**6. Conclusions**

Due to the multiple desirable characteristics of PLA including renewability, biocompatibility, transparency, and thermoplasticity, it is being used or is a potential candidate for many consumer and biomedical applications (Jamshidian et al., 2010). Ever increasing environmental concerns associated with conventional polymers derived from petrochemicals lead to constantly expanding applications for PLA since its discovery in 1932 by Carothers at DuPont.

In previous years, the most negative point of PLA was its higher price as compared with petrochemical-based polymers. Today, by optimizing the LA and PLA production processes, and with increasing PLA demand, a reduction in its price can be achieved. The price of PLA is currently much lower than in previous years. Meanwhile, PLA is mainly synthesized in the industry by ROP employing tin(II) bis(2-ethylhexanoate) (SnOct2) as a catalyst, which has been approved as a food additive by the FDA, but the potential toxicity associated with most tin compounds cannot be ignored for biomedical applications. Scientists all over the world are now exploring novel, well-defined catalysts with good biocompatibility, high catalytic activity, low toxicity, and excellent stereoselectivity. This should remain an everlasting interest area. Finally, the possibility of obtaining 100% biosourced opens the way for PLA to become more independent from petrochemical-based polymers, free of environmental and health concerns.

However, the major disadvantages of PLA such as its poor ductility, slow degradation rate, and poor hydrophilicity somewhat limit its applications. The modification of PLA bulk and surface properties has thus become crucial to increase its applicability. Many of the bulk and surface modification strategies discussed above have been designed to tune the PLA surface properties according to the demands of biomedical applications. Unfortunately, all these established methods for surface modification are somewhat deficient and while they provide control over the wettability, degradation rate, and functionality, it is still compulsory to minimize their negative impact on PLA bulk properties. Thus a combined modification strategy (e.g. irradiation followed by grafting) or a better balance of PLA surface and bulk properties should be sought. Ideally, with respect to a better balance of properties and shorter modification times, one-step approaches need to be developed because it is time-consuming to carry out surface and bulk modifications separately, and the solvents and reagents involved in multiple modification steps tend to affect PLA properties significantly.

All these modification strategies aim at tailoring the properties of PLA-based materials for certain applications. Fortunately, more and more encouraging results have been reported, but the present conclusions from most of these reports cannot be directly generalized to truly biomedical applications since most of the experiments were carried out in vitro. Nevertheless, these findings offer some clues for further improvements. The increasing number of functional PLA-based polyesters provides the opportunity to study the relationships between structure and functionality of these polymers such as cell adhesion and degradability in vitro and in vivo, as well as to develop applications of these materials for delivery system in the form of micro- and nanoparticles or scaffolds for tissue engineering. Finally, cancers and acquired or inherited genetic diseases represent one of the most serious threats to the health of human beings, but no effective therapies are available so far. It is suggested that the development of effective and ideal tools for drug, peptide/protein, and RNA/DNA delivery will represent a good alternative in drug development. It therefore appears that it would be best to focus future research work on the rational design of novel carriers for biomedical uses and targeted delivery systems. Obviously, this requires plenty of relevant experiments on animal model and enough clinical trials before they are widely utilized.

Even though countless studies have focused on the synthesis and the modification of PLA and remarkable progresses has been achieved over the last two decades, vast opportunities as well as challenges remain in terms of exploring the characteristics of PLA-based materials and expanding their domains of applications.
