Biodegradable polymers polycaprolactone

All liposphere formulations prepared remained stable during the 3-month period of the study, and no phase separation or appearance of aggregates were observed. The difference between polymeric lipospheres and the standard liposphere formulations is the composition of the internal core of the particles. Standard lipospheres, such as those previously described, consist of a solid hydrophobic fat core composed of neutral fats like tristearin, whereas, in the polymeric lipospheres, biodegradable polymers such as polylactide or polycaprolactone were substituted for the triglycerides. Both types of lipospheres are thought to be stabilized by one layer of phospholipid molecules embedded in their surface. 

As pointed out by Heller (2), polymer erosion can be controlled by the following three types of mechanisms (1) water-soluble polymers insolubilized by hydrolytically unstable cross-links (2) water-insoluble polymers solubilized by hydrolysis, ionization, or protonation of pendant groups (3) hydrophobic polymers solubilized by backbone cleavage to small water soluble molecules. These mechanisms represent extreme cases the actual erosion may occur by a combination of mechanisms. In addition to poly (lactic acid), poly (glycolic acid), and lactic/glycolic acid copolymers, other commonly used bioerodible/biodegradable polymers include polyorthoesters, polycaprolactone, polyaminoacids, polyanhydrides, and half esters of methyl vinyl ether-maleic anhydride copolymers (3). 

While PHB and PHV are not considered true plastics, another biodegradable polymer polycaprolactone (PCL) is a plastic material because its monomer e-caprolactone is obtained on an industrial scale from petrochemical products (cyclohexanone and peroxyacetic acid). This synthetic plastic with its low melting point is easily extrudable and applications in the packaging area are envisioned. 

The price of synthetic biodegradable polymers has come down a little during the last three years. In 2003, for example, the average price of Eastar Bio and BASF s Ecoflex was around 3.5-4.0 per kg. In 2005, the average cost of an aliphatic aromatic polyester biopolymer was between 2.75-3.65 per kg. The more specialised polymers, such as DuPont s Biomax, cost as much as 5-6 per kg. Polycaprolactones cost between 4-7 per kg. Synthetic biodegradable polymer prices are expected to fall further over time as production volumes increase and unit costs fall further. 

Pitt, C., Polycaprolactone and its copolymers, in Biodegradable Polymers as Drug Delivery Systems, Chasin, M. and Langer, R., Eds., Marcel Dekker, New York, 1990, pp. 71-120. 

For matrices made from biodegradable polymers, longer release periods have been reported. When loaded with malaria antigen, one single injection was sufficient to induce an immune response without the help of adjuvant. Polycaprolactone proved to be superior to polylactide, which was explained by polycaprolactone s slower degradation behavior [20],... 

U.S. Pat. No. 6,274,652 [127] discloses a biodegradable composite material comprising bacterial cellulose in a powdery state and a polymeric material such as poly-hydroxybutyrate, polyhydroxyvalerate, polycaprolactone, polybutylenesuccinate, polyethylenesuccinate, polylactic acid, polyvinylalcohol, cellulose acetate, starch, and other biodegradable polymers. 

The above mentioned scaffolds were made completely of the ceramic materials. Other potential materials which could be used to fabricate a novel construct for the repair of ciitical-sized bone defects is a novel material made of biodegradable polymer reinforced with ceramics particles. The properties of such a composite depend on 1) properties of the polymer used for the matrix and properties of the ceramics used for the reinforcement, 2) composition of the composite (i.e. content of ceramic particles) and 3) size, shape and arrangement of the particles in the matrix. Several polymer-composite composites have been used for scaffolds fabrication including polylactide (PLA) and polycaprolacton (PCL) reinforced with calcium phosphate (CaP) micro and nanoparticles. Authors proposed a novel composite material by blending copolymer -Poly(L-lactide-co-D,E-lactide) (PLDLLA) a copolymer with a ceramic - Tri-Calcium Phosphate... 

Torres A, Li S, Roussos S, Vert M (1996) Screening of microorganisms for biodegradation of poly(lactic acid) and lactic acid-containing polymers. Appl Environ Microbiol 62 2393-2397 Urakami T, Imagawa S, Harada M, Iwamoto A, Tokiwa Y (2000) Development of biodegradable plastic-poly-beta-hydroxybutyrate/polycaprolactone blend polymer. Kobunshi Ronbunshu 57 263-270... 

Poly(a-hydroxyacid)s are the leading biodegradable polymers that have been developed. The poly(a-hydroxyacid)s series of polymers includes PLA and PLGA as well as other polymers such as polycaprolactone and poly (butyric acid) (see Section 4.2). These well-known polymers have been studied extensively for implant applications, and many drug-delivery systems based on these polymers are now commercialised. 

Eco-friendly biodegradable polymers and biocomposites are relatively novel materials that can contribute to reduce the dependence on fossil sources. Because of their renewable nature and biodegradability, environmentally benign composite materials with properties comparable to those of some widely used commodities can be produced. Py-GC/MS has developed as a useful tool for the study of thermal degradation of such polymers and composites, and many studies have recently been published for biodegradable polymers, such as polycaprolactone (PCL), polyhydroxyalcanoates (PHAs) and their copolymers,poly(lactic acid) (PLA), and carbohydrates, including starch and cellulose. 

PHB and other PHAs can also be blended with other biodegradable polymers. In Japan, the Ministry of International Trade and Industry s Biological Industry Institute in 1990 announced the development of blends of PHB and polycaprolactone (PCL). The blends can be processed with conventional equipment, and the ratio of the two polymers determines the rate of degradation. ... 

The majority of synthetic pol)miers showing biodegradability are aliphatic polyesters. Among them, PLA, PGA, and polycaprolactone (PCL) are arguably the most commonly used biodegradable polymers in the development of biomedical products. These polymers are generally insoluble in water, while with the exception of PGA, other polymers in this family are soluble in many common organic solvents and thus can be processed by a variety of thermal and solvent-based methods. 

Another important biodegradable polymer is the thermoplastic polycaprolactone (PCL), which is FDA approved for drug delivery, sutures, and several implants especially for bone tissue regeneration [21]. PCL is usually shipped in granules and can be processed into films and nanofibers or shaped and plotted under heat exposure due to its low melting point at around 60° C. 

The remaining polymers listed in Table I are not soluble in aqueous solutions and require organic solvents or elevated temperatures for fabrication into microspheres and encapsulation of proteins. Two recent reviews describe the use of polylactides, poly(ortho esters), and polyanhydrides, all of which have been used for the controlled release of several proteins and peptides (Langer, 1993 Heller, 1993). Polyiminocarbonates are relatively new biodegradable polymers that, like polycaprolactones, have not yet been extensively characterized as controlled release matrices for therapeutic proteins (Pulapura et al, 1990). While all of these polymers require relatively harsh conditions for entrapment of the protein, their release properties may allow for a prolonged delivery (e.g., up to one year) because... 

Numerous other papers and patents have been published regarding the polymerization and physical properties of polycaprolactone (Pitt Schindler, 1983a Schindler, et al, 1977 Erode Koleske, 1973 Schindler, et al, 1982 Hostettler, et al, 1966). A comparison of the various physico-mechanical properties of a number of biodegradable polymers was published by Engelberg and Kohn (1991). 

Among the most important biodegradable polymers, we can specially mention thermoplastic starch (TPS), polylactide (PLA), polycaprolactone (PCL), and polyhydroxybutyrate and polyhydroxyalkanoate (PHA) due to their promising properties. 

Urakami, T., et al. (2000) Development of biodegradable plastic poly-beta hydroxybutyrate/polycaprolactone blend polymer. Kobunshi Ronbunshu, 57(5) 263. 

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