Yaling Lin

The synthesis and characterization of supramolecular elastomers based on linear carboxyl-terminated polydimethylsiloxane oligomers

Supramolecular elastomers obtained through a two-step reaction of linear carboxyl-terminated polydimethylsiloxane oligomers (PDMS–COOH2) with diethylenetriamine (DETA) and urea show reasonable hysteresis and acceptable self-healing properties. The results of temperature-dependent infrared analysis suggest the existence of hydrogen bonding interactions with good thermal reversibility in the matrix. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses demonstrate that the supramolecular network structure is totally amorphous at room temperature. The rheological, mechanical and self-healing properties are closely related to the PDMS chain length, whereas the stability seems to be independent of the PDMS chain length. The viscoelastic properties of these materials are believed to be the result of entangled chains in the amorphous matrix. Only the hydrogen bonds formed by 1,1-dialkylurea groups and imidazolidone derivatives serve as effective crosslinks for contributing to the stability of the supramolecular network.

The synthesis and characterization of carboxybetaine functionalized polysiloxanes for the preparation of anti-fouling surfaces

Nonspecific protein adsorption and bacterial adhesion have caused serious problems in biomedical devices, marine engineering, membrane separation and many other areas. In order to develop a water-soluble bio-adhesion resistant material, a series of novel zwitterionic polymers, carboxybetaine functionalized polysiloxanes (PDMS-g-CB), were synthesized via a three-step procedure. FT-IR and NMR were used to characterize the chemical structures of PDMS, and the solution properties (i.e. CMC) and biological characteristics were investigated. The high biocompatibility of PDMS-g-CB was demonstrated by hemolysis assay, skin irritation evaluation and acute oral toxicity testing. To evaluate the anti-fouling and hydrophilic properties of PDMS-g-CB, it was blended with PDMS elastomer to form films (b-PDMS). Water contact angle and ATR-FTIR measurements revealed that the hydrophobic PDMS surfaces were converted to hydrophilic surfaces after the introduction of PDMS-g-CB. The anti-fouling properties of b-PDMS were evaluated by protein adsorption and bacterial adhesion tests. Results showed that the amount of adsorbed protein and bacteria adhesion were significantly reduced compared with the untreated PDMS. These findings suggest that PDMS-g-CB is a biocompatible and promising material for the construction of anti-fouling surfaces.

Preparation of anti-fouling silicone elastomers by covalent immobilization of carboxybetaine

Polydimethylsiloxane (PDMS) is a widely used material for biomedical applications. In this work, a convenient method for the covalent modification of PDMS with carboxybetaine was developed and used to construct a biocompatible and anti-fouling coating. Following the preparation of a Si–H functionalized PDMS film by adjusting the molar ratio of the two components used in Sylgard 184 silicone elastomer networks, the allyl carboxybetaine (ACB) was grafted to the PDMS surface via a hydrosilylation reaction in the presence of a Karstedts catalyst. ATR-FTIR and water contact angle measurements revealed that carboxybetaine was introduced to the PDMS surface successfully. The biocompatibilities of PDMS and carboxybetaine-modified PDMS (PDMS-CB) films were evaluated by cytotoxicity, hemocompatibility, and dynamic clotting time. The anti-fouling properties of PDMS-CB were evaluated by protein adsorption and bacterial adhesion measurements. The results showed that the carboxybetaine layer could enhance the biocompatibility of PDMS and reduce the adsorption of protein and adhesion of bacteria efficiently.

Synthesis and Characterization of Carboxyl Terminated Polydimethylsiloxanes

A series of hydrogen terminated polydimethylsiloxanes (PDMS-H) had been controlled synthesized via ring-opening polymerization. Then, methylmethacrylate (MMA) and tert-butyl methacrylate (tBMA) were grafted to PDMS-H via hydrosilylation reactions in the presence of Speiers catalyst, the hydrosilylation addition patterns of MMA and tBMA showed a strong preference toward β-1,2 addition, no α-1,2 addition product or 1,4-addition product was observed. Carboxyl terminated polydimethylsiloxanes were prepared by subsequent hydrolysis reaction in an aqueous NaOH/ethanol solution and under acid condition, respectively. Both methods could obtain carboxyl terminated polydimethylsiloxanes successfully. However, a significant decrease of the molecular weight of products was observed in the alkaline hydrolysis process, while the acid hydrolysis of tertiary butyl ester group terminated polydimethylsiloxanes could be conducted in a highly controlled manner. Besides, the synthesis of carboxyl terminated polydimethylsiloxanes via acid hydrolysis reaction can be conducted well only when the terminal group of polydimethylsiloxanes is tertiary butyl, this can be explained by the specificity of tertiary butyl.

Supramolecular elastomer based on polydimethylsiloxanes (SESi) film: synthesis, characterization, biocompatibility, and its application in the context of wound dressing.

Supramolecular elastomer based on polydimethylsiloxanes (SESi) is a kind of novel elastomer cross-linked by the multihydrogen bonds supplied by the functional groups linked to the end of the PDMS chains, such as amide, imidazolidone, pending urea (1,1-dialkyl urea), and bridging urea (1,3-dialkyl urea). SESi showed lower glass transition temperature (T g) at about −113 °C because of the softer chain of PDMS, and could show real rubber-like elastic behaviors and acceptable water vapor transmission rate under room temperature. The high biocompatibility of SESi in the form of films was demonstrated by the cytotoxicity evaluation (MTT cytotoxicity assay and direct contact assay), hemolysis assay, and skin irritation evaluation. Based on detailed comparisons between commercial Tegaderm™ film and SESi film using a full-thickness rat skin model experiment, it was found that SESi film showed similar wound contraction rate as that of Tegaderm™ film on day seven, 10, and 14; only on day five, SESi film showed a significant (p < 0.05) lower wound contraction rate. And, the wounds covered with SESi film were filled with new epithelium without any significant adverse reactions, similar with that of Tegaderm™ film.

Novel supramolecular elastomer films based on linear carboxyl-terminated polydimethylsiloxane oligomers: preparation, characterization, biocompatibility, and application in wound dressings

A novel supramolecular elastomer (SESi) based on multiple hydrogen bond associations between low-molecular-weight polydimethylsiloxane chains was obtained through a two-step reaction of linear carboxyl-terminated polydimethylsiloxane oligomers with diethylenetriamine and urea, and the reaction mechanism was characterized. The results of differential scanning calorimetry and X-ray diffraction analyses indicated that the supramolecular network structure is completely amorphous, endowing SESi with rubber-like elastic behavior at room temperature. The transparent SESi film prepared by hot pressing displayed nice viscoelasticity, benign water absorption, water vapor transition rates, and ideal biocompatibility; and did not show cytotoxicity or skin irritation. These properties allow the elastomer to function as an occlusive wound dressing. To demonstrate its potential in wound dressings, a detailed comparison of commercial 3M Tegaderm™ film and the SESi film was conducted. The SESi film exhibited similar effects in wound healing, and the wound bed was covered by the SESi film without the occurrence of significant adverse reactions.

Absorptive supramolecular elastomer wound dressing based on polydimethylsiloxane–(polyethylene glycol)–polydimethylsiloxane copolymer: preparation and characterization

Polydimethylsiloxanes (PDMS) are soft materials with high elasticity and excellent biocompatibility, giving them high potential for widespread applications as biomaterials. However, the application of PDMS to wound dressing is limited due to its shortcomings, particularly its non-absorptive and poor adhesive properties. This work addresses these limitations in two ways: first, a hydrophilic and biocompatible polyethylene glycol (PEG) block was introduced to the PDMS main chain to obtain carboxyl acid terminated PDMS-b-PEG-b-PDMS copolymers (EPMDS–COOH2); second, EPMDS–COOH2 polymers were reacted with diethylenetriamine and urea via a two-stage route to obtain a novel supramolecular elastomer (ESESi) based on multiple hydrogen bond association. Compared with the supramolecular elastomer based on simple PDMS (SESi), the hydrophilicity, water-absorption rate, adhesive ability and rate of water vapor permeation were significantly improved, enhancing the properties of ESESi films for application to wound dressing. After fully evaluating the bio-compatibilities of ESESi films, a full-thickness dermal wound model was chosen to estimate the healing performance, and traditional vaseline gauze, SESi film and commercialized Tegaderm™ film were chosen as controls. The results confirmed that the ESESi polymer could promote the healing of a skin wound to some extent, mainly due to its improved absorption and adhesive properties.

The interactions between bovine serum albumin and carboxybetaine-functionalized polysiloxanes in solution

The interactions between carboxybetaine-functionalized polydimethylsiloxanes (PDMS-g-CB) and bovine serum albumin (BSA) in water solution were investigated from varied aspects based on different techniques, including fluorescence spectroscopy, UV-Vis spectroscopy, circular dichroism spectroscopy, isothermal titration calorimetry, and atomic force microscopy. Due to the weak interaction between PDMS-g-CB and BSA, another polymer with similar structure as PDMS-g-CB, i.e., quaternary ammonium salt-functionalized polydimethylsiloxanes (PDMS-g-QAS), was synthesized and chosen as the positive control, and the results indicated that the free PDMS-g-CB in solution could exhibit good resistance against proteins, which was mainly due to the zwitterions-side groups’ binding ability between PDMS chain and protein. Both the characterization methods and the results could help us to understand the interaction between free water-soluble polymers and protein, and extend the application of PDMS-g-CB and design new antifouling materials.