Self-healing materials with microvascular networks

Self-healing polymers composed of microencapsulated healing agents exhibit remarkable mechanical performance and regenerative ability, but are limited to autonomic repair of a single damage event in a given location. Self-healing is triggered by crack-induced rupture of the embedded capsules; thus, once a localized region is depleted of healing agent, further repair is precluded. Re-mendable polymers can achieve multiple healing cycles, but require external intervention in the form of heat treatment and applied pressure. Here, we report a self-healing system capable of autonomously repairing repeated damage events. Our bio-inspired coating-substrate design delivers healing agent to cracks in a polymer coating via a three-dimensional microvascular network embedded in the substrate. Crack damage in the epoxy coating is healed repeatedly. This approach opens new avenues for continuous delivery of healing agents for self-repair as well as other active species for additional functionality.     

Sensing of damage and healing in three-dimensional braided composites with vascular channels

With the rise of composite materials as replacements for traditional monolithic materials comes an increase in demand for multifunctionality. Prior studies have demonstrated the ability of an embedded, electrically percolating carbon nanotube network to respond electrically to the onset and progression of damage in composite structures. We build upon this work by incorporating healing functionality into braided composites through the use of a hollow channel resin delivery system. This study demonstrates the ability of a carbon nanotube network to sense crack filling during resin injection, thus providing the scientific basis required for sensing healing in advanced composites. With practical application in mind, a two-part healant system is employed in this study. Two methods for qualitatively assessing healing are employed and compared; these include elastic modulus/strain energy recovery and FTIR spectroscopy.     

Critical evaluation of permeation enhancers for oral mucosal drug delivery

Background: Drug delivery via oral mucosa is an alternative method of systemic administration for various classes of therapeutic agents. Among the oral mucosae, buccal and sublingual mucosae are the primary focus for drug delivery. Buccal delivery offers a clear advantage over the peroral route by avoidance of intestinal and hepatic first-pass metabolism. However, despite offering the possibility of improved systemic drug delivery, buccal administration has been utilized for relatively few pharmaceutical products so far. One of the major limitations associated with buccal delivery is low permeation of therapeutic agents across the mucosa. Various substances have been explored as permeation enhancers to increase the flux/absorption of drugs through the mucosa, but irritation, membrane damage, and toxicity are always associated with them and limit their use. A clinically accepted permeation enhancer must increase membrane permeability without causing toxicity and permanent membrane damage. To date, the information available on oral mucosal permeation enhancement is much less than transdermal enhancement, though oral mucosa is more resistant to damage than other mucosal membranes. This article reviews the various categories of permeation enhancers for oral mucosal drug delivery, their mechanism of action, their usefulness, and the limitations associated with their use. Conclusion: To optimize the concentration of enhancer to limit its toxicity while facilitating an enhancing effect reproducibly will be a big challenge for future developments. Advances in permeability modulation and formulation with appropriate enhancers can provide for effective and feasible buccal drug delivery for many drugs, which otherwise have to be injected or ingested with water.     

Development of a polymer stent with shape memory effect as a drug delivery system

The article presents a new concept for vascular endoprothesis (stent). Almost all commercially available stents are made of metallic materials. A common after effect of stent implantation is restenosis. Several studies on metal stents coated with drug show, that the use of a drug delivery system may reduce restenosis. The purpose of this work is to develop a new stent for the drug delivery application. The shape memory properties of thermoplastic polyurethane allow to design a new fully polymeric self-expandable stent. The possibility to use the stent as a drug delivery system is described.     

Self-healing of damage in fibre-reinforced polymer-matrix composites

Self-healing resin systems have been discussed for over a decade and four different technologies had been proposed. However, little work on their application as composite matrices has been published although this was one of the stated aims of the earliest work in the field. This paper reports on the optimization of a solid-state self-healing resin system and its subsequent use as a matrix for high volume fraction glass fibre-reinforced composites. The resin system was optimized using Charpy impact testing and repeated healing, while the efficiency of healing in composites was determined by analysing the growth of delaminations following repeated impacts with or without a healing cycle. To act as a reference, a non-healing resin system was subjected to the same treatments and the results are compared with the healable system. The optimized resin system displays a healing efficiency of 65% after the first healing cycle, dropping to 35 and 30% after the second and third healing cycles, respectively. Correction for any healability due to further curing showed that approximately 50% healing efficiency could be achieved with the bisphenol A-based epoxy resin containing 7.5% of polybisphenol-A-co-epichlorohydrin. The composite, on the other hand, displays a healing efficiency of approximately 30%. It is therefore clear that the solid-state self-healing system is capable of healing transverse cracks and delaminations in a composite, but that more work is needed to optimize matrix healing within a composite and to develop a methodology for assessing recovery in performance.     

Dextran-based hydrogel containing chitosan microparticles loaded with growth factors to be used in wound healing

Skin injuries are traumatic events, which are seldom accompanied by complete structural and functional restoration of the original tissue. Different strategies have been developed in order to make the wound healing process faster and less painful. In the present study in vitro and in vivo assays were carried out to evaluate the applicability of a dextran hydrogel loaded with chitosan microparticles containing epidermal and vascular endothelial growth factors, for the improvement of the wound healing process. The carriers' morphology was characterized by scanning electron microscopy. Their cytotoxicity profile and degradation by-products were evaluated through in vitro assays. In vivo experiments were also performed to evaluate their applicability for the treatment of skin burns. The wound healing process was monitored through macroscopic and histological analysis. The macroscopic analysis showed that the period for wound healing occurs in animals treated with microparticle loaded hydrogels containing growth factors that were considerably smaller than that of control groups. Moreover, the histological analysis revealed the absence of reactive or granulomatous inflammatory reaction in skin lesions. The results obtained both in vitro and in vivo disclosed that these systems and its degradation by-products are biocompatible, contributed to the re-establishment of skin architecture and can be used in a near future for the controlled delivery of other bioactive agents used in regenerative medicine.     

Comparison of cavern formation in massive salt blocks with single-well and two-well systems

The authors of this article have conducted a comparison study to investigate the construction characteristics of both single-well and two-well systems; two model experiments were conducted using large-size moulded rock salt specimens. An experimental platform was designed to simulate the process of leaching and a theoretical equation of calculating and predicting the cavern volume was derived. The experimental results illustrate that the variation trend of brine instantaneous concentration for single-well and two-well systems is identical, and an equilibrium state appears at last. Moreover, the equilibrium is reached early, after 5–8 pumping cycles. The construction rate in the two-well system is faster than the single-well system, and this phenomenon is observed mainly in the early periods (1–3 pumping cycles). Besides, the cavern shapes for the two construction methods are also found to be distinctive. The cavern of the single-well system has a circular cross section and an axisymmetric profile while that of the two-well system has an ovular cross section and a non-axisymmetric profile.     

Defect dynamics and damage of cement-based materials,studied by electrical resistance measurement

Defect dynamics, as studied by DC electrical resistance measurement during repeated compression of cement paste, mortar and concrete in the elastic regime, are characterized by defect generation that dominates during the first loading, defect healing that dominates during subsequent loading, and defect aggravation that dominates during subsequent unloading. The interface between sand and cement, that between silica fume and cement, and that between coarse aggregate and mortar contribute to the defect dynamics, particularly the defect healing. Electrical resistance measurement is also effective for monitoring damage, which causes the resistance to increase. Defect generation results in an irreversible increase in the baseline resistance as stress cycling progresses, whereas defect healing results in a reversible decrease in the resistivity upon compression within a stress cycle. Defect generation is relatively significant in the early cycles and diminishes upon cycling. As the cumulative damage increases, the extent of defect healing within a cycle also increases.     

Adsorption of hydrogen,neon, and helium on 5A molecular sieve at 20.4 K and 4.2 K in the low pressure range

The quality of the heat contact existing between adsorbent and cooled surface has a decisive influence on pumping speed. By gluing the adsorbent onto the surface by means of a water glass-talcum mixture, the pumping speed, as compared to that of the loose layers, could be increased by a factor of about 200.The pumping speed is not considerably reduced when several load cycles are made with the adsorbent being heated to room temperature only between cycles.     

Lifting options for stratospheric aerosol geoengineering: advantages of tethered balloon systems

The Royal Society report 'Geoengineering the Climate' identified solar radiation management using albedo-enhancing aerosols injected into the stratosphere as the most affordable and effective option for geoengineering, but did not consider in any detail the options for delivery. This paper provides outline engineering analyses of the options, both for batch-delivery processes, following up on previous work for artillery shells, missiles, aircraft and free-flying balloons, as well as a more lengthy analysis of continuous-delivery systems that require a pipe connected to the ground and supported at a height of 20 km, either by a tower or by a tethered balloon. Towers are shown not to be practical, but a tethered balloon delivery system, with high-pressure pumping, appears to have much lower operating and capital costs than all other delivery options. Instead of transporting sulphuric acid mist precursors, such a system could also be used to transport slurries of high refractive index particles such as coated titanium dioxide. The use of such particles would allow useful experiments on opacity, coagulation and atmospheric chemistry at modest rates so as not to perturb regional or global climatic conditions, thus reducing scale-up risks. Criteria for particle choice are discussed, including the need to minimize or prevent ozone destruction. The paper estimates the time scales and relatively modest costs required if a tethered balloon system were to be introduced in a measured way with testing and development work proceeding over three decades, rather than in an emergency. The manufacture of a tether capable of sustaining the high tensions and internal pressures needed, as well as strong winds, is a significant challenge, as is the development of the necessary pumping and dispersion technologies. The greatest challenge may be the manufacture and launch of very large balloons, but means have been identified to significantly reduce the size of such balloons or aerostats.     

CFD analysis of thermodynamic cycles in a pulse tube refrigerator

The objectives of this paper are to study the thermodynamic cycles in an inertance tube pulse tube refrigerator (ITPTR) by means of CFD method. The simulation results show that gas parcels working in different parts of ITPTR undergo different thermodynamic cycles. The net effects of those thermodynamic cycles are pumping heat from the low temperature part to the high temperature part of the system. The simulation results also show that under different frequencies of piston movement, the gas parcels working in the same part of the system will undergo the same type of thermodynamic cycles. The simulated thermal cycles are compared with those thermodynamic analysis results from a reference. Comparisons show that both CFD simulations and theoretical analysis predict the same type of thermal cycles at the same location. However, only CFD simulation can give the quantitative results, while the thermodynamic analysis is still remaining in quality.     

基于碳纳米管的纳米泵浦系统模拟研究

碳纳米管的纳米泵浦效应在药物传输、新型纳米推进器与传感器等方面有着广泛的潜在应用,而纳米泵浦效应能够获得应用的前提是建立稳定的纳米泵浦系统。通过分子动力学模拟,研究了基于碳纳米管的稳定纳米泵浦系统的建立方法和影响纳米泵浦效应的关键因素＂泵浦系统的边界势垒＂;在建立稳定泵浦系统和克服边界势垒的条件下,模拟了在外界驱动下的纳米泵浦过程。该项研究的结果为碳纳米管纳米泵浦效应的应用提供了重要理论参考。     

State of the art in sorption heat pumping and cooling technologies

Heat transformation with sorption systems has received increased attention in recent years. In this review it is intended to discuss current trends as well as forthcoming applications with the respective appropriate technology as it is deduced from activities in the field. Especially, we report about the papers and discussions of the International Sorption Heat Pump Conference (ISHPC'99) which was held in March 1999 in Munich, Germany. The review is grouped into a fundamentals part, a part about thermodynamic cycles, and an applications part. In the fundamentals part the discussion about working pairs and heat and mass transfer is reflected. Thermodynamic cycles which are being discussed are special solid sorption cycles, cycles fit for low-temperature driving heat, compression-sorption hybrids, and open cycles. In the applications part the classical cooling business is the main issue. The review comprises chillers and refrigerators which may be direct fired or waste heat driven. Interest is given to the improvement of efficiency on the one hand as well as to adaptation to low temperature waste heat use on the other hand — two very different developments. The use of solar energy as a heat source belongs to that area also. An additional important role — for decades — is played by automotive application. The area of heat pumping for heating purposes is less prominent but not negligible. Systems with a large capacity are being installed every once in a while, but the small scale domestic market still is not really covered with appropriate technology. Finally, industrial heat pumping involves the reverse cycle (heat transformer) also. Activity in this field is rather small. In summary, no unexpected developments can be reported on, but progress is steady and the market increases continuously, especially in the far east.     

Programmable DNA Hydrogel Provides Suitable Microenvironment for Enhancing TSPCS Therapy in Healing of Tendinopathy

Tendon stem/progenitor cells (TSPCs) therapy is a promising strategy for enhancing cell matrix and collagen synthesis, and regulating the metabolism of the tendon microenvironment during tendon injury repair. Nevertheless, the barren microenvironment and gliding shear of tendon cause insufficient nutrition supply, damage, and aggregation of injected TSPCs around tendon tissues, which severely hinders their clinical application in tendinopathy. In this study, a TSPCs delivery system is developed by encapsulating TSPCs within a DNA hydrogel (TSPCs-Gel) as the DNA hydrogel offers an excellent artificial extracellular matrix (ECM) microenvironment by providing nutrition for proliferation and protection against shear forces. This delivery method restricts TSPCs to the tendons, significantly extending their retention time. It is also found that TSPCs-Gel injections can promote the healing of rat tendinopathy in vivo, where cross-sectional area and load to failure of injured tendons in rats are significantly improved compared to the free TSPCs treatment group at 8 weeks. Furthermore, the potential healing mechanism of TSPCs-Gel is investigated by RNA-sequencing to identify a series of potential gene and signaling pathway targets for further clinical treatment strategies. These findings suggest the potential pathways of using DNA hydrogels as artificial ECMs to promote cell proliferation and protect TSPCs in TSPC therapy.     

Novel carboxymethyl derivatives of chitin and chitosan materials and their biomedical applications

Chitin and chitosan are natural biopolymers that are non-toxic, biodegradable and biocompatible. In the last decade, chitin and chitosan derivatives have garnered significant interest in the biomedical and biopharmaceutical research fields with applications as biomaterials for tissue engineering and wound healing and as excipients for drug delivery. Introducing small chemical groups to the chitin or chitosan structure, such as alkyl or carboxymethyl groups, can drastically increase the solubility of chitin and chitosan at neutral and alkaline pH values without affecting their characteristics; substitution with carboxyl groups can yield polymers with polyampholytic properties. Carboxymethyl derivatives of chitin and chitosan have shown promise for adsorbing metal ions, as drug delivery systems, in wound healing, as anti-microbial agents, in tissue engineering, as components in cosmetics and food and for anti-tumor activities. This review will focus on the preparative methods and applications of carboxymethyl and succinyl derivatives of chitin and chitosan with particular emphasis on their uses as materials for biomedical applications.     

A Self‐Pumping Dressing for Draining Excessive Biofluid around Wounds

Excessive biofluid around wounds often causes infection and hinders wound healing. However, the intrinsic hydrophilicity of the conventional dressing inevitably retains excessive biofluid at the interface between the dressing and the wound. Herein, a self‐pumping dressing is reported, by electrospinning a hydrophobic nanofiber array onto a hydrophilic microfiber network, which can unidirectionally drain excessive biofluid away from wounds and finally accelerate the wound healing process. The hydrophilic microfiber network offers a draining force to pump excessive biofluid through the hydrophobic nanofiber array, which can further keep those pumped biofluids from rewetting the wounds. In the proof of concept, the self‐pumping dressing unidirectionally drains the biofluid from murine dorsum wounds, thereby resulting in faster wound healing than conventional dressings. This unique self‐pumping dressing has enormous potential to be a next‐generation dressing for healing wounds clinically.     

Mesoporous silicon particles as a multistage delivery system for imaging and therapeutic applications

Many nanosized particulate systems are being developed as intravascular carriers to increase the levels of therapeutic agents delivered to targets, with the fewest side effects. The surface of these carriers is often functionalized with biological recognition molecules for specific, targeted delivery. However, there are a series of biological barriers in the body that prevent these carriers from localizing at their targets at sufficiently high therapeutic concentrations. Here we show a multistage delivery system that can carry, release over time and deliver two types of nanoparticles into primary endothelial cells. The multistage delivery system is based on biodegradable and biocompatible mesoporous silicon particles that have well-controlled shapes, sizes and pores. The use of this system is envisioned to open new avenues for avoiding biological barriers and delivering more than one therapeutic agent to the target at a time, in a time-controlled fashion.     

Self-healing mortars based on hollow glass tubes and epoxy–amine systems

In the present work key parameters of different epoxy systems (such as viscosity and gel time) were evaluated to be used as healing agents when were included in a cement matrix. Epoxy systems were encapsulated in hollow glass tubes and were introduced in a mortar matrix. Samples were preloaded under three point bending in order to create a crack and release the healing system. After that, they were loaded to measure the residual strength and estimate the healing efficiency. The influence of temperature and the volume of the glass tubes were examined. Regarding the healing efficiency, a higher temperature led to an improvement of autogenous healing of the mortar matrix and a higher degree of crosslinking of the healing agent. For the studied systems, the use of glass tubes with smaller diameter containing the healing system seemed to be better in order to maintain the mechanical properties of the mortar-based composite.     

Thermally activated healing in a mendable resin using a non woven EMAA fabric

This paper explores the efficacy of polyethylene-co-ethacrylic acid (EMAA), as a thermally activated thermoplastic healing agent embedded within a carbon fibre reinforced epoxy composite. EMAA fibres have been shown to effectively restore mode I properties in a fibre reinforced composite after thermal activation yet other forms of the healing agent or modes of deformation have so far not been studied at all. This work, uses EMAA in the form of a non-woven mesh, rather than a woven fabric to study the healing mechanism and effectiveness of property restoration for mode I (crack opening) and mode II (shear) failure as well as for high speed impact. Property restoration after mode I damage was found to be over 200% and increased with increasing EMAA concentration. For mode II shear failure, the property restoration was reduced to a little over 100% regardless of EMAA concentration. Mode II analysis also showed that the modulus could be restored to about 80% of its original value when modified with EMAA. Repeated impacting using a falling weight test produced no property restoration after healing, yet the modified laminates appeared protected from further damage compared with an unmodified laminate. This was attributed to the formation of a ductile thermoplastic layer mitigating further damage. Scanning electron microscopy revealed that regardless of the extent of healing, the form of the healing agent or the mode of damage, the unique pressure delivery mechanism previously identified, was always observed to occur.     

Filament-wound composite soft tissue prostheses:controlling compliance and strength by water absorption and degradation

This paper deals with the effect of water absorption on the mechanical performance of selectively biodegradable filament-wound composite soft tissue prostheses. It shows how the water absorption phenomenon can be utilized as a new concept of material design, in contrast to the current view that associates moisture absorption by composite materials exclusively with damage. Harnessing water absorption to property design of vascular grafts has two advantages. The first is the controlled increase of the compliance of the graft during healing, aiming to reach a final stage of isocompliance with the host artery. The second is the water-induced biodegradation which enables regulation of the mural porosity during healing of an initially impervious graft. Filament-wound composite vascular prostheses comprising partially biodegradable matrices, different compositions and various winding angles are studied. Water absorption and material degradation are expressed in terms of relative weight gain/loss, which in turn is correlated with changes in the compliance and in the ultimate strength of the grafts.