Healing substrates with mobile, particle-filled microcapsules: designing a ‘repair and go’ system

We model the rolling motion of a fluid-driven, particle-filled microcapsule along a heterogeneous, adhesive substrate to determine how the release of the encapsulated nanoparticles can be harnessed to repair damage on the underlying surface. We integrate the lattice Boltzmann model for hydrodynamics and the lattice spring model for the micromechanics of elastic solids to capture the interactions between the elastic shell of the microcapsule and the surrounding fluids. A Brownian dynamics model is used to simulate the release of nanoparticles from the capsule and their diffusion into the surrounding solution. We focus on a substrate that contains a damaged region (e.g. a crack or eroded surface coating), which prevents the otherwise mobile capsule from rolling along the surface. We isolate conditions where nanoparticles released from the arrested capsule can repair the damage and thereby enable the capsules to again move along the substrate. Through these studies, we establish guidelines for designing particle-filled microcapsules that perform a ‘repair and go’ function and thus, can be utilized to repair damage in microchannels and microfluidic devices.     

Healing substrates with mobile, particle-filled microcapsules: designing a 'repair and go' system.

We model the rolling motion of a fluid-driven, particle-filled microcapsule along a heterogeneous, adhesive substrate to determine how the release of the encapsulated nanoparticles can be harnessed to repair damage on the underlying surface. We integrate the lattice Boltzmann model for hydrodynamics and the lattice spring model for the micromechanics of elastic solids to capture the interactions between the elastic shell of the microcapsule and the surrounding fluids. A Brownian dynamics model is used to simulate the release of nanoparticles from the capsule and their diffusion into the surrounding solution. We focus on a substrate that contains a damaged region (e.g. a crack or eroded surface coating), which prevents the otherwise mobile capsule from rolling along the surface. We isolate conditions where nanoparticles released from the arrested capsule can repair the damage and thereby enable the capsules to again move along the substrate. Through these studies, we establish guidelines for designing particle-filled microcapsules that perform a 'repair and go' function and thus, can be utilized to repair damage in microchannels and microfluidic devices.     

The Interaction between Microcapsules with Different Sizes and Propagating Cracks

The microcapsule-contained self-healing materials are appealing since they can heal the cracks automatically and be effective for a long time. Although many experiments have been carried out, the influence of the size of microcapsules on the self-healing effect is still not well investigated. This study uses the two-dimensional discrete element method (DEM) to investigate the interaction between one microcapsule and one microcrack. The influence of the size of microcapsules is considered. The potential healing time and the influence of the initial damage are studied. The results indicate that the coalescence crack is affected by the size of holes. The elastic modulus, the compressive strength and the coalescence stress decrease with the rising radius of holes. The initial damage in experiments should be greater than 95% of the compressive strength to enhance the self-healing effect. The large microcapsules require slight initial damage. Both a new type of displacement field near the crack and a new category of coalescence crack are observed. The influence of sizes of holes on the cracking behavior of concrete with a circular hole and a pre-existing crack is clarified.     

Ibuprofen Microcapsules: the Effect of Production Variables on Microcapsule Properties

Ibuprofen was microencapsulated with ethylcellulose using the solvent evaporation method. The effect of production variables on the properties of the microcapsules and drug release from them is described. Results show that size distribution, drug loading and the amount of free drug on the surface of the microcapsules is affected by production variables. The release of drug from the microcapsules was observed to be strongly influenced by parameters affecting the presence of uncoated drug on the microcapsule surface.     

微胶囊埋植型自修复涂层研究进展

微胶囊埋植型自修复涂层是自修复复合材料的研究热点之一,它是模拟生物体损伤自愈合的原理,实现对涂层微裂纹、划痕等缺陷的自我修复,可有效提升涂层的耐蚀性能和使用寿命。从修复机理进行分类,微胶囊埋植型自修复涂层可分为腐蚀抑制型和反应修复型。腐蚀抑制型是通过微胶囊释放缓蚀剂延缓基体的腐蚀进程,反应修复型则是通过微胶囊释放的修复剂实现对涂层损坏处的修补。系统地回顾了微胶囊埋植型自修复涂层的典型研究成果和近期动态,详细阐述了自修复涂层的设计和修复机制,着重对不同涂层修复体系的优缺点和适用范围进行了讨论。最后,根据微胶囊埋植型自修复涂层的研究现状,提出了该领域存在的缺陷以及未来的发展方向。     

Fatigue crack propagation in microcapsule-toughened epoxy

The addition of liquid-filled urea-formaldehyde (UF) microcapsules to an epoxy matrix leads to significant reduction in fatigue crack growth rate and corresponding increase in fatigue life. Mode-I fatigue crack propagation is measured using a tapered double-cantilever beam (TDCB) specimen for a range of microcapsule concentrations and sizes: 0, 5, 10, and 20% by weight and 50, 180, and 460 μm diameter. Cyclic crack growth in both the neat epoxy and epoxy filled with microcapsules obeys the Paris power law. Above a transition value of the applied stress intensity factor ΔK _T, which corresponds to loading conditions where the size of the plastic zone approaches the size of the embedded microcapsules, the Paris law exponent decreases with increasing content of microcapsules, ranging from 9.7 for neat epoxy to approximately 4.5 for concentrations above 10 wt% microcapsules. Improved resistance to fatigue crack propagation, indicated by both the decreased crack growth rates and increased cyclic stress intensity for the onset of unstable fatigue-crack growth, is attributed to toughening mechanisms induced by the embedded microcapsules as well as crack shielding due to the release of fluid as the capsules are ruptured. In addition to increasing the inherent fatigue life of epoxy, embedded microcapsules filled with an appropriate healing agent provide a potential mechanism for self-healing of fatigue damage.     

Surface-enhanced Raman scattering of rhodamine 6G on nanowire arrays decorated with gold nanoparticles

We investigate the surface-enhanced Raman scattering (SERS) of rhodamine 6G (R6G) adsorbed on Au nanoparticles attached to InP nanowires. We find that nanowire arrays act as frameworks for effective SERS substrates with a significantly higher Raman signal sensitivity than a planar framework of Au nanoparticles adsorbed two-dimensionally on a flat surface. The SERS signal displays a clear polarization-dependent effect when the nanowires are arranged in a row. We also find that the SERS signal increases with time during continuous laser illumination. The plasmon-enhanced optical forces between Au nanoparticles may either move pairs of nanoparticles closer together or attract adsorbed molecules by moving them to the junctions of Au nanoparticle aggregates. Such effects by plasmon optical forces may cause the observed increase of the SERS signal with continuous laser illumination.     

双乳液体系在微胶囊制备中的应用研究进展

双乳液是一类多重乳状液体系,它具有保护物质并且可以控制这些物质从一个相释放到另一个相的能力。近年来这类乳液体系与传统微胶囊制备方法的结合在药物输送(如抗癌药物、激素等)、食品等领域得到了一定的应用,解决了传统微胶囊制备方法无法有效封装高度水溶性物质等问题。基于此,综述了双乳液体系与微胶囊制备方法结合延伸出的一些新方法,包括双乳液-复凝聚法、复乳溶剂挥发法以及膜乳化复乳法等;同时,评述了影响双乳液体系制备微胶囊的各种因素,展望了双乳液体系在农药微胶囊制备中的应用前景。     

Evaluation of a Microreservoir-Type Biodegradable Microcapsule for Controlled Release of Proteins

For the controlled release of a model protein bovine serum albumin, a biodegradable microreservoir-type microcapsule was prepared. BSA was incorporated into the microcapsules with high efficiency of 96.1 (±3.1)%. The encapsulation did not cause any changes in the molecular weight and conformation of BSA, which was proven by biochemical analyses such as gel electrophoresis, circular dichroism, and HPLC.

The compositions and fabrication technique of microcapsules were found to be closely related to the release of BSA from the microcapsules and their degradation. Depending on microcapsule formulations, the in vitro release profile of BSA was either monophasic or biphasic. The microcapsules provided various release rates. It was also possible to control the delay before the initiation of BSA release and total duration of its delivery.     

Evaluation of a Microreservoir-Type Biodegradable Microcapsule for Controlled Release of Proteins

Abstract

For the controlled release of a model protein bovine serum albumin, a biodegradable microreservoir-type microcapsule was prepared. BSA was incorporated into the microcapsules with high efficiency of 96.1 (±3.1)%. The encapsulation did not cause any changes in the molecular weight and conformation of BSA, which was proven by biochemical analyses such as gel electrophoresis, circular dichroism, and HPLC.

The compositions and fabrication technique of microcapsules were found to be closely related to the release of BSA from the microcapsules and their degradation. Depending on microcapsule formulations, the in vitro release profile of BSA was either monophasic or biphasic. The microcapsules provided various release rates. It was also possible to control the delay before the initiation of BSA release and total duration of its delivery.     

疏水改性海藻酸钠衍生物包埋丁香油的释放性

目的通过化学方法将月桂醇与海藻酸钠接枝共聚形成两亲共聚物,对丁香油进行包埋形成微胶囊,使其具有一定的缓释性和良好的抗菌效果。方法利用两亲共聚物包埋丁香油形成包合物,采用单因素实验法,以包埋率为指标,评价月桂醇与海藻酸的接枝率对包埋率的影响,并在此基础上评价接枝率对缓释性以及不同环境下的稳定性和抗菌性能。结果在一定范围内包埋率随着接枝率的增大而升高;丁香油微胶囊的挥发率为14.11%,远低于丁香油的挥发率61.25%;释放试验中,丁香油微胶囊的缓释性明显优于未改性海藻酸纳,丁香油微胶囊能稳定缓慢地释放抗菌成分,控制大肠杆菌的生长。结论月桂醇改性海藻酸钠包埋丁香油形成的微胶囊具有一定的缓释和抗菌性能,突破了丁香油因挥发性强而存在的应用限制。     

Flow Focusing: a versatile technology to produce size-controlled and specific-morphology microparticles

The Flow Focusing platform is especially advantageous for micro- and nanoparticle production. This versatile technique is amenable to designing the size, surface treatment and internal topology of the particles; mechanical stresses are minimal-an optimal feature for the manipulation of delicate substances. Multiplexing and high-rate production are readily implemented. Adaptive operational design can lead, in one single step, to finely tuned microcapsules encasing different products within a targeted morphology. This achievement is of great significance for most microcapsule applications in the biosciences (for example, drug delivery, cell encapsulation, and the production of bead arrays).     

Formulation factors affecting drug release from poly(lactic acid) (PLA) microcapsule tablets

A sustained-release (SR) formulation of phenobarbital (PB) microcapsule tablet was prepared using low molecular weight (MW) DL- and high MW L-poly(lactic acid) (PLA) polymer. Microencapsulation of PB showed a unimodal size distribution (375 to 550 microns) of the microcapsules with high loading capacity (> 84%). Drug release from the microcapsule was influenced by the polymer ratios and increased with an increase in L-PLA amount. Microcapsules and physical mixtures of PB and the PLA were directly compressed independently to form microcapsule and matrix tablets, respectively. Drug release from the microcapsule tablets was significantly lowered (p < .001) compared to matrix tablets or free microcapsule (free microcapsule > matrices > microcapsule tablets). We also investigated the effect of tablet adjuvants, compression pressures, and microcapsule loading on the tablet performance in terms of friability, hardness, porosity, tensile strength, and the release kinetics of PB. The drug release rate increased with increasing compression pressure in the case of Emcompress or lactose, but not Avicel. The drug release rate was three- to fivefold increased with sodium starch glycolate compared to tablets without a disintegrant. With an increase in microcapsule loading, a decrease in the drug release rate was observed; however, the tablet performance remained satisfactory. The morphology of the microcapsules was monitored microscopically after the dissolution and the disintegration of tablets. The drug release accelerated with compression pressures and microcapsule loading from the tablets due to mechanical destruction of the microcapsule wall, which was more clearly seen after disintegration and dissolution of the tablets. Our data suggest that the PLA microcapsule can be tableted to make a SR product without significantly affecting its release kinetics.     

The permeability and stability of microencapsulated epoxy resins

Microcapsules containing self-healing agents have been introduced into polymer to self-heal the microcracks and toughen the brittle matrix. Poly(urea–formaldehyde) (PUF) microcapsules containing epoxy resins are potential for the self-healing and toughening polymer. The resistance to medium surroundings of microcapsules is required. In the present study, PUF microcapsules containing epoxy resins were prepared by in situ polymerization. The effects of diameter, surface morphology and wall thickness on the permeability and stability of microcapsules in thermal and solvent surroundings were investigated. The morphology of microcapsule was investigated using optical microscope (OM), metalloscope (MS) and scanning electron microscope (SEM), respectively. The composition on the surface of microcapsule was analyzed by using energy dispersive analysis of X-ray (EDAX). The thermal properties of microcapsules were investigated using differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The thermal permeability of core increases and the stability of microcapsule decreases with the enhancement of heating temperature mainly due to the expansion of epoxy resins below 251 °C and the decomposition of PUF above 251 °C. At room temperature, the permeability constants of core materials of microcapsules in acetone solvent are small and they are 1.20 × 10⁻³ m s⁻¹, 1.39 × 10⁻³ m s⁻¹ and 1.60 × 10⁻³ m s⁻¹ corresponding to the microcapsules with diameters of 400 ± 50 μm, 230 ± 40 μm and 120 ± 30 μm. Increasing the surface smoothness, diameter and wall thickness can decrease the permeability and improve the stability of microcapsules in thermal and solvent surroundings.     

微流控技术构建单分散微囊膜的研究新进展

单分散微囊膜在控制释放领域显示出许多优势而备受重视,而近期出现的微流控技术为制备单分散微囊膜提供了可靠的新方法.综述了微流控技术构建单分散微囊膜的研究新进展,着重介绍了微流控技术制备基于乙基纤维素、壳聚糖和海藻酸钙等生物相容性材料的单分散微囊膜以及基于聚N-异丙基丙烯酰胺的温敏型和离子识别型的单分散微囊膜的研究现状.     

Effects of hydrophilic excipients and compression pressure on physical properties and release behavior of aspirin-tableted microcapsules.

Aspirin ethylcellulose microcapsules were tableted by compression with or without excipients (lactose or polyvinylpyrrolidone [PVP]). The effects of the amount of the excipients and microcapsule size on the crushing strength and release rate of aspirin from tableted microcapsules were investigated. Tablets without excipients had a crushing strength that was independent of the applied pressure and microcapsule size. An increase in compression pressure from 15 to 60 MPa resulted in an increase in the crushing strength of tablets containing 20% or 40% w/w lactose, but the reverse results were obtained for the tableted microcapsules containing 20% or 40% w/w PVP. Results showed that the release rate of aspirin from microcapsules containing lactose or PVP was independent of the compression pressure with the exception of tablets containing 40% w/w lactose. In vitro release profiles of aspirin from tableted microcapsules containing lactose or PVP showed that increasing the concentration of the excipients resulted in an increase in the release rate of aspirin. Values of n were changed by the compression pressure and the added excipients.     

Drug Release Properties of the Microcapsules of Adriamycin Hydrochloride with Ethylcellulose Prepared by a Phase Separation Technique

Adriamycin hydrochloride was microencapsulated with ethylcellulose by a phase separation method to develop a prolonged release dosage form. Polyisobutylene (PIB) was used as a coacervation-inducing agent to control the particle size and drug release rate of the resultant microcapsules. With increasing the concentration of PIB (1 to 3 %) the average diameter of the microcapsules decreased, due to the fact that the microcapsules were discreted to a single microcapsule. At low concentration of PIB, the resultant microcapsules were agglomerated, which resulted in increasing the size. The microcapsules prepared with PIB 2 % prolonged desirably the drug release from the microcapsules. A little size effects of the microcapsules on the drug release rate was found for the microcapsules with PIB 2 % and 3 %.     

Synthesis and characterization of photocatalytic polyurethane and poly(methyl methacrylate) microcapsules for the controlled release of methotrexate

Abstract

The aim of this work is to prepare ultraviolet (UV) triggered controlled release of compounds from microcapsule systems (MCs). Polyurethane (PU) and poly(methyl methacrylate) (PMMA) microcapsules were studied with/without chemical functionalization using photocatalytic TiO₂ nanoparticles (NPs) on their surface. Once TiO₂ nanoparticles are illuminated with UV light (λ?=?370?nm), they initiate the rupture of the polymeric bonds of the microcapsule and subsequently initiate the encapsulated compound release, methotrexate (MTX) or rhodamine (Rh), in the present work. The size, polydispersity, charge, and yield of all MCs were measured, being the methotrexate drug release for all systems determined and compared with and without functionalization with TiO₂ NPs, under dark, visible light and UV illumination in vitro. Finally, the Rh release was characterized using fluorescence microscopy. The TiO₂ NPs size is around 10?nm, as determined by X-ray diffraction experiments. The PU MCs average size is around 60?µm, its electric charge +3.11?mV and yield around 85%. As for the PMMA MCs, the average size is around 280?µm, its electric charge ?7.2?mV and yield around 25% and 30% for both MTX and Rh, respectively. In general, adding TiO₂ NPs or the encapsulated products to the MCs does not affect the size but functionalization with TiO₂ NPs lowers the electric charge. Microcapsules functionalized with TiO₂ nanoparticles and irradiated with UV light presented the highest release of MTX and Rh. All other samples showed lower drug release levels when studied under the same conditions.     

An element‐free Galerkin method for 3D crack propagation simulation under complicated stress conditions

This study develops an element‐free Galerkin method based on the moving least‐squares approximation to trace three‐dimensional crack propagation under complicated stress conditions. The crack surfaces are modelled by a collection of planar triangles that are added when cracks propagate. The visibility criterion is adopted to treat the screening effect of the cracks on the influenced domain of a Gaussian point. Cracks are assumed to propagate in the perpendicular planes at crack front points when the strain energy release rates reach the material fracture toughness. This method is unique in that it uses a nonlinear contact iterative algorithm to consider contributions of crack surface interaction to the global equilibrium equations, so that crack opening, sliding and closing under complicated stress states can be efficiently modelled. Two numerical examples of three‐dimensional quasi‐static crack propagation were modelled with satisfactory results. Copyright © 2012 John Wiley & Sons, Ltd.     

Comparison studies between two wavelet based crack detection methods of a beam subjected to a moving load

In this paper, the performances of two wavelet based damage detection approaches to find the location and the size of a crack in a beam subjected to a moving load are compared. In the first approach, designated as ‘Fixed Sensor Approach’, a sensor is assumed to be located at the mid span of the beam. Thus in this approach, Continuous Wavelet Transform (CWT) coefficient of the time varying deflection attributed to the beam at mid span is used. In the second approach, the sensor is attached to the moving load and CWT coefficient of moving sensor is analyzed. The crack is modeled as a rotational spring which its stiffness is obtained from fracture mechanics, and modal expansion theory is used to find the deflection of cracked beam. The two approaches are compared for several cases of moving load speeds, crack sizes and crack locations, and also several scales of CWT. In the both approaches, wavelet Gaussian 4 is employed. It is shown that, the highest magnitude of CWT coefficient occurs at the exact location of crack and its value depends on damage size. As a result, it can be considered as a damage index. It is found that the moving sensor approach is more effective than the fixed sensor. Thereafter, the effect of beam parameters such as length, width, modulus of elasticity and density and also, crack size and location on the damage index were investigated based on the moving sensor approach. The obtained damage index has two significant features: (a) it has an explicit expression and shows the effects of all parameters clearly, (b) it is not dependent upon the response of the undamaged beam. From the obtained explicit relation for damage index, it is illustrated that the damage index does not depend on material properties of a homogeneous beam. Moreover in a rectangular cross section beam, the damage index is independent of width and has a linear relationship with the height to length ratio. It is shown that using this damage index, small cracks with a depth more than 10% of the beam height can be detected.