Physico-Mechanical Properties of Biodegradable Rubber Toughened Polymers

Summary: In this study, blends of poly(lactic acid) (PLA) with poly(butylene adipate-co-terephthalate) (PBAT) were studied for their mechanical and thermal properties as a function of the PBAT content. Tensile testing, impact testing, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMTA) and scanning electron microscopy (SEM) were used to characterize the blends. It was observed that PLA/PBAT blends maintained quite high modulus and tensile strength compared to pure PLA. Small amounts of PBAT improved the elongation at break and the impact resistance showing a debonding effect typical of rubber toughened systems.     

Branched Macromolecular Architectures for Degradable,Multifunctional Phosphorus‐Based Polymers

This feature article briefly highlights some of the recent advances in polymers in which phosphorus is an integral part of the backbone, with a focus on the preparation of functional, highly branched, soluble polymers. A comparison is made between the related families of materials polyphosphazenes, phosphazene/phosphorus‐based dendrimers and polyphosphoesters. The work described herein shows this to be a rich and burgeoning field, rapidly catching up with organic chemistry in terms of the macromolecular synthetic control and variety of available macromolecular architectures, whilst offering unique property combinations not available with carbon backbones, such as tunable degradation rates, high multi­valency and facile post‐polymerization functionalization. As an example of their use in advanced applications, we highlight some investigations into their use as water‐soluble drug carriers, whereby in particular the degradability in combination with multivalent nature has made them useful materials, as underlined by some of the recent studies in this area.

     

Exploring Microfluidic Routes to Microgels of Biological Polymers

Polymer microgels in the size range from several micrometers to hundreds of micrometers are used in the pharmaceutical, cosmetics, nutrition, pesticide, and food industries, as well as in the encapsulation of cells. To date, a broad range of strategies for the generation of polymer microgels exist, however, these methods involve multistage processes, do not utilize biocompatible components or do not allow precise control of the dimensions and internal structure of the microgels. Recently, microfluidic strategies for the production of polymer particles have offered precise control over the shapes, morphologies, and size distributions of polymer colloids. This paper discusses the most recent results obtained by the authors in the area of the microfluidic production of biopolymer microgels. It provides a brief review of the microfluidic methods for the continuous synthesis and fabrication of microgels, sets the criteria for the successful microfluidic generation of biomicrogels, and describes two methods for the preparation of microgels by microfluidic means. The article concludes with a summary and an outlook.

     

Multifunctional Polyesters for Bioartificial Vascular Prostheses

Aliphatic polyesters of controlled molecular weight and low molecular weight distribution were prepared via anionic ring-opening polymerization using a multifunctional star-shaped initiator. Functionalization results in star-shaped functional polyesters bearing methacrylate end groups. Novel biodegradable polyester resins were prepared by photochemical crosslinking of the functional polyesters. Three-dimensional microstructuring via UV replica molding shows the potential of this material as substrate for biomedical devices.     

Crosslinkable citronellol containing polyphosphazenes and their biomedical potential

An increased focus exists on the development of materials that might serve as ligament or tendon tissue engineering scaffolds. Requirements for a suitable candidate polymer include biodegradability, biocompatibility, and elasticity. In an attempt to meet these requirements novel citronellol‐containing polyphosphazenes were synthesized, characterized, and crosslinked to generate elastomers. Citronellol was chosen as a side group due to its anti‐inflammatory properties in addition to the presence of a double bond in its structure to permit polymer crosslinking. Alanine ethyl ester was chosen as a co‐substituent to tune hydrolysis rates without severely affecting the glass transition temperatures of the final polymers. Hydrolysis of the uncrosslinked polymers in the form of films in deionized water at 37 °C showed between ～8 and 16% mass loss and between a ～28 and 88% molecular weight decline over 12 weeks. Polymers were also crosslinked using ultraviolet radiation for increasing amounts of time. Preliminary mechanical testing of the homo‐citronellol polymer indicated increasing modulus and decreasing tensile strength with increased crosslink density. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2258–2265     

Polymers for neural implants

Neural implants are technical systems that restore sensory or motor functions after injury and modulate neural behavior in neuronal diseases. Neural interfaces or prostheses have lead to new therapeutic options and rehabilitation approaches in the last 40 years. The interface between the nervous tissue and the technical material is the place that determines success or failure of the neural implant. Recording of nerve signals and stimulation of nerve cells take place at this neuro‐technical interface. Polymers are the most common material class for substrate and insulation materials in combination with metals for interconnection wires and electrode sites. This work focuses on the neuro‐technical interface and summarizes its fundamental specifications first. The most common polymer materials are presented and described in detail. We conclude with an overview of the different applications and their specific designs with the accompanying manufacturing processes from precision mechanics, laser structuring and micromachining that are introduced in either the peripheral or central nervous system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Synthesis and chemical structural analysis of nitroxyl‐radical‐incorporated poly(acrylic acid/lactide/ϵ‐caprolactone) copolymers

The goal of this research is to synthesize biodegradable polymers that would have nitroxyl radical biological functions. Linear aliphatic polyesters were chosen as the starting materials. The hydroxyl‐terminated polylactide/?‐caprolactones (PBLC‐OHs) were first synthesized by melt ring‐opening copolymerization in the presence of benzyl alcohol and stannous octoate. PBLC‐OHs were used as the precursor for the synthesis of double bond‐functionalized polylactide/?‐caprolactones (PBLC‐Mas) by reacting the hydroxyl end groups of PBLC‐OH with maleic anhydride in melt at 130 °C. Acrylic acid/lactide/?‐caprolactone graft copolymers (PBLCAs) were then successfully carried out by the radical copolymerization of acrylic acid and PBLC‐Ma initiated by azobisisobutyronitrile. Finally, nitroxyl radicals [4‐amino‐2,2,6,6‐tetramethylpiperidine‐1‐oxy (TAM)] were incorporated into the carboxylic acid sites of the acrylic acid/lactide/?‐caprolactone copolymer (TAM‐PBLCA) by reacting TAM with PBLCA in the presence of N,N′‐carbonyl diimidazole. A high content of TAM was incorporated into the PBLCA copolymer. The polymers synthesized were characterized by ¹H and ¹³C NMR, Fourier transform infrared spectroscopy, and electron paramagnetic resonance spectra. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4214–4226, 2001     

Surface‐treated and multilayered poly(ε‐caprolactone) nanofiber webs exhibiting enhanced hydrophilicity

To improve the hydrophilic properties of poly(ε‐caprolactone) (PCL) nano/microfiber webs for tissue engineering scaffolds, PCL webs of various structures were fabricated by electrospinning with single or double nozzles connected to an auxiliary electrode. Surface‐modified and layered PCL fiber webs were made by including water‐soluble poly(ethylene oxide) (PEO) in the PCL electrospinning solution (single‐nozzle method) or by electrospinning of alternating PCL and PEO solutions using two nozzles (double‐nozzle method), respectively. When the PEO component within the resulting webs was removed by dissolution with distilled water, the remnant PCL webs exhibited two distinct structures. Those made by the single‐nozzle method consisted of nanofibers with high surface roughness, whereas those made by the double‐nozzle method consisted of stacked layers of PCL nanofibers. Both types of structured PCL web showed improved hydrophilicity characteristics compared with those of nanofiber webs generated from a pure PCL solution using a typical electrospinning process. Cell culturing and scanning electron microscopy showed that the interactions between human dermal fibroblasts and the structured PCL scaffolds were very favorable. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2038–2045, 2007     

Polydioxanone Polymers for Annuloplasty in Valve Repair

The Kalangos biodegradable ring® was recently developed fpr mitral and tricuspid annuloplasty to allow for flexibility, remodeling and preservation of growth potential of the native annulus. In this article, the results of the experimental trials carried out to assess its safety and potential advantages will be discussed.     

In Vitro Degradation of Poly(lactic-co2-glycolic) Acid Random Copolymers

We have investigated the in vitro degradation of poly(lactic-co-glycolic) acid copolymer with a lactic to glycolic ratio of 65/35. The degradation studies were performed on solvent-cast films of controlled thickness and shape. The samples were then incubated at 37 °C in phosphate buffered saline solution. The degradation was followed using potentiometry, light microscopy, gravimetry, gel permeation chromatography and differential scanning calorimetry. Water was found to diffuse inside the film as soon as the sample was placed in the degradation media. Wrinkles formed on the upper layer while degradation took place via chain scission in the bulk of the film. After 10 days, this led to the creation of a vesicle where liquid low molecular weight oligomers were trapped inside a thin film of high molecular weight polymer. This thin film acted as a membrane allowing only low molecular weight compounds to diffuse out of the film.     

Scaffold Design for Tissue Engineering

Tissue engineering has emerged as a promising alternative approach in the treatment of malfunctioning or lost organs. In this approach, a temporary scaffold is needed to serve as an adhesive substrate for the implanted cells and a physical support to guide the formation of the new organs. In addition to facilitating cell adhesion, promoting cell growth, and allowing the retention of differentiated cell functions, the scaffold should be biocompatible, biodegradable, highly porous with a large surface/volume ratio, mechanically strong, and malleable. A number of three‐dimensional porous scaffolds fabricated from various kinds of biodegradable materials have been developed. This paper reviews some of the advances in scaffold design focusing on the hybrid scaffolds recently developed in the authors' laboratory.     

Polymeric Scaffolds for Cartilage Tissue Engineering

Polymeric scaffolds are three-dimensional, porous structures that may be used as a vehicle to deliver cells or therapeutic factors to repair tissue defects. Both biodegradable and non-biodegradable polymers have been developed for this purpose. In this review, we survey the polymers that have been investigated for cartilage tissue engineering and discuss the critical parameters for successful applications in the future.     

Nano‐Star‐Shaped Polymers for Drug Delivery Applications

With the advancement of polymer engineering, complex star‐shaped polymer architectures can be synthesized with ease, bringing about a host of unique properties and applications. The polymer arms can be functionalized with different chemical groups to fine‐tune the response behavior or be endowed with targeting ligands or stimuli responsive moieties to control its physicochemical behavior and self‐organization in solution. Rheological properties of these solutions can be modulated, which also facilitates the control of the diffusion of the drug from these star‐based nanocarriers. However, these star‐shaped polymers designed for drug delivery are still in a very early stage of development. Due to the sheer diversity of macromolecules that can take on the star architectures and the various combinations of functional groups that can be cross‐linked together, there remain many structure–property relationships which have yet to be fully established. This review aims to provide an introductory perspective on the basic synthetic methods of star‐shaped polymers, the properties which can be controlled by the unique architecture, and also recent advances in drug delivery applications related to these star candidates.     

Supramolecular Materials Comprising Nucleic Acid Biopolymers

We have generated a supramolecular self-assembling film by exchanging the counter-ions of the phosphate moieties in nucleic acid with those of cationic amphiphiles as didodecyldimethylammonium bromide (or DDAB). SAXS and WAXS data for all film samples showed similar harmonic peaks suggesting a lamellar multilayer structure with layers of nucleic acids being separated by lipid bilayers of DDAB. AFM height images also showed that double stranded nucleic acid film can form the step or plateau type of structure and shorter nucleic acid film showed shorter step feature. Moreover, the length and the molecular structure of DNA and RNA can be used to manipulate the mechanical properties of these self-assembled films.     

Oligoethylene‐end‐capped polylactides

Oligoethylene‐end‐capped polylactides were synthesized through the ring‐opening polymerization of L ‐lactide with alcohol‐terminated oligoethylenes as macroinitiators. The polymerization of L ‐lactide was carried out in bulk at 130 °C in the presence of stannous octoate and primary alcohols with four different molecular weights: 350, 425, 550, and 700 g/mol. The end‐capped copolymers that formed had a number‐average molecular weight of approximately 40,000 (weight‐average molecular weight/number‐average molecular weight = 1.7) according to gel permeation chromatography and were highly crystalline in comparison with the similarly formed homopolymer of L ‐lactide. The copolymer structure was characterized by Fourier transform infrared, NMR, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, and differential scanning calorimetry analysis. This work focused on developing more crystallizable and hydrolytically stable polylactide derivatives that could potentially be used as compatibilizers in polylactide–polyolefin blends or as nucleating agents for poly(L ‐lactide) or other polyesters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5257–5266, 2005     

Synthesis and characterizations of bis(phenoxy)‐amine tin(II) complexes for ring‐opening polymerization of lactide

A series of tin(II) complexes supported by N₂O₂ bis(phenol)‐amine ligands were prepared from the reactions of the corresponding ligands with Sn[N(SiMe₃)₂]₂ in benzene at room temperature. The ligands were designed to have different substituted group at the ortho‐position on the aryl rings (R = ^tBu, CH₃) and N‐containing side arm (E = ? CH₂NEt₂ and pyridine) giving a variation of tin(II) complexes (R = ^tBu, E = CH₂NEt₂, 2a ; R = ^tBu, E = py, 2b ; R = CH₃, E = CH₂NEt₂, 2c ; R = CH₃, E = py, 2d ). All complexes were characterized by NMR spectroscopy and single‐crystal X‐ray analysis. The single‐crystal X‐ray crystallography revealed that all complexes have a monomeric four‐coordinate tin center with a distorted seesaw structure. All complexes are active for solvent‐free polymerization of l ‐lactide at 120 °C giving poly(l ‐lactide) with narrow to moderate dispersity (Ð = 1.12–1.56). In the presence of benzyl alcohol during the polymerization, the resulting polymer was found to be linear having benzyl alcohol as the end group while, in the absence of benzyl alcohol, the polymer was cyclic. The large ^tBu group at the ortho‐position was found to decrease polymerization activity while the more basic ? CH₂NEt₂ group was found to increase the polymerization activity. The polymerization of rac‐lactide under a similar condition gave PLA having a slight heterotactic bias for all catalysts. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2104–2112