Zaochuan Ge

Enhanced water-solubility and antibacterial activity of novel chitosan derivatives modified with quaternary phosphonium salt

Chitosan (CS) has been widely recognized as an important biomaterial due to its good antimicrobial activity, biocompatibility and biodegradability. However, CS is insoluble in water in neutral and alkaline aqueous solution due to the linear aggregation of chain molecules and the formation of crystallinity. This is one of the key factors that limit its practical applications. Therefore, improving the solubility of CS in neutral and alkaline aqueous solution is a primary research direction for biomedical applications. In this paper, a reactive antibacterial compound (4-(2,5-Dioxo-pyrrolidin-1-yloxycarbonyl)-benzyl)-triphenyl-phosphonium bromide (NHS-QPS) was synthesized for chemical modification of CS, and a series of novel polymeric antimicrobial agents, N-quaternary phosphonium chitosan derivatives (N-QPCSxy, x=1-2,y=1-4) were obtained. The water solubilities and antibacterial activities of N-QPCSxy against Escherichia coli and Staphylococcus aureus were evaluated compare to CS. The water solubility of N-QPCSxy was all better than that of CS at neutral pH aqueous solution, particularly, N-QPCS14 can be soluble in water over the pH range of 3 to 12. The antibacterial activities of CS derivatives were improved by introducing quaternary phosphonium salt, and antibacterial activity of N-QPCSxy increases with degree of substitution. Overall, N-QPCS14 represents a novel antibacterial polymer material with good antibacterial activity, waters solubility and low cytotoxicity.

Enhanced water-solubility, antibacterial activity and biocompatibility upon introducing sulfobetaine and quaternary ammonium to chitosan.

Chitosan (CS) has attracted much attention due to its good antibacterial activity and biocompatibility. However, CS is insoluble in neutral and alkaline aqueous solution, limiting its biomedical application to some extent. To circumvent this drawback, we have synthesized a novel N-quaternary ammonium-O-sulfobetaine-chitosan (Q3BCS) by introducing quaternary ammonium compound (QAC) and sulfobetaine, and its water-solubility, antibacterial activity and biocompatibility were evaluated compare to N-quaternary ammonium chitosan and native CS. The results showed that by introducing QAC, antibacterial activities and water-solubilities increase with degrees of substitution. The largest diameter zone of inhibition (DIZ) was improved from 0 (CS) to 15mm (N-Q3CS). And the water solution became completely transparent from pH 6.5 to pH 11; the maximal waters-solubility was improved from almost 0% (CS) to 113% at pH 7 (N-Q3CS). More importantly, by further introducing sulfobetaine, cell survival rate of Q3BCS increased from 30% (N-Q3CS) to 85% at 2000μg/ml, which is even greater than that of native CS. Furthermore, hemolysis of Q3BCS was dropped sharply from 4.07% (N-Q3CS) to 0.06%, while the water-solution and antibacterial activity were further improved significantly. This work proposes an efficient strategy to prepare CS derivatives with enhanced antibacterial activity, biocompatibility and water-solubility. Additionally, these properties can be finely tailored by changing the feed ratio of CS, glycidyl trimethylammonium chloride and NCO-sulfobetaine.

Development of zwitterionic polyurethanes with multi-shape memory effects and self-healing properties

Recently, multi-shape-memory polymers have attracted significant attention due to their technological impact. This study reports novel zwitterionic multi-shape-memory polyurethanes (ZSMPUs) from N-methyldiethanolamine (MDEA), hexamethylene diisocyanate (HDI) and 1,3-propanesultone (PS). The ZSMPUs feature excellent multi-shape-memory properties that are capable of remembering four different shapes, and shape recovery decreases with increasing sulfobetaine content. Ionic interactions greatly influence the structure, morphology and properties. Increasing the sulfobetaine content promotes the phase mixing and zwitterions serve as organic fillers in the zwitterionic polyurethane. Immersing the zwitterionic polyurethane in moisture-rich conditions and drying at low temperature preserves the shape-memory capabilities and demonstrates good self-healing properties. Furthermore, both the shape memory effect and self-healing effects are repeatable. The self-healing mechanism is ascribed to the spontaneous attraction of zwitterions, followed by slower re-entanglement.

Insights into liquid-crystalline shape-memory polyurethane composites based on an amorphous reversible phase and hexadecyloxybenzoic acid

Liquid-crystalline polymers and shape-memory polymers are attractive to many researchers. This paper proposes a strategy to prepare liquid-crystalline shape-memory polyurethane (LC-SMPU) composites having both liquid-crystalline properties and shape-memory properties. A series of LC-SMPU composites are successfully prepared by doping different concentrations of 4-hexadecyloxybenzoic acid (HOBA) into shape-memory polyurethanes (SMPUs). The results show that the HOBA is physically mixed with the polyurethane matrix. The doped HOBA is categorised as HOBA captured by the polyurethane chains and free HOBA in the LC-SMPU composite. A higher content of HOBA results in a higher fraction of free HOBA, and more HOBA molecules enter into the polyurethane matrix at higher annealing temperatures. The resulting LC-SMPU composites keep their intrinsic liquid-crystalline properties and the crystallisation properties of HOBA. The LC-SMPU composites contain a two-phase, separated structure: a HOBA crystalline phase and the polyurethane matrix. Thus, the LC-SMPU composites show a two-stage decrease in modulus. Finally, shape-memory tests show that the LC-SMPU composites exhibit a triple shape-memory effect; in the first step, strain recovery is associated with the glass transition of the amorphous polyurethane matrix, and in the second step, strain recovery results from the melting transition of the HOBA crystal dopants.

Development of supramolecular liquid-crystalline polyurethane complexes exhibiting triple-shape functionality using a one-step programming process

Supramolecular liquid crystalline polymers and shape memory polymers are attracting increasing interest as materials. In this paper, we describe the development of a supramolecular liquid crystalline shape memory polyurethane (SLCSMPU) complex that exhibits both liquid crystalline properties and shape memory properties. The complex is formed by incorporating 4-hexadecyloxybenzoic acid (HOBA) into a pyridine-containing shape memory polyurethane (PySMPU). The HOBA is tethered to the PySMPU by strong hydrogen bonding between the pyridine rings and the COOH of the HOBA, forming a SLCSMPU complex. Heat treatment plays an important role in the formation of hydrogen-bonded supramolecular liquid crystalline structures in these SLCSMPU complexes. Thus, the SLCSMPU complex not only maintains the intrinsic liquid-crystalline properties of HOBA, but can also form a stable polymeric film for various shape memory applications. Additionally, the SLCSMPU complex forms a two-phase separated structure composed of an amorphous polyurethane matrix and a HOBA crystalline phase, which includes the hydrogen-bonded crystalline HOBA phase and the free HOBA crystalline phase. Therefore, a simple one-step programming process is developed that produces SLCSMPU complexes with excited triple-shape functionalities due to their multiple phase transitions, especially when the molar ratio of HOBA/BINA is less than 0.8.

Development of zwitterionic copolymers with multi-shape memory effects and moisture-sensitive shape memory effects

Shape memory polymers (SMP) and zwitterionic polymers both have great applications in biomedical fields. This works successfully combines functionalities of zwitterionic polymers and SMP, developing new kind of zwitterionic copolymers having a multi-shape memory effect (SME) and a moisture-sensitive SME. The results demonstrate that a series of zwitterionic multi-SMPs, coded as p(DMAPS-co-AA), were synthesized from DMAPS and acrylic acid (AA). A micro-phase separated structure is formed in the resulting p(DMAPS-co-AA). The strong hydrogen bonding between AA segments serves as a reversible switch, while the strong electrostatic forces among DMAPS segments serve as physical crosslinkers. Therefore, shape memory testing demonstrates that p(DMAPS-co-AA) shows not only dual-SME, but also triple-SME and quadruple-sSME. Moreover, in addition to the thermally-induced SME, p(DMAPS-co-AA) also shows moisture-sensitive SME. It is thus proposed that this zwitterionic multi-SMP could find great potential applications in smart biomedical fields.

Development of liquid-crystalline shape-memory polyurethane composites based on polyurethane with semi-crystalline reversible phase and hexadecyloxybenzoic acid for self-healing applications

Shape memory materials and self-healing materials have attracted considerable attention in recent years. This paper reports the development of a liquid-crystalline shape-memory-polyurethane (LC-SMPU) composite based on SMPU and hexadecyloxybenzoic acid (HOBA) for self-healing applications. The results demonstrate that HOBA is physically mixed with SMPU resulting in a semi-crystalline reversible phase and forming LC-SMPU composites. The two-phase separated structure comprises an SMPU matrix and a HOBA phase. The HOBA phase exhibits a reversible nematic phase within a temperature range of 101–130 °C, while the SMPU matrix acts as a stable polymeric film for various applications. Both the semi-crystalline soft phase of the SMPU matrix and the HOBA crystalline phase can be used to trigger shape memory effects. The LC-SMPU composites display not only triple-shape memory behaviours but also self-healing behaviours due to the heating-induced “bleeding” behaviour of HOBA in the liquid crystalline state and their subsequent recrystallisation upon cooling.

Pyridine type zwitterionic polyurethane with both multi-shape memory effect and moisture-sensitive shape memory effect for smart biomedical application

This paper reports a new type of zwitterionic polyurethane containing pyridine type zwitterionic segments for shape memory materials. The pyridine type zwitterionic shape memory polyurethanes (SMPUs) were synthesized using polyurethane polymerization from N,N-bis(2-hydroxylethethyl)isonicotinamide (BINA), hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO), followed by a ring-opening reaction with 1,3-propanesultone (PS). The structure and properties of the pyridine-type zwitterionic SMPUs (PyZPUs) were investigated systematically. The results demonstrate that the PyZPUs form phase-separation structures composed of a hard phase and an amorphous soft phase with a broad glass transition. The shape memory tests show that the PyZPUs have thermal-induced dual-shape memory effects (SMEs), triple-SMEs and quadruple-SMEs and also moisture-sensitive SMEs. Comparatively, the samples with PS/BINA molar ratios of 0.6–0.8 have more than 86% shape recovery and more than 95% shape fixity with a heat stimulus. Under moisture conditions, these samples also show the quickest moisture-sensitive strain recovery, up to 86%. Moreover, the PyZPUs show good biocompatibility when the content of pyridine type zwitterionic segments is beyond 21 wt%. Thus, the PyZPUs are expected to have many promising applications in smart biomedical fields.

New insights into multi-shape memory behaviours and liquid crystalline properties of supramolecular polyurethane complexes based on pyridine-containing polyurethane and 4-octyldecyloxybenzoic acid

Both liquid crystalline polymers and shape memory polymers are attractive to researchers. This paper describes the development of a supramolecular liquid crystalline complex exhibiting a multi-shape memory effect and liquid crystalline properties. 4-n-Octyldecyloxybenzoic acid (OOBA) is connected to a pyridine-containing polyurethane (PySMPU), forming a new PySMPU/OOBA complex. The results of this study demonstrate that the complex maintains the intrinsic crystallization and liquid-crystalline properties of OOBA and combines the shape memory effects of PySMPUs. Shape memory investigations demonstrate that the PySMPU/OOBA complexes have a good multi-shape memory effect, exhibiting triple- and quadruple-shape memory behaviours. For the triple-shape memory behaviours, the strain fixity at the first stage is lower than that at the second stage, while the strain recovery at the first stage is higher than that at the second stage. Overall, increasing the OOBA content improves the strain fixity but reduces the strain recovery due to the lubrication of the OOBA long chains. The successful combination of the liquid crystalline properties and multi-shape memory effect makes the PySMPU/OOBA complexes potentially applicable in smart optical devices, smart electronic devices and smart sensors.

Development of humidity-responsive self-healing zwitterionic polyurethanes for renewable shape memory applications

This paper reports a novel humidity-responsive self-healing material based on zwitterionic polyurethanes. The material was synthesized from N,N-bis(2-hydroxylethyl) isonicotinamide (BINA), hexamethylene diisocyanate (HDI) and 1,3-propanesultone (PS). The self-healing of its structure, its mechanical properties and shape memory properties were carefully investigated. Results demonstrate that self-healing zwitterionic polyurethanes contain pyridine type sulfobetaines and that strong electrostatic interactions are formed between zwitterions acting as physical crosslinkers. The aggregation of zwitterions strongly influences the phase transition behavior of polyurethane. Bulk polyurethane shows a phase-separated structure with an amorphous soft phase. The damaged zwitterionic polyurethane structure can self-heal several times in the presence of moisture without any additive or external energy. As the proportion of zwitterions increases, the self-healing efficiency increases. The self-healing efficiency results are higher when the relative humidity is increased. The self-healing mechanism is ascribed to the improved ionic mobility upon hydration and to electrostatic forces which occur during drying. Furthermore, pyridine based zwitterionic polyurethanes also show good self-healing of their shape memory properties. Self-healed polyurethanes show both a good shape fixity and recovery. This work paves the way to develop stimulus-responsive self-healing materials for renewable shape memory applications.