Biomedical applications, aliphatic

This review aims at reporting on the synthesis of aliphatic polyesters by ROP of lactones. It is worth noting that lactones include cyclic mono- and diesters. Typical cyclic diesters are lactide and glycolide, whose polymerizations provide aliphatic polyesters widely used in the frame of biomedical applications. Nevertheless, this review will focus on the polymerization of cyclic monoesters. It will be shown that the ROP of lactones can take place by various mechanisms. The polymerization can be initiated by anions, organometallic species, cations, and nucleophiles. It can also be catalyzed by Bronsted acids, Lewis acids, enzymes, organic nucleophiles, and bases. The number of processes reported for the ROP of lactones is so huge that it is almost impossible to describe aU of them. In this review, we will focus on the more... 

Malberg S, Plikk P, Fiime-Wistrand A, Albertsson A-C (2010) Design of elastomeric homo-and copolymer networks of functional aliphatic polyester for use in biomedical applications. Chem Mater 22 3009-3014... 

Aliphatic polyesters have received great interest for potential biomedical application. Polythioesters (polyesters in which one of the oxygen atoms of the ester groups has been replaced by a sulfur atom) have received less attention, although these materials are expected to show interesting material properties such as higher... 

Aliphatic polyesters are an attractive class of polymer that can be used in biomedical and pharmaceutical applications. One reason for the growing interest in this type of degradable polymer is that their physical and chemical properties can be varied over a wide range by, e.g., copolymerization and advanced macro-molecular architecture. The synthesis of novel polymer structures through ringopening polymerization has been studied for a number of years [1-5]. The development of macromolecules with strictly defined structures and properties, aimed at biomedical applications, leads to complex and advanced architecture and a diversification of the hydrolyzable polymers. 

A report on the biomedical application of activated carbon adsorption [600] is also revealing. The authors analyzed the uptakes of an aromatic compound, acetaminophen (active ingredient in Tylenol, pKj = 9.5), and an aliphatic one, (V-acetylcysteine (which provides a protective effect against acetaminophen overdose pKa = 3.3), under both gastric (pH = 1.2) and intestinal (pH = 7.0) conditions. Their results are reproduced in Table 24. 

Aliphatic polyesters (such as PLA, polyglycolic acid and their copolymers) are the most important class of biocompatible polymers used in biomedical applications. This class of polymers has shown superior properties over conventional polymers, such as excellent biocompatibility, biodegradation, and thermal, physical and mechanical properties, which make them suitable for applications in drug delivery and tissue engineering [19-21]. 

Polyesters can be synthesized either by ring-opening polymerization (ROP) or polycondensation. Both of these approaches have merit in the manipulation of properties of degradable polymers. Commercially, ROP is the most widely used practice for the synthesis of PHAs for consumer applications due to the ease of scale up, acceptable purity, and cost considerations. However, for biomedical applications where cost pressures are low and purity and function are paramount, condensation polymerization can yield superior outcomes [20]. Although the class of degradable polymers is rather large and includes poly(butyrolactones), poly(dioxanone), aliphatic poly(carbonates), poly(anhydrides), and poly(hydroxyalkanoates), the focus of the subsequent sections will be on the PGA, PLA, and poly(caprolactone) (PCL) family of polymers, as these are the most widely used polymers in both medical and consumer products arena. 

Feng, R.-X. Zhuo, X.-Z. Zhang, Construction of functional aliphatic polycarbonate for biomedical applications, Prog. Polym. Sci. 37(2012)211-236. 

Bioabsorbable polymers such as aliphatic polyesters from the poly ((z-hydroxy acids) family, especially polylactic acid (PLA), are well known bioabsorbable materials and are widely used for biomedical applications... 

PGS is a bioresorbable elastomeric polymer and extensively evaluated for various biomedical applications such as soft and hard tissue engineering and controlled drug delivery [8]. In a similar way, a number of aliphatic polyester elastomers for various biomedical applications were prepared from diacid monomers such as citric acid and a-ketoglutaric acid with aliphatic diols and triols using thermal polycondensation reactions [9-12]. 

Polyurethanes (PUs), one of the most commonly used polymers for various blood-contacting biomedical applications, are generally prepared by the polycondensation reactions of diisocyanates with diols or amines [35, 36]. Reactions of diisocyanates with diols result in the formation of urethane linkages while diisocyanates reactions with amines result in urea linkages. Both aliphatic, as well as aromatic diisocyanate monomers, are commonly used for preparing polyurethane biomaterials. Examples include 1,4-butane diisocyanate (BDI), 1,6-hexamethylene diisocyanate (HDI), 4,4-dicyclohexylmethane diisocyanate (HMDI), and 4,4-diphenylmethane diisocyanate (MDl) [37]. Commonly used diols (or termed as polyols) for preparing polyurethanes includes poly ethers, polycaprolactone, and polyesters with molecular weights up to 5000 Da. 

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