Shouhong Xu

A lattice model for thermally-sensitive core-shell hydrogels

A lattice molecular thermodynamic model for describing the swelling behavior of thermally-sensitive core-shell hydrogels was developed by integrating a close-packed lattice model for mixing free energy and a Flory Gaussian chain model for the elastic free energy. The thermodynamic model is characterized with two parameters: the temperature-dependent exchange energy parameter ε and the Topology-dependent size parameter V(*). The input values of both parameters can be obtained by experimental results of pure polymer hydrogels. With the help of proposed model, swelling behaviors of two kinds of hydrogel systems were analyzed: one is a doubly thermally-sensitive core-shell hydrogels (with two LCSTs) and the other comprises a thermally-sensitive hydrogel shell with a hard internal core. We show that the calculated results are in good agreement with the experimental data.

Disclosing the distinct interfacial behaviors of structurally and configurationally diverse triazologlycolipids.

1- or 6-Triazologluco- and galactolipid derivatives bearing a lipid chain length of 16 carbons were efficiently constructed via click chemistry. The differentiation in their surface pressure-molecular area (π-A) isotherms first implies that these structurally and configurationally diverse amphiphiles adopt different distribution manner at air-water interfaces. The Langmuir-Blodgett (LB) films of the synthesized glycoconjugates on mica surface were subsequently prepared and visualized via atomic force microscopy (AFM), which exhibited diverse topographies and possess different contact angles with water. These data further suggest that the structural variation as well as epimeric identity of triazologlycolipids may result in their distinct interfacial behaviors at the air-solid interface. Furthermore, the addition of increasing amounts of 1-triazologalactolipid 2 to poly-diacetylene (PDA) was determined to impact the π-A isotherm of the latter, prompting us to further fabricate new colorimetrically detectable mixed-type vesicles containing triazologlycolipids for biochemical studies.

Lock/unlock mechanism of solvent-responsive binary polymer brushes: density functional theory approach.

A density functional theory (DFT) approach based on a weighted density approximation has been employed to study the perpendicular microphase separation of symmetric binary polymer brushes with weak incompatibility in explicit solvents with different selectivities. Characterized by the relation between the grand potential and vertical structures (including nonlayered and layered structures), a dry binary brush can be categorized as W-type or U-type according to whether the characteristic relation contains a structure that undergoes spontaneous symmetry breaking. A W-type brush can memorize the selectivity of the induced solvent in one of its two layered structures after the removal of solvent, which can be seen as a kind of lock state with the nonselective solvent used as its key to unlock. A U-type brush is lockless but can adapt to the environment without the nonselective solvents triggering. Also, the boundary described in chain-length-incompatibility space is investigated by the DFT approach, which also verifies that the spontaneous symmetry breaking of the W-type brush originates from the molecular contributions to asymmetry, such as the enthalpic contribution of incompatibility and the entropic contribution of chain connectivity.

The effect of a P123 template in mesopores of mesocellular foam on the controlled-release of venlafaxine.

A series of mesocellular foams (MCFs)-based mesoporous silica nanospheres (DH-MCF-P123-n, (n=12, 2, 0.5)) were synthesized as controlled-release deliveries for a typical antidepressant drug, venlafaxine. The foams were 3-(2,3-dihydroxypropoxyl)propyl-grafted and the P123 template partially preserved. We studied the release profiles of venlafaxine-loaded DH-MCF-P123-n in simulated gastric fluid (SGF) and simulated intestinal fluid (SIF), respectively, as well as their corresponding venlafaxine loading capacities. Appropriate amounts of P123 template preserved in mesopores showed an efficient synergetic effect on increasing venlafaxine loading capacity and controlled-release property. Up to 90.87% (mass fraction) of venlafaxine could be loaded into DH-MCF-P123-2. For this carrier, 36% of venlafaxine was released after 1h of incubation in SGF and 53% of venlafaxine was released after 12h in SIF. The mechanisms of the loading and releasing processes were tentatively described based on the release behaviors.

Characterization and release kinetics of liposomes inserted by pH-responsive bola-polymer

One important thing in tumor chemotherapy is to develop the targeting, precise timing, and quantitative drug delivery/release system. According to the weak acid of tumor extracellular environment, a pH-sensitive bola-type triblock copolymer (PEGm-PDPAn-PEGm) was synthesized and mixed with phospholipid to form functional hybrid liposomes (liposome@Bola). When compared to pure liposome, the stability of the liposome@Bola was enhanced greatly and the drug leakage was inhibited at pH 7.4. However, under pH 6.0, the drug released quickly through the nanopores on the lipid bilayer created by the escape of copolymers. Under a strongly acidic environment, the drug release of liposome@Bola could be blocked again due to the coverage of free copolymers. The kinetic curves of drug release had been modeled by using some frequently used models. It was found that the release of liposome@Bola under pH 6.0 was biphasic with a slow release by means of membrane permeation and a rapid second phase which was released through nanopores on liposome membrane. The results indicated that the pH-responsive liposome@Bola could be expected to be a good potential in controllable drug delivery system.

Density functional theory for the selective adsorption of small molecules on a surface modified with polymer brushes

A density functional method based on weighted density approximation is extended to study the selective adsorption of small molecules on a surface modified with end-grafted square-well chains. The excess part of the Helmholtz free energy functional is divided into two components: the hard sphere repulsion and the square-well attraction. The equation of state for hard sphere chain fluids developed by Liu et al. is used to calculate the repulsive part of the excess Helmholtz free energy functional, and the equation of state for square-well chain fluid with variable range developed by Li et al. is employed to calculate the attractive part. With this theoretical model, we examine the physical properties of the grafted polymer and the selective adsorption of small molecules on the modified surface.

Insertion of pH-sensitive bola-type copolymer into liposome as a "stability anchor" for control of drug release.

How to design intelligent carriers for delivering drugs to the target accurately and releasing drug timely with the help of a certain environmental stimulus is still a challenge in tumor treatment. In this work, pH-sensitive bola-type triblock copolymers, composed of poly(2-(diisopropylamino) ethylmethacrylate) (PDPA) and methoxy-poly(ethyleneglycol) (mPEG), were synthesized. Liposomes containing these copolymers (Liposome@Bola) have been prepared by simply mixing the copolymer with phospholipids and cholesterol. From the fluorescence polarization measurement, the stability of Liposome@Bola was found to be increased a lot comparing to the pure liposome. As a result, the doxorubicin (DOX) leakage of the former was restrained in neutral environment. However, when pH decreased from 7.4 to 6.0, DOX released percentage had been increased 30-60 points, which was heavily depend on the phospholipid composition. Furthermore, the size effects of PEG and PDPA segments were also investigated. These results indicated the synthesized bola-type copolymers improved the pH-controllability of drug release of liposome, i.e., increased the difference between the release amount under pH 7.4 and pH 6.0. The bola-type copolymer exhibited a good potential application in smartly controlling drug delivery system.

Self-assembly nano-structure of type I collagen adsorbed on Gemini surfactant LB monolayers

The self-assembly nano-structures of type I collagen adsorbed on anionic Gemini surfactant LB monolayer were observed by using atomic force microscopy (AFM) images. It was found that the adsorption behavior and self-assembly structure of collagen could be controlled by the concentration of the collagen solution, adsorption interval and the properties of substrates. With the increase of the adsorption interval and concentration of collagen, the strands size of collagen changed. The self-assembly structures of collagen were also influenced by the interaction between collagen molecules and Gemini surfactant monolayer substrates. Finally, the adsorption behaviors of collagen molecules on cationic Gemini monolayer were compared with those on anionic Gemini monolayer.

Photocontrollable Intermittent Release of Doxorubicin Hydrochloride from Liposomes Embedded by Azobenzene-Contained Glycolipid

Azobenzene-contained glycolipids GlyAzoCns, newly structured azobenzene derivatives, which have an azobenzene moiety between the galactosyl and carbon chains of various sizes, have been synthesized. The GlyAzoCns undergo reversible photoinduced isomerization in both ethanol solution (free state) and liposomal bilayer (restricted state) upon irradiation with UV and vis light alternately. The drug release of Liposome@Gly induced by isomerization was found to be an instantaneous behavior. The photoinduced control of DOX release from liposome was investigated in various modes. The Liposome@Glys have been found to keep the entrapped DOX stably in the dark with less than 10% leakage in 10 h but release nearly 100% of cargos instantaneously with UV irradiation. The molecular structure of GlyAzoCns and the property of the liposomal bilayer were considered as important factors influencing drug release. Among the synthesized GlyAzoCns, GlyAzoC7 was shown to be the most efficient photosensitive actuator for controlling drug release. A lower proportion of cholesterol in Liposome@Glys was conducive to promote the release amount. Results indicated that the synthesized GlyAzoCns could act as a role of smart actuators in the liposome bilayer and control the drug to release temporarily and quantitatively.

A lattice molecular thermodynamic model for thermo-sensitive random copolymer hydrogels

AbstractRecent advances in polymer chemistry have enabled the design of a wide range of copolymer hydrogels consisting of stimulus-responsive blocks and other functional blocks used in many fields. In this work, a new molecular thermodynamic model is developed based on our previous work for the swelling behavior of temperature-sensitive random copolymer hydrogels. The influences of polymer species, the molar fraction f, and the cross-linking degree on the swelling behaviors of copolymer hydrogels are investigated. The calculated swelling curves of PNIPAm-ENAG copolymer hydrogels have been compared with the corresponding experimental results. It is shown that the results obtained by model are quite consistent with the experimental data, and this indicates the validity of our model. Graphical abstractSwelling behaviors of PNIPAm-ENAG copolymer hydrogels