**1. Introduction**

246 Biomedical Science, Engineering and Technology

Zhu, Y. B., Gao, C. Y., Liu, X. Y. & Shen, J. C. 2002. Surface modification of

Zhu, Y. B., Gao, C. Y., Liu, Y. X. & Shen, J. C. 2004. Endothelial cell functions in vitro

*Journal of Biomedical Materials Research Part A,* 69A**,** 436-443.

*Biomacromolecules,* 3**,** 1312-1319.

polycaprolactone membrane via aminolysis and biomacromolecule immobilization for promoting cytocompatibility of human endothelial cells.

cultured on poly(L-lactic acid) membranes modified with different methods.

Social and economic development has driven considerable scientific and engineering efforts on the discovery, development, and utilization of polymers. Widespread reliance in everyday life on conventional polymeric materials such as polyolefins has resulted in serious pollution which cannot be resolved in a straightforward fashion. Sustainable development and a green economy both require brand new materials which can avoid the occurrence of these problems.

Poly(lactic acid) (PLA), an aliphatic polyester, has outstanding advantages over other polymers, and may thus be part of the solution. As early as the 1970's, PLA products have been approved by the US Food and Drug Administration (FDA) for direct contact with biological fluids. Four of its most attractive advantages are renewability, biocompatibility, processability, and energy saving (Rasal, 2010). First of all, PLA is derived from renewable and degradable resources such as corn and rice, which can help alleviate the energy crisis as well as reduce the dependence on fossil fuels of our society; PLA and its degradation products, namely H2O and CO2, are neither toxic nor carcinogenic to the human body, hence making it an excellent material for biomedical applications including sutures, clips, and drug delivery systems (DDS). Furthermore, PLA can be processed by film casting, extrusion, blow molding, and fiber spinning due to its greater thermal processability in comparison to other biomaterials such as poly(ethylene glycol) (PEG), poly(hydroxyalkanoates) (PHAs), and poly(ε-caprolactone) (PCL) (Rhim et al., 2006). These thermal properties contribute to the application of PLA in industry in fields such as textiles and food packaging. Last but not least, PLA production consumes 25-55% less fossil energy than petroleum-based polymers. Cargill Dow has even targeted a reduction in fossil energy consumption by more than 90% as compared to any of the petroleum-based polymers for the near future, which will surely also lead to significant reductions in air and water pollutant emissions. It is also noteworthy that the total amount of water required for PLA production is competitive with the best performing petroleum-based polymers. This energy-saving feature perfectly caters to the

<sup>\*</sup> Corresponding author

new concept of "low-carbon economy" which emerged recently in response to the global warming and energy crisis concerns, and makes investment in PLA a necessary and wise strategy in the future (Vink et al., 2003). Fig. 1 shows the cycle of PLA in nature.

Fig. 1. The cycle of PLA in nature.

While PLA can be considered an eco-friendly biomaterial with excellent properties, it also has many obvious drawbacks when confronted with requirements for certain applications: 1) Its degradation rate through hydrolysis of the backbone ester groups is too slow. This process sometimes takes several years, which can impede its biomedical and food packaging applications (Bergsma et al., 1995). 2) PLA is very brittle, with less than 10% elongation at break, thus it is not suitable for demanding mechanical performance applications unless it is suitably modified (Rasal & Hirt, 2009). 3) PLA is strongly hydrophobic and can elicit an inflammatory response from the tissues of living hosts, because of its low affinity with cells when it is used as a tissue engineering material. 4) Another limitation of PLA towards its wider industrial application is its limited gas barrier properties which prevent its complete access to industrial sectors such as packaging (Singh et al., 2003). Considering the disadvantages of PLA stated above and its high cost (another shortcoming of that material), it is not surprising that PLA has not received the attention it deserves. Nevertheless, researchers have examined different methods for the bulk or surface modification of PLA, the introduction of other components, or the control of its surface energy, surface charge and surface roughness, depending on the requirements of specific applications.

Previous reviews have examined different aspects of PLA chemistry and engineering. Thus Maharana et al. (Maharana et al., 2009) presented a review on the melt-solid polycondensation of lactic acid (LA). Gupta et al. (Gupta et al., 2007) presented an overview of the production of PLA fibers by various methods, along with correlations between the

new concept of "low-carbon economy" which emerged recently in response to the global warming and energy crisis concerns, and makes investment in PLA a necessary and wise

While PLA can be considered an eco-friendly biomaterial with excellent properties, it also has many obvious drawbacks when confronted with requirements for certain applications: 1) Its degradation rate through hydrolysis of the backbone ester groups is too slow. This process sometimes takes several years, which can impede its biomedical and food packaging applications (Bergsma et al., 1995). 2) PLA is very brittle, with less than 10% elongation at break, thus it is not suitable for demanding mechanical performance applications unless it is suitably modified (Rasal & Hirt, 2009). 3) PLA is strongly hydrophobic and can elicit an inflammatory response from the tissues of living hosts, because of its low affinity with cells when it is used as a tissue engineering material. 4) Another limitation of PLA towards its wider industrial application is its limited gas barrier properties which prevent its complete access to industrial sectors such as packaging (Singh et al., 2003). Considering the disadvantages of PLA stated above and its high cost (another shortcoming of that material), it is not surprising that PLA has not received the attention it deserves. Nevertheless, researchers have examined different methods for the bulk or surface modification of PLA, the introduction of other components, or the control of its surface energy, surface charge

and surface roughness, depending on the requirements of specific applications.

Previous reviews have examined different aspects of PLA chemistry and engineering. Thus Maharana et al. (Maharana et al., 2009) presented a review on the melt-solid polycondensation of lactic acid (LA). Gupta et al. (Gupta et al., 2007) presented an overview of the production of PLA fibers by various methods, along with correlations between the

strategy in the future (Vink et al., 2003). Fig. 1 shows the cycle of PLA in nature.

Fig. 1. The cycle of PLA in nature.

structure and the properties of the fibers. Butterwick et al. (Butterwick et al., 2009) discussed the applications of PLA in Europe and the United States with respect to practitioner experiences and techniques to optimize the outcomes. Rasal et al. (Rasal et al., 2010) examined the chemical modification of PLA, while Graupner et al. (Graupner et al., 2009) assessed the production and the mechanical characteristics of composites prepared from PLA and renewable raw materials including cotton, hemp, kenaf, and man-made cellulose fibres (Lyocell) by compression molding.

In this chapter we will underline novel ideas or technologies introduced over the last 5-10 years, emphasizing some ambitious work which, even though it appears less successful than other mature methods, introduces concepts that may prove extremely positive in the near future. We will also attempt to foretell developmental trends on the basis of social demands and the progress achieved so far. More traditional topics including the synthesis, modification, and applications of PLA in biomedical field will be introduced mainly to provide a more comprehensive picture of PLA as a biomaterial.
