Embedding of microcapsules

Particular attention should be given during the preparation of the textile substrate for more efficient embedding of microcapsules. The pretreatments of textiles include chemical modification driving the material to be in a more functionalized state for bonding with other entities. These modifications could be based on treatment in aqueous media to improve the accessibility of fibers toward chemical reaction (Salaiin et al., 2012) or even using plasma technology for creation of reactive sites (Chatteijee et al., 2014). 

For these experiments, in order to protect the cells from environmental shear stress, an 5 p.m thin membrane made of alginate and poly-L-lysine was created around the immobilized micro-carrier [31]. The movement of microcapsules with immobilized chromatophores was observed microscopically in a glass microtube (d = 700 pm 1 = 5 cm) with the magnetic field conduit embedded in the wall. The experimental setup is presented in Figure 32.4. Fluid (L-15 medium) velocities applied were in the range from 1.6 to 6.4mm/s and corresponded to the predicted operational fluid velocities of the biosensor [11]. Fluid flow was provided by microsyringe pump (LabTronix, USA). 

It can be concluded from the above-mentioned differential capacitance curve and cathodic polarization curve analyses that the mechanistic model of electrolytic codeposition of Hquid microcapsules is associated with the stable chelation of—OH and -O groups of the wall material (e.g., PVA, gelatin) with metal ions (e.g., Ni ", Cu +), and this gives rise to positively charged microcapsules. This in turn helps to accelerate the electrophoretic migration of microcapsules in the plating solution. The liquid microcapsules were also adsorbed onto the electrode due to the presence of a surfactant. Consequently, it is feasible for microcapsules to enter the electrical double layer at the interface and to become embedded in the co-deposited coating. 

The purpose of incorporating microcapsules into coatings is to improve or repair the surface function of the metal by gradual release of the core materials. In this context, it is very important to study the controlled-release behavior of microcapsules embedded in the composite coating, and of their self-repairing capability for the plating surface. 

The large surface area of microcapsules allows for the formation of a uniform and continuous coating on the surface of the fabric as well as in between the fibers (Liu et al., 2013). The reasons for microcapsules playing an important role in the controlled release of active agents could be found in the uniformity and reproducibility in release (Singh et al., 2010). The following sections will focus on microcapsule formation and their embedding into textile stmctures. 

In addition, for encapsulated material to be released in a controlled manner, mechanical properties of microcapsules are of considerable significance. This particularly refers to microcapsules embedded in textile structures intended for the topical release of an active agent, when they demand sufficient stability to withstand wear and tear (Neubauer et al., 2014). 

Monllor et al. (2007) investigated impregnation and bath exhaustion (in the presence of acrylic resin) of cotton fabrics using melamine formalin microcapsules loaded with a mint flavor. Fig. 5.8 shows the difference in the effect of both methods of embedding microcapsules into a cotton textile structure. Since there was no affinity between microcapsules and fabrics, impregnation resulted in a higher amount of microcapsules in the substrate. In both cases, microcapsules were sensitive to rubbing. 

A considerable number of microcapsules intended for textile applications are fabricated using melamine-formaldehyde resin. The reason for this is its superior performance, including high hardness and mechanical robustness, excellent heat resistance, water resistance, outdoor weatherability, and unlimited colorability (Fei et al., 2015). Properties of polymer wall material should be carefully considered when opting for the best embedding method and choice of a compatible binder. Salaiin et al. (2009) investigated the adhesive properties of microcapsule wall material, melamine... 

However, functions of these smart textile stmctures could still be improved and their role optimized. Bringing the textile/microcapsule systems for controlled release of active agents to a higher level demands a multidisciplinary approach. Considering all aspects of the controlled release systems such as active agent formulations, microcapsule polymer wall composition, encapsulation approach, and embedding loaded microcapsules into textile structures could push the limits of smart textiles even further. 

Figure 10.2 Assortment of microcapsules containing ROMP-based healing monomers, (a) ENB in a MUF shell, (b) ruptured UF shell embedded in a fracture surface, and (c) nanocapsules containing DCPD in a UF shell. Reprinted with permission from Refs. [3, 23, 56].

Figure 11.21 Charge-transfer complexes (CTCs) as indicators for damage and deformation in microcapsule-filled PDMS. (A) A mixture of microcapsules containing HMB (donor) or CA (acceptor), respectively, is embedded in PDMS films. Mechanical perturbation of the capsules releases the two species, which then form CTCs in the material. (B) Local colour change after cutting a PDMS film with a razor blade. (C) PDMS films before and after uniaxial tensile tests with different proportions of donor capsules and acceptor capsules. (D) UV-vis spectra showing changes in the absorbance corresponding to the formation of CTCs after stretching of the films.

Embedding the microcapsules directly within the fibre adds durability as the PCM is protected by a dual wall, the first being the wall of the microcapsule and the second being the surrounding fibre itself Thus, the PCM is less likely to leak from the fibre during its liquid phase, thus enhancing its life and the repeatability of the thermal response. 

The appearance of the individual microcapsules is shown in Fig. 1. Most individual microcapsules are approximately spherical and show a surface made up of deposited plates of poly(DL-lactic acid) in which the drug is embedded. Many of the larger microcapsules are cemented together by further plates of poly(DL-lactic acid). The effect of compression on these microcapsules is shown in Fig. 2. At a compressive force of 2 kN (Fig. 2(a)) the electron micrograph of the tablet fracture surface shows that the microcapsules, while distorted, remain essentially intact and rounded, with a relatively open porous structure to the tablet as a whole. At 10 kN force (Fig. 2(b)) the microcapsules at the fracture are flattened, cracked and distorted so that the fracture surface shows a far less open, porous aspect. Both of these microcap tablets have a very different appearance from that produced by the simple mixture (Fig. 3), where the individual plates of poly(DL-lactic acid) are mixed with the drug crystals in an open structure from which release would be easily... 

The mechanical properties of single hydrated dextran microcapsules (< 10 pm in diameter) with an embedded model protein drug have also been measured by the micromanipulation technique, and the information obtained (such as the Young s modulus) was used to derive their average pore size based on a statistical rubber elasticity theory (Ward and Hadley, 1993) and furthermore to predict the protein release rate (Stenekes et al., 2000). 

An important feature is film activation with micrometer precision by external stimulation with biofriendly near-IR light, which results in controlled release of film-embedded material [98,100], Laser activation of film-supported microcapsules shows remote release of encapsulated dextran by selective stimulation of the capsules with near-IR light (Fig. 6). Destruction of the HA/PLL film functionalized with gold nanoparticles occurs at irradiation with a light power of over 20 mW. Microcapsules modified with nanoparticles keep their integrity under the same conditions but become more permeable. 

Lu Z, Prouty MD, Guo Z et al (2005) Magnetic switch of permeability for polyelectrolyte microcapsules embedded with Co Au nanoparticles. Langmuir 21 2042-2050... 

The University of Illinois developed a technology for repairing hairline cracks in RPs by embedding microcapsules containing monomers corresponding to the plastic matrix.403 404... 

Figure 5.45. Schematic illustrating the mode of action of self-healing polymers through embedded healing-agent microcapsules that are activated by a propagating crack. Also shown is a polymeric microcapsule following rupture. Reproduced with permission from White, S. R. Sottos, N. R. Geubelle, R H. Moore, J. S. Kessler, M. R. Sriram, S. R. Brown, E. N. Viswanathan, S. Nature, 2001, 409, 794. Copyright 2001 Macmillan Magazines.

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