Relationships between the morphology,swelling and mechanical properties of poly(dimethyl siloxane)/poly(acrylic acid) interpenetrating networks

A limitation in the use of hydrophilic polymers as implantable devices is their inherently poor mechanical strength. Using interpenetrating polymer networks (IPNs) consisting of both hydrophilic and hydrophobic networks is an effective method of strengthening these polymers. In this work, a series of poly(dimethyl siloxane) (PDMS)/poly(acrylic acid) (PAAc) sequential IPNs were synthesized and their properties, including swelling, morphology, and mechanical strength, were investigated. A reinforcing effect of the addition of PAAc to PDMS was observed at a concentration of 20 wt%, where this component had a bimodal size distribution. All of the IPNs exhibited rubbery behavior in the swollen state. Phase inversion in the IPNs occurred at about 60 wt% of PAAc. However, the swelling data showed that the phase inversion in the swollen state occurred at PAAc contents lower than those for dry IPNs. The improved cell behavior, reported in previous works for PDMS/PAAc IPNs with about 20 wt% PAAc, can, in addition to the increased surface wettability, be attributed to the bimodality of PAAc particles size distribution in the IPN.     

Synthesis, characterization, and platelet adhesion studies of novel aliphatic polyurethaneurea anionomers based on polydimethylsiloxane-polytetramethylene oxide soft segments

Two novel aliphatic polyurethaneurea anionomers were synthesized based on polydimethylsiloxane (PDMS)-polytetramethylene oxide (PTMO) soft segments. The hard segments consisted of either 4,4'-methylene dicyclohexyl diisocyanate (H12MDI), sulfonic acid-containing diol and 1,4-butandiol (BD) or H12MDI, carboxylic acid-containing diol and BD. The nonionic counterpart chain extended with BD was prepared. In addition, the base nonionic polyurethaneurea containing a pure PDMS soft segment, which is denote H-D-BD, was also studied for comparison. The effects of soft segment type and ion incorporation on the physical properties, surface properties, and plateled adhesion are discussed. The ionic polyurethaneureas exhibited poor phase separation, a smaller fraction of PTMO present at the surface, and a smaller contact angle. On the other hand, it also showed a larger fraction of PDMS present at the surface and a higher water absorption value than its nonionic counterpart. H-D-BD had more phase-separated structure, a larger fraction of PDMS present at the surface, and larger contact angle but lower water absorption value than the PTMO-containing polyurethaneureas. The in vitro platelet adhesion experiments indicated that the ionic groups, especially for carboxylate, and surface enrichment PDMS soft segment could effectively inhibit platelet adhesion.     

High‐Performance Polybenzoxazine Derived from Polyfunctional Benzoxazine Composed of an Oligonuclear Phenolic Compound Having a 4,4′‐Dimethylenebiphenyl Linker

A novel polyfunctional benzoxazine monomer, OP‐a , is synthesized from aniline, formaldehyde, and an oligonuclear phenolic compound (OP) with a 4,4′‐dimethylenebiphenyl group as the phenol linker. After thermal curing of OP‐a up to 240 °C, a brown‐colored, transparent polybenzoxazine ( POP‐a ) film is obtained. The mechanical and thermal properties of the POP‐a film are investigated by tensile test, dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). The POP‐a film is extremely tough compared with a typical polybenzoxazine ( PB‐a ) film. The elongation at break of the POP‐a film is 7.6%, which is surprisingly large for the highly cross‐linked thermoset. The high cross‐link density is suggested from the very high storage modulus (over 1 GPa) above the glass transition temperature (T _g) observed by DMA. The T _g of POP‐a is also improved significantly to T _g = 223 °C, which is approximately 50 °C higher than that of PB‐a . Moreover, TGA reveals that the thermal stability of POP‐a is also enhanced.     

Synthesis,characterization, and platelet adhesion studies of novel aliphatic polyurethaneurea anionomers based on polydimethylsiloxane-polytetramethylene oxide soft segments

Two novel aliphatic polyurethaneurea anionomers were synthesized based on polydimethylsiloxane (PDMS)-polytetramethylene oxide (PTMO) soft segments. The hard segments consisted of either 4,4'-methylene dicyclohexyl diisocyanate (H₁₂MDI), sulfonic acid-containing diol and 1,4-butandiol (BD) or H₁₂MDI, carboxylic acid-containing diol and BD. The nonionic counterpart chain extended with BD was prepared. In addition, the base nonionic polyurethaneurea containing a pure PDMS soft segment, which is denote H-D-BD, was also studied for comparison. The effects of soft segment type and ion incorporation on the physical properties, surface properties, and plateled adhesion are discussed. The ionic polyurethaneureas exhibited poor phase separation, a smaller fraction of PTMO present at the surface, and a smaller contact angle. On the other hand, it also showed a larger fraction of PDMS present at the surface and a higher water absorption value than its nonionic counterpart. H-D-BD had more phase-separated structure, a larger fraction of PDMS present at the surface, and larger contact angle but lower water absorption value than the PTMO-containing polyurethaneureas. The in vitro platelet adhesion experiments indicated that the ionic groups, especially for carboxylate, and surface enrichment PDMS soft segment could effectively inhibit platelet adhesion.     

A Simple and Low‐Cost Synthesis of Antibacterial Polyurethane with High Mechanical and Antibacterial Properties

In this paper, a simple and low‐cost approach for the preparation of quaternary ammonium salt (QAS)‐containing antibacterial polyurethane (APU) films is described. Epichlorohydrin (ECH), an inexpensive and commercially available chemical, is used to prepare the low‐cost antimicrobial PECH‐QAS. Then PECH‐QAS, three‐armed PPG, linear PPG, and diisocyanate are introduced for the synthesis of the APU prepolymer without any solvent in one pot for the first time. Water and three‐armed PPG act as the cross‐linking initiator and cross‐linker in the preparation of the APU films. Using water as the initiator makes the preparation process more environment‐friendly, and the cross‐linked network guarantees the resistance of the film toward solvent corrosion. The influence of molecule weight of PECH‐QAS, PECH‐QAS concentration, cross‐link density, and diisocyanate types on the mechanical properties and antibacterial properties of the APU films is extensively investigated. The optimized APU films exhibit high mechanical performance and excellent antibacterial properties.     

Bulk, surface and blood-contacting properties of polyether polyurethanes modified with polydimethylsiloxane macroglycols

The bulk, surface and blood-contacting properties of a series of polyether polyurethanes, modified with three different polydimethylsiloxane (PDMS) macroglycol segments, were evaluated. The PDMS oligomers were terminated with hydroxy-tipped end groups of varying polarity. The effect of substituting the polytetramethylene oxide (PTMO) soft segment of a base polyurethane with 5 and 15 wt% of these PDMS-containing polyols was investigated. The ultimate tensile strength and elongation at break appeared to be the bulk properties most significantly affected by the addition of the PDMS-containing polyols. Underwater contact angle data indicate that the block copolymer surface became more hydrophilic with increasing PDMS content. In a vacuum, as determined from the ESCA data, the relatively non-polar PDMS soft segments preferentially oriented at the surface with increasing PDMS incorporation. Despite the variation in the surface properties, the blood compatibility of these polymers was not significantly affected by the addition of the PDMS-containing polyols.     

In vitro biocompatibility of PTMO-based polyurethanes and those containing PDMS blocks

In this work, a series of different polyurethanes based on poly(tetramethylene oxide) (PTMO, MW approximately 2000) and chain extended with butenediol were synthesized by a two-step solution polymerization. Three of them contained silanol terminated polydimethylsiloxane (PDMS, MW approximately 2000) blocks. It was shown that these polymers exhibited various degrees of micro-phase separation that further influenced their biological performances in vitro. The formulation with diphenylmethane diisocyanate/PTMO/PDMS/2-butene-1,4-diol at a molar ratio of 2: 0.75: 0.5: 1 in synthesis was favorable due to a combination of enhanced mechanical properties, biostability, cellular affinity as well as platelet nonadherence.     

Interplay between Mechanical Fatigue and Network Structure and Their Effects on Mechanical and Electrical Properties of Thin Silicone Films with Varying Stoichiometric Imbalance

Thin silicone films for applications as dielectric electroactive polymer (DEAP) are fatigued under mechanical cycling (Wöhler tests) until rupture. The silicones are based on linear vinyl‐terminated poly(dimethylsiloxane) (PDMS) cross‐linked with tetrafunctional methylhydrosiloxane–dimethylsiloxane copolymer. Stoichiometric imbalance of the hydrosilane to vinyl groups is varied (1.3, 1.7, and 3). Complementary, all silicones are compounded with silicone oil (55 wt%) and silica (4.5 wt%). Changes in cross‐linking density, elastic modulus, dielectric permittivity, and dielectric breakdown are examined. The fatigued specimens show increased cross‐linking density due to mechanically induced secondary cross‐linking of excessive hydrosilane groups. This leads to significant changes in the elastic modulus and permittivity of the material, which can negatively affect the performance of the DEAP device. The “critical loading conditions,” where the fatigued specimens show maximum changes in properties, are found to depend on excess hydrosilane content.

     

Phase Segregation in Supramolecular Polymers Based on Telechelics Synthesized via Multicomponent Reactions

The properties of supramolecular polymers in the solid state are strongly dependent on the binding strength of the supramolecular motifs used; however, It has been previously shown that the nanostructure of supramolecular polymers plays an equally important role. Supramolecular polymers are commonly synthesized via end‐group functionalization of low‐glass transition telechelics with supramolecular units. In these systems, the binding motifs segregate from the soft telechelic backbone and form a hydrogen bonded crystalline hard phase that provides physical cross‐links. To date, the reported synthetic approaches do not permit the introduction of a wide variety of supramolecular units with low synthetic effort, which would facilitate studying the structure‐property relationships. The use of the Passerini and Ugi multicomponent reactions to synthesize various poly(ethylene‐co‐butylene) telechelics with diverse amide end‐groups is reported. The thermal properties of the supramolecular polymers obtained through their solid‐state assembly are investigated and their nanophase‐segregation is studied, which is dictated by the end‐group volume fraction and the amide–amide hydrogen bonding.     

Synthesis, characterization and platelet adhesion studies of novel ion-containing aliphatic polyurethanes

Two novel ion-containing aliphatic polyurethanes based on 4,4'-methylene dicyclohexyl diisocyanate (H12MDI), polytetramethyl oxide (PTMO) were synthesized using either sulfonated or carboxylated chain extender. The nonionic polyurethane chain extended with 1,4-butanediol, which is denoted as H-M-BD, was synthesized. Pellethane, a biomedical-grade polyurethane, was also studied for comparison. The polymer's bulk, surface, and platelet-contacting properties were studied using Fourier transform infrared spectrophotometry, differential scanning calorimetry, water absorption analysis, electron spectroscopy for chemical analysis, static contact angle analysis, and in vitro platelet adhesion experiments. The effects of ion incorporation on the morphology, surface properties and blood compatibility are discussed. Unlike MDI-based Pellethane, all H12MDI-based polyurethanes are not composed of crystalline hard segment domain but are amorphous. The ionic polyurethanes exhibit a smaller fraction of hydrogen-bonded carbonyl groups, poorer phase separation, smaller fraction of PTMO residing at the surface, and smaller contact angle; however, significant higher water absorption value than H-M-BD and Pellethane. The in vitro platelet adhesion experiments indicated that ion incorporation, especially for carboxylate, significantly reduced the number and the degree of activation of the adherent platelets.     

Novel polyisobutylene/polydimethylsiloxane bicomponent networks: III. Tissue compatibility

The tissue biocompatibility of a series of novel rubbery polyisobutylene (PIB)/polydimethylsiloxane (PDMS) bicomponent networks was investigated by in vivo implantation into rats. Bicomponent networks of varying composition (PIB wt%/PDMS wt% = 70/30, 50/50, 35/65) as well as a standard polyethylene control were implanted intraperitoneally. After eight weeks the implants and surrounding tissue were removed for histological evaluation. In all scoring categories (i.e. collagen thickness, fibrous tissue orientation, collagen deposition in muscle tissue, lymphocyte infiltration, angiogenesis) the PIB/PDMS bicomponent network implants elicited either less or similar tissue and cellular response than polyethylene. To determine which implant elicited the least tissue and cellular response overall, a weighted score including collagen thickness, lymphocyte infiltration, and angiogenesis was calculated for each implant. According to these preliminary investigations, PIB/PDMS bicomponent networks are suitable for implant applications.     

Properties and Phase Structure of Polycaprolactone‐Based Segmented Polyurethanes with Varying Hard and Soft Segments: Effects of Processing Conditions

A series of segmented polycaprolactone polyurethane (PU) polymers is synthesized. One set of polymers ranges in composition from 0 to 100 wt% hard segments (HSs). The syntheses are carried out in solution and the polymers are melt‐processed by compression molding. Another subset of polymers is formed in bulk from a blocked isocyanate prepolymer. The blocked polymer's thermal and mechanical properties are compared with the melt‐processed materials. The emphasis in this paper is on the effects of varying the chemical structures of the PUs on their phase structures and physical cross‐linking due to nanocrystalline hard domains. The thermal properties indicate that nanophase separation and the formation of hard domains occur at HS contents above ≈8 wt%. Property differences resulting from varying the hard segment amounts are directly related to differences in morphology at the nanoscale. Atomic force microscopy images show that the best elastomeric mechanical properties are found when nanocrystallites are 4–5 nm in size.     

Thermo-Sensitive Hydrogels Based on Interpenetrating Polymer Networks Made of Poly(N-isopropylacrylamide) and Polyurethane

A series of interpenetrating polymer networks (IPNs) of vinyl-terminated polyurethane (VTPU) and poly(N-isopropylacrylamide) (PNIPAAm) was prepared by free radical polymerization. The effects of IPN composition and cross-linking density on the thermo-responsive and mechanical properties have been studied in terms of particle size, dynamic mechanical thermal properties, transmittance, swelling and de-swelling behavior and water transport mechanism. Results showed that the swelling ability of hydrogels increased over four orders of magnitude in terms of diffusivity, and phase transition became faster with increasing N-isopropylacrylamide (NIPAAm) content. Regarding the mechanical reinforcement of swollen gel, a significant increase in compression properties has been obtained by forming IPNs with polyurethane, which was tailor-made depending on the IPN composition and structure of polyurethane. Furthermore, a cross-linking density increase in the NIPAAm domain augmented rubbery modulus, decreased water swelling and increased water deswelling of the IPNs.     

Hydrogels based on poly(ethylene oxide) and poly(tetramethylene oxide) or poly(dimethyl siloxane). III. In vivo biocompatibility and biostability

To investigate the effects of polymer chemistry and topology (linear or graft copolymer) on in vivo biocompatibility and biostability based on cage implant system, various hydrogels, composed of short hydrophilic [polyethylene oxide (PEO)] and hydrophobic block, were prepared by polycondensation reaction. Poly(tetramethylene oxide) (PTMO) or poly(dimethyl siloxane) (PDMS) was chosen as a hydrophobic block because of their wide utilization as a biomaterial. By using the specimens retrieved from rats killed after 1, 2, 3, 5, and 7 weeks' implantation, cellular and material responses were assessed. Most hydrogels showed a comparable value of macrophage density to Pellethane(R), control polymer, whereas they did significantly lower foreign body giant cell (FBGC) density and coverage because of the presence of PEO. However, PEO block length and polymer topology did not affect macrophage adhesion and FBGC formation in our polymer composition. The hydrogel based on PDMS alone showed significantly lower macrophage density and FBGC density than Pellethane(R), indicating that PDMS plays a role in inhibiting cellular adhesion. The results obtained from gel permeation chromatography curve and Fourier transform infrared spectra exhibited that all the polymers were susceptible to oxidative degradation in vivo. Although Pellethane(R) revealed surface degradation by 5 weeks in vivo, hydrogels showed rapid degradation in the bulk within 2 weeks because of the penetration of oxidative chemicals released from phagocytic cells into PEO domain of phase-separated hydrogels. The more significant degradation was observed in the hydrogels with longer PEO block and PTMO as a hydrophobic block instead of PDMS. It was evident that the minor degradation could be achieved by grafting PEO and adopting PDMS as a hydrophobic block in the hydrogel.     

Interpenetrating polymer networks of poly(dimethylsiloxane) with polystyrene,polybutadiene and poly(glycerylpropoxytriacrylate)

The synthesis of full and semi interpenetrating networks (IPNs) based on poly(dimethy1-siloxane) (PDMS)/polystyrene, PDMS/polybutadiene and PDMS/poly(glycerylpropoxytriacry-late) 1

1 Glycerylpropoxytriacrylate (GFTA):

is described. PDMS was used as host polymer in most cases. PDMS networks were prepared with two prepolymers having different number-average molecular weights between junctions, M?_c = 15 · l0³ and M?_c = 75 · l0³. Physical properties of IPN samples such as stress-strain behaviour, swelling and glass transition temperature (T_g) were examined. IPNs of both PDMS/polystyrene and PDMS/poly(glycerylpropoxytriacrylate) exhibit superior mechanical and elastomeric properties with respect to pure PDMS network. Most of the IPN systems studied in this work display two T_gs and indicate phase separation.     

Bioinspired Strategy to Reinforce Hydrogels via Cooperative Effect of Dual Physical Cross‐Linkers

Many biological tissues including cartilage and tendons are composed of polymeric hydrogels, which exhibit high toughness and rapid self‐recovery. However, developing hydrogels with both high toughness and rapid recovery remains a challenge. Inspired by the nacre of abalone shell, two non‐covalent cross‐linkers (Al³⁺ and diethylenetriamine [DETA]) with different relaxation times are introduced into a polyacrylic acid network. Compared with mono cross‐linked hydrogels, the dual physical cross‐linked hydrogel exhibits both high toughness (work of extension at fracture up to 8.0 MJ m^?3) and rapid self‐recovery ability without loss of extensibility. Strong carboxylate‐DETA ionic cross‐links with longer relaxation time endow the hydrogels with high strength and help to localize the reformation of carboxylate‐Al³⁺ coordinate bonds; weak carboxylate‐Al³⁺ coordinate bonds with shorter relaxation time dissociate and reform to dissipate energy. Therefore, the hydrogels can dissipate massive energy effectively without any residual strain. More notably, the toughness and hysteresis of hydrogels can be completely recovered in 20 min. This finding unravels a new path to reinforce the hydrogels by the cooperation of different non‐covalent interactions, which can be applied in more material systems.     

Hydrogels based on poly(ethylene oxide) and poly(tetramethylene oxide) or poly(dimethyl siloxane): synthesis, characterization, in vitro protein adsorption and platelet adhesion

In vitro protein adsorption, platelet adhesion and activation on new hydrogel surfaces, composed of poly(ethylene oxide) (PEO) and poly(tetramethylene oxide) (PTMO) or poly(dimethyl siloxane) (PDMS), were investigated. By varying PEO length (MW = 2000 or 3400), hydrophobic components (PTMO or PDMS) or polymer topology (block or graft copolymers), various physical hydrogels were produced. Their structures were verified by 1H NMR and ATR-IR and the molecular weights were determined by gel permeation chromatography. The hydrogels were soluble in a variety of organic solvents, while absorbed a significant amount of water with preserved three-dimensional structure by physical crosslinking. The dynamic contact angle measurement revealed that the surface hydrophilicity increased by incorporating longer PEO, PEO grafting, and adopting PDMS as a hydrophobic segment instead of PTMO. It was observed from in vitro protein adsorption study that the hydrogels exhibited significantly lower adsorption of human serum albumin (HSA), human fibrinogen (HFg), and IgG, when compared with Pellethane, a commercial polyurethane taken as a control. The hydrogels were attractive for HSA but not sensitive to HFg and IgG. And more than 65% of the proteins detected on the surfaces of the hydrogels were reversibly detached by being treated with an SDS solution. It was evident that the hydrogels synthesized in this study were much more resistant to platelet adhesion than the control, which might depend on the composition of proteins adsorbed on the surfaces and their degree of denaturation. Among the hydrogels tested, PEO3,4kPDMS exhibited albumin-rich and platelet-resistant surfaces, implying a potential candidate for biomaterial.     

Investigation of Soft Component Mobility in Thermoplastic Elastomers using Homo‐ and Heteronuclear Dipolar Filtered 1H Double Quantum NMR Experiments

Summary: Information about segmental mobility in thermoplastic elastomers was obtained using static ¹H double quantum (DQ) NMR experiments in combination with homo‐ and heteronuclear dipolar filters, e.g. ¹³C editing of ¹H DQ buildup curves. Block copolymers of poly(butylene terephthalate) (PBT) as hard blocks and poly(tetramethylene oxide) (PTMO) as soft blocks (PBT‐block‐PTMO) were investigated by varying composition and block length. By simulation of the DQ buildup curves, residual dipolar couplings and with this the average order parameter were deduced for the mobile PTMO blocks which are sensitive to the segmental mobility responsible for the viscoelastic properties of thermoplastic elastomers. A strong correlation exists between residual dipolar coupling and composition. Furthermore, the average order parameter correlates linearly with the amount of PTMO in a PTMO‐rich phase as determined in previous studies. Additionally, ¹H transverse magnetization relaxation measurements revealed a direct correlation between the effective T₂ relaxation time of the soft domain and the composition of the thermoplastic elastomers.

Correlation of the average order parameter vs. the fraction of PTMO in the PTMO‐rich phase.     

Importance of viral genomic composition in modulating glycoprotein content on the surface of influenza virus particles

Despite progress in our knowledge of the internal organisation of influenza virus particles, little is known about the determinants of their morphology and, more particularly, of the actual abundance of structural proteins at the virion level. To address these issues, we used cryo-EM to focus on viral (and host) factors that might account for observed differences in virion morphology and characteristics such as size, shape and glycoprotein (GP) spike density. Twelve recombinant viruses were characterised in terms of their morphology, neuraminidase activity and virus growth. The genomic composition was shown to be important in determining the GP spike density. In particular, polymerase gene segments and especially PB1/PB2 were shown to have a prominent influence in addition to that for HA in determining GP spike density, a feature consistent with a functional link between these virus components important for virus fitness.     

Chiral pH‐Responsive Amphiphilic Polymer Co‐networks: Preparation,Chiral Recognition,and Release Abilities

Novel amphiphilic polymer co‐networks (APCNs), poly(N‐acryloyl‐L ‐alanine)‐l‐polydimethylsiloxane (denoted as PNAA‐l‐PDMS), are prepared, and exhibit remarkable pH‐responsiveness, chiral‐recognition, and enantioselective‐release abilities. The APCNs are prepared by free‐radical copolymerization starting from N‐acryloyl‐L ‐alanine (NAA) and methacrylate‐terminated poly(dimethylsiloxane) (M‐PDMS) as co‐(macro)monomers. The APCNs show pronounced pH‐sensitivity, evidenced by a reversible swelling–deswelling transition upon a cyclicly altering pH. The chiral co‐networks are applied for enantioselective recognition and release. A maximum adsorption is achieved towards D ‐proline (61%), whereas for L ‐proline, it is only 10%. More interestingly, the release for the L ‐proline is 90%, whereas for the D ‐proline, only 70% is released.