Polymer degradation bioresorbable polymers

Vert M (1998) Chemical routes to poly( P-malic acid) and potential applications to this water-soluble bioresorbable poly(P-hydroxy alkanoate). Polym Degrad Stab 59 169-175... 

The growth in polymer-made biomedical devices has in part been made possible thanks to the discovery of a new class of materials bioresorbable polymers. The term bioresorbable has become a common expression, used in order to qualify this type of macromolecules. A scientifically accepted definition for such materials is the following a material for which the degradation is mediated, at least partly, from a biological system (Ottenbiight and Scott, 1992). This statement shows one of the most important features of these materials. Devices made of bioresorbable polymers are subjected to degradation in the human body which means they do not need to be removed. 

This phenomenon is related to another interesting feature of bioresorbable polymers. Degradation products are removed by the cells themselves in order to achieve a complete degradation of the implanted device. As an example. 

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. 

Abstract The main families of synthetic bioresorbable polymers, which find wide medical application as temporary mechanical supports such as sutures, as tissue engineering scaffolds, and as mediators of release rate for the controlled release of drugs are outlined. The physical and chemical mechanisms by which they degrade are discussed and the factors that can affect their rates of degradation are examined. 

Note This chapter was previously published as Chapter 3 Synthetic bioresorbable polymers by R. E. Cameron and A. Kamvari-Moghaddam, originally published in Degradation rate of bioresorbable materials predication and evaluation, ed. F. J. Buchanan, Woodhead Publishing Limited, 2008 ISBN 978-1-84569-329-9. 

Polymer chemical stracture can be tailored to control degradation behaviour, making them, under physiological conditions, bioinert or bioresorbable over a defined period. Polymer degradation is generally denoted by a deterioration in the functionality of the polymeric material caused by a change in its physical and/or chemical properties. In this chapter, the different degradation... 

The degradation rate of bioresorbable polymers depends on their intrinsic properties such as reactivity, hydrophilicity, molecular weight, degree of crystallinity, and glass transition temperature. However, other external factors such as the degradation media, sterilisation and sample size also play a role in the degree of degradation. 

Bioresorbable polymers are put to extensive use as medical materials because of their diverse biodegradability, good mechanical properties and biocompatibility. The ability to tailor their chemical structures to control their degradation behaviour and rate is a great advantage when it comes to designing implants with suitable mechanical and degradational properties for their intended use. 

Cameron, R.E., Kamvari-Moghaddam, A., 2008. Synthetic bioresorbable polymers. Degradation Rate of Bioresorbable Materials. Woodhead Pubishing Limited, Cambridge England, pp. 43 6. 

First, a brief overview of the degradation mechanism and the main factors that influence hydrolysis of bioresorbable polymers is provided. Then, the modeling approaches that can be used for characterizing the behavior of biodegradable devices will be summarized. 

As mentioned, the overall degradation rate is affected by numerous phenomena. Today, it is still not possible to bmld a mathematical model that predicts the final degradation rate and accounts for aU possible variables, starting from polymer processing and manufacturing to device hydrolysis. The description is even more compUcated in vivo, where polymer—tissue interactions also can play a significant role in the final behavior of bioresorbable polymers. 

The industrial production of a medical device is a complex activity that requires fine-tuning of the technical parameters to satisfy the requirements of quality, reproducibility, and reliability that are necessary to meet customer needs and regulatory directives. For bioresorbable polymers, this activity is even more complex, due mainly to the following factors (1) aptitude to degradation of resorbable polymers, (2) high costs of production, and (3) scarcity of suppliers. 

When designing a medical device based on a bioresorbable polymer, the degradation ability of the material during all the phases from the synthesis to the complete resorption in vivo must be carefully considered. In this regard, synthetic polymers are more versatile compared to natural origin polymers, thereby allowing a finer control of the theoretical degradation rate. However, this rate depends from a number of external factors such as production process conditions (eg, humidity, temperature) and site of implantation (eg, pH, mechanical stress) [13—18]. 

---