Bioresorbable polymers poly

Ignatius, A. A., Claes, L. E. In vitro biocompatibility of bioresorbable polymers poly(l, dl-lactide) and poly(l-lactide-co-glycolide). 1996,17(8), 831-839. 

Polyammonium-containing ligands, 24 44 Polyammonium macropolycycles, 76 780 Polyampholytes, 20 475 479 solution properties of, 20 479 synthesis of, 20 477- 478 Poly(anhydrides), bioresorbable polymers, 3 740... 

Polyesterl-Woc -polyester2, 7 646 Poly(ester amides), bioresorbable polymers, 3 739-740... 

Polyethylene bags, woven, 18 12 Poly(ethylene carbonate), bioresorbable polymers, 3 738-739 Poly(ethylene-chlorotrifluorethylene) (ECTFE), 23 785 Poly(ethylene-co-l,4-... 

Polyethyleneoxide-co-polypropyleneoxides, dispersants, S 710t Poly(ethylene oxide) film, physical properties of, 10 68It Poly(ethylene oxide) floe, 11 638 Poly(ethylene oxide)-poly(ethylene terephthalate) copolymers, bioresorbable polymers, 3 738 Poly(ethylene oxide) resins, molecular weight of, 10 684-685 Polyethylene oxides, dispersants, S 706t, 710t... 

Poly(glycidyl methacrylate), 23 728 Polyglycolic acid, bioresorbable polymer, 3 736-737... 

Fig. 4 Structures of some bioresorbable polymers (A) poly-glycolide acid and (B) polylactide.

Nowadays, the most attractive family of bioresorbable polymers is composed of poly(a-hydroxy acids) derived from lactic and glycolic acids (PLAGA) (Table2)... 

In order to make water soluble polymer and to enlarge the bioresorbable polymer family on the basis of the same strategy, carboxylic acid bearing polymers derived from malic acid, namely (poly(p-malic acid) or PMLA, were synthesized for the first time many years ago. 

In the field of biomedical devices, bioresorbable polymers can be used for several purposes. Suture threads represent an established example of a bioabsorbable device. They were introduced for the first time during the early 1970s. They were first made of poly(glycolic acid). Threads made of poly (lactic acid) and polydioxanone appeared later in 1981. Currently there is a wide variety of types of commercial suture thread (monofilament or polyfilament) depending on requirements such as degradation time and mechanical behavior. 

A plethora of bioresorbable polymer materials are adopted for medical and pharmaceutical applications. Among them, aliphatic polyesters, polycarbonates, poly (amino acids), and polyphosphoesters are the main representatives. For the synthesis of NPs, aliphatic polyesters are the most adopted materials. Data on a huge number of different polyesters can be found in the literature, but this chapter focuses on the main polyesters poly (lactic acid) (PLA), poly(glycolic acid) (PGA), polycaprolactone (PCL), and their copolymers [4]. 

As mentioned, the most adopted bioresorbable polymers to synthesize NPs for medical and pharmaceutical applications are polyesters such as PLA, PGA, poly(lactic-co-glycolic acid) (PLG A), and PCL. However, such polymers are generally synthesized in bulk phase via ROP and obtained as solids. Therefore, for producing biodegradable polymeric NPs, physical processes are required that allow for obtaining a stable suspension starting from the dry polyesters. Several methods have been proposed to synthesize NPs by dispersing a preformed polymer, but the most widely adopted methods are emulsification-evaporation and nanoprecipitation (Fig. 12.3) [5,6]. 

One of the major classes of synthetic bioresorbable polymers is that of aliphatic polyesters or poly(a-hydroxy acids). Poly(a-hydroxy acids) such as PGA, poly(lactic acid) (PLA) stereoisomers poly(L-lactic acid) (PLLA) and poly(D-lactic acid), and pol-y(lactic-co-glycolic acid) (PLGA) copolymers are the most widely used and most popular bioresorbable polymers since they received Food and Drug Administration (FDA) approval for clinical use in humans in different forms (eg, fibers for sutures, injectable forms) (Nair and Laurencin, 2007). These polymers are commonly used in regenerative medicine applications. An example is the InQu Bone Graft Extender Substitute (ISTO Technologies), an osteoconductive biosynthetic product used as bone graft substitute in the skeletal system to support new bone formation. The resorption rate of... 

Another interesting bioresorbable polymer that has been investigated to develop highly porous scaffolds for TE is Degrapol, an elastic poly(ester methane) (Saad et al., 1997). 

Because of such complex requirements, the number of synthetic bioresorbable polymers for practical use is limited. This must have been the limitation faced by nature too since all life on earth is based on only three polymeric backbones, namely, polynucleotide, poly(a-amino acid), and polysaccharide chains [11]. For the same reasons, synthetic bioresorbable polymers have been restricted only to certain classes of polymers and till now only a few of them have been approved by the FDA for certain specific applications. 

Inorganic bioresorbable polymers like polyphosphazene and poly [bis (carb-oxylatophenoxy) phosphazene] which have a nitrogen-phosphoms backbone instead of an ester linkage. 

Poly(ot-esters) are the earliest, most extensively studied, and commercially widely used bioresorbable polymers. Especially, the poly(a-hydroxy acids), including poly(glycolic acid) (PGA), stereoisomers of poly(lactic acid) (PLA) and their copolymers which have been extensively investigated for their degradation mechanisms and structure—property relationships [1—4]. Aliphatic polyesters based on poly(a-ester)s are discussed below. 

Poly(glycolic acid) (PGA) is one of the first bioresorbable polymers investigated for biomedical applications. Dexon , the first biodegradable synthetic suture to be approved by the Food and Drug Administration (FDA) in 1969, was based on... 

Various copolymers with a high PDO content have been synthesized and studied to improve the mechanical performance and increase the rate of resorption [40]. A copolymer with 80 % PDO and up to 20 % PGA has a resorption profile similar to Dexon and Vicryl and yet maintains a compliance similar to PDS . The copolymer with 85 % PDO and up to 15 % PLLA exhibits higher compliance and a lower modulus than the PDO homopolymer, yet its resorption profile is similar to PDS [41]. Copolymers with three or more different monomer units have also been explored. One such example is poly(GA-co-PDO-co-LA), which has been proposed as a possible suture material with suitable crystallinity, good flexibility, better strength retention, and a reasonably rapid resorption rate [42]. Until recently, there was not much interest in developing PDO as a biomaterial, mainly because of the lack of commercial availability and difficulties in its synthesis. However, with the development of new alternative synthesis procedures and the availability of the PDO monomer, there has been more commercial interest in developing PDO as a bioresorbable polymer in recent years (Table 4.6). 

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