It can be prepared get downing from glycolic acid by agencies of polycondensation or ring-opening polymerisation.
PGA has been known since 1954 as a tough fiber-forming polymer. Owing to its hydrolytic instability, nevertheless, its usage has ab initio been limited. Currently polyglycolide and its copolymers ( poly ( lactic-co-glycolic acid ) with lactic acid, poly ( glycolide-co-caprolactone ) with Iµ-caprolactone, and poly ( glycolide-co-trimethylene carbonate ) with trimethylene carbonate ) are widely used as a stuff for the synthesis of absorbable suturas and are being evaluated in the biomedical field.
Polyglycolide has a glass passage temperature between 35-40 A°C and its thaw point is reported to be in the scope of 225-230 A°C.
PGA besides exhibits an elevated grade of crystallinity, around 45-55 % , therefore ensuing in unsolvability in H2O. [ 2 ] The solubility of this polyester is slightly alone, in that its high molecular weight signifier is indissoluble in about all common organic dissolvers ( propanone, methylene chloride, trichloromethane, ethyl ethanoate, tetrahydrofuran ) , while low molecular weight oligomers sufficiently differ in their physical belongingss to be more soluble.
However, polyglycolide is soluble in extremely fluorinated dissolvers like hexafluoroisopropanol ( HFIP ) and hexafluoroacetone sesquihydrate, that can be used to fix solutions of the high MW polymer for thaw spinning and movie readying. [ 3 ] Fibers of PGA exhibit high strength and modulus ( 7 GPa ) and are peculiarly stiff.
[ 2 ] Polycondensation of glycolic acid is the simplest procedure available to fix PGA, but it is non the most efficient because it yields a low molecular weight merchandise. Briefly, the process is as follows: glycolic acid is heated at atmospheric force per unit area and a temperature of about 175-185A°C is maintained until H2O ceases to purify. Subsequently, force per unit area is reduced to 150A millimeter Hg, still maintaining the temperature unaltered for about two hours and the low MW polyglycolide is obtained. [ 4 ]The most common synthesis used to bring forth a high molecular weight signifier of the polymer is ring-opening polymerisation of “ glycolide ” , the cyclic diester of glycolic acid.
Glycolide can be prepared by heating under reduced force per unit area low MW PGA, roll uping the diester by agencies of distillment. Ring-opening polymerisation of glycolide can be catalyzed utilizing different accelerators, including antimony compounds, such as antimony trioxide or Sb trihalides, Zn compounds ( zinc lactate ) and tin compounds like stannic octoate ( Sn ( II ) 2-ethylhexanoate ) or Sn alkoxides.Stannic octoate is the most normally used instigator, since it is approved by the FDA as a nutrient stabilizer. Use of other accelerators has been disclosed every bit good, among these are aluminium isopropoxide, Ca acetylacetonate, and several rare earth alkoxides ( e.
g. Y isopropoxide ) . [ 4 ] [ 5 ] [ 6 ] The process followed for ring-opening polymerisation is briefly outlined: a catalytic sum of instigator is added to glycolide under a N atmosphere at a temperature of 195A°C. The reaction is allowed to continue for approximately two hours, so temperature is raised to 230A°C for approximately half an hr.
After hardening the ensuing high MW polymer is collected. [ 4 ]Ring-opening polymerisation of glycolide to polyglycolideAnother process consists in the thermally induced solid-state polycondensation of halogenoacetates with general expression X — CH2COO-M+ ( where M is a monovalent metal like Na and X is a halogen like Cl ) , ensuing in the production of polyglycolide and little crystals of a salt. Polycondensation is carried out by heating an halogenoacetate, like Na chloroacetate, at a temperature between 160-180A°C, continuously go throughing N through the reaction vas. During the reaction polyglycolide is formed along with Na chloride which precipitates within the polymeric matrix ; the salt can be handily removed by rinsing the merchandise of the reaction with H2O.
PGA can besides be obtained by responding C monoxide, methanal or one of its related compounds like paraformaldehyde or trioxane, in presence of an acidic accelerator. In a C monoxide atmosphere an sterilizer is loaded with the accelerator ( chlorosulfonic acid ) , methylene chloride and trioxane, so it is charged with C monoxide until a specific force per unit area is reached ; the reaction is stirred and allowed to continue at a temperature of about 180A°C for two hours. Upon completion the unreacted C monoxide is discharged and a mixture of low and high MW polyglycolide is collected. [ 8 ]Polyglycolide is characterized by hydrolytic instability owing to the presence of the ester linkage in its anchor.
The debasement procedure is erosive and appears to take topographic point in two stairss during which the polymer is converted back to its monomer glycolic acid: first H2O diffuses into the formless ( non-crystalline ) parts of the polymer matrix, spliting the ester bonds ; the 2nd measure starts after the formless parts have been eroded, go forthing the crystalline part of the polymer susceptible to hydrolytic onslaught. Upon prostration of the crystalline regions the polymer concatenation dissolves.When exposed to physiological conditions, polyglycolide is degraded by random hydrolysis, and seemingly it is besides broken down by certain enzymes, particularly those with esterase activity. The debasement merchandise, glycolic acid, is atoxic, and it can come in the tricarboxylic acid rhythm, after which it is excreted as H2O and C dioxide.
A portion of the glycolic acid is besides excreted by piss. [ 9 ]Surveies undergone utilizing polyglycolide-made suturas have shown that the stuff loses half of its strength after two hebdomads and 100 % after four hebdomads. The polymer is wholly resorbed by the being in a clip frame of four to six months. [ 2 ] Degradation is faster in vivo than in vitro, this phenomenon thought to be due to cellular enzymatic activity.
[ 10 ]While known since 1954, PGA had found little use because of its sensitiveness to hydrogenolysis when compared with other man-made polymers. However in 1962 this polymer was used to develop the first man-made absorbable sutura which was marketed under the tradename of Dexon [ 1 ] by the Davis & A ; Geck subordinate of the American Cyanamid Corporation. It is sold today as Surgicryl.PGA sutura is classified as a man-made, absorbable, braided multifilament.
It is coated with N-laurin and L-lysine, which render the yarn highly smooth, soft and safe for knotting. It is besides coated with Mg stearate and eventually sterilized with ethylene oxide gas. It is of course degraded in the organic structure by hydrolysis and is absorbed as water-soluble monomers, completed between 60 and 90 yearss. Aged, anaemic and malnourished patients may absorb the sutura more rapidly.
Its colour is either violet or unbleached and it is sold in sizes USP 6-0 ( 1 metric ) to USP 2 ( 5 metric ) . It has the advantages of high initial tensile strength, smooth transition through tissue, easy handling, first-class knotting ability, and unafraid knot binding. It is normally used for hypodermic suturas, intradermal closings, abdominal and pectoral surgeries.The traditional function of PGA as a biodegradable sutura stuff has led to its rating in other biomedical Fieldss.
Implantable medical devices have been produced with PGA, including inosculation rings, pins, rods, home bases and prison guards. [ 2 ] It has besides been explored for tissue technology or controlled drug bringing. Tissue technology scaffolds made with polyglycolide have been produced following different attacks, but by and large most of these are obtained through fabric engineerings in the signifier of non-woven meshes.The Kureha Corporation has announced its commercialisation of high molecular weight polyglycolide for nutrient packaging applications under the tradename of KureduxA® .
Production is at Belle, West Virginia, with an intended capacity of 4000 one-year metric dozenss, harmonizing to a Chemicals Technology study. Its properties as a barrier stuff consequence from its high grade of crystallisation, the footing for a Byzantine way mechanism for low permeableness.It is anticipated that the high molecular weight version will hold usage as an interlayer between beds of polythene terephthalate to supply improved barrier protection for perishable nutrients, including carbonated drinks and nutrients that lose freshness on drawn-out exposure to air. Thinner plastic bottles which still retain desirable barrier belongingss may besides be enabled by this polyglycolide interlayer engineering.
A low molecular weight version ( about 600 amu ) is available from the DuPont Co. and is purported to be utile in oil and gas applications.What Is Polyglycolic Acid?By Nacie Carson, eHow ContributorPolyglycolic acid, besides referred to Polyglycolide or PGA, is a simple yet lasting fiber-based polymer foremost discovered in 1954. It is derived from chitin, a biological stuff responsible for the strength and rigidness of the exoskeletons aquatic life, such as pediculosis pubiss and runt, every bit good as the midst walls of fungi growings.
PGA is used predominately as an absorbable surgical sutura ; nevertheless, due to the ductile chemical construction of the basic PGA molecule, the complete scope of usage for this compound is as yet unknown.UsesThe most good known usage of PGA is as an absorbable medical sutura. An absorbable sutura means the stuff used to shut a lesion does non necessitate to be removed as it will finally fade out into the environing tissue. The stiff yet natural belongingss of PGA make it an ideal absorbable sutura ; it is normally used to shut internal scratchs during bariatric, abdominal and cardiac surgeries.
Its success as a sutura has besides led to the development of other PGA-based medical implants, such as impermanent pins, home bases, rods and connective rings. There is besides the potency that PGA in mesh signifier can progress the field of man-made tissue technology.PotentialOne of the cardinal facets of PGA ‘s potency is the ability for extra chemical ironss to be attached to the basic polyglycolic compound. This means that extra belongingss can be integrated into the basic absorbable fibre make-up of the compound, increasing its scope of applications.
Some research has already been performed sing the add-on of side ironss, ensuing in varied snap, length of service and strengths of suturas and other devices.Creation and DegradationPGA is most normally derived from the procedure of the polymerisation of glycolic acid, which involves utilizing zinc-based compounds to catalyst a reaction between a polymer and a sodium-based acid. Sodium chloride, besides known as table salt, is a by-product of the reaction and can be easy removed from the ensuing PGA fibres. Over clip, PGA can be broken down by assorted biological enzymes and will finally degrade into the simple and non-toxic constituents of glycolic acid, H2O, and C dioxide.
Inside the human organic structure, it will take four to six months for PGA to be wholly absorbed.Physical PropertiesAs a chemical compound, polyglycolic acid has several distinguishable physical belongingss that support its usage as an absorbable medical tool. First, and possibly most of import, due to its crystalline construction, PGA is H2O indissoluble, which means it will non disintegrate in the human organic structure. However, the bendability of PGA fibres increases when moisture, leting them to be shaped easy.
Second, the runing point of PGA is estimated to be between 225 and 230 grades Celsius, far above even the highest temperature possible in the human organic structure. A concluding key physical belongings of PGA is the flexible rigidness of the fibres, which allows them a grade of motion while still keeping a steadfast form.BenefitsMaterials made from polyglycolic acid are preferred to standard, non-biodegradable surgical options due to the many benefits they yield. One major benefit of PGA suturas is that they support faster wound mending than traditional man-made suturas that can decelerate or even endanger proper healing.
Similarly, the enzyme reaction that occurs between tissue and the PGA is negligible and does non bring forth any inauspicious consequence for the lesion or environing tissue. Besides, as they are absorbed into the environing tissue, there is no demand to foster traumatise the country with their remotion.
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