The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "Hydrogel capsules are water-swollen cross-linked polymeric structures that are typically used when there is a need to provide a stable environment for a volatile or oxygen-sensitive active ingredient in contact with a high moisture environment.
"They are used in medical applications and, more recently, in flavor and fragrance applications. For instance WO-A1-2006/119660 and EP-A1-1841521 (both to
"Hydrogel capsules are typically formed by the process of coacervation, about which many publications exist, such as WO-A1-96/32017 (Tastemaker), FR1165805 (
"In the standard complex coacervation process, there is separation of a colloid into a colloid-rich phase (the coacervate) and an aqueous solution of the coacervating agent (the equilibrium liquid), forming an oil coated with protein, carbohydrate, or polymeric droplets so as to suspend the oil in water. The phases are absorbed into one lipid phase and one aqueous phase. The first lipid phase forms the core which is surrounded by a hydrogel capsule. The hydrogel capsule is a colloid in which the dispersed phase has combined with the continuous phase (water) to produce a viscous gelatinous product.
"Whilst coacervation is useful for encapsulating active ingredients such as flavors and fragrances, the gel-like nature of conventional coacervates limits their applicability. It would therefore be desirable to address this problem.
"In particular, classical coacervate capsules remain resistant to mechanical rupture under both small and large mechanical deformations. However, while mechanical resistance at small loads (such as those encountered during storage or processing) is desirable, mechanical resistance becomes problematic if it prevents the intended rupture of the capsule under strong deformations such as those encountered during chewing, rubbing, or squeezing the capsule in the final application (where the capsule is expected to burst, rather than to be mechanically resistant). Under those 'high deformation' conditions, classical coacervate capsules are deformed in a manner similar to a crosslinked 'rubber', but it would be advantageous to have capsules that behave like a 'rigid' and brittle solid shell at high loads.
"Capsules with desirable mechanical properties in the context of this invention are therefore capsules that are resistant to weak mechanical loads, but that can be made to burst easily when subjected to an imposed deformation.
"The use of Si(OEt).sub.4 (hereinafter also referred to as 'TEOS') in the formation of capsules has been described in the publication 'Synthesis of Mesoporous Silica Nanospheres Promoted by Basic Amino Acids and their Catalytic Application',
"U.S. Pat. No. 7,611,731 (
"GB 2473870 (
"US2010/0143422A1 describes microcapsules composed of a sol-gel material that contain active ingredients. The examples given therein are based on emulsification of fragrance oils containing TEOS, emulsification of fragrance oils with subsequent addition of TEOS, or emulsification of fragrance oils with subsequent addition of TEOS where the TEOS has been previously hydrolyzed. The structure of the microcapsules consists of a fragrance core and a sol-gel wall material. The process, which consists of precipitation, is to not confined to the scaffold of a hydrogel shell and so does not allow for localized and controlled formation of the TEOS inorganic phase. It also may result in excessive precipitation in a core liquid. It would be desirable to avoid such drawbacks.
"Moreover, said document discloses a shell which is made only of silica and although silica-only microcapsules, which are brittle, might offer good mechanical properties for the release of the active ingredient, it is known to the experimenter skilled in the art that microcapsules with silica-only shells are highly porous material, and as such it is a poor protective barrier for active ingredients such as volatile perfume oils or flavors. The prior art document suggests to solve this problem by adding a spray-drying step to entrap the core-shell capsules into an additional starch matrix.
"However, while matrix encapsulates are known to provide good barrier properties, they do not possess any of the highly desirable mechanical properties of core/shell capsules for a controlled release. In particular, it would be desirable to have a capsule that provides both excellent barrier properties during storage and processing of the final product (such a food or consumer product) while also providing the mechanical properties needed for a 'burst'-type release upon fracture.
"Our present invention overcomes the above-mentioned drawbacks by providing a core/shell capsule with a composite shell comprising an organic and an inorganic phase based on polymeric strands with silica interspersed therein.
"In the publication 'Facile method for preparing organic/inorganic hybrid capsules using amino-functional silane coupling agent in aqueous media' by Kurayama et al,
"WO 2004/103351 A1 (Tirelli and Cellesi, The University of
"Neither the intermediate product nor the final product contains silica in the shell of the capsule. Silica is only part of the sacrificial core template and is later dissolved. The barrier and mechanical properties of the capsule are therefore those of the organic polymer shell alone. Since such hydrogel shells alone are known to be permeable and poorly suited for volatile ingredients such as flavor and fragrance molecules, it would be desirable to overcome this physical limitation and make core/shell capsules wherein the shell becomes a dense, reinforced barrier superior to a traditional hydrogel shell.
"It becomes obvious from the above review of the background and prior art that classical hydrogel and coacervate capsules do not possess the mechanical properties desired for a capsule that provides a good protective barrier and is mechanically resistant to small loads, but that easily bursts as it is deformed.
"The present invention seeks to provide a new hydrogel encapsulation system that addresses one or more of the problems highlighted above. Preferably, the present invention addresses the problems associated with conventional hydrogel systems, such as lack of ridigity."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Accordingly, the invention provides a process for preparing a core-shell capsule comprising the steps of: (i) mixing a solid active ingredient and/or an oily liquid active ingredient with a polymeric material capable of forming a hydrogel shell around the active ingredient(s); (ii) forming a shell comprising a hydrogel scaffold formed of a polymeric lattice around the core; (iii) optionally cross-linking the polymeric lattice; (iv) contacting the optionally cross-linked core-shell hydrogel shell with a liquid silica precursor so as to cause precipitation of silica particles within the scaffold structure thereby forming a composite shell of silica particles interspersed between the polymeric lattice.
"The present invention further provides a core-shell capsule wherein (a) the shell is a composite comprising an organic and an inorganic phase, the organic phase comprising a network of polymeric strands and the inorganic phase comprising silica, and wherein the inorganic phase is physically interspersed between at least a proportion of the organic phase; and (b) the core comprises a solid active ingredient and/or an oily liquid active ingredient.
"Preferably, the composite shell provides a barrier against loss of the active ingredient into the environment.
"Preferably, the composite shell provides excellent mechanical stability to the capsule under small mechanical loads but easily bursts to allow release of the ingredient under higher mechanical loads.
"'Oily' in the context of this invention means that the liquid active ingredient in water is fully or partially immiscible with water so that it can be dispersed in the form of discrete emulsion drops within an aqueous phase during the manufacturing of the capsules.
"Preferably, oily means that the liquid active ingredient has an interfacial tension against to water of at least 0.0001 N/m, preferably an interfacial tension of at least 0.001 N/m.
"Preferably, the oily liquid typically contains at least one component for which the value of the base-ten logarithm of the partition coefficient between octanol and water (log P) is greater than 4; the oil may contain additional components with log P less than 4.
"In another aspect, the invention provides the use of silica physically interspersed in the shell portion of a hydrogel core-shell capsule comprising a liquid flavor or fragrance in the core portion to increase the rigidity and/or mechanical stability of the capsule.
BRIEF DESCRIPTION OF THE DRAWINGS
"FIG. 1 shows the absorption of TEOS into the scaffold of a hydrogel shell;
"FIG. 2 shows the content of silica within a hydrogel shell;
"FIG. 3 shows the measured silicon content in a hydrogel shell; and
"FIG. 4 shows the shape of a silica/hydrogel capsule according to the invention.
"FIG. 5 shows the mechanical behavior of a core-shell capsule according to the invention, a traditional core-shell capsule without silica, and a matrix (non-core/shell) encapsulate. Force (normalized with the force at rupture) is plotted against deformation."
For additional information on this patent application, see: Dardelle, Gregory;
Keywords for this news article include: Alcohols, Hydrogel,
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