Starch-based isocyanate- and non-isocyanate polyurethane hybrids: A review on synthesis, performance and biodegradation.

The challenges related to the persistence of plastics in natural ecosystems fostered strong interest in developing biodegradable bioplastics. Among natural biopolymers, starch gained both academic and industrial interest owing to its impressive physicochemical properties. The use of starch in production of polyurethane (PU) composites not only yields PUs with outstanding mechanical properties but also makes the final PU products biodegradable. The hydrophilic nature of starch limits its dispersion in hydrophobic PU polymers, although it is a significant benefit in creating starch-embedded non-isocyanate polyurethane (NIPU) composites. We present a comprehensive overview to highlight important strategies that are used to improve the compatibility of starch with various PU matrices. This review also gives an overview of the recent advances in the synthesis of starch-NIPU hybrids. Moreover, we aim to deliver critical insight into strategies that boost the biodegradation characteristics of PUs along with a discussion on various methods to assess their biodegradation.

In vitro oxidative stability of high strength siloxane poly(urethane-urea) elastomers based on linked-macrodiol.

In vitro oxidative stability of two siloxane poly(urethane urea)s synthesized using 4,4'-methylenediphenyl diisocyanate (in SiPUU-1) and Isophorone diisocyanate (in SiPUU-2) linked soft segment was evaluated using 20% H2 O2 and 0.1 mol/L CoCl2 solution at 37°C under 150% strain. Commercially available siloxane polyurethane (Elast-Eon™ 2A) and polyether polyurethane (ChronoThane P™ 80A) were used as negative and positive controls, respectively. ChronoSil™ 80A was included as another commercially available polycarbonate polyurethane. Scanning electron microscopic (SEM) examinations, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and molecular weight reduction revealed the extensive degradation of ChronoThane P™ 80A after 90 days while SiPUU-1, SiPUU-2 and Elast-Eon™ 2A showed no noticeable surface degradation. ChronoSil™ 80A showed degradation in both soft and hard segments. Tensile testing was carried out only on unstrained polyurethanes for 90 days. ChronoThane P™ 80A showed 35% loss in ultimate tensile strength and it was only 13-14% for SiPUU-1 and Elast-Eon™ 2A. However, the tensile strength of ChronoSil™ 80A was not significantly affected. The results of this study proved that SiPUU-1 possess oxidative stability comparable with Elast-Eon™ 2A. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2557-2565, 2019.

Investigation of oil distribution in spray-dried chia seed oil microcapsules using synchrotron-FTIR microspectroscopy.

In this study, chia seed oil (CSO) microcapsules were produced using three types of shell materials, including chia seed protein (CPI), chia seed gum (CSG) and CPI-CSG complex coacervates. Synchrotron-Fourier transform infrared (S-FTIR) microspectroscopy was used to investigate the effect of shell materials on the distribution of CSO both on the surface and in the interior of the solid microcapsules. S-FTIR measurements were carried out in macroscopic attenuated total reflection (macro ATR) and transmission modes, to determine the surface lipid and the encapsulated lipid fractions, respectively. The amounts of lipid and protein distributed on the surface and in the interior of the microcapsules were compared based on the average spectra extracted from S-FTIR chemical images obtained from each type of the microcapsules. The unsaturated fatty acids (UFAs) to total oil ratios in all the three types of the microcapsules were closely similar to the original non-processed CSO, suggesting an effective encapsulation and thereby shielding protection of UFAs from oxidative damage during microencapsulation process. The type of the shell materials was found to affect the distribution of CSO on the surface and within the microcapsules. The complex coacervation based microcapsules had a significantly lower oil content (∼2% w/w) on the surface compared to those observed for the other two types of microcapsules (>5%, w/w).

Morphology and surface properties of high strength siloxane poly(urethane-urea)s developed for heart valve application.

A series of siloxane poly(urethane-urea) (SiPUU) were developed by incorporating a macrodiol linked with a diisocyanate to enhance mixing of hard and soft segments (SS). The effect of this modification on morphology, surface properties, surface elemental composition, and creep resistance was investigated. The linked macrodiol was prepared by reacting α,ω-bis(6-hydroxyethoxypropyl) poly(dimethylsiloxane)(PDMS) or poly(hexamethylene oxide) (PHMO) with either 4,4'-methylenediphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), or isophorone diisocyanate (IPDI). SiPUU with PHMO-MDI-PHMO and PHMO-IPDI-PHMO linked macrodiols showed enhanced creep resistance and recovery when compared with a commercial biostable polyurethane, Elast-Eon™ 2A. Small and wide-angle X-ray scattering data were consistent with significant increase of hydrogen bonding between hard and SS with linked-macrodiols, which improved SiPUU's tensile stress and tear strengths. These SiPUU were hydrophobic with contact angle higher than 101° and they had low water uptake (0.7%·w/w of dry mass). They also had much higher siloxane concentration on the surface compared to that in the bulk. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 112-121, 2019.

Flexible starch-polyurethane films: Effect of mixed macrodiol polyurethane ionomers on physicochemical characteristics and hydrophobicity.

One of the most critical limitations in synthesizing starch-polyurethane (PU) hybrid materials is their microphase separation caused by physical incompatibility. This paper reports that the physical incompatibility and microphase separation between starch and PU can be overcome by using specifically designed anionic poly(ether-ester) polyurethane (AEEPU). The AEEPU was synthesised by preparing isocyanate (NCO)-terminated prepolymer using Isophorone diisocyanate (IPDI), 2,2-bis(hydroxymethyl)propionic acid (BMPA), poly (ethylene glycol) (PEG) and polycaprolactone (PCL). This AEEPU was physically mixed with glycerol plasticized high amylose starch (HAGS) at HAGS to AEEPU mass ratios of 90/10, 80/20, 70/30, 60/40, 50/50. Higher AEEPU content in HAGS-AEEPU increased surface hydrophobicity and elasticity while the Young's modulus remained unaffected. HAGS-AEEPU film at 50:50 ratio was comparable to LDPE film in terms of elongation at break (187%), Young's modulus (383 MPa), and contact angle (112°) and good transparency. These starch-PU films are expected to find increased application as biodegradable packaging materials.

Development of high strength siloxane poly(urethane-urea) elastomers based on linked macrodiols for heart valve application.

Mixed macrodiol based siloxane poly(urethane-urea)s (SiPUU) having number average molecular weights in the range 87-129 kDa/mol were synthesized to give elastomers with high tensile and tear strengths required to fabricate artificial heart valves. Polar functional groups were introduced into the soft segment to improve the poor segmental compatibility of siloxane polyurethanes. This was achieved by linking α,ω-bis(6-hydroxyethoxypropyl) poly(dimethylsiloxane) (PDMS) or poly(hexamethylene oxide) (PHMO) macrodiols with either 4,4'-methylenediphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI) prior to polyurethane synthesis. The hard segment was composed of MDI, and a 1:1 mixture of 1,3-bis(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane and 1,2-ethylene diamine. We report the effect of urethane linkers in soft segments on properties of the SiPUU. PHMO linked with either MDI or IPDI produced SiPUU with the highest tensile and tear strengths. Linking PDMS hardly affected the tensile strength; however, the tear strength was improved. The stress-strain curves showed no plastic deformation region typically observed for conventional polyurethanes indicating good creep resistance. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1712-1720, 2018.

Thermoplastic starch-nanohybrid films with polyhedral oligomeric silsesquioxane.

Thermoplastic starch forms packaging films that have low gas permeability, but they are more permeable to water vapour and they are attacked by water. Our approach was to create surface and internal localised hydrophobicity using added reactive nano-materials to form nano-silica hybrids with emphasis on enhancing surface water resistance. Functionalization was via epoxy-POS, that were further linked to hydrophobic erucamide or an amphiphilic poly(oxyethylene-co-oxypropylene) mono-amine. High amylose thermoplastic starch was combined with mono-functionalised hepta-isobutyl polyhedral oligomeric silsesquioxane (POS). POS modified thermoplastic starch increased water resistance of TPS film. Wettability kinetics was a function of two distinct mechanisms each with independent linear behaviour. Surface water resistance increased and is proposed to be due to preferential location of the POS derivatives at the surface with associated increase of hydrophobicity due a surface change.

Flexible starch-polyurethane films: Physiochemical characteristics and hydrophobicity.

Starch-polyurethane (PU) composite films with improved mechanical and hydrophobic properties were developed in this work. A simple and effective microwave-aided starch gelatinisation instrument was used to prepare glycerol plasticized high amylose starch (HAGS) material. Polyethylene glycol-isocyanate (PEG-iso) linker was prepared by reacting PEG 1000 with hexamethylene diisocyanate (HMDI). PEG-iso linker was then grafted into HAGS forming three dimensional urethane networks (PEG-PU). HAGS-PEG-PU composite blends were prepared and dried at ambient temperature to obtain HAGS-PEG-PU films. The mechanical properties and hydrophobicity (as contact angle, CA) of the HAGS-PEG-PU films were measured and analysed. Fourier transform infrared spectroscopy showed good grafting of PEG-iso into starch structure. Increase of PEG-iso concentration up to 20% (w/w) improved the molecular mixing and interpenetration between the starch and PEG-PU. The HAGS-PEG-PU films had improved hydrophobicity as indicated by CA values ranging from 51 to 110°and very high flexibility as evidenced from elongation at break (εB) values from 17 to 1000%. The HAGS-PEG-PU film formulation containing 20% (w/w) PEG-iso provided the best flexibility (εB>1000%) and hydrophobicity (CA>110°).

Physicochemical and thermal characteristics of Australian chia seed oil.

Physicochemical and thermal characteristics of Australian chia seed oil (CSO) were studied. The specific gravity, viscosity and refractive index of CSO at ambient temperature were 0.93, 43.2mPa.s and 1.48, respectively. The acid, peroxide, saponification and iodine values and unsaponifiable matter content of CSO were 2.54gKOH/kg oil, 4.33meqO2/kg oil, 197gKOH/kg oil, 204gI2/kg oil and 1.12%, respectively. α-linolenic acid is the most abundant fatty acid comprising (64.39% of total oil) followed by linoleic acid (21.46%), while saturated fatty acid content is less than 10%. This CSO contained twelve triacylglycerols (TAGs) out of which trilinolenin (αLnαLnαLn) was the most abundant comprising 33.2% of total TAG. Melting point and melting enthalpy of CSO were -34°C and 77.48J/g, respectively. CSO remained stable up to 300°C with negligible degradation. Due to these physicochemical and thermal properties, CSO is an excellent source of essential fatty acids for food industries.

Effect of extraction temperature on composition, structure and functional properties of flaxseed gum.

Flaxseed gum (FG) was extracted at four different temperatures (30, 50, 70 and 90°C). Chemical composition and structural features of FG extracted at different temperatures were investigated to determine the effect of temperature. Content of acidic monosaccharides and denatured protein increased with increasing FG extraction temperature. The ratio of neutral to acidic monosaccharides decreased from 6.7 to 5.7 as the extraction temperature was increased from 30 to 90°C. Physiochemical and functional properties, including zeta-potential, surface morphology, emulsifying activity index (EAI) and emulsion stability index (ESI), water absorption capacity (WAC) and fat absorption capacity (FAC) of FG samples, were also investigated as a function of extraction temperature. EAI and WAC of FG samples reduced significantly with rise in extraction temperature. Our study suggests that FG extracted at different temperatures may be specifically targeted for different applications, such as for emulsification or gel formation in food systems.

Physicochemical and functional properties of protein isolate produced from Australian chia seeds.

Protein was isolated from Australian chia seeds and converted to powders using spray, freeze and vacuum drying methods, to investigate the effect of drying methods on physicochemical and functional attributes of chia-seed protein isolate (CPI). It was found that there was no significant difference in the proximate composition; however vacuum dried CPI (VDCPI) had the highest bulk density and oil absorption capacity, whereas spray dried powder (SDCPI) demonstrated the highest solubility, water absorption capacity and lowest surface hydrophobicity. Solubility of all powders was higher at elevated temperature and alkaline pH. Foaming capacity and foam stability of CPI were found to increase with increasing pH and protein concentration. SDCPI was the least denatured and VDCPI the most denatured, demonstrating the poorest solubility and foaming properties of the latter. These findings are expected to be useful in selection of a drying process to yield chia seed protein powders with more desirable functionality.

Microencapsulation of chia seed oil using chia seed protein isolate-chia seed gum complex coacervates.

Chia seed oil (CSO) microcapsules were produced by using chia seed protein isolate (CPI)-chia seed gum (CSG) complex coacervates aiming to enhance the oxidative stability of CSO. The effect of wall material composition, core-to-wall ratio and method of drying on the microencapsulation efficiency (MEE) and oxidative stability (OS) was studied The microcapsules produced using CPI-CSG complex coacervates as wall material had higher MEE at equivalent payload, lower surface oil and higher OS compared to the microcapsules produced by using CSG and CPI individually. CSO microcapsules produced by using CSG as wall material had lowest MEE (67.3%) and oxidative stability index (OSI=6.6h), whereas CPI-CSG complex coacervate microcapsules had the highest MEE (93.9%) and OSI (12.3h). The MEE and OSI of microcapsules produced by using CPI as wall materials were in between those produced by using CSG and CPI-CSG complex coacervates as wall materials. The CSO microcapsules produced by using CPI-CSG complex coacervate as shell matrix at core-to-wall ratio of 1:2 had 6 times longer storage life compared to that of unencapsulated CSO. The peroxide value of CSO microcapsule produced using CPI-CSG complex coacervate as wall material was <10meq O2/kg oil during 30 days of storage.

Molecular and functional characteristics of purified gum from Australian chia seeds.

Chia seed gum (CSG) was extracted from the seed coat of Salvia hispanica, purified in the laboratory and its chemical composition and functional properties were investigated. CSG was found to comprise 93.8% carbohydrate consisting of xylose, glucose, arabinose, galactose, glucuronic acid and galacturonic acid as monosaccharide units. The presence of uronic acids was reflected in the anionic behavior of the CSG solution over a wide range of pH (≥ 1.8). The solubility of CSG increased slightly with temperature and pH of the aqueous medium. CSG was able to resist pyrolytic decomposition at temperatures well in excess of 250 °C, and exhibited a high water holding capacity (23 times of its own weight). The surface activity and emulsifying properties of CSG were found to be either superior or comparable to other common gums and industrial polysaccharides indicating the potential of CSG as an effective thickener and stabilizer of processed foods.

Rheological and microstructural properties of the chia seed polysaccharide.

Chia seed polysaccharide (CSP) was extracted from chia (Salvia hispanica) seeds, and its rheological and microstructural properties in aqueous solutions were studied. CSP solution exhibited Newtonian and shear thinning flow patterns depending on shear rate when the concentration was ≤0.06% (w/v). CSP solutions at concentrations >0.06% (w/v) exhibited strong shear thinning behaviour within the shear rate tested (0.001-300s(-1)). The transition from dilute to semi-dilute regime occurred at a critical concentration (C*) of 0.03gdL(-1). The intrinsic viscosity was high (∼16dLg(-1)) and concentration dependence of zero shear viscosity in the semi-dilute regime followed η0∝C(2.7) relationship. The storage modulus (G') was higher than the loss modulus (G″) at all experimental frequencies and their frequency dependence was negligible at all tested concentrations. Apparent shear viscosity was smaller than dynamic complex viscosity at equivalent values of deformation and G' varied with the square of concentration indicating a gel-like behaviour in CSP solutions within 0.02-3.0% (w/v) concentrations. Controlled acid hydrolysis of purified CSP yielded various low molecular fractions with fairly uniform polydispersity giving a Mark-Houwink-Sakurada relationship of intrinsic viscosity equaling to 1.52×10(-4) (molecular weight)(0.803) (dLg(-1)).

High Modulus Biodegradable Polyurethanes for Vascular Stents: Evaluation of Accelerated in vitro Degradation and Cell Viability of Degradation Products.

We have recently reported the mechanical properties and hydrolytic degradation behavior of a series of NovoSorb™ biodegradable polyurethanes (PUs) prepared by varying the hard segment (HS) weight percentage from 60 to 100. In this study, the in vitro degradation behavior of these PUs with and without extracellular matrix (ECM) coating was investigated under accelerated hydrolytic degradation (phosphate buffer saline; PBS/70°C) conditions. The mass loss at different time intervals and the effect of aqueous degradation products on the viability and growth of human umbilical vein endothelial cells (HUVEC) were examined. The results showed that PUs with HS 80% and below completely disintegrated leaving no visual polymer residue at 18 weeks and the degradation medium turned acidic due to the accumulation of products from the soft segment (SS) degradation. As expected the PU with the lowest HS was the fastest to degrade. The accumulated degradation products, when tested undiluted, showed viability of about 40% for HUVEC cells. However, the viability was over 80% when the solution was diluted to 50% and below. The growth of HUVEC cells is similar to but not identical to that observed with tissue culture polystyrene standard (TCPS). The results from this in vitro study suggested that the PUs in the series degraded primarily due to the SS degradation and the cell viability of the accumulated acidic degradation products showed poor viability to HUVEC cells when tested undiluted, however particles released to the degradation medium showed cell viability over 80%.

Enhanced efficiency fertilisers: a review of formulation and nutrient release patterns.

Fertilisers are one of the most important elements of modern agriculture. The application of fertilisers in agricultural practices has markedly increased the production of food, feed, fuel, fibre and other plant products. However, a significant portion of nutrients applied in the field is not taken up by plants and is lost through leaching, volatilisation, nitrification, or other means. Such a loss increases the cost of fertiliser and severely pollutes the environment. To alleviate these problems, enhanced efficiency fertilisers (EEFs) are produced and used in the form of controlled release fertilisers and nitrification/urease inhibitors. The application of biopolymers for coating in EEFs, tailoring the release pattern of nutrients to closely match the growth requirement of plants and development of realistic models to predict the release pattern of common nutrients have been the foci of fertiliser research. In this context, this paper intends to review relevant aspects of new developments in fertiliser production and use, agronomic, economic and environmental drives for enhanced efficiency fertilisers and their formulation process and the nutrient release behaviour. Application of biopolymers and complex coacervation technique for nutrient encapsulation is also explored as a promising technology to produce EEFs.

Effect of spatial distribution of wax and PEG-isocyanate on the morphology and hydrophobicity of starch films.

This study proposes a novel method for improving surface hydrophobicity of glycerol plasticized high amylose (HAG) films. We used polyethylene glycol isocyanate (PEG-iso) crosslinker to link HAG and three natural waxes (beeswax, candelilla wax and carnauba wax) to produce HAG+wax+PEG-iso films. The spatial distributions of wax and PEG-iso across the thickness of these films were determined using Synchrotron-based Fourier transform infrared spectroscopy. The hydrophobicity and surface morphology of the films were determined using contact angle (CA) and scanning electron microscopic measurements, respectively. The distribution patterns of wax and the PEG-iso across the thickness of the film, and the nature of crystalline patterns formed on the surface of these films were found to be the key factors affecting surface hydrophobicity. The highest hydrophobicity (CA >90°) was created when the PEG-iso was primarily distributed in the interior of the films and a hierarchical circular pinnacle structure of solidified wax was formed on the surface.

Properties and in vitro evaluation of high modulus biodegradable polyurethanes for applications in cardiovascular stents.

This study examined the suitability of a family of biodegradable polyurethanes (PUs) NovoSorb developed for the vascular stent application. These segmented PUs are formulated to be biodegradable using degradable polyester and PU blocks. A series of PUs comprising different hard segment weight percentage ranging from 60 to 100 were investigated. The mechanical properties of the PUs were evaluated before and after gamma sterilization to assess their suitability for vascular implants. The real-time (PBS/37°C/pH 7.4) hydrolytic degradation studies were carried out under sterile conditions and PU glass transition temperature, molecular weight, and mass loss at 3, 6, and 9 months were determined. The viability and growth of Human Umbilical Vein Endothelial Cells (HUVEC) on PU surfaces were determined to assess the effect of PU degradation. The effect of coating of extracellular matrix (ECM) components on cell viability was also investigated. The study showed that the PUs possess excellent mechanical properties exhibiting high tensile strength (41-56 MPa) and tensile modulus (897-1496 MPa). The PU films maintained mechanical strength during the early phase of the degradation but lost strength at latter stages. The unmodified polymer surface of each PU promotes endothelial cell growth and proliferation, with a HUVEC retention rate of >70%.

Evaluation of in situ curable biodegradable polyurethanes containing zwitterion components.

Porous polyurethane networks containing covalently attached zwitterionic compounds dihydroxypolycaprolactone phosphorylcholine and 1,2-dihydroxy-N,N-dimethylamino-propane sulfonate have been prepared and characterised. Three polymers were prepared by reacting methyl 2,6-diisocyanato hexanoate functionalised D: -glucose as prepolymer A with either polycaprolactone triol alone or with addition of 10 mol% zwitterion as prepolymer B. All polymer compositions were mixed with 10 wt% hydrated gelatin beads. The cured polymers with the gelatin beads showed compression strengths that were still suitable for use in articular cartilage repair. The incorporation of zwitterions yielded more hydrophilic polymers that showed increased water absorption and increased porosity. After four months degradation in phosphate buffered saline, the polymers containing zwitterions had approximately 50% mass loss compared with 30% mass loss for that with polycaprolactone triol alone. All polymers were non-toxic in chondrocyte-based assays. Subcutaneous implantation of these polymers into rats confirmed that the polymers degraded slowly. Only a very mild inflammatory response was observed and the polymers were able to support new, well vascularised tissue formation.

Biodegradable injectable polyurethanes: synthesis and evaluation for orthopaedic applications.

Biodegradable polyurethanes offer advantages in the design of injectable or preformed scaffolds for tissue engineering and other medical implant applications. We have developed two-part injectable prepolymer systems (prepolymer A and B) consisting of lactic acid and glycolic acid based polyester star polyols, pentaerythritol (PE) and ethyl lysine diisocyanate (ELDI). This study reports on the formulation and properties of a series of cross linked polyurethanes specifically developed for orthopaedic applications. Prepolymer A was based on PE and ELDI. Polyester polyols (prepolymer B) were based on PE and dl-lactic acid (PEDLLA) or PE and glycolic acid (PEGA) with molecular weights 456 and 453, respectively. Several cross linked porous and non-porous polyurethanes were prepared by mixing and curing prepolymers A and B and their mechanical and thermal properties, in vitro (PBS/37 degrees C/pH 7.4) and in vivo (sheep bi-lateral) degradation evaluated. The effect of incorporating beta-tricalcium phosphate (beta-TCP, 5 microns, 10 wt.%) was also investigated. The cured polymers exhibited high compressive strength (100-190 MPa) and modulus (1600-2300 MPa). beta-TCP improved mechanical properties in PEDLLA based polyurethanes and retarded the onset of in vitro and in vivo degradation. Sheep study results demonstrated that the polymers in both injectable and precured forms did not cause any surgical difficulties or any adverse tissue response. Evidence of new bone growth and the gradual degradation of the polymers were observed with increased implant time up to 6 months.