drying. We observed that disentangling promoted not only the crystallization rate but also the crystallinity of SCs in both the nonisothermal and isothermal processes. The less-entangled samples crystallized exclusively as the high-crystallinity SCs at different temperatures, in contrast to the predominant homocrystallization that occurred in the common entangled samples. This study provides deep insight into the SC crystallization mechanism of polymers and paves the way for future research attempting to prepare SC materials.
Asunto(s)
Poliésteres , Polímeros , Cristalización , Poliésteres/química , Polímeros/química , EstereoisomerismoRESUMEN
In this work, three different polyether-modified siloxanes (PMS1, PMS2, and PMS3) were applied to stabilize water-in-oil emulsions, and sodium caseinate (SC) was used to establish water-in-oil-in-water (W/O/W) emulsions. Here, PMS polymers were modified by Isolan GPS and SC by Tween 80. The impact of modifications on the physical stability and controlled release of W/O/W emulsions were investigated. It was found that the storage stability and control release of double emulsions were dependent on the types of PMS used, percent of Isolan GPS, and Tween 80. When PMS1 and PMS2 were combined with low percent of Isolan GPS and Tween 80, the dispersed droplet sizes were reduced, lower percent in the gravitational sedimentation were achieved than using PMS3 emulsions. The controlled releases of Mg2+ from W/O/W emulsions by using PMS3 were slower than using other PMS. PMS3 had a strong influence in controlling the release of Mg2+ from the double emulsions.
Asunto(s)
Emulsiones/química , Siloxanos/química , Caseínas/química , Conductividad Eléctrica , Magnesio/metabolismo , Aceites/química , Tamaño de la Partícula , Polisorbatos/química , Tensión Superficial , Agua/químicaRESUMEN
The widespread application of thermo-responsive hydrogels requires materials with robust mechanical properties and tunable responsiveness. Herein, we report robust thermo-responsive physical hydrogels with a tunable network structure and responsiveness by controlling the manner of crystallization of hydrophobic blocks. Biocompatible, stereocomplexable poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) were introduced into thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) to obtain the enantiomeric grafted copolymers PNIPAM-g-PLLA and PNIPAM-g-PDLA and their corresponding hydrogels. The hydrophobic PLLA/PDLA domains served as physical crosslinking junctions in the hydrogels. The crystalline structure of the hydrogels can be facilely tuned by varying the ratio of PLLA/PDLA enantiomeric blocks. Stereocomplex (SC) crystallization between PLLA and PDLA facilitates the formation of H-bonded hydrophobic domains with denser chain packing, which endows the racemic hydrogels with a stronger network structure, higher mechanical strength, and better solvent resistance compared to enantiopure examples. The hydrogels exhibit good thermo-sensitivity in water; the stronger racemic hydrogel network restricts volume shrinkage and water desorption at high temperatures, enabling the facile control of thermo-responsiveness. The crystallization-tuned thermo-responsiveness of racemic and enantiopure hydrogels also allows for the design of assembled bilayer hydrogels capable of thermally triggered reversible shape morphing.
Asunto(s)
Hidrogeles/química , Temperatura , Resinas Acrílicas/química , Interacciones Hidrofóbicas e Hidrofílicas , Poliésteres/química , EstereoisomerismoRESUMEN
Interaction between networks has been proven to be of importance for mechanical property enhancement of double-network (DN) hydrogels. In this work, inter-network ionically cross-linked hybrid DN hydrogels have been prepared using poly(sodium 2-acrylamide-2-methylpropanesulfonate) (PNaAMPS) as the first network, and a co-polymer of a cationic monomer and acrylamide (AM) as the second network. Ionic complexes were formed between the two oppositely charged networks after dialyzing the hydrogels in water. Near the ion-balance point, hybrid DN hydrogels with enhanced strengths were achieved compared to the unmodified PNaAMPS/polyacrylamide (PAM) DN hydrogel. Synchrotron radiation small-angle X-ray scattering (SAXS) analyses were performed on the DN hydrogels. It was found that large and compact cross-linked domains were formed in the hybrid DN hydrogels, especially near the ion-balance point, as demonstrated by the SAXS results. These large and compact cross-linked domains, which indicate enhanced interactions between networks containing ionic bonds besides physical entanglements, dissipate additional concentrated stress, resulting in high strength of the hybrid DN hydrogels.
Asunto(s)
Materiales Biocompatibles/química , Hidrogeles/química , Resinas Acrílicas/química , Reactivos de Enlaces Cruzados/química , Agua/químicaRESUMEN
Although stereocomplex (sc) crystallization is highly effective for improving the thermal resistance of poly(lactic acid) (PLA), it is much less predominant than homocrystallization in high-molecular-weight (HMW) poly(l-lactic acid)/ poly(d-lactic acid) (PLLA/PDLA) racemic blends. In this contribution, the sc crystallization of HMW PLLA/PDLA racemic blends was facilitated by using comblike PLAs with cellulose acetate as the backbone. Competing crystallization kinetics, polymorphic crystalline structure, and structural transition of comblike PLLA/PDLA blends with a wide range of MWs were investigated and compared with the corresponding linear/comblike and linear blends. The HMW comblike blend is preferentially crystallized in sc polymorphs and exhibits a faster crystallization rate than does the corresponding linear blend. The sc crystallites are predominantly formed in nonisothermal cold crystallization and isothermal crystallization at temperatures above 120 °C for the comblike blends. Except for the facilitated sc formation in primary crystallization, synchrotron radiation WAXD analysis indicates that the presence of a comblike component also facilitates the transition or recrystallization from homocrystallite (hc) to sc crystallite upon heating. Preferential sc formation of comblike blends is probably attributable to the favorable interdigitation between enantiomeric branches and the increased mobility of polymer segments. After crystallization under the same temperature, the comblike blends, which mainly contain sc crystallites, show smaller long periods and thinner crystalline lamellae than do the corresponding PLLA with homocrystalline structures.
Asunto(s)
Celulosa/análogos & derivados , Ácido Láctico/química , Polímeros/química , Rastreo Diferencial de Calorimetría , Celulosa/química , Cromatografía en Gel , Cristalización , Cinética , Poliésteres , EstereoisomerismoRESUMEN
Competitive crystallization kinetics, polymorphic crystalline structure, and transition of poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) racemic blends with a wide range of molecular weights (MWs) were symmetrically investigated. Stereocomplex (sc) crystallites are exclusively formed in the low-MW racemic blends. However, stereocomplexation is remarkably depressed, and homocrystallization becomes prevailing with increasing MWs of PLLA and PDLA. Suppressed stereocomplexation in high-MW (HMW) racemic blends is proposed to be due to the low chain diffusion ability and restricted intermolecular crystal nucleation/growth. Equilibrium melting point of sc crystallites first increases and then decreases as MW increases. Crystallinity and relative fraction of sc crystallites in racemic blends enhance with crystallization temperature (Tc), and the sc crystallites are merely formed at Tc > 170 °C because of their higher thermodynamic stability. In situ wide-angle X-ray diffraction (WAXD) analysis reveals that the stereocomplexation and homocrystallization are successive rather than completely simultaneous, and the stereocomplexation is preceding homocrystallization in isothermal crystallization of HMW racemic blends. Both initial crystalline structure of homocrystallites (hc) and MW influence the heating-induced hc-to-sc transition of HMW racemic blend drastically; the hc-to-sc transition becomes easier with decreasing Tc and MW. After crystallization at the same temperature, sc crystallites show smaller long period than their hc counterparts.