Review of Literature Novel Block Polyurethane

Question: Describe about the Review of Literature for Novel Block Polyurethane. Answer: Wang et al in 2016 has designed and synthesized novel block polyurethane which is a biodegradable material that is based on poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly (ethylene glycol) (PEG) as effective biomaterials which aids in the improvement of mechanical properties as well as hemocompatibility [1]. They characterized the resultant polyurethanes by various imaging techniques and evaluated the biodegradability rate at the temperature of 37 C kept in phosphate buffer solution (PBS) at the pH level of 7.4. The results of this study shows that the PHBV based polyurethanes produced a faster degradation rate in PBS than that of plain PHBV films due to the introduction of ester bond. This indicates that it is more suitable for its application in biomedical science that needs a longer period of degradation. They have also evaluated the hemocompatibility by carrying out hemolytic test and noted the time of dynamic coagulation of blood and adhesion of platelets. They fo und that the polyurethanes that are based on PHBV has an excellent hemocompatibility with an increased soft segment content that too mainly due to the influence of introduced PHBV block. Therefore polyurethanes based on PHBV could be better used in the field of vascular grafts. A study on degradation property of polyurethanes was conducted by Rodriguez (2013) to find its application in cardiovascular system [2]. Though the polyurethane biomaterials have good chemical and mechanical properties with better biocompatibility they are at increased risk of degradation in certain circumstances such as hydrolysis, environmental stress, oxidation, enzyme or lipid related degradation which is identified in vivo at the time of device usage. Using in vitro method, they studied the degradation under these circumstances and found that the polyurethanes are not inert biomaterials that are placed in the body but are capable of degradation and this has to be modified by changing the composition and segment chemistry of polyurethanes to be used in cardiovascular grafts. In 2005, Santerre et al has proposed a study to understand the polyurethanes biodegradable property: from classical old implants to recent tissue engineering biomaterials [3]. They have reviewed all the literatures related to the application of polyurethanes in medical field. They analyzed the details and identified the problems related to the use of polyurethane materials from past to present days. They gained a better knowledge about polyurethane materials mainly by careful analysis of environmental biodegradation mechanisms in vivo and its application in health field. Huang, 2008 has proposed a study to help bone tissue engineering by using biodegradable and bioactive polyurethanes (porous) scaffolds [4]. Even though the biodegradable polyurethanes (porous) scaffolds have appropriate rate of degradation rate with no toxicity, they lack bioactive groups, which reduces its usage. This study proposes some common modification methods, surface functionalization and modifications in blending. Finally, the review suggests having bulk modification as a newer method to improve the bioactive property of polyurethanes. Punnakitikashem, 2014 has conducted a study on acellular biodegradable vascular grafts with small diameter [5]. He determined that the small diameter vascular grafts (SDVGs) that are biodegradable should posses anti thrombotic property, inhibition of hyperplasia of tunica intima (middle layer of arteries) and fast endothelialization to increase the patency of graft. He also found that there is no clear treatment to prevent thrombotic property and proliferation of tunica intima which in turn affects the formation of cells in the endothelial layer on SDVGs. He suggested that to prevent this limitation, elastic polyurethane urea (biodegradable) and dipyridamole (drug) (DPA) could be combined and introduced into a fibrous scaffold that is biodegradable by the process of electrospun. The expected mechanical support will be provided by the elastic polyurethane urea (biodegradable) whereas bio functions will be offered by the dipyridamole in the scaffold. They analyzed that whether the resu lting scaffold has caused strains as comparable with that of the normal coronary artery. The dipyridamole used in the scaffolds was released in the phosphate buffer solution continuously for 91 days at a temperature of 37 C, with a low level release for the first 3 days. When elastic polyurethane urea (biodegradable) was studied, the improvement in non thrombotic property is less when compared to that of the dipyridamole loaded elastic polyurethane urea (biodegradable) scaffolds which was determined by the extended clotting time, lowered concentration of titration complex, decreased hemolysis and lowered deposition of human platelet. It was noted that the scaffolds with higher dipyridamole content of 5% and 10% inhibited the proliferation of smooth muscle cells of aorta apparently. Additionally it was found that the dipyridamole loaded scaffolds presented with no adverse effects on the growth of endothelial cells in aorta but it has improved their proliferation. Due to these beneficial properties, dipyridamole loaded elastic polyurethane urea can be used for vascular replacement. In 2010, Hong studied about tailoring the degradation kinetics of poly (ester carbonate urethane) urea that is thermoplastic elastomer to be used as tissue engineering scaffolds due to their uses in repair and regeneration of soft tissue [6]. The main objective of this study was to generate a group of polyurethane elastomer (biodegradable) by partially substituting polyester by polycarbonate segments in the polymer backbone which might slow the degradation process. They have investigated the soft segment molar ratios and polymer tensile strengths and noted that increased poly (1, 6-hexamethylene carbonate) content produced soft and more distensible films. Salt leaching produced scaffolds supported the adhesion and growth of smooth muscle in vitro. These slower degrading thermoplastic polyurethanes increase its application in various repair and reconstructive procedures of soft tissue. Reference Wang, Y. Zheng, Y. Sun, J. Fan, Q. Qin and Z. Zhao, A novel biodegradable polyurethane based on poly (3-hydroxybutyrate-co-3-hydroxyvalerate) and poly (ethylene glycol) as promising biomaterials with the improvement of mechanical properties and hemocompatibility, The Royal Society of Chemistry, 2016 V. C. Rodriguez, L. H. Chan-Chan, F. H. Snchez and J. M. Cervantes, Degradation of Polyurethanes for Cardiovascular Applications, Advances in Biomaterials Science and Biomedical Applications, pp. 55-82, 2013 P. Santerrea, K. Woodhouseb, G. Laroched and R.S. Labow, Understanding the biodegradation of polyurethanes: From classical implants to tissue engineering materials, Biomaterials, 26, pp. 74577470, July 2005 N. Huang, Y. L. Wang and Y. F. Luo, Biodegradable and bioactive porous polyurethanes scaffolds for bone tissue engineering, J. Biomedical Science and Engineering, vol. 2, pp. 36-40, November, 2009 Punnakitikashem, D. Truong, J. U. Menon, K. T. Nguyen and Y. Hong, Acellular biodegradable small diameter vascular grafts (SDVGs), Acta Biomater, vol.10, no. 11, pp.46184628, November 2014 Y. Hong, J. Guan, K. L. Fujimoto, R. Hashizume, A. L. Pelinescu and W. R. Wagner, Tailoring the degradation kinetics of poly (ester carbonate urethane) urea thermoplastic elastomers for tissue engineering scaffolds, Biomaterials, vol. 31, pp. 42494258, 2010