Yongkang Bai

A tough shape memory polymer with triple-shape memory and two-way shape memory properties

In this study, a tough shape memory polymer network based on polydopamine, poly(e-caprolactone) and diisocyanate was synthesized in three steps. Fourier transform infrared spectroscopy was used to confirm the synthesis process. The tensile tests demonstrated the good mechanical properties of the materials with a tensile modulus and tensile strength reaching 362 and 43 MPa, respectively, at room temperature. The thermal properties of the polymer networks were investigated using differential scanning calorimetry and dynamic mechanical analysis. With two broad transition temperatures, the dual-shape memory properties were greatly affected by the deformation temperature, which was investigated in detail. Moreover, the polymers also showed good triple-shape memory and two-way shape memory effects.

High performance shape memory polyimides based on π–π interactions

A series of polyimides (PIs) with different chain structures were synthesized by a two-step method. The influences of chain conformations on their thermal and mechanical properties were investigated by dynamic mechanical analysis, thermogravimetric analysis, as well as by a universal testing machine. All PIs exhibited high glass transition temperature (>240 °C) and thermal decomposition temperature (>480 °C). Moreover, all these PIs could show shape memory properties more or less, especially ODA–BPDA with a shape recovery ratio (Rr) greater than 93%. The high value of Rr was mainly due to the existence of π–π interaction, a type of non-covalent interaction. The dependence of Rr on π–π interaction was investigated in detail by UV-vis spectroscopy. Finally, atomic oxygen (AO) exposure experiments showed that the shape memory properties of ODA–BPDA were affected little by the erosion due to AO.

Stimuli-responsive composite particles as solid-stabilizers for effective oil harvesting.

The polymer-grafted magnetic composite particles have been synthesized and developed to harvest oil by use of their speical wettability. Different from gravity-driven oil-water separation, the prepared polymer brushes-grafted magnetic composite particles can act as solid-stabilizers that diffuse to the oil-water interfical region and effectively minimize the direct oil-water interfical area by volume exclusion, whereas the magnetic Fe3O4 core allows easy separation of Pickering emulsions from oil-water mixture under an external magnetic field. When the emulsions were heated from room temperature to 50 °C, the coil-to-globule transition of poly(N-isopropylacrylamide) (PNIPAM) acts as the driving force for the destabilization of the emulsion, thereby achieving the release of oil. The novel materials can be used in aspects of oil-water separation, inducing oil droplet transport and release of lipophilic substrates.

A novel high mechanical strength shape memory polymer based on ethyl cellulose and polycaprolactone.

A novel biological friendly shape memory polymer (SMP) based on ethyl cellulose (EC) and polycaprolactone (PCL) was prepared. The network structure of the polymer was formed by linear EC backbones which were linked by grafted PCL chains, and the results showed outstanding mechanical strength and shape memory property of this polymer. The tensile modulus varied from 104.9 to 373.4 MPa while the tensile strength ranged from 155.4 to 323.6 MPa. And the elongations at break were all above 621%. The shape memory switching temperature could be modulated to 37.2°C by decreasing the chain length of graft PCL. As EC and PCL are both biodegradable and biocompatible materials, this new polymer has potential application in biomedical field, like biomedical suture, which would be further studied in the future.

AO-resistant shape memory polyimide/silica composites with excellent thermal stability and mechanical properties

Shape memory polyimide/silica (PI/silica) composites with atomic oxygen resistance, good thermal stability and mechanical properties are synthesized by co-condensation of poly(amic acid) terminated with (3-aminopropy)triethoxysilane (APTES) and tetraethoxysliane (TEOS) via a sol–gel method. The silica networks formed in the hybrid films act not only as permanent crosslink points, but as atomic oxygen (AO) resistant moieties. The results show that the PI/silica composite films possess high thermal decomposition temperature (Td > 550 °C), high glass transition temperature (Tg > 265 °C) as well as good shape fixation ratio (Rf > 98%) and shape recovery ratio (Rr > 90%). The mechanical properties, surface topography and shape memory performance of PI/silica composite films were evaluated before and after AO irradiation in simulated space environment. Compared to pristine PI, the mechanical properties, surface topography, and shape memory performances of PI–SiO2-15 were less affected by AO exposure, which results from the silica protective layer formed on the composite film surface, indicating good AO-resistant ability of PI/silica composite films. This work may provide a strategy toward the design of promising shape memory materials for applications in the field of severe conditions.

Shape memory property of microcrystalline cellulose–poly(ε-caprolactone) polymer network with broad transition temperature

Preparation of shape memory polymers (SMPs) with broad transition temperature was an effective method to realize multishape memory effect. In this study, a novel SMP with a broad glass transition temperature (Tg) based on microcrystalline cellulose was prepared. The structure of the SMP was analyzed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, which can prove the successful synthesis of the material. The thermal properties were investigated with differential scanning calorimetry and dynamic mechanical analysis (DMA). The dual- and multishape memory effects were also quantificationally analyzed by DMA. Further, the influence of programming temperature within Tg on dual-shape memory effect was investigated, and a 1D model was built to explain their relationship.

Dual responsive hydrogels based on functionalized mesoporous silica nanoparticles as an injectable platform for tumor therapy and tissue regeneration

To achieve effective tumor therapy and regenerate new tissue from defects formed by tumor atrophy, a dual responsive hydrogel integrating the stepwise delivery of anti-tumor drugs/growth factors and pH/thermo induced structural transformation is developed, based on polymer (poly N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA)) functionalized mesoporous silica nanoparticles (MSNs). Due to the thermally responsive tangle between PNIPAM chains and the pH triggered hydrogen bonds in PAA chains, these injectable MSNs would immediately switch from nanoparticles to compact hydrogels in a tumor environment (37.5 °C, pH 6.8), where the concentrated network structure in the hydrogel is in charge of the loading and local delivery of anti-tumor drugs. The MSNs serve as nanocarriers for growth factors, which are localized by crosslinked networks. The sustained release of growth factors only occurred with the cleavage of hydrogen bonds in PAA chains, which is triggered by the pH increase to 7.4 after the cure of the tumor. Moreover, the hydrogen bond cleavage would also cause the swelling of the hydrogel, which not only fills the defects but generates plenty of cell-level pores, resulting in an excellent scaffold for attachment and proliferation of healthy cells. Therefore, the dual responsive MSN-hydrogels offer a promising strategy for sequential tumor therapy and tissue regeneration.

Fabrication of Self-Healing Hydrogels with On-Demand Antimicrobial Activity and Sustained Biomolecule Release for Infected Skin Regeneration

Microbial infection has been considered as one of the most critical challenges in bioengineering applications especially in tissue regeneration, which engenders severe threat to public health. Herein, a hydrogel performing properties of rapid self-healing, on-demand antibiosis and controlled cargo release was fabricated by a simple assembly of Fe complex as the cross-linker and hyaluronic acid as the gel network. This hydrogel is able to locally degrade and release Fe3+ to kill bacteria as needed because of hyaluronidase excreted by surrounding bacteria, resulting in efficient antibacterial activity against different types of bacteria. The sustained release property of certain types of growth factors was also observed from this hydrogel owing to its dense network. Moreover, this hydrogel could repeatedly heal itself in minutes because of the coordination interaction between Fe3+ and COOH, exhibiting good potential in bioengineering applications on the exposed tissue, where the materials are easily damaged during daily life. When topically applied onto damaged mouse skin with infection of Staphylococcus aureus, the hydrogel is able to inhibit microbial infections, meanwhile promoting cutaneous regeneration, which formed new skin with no inflammation within a 10 day treatment. These results demonstrate the potential application of this self-healing hydrogel for the integrated therapy of antibiosis and tissue regeneration.

Stepwise co-delivery of an enzyme and prodrug based on a multi-responsive nanoplatform for accurate tumor therapy

Tumors have characteristic physiochemical conditions different from normal tissue, which makes therapy combining chemotherapeutic drugs and tumor microenvironment-responsive nanocarriers a promising route for cancer treatment. Here, we introduce a concept of integrating catalytic nanomedicine and selective chemotherapy for accurate therapy of early stage tumors by co-delivery of enzymes and prodrugs into tumor sites through a multi-responsive nanoplatform. The nanoplatform consists of a polyester-hyaluronic acid-doxorubicin (PE-HA1000k-DOX) prodrug as the corona, physiologically biodegradable silica containing disulfide bonds as the shell and hyaluronidase (absent in early stage tumors) as the core. This nanoplatform is able to quickly enter tumor cells through CD44-HA affinity. Then, the esterase and glutathione rich in tumor cells would respectively degrade the polyester and silica to release HA-DOX and hyaluronidase in a stepwise manner. Finally, highly toxic dissociative DOX is produced through decomposition of the resulting HA-DOX, catalyzed by hyaluronidase, for the apoptosis and death of the tumor cells. The properties of tumor-targeting uptake, tumor microenvironment responsiveness, efficient co-delivery of the enzyme and prodrug, and intracellular enzymatic reaction induced cytotoxicity resulted in a four-fold efficacy against tumor cells over normal cells, indicating that our nanoplatform is a promising material able to achieve both selectivity and efficiency concurrently for tumor therapeutics.

Redox-Responsive Supramolecular Micelles for Targeted Imaging and Drug Delivery to Tumor

The tumor-selective drug delivery system based on supramolecular micelles that were self-assembled by amphiphilic β-cyclodextrins (β-CD) with redox-responsiveness and fluorescence have been developed. The amphiphilic β-CD were formed by anthraquinone (AQ) and cyclodextrins with disulfide bond in between. The disulfide bond is in charge of the responsiveness, while the AQ moiety serves as fluorescent probe. The tumor targeting was introduced by the host-guest inclusion complex between β-CD and folate (FA), due to the known folate-receptor mediated endocytosis. The responsive disintegration of this β-CD-AQ-FA micelles and coinstantaneous drug releases happened with cleavage of disulfide bond following tumor targeting and cell endocytosis, which was triggered by massive glutathione in the cytoplasm of tumor cells. The highly selective particle uptake by tumor cells and subsequent efficient drug delivery to these cells, which were directly demonstrated by fluorescence microscopy, resulted in an over twofold efficacy against tumor cells compared with normal cells, as well as higher tumor cytotoxicity than that caused by free drugs. These results indicate that these β-CD-AQ-FA micelles, with performance of selective drug delivery, responsive drug release, effective drug tracking and tumor labeling, could be a promising platform for better therapeutic effects in cancer treatment.