Progress in Organic Coatings 78 (2015) 474–479 Contents lists available at ScienceDirect Progress in Organic Coatings j o ur nal ho me pag e: www.elsevier.com/locate/porgcoat Functional substrates for the gradual release of agents R. Neto ∗ , A.P. Cardoso, C.J.S.M. Silva CeNTI, Centre for Nanotechnology and Smart Materials, Rua Fernando Mesquita, 2785, V. N. Famalicão 4760-034, Portugal a r t i c l e i n f o Article history: Available online 10 August 2014 Keywords: Functional textiles Gradual release Cyclodextrins a b s t r a c t This work describes the functionalization of a natural and a man-made textile substrate, namely cotton and polyamide 6.6, with inclusion agents, -cyclodextrins (-CDs) that are able to release gradually to the user active ingredients. In this study we used aescin (aesculus hippocastanum extract), which is a natural agent with benefits for the treatment of varicose veins. 1 H NMR and UV–vis data supported the role of -CDs as an aescin complexing agent, and the covalent nature of the linkage between -cyclodextrins and the textile substrates, which showed a wash fastness to more than 45 washing cycles. © 2014 Elsevier B.V. All rights reserved. 1. Introduction –1 Cyclodextrins (CDs) belong to the family of cyclic oligosaccha- rides, resulting from the linkage of several glucose units and have the shape of truncated cones [1]. Its most interesting property is the ability to include within its hydrophobic cavity different molecules (vitamins, colorants, flavorings, essential oils, among other com- pounds) [2]. Among the various natural CDs (-, -, -, corresponding, respectively, to the union of 6, 7, 8 glucose molecules), the - CDs expresses the relatively unusual characteristic of exchanging water with the environment in a quick and very effective way, which allows to form stable inclusion complexes with a wide vari- ety of molecules [3]. Hydrogen bonds, van der Waals interactions or hydrophobic interactions have been proposed as the interaction forces between the CDs and the encapsulated molecules [4]. One requirement for a favorable complexation is the size of the molecule to be encapsulated, which must be compatible with the size of the -CDs cavity. Another requirement is the polarity of the encapsulated molecule that must be hydrophobic, or contain hydrophobic parts. The competition with others compounds in the environment can also influence the complexation process. These limitations reduce the number of active principles, fragrances and other molecules that can be used for the complexation with CDs. Additionally, the different types of CDs show different capacities to form inclusion complexes due to stereochemistry limitations [5]. ∗ Corresponding author. Tel.: +351 252 104 152. E-mail addresses: rneto@centi.pt, ricardo net0@hotmail.com (R. Neto). As we can see in Table 1, the cavity diameter increases consider- ably from - to -CDs, as does the solubility in water at 25 ◦ C. This increment in solubility can be one factor of decision when we need to choose between the different types of cyclodextrins, for instance to increase the cellular permeability of different active principles. The process of complexation is showed schematically in Fig. 1. In general terms, the CDs are called the Host compounds and the molecule that will be included in the CDs is called the Guest. These types of interactions are designated as Host–Guest interactions. Among all the CDs the aspect that makes the -CDs so attrac- tive is the fact that they are one of the few complexing agents with unlimited availability and low cost, being usually produced by enzymatic hydrolysis of starch. On the other hand, they have no toxicity and are biologically degradable, glucose being the main degradation product [5]. Due to the large availability and non-toxicity, in the last decade, several advances were observed in the development of encapsu- lated substances in CDs, and specifically in the textile area, most of the performed studies concern the encapsulation and release of aromas [6]. CDs were also reported as forming complexes with detergent molecules [6]. Thus, they can be considered as a new class of auxiliary substances for the textile industry, with associ- ated advantages, including greater efficiency of the detergents and a reduction in the water used for washings. CDs can be used in washing processes for the removal of active agents retained on the fiber surface and can also form complexes in aqueous solution with the dyes used in dyeing processes, removing the fiber unfixed dyes in the subsequent washing step [7]. Other examples include the application of CDs for the removal of sweat [3,6]. One of the most important requirements for textiles is the wash- ing fastness property. To ensure a high wash fastness, there must be a covalent linkage between finishing products (inclusion agents, http://dx.doi.org/10.1016/j.porgcoat.2014.07.006 0300-9440/© 2014 Elsevier B.V. All rights reserved.