Three-dimensional Polyurethane Research Articles

Theranostic nano-enabled polyurethane eso-sponges coupled to surface enhanced Raman scattering for detection and control of bacteria killing

Herein, a facile approach toward converting a three-dimensional polyurethane sponge (PUS), employed in endoluminal vacuum-assisted closure (endo-VAC) therapies, in a theranostic material able to detect and to inhibit bacteria growth, has been reported. The endo-VAC PUS presented sensitivity to Gram-positive and Gram-negative bacterial species thanks to its functionalization with gold and silver antibacterial nanoparticles (NPs). PUS with chitosan-stabilized Au-NPs achieved 5.26 ± 0.17 logs and 2.78 ± 0.34 logs of reduction of bacteria growth, whereas the sponges functionalized with phenolated lignin Ag-NPs offered slightly inferior values (4.77 ± 0.36 logs and 2.03 ± 0.37 logs, respectively), against Escherichia coli and Staphylococcus aureus pathogens, respectively, after the application of photothermal ablation. The in vitro antimicrobial studies were contrasted with the in-situ monitoring of bacteria localization and inactivation with excitation lasers of 532 and 785 nm wavelengths, respectively, in the Raman equipment. The novel theranostic nano-enabled antimicrobial PU sponges offer unprecedented possibilities for the improvement of the endo-VAC treatments and extrapolation of the methodology to other plastic-based implants to combat antimicrobial resistances.

Low-cost, reliable and flexible piezoresistive pressure sensors coated with single layer graphene and silver nanowires on three-dimensional polyurethane sponge

Flexible wearable sensors perform a significant role in practical applications such as medical monitoring, rehabilitation exercises, and artificial skin, as they can quantify and visualize external stress and strain. Polyurethane (PU) sponge stands out as a highly elastic and reproducible material frequently employed as a substrate in flexible electronic devices. Sponge materials with different pore sizes and densities exhibit varying degrees of deformation resistance under long-term cyclic pressure, thereby affecting the performance of sensors. Herein, piezoresistive pressure sensors based on PU with different pore diameters were successfully fabricated by dip-coating technology. By incorporating silver nanowires (AgNWs) and single layer graphene (SLG) into the sponge, both the low-density and high-density composite sponges can withstand over 70 % compressive strain, with stresses of 62.57 kPa and 31.79 kPa, respectively. Moreover, high-density composite sponge demonstrates a more stable conductive structure, more consistent relative resistance and better flame-retardant performance. The response and recovery time between 10 % and 40 % strains of the resulting pressure sensor based on high-density composite sponge (PU@AgNWs@SLG) are 110 ms and 106 ms and its gauge factor reaches 2.39. The pressure sensor exhibits a satisfactory reproducibility after over 3000 compression-release cycles, and performs during various applications, such as controlling brightness of LEDs, monitoring human activities, sensing finger movements.

Porous Three-Dimensional Polyurethane Scaffolds Promote Scar-Free Endogenous Regeneration After Acute Brain Hemorrhage.

Intracerebral hemorrhage (ICH) is the most lethal subtype of stroke and is associated with significant morbidity and mortality. Despite advances in the clinical treatment of ICH, limited progress has been made regarding endogenous brain regeneration after ICH. Failure of brain regeneration is mainly attributed to the inhibitive regenerative microenvironment caused by secondary injury after ICH. In this study, we investigated a three-dimensional biodegradable waterborne polyurethane (BWPU) scaffold as a tool to promote brain regeneration after ICH. After implantation into the cavity following hematoma evacuation, these implanted scaffolds could act as a reservoir; store a series of necrotic debris, cytokines, and chemokines; and attract microglia/macrophages to their pores. Subsequently, these microglia/macrophages were polarized into the M1-like subtype to eliminate these substances. This process disperses M1-like immune cells and prevents the formation of dense glial scar-free structures after ICH. Inflammatory cells in scaffolds include scar-free secreted growth factors and extracellular matrix (ECM) proteins, and further induce a M2-like immune cells enriched regeneration-predominant microenvironment to promote endogenous brain regeneration with functional recovery. In summary, in this work, we have revealed the potential and mechanism of the BWPU scaffold as a tool to promote endogenous brain tissue regeneration after ICH.

Polyurethane sponge assisted recoverable photocatalyst for outdoor weak sunlight-driven efficient water purification

Photocatalysis is an effective technology to address wastewater issue. However, the difficult recoverability of sample powders and poor degradation performance of catalysts under weak sunlight irradiation restrict the commercialization applications. In this work, the Bi2WO6/g-C3N4 heterojunction is synthesized by hydrothermal and calcination techniques, and a three-dimensional polyurethane sponge is introduced to assist the catalyst powder. On the one hand, weather variations produce less affection for Bi2WO6 sample, which exhibits the efficient photocatalytic activity driven by weak sunlight. The construction of Bi2WO6/g-C3N4 heterojunction speeds up separation and transfer of photogenerated carriers, further improving the catalytic performances of pristine Bi2WO6. Under cloudy (solar power density 21.93–52.97 mW/cm2) and overcast (solar power density 3.66–18.99 mW/cm2) weathers, tetracycline degradation efficiencies of Bi2WO6/g-C3N4 reach 64.66% and 55.19% after 150 min of sunlight irradiation, respectively. On the other hand, catalyst powder is tightly loaded onto the surface of polyurethane sponge via polyurethane waterproof coating, which is convenient for material recovery and reuse. After 4 cycles, tetracycline degradation efficiencies of Bi2WO6/g-C3N4 present no significant decrease, saving reaction cost and causing no secondary pollution to water environment. This work provides a promising candidate for large-scale commercialization applications of wastewater treatment.

Biomineralized Piezoelectrically Active Scaffolds for Inducing Osteogenic Differentiation.

There is an endogenous electric field in living organisms, which plays a vital role in the development and regeneration of bone tissue. Therefore, self-powered piezoelectric material for bone repair has become hot research in recent years. However, the current piezoelectric materials for tissue regeneration still have the shortcomings of lack of biological activity and three-dimensional structure. Here, we proposed a three-dimensional polyurethane foam (PUF) scaffold coated with piezoelectric poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and modified by a calcium phosphate (CaP) mineralized coating. The preferred scaffold has an open circuit voltage and short circuit current output of 5 V and 200 nA. Combining the physical and chemical properties of the CaP coating, the piezoelectric signal of PVDF-HFP and the three-dimensional structure of PUF, the scaffold exhibits superior promotion of cell osteogenic differentiation and ectopic bone formation in vivo. The mechanism is attributed to an increase in intracellular Ca2+ levels in response to chemical and piezoelectric stimulation with the material. This research not only paves the way for the application of piezoelectric scaffolds to stimulate osteoblasts differentiation in situ, but also lays the foundation for the clinical treatment of long-term osteoporosis.

Flexible conductive Ag-CNTs sponge with corrosion resistance for wet condition sensing and human motion detection

Three-dimensional (3D) polyurethane (PU) sponges featuring high mechanical elasticity, compressibility, and durability have emerged as an ideal substrate for building wearable strain sensors. However, the 3D porous structures easily soak up rain, water vapor, sweat, etc., and the constructed sensor’s long-term conductivity may be eroded by droplets and experience irreversible damage, rendering the preparation of a wearable flexible sponge sensor with environmental adaptation challenging. Here, by reducing the Ag particles in the carbon nanotube (CNT) suspension, forming a conductive filler Ag-CNTs, and combining with poly (vinylidene fluoride) (PVDF) solution, surface modification with polydimethylsiloxane (PDMS) solution, the PDMS/Ag-CNT-PVDF/PU sponge sensor with 3D conductive network and superhydrophobic structure was fabricated. The results revealed that this modified sponge had a wide strain detection range of 0–80 %, superior conductive sensitivity up to 4.24 kPa−1 in 0–20 kPa, and a fast and stable response time (170 ms) with great reproducibility over 1200 compression-resilience cycles. Furthermore, good superhydrophobicity endows the sensor with remarkable resistance to mechanical wear and chemical corrosion, which can be effectively used to detect human motion in high air humidity environment. This PDMS/Ag-CNTs-PVDF/PU sponge sensor is expected to be used as a practical, flexible wearable sensor and demonstrates potential application prospects in complex environments.

MODIFICATION OF CERAMIC MEMBRANES BY PYROCARBON FROM CARBONIZED POLY(URETHANE UREA)S

Modification of tubular ceramic membranes made of clay minerals, which were obtained by slip casting (produced by the Dumansky Institute of Colloid Chemistry and Water Chemistry of the National Academy of Sciences of Ukraine) was carried out. The membranes were modified with pyrocarbon, which was obtained by carbonization of a precursor – poly(urethane urea)s. The carbonization precursor was synthesized from polyisocyanate (average functionality 2.7) and laprol grade 5003, which was introduced into the membrane by impregnation of the corresponding solutions in ethylacetate. When laprol reacts with polyisocyanate, three-dimensional polyurethane is formed. Since undried reagents were used, water entered the pores of the membrane, which reacted with the NCO groups of the polyisocyanate to form polyurea. The parallel course of these reactions leads to the formation of poly(urethane urea)s in the pores of the membrane. Carbonization was carried at 800 °C in an argon flow. The apparent density and open porosity of the membranes were determined by CCl4 uptake. After modification, the open porosity of the membrane decreased from 29.9 to 27.3 %, the apparent density increased from 1.86 to 1.87 g/cm3. The composition and structure of the membranes were studied by X-ray diffraction analysis and SEM. It is shown that the obtained modifier is pyrocarbon - the relative intensity of reflexes increases at 26,0 - 26,4 and 41,3 and 44,2° 2Θ. Pyrocarbon covers the surface of the pores with a continuous layer, and there are also three-dimensional formations of various shapes and sizes from several nm to several microns. Testing of modified membranes was carried out by water purification from direct scarlet dye and from Ca2+ of calcium chloride using the baromembrane method at a working pressure of 0.7 MPa. The unmodified membrane does not retain direct scarlet dye and Ca2+ at all. Tests of modified membranes have shown that the membranes acquire ultrafiltration properties. The retention factor (R) for direct scarlet dye is 100 % and 25 % for Ca2+.

Investigation of the Mechanical Properties of Three-Dimensional Polyurethane Composites Reinforced with Warp-Knitted Spacer Fabrics

In this study, a novel composite having a unique three-dimensional structure was investigated. Warp-knitted spacer fabrics with glass fiber woven fabric were chosen as the reinforcement, while polyurethane foam was used as the matrix materials. The glass fiber woven fabric was pretreated with the warp-knitted spacer fabric first, and then a hand lay-up method was used to fabricate the three-dimensional polyurethane-based composites. The mechanical properties of the finished composites were determined. The influence of the fabric thickness, the surface structure of the fabric, and whether the woven fabric is laminated or not on the mechanical properties of the three-dimensional polyurethane composites were determined. The results show that the fabric thickness is positively related to the tensile and compressive properties and inversely related to the bending properties of the three-dimensional knitted/woven hybrid polyurethane matrix composites, provided that the surface structure is the same. The tensile and compressive strengths of the composites were higher when the glass fiber woven fabric was laminated with the spacer fabric than when the three-dimensional knitted/woven hybrid polyurethane matrix composites were not taken. Therefore, the knitted/woven fabric as reinforcement improved the tensile and compressive properties of the composites.

A novel flexible, conductive, and three-dimensional reduced graphene oxide/polyurethane scaffold for cell attachment and bone regeneration

Development of conductive and three-dimensional scaffolds with elastic properties and shape-recovery capability for bone regeneration within irregular bone cavities has been challenging. Polyurethanes (PUs) are intrinsically elastic polymers; however, their mechanical performance, biocompatibility, and functionality need to be improved for application as implants and biomedical devices. Herein, application of a novel flexible, conductive, and three-dimensional polyurethane scaffold (3DPU), fabricated through coating a commercial PU foam with graphene oxide (GO) and its subsequent reduction with ascorbic acid, described as 3DrGO/PU, is investigated for bone regeneration. The 3DrGO/PU scaffold supported the growth and proliferation of mouse osteoblast cells (MG-63) with strong mineralization and cell attachment. It is likely that the electrically conductive macro-porous 3DrGO/PU scaffold, provides bioactivity and promote nucleation and growth of hydroxyapatite (HA) in the simulated body fluid. Experiments assessing in vivo bone formation in rat calvarial skull defects provided clear evidence for efficacy of the 3D scaffold for treatment of irregular bone defects. The results of this study are promising, as they present easy production of a cost-effective green fabricated scaffold. It also offers a potential for cell attachment and capture, to be used in future tissue engineering and even biosensing applications.

Carbon-based aerogel in three-dimensional polyurethane scaffold: The effect of in situ unidirectional aerogel growth on piezoresistive properties

Carbon-based aerogels (CA) with durable piezoresistive properties possess great promise for applications in wearable electronics. However, it is still a great challenge to fabricate high performance aerogel sensors due to the limits of mechanical properties. We recently developed a novel strategy to build aerogel/foam hybrid structure that can effectively enhance the mechanical properties of aerogel-based sensors. Herein, CA/polyurethane foam (PUF) composite was fabricated via in situ unidirectional freeze-drying process starting from a carbon nanotubes (CNTs)/graphene oxide (GO) aqueous dispersion stabilized with chitosan (CS) which was filled into the porosity of an open cell PUF. The resulting composite shows a microscopic anisotropy in the CA with electrical conductivity as high as 10.54 S m−1. The piezoresistive sensitivity of the resulting composite can be simply modulated over a wide range from 1.1 to 3.6 by adequately selecting its initial pre-strain. The CA/PUF composite exhibits excellent compressible resilience at the strain of 50% for at least 100 cycles. In addition, the sensor was successfully applied for detecting various human motions. These unique properties make the realized composite a promising candidate for effective flexible piezoresistive strain sensors in wearable applications.

Superhydrophobic polyurethane sponges modified by sepiolite for efficient oil-water separation

The oil spill and the illegal discharge of organic solvents not only cause the waste of resources but also damage to the ecological environment, so it is very important to deal with it immediately. In this paper, the natural sepiolite（SEP） was modified by vinyltriethoxysilane(VTES) and 3-chloropropyltriethoxysilane(CTES) to gain excellent hydrophobicity. Then the modified superhydrophobic sepiolite（MSEP） powder was loaded onto the three-dimensional polyurethane(PU) sponge by repetitive dipping and drying. The water contact angle of [email protected] reached 155°, and its adsorption capacity for various oils and organic solvents was 26–71 times higher than its own weight. After 15 cycles of squeeze-adsorption, the adsorption capacity of [email protected] just decreased slightly for n-hexane, rice oil, diesel oil and chloroform. Moreover, after continuous separation of the diesel and water mixture for 10 times, [email protected] still showed hydrophobicity. At the same time, the prepared sponges showed excellent stability under extreme environment and good mechanical property after 200 compression cycles.

Differentiation Behaviour of Adipose-Derived Stromal Cells (ASCs) Seeded on Polyurethane-Fibrin Scaffolds In Vitro and In Vivo.

Adipose-derived stromal cells (ASCs) are a promising cell source for tissue engineering and regenerative medicine approaches for cartilage replacement. For chondrogenic differentiation, human (h)ASCs were seeded on three-dimensional polyurethane (PU) fibrin composites and induced with a chondrogenic differentiation medium containing TGF-ß3, BMP-6, and IGF-1 in various combinations. In addition, in vitro predifferentiated cell-seeded constructs were implanted into auricular cartilage defects of New Zealand White Rabbits for 4 and 12 weeks. Histological, immunohistochemical, and RT-PCR analyses were performed on the constructs maintained in vitro to determine extracellular matrix (ECM) deposition and expression of specific cartilage markers. Chondrogenic differentiated constructs showed a uniform distribution of cells and ECM proteins. RT-PCR showed increased gene expression of collagen II, collagen X, and aggrecan and nearly stable expression of SOX-9 and collagen I. Rabbit (r)ASC-seeded PU-fibrin composites implanted in ear cartilage defects of New Zealand White Rabbits showed deposition of ECM with structures resembling cartilage lacunae by Alcian blue staining. However, extracellular calcium deposition became detectable over the course of 12 weeks. RT-PCR showed evidence of endochondral ossification during the time course with the expression of specific marker genes (collagen X and RUNX-2). In conclusion, hASCs show chondrogenic differentiation capacity in vitro with the expression of specific marker genes and deposition of cartilage-specific ECM proteins. After implantation of predifferentiated rASC-seeded PU-fibrin scaffolds into a cartilage defect, the constructs undergo the route of endochondral ossification.

Polyurethane foam: A novel support for metal oxide packing used in the non-thermal plasma decomposition of CO2

Regarding the growing rate of CO2 emission into the environment which is accompanied by environmental issues, its recovery and utilization are of great importance, but the existing conventional methods are not sufficiently economical due to high energy requirements. Thus, in this study, low temperature CO2 dissociation through a packed dielectric barrier discharge (DBD) plasma reactor is investigated. Three-dimensional polyurethane foam (PU foam) with inter-connected porous structure is incorporated in the discharge volume of the DBD for the first time to evaluate its effects on the conversion and efficiency. In addition, for further improvement of the process, various packing materials including BaTiO3, TiO2, CeO2, ZrO2, CaO, Al2O3, Fe3O4, and SiO2 are coated over the PU foam and the corresponding results are compared. Results demonstrate that the foam-filled configuration can boost the conversion and energy efficiency relative to empty plasma. Interestingly, the plasma performance enhances more remarkably when the packing materials are coated over the foam. According to the results, presence of packing materials can exert physical effects over the performance of plasma. BaTiO3 exhibits the best performance regarding its highest effects. The highest obtainable conversion for the BaTiO3-coated configuration at the Specific Energy Input (SEI) of 60 kJ/L is nearly 27.4 %, showing 124 and 203 % enhancement in comparison with foam-filled and empty plasma configurations, respectively.

Thermoresponsive Polyurethane Sponges with Temperature-Controlled Superwettability for Oil/Water Separation

Here we have obtained a thermoresponsive three-dimensional (3D) polyurethane (PU) sponge with temperature-controlled superwettability. First, silanization was used to enhance the surface roughness ...

Highly Stretchable Conductor by Self-Assembling and Mechanical Sintering of a 2D Liquid Metal on a 3D Polydopamine-Modified Polyurethane Sponge.

A highly stretchable conductor was fabricated through dip-coating a new liquid metal (LM) electric ink on a polydopamine (PDA)-modified three-dimensional (3D) polyurethane sponge (PUS) followed by mechanical sintering. The LM was first sonicated to nanodroplets to reduce the consumption of LM and then modified by 3-mercaptopropionic acid (LMNPS-MPA) to improve the interfacial adhesion between LM and PUS. The denser and even distribution of LMNPS-MPA self-assembling on PDA-treated PUS (PUS-PDA) was successfully prepared via hydrogen bonding interactions. Mechanical sintering of 3D PUS-PDA coated by a two-dimensional (2D) LM layer was then conducted to obtain a continuous conductive network. Comparing with those of the reported 3D conductors, the resulting PUS-PDA-LM composite conductor shows both high electrical conductivity (478 S cm-1) under a low LM consumption of 10 vol% and excellent conductivity stability with the relative resistance change, ΔR/R0, of 2% at 50% strain under stretching deformation. The as-prepared PUS-PDA-LM composites were then successfully applied as flexible and stretchable light-emitting diode (LED) arrays with excellent conductivity and conductivity stability at different deformations. We believe that the 3D stretchable PUS-PDA-LM conductor has many potential applications in flexible sensors, flexible circuits, rollable displays, etc.

The fabrication and tribological behavior of epoxy composites modified by the three-dimensional polyurethane sponge reinforced with dopamine functionalized carbon nanotubes

Three-dimensional (3D) interpenetrating network structure epoxy composites were fabricated based on the modified carbon nanotube (CNT) reinforced flexible polyurethane (PU) sponge. CNTs were first functionalized with polydopamine (PDA) as revealed by TEM imaging, which is formed via the oxidative self-polymerization of dopamine. Then the functionalized CNTs (CNT–PDA) were successfully anchored on the skeleton surfaces of sponge, forming a continuous 3D carbon network. The interfacial interaction between modified PU sponge and epoxy (EP) matrix was significantly enhanced due to the covalent linkage of PDA. Improvement in the thermal stability of CNT–PDA/PU3D/EP composites was observed by TG analysis and related to the CNTs anchored on the skeleton of sponge. The tribological properties of pure EP, PU3D/EP and CNT–PDA/PU3D/EP composites were comparatively investigated in terms of different loads and velocities. Results demonstrated that CNT–PDA/PU3D/EP composites exhibited the best tribological performance owing to the strong interfacial interaction and the 3D carbon network structure. In particular, the wear resistance of CNT–PDA/PU3D/EP composites was 6.2 times and 3 times higher than those of pure EP and PU3D/EP composites under the applied load of 1.6MPa, respectively.

Influence of extremely low frequency, low energy electromagnetic fields and combined mechanical stimulation on chondrocytes in 3‐D constructs for cartilage tissue engineering

Articular cartilage, once damaged, has very low regenerative potential. Various experimental approaches have been conducted to enhance chondrogenesis and cartilage maturation. Among those, non-invasive electromagnetic fields have shown their beneficial influence for cartilage regeneration and are widely used for the treatment of non-unions, fractures, avascular necrosis and osteoarthritis. One very well accepted way to promote cartilage maturation is physical stimulation through bioreactors. The aim of this study was the investigation of combined mechanical and electromagnetic stress affecting cartilage cells in vitro. Primary articular chondrocytes from bovine fetlock joints were seeded into three-dimensional (3-D) polyurethane scaffolds and distributed into seven stimulated experimental groups. They either underwent mechanical or electromagnetic stimulation (sinusoidal electromagnetic field of 1 mT, 2 mT, or 3 mT; 60 Hz) or both within a joint-specific bioreactor and a coil system. The scaffold-cell constructs were analyzed for glycosaminoglycan (GAG) and DNA content, histology, and gene expression of collagen-1, collagen-2, aggrecan, cartilage oligomeric matrix protein (COMP), Sox9, proteoglycan-4 (PRG-4), and matrix metalloproteinases (MMP-3 and -13). There were statistically significant differences in GAG/DNA content between the stimulated versus the control group with highest levels in the combined stimulation group. Gene expression was significantly higher for combined stimulation groups versus static control for collagen 2/collagen 1 ratio and lower for MMP-13. Amongst other genes, a more chondrogenic phenotype was noticed in expression patterns for the stimulated groups. To conclude, there is an effect of electromagnetic and mechanical stimulation on chondrocytes seeded in a 3-D scaffold, resulting in improved extracellular matrix production.

Reducing railway track settlement using three-dimensional polyurethane polymer reinforcement of the ballast

This paper presents the measured settlement results of full-scale testing of unreinforced and polymer reinforced ballast railway track under laboratory conditions, using the GRAFT I (Geopavement and Railways Accelerated Fatigue Testing) facility to show the significant reduction in track settlement that can be obtained using in-situ ballast reinforcement techniques. The measured settlement profile of each track specimen is monitored up to a maximum of 500,000 load cycles at different load levels and formation conditions, ranging from a subgrade Young’s modulus of 25–51MPa. The results of a 3-dimensional polyurethane ballasted track reinforcement technique called XiTRACK, at an equivalent axle load of 44.4tonnes, are then directly compared to the unreinforced settlement profile using developed settlement models from the tests. The polymer treated track is observed to reduce permanent track settlement by 99%, effectively giving slab-track like performance. The free draining properties of the formed GeoComposite are also highlighted. The paper concludes by presenting and commenting on, the application of the technique to real UK Switch & Crossing sites on the West Coast Main Line and at Clapham Junction. In the former case, at Points 215D, the application of the technique eliminated the need for track maintenance over the 10year operating cycle at axle loads of 25tonne and main line speeds of 125mph confirming the measured laboratory observations.

Maintaining absolute clearances in ballasted railway tracks using in situ three-dimensional polyurethane GeoComposites

Maintaining track clearances in ballasted railway tracks are a critical issue for the safety and operational performance of the railway environment. In general, railway standards aredefined with respect to the minimum gauge clearance allowed between the dynamic swept envelope of the train vehicles and the fixed structure for a given vehicle speed. Absolute clearance of a line is categorized based on the clearance level, for example, in the UK, it is defined in terms of normal, reduced, or special reduced clearance. In special reduced clearance, the level of track fixity is defined as high fixity, medium fixity, and low fixity. In high track fixity, a concrete-slab track solution must be adopted; in medium track fixity, some form of ballast stabilization and/or reinforcement can be used. The principal requirement is that using a standard methodology, the clearances should always be greater than zero; the clearance representing the margin for unknown events. In this article, an in situ three-dimensional (3D) polyurethane ballast reinforcement technique is used to provide a very robust level of track fixity. The performance of the reinforcement technique is shown through experimental tests using a 200 ton capacity cyclic compression machine. The experimental tests are used to show the performance of the technique for applications like railway tunnels and station platforms where clearances issues are paramount. The base and shoulder GeoComposite experimental tests are performed with the initial ballast poorly compacted thus representing a worse case on-site scenario. Based on the experimental results, a new track fixity category is proposed termed virtual high fixity. A case study showing the impact and site application of the 3D polyurethane reinforcement research to Grovehill Tunnel UK is presented and reference is also made to another reinforced clearance issue site at Hoxton Station UK.

Poly(dopamine) coating of scaffolds for articular cartilage tissue engineering

A surface modification technique based on poly(dopamine) deposition developed from oxidative polymerization of dopamine is known to promote cell adhesion to several cell-resistant substrates. In this study this technique was applied to articular cartilage tissue engineering. The adhesion and proliferation of rabbit chondrocytes were evaluated on poly(dopamine)-coated polymer films, such as polycaprolactone, poly( l-lactide), poly(lactic-co-glycolic acid) and polyurethane, biodegradable polymers that are commonly used in tissue engineering. Cell adhesion was significantly increased by merely 15 s of dopamine incubation, and 4 min incubation was enough to reach maximal cell adhesion, a 1.35–2.69-fold increase compared with that on the untreated substrates. Cells also grew much faster on the poly(dopamine)-coated substrates than on untreated substrates. The increase in cell affinity for poly(dopamine)-coated substrates was demonstrated via enhancement of the immobilization of serum adhesive proteins such as fibronectin. When the poly(dopamine)-coating technique was applied to three-dimensional (3-D) polyurethane scaffolds, the proliferation of chondrocytes and the secretion of glycosaminoglycans were increased compared with untreated scaffolds. Our results show that the deposition of a poly(dopamine) layer on 3-D porous scaffolds is a simple and promising strategy for articular cartilage tissue engineering, and may be applied to other types of tissue engineering.