Biodegradable polymers types

In 2003, the average price of starch blends was around 3.0-5.0 per kg. In 2005, the average price range of starch blends was down to 1.5-3.5 per kg. PLA is now being sold at prices between 1.37-2.75 per kg compared to a price range of 3.0-3.5 per kg three years ago, and is now almost price competitive with PET. The average cost of an aliphatic aromatic co-polyester has fallen from 3.5-4.0 per kg in 2003 to 2.75-3.65 per kg in 2005. Prices are expected to fall further for all biodegradable polymer types over time as production volumes increase and unit costs fall. 

The following sections discuss the chemical composition, properties and production of each biodegradable polymer type in more detail. 

Starch-based biopolymers are lower cost materials than some other biodegradable polymer types such as synthetic co-polyesters and PLA. They are produced from relatively cheap agricultural feedstock and have simpler manufacturing processes compared with synthetic biopolymers. 

The main body of the study (Chapters 5-8) is divided into four core sections based on biodegradable polymer types. 

Heller classified three types of degradation mechanism for biodegradable polymers. Type 1, 2 and 3 and classified polymers based upon the degradation mechanism they follow [10]. 

While this book is focused on drug delivery, the value of biodegradable polymers is not limited to this field. Biodegradable polymers will be useful in other areas of medical therapeutics, such as sutures and bone plates and other types of prostheses. The polymers will also be useful in nonmedical fields, for disposable plastics, bottles, diapers and many other entities. 

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. 

This book is a companion volume to Pharmaceutical Technology Controlled Drug Release, Volume 1, edited by M.H.Rubinstein and published in 1987. It focused on the different types of polymeric materials used in controlled release. This book extends these concepts to include drug properties, design and optimization, coating, the effect of food and pharmacokinetics. It also reflects the growing interest in biodegradable polymers in oral and topical formulations and the use of sterile implants. 

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). 

Many excellent options exist for synthetic and natural polymer-mediated delivery of shRNA. At present, synthetic polymers are limited by safety concerns and natural, biodegradable polymers are limited by efficacy issues. Active research in the field is causing these limitations to become less meaningful, but at present the choice to use a synthetic or a natural polymer for shRNA delivery must be made by considering the nature and location of the tumor(s) to be treated as well as the type of transcript to be targeted in order to maximize safety and optimize effectiveness. 

New types of renewable feedstock such as palm oil for manufacture of starch-based biodegradable polymers. 

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