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Ring-Opening Polymerization and Metathesis Polymerizations
Published in Samir H. Chikkali, Metal-Catalyzed Polymerization, 2017
Aliphatic polyesters are important industrial polymers that have applications as fibers, coatings, bulk packaging materials, and films. Their biodegradable nature makes them an environmentally friendly alternative to the nondegradable plastics.1 Copolymers of lactide and trimethylene carbonate (TMC) are used as thermoplastic elastomers and biomaterials for applications in tissue engineering, drug delivery, as biodegradable devices for bone fracture repair and sutures. The monomer for poly(lactic acid) (PLA), d,l-lactide is a dimer of lactic acid (LA), which is produced from natural sources such as a starch or sugar via bacterial fermentation of D-glucose.2 Hence, production of poly(lactide) is environmentally friendly. Manufacturing of PLA has become profitable over the years. Natureworks LLC, a joint venture between Cargill and Teijen Limited, set up a 300 million pounds per year PLA production plant and sells PLA under the trade name Ingeo™, which is produced in isotactic form by a carbon neutral process. Its physical properties are similar to polyolefins and polystyrene.3 The polycondensation route for PLA is undesirable since it is difficult to produce high molecular weight polymer, making ring-opening polymerization (ROP) the method of choice. In this chapter, ROP toward sustainable polymers such as PLA and poly(ε-caprolactone) (PCL) only will be discussed. ROP is a living polymerization, that is, it shows fast initiation and minimal termination and transfer reactions, however it follows step-growth kinetics. Polydispersity is usually low but can be influenced by trans-esterification reactions and is of concern while making block copolymers. The thermodynamic driving force for the polymerization is the relief of ring strain, which helps to overcome the high entropy values (Lactide: ΔS = 25.0 J mol−1 K−1; ε-CL: ΔS = 53.9 J mol−1 K−1).4 ROP performed using metal catalysts that operate through cationic mechanism do not yield high molecular weight polymer desirable for practical applications. Therefore immortal ROP that follows chain-transfer pathway and involves a catalyst and a nucleophile (either part of the catalyst or externally added) that acts simultaneously as the initiator and chain-transfer agent (CTA), was developed as an efficient alternative to the classical living cationic polymerization.
Regeneration of annulus fibrosus tissue using a DAFM/PECUU-blended electrospun scaffold
Published in Journal of Biomaterials Science, Polymer Edition, 2020
Chen Liu, Liang Xiao, Yu Zhang, Quanlai Zhao, Hongguang Xu
At present, regeneration of degenerated or ruptured AF tissue using tissue engineering technology received more and more attention. Various kinds of scaffolds have been applied in AF tissue engineering. Poly(ether carbonate urethane) urea (PECUU) is a kind of poly(trimethylene carbonate)-based copolymer whose mechanical properties remain unchanged during scaffod degradation [8]. In our previous study, a series of PECUU scaffolds with different elastic moduli were synthesized to simulate the mechanics of actual AF tissue and would allow differentiation of AF-derived stem cells (AFSCs) into AF-like cells [9]. However, PECUU scaffolds still have some shortcomings with respect to AF tissue engineering. On one hand, AFSCs cannot secret as much extracellular matrix (ECM) as actual AF tissue on PECUU scaffolds, which may cause eventual failure of the engineered tissue. On the other hand, PECUU and its degradation products could induce inflammatory responses, which is not good for implantation in vivo.
Study of functional drug-eluting stent in promoting endothelialization and antiproliferation
Published in Journal of Biomaterials Science, Polymer Edition, 2020
Ruixia Hou, Leigang Wu, Yabin Zhu, Jin Wang, Zhilu Yang, Qiufen Tu, Nan Huang
Currently, biodegradable polymers instead of non-biodegradable polymers are widely used as DES coatings. Biodegradable polymers such as poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) have been widely used as drug carriers in DESs [10, 11]. However, PLA and PLGA polymers undergo bulk erosion, and they can induce internal catalysis leading to high local acidity during the degradation process and cause unfavorable effects [12]. Poly(1,3-trimethylene carbonate) (PTMC), which is approved by the Food and Drug Administration (FDA) of the United States, undergoes surface erosion. PTMC demonstrates unique mechanical properties and a uniform surface during the degradation process, and less platelet adhesion and activation, and the degradation products are not acidic [13–16]. Therefore, we chose PTMC as a stent coating material in the current study.
Photo-crosslinked synthetic biodegradable polymer networks for biomedical applications
Published in Journal of Biomaterials Science, Polymer Edition, 2019
Bas van Bochove, Dirk W. Grijpma
There are many biodegradable polymers and oligomers that have been used to prepare photo-crosslinkable macromers for biodegradable polymer networks. Examples include poly(D,L-lactide) (PDLLA) [17], poly(ε-caprolactone) (PCL) [18,19], poly(trimethylene carbonate) (PTMC) [20], poly(ethylene carbonate) (PEC) [21], and block copolymers containing poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG) or poly(tetramethylene glycol) (PTMG) and poly(glycolide) (PGA), PDLLA or PCL segments [22,23]. Most of these polymers can readily synthesized by the ring opening polymerization of their cyclic monomers. The polymerization is usually initiated by an alcohol and catalyzed by stannous octoate [24] This reaction is usually performed in the melt at temperatures between 90 and 180 °C [1]. By adjusting the amount and the functionality of the hydroxyl-group terminated alcohols used as initiator, the molecular weight and architecture of the synthesized oligomers can be precisely controlled [25].