Poly L-Lactic Acid PLLA

Poly(hydroxy acid)s are an important class of degradable polymers for biomedical applications due to their biocompatibility and physiologically tolerable degradation products 886302. Poly(L-lactic acid) or poly(L-lactide) (PLLA) has been used as a biomaterial for tissue engineering, bone fracture fixation and controlled drug delivery 

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PLA degradation, 43 Planar polymer, synthesis of, 505 PLLA. See Poly(L-lactic acid) (PLLA) PMDA. See Pyromellitic dianhydride (PMDA)... 

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

As the data from Fig. 10.5 suggests, the PHis-PEG micelles are unstable and can release their contents at neutral pH. In order to deal with this problem, an amphiphilic block copolymer, PLLA-PEG, was added to make mixed micelles, in which the core was expected to contain poly(L-lactic acid) (PLLA) and PHis chains. The PLLA block in the core stabilized the micelles and hence suppressed the drug release at the near neutral pH. The optimum content of PLLA-PEG was found to be about 25 0% (Fig. 10.7). The DOX delivered from such mixed micelles showed low cytotoxicity at pH above 7.0 but high cytotoxicity at pH 6.8 [143]. 

Some materials can be produced only in amorphous or polycrystalline phase. For example, SCF precipitation of polymers such as poly(L-lactic acid)(PLLA) and proteins such as lysozyme and insulin have been widely investigated (see, e.g., Chapters 6, 9, and 10 in this book). These molecules form amorphous (proteins) or semicrystalline (PLLA) structures and typically have small values of both Ceq and tn, combined with a relatively large Tg constant (small growth rate). Similarly, organic or inorganic salts usually have very small Cgq and Tn constants. This explains why it is easy to produce very small (often submicrometer), spherical particles of these materials, al-... 

Biodegradable polymers, such as poly(L-lactic acid) (PLLA) and PLGA are suitable for drug-delivery applications due to their non-toxicity and adjustable biodegradability [25, 26]. PLGA and PLLA films have been used for the treatment of periodontal disease [27], glaucoma [28] and cancer [29], and as a component of biodegradable stents [30, 31]. 

Polylactide (PLA) possesses chiral molecules, polylactides exist in four forms poly(L-lactic acid) (PLLA), poly(D-lactic acid) (PDLA), poly(D,L-lactic acid) (PDLLA)—a racemic mixture of PLLA and PDLA, and mesopoly(lactic acid). Figure 30.4a illustrates the molecular structure of PLA. 

Despite these restrictions, a variety of polymers including poly[L-lactic acid] [PLLA], poly[ -caprolactone] (PCL], agarose, gelatin, chitosan and polyelectrolytes have already been applied as starting materials to develop porous scaffolds using the Bioscaffolder technology [120,129]. 

Tsuneizumi et al. [13] studied the chemical recycling of poly(lactic acid)-based polymer blends using environmentally benign catalysts, clay catalysts, and enzymes. Poly(L-lactic acid) (PLLA)-based polymer blends (e.g., PLLA/polyethylene [PE] and PLLA/poly(butylenes succinate) [PBS]) were degraded into repolymerizable oligomer. 

Poly(lactic acid) has three typical optical isomeric forms (i) optically active and crystalliz-able poly(L-lactide) (i.e. poly(L-lactic acid) (PLLA)), (ii) optically active and crystallizable poly(D-lactide) (i.e. poly(D-lactic acid) (PDLA)), and (iii) optically inactive and noncrystal-lizable poly(DL-lactide) [i.e. poly(DL-lactic acid) (PDLLA)]. Of these isomeric polymers, PLLA is most frequently used because its production cost is lower due to its joint mass production of 1.4 X 10 metric tons per year by NatureWorks LLC, which is owned by Cargil... 

A handful of drugs have been studied in DES, such a paclitaxel, sirolimus, and its related family members (zotarolimus, biolimus A9, and everolimus). Many polymeric materials such as polylactic acid (PLA), polyethylene-co-vinyl acetate (PEVA), poly(styrene-b-isobutylene-b-styrene) (SIBBS), poly-L-lactic acid (PLLA), phosphorylcholine (PC), and poly-n-butyl methacrylate (PBMA), were used for drug coatings, all of which are unique to each class of DES. 

PHA chemical modification can be done via block copolymerizadon and grafting reactions, chlorination, cross-linking, epoxidation, hydroxyl and carboxylic acid functionalization, etc. (Chen et al. 2009 Wu et al. 2008 Li et al. 2003 Loh et al. 2007). A common approach to confer toughness to PLA is the use of a flexible monomer or macromolecules for copolymerization with lactide to form PLA-based random or block copolymers. Reported PLA-based block copolymers include diblock, triblock, and multiblock copolymers, such as poly(L-lactic acid) (PLLA)-polycaprolactone (Jeon et al. 2003), poly(ethylene glycol)-PLLA (Chen et al. 2003), poly(trimethylene carbonate)-PLLA (Tohru et al. 2003), and PLA-PBS-PLA. 

Figure 73 Representative 3-D nanostructured scaffolds for bone-specific drug delivery systems, (a) Electrospun sitk scaffold with BMP-2 loaded, scale bar=5 pm (reprinted from Ref. [86] with permission) (b) Self-assembled peptide-amphiphile (PA) nanofibers network, scale bar= 1 mi (reprinted from Ref. [87] with permission) (c) Nanocrystalline apatite modified poly(lactide-co-glycolide) (PLAGA) microsphere scaffolds, scale bar=2pm (reprinted from Ref. [88] with permission) and (d) poly(L-lactic acid) (PLLA) nanofibrous scaffolds incorporated with poly(lactic-co-glycolic acid) (PLGA) nanospheres, scale bar=2 pm (reprinted from Ref. [89] with permission).

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