Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-02-09
2004-08-24
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C264S004100, C264S004300, C264S004330, C264S004700, C424S405000, C424S408000, C424S410000, C424S490000, C424S491000, C428S402220, C428S402240, C428S403000, C427S487000
Reexamination Certificate
active
06780507
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a novel method and apparatus for encapsulating discrete droplets of liquid by generating a continuous coating or layer of a polymerizable liquid which is substantially immiscible with the core liquid.
2. Background
Encapsulation refers to processes whereby an active ingredient is placed into a stabilized form in order to allow it to be conveniently stored, or protected from unfavorable conditions, until needed. The active ingredient may be dispersed in a protective matrix, or it may be surrounded by a coating, a shell, or a membrane. The release of active ingredient from the protected form may be rapid (such as by crushing, or by ingestion), or gradual (such as by dissolution, diffusion, or bio-degradation). In this manner it is possible to maximize the effectiveness of the active ingredient by ensuring that it is released at the proper time. This “controlled release” can also be made to occur over a programed time interval (sustained release), or on demand (stimulated release).
The term “microcapsule” has been used to describe small particles or beads, which range in size from less that one micron, up to several millimeters, which may contain a wide variety of active ingredients (Thies, 1994; Thies, 1987; Goodwin, 1974; Deasy, 1984; Hegenbart, 1993). Microcapsules can be divided into two broad groups: (1) “Aggregate” type microcapsules have the active ingredient dispersed uniformly throughout a continuous matrix. The matrix may be a solid dry polymer or a gel swollen with solvent. In the case where the gel is swollen with water, the term “hydrogel” is applied. Hydrogel encapsulation systems of this type are generally based on cross-linked forms of water-soluble polymers such as alginate, gelatin, pectin, agar, gellan, or starch (Sanderson, 1989). (2) “Mononuclear” microcapsules, on the other hand, consist of materials which show a true “shell-core” morphology. These are similar to an egg in that they have a solid shell or flexible membrane surrounding a core which may be a liquid, a solid, or even a gel.
Methods of producing microcapsules are the subject of several review articles (Sparks, 1981; Benita; 1996, Thies, 1994; Goodwin, 1974; Deasy, 1984; Hegenbart, 1993). Although numerous methods are described in these articles, the majority are simply not suitable for producing large (>500 micron diameter) mononuclear microcapsules which show a true shell-core morphology, and are capable of containing an aqueous-based solution as a core. Such capsules can be prepared with some degree of success, however, by using a method termed “concentric extrusion”. In this approach to microcapsule manufacture, two mutually immiscible liquids are extruded through concentric orifices in order to produce a biliquid column, with the core fluid on the inside. Under the influence of gravitational or other forces, this biliquid column fragments into discrete droplets having a shell/core morphology. The liquid shell is then made to harden by some mechanism to give liquid-core microcapsules with a solid shell.
Hardening of the shell is generally effected either by heating to remove a solvent, or by cooling to solidify the molten shell material. The outer coating in these systems is often either a molten wax, or a solution of aqueous polymer such as gelatin or alginate. The use of heat, either to melt the shell material, or to drive off solvent, can be detrimental to sensitive core materials such as protein solutions or suspensions of living organisms. Similarly, the use of solvent-based shell formulations can lead to undesirable contamination of the core material, as well as health and safety concerns. Aqueous-based shell formulations such as gelatin cannot be used in conjunction with aqueous core materials since phase incompatibility is a necessary prerequisite for formation of a shell/core morphology using this technique. Also, these types of shells are, by nature, easily affected by water, and also very susceptible to dehydration. Another drawback of the existing techniques is that the physical and mechanical properties of the shell materials suitable for use in these approaches are limited. Waxes, for instance, have very poor elasticity and mechanical strength, and also low melt viscosity which makes production of very thin membranes impractical. Low molecular weight thermoplastic polymers are generally too brittle and lack the flexibility to give strong, thin-walled, individual capsules. In fact, very few polymeric shell materials have melting points low enough to make existing approaches widely practical. Thin, flexible, and durable membranes are generally only associated with crosslinked elastomeric polymers. By nature, such polymers are insoluble and will not melt even at extreme temperatures, so they cannot be used in liquid form. It has been demonstrated that even though some strong high molecular weight thermoplastic polymers have suitably low melting points, they tend to “fiberize” rather than give individual droplets when extruded through an orifice. Related microcapsule fabrication techniques such as “centrifugal extrusion” suffer from similar drawbacks.
Examples of these existing techniques and their shortcomings can be found in various U.S. patents. Probably the first use of concentric fluid streams to accomplish the encapsulation of liquid agents was described in U.S. Pat. No. 2,275,154 (Merrill et al., Mar. 3, 1942). In that invention a medicinal component is surrounded by gelatin in a liquid form, and then the gelatin is caused to harden. Since gelatin is soluble in water, this method is useless for the encapsulation of aqueous liquids.
Similar methods are reported in the following U.S. Pat. No. 2,766,478 (Raley et al., Oct. 16, 1956); U.S. Pat. No. 2,799,897 (Jansen et al., Jul. 23, 1957); U.S. Pat. No. 2,911,672 (van Erven Dorens, Nov. 10, 1959); U.S. Pat. No. 3,015,128 (Somerville, Jan. 2, 1962); U.S. Pat. No. 3,310,612 (Somerville, Mar. 21, 1967); U.S. Pat. No. 3,389,194 (Somerville, Jun. 18, 1968); U.S. Pat. No. 3,423,489 (Arens et al., Jan. 21, 1969); and U.S. Pat. No. 3,779,942 (Bolles, Dec. 18, 1973). The shortcomings of these methods are described above, and are also discussed in U.S. Pat. No. 3,423,489. More recently, these shortcomings have been discussed in U.S. Pat. No. 5,478,508 (Suzuki et al., Dec. 26, 1995). This patent fails to successfully overcome the stated shortcomings, as it utilizes materials such as waxes, oils, fats, paraffins, thermoplastic resins, gelatin, or other water-soluble polymers for the shell material. The insufficiencies of these coatings have been described above.
Currently, there is a small specialty market for the sale of beneficial insects (such as lady beetles and parasitic wasps) for use in pest control on high value crops, such as greenhouses and nurseries producing “organically-grown” produce. Since the cost of naturally-produced beneficial insects is high, the resulting “green” produce that goes to market is sold only to a small number of customers willing to pay substantially higher prices. While mass rearing of phytophagous insects (plant feeding insects) is well developed and has been implemented in most entomological research organizations world-wide, mass rearing of entomophagous insects (insects that eat other insects) generally lags far behind. The reason for this large gap in rearing methods has been largely due to the lack of a suitable artificial substitute for the natural insect host diet. Although useful liquid diet formulations are currently being developed, there exist no suitable technologies for incorporating these aqueous-based liquid diets into practical forms for storage and presentation. Liquid-core hydrocapsules are a promising solution to this problem.
A laboratory method for encapsulating artificial diet for rearing predators of harmful insects by forming a paraffin coating over an artificial liquid diet has been described by Hagen and Tassan (1965). This method utilized a molten waxy polymer for the coating material, and as such i
Manukian Ara
Strohschein Rudolph
Toreki William
Acquah Samuel A.
Analytical Research Systems, Inc.
Van Oyke & Assoc., P.A.
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