Bioresorbable polymers systems

There are many different bioresorbable polymer systems based on different degradation mechanisms and having a range of physical and mechanical properties. However, the scope of our review will be restricted to only fiber-forming polymers. Those that are hydrolytically sensitive are discussed in this chapter, while enzymatically catalyzed bioresorbable polymers are presented in Chap. 6. Table 4.1 shows the classification of fiber-forming hydrolytically sensitive bioresorbable polymers. 

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. 

The lactide/glycolide bioresorbable polymers are thermoplastics which can be processed by many methods, including fibre spinning, extrusion, and injection moulding, which means they can be fabricated into a variety of wound closure items (e.g. sutures), implantable devices (e.g. bone plates, bone screws), and drug delivery systems, which include microspheres, fibres, films, rods and others. 

For biomedical applications, there are several uses for bioresorbable polymers. Some of these polymers have a support function (eg, SmartBone, sumres), and others serve as drug delivery systems (eg, antibiotics, chemotherapeutic dmgs). 

The choice of the right suppliers for raw materials is critical because validation of a bioresorbable polymer includes the characteristics of all the suppliers involved in the production process, ie, their quality systems and certifications. An unreliable supplier represents a possible source of issues when producing a device under regulatory approval. For example, a supplier could fail obliging the company to begin a validation process for the new supplier, the quality of the raw material could be erratic, or the supply of a determined material could be discontinued [20]. Moreover, in the past years the number of suppliers of bioresorbable materials did not increase as expected,... 

In the field of bioresorbable polymers, dendrimers are usually not included. In contrast, polymerosomes, polymeric micelles, and polymeric NPs find a large number of applications as bioresorbable systems, mainly in dmg delivery. It is an extremely vast field of research that covers the development and use of innovative systems for the administration of pharmaceutically active ingredients. In this case there are numerous administration routes for dehvering the active ingredients loaded in these systems, such as oral, transmucosal, pulmonary, and intravenous. The preferable route is oral (noninvasive dehvery), although very often it is not feasible, as with anticancer compounds for which the intravenous route (invasive delivery) is preferred (Fig. 12.1) [1]. 

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... 

Applications of bioresorbable polymers in the skeletal systems (cartilages, tendons, bones)... 

This chapter separately discusses the peculiarities of these tissues and the most promising applications of bioresorbable polymers in all three systems, thus giving insight for the development of next-generation replacements that aim to be pathologically, anatomically, and mechanically specihc. 

Major advances are being made in the field of cardiac TE. So far, it is possible to engineer all the components of the cardiovascular system including blood vessels, heart valves, and cardiac muscle by using bioresorbable polymers. Regarding cardiac muscle repair, this chapter has reviewed how bioresorbable polymers administered either alone or as delivery vehicles have shown positive results such as cardiac function improvement, infarct size reduction, and increase in neovascularization in precUnical studies. 

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