Editing Micro-encapsulation

{{Short description|Process which surrounds tiny particles or droplets with a coating}}
{{More citations needed|date=January 2017}}
'''Microencapsulation''' is a process in which tiny [[Particle|particles]] or [[Drop (liquid)|droplets]] are surrounded by a [[coating]] to give small capsules, with useful properties.<ref>{{Cite book |last1=Amaral |first1=Pedro Henrique Rodrigues do |url=https://www.intechopen.com/chapters/67432 |title=Microencapsulation and Its Uses in Food Science and Technology: A Review |last2=Andrade |first2=Patrícia Lopes |last3=Conto |first3=Leilane Costa de |date=2019-09-27 |publisher=IntechOpen |isbn=978-1-83881-870-8 |language=en}}</ref><ref name=Ullmann>{{cite book|doi=10.1002/14356007.a16_575.pub2 |chapter=Microencapsulation |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2010 |last1=Lamprecht |first1=Alf |last2=Bodmeier |first2=Roland |isbn=978-3-527-30385-4 }}</ref> In general, it is used to incorporate [[Ingredient|food ingredients]],<ref>{{Cite journal |last1=Silva |first1=Pablo Teixeira da |last2=Fries |first2=Leadir Lucy Martins |last3=Menezes |first3=Cristiano Ragagnin de |last4=Holkem |first4=Augusto Tasch |last5=Schwan |first5=Carla Luisa |last6=Wigmann |first6=Évelin Francine |last7=Bastos |first7=Juliana de Oliveira |last8=Silva |first8=Cristiane de Bona da |date=2014|title=Microencapsulation: concepts, mechanisms, methods and some applications in food technology |journal=Ciência Rural |language=en |volume=44 |issue=7 |pages=1304–1311 |doi=10.1590/0103-8478cr20130971 |s2cid=42045080 |issn=0103-8478|doi-access=free }}</ref> [[Enzyme|enzymes]], [[Cell (biology)|cells]] or other materials on a [[Micrometre|micro metric]] scale. Microencapsulation can also be used to enclose [[Solid|solids]], [[Liquid|liquids]], or [[Gas|gases]] inside a micrometric wall made of hard or soft [[Solubility|soluble]] film, in order to reduce dosing frequency and prevent the degradation of [[pharmaceuticals]].<ref name="singh">{{cite journal|pmc=3093624|year=2010|last1=Singh|first1=M. N.|title=Microencapsulation: A promising technique for controlled drug delivery|journal=Research in Pharmaceutical Sciences|volume=5|issue=2|pages=65–77|last2=Hemant|first2=K. S.|last3=Ram|first3=M|last4=Shivakumar|first4=H. G.|pmid=21589795}}</ref>

In its simplest form, a '''microcapsule''' is a small sphere comprising a near-uniform wall enclosing some material. The enclosed material in the microcapsule is referred to as the core, internal phase, or fill, whereas the wall is sometimes called a shell, coating, or membrane. Some materials like lipids and [[Polymer|polymers]], such as [[alginate]], may be used as a mixture to trap the material of interest inside. Most microcapsules have pores with diameters between a few nanometers and a few micrometers. Materials generally used for coating are:
* [[Ethyl cellulose]]
* [[Polyvinyl alcohol]]
* [[Gelatin]]
* [[Alginic acid#Sodium alginate|Sodium alginate]]
* [[Formaldehyde resin]]
* [[Urea-formaldehyde]]
* [[Polyurea]]

The definition has been expanded, and includes most foods, where the encapsulation of [[Flavor (taste)|flavors]] is the most common.<ref>{{Cite journal |last1=Choudhury |first1=Nitamani |last2=Meghwal |first2=Murlidhar |last3=Das |first3=Kalyan |date=2021-06-18 |title=Microencapsulation: An overview on concepts, methods, properties and applications in foods |journal=Food Frontiers |volume=2 |issue=4 |pages=426–442 |doi=10.1002/fft2.94 |s2cid=237925118 |issn=2643-8429|doi-access=free }}</ref> The technique of microencapsulation depends on the [[Physical property|physical]] and [[Chemical property|chemical properties]] of the material to be encapsulated.<ref>{{Citation |last=Fanger |first=Gene O. |title=Microencapsulation: A Brief History and Introduction |date=1974 |url=https://doi.org/10.1007/978-1-4684-0739-6_1 |work=Microencapsulation: Processes and Applications |pages=1–20 |editor-last=Vandegaer |editor-first=Jan E. |place=Boston, MA |publisher=Springer US |language=en |doi=10.1007/978-1-4684-0739-6_1 |isbn=978-1-4684-0739-6 |access-date=2022-02-28|url-access=subscription }}</ref>

Many microcapsules however bear little resemblance to these simple spheres. The core may be a [[crystal]], a jagged [[Adsorption|adsorbent]] particle, an [[emulsion]], a [[Pickering emulsion]], a [[Suspension (chemistry)|suspension]] of solids, or a suspension of smaller microcapsules. The microcapsule even may have multiple walls.
{{Quote box
 |title =[[International Union of Pure and Applied Chemistry|IUPAC]] definition
 |quote = '''Microcapsule''': Hollow ''microparticle'' composed of a solid shell surrounding a<br/>core-forming space available to permanently or temporarily entrapped substances.

''Note'': The substances can be flavour compounds, pharmaceuticals, pesticides, dyes, or similar materials.
}}

==Techniques of microcapsule manufacture==

Ionotropic gelation occurs when units of [[uric acid]] in the chains of the polymer [[alginate]], crosslink with multivalent cations. These may include, calcium, zinc, iron and aluminium.

Coacervation-phase separation consists of three steps carried out under continuous agitation.
# Formation of three immiscible chemical phases: liquid manufacturing vehicle phase, core material phase and coating material phase.
# Deposition of coating: core material is dispersed in the coating polymer solution. Coating polymer material coated around core. Deposition of liquid polymer coating around core by polymer adsorbed at the interface formed between core material and vehicle phase.
# Rigidization of coating: coating material is immiscible in vehicle phase and is made rigid. This is done by thermal, cross-linking, or dissolution techniques.

=== Interfacial polycondensation ===
In interfacial polycondensation, the two reactants in a [[polycondensation]] meet at an interface and react rapidly. The basis of this method is the classical [[Schotten-Baumann reaction]] between an [[acid chloride]] and a compound containing an active hydrogen atom, such as an [[amine]] or [[Alcohol (chemistry)|alcohol]], [[polyester]]s, [[polyurea]], [[polyurethane]]. Under the right conditions, thin flexible walls form rapidly at the interface. A solution of the pesticide and a diacid chloride are emulsified in water and an aqueous solution containing an amine and a polyfunctional [[isocyanate]] is added. Base is present to neutralize the acid formed during the reaction. Condensed polymer walls form instantaneously at the interface of the emulsion droplets.

=== Interfacial cross-linking ===
Interfacial cross-linking is derived from interfacial polycondensation, and was developed to avoid the use of toxic diamines, for pharmaceutical or cosmetic applications. In this method, the small bifunctional monomer containing active hydrogen atoms is replaced by a biosourced polymer, like a protein. When the reaction is performed at the interface of an emulsion, the acid chloride reacts with the various functional groups of the protein, leading to the formation of a membrane. The method is very versatile, and the properties of the microcapsules (size, porosity, degradability, mechanical resistance) can be customized. Flow of artificial microcapsules in microfluidic channels:

=== In situ polymerization ===
In a few microencapsulation processes, the direct polymerization of a single [[monomer]] is carried out on the particle surface. In one process, e.g. [[cellulose]] fibers are encapsulated in [[polyethylene]] while immersed in dry [[toluene]]. Usual deposition rates are about 0.5μm/min. Coating thickness ranges {{convert|0.2|-|75|μm|mil|abbr=on}}. The coating is uniform, even over sharp projections. Protein microcapsules are [[biocompatible]] and [[biodegradable]], and the presence of the protein backbone renders the membrane more resistant and elastic than those obtained by interfacial polycondensation.

=== Matrix polymerization ===
In a number of processes, a core material is imbedded in a polymeric matrix during formation of the particles. A simple method of this type is spray-drying, in which the particle is formed by evaporation of the solvent from the matrix material. However, the solidification of the matrix also can be caused by a chemical change.

==Release methods and patterns==
Even when the aim of a microencapsulation application is the isolation of the core from its surrounding, the wall must be ruptured at the time of use. Many walls are ruptured easily by pressure or [[shear stress]], as in the case of breaking dye particles during writing to form a copy. Capsule contents may be released by melting the wall, or dissolving it under particular conditions, as in the case of an [[enteric drug coating]].<ref>{{cite web |publisher=Freedictionary.com | title=Medical Dictionary: Enteric coating | url=http://medical-dictionary.thefreedictionary.com/coating%2c+enteric |accessdate = 9 February 2009}}</ref> In other systems, the wall is broken by solvent action, [[enzyme]] attack, chemical reaction, [[hydrolysis]], or slow disintegration.

Microencapsulation can be used to slow the release of a drug into the body. This may permit one controlled release dose to substitute for several doses of non-encapsulated drug and also may decrease toxic side effects for some drugs by preventing high initial concentrations in the blood. There is usually a certain desired release pattern. In some cases, it is zero-order, i.e. the release rate is constant. In this case, the microcapsules deliver a fixed amount of drug per minute or hour during the period of their effectiveness. This can occur as long as a solid reservoir or dissolving drug is maintained in the microcapsule.
 
A more typical release pattern is first-order in which the [[Rate (mathematics)|rate]] [[exponential decay|decreases exponentially]] with time until the drug source is exhausted. In this situation, a fixed amount of drug is in solution inside the microcapsule. The concentration difference between the inside and the outside of the capsule decreases continually as the drug diffuses.

Nevertheless, there are some other mechanisms that may take place in the liberation of the encapsulated material. These include, biodegradation, osmotic pressure, diffusion, etc. Each one will depend on the composition of the capsule made and the environment it is in. Therefore, the liberation of the material may be affected by various mechanisms that act simultaneously.<ref>{{cite journal | last1 = Barba | first1 = A.A. | last2 = d'Amore | first2 = M. | last3 = Chirico | first3 = S. | last4 = Lamberti | first4 = G. | last5 = Titomalino | first5 = G. | year = 2009 | title = A general code to predict the drug release kinetics from different shaped matrices | journal = European Journal of Pharmaceutical Sciences | volume = 36 | issue = 2–3| pages = 359–368 | doi=10.1016/j.ejps.2008.10.006|pmid=19022380}}</ref>

==Applications==
Applications of micro-encapsulation are numerous.  It is mainly used to increase the stability and life of the product being encapsulated, facilitate the manipulation of the product and provide for the controlled release of the contents.  
*Microencapsulation is used to preserve [[vitamin A]] from the deteriorating effects of [[oxygen]].<ref name=Ullmann/>
*In other cases, the objective is not to isolate the core completely but to control the rate at which it releases the contents, as in the [[Modified-release dosage|controlled-release]] of drugs<ref>{{Cite journal |last1=Singh |first1=M.N. |last2=Hemant |first2=K.S.Y. |last3=Ram |first3=M. |last4=Shivakumar |first4=H.G. |date=2010 |title=Microencapsulation: A promising technique for controlled drug delivery |journal=Research in Pharmaceutical Sciences |volume=5 |issue=2 |pages=65–77 |issn=1735-5362 |pmc=3093624 |pmid=21589795}}</ref>  Ferrous sulfate, a nutritional supplement, is microencapsulated in a way that it passes through the stomach but releases in the intestine.  In this way, gastric upset is minimized.  Aspirin is treated similarly.
*Some sunscreens are encapsulated in [[silica gel]].  One brand is "Eusolex UV-Pearls". These chemicals are potentially [[hormone disrupting]], so the encapsulation protects the user until the time of application.<ref>{{cite journal |doi=10.1021/cr100161x |title=From Molecules to Systems: Sol−Gel Microencapsulation in Silica-Based Materials |date=2011 |last1=Ciriminna |first1=Rosaria |last2=Sciortino |first2=Marzia |last3=Alonzo |first3=Giuseppe |last4=Schrijver |first4=Aster de |last5=Pagliaro |first5=Mario |journal=Chemical Reviews |volume=111 |issue=2 |pages=765–789 |pmid=20726523 }}</ref>
*[[Pesticide|pesticides]] are dangerous to handle but less so when encapsulated.<ref>{{cite journal | last1 = Hedaoo | first1 = Rahul K. |display-authors=etal  | year = 2014 | title = Fabrication of Core–Shell Novel Polyurea Microcapsules Using Isophorone Diisocyanate (IPDI) Trimer for Release System | journal = International Journal of Polymeric Materials and Polymeric Biomaterials | volume = 63 | issue = 7| pages = 352–360 | doi=10.1080/00914037.2013.845191| s2cid = 94019457 }}</ref><ref>RK Hedaoo, PP Mahulikar, VV Gite, Synthesis and characterization of resorcinol-based cross linked phenol formaldehyde microcapsules for encapsulation of pendimethalin, Polymer-Plastics Technology and Engineering 52 (3), 243-249, https://doi.org/10.1080/03602559.2012.745555</ref>
*The problem may be as simple as masking the [[taste]] or [[odor]] of the core, or as complex as increasing the selectivity of an [[adsorption]] or [[solvent extraction|extraction]] process.  In [[environmental science]], a [[pesticide]] may be microencapsulated to minimize leaching or volatilization risks.<ref>{{cite journal|last=Mervosh|first=T.L.|author2=EW Stoller |author3=FW Simmons |author4=TR Ellsworth |author5=GK Sims |title=Effects of starch encapsulation on clomazone and atrazine movement in soil and clomazone volatilization|journal=Weed Science|year=1995|volume=43|issue=3|pages=445–453|doi=10.1017/S0043174500081455|s2cid=138347374 }}</ref>  

<!--
 [[Adhesive]]s
* [[Coating|Anti-corrosive coatings]]
* [[Carbonless copy paper]]
* [[Electronic Paper#Electrophoretic|E-paper or e-ink]]
* [[Essential oil]]s, [[Flavoring|flavor]]s and other volatile bioactives for food or in [[feed additive]]s
* [[Phase-change material|Phase change materials]]
* [[Perfume|Powder perfume]]
* [[Scratch-n-sniff]]
* [[Self-healing material]] such as novel plastics that can automatically repair damage: 
* [[Textile]]s
* Temperature release (controlled release) in baking 
* [[Thermochromic]] dyes
* [[Time release technology]] for [[pharmaceutical]]s
* Visual [[wikt:indicator|indicators]]
* Self healing coatings-->
* DNA protection from degradation for product tracing<ref name=Puddu>{{Cite journal | doi = 10.1021/nn4063853| pmid = 24568212| title = Magnetically Recoverable, Thermostable, Hydrophobic DNA/Silica Encapsulates and Their Application as Invisible Oil Tags| journal = ACS Nano| volume = 8| issue = 3| pages = 2677–2685| year = 2014| last1 = Puddu | first1 = M. | last2 = Paunescu | first2 = D. | last3 = Stark | first3 = W. J. | last4 = Grass | first4 = R. N. }}</ref> and [[DNA digital data storage|data storage]]<ref name=grass>{{Cite journal | doi = 10.1002/anie.201411378| title = Robust Chemical Preservation of Digital Information on DNA in Silica with Error-Correcting Codes| journal = Angewandte Chemie International Edition| volume = 54| issue = 8| pages = 2552–2555| year = 2015| last1 = Grass | first1 = R. N. | last2 = Heckel | first2 = R. | last3 = Puddu | first3 = M. | last4 = Paunescu | first4 = D. | last5 = Stark | first5 = W. J. | pmid=25650567}}</ref>
* Protection of bioactive compounds that are easily degradated under normal environmental conditions.<ref>{{Cite journal|last1 = Aizpurua-Olaizola|first1 = Oier|last2 = Navarro|first2 = Patricia|last3 = Vallejo|first3 = Asier|last4 = Olivares|first4 = Maitane|last5 = Etxebarria|first5 = Nestor|last6 = Usobiaga|first6 = Aresatz|date = 2016-01-01|title = Microencapsulation and storage stability of polyphenols from Vitis vinifera grape wastes|journal = Food Chemistry|volume = 190|pages = 614–621|doi = 10.1016/j.foodchem.2015.05.117|pmid = 26213018| url=https://figshare.com/articles/journal_contribution/5028350 }}</ref>

== See also ==

* [[Dry water]]
* [[Alcohol powder]]

==References==
{{Reflist}}

==Bibliography==
* Prakash, S. et al. "The Gut Microbiota and Human Health with an Emphasis on the Use of Microencapsulated Bacterial Cells",  [http://www.hindawi.com/journals/jbb/2011/981214/ Journal of Biomedicine and Biotechnology (2011)],
* {{cite journal | last1 = Brandau | first1 = T | year = 2002 | title = Preparation of monodisperse controlled release microcapsules | journal = Int. J. Pharm. | volume = 242 | issue = 1–2| pages = 179–184 | doi=10.1016/S0378-5173(02)00151-5| pmid = 12176243 }}

==External links==
* [http://www.swri.org/4org/d01/microenc/microen/ Southwest Research Institute]
* [https://www.maxxperformance.com/?gclid=CjwKCAiAgvKQBhBbEiwAaPQw3KHM_FWfdQv8PbuuKcOPFpTtNQl919E2m2K_dlGG0iLUEFfukyjBFhoC61gQAvD_BwE|Maxx Performance - Food & Animal Feed Solutions]
* [https://calyxia.com/technology |Advanced, Customizable & Biodegradable Microcapsules | Calyxia]
* [https://microporetech.com/making-products-better/membrane-encapsulation?ppc_keyword=&gclid=CjwKCAiAgvKQBhBbEiwAaPQw3OxLxEwjZ4aEVGhcsRqou-C-ln5a1dyRfQdjtoVppmE9RV3WlgJg6hoCIEQQAvD_BwE |Micropore]

{{Authority control}}

{{DEFAULTSORT:Micro-Encapsulation}}
[[Category:Polymers]]