مواد پلیمری زیست تجزیه پذیر مبتنی بر نشاسته Starch-based completely biodegradable polymer materials

۱٫ Introduction As well known, synthetic polymer materials have been widely used in every field of human activity [1] during last decades, i.e. post-Staudinger times. These artificial macromolecular substances are usually originating from petroleum and most of the conventional ones are regarded as non-degradable. However, the petroleum resources are limited and the blooming use of non-biodegradable polymers has caused serious environmental problems. In addition, the non-biodegradable polymers are not suitable for temporary use such as sutures. Thus, the polymer materials which are degradable and/or biodegradable have being paid more and more attention since 1970s. Both synthetic polymers and natural polymers that contain hydrolytically or enzymatically labile bonds or groups are degradable. The advantages of synthetic polymers are obvious, including predictable properties, batch-to-batch uniformity and can be tailored easily [2]. In spite of this, they are quite expensive. This reminds us to focus on natural polymers, which are inherently biodegradable [3] and can be promising candidates to meet different requirements. Among the natural polymers, starch is of interest. It is regenerated from carbon dioxide and water by photosynthesis in plants [4]. Owing to its complete biodegradability [5], low cost and renewability [6], starch is considered as a promising candidate for developing sustainable materials. In view of this, starch has been receiving growing attention since 1970s [7, 8]. Many efforts have been exerted to develop starch-based polymers for conserving the petrochemical resources, reducing environmental impact and searching more applications [9–۱۱]. In this paper, the status of preparation and applications of starch-based completely biodegradable (SCBP) polymers is reviewed and presented. ۴٫۳٫ In medical field Starch-based biodegradeable polymers have some advantages to be medical polymer materials [76–۸۱]: a) good biocompatibility b) biodegradable and its degradation products are non-toxic c) proper mechanical properties d) degradation as requirement Starch-based biodegradeable polymers have been widely investigated in bone tissue engineering. Starch-based biodegradable bone cements can provide immediate structural support and degrade from the site of application. Moreover, they can be combined with bioactive particles, which allow new bone growth to be induced in both the interface of cement-bone and the volume left by polymer degradation [82]. In addition, starch-based biodegradeable polymer can also be used as bone tissue engineering scaffold [83]. Starch-based biodegradable polymers, in the form of microsphere or hydrogel, are suitable for drug delivery [84, 85]. There is no need for surgical removal of the device after drug depletion. The unique properties, such as hydrophilicity, permeability, biocompatibility, and to some extent similar to soft biological systems, of starch-based hydrogels make them useful for various biomedical applications [86]. The 3D structure of starch-based hydrogels enable them absorb and reserve a plenty of water and keep good enough mechanical property at the same time. Starch-based hydrogels have received growing interest for biomedical applications. In our lab, physically cross-linked starch-gPVA and starch-g-PVA/hydroxyapatite hydrogel are obtained via repeated freezing/thawing circles, and hydroxyapatite (HA) can be well dispersed in such a matrix (Figure 2) [55, 87]. The water content in the fresh starch-g-PVA/HA hydrogel is comparable to that of PVA/HA hydrogel, and the dried starch-g-PVA/HA films can re-adsorb water soon and reach swelling equilibrium within 12 minutes. ۵٫ Conclusions Starch is renewable from carbon dioxide, water and sunshine. It is biodegradable, cheap and to be physical or chemical modified easily. This means someday it is unnecessary to rely on petroleum to prepare polymers, people may ‘plant’ polymers of suitable performances from the earth, and the environmental problems will be no longer as severe as today. At present and in the near future, different physical and chemical approaches are effective strategies to develop starch-based completely biodegradable polymers of appropriate biocompatibility, degradation rate and physical properties for various applications.