Effect of soft segment crystallization and hard segment physical crosslink on shape memory function in antibacterial segmented polyurethane ionomers

The Role of Diisocyanate Structure to Modify Properties of Segmented Polyurethanes

Segmented thermoplastic polyurethanes (PU) were synthetized using a polycarbonatediol macrodiol as a flexible or soft segment with a molar mass of 2000 g/mol, and different diisocyanate molecules and 1,4-butanediol as a rigid or hard segment. The diisocyanate molecules employed are 3,3'-Dimethyl-4,4'-biphenyl diisocyanate (TODI), 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-Methylenebis(phenyl isocyanate) 1-isocyanato-4-[(4-phenylisocyanate)methyl]benzene and 1-isocyanate-4-[(2-phenylisocyanate) methyl]benzene (ratio 1:1) (MDIi), isophorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). The polyurethanes obtained reveal a wide variation of microphase separation degree that is correlated with mechanical properties. Different techniques, such as DSC, DMA, and FTIR, have been used to determine flexible-rigid segment phase behavior. Mechanical properties, such as tensile properties, Shore D hardness, and "compression set", have been determined. This work reveals that the structure of the hard segment is crucial to determine the degree of phase miscibility which affects the resulting mechanical properties, such as tensile properties, hardness, and "compression set".

A Synthetic Overview of Preparation Protocols of Nonmetallic, Contact-Active Antimicrobial Quaternary Surfaces on Polymer Substrates

Antibacterial surfaces have been researched for more than 30 years and remain highly desirable. In particular, there is an interest in providing antimicrobial properties to commodity plastics, because these, in their native state, are excellent substrates for pathogens to adhere and proliferate on. Therefore, efficient strategies for converting surfaces of commodity plastics into contact-active antimicrobial surfaces are of significant interest. Many systems have been prepared and tested for their efficacy. Here, the synthetic approaches to such active surfaces are reviewed, with the restriction to only include systems with tested antibacterial properties. The review focuses on the synthetic approach to surface functionalization of the most common materials used and tested for biomedical applications, which effectively has limited the study to quaternary materials. For future developments in the field, it is evident that there is a need for development of simple methods that permit scalable production of active surfaces. Furthermore, in terms of efficacy, there is an outstanding concern of a lack of universal antimicrobial action as well as rapid deactivation of the antibacterial effect through surface fouling.

Fabrication of Au Nanoparticle Arrays on Flexible Substrate for Tunable Localized Surface Plasmon Resonance

In this work, Au nanoparticle (AuNP) arrays on shape memory polyurethane (SMPU) substrates serve as flexible materials for tunable localized surface plasmon resonance (LSPR). AuNP arrays prepared by diblock copolymer self-assembly are transferred from rigid silicon wafers onto flexible SMPU substrates with ultrasonic treatment rather than peeling off directly. The resultant AuNP array SMPU films have excellent mechanical properties and stable thermodynamic properties. The LSPR arising from AuNP arrays is increased by negative bending on SMPU substrates, whereas the LSPR is decreased by positive bending. Besides, upon uniaxial tension, the vertical LSPR is increased first then decreased, whereas the parallel LSPR is similar, resulting in the overall LSPR of AuNP arrays being increased first and then decreased with the mechanical uniaxial tension of SMPU. Moreover, the resultant AuNP array SMPU films exhibit excellent flexibility, stability, and homogeneity in practical surface-enhanced Raman scattering (SERS) application. This approach of incorporating AuNP arrays on SMPU substrates for tuning plasmonic properties have great potential applications in SERS, fluorescence enhancement, and newly optoelectronic materials.

Computational development and validation of a representative MDI-BDO-based polyurethane hard segment model

Segmented polyurethanes show extraordinary physicochemical properties, mainly owing to the nature and the chemistry of the hard segment domains. There are yet many inexplicable physiochemical properties of MDI-BDO-based hard polyurethane segments such as the geometry, cis-trans isomerism, electronic structure, chemical reactivity, the inter-hard-segment interactions, and the photo-response. In the present study, it was attempted to develop and validate a model system that would facilitate further research on the structural and chemical properties of the MDI-BDO hard segments. It was found that the trans isomer of urethane bond is more stable than the cis isomer, and it is argued here that thermal transformation from trans to cis not possible due to the high rotational energy barrier. The differences between the calculated IR spectra of the cis and trans isomers are proposed as a powerful differentiation tool. The calculated Fukui indices show that cis and trans isomers are different in their chemical reactivity. The findings of the present study suggest intermolecular and intramolecular pi-stacking and highly plausible two significant types of hydrogen bond types between hard segments. In the present study, a model system for MDI-BDO hard segment was developed and successfully validated via computational experiments. Further calculations done with the new model provided an indispensable understanding of the structure, cis-trans isomerism, reactivity, and intermolecular interactions of the MDI-BDO hard segments. The proposed model can be further improved in the future by incorporating suitable soft segments. In summary, the model system developed and validated in the present study has provided new opportunities to understand and further study the structural and chemical features of the hard segments of the MDI-BDO-based polyurethane.

Stimuli-Responsive Graphene Nanohybrids for Biomedical Applications

Stimuli-responsive materials, also known as smart materials, can change their structure and, consequently, original behavior in response to external or internal stimuli. This is due to the change in the interactions between the various functional groups. Graphene, which is a single layer of carbon atoms with a hexagonal morphology and has excellent physiochemical properties with a high surface area, is frequently used in materials science for various applications. Numerous surface functionalizations are possible for the graphene structure with different functional groups, which can be used to alter the properties of native materials. Graphene-based hybrids exhibit significant improvements in their native properties. Since functionalized graphene contains several reactive groups, the behavior of such hybrid materials can be easily tuned by changing the external conditions, which is very useful in biomedical applications. Enhanced cell proliferation and differentiation of stem cells was reported on the surfaces of graphene-based hybrids with negligible cytotoxicity. In addition, pH or light-induced drug delivery with a controlled release rate was observed for such nanohybrids. Besides, notable improvements in antimicrobial activity were observed for nanohybrids, which demonstrated their potential for biomedical applications. This review describes the physiochemical properties of graphene and graphene-based hybrid materials for stimuli-responsive drug delivery, tissue engineering, and antimicrobial applications.

Bioinspired Fabrication of Polyurethane/Regenerated Silk Fibroin Composite Fibres with Tubuliform Silk-Like Flat Stress⁻Strain Behaviour

Tubuliform silk is one of the seven different types of spider silks, which is well known for its unique tensile behaviour with Flat Tensile Stress⁻Strain (FTSS) curve. It is found that anisotropic microstructure of β-sheets is responsible for this property. In recent years, bioinspired approaches to engineer fibres supported by modern manufacturing systems have been attracting considerable interest. The present paper aims to investigate a strategy to biomimic the FTSS behaviour of tubuliform silk in synthetic polymer composite fibres by blending polyurethane (PU) and regenerated silk fibroin (RSF) at different ratios. Wet spinning of composite fibres results in the reconstruction of β-sheets in the synthetic fibre matrix. PU/RSF composite fibre at a ratio of 75/25 produce a tensile curve with FTSS characteristics. Secondary structural changes in RSF and interchain directions of β-sheets within the fibre are studied using Fourier Transform Infra-red (FTIR) spectroscopy and Transmission Electron Microscopy (TEM), respectively. Interestingly, results of TEM patterns confirm transverse anisotropic properties of RSF β-sheets. The composite fibres also display tuneable mechanical properties with respect to RSF contents.

Bio-based polyurethane reinforced with cellulose nanofibers: a comprehensive investigation on the effect of interface

Novel bio-based polyurethane (PU) nanocomposites composed of cellulose nanofiller extracted from the rachis of date palm tree and polycaprolactone (PCL) diol based PU were prepared by casting/evaporation. Two types of nanofiber were used: cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs). The mechanical and thermal properties of the nanocomposite films were studied by DMA, DSC, and tensile tests and the morphology was investigated by SEM. Bionanocomposites presented good mechanical properties in comparison to neat PU. While comparing both nanofillers, the improvement in mechanical and thermal properties was more pronounced for the nanocomposites based on CNF which could be explained, not only by the higher aspect ratio of CNF, but also by their better dispersion in the PU matrix. Calculation of the solubility parameters of the nanofiller surface polymers and of the PU segments portend a better interfacial adhesion for CNF based nanocomposites compared to CNC.

Synthesis and characterization of a polyurethane ionene/zinc chloride complex with antibacterial properties

Antibacterial polyurethane ionene/zinc chloride complexes were synthesized and their properties were systematically investigated.

Synthesis and characterization of biobased isosorbide-containing copolyesters as shape memory polymers for biomedical applications

Novel biobased isosorbide-containing copolyesters (PBISI copolyesters) with both biocompatibility and sustainability were synthesized by using commercially available biobased diols and diacids. Due to the presence of itaconate in copolyesters, it can be readily crosslinked by peroxide into a crystallizable network. The structure and thermal properties of PBISI copolyesters were determined by ¹H NMR, FTIR, DSC, and WAXD. The chain composition, melting point and crystallinity of the PBISI copolyesters can be tuned continuously by changing the content of isosorbide. The crosslinked copolyester is demonstrated to be a promising shape memory polymer (SMP) with excellent shape memory properties including shape fixity and shape recovery rate close to 100%. The switching temperatures of PBISI-based SMPs can be tuned between 26 °C and 54 °C by altering the composition of PBISI copolyesters and curing extent. Cell adhesion and proliferation were adopted to evaluate the potential biocompatibility of PBISI-based SMPs, and the results indicated that all the PBISI-based SMPs were essentially noncytotoxic, making them suitable for fabricating biomedical devices.

Triple shape memory effect of star-shaped polyurethane

In this study, we synthesized one type of star-shaped polyurethane (SPU) with star-shaped poly(ε-caprolactone) (SPCL) containing different arm numbers as soft segment and 4,4'-diphenyl methane diisocyanate (MDI) as well as chain extender 1,4-butylene glycol (BDO) as hard segment. Proton nuclear magnetic resonance (1H-NMR) confirmed the chemical structure of the material. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) results indicated that both the melting temperature (Tm) and transition temperature (Ttrans) of SPU decreased with the hard segment composition increase. X-ray diffraction (XRD) results demonstrated that the increase of the crystallinity of SPU following the raised arm numbers endowed a high shape fixity of six-arm star-shaped polyurethane (6S-PU) and a wide melting temperature range, which resulted in an excellent triple-shape memory effect of 6S-PU. The in vitro cytotoxicity assay evaluated with osteoblasts through Alamar blue assay demonstrates that this copolymer possessed good cytocompatibility. This material can be potentially used as a new smart material in the field of biomaterials.

Synthesis and evaluation of novel absorptive and antibacterial polyurethane membranes as wound dressing

Preparation and evaluation of new polyurethane membranes for wound dressing application was considered in this work. The membranes were prepared through amine curing reaction of epoxy-terminated polyurethane prepolymers and an antibacterial epoxy-functional quaternary ammonium compound (glycidyltriehtylammonium chloride, GTEACl. To render the prepared membranes to be highly absorptive of wound exudates, poly (ethylene glycol) polyols were introduced into the polyurethane networks. Evaluation of biocompatibity via both MTT assay and direct contact with two different cell lines (fibroblast and epidermal keratinocytes) reveled that membranes with appropriate loading of GTEACl showed proper biocompatibility. Promising antibacterial activity of the prepared membranes against Staphylococcus aureus and Escherichia coli bacteria was confirmed by both agar diffusion and shaking flask methods. The membranes with balanced crosslink density and ionic groups' concentration possessed appropriate hydrophilicity and water vapor transmission rate; therefore, they could prevent the accumulation of exudates and decrease the surface inflammation in the wounded area.

Synthesis and characterization of antibacterial polyurethane coatings from quaternary ammonium salts functionalized soybean oil based polyols

In this study, a simple and versatile synthetic approach was developed to prepare bactericidal polyurethane coatings. For this purpose, introduction of both quaternary ammonium salts (QASs), with well-known antibacterial activity, and reactive hydroxyl groups on to the backbone of soybean oil was considered. Epoxidized soybean oil was reacted with diethylamine and the intermediate tertiary amine containing polyol was reacted with two different alkylating agents, methyl iodide and benzyl chloride, to produce MQAP and BQAP, respectively. These functional polyols were reacted with different diisocyanate monomers to prepare polyurethane coatings. Depending on the structure of monomers used for the preparation of polyurethane coatings, initial modulus, tensile strength and elongation at break of samples were in the ranges of 122-339 MPa, 4.6-12.4 MPa and 8.4-46%, respectively. Polyurethane coatings based on isophorone diisocyanate showed proper mechanical properties and adhesion strength (0.41 MPa) for coating application. Study of fibroblast cells interaction with prepared polyurethanes showed promising cells viability in the range of 78-108%. Meanwhile, MQAP based samples with higher concentration of QASs showed better adhesion strength, surface hydrophilicity and antibacterial activity (about 95% bacterial reduction). Therefore, these materials can find applications as bactericidal coating for biomedical devices and implants.

Comparison of phase structures and surface free energy values for the coatings synthesised from linear polyurethanes and from waterborne polyurethane cationomers

WAXS, DSC and AFM methods were employed to compare phase structures of the coatings obtained from waterborne polyurethane cationomers which had been synthesised in the reaction of some diisocyanates (MDI, IPDI, TDI and HDI) with polyoxyethylene glycols (M = 600 and 2,000) and butane1,4-diol or N-methyl- or N-butyldiethanolamine and 2,2,3,3-tetrafluoro-1,4-butanediol. The structures were also analysed of the coatings derived from linear polyurethanes which had been synthesised on the basis of similar raw materials. Better rigidity was found for generally amorphous cationomer coats. Changes were discussed in the surface free energy (SFE) values and in their components, as calculated independently with the use of the van Oss-Good and Owens-Wendt methods. Polyurethane coats turned out more hydrophobic as compared to cationomer ones. In both coat types, fluorine incorporated into cationomers contributed to lower SFE values: from 50 down to about 30 mJ/m(2).