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Special Issue "Natural Polymers"

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A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (31 August 2010)

Special Issue Editors

Guest Editor
Dr. Jennie B. Leach (Website)

Chemical, Biochemical & Environmental Engineering, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
Interests: biomaterials synthesis and characterization; sensors for tissue engineering applications; cell response in 3D microenvironments; tissue engineering in the nervous system
Guest Editor
Prof. Dr. Christine E. Schmidt

Department of Biomedical Engineering, University of Florida, BMSB JG-42, P.O. Box 116131, Gainesville, FL 32611, USA
Phone: +1 352-273-9222
Fax: +1 352-273-9221
Interests: biomaterials; scaffolds; natural polymers; electrically conducting polymers

Special Issue Information

Dear Colleagues,

Contributions are invited that specifically involve polymers of a natural or biological origin, namely proteins, nucleic acids, and polysaccharides. Of particular interest are research studies or review articles related to the following areas: (1) connections between polymer science fundamentals with the understanding and applications of natural polymers, including the structure, behavior and uses of natural polymers in solutions, complexes and at interfaces with other materials; (2) bioengineering applications of natural polymers, including tissue engineering, clinical medicine, as well as pharmaceutical and food technologies; and we particularly encourage (3) novel applications of natural polymers, including their use in bioMEMs devices and nanotechnology as well as novel modifications of natural polymers to enhance their properties by functionalization, cross-linking, or forming composite or co-polymer structures with other materials.

Prof. Dr. Christine E. Schmidt
Dr. Jennie B. Leach
Guest Editors

Published Papers (11 papers)

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Research

Jump to: Review

Open AccessArticle Modeling Textural Processes during Self-Assembly of Plant-Based Chiral-Nematic Liquid Crystals
Polymers 2010, 2(4), 766-785; doi:10.3390/polym2040766
Received: 11 October 2010 / Revised: 22 November 2010 / Accepted: 29 November 2010 / Published: 15 December 2010
Cited by 10 | PDF Full-text (1068 KB) | HTML Full-text | XML Full-text
Abstract
Biological liquid crystalline polymers are found in cellulosic, chitin, and DNA based natural materials. Chiral nematic liquid crystalline orientational order is observed frozen-in in the solid state in plant cell walls and is known as a liquid crystal analogue characterized by a [...] Read more.
Biological liquid crystalline polymers are found in cellulosic, chitin, and DNA based natural materials. Chiral nematic liquid crystalline orientational order is observed frozen-in in the solid state in plant cell walls and is known as a liquid crystal analogue characterized by a helicoidal plywood architecture. The emergence of the plywood architecture by directed chiral nematic liquid crystalline self assembly has been postulated as the mechanism that leads to optimal cellulose fibril organization. In natural systems, tissue growth and development takes place in the presence of inclusions and secondary phases leaving behind characteristic defects and textures, which provide a unique testing ground for the validity of the liquid crystal self-assembly postulate. In this work, a mathematical model, based on the Landau-de Gennes theory of liquid crystals, is used to simulate defect textures arising in the domain of self assembly, due to presence of secondary phases representing plant cells, lumens and pit canals. It is shown that the obtained defect patterns observed in some plant cell walls are those expected from a truly liquid crystalline phase. The analysis reveals the nature and magnitude of the viscoelastic material parameters that lead to observed patterns in plant-based helicoids through directed self-assembly. In addition, the results provide new guidance to develop biomimetic plywoods for structural and functional applications. Full article
(This article belongs to the Special Issue Natural Polymers)
Open AccessArticle Preparation and Characterization of Insoluble Silk Fibroin/Chitosan Blend Films
Polymers 2010, 2(4), 719-727; doi:10.3390/polym2040719
Received: 25 October 2010 / Revised: 26 November 2010 / Accepted: 2 December 2010 / Published: 13 December 2010
Cited by 25 | PDF Full-text (219 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this study was to prepare and characterize membranes of silk fibroin (SF) and chitosan (CHI) blends. Moreover, a conformation transition of SF to a more stable form induced by the addition of CHI was verified. Blend membranes were prepared, [...] Read more.
The aim of this study was to prepare and characterize membranes of silk fibroin (SF) and chitosan (CHI) blends. Moreover, a conformation transition of SF to a more stable form induced by the addition of CHI was verified. Blend membranes were prepared, after pH adjustment, in different ratios, and physical integrity, crystallinity, structural conformation and thermal stability were characterized. The results of crystallographic analysis (XRD) indicated the tendency to higher structural organization caused by the addition of CHI. Fourier transformed infrared spectroscopy (FTIR) showed that SF is present in a more stable form in the presence of a CHI content of only 25 wt%. Thermal analysis indicated that SF is thermally stable and that when its proportion in the blend increases, the temperature at which degradation is initiated also increases. Full article
(This article belongs to the Special Issue Natural Polymers)
Open AccessArticle Tailoring Mechanical Properties of Collagen-Based Scaffolds for Vascular Tissue Engineering: The Effects of pH, Temperature and Ionic Strength on Gelation
Polymers 2010, 2(4), 664-680; doi:10.3390/polym2040664
Received: 8 October 2010 / Revised: 27 October 2010 / Accepted: 2 December 2010 / Published: 6 December 2010
Cited by 43 | PDF Full-text (561 KB) | HTML Full-text | XML Full-text
Abstract
Collagen gels have been widely studied for applications in tissue engineering because of their biological implications. Considering their use as scaffolds for vascular tissue engineering, the main limitation has always been related to their low mechanical properties. During the process of in [...] Read more.
Collagen gels have been widely studied for applications in tissue engineering because of their biological implications. Considering their use as scaffolds for vascular tissue engineering, the main limitation has always been related to their low mechanical properties. During the process of in vitro self-assembly, which leads to collagen gelation, the size of the fibrils, their chemical interactions, as well as the resulting microstructure are regulated by three main experimental conditions: pH, ionic strength and temperature. In this work, these three parameters were modulated in order to increase the mechanical properties of collagen gels. The effects on the gelation process were assessed by turbidimetric and scanning electron microscopy analyses. Turbidity measurements showed that gelation was affected by all three factors and scanning electron images confirmed that major changes occurred at the microstructural level. Mechanical tests showed that the compressive and tensile moduli increased by four- and three-fold, respectively, compared to the control. Finally, viability tests confirmed that these gels are suitable as scaffolds for cellular adhesion and proliferation. Full article
(This article belongs to the Special Issue Natural Polymers)
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Open AccessArticle Functionalization, Compatibilization and Properties of Polyolefin Composites with Natural Fibers
Polymers 2010, 2(4), 554-574; doi:10.3390/polym2040554
Received: 14 October 2010 / Revised: 2 November 2010 / Accepted: 10 November 2010 / Published: 15 November 2010
Cited by 43 | PDF Full-text (854 KB) | HTML Full-text | XML Full-text
Abstract
The article is focused on analyzing the effect of functionalization and reactive processing on the morphological, thermal, rheological and mechanical properties of composites of isotactic polypropylene (PP), polystyrene (PS), poly(ethylene-vinyl acetate) (EVA), with cellulose fibers, hemp or oat as natural fillers. Both [...] Read more.
The article is focused on analyzing the effect of functionalization and reactive processing on the morphological, thermal, rheological and mechanical properties of composites of isotactic polypropylene (PP), polystyrene (PS), poly(ethylene-vinyl acetate) (EVA), with cellulose fibers, hemp or oat as natural fillers. Both polymers and fibers were modified with bi-functional monomers (glycidyl methacrylate, GMA; maleic anhydride, MA) capable of facilitating chemical reactions between the components during melt mixing. Polyolefin copolymers containing reactive groups (PP-g-GMA, SEBS-g-MA, PS-co-MA, etc.) were used as compatibilizers. Optical and SEM microscopy, FTIR, RX, DSC, TGA, DMTA, rheological and mechanical tests were employed for the composites characterization. The properties of binary and ternary systems have been analyzed as a function of both fiber and compatibilizer content. All compatibilized systems showed enhanced fiber dispersion and interfacial adhesion. The phase behavior and the thermal stability of the composites were affected by the chemical modification of the fibers. Marked changes in the overall crystallization processes and crystal morphology of PP composites were observed owing to the nucleating effect of the fibers. The tensile mechanical behavior of the compatibilized composites generally resulted in a higher stiffness, depending on the fiber amount and the structure and concentration of compatibilizer. Full article
(This article belongs to the Special Issue Natural Polymers)
Open AccessArticle Periodate Oxidation of Methylcellulose: Characterization and Properties of Oxidized Derivatives
Polymers 2010, 2(4), 505-521; doi:10.3390/polym2040505
Received: 23 August 2010 / Revised: 19 October 2010 / Accepted: 28 October 2010 / Published: 29 October 2010
Cited by 7 | PDF Full-text (401 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, the behavior of oxidized methylcelluloses is compared with that of the initial methylcellulose, an amphiphilic cellulose derivative. Methylcelluloses are important for many applications in the cosmetic and food industries. The mechanism of thermo-gelation of methylcellulose is briefly explained as [...] Read more.
In this paper, the behavior of oxidized methylcelluloses is compared with that of the initial methylcellulose, an amphiphilic cellulose derivative. Methylcelluloses are important for many applications in the cosmetic and food industries. The mechanism of thermo-gelation of methylcellulose is briefly explained as well as the method of oxidation of polysaccharides. Then, our experiments involve the preparation of oxidized methylcelluloses: three degrees of oxidation are prepared and the new polymers are characterized by NMR, IR, SEC and rheology. Oxidation with periodate theoretically allows introduction of two aldehydic groups on C2–C3 glycol positions of anhydroglucose units. This reaction not only enhances the flexibility of the cellulosic backbone, but also causes a decrease in the molecular weight. In particular, the rheological behavior of methylcellulose and oxidized methylcellulose as a function of temperature is examined. The oxidized methylcelluloses prepared, being rich in aldehyde functions, become interesting intermediaries to prepare new cellulose derivatives. In this paper, three examples of reductive amination based on the reaction of modified methylcelluloses and −NH2 groups of different molecules are described: β-alanine produces a polyelectrolyte; chitosan and hyaluronan-ADH (derivative obtained with adipic dihydrazide allowing introduction of −NH2 functions on HA backbone) are crosslinked and give new biocompatible hydrogels. Full article
(This article belongs to the Special Issue Natural Polymers)
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Open AccessArticle Synthesis and Characterization of Carboxymethylcellulose-Methacrylate Hydrogel Cell Scaffolds
Polymers 2010, 2(3), 252-264; doi:10.3390/polym2030252
Received: 13 July 2010 / Revised: 16 August 2010 / Accepted: 25 August 2010 / Published: 26 August 2010
Cited by 24 | PDF Full-text (563 KB) | HTML Full-text | XML Full-text
Abstract
Many carbohydrates pose advantages for tissue engineering applications due to their hydrophilicity, degradability, and availability of chemical groups for modification. For example, carboxymethylcellulose (CMC) is a water-soluble cellulose derivative that is degradable by cellulase. Though this enzyme is not synthesized by mammalian [...] Read more.
Many carbohydrates pose advantages for tissue engineering applications due to their hydrophilicity, degradability, and availability of chemical groups for modification. For example, carboxymethylcellulose (CMC) is a water-soluble cellulose derivative that is degradable by cellulase. Though this enzyme is not synthesized by mammalian cells, cellulase and the fragments derived from CMC degradation are biocompatible. With this in mind, we created biocompatible, selectively degradable CMC-based hydrogels that are stable in routine culture, but degrade when exposed to exogenous cellulase. Solutions of CMC-methacrylate and polyethylene glycol dimethacrylate (PEG-DM) were co-crosslinked to form stable hydrogels; we found that greater CMC-methacrylate content resulted in increased gel swelling, protein diffusion and rates of degradation by cellulase, as well as decreased gel shear modulus. CMC-methacrylate/PEG-DM gels modified with the adhesive peptide RGD supported fibroblast adhesion and viability. We conclude that hydrogels based on CMC-methacrylate are suitable for bioengineering applications where selective degradability may be favorable, such as cell scaffolds or controlled release devices. Full article
(This article belongs to the Special Issue Natural Polymers)
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Open AccessArticle Borate Minerals and RNA Stability
Polymers 2010, 2(3), 211-228; doi:10.3390/polym2030211
Received: 21 May 2010 / Revised: 7 July 2010 / Accepted: 12 August 2010 / Published: 16 August 2010
Cited by 5 | PDF Full-text (702 KB) | HTML Full-text | XML Full-text
Abstract
The abiotic origin of genetic polymers faces two major problems: a prebiotically plausible polymerization mechanism and the maintenance of their polymerized state outside a cellular environment. The stabilizing action of borate on ribose having been reported, we have explored the possibility that [...] Read more.
The abiotic origin of genetic polymers faces two major problems: a prebiotically plausible polymerization mechanism and the maintenance of their polymerized state outside a cellular environment. The stabilizing action of borate on ribose having been reported, we have explored the possibility that borate minerals stabilize RNA. We observe that borate itself does not stabilize RNA. The analysis of a large panel of minerals tested in various physical-chemical conditions shows that in general no protection on RNA backbone is exerted, with the interesting exception of ludwigite (Mg2Fe3+BO5). Stability is a fundamental property of nucleic polymers and borate is an abundant component of the planet, hence the prebiotic interest of this analysis. Full article
(This article belongs to the Special Issue Natural Polymers)

Review

Jump to: Research

Open AccessReview Cellulosic Bionanocomposites: A Review of Preparation, Properties and Applications
Polymers 2010, 2(4), 728-765; doi:10.3390/polym2040728
Received: 9 October 2010 / Revised: 29 October 2010 / Accepted: 8 December 2010 / Published: 13 December 2010
Cited by 296 | PDF Full-text (712 KB) | HTML Full-text | XML Full-text
Abstract
Cellulose is the most abundant biomass material in nature. Extracted from natural fibers, its hierarchical and multi-level organization allows different kinds of nanoscaled cellulosic fillers—called cellulose nanocrystals or microfibrillated cellulose (MFC)—to be obtained. Recently, such cellulose nanoparticles have been the focus of [...] Read more.
Cellulose is the most abundant biomass material in nature. Extracted from natural fibers, its hierarchical and multi-level organization allows different kinds of nanoscaled cellulosic fillers—called cellulose nanocrystals or microfibrillated cellulose (MFC)—to be obtained. Recently, such cellulose nanoparticles have been the focus of an exponentially increasing number of works or reviews devoted to understanding such materials and their applications. Major studies over the last decades have shown that cellulose nanoparticles could be used as fillers to improve mechanical and barrier properties of biocomposites. Their use for industrial packaging is being investigated, with continuous studies to find innovative solutions for efficient and sustainable systems. Processing is more and more important and different systems are detailed in this paper depending on the polymer solubility, i.e., (i) hydrosoluble systems, (ii) non-hydrosoluble systems, and (iii) emulsion systems. This paper intends to give a clear overview of cellulose nanoparticles reinforced composites with more than 150 references by describing their preparation, characterization, properties and applications. Full article
(This article belongs to the Special Issue Natural Polymers)
Open AccessReview Tri-n-Butylborane/WaterComplex-Mediated Copolymerization of Methyl Methacrylate with Proteinaceous Materials and Proteins: A Review
Polymers 2010, 2(4), 575-595; doi:10.3390/polym2040575
Received: 23 August 2010 / Revised: 8 October 2010 / Accepted: 5 November 2010 / Published: 15 November 2010
PDF Full-text (282 KB) | HTML Full-text | XML Full-text
Abstract
Previous studies of tri-n-butylborane–initiated graft copolymerization of methyl methacrylates with hydrated proteinous materials and proteins have focused on the number of grafted-poly (MMA) branches as well as the percent graft and graft efficiency. The number of branches in silk fibroin [...] Read more.
Previous studies of tri-n-butylborane–initiated graft copolymerization of methyl methacrylates with hydrated proteinous materials and proteins have focused on the number of grafted-poly (MMA) branches as well as the percent graft and graft efficiency. The number of branches in silk fibroin is 1.3, whereas the number in collagen, gelatin, ovalbumin and wool are 0.1, 0.04, 0.02 and 0.03, respectively. The number of grafted-PMMA branches in synthetic poly-L-peptides is approximately 10-fold less than that in gelatin, and decline, in the order poly-Ala > poly-Ser > poly-Pro > poly-Glu > poly-Lys. By contrast, poly-Gly, poly-Tyr and poly-Leu have no branches. The co-catalytic effect (the ratio of the number of polymer formed relative to that of control) of amino acids on tri-n-butylborane-initiated polymerization of MMA in the presence of water has been linearly correlated with their ionization potential (IPkoopman); |Äå HOMO (Highest Occupied Molecular Orbital)| (r2 = 0.6, outliers: Cys and His); Äå HOMO = [åHOMOaqua − åHOMOvacuum] calculated using the semiempirical AM1 method. Also, a significant exponential relationship between the number of branches of poly-L-polypeptides and the Äå HOMO of the corresponding amino acids has been observed (r2 = 0.9). A possible grafting site of protein (polypeptide) is discussed. Full article
(This article belongs to the Special Issue Natural Polymers)
Open AccessReview The Use of Natural Polymers in Tissue Engineering: A Focus on Electrospun Extracellular Matrix Analogues
Polymers 2010, 2(4), 522-553; doi:10.3390/polym2040522
Received: 1 September 2010 / Revised: 29 September 2010 / Accepted: 4 November 2010 / Published: 9 November 2010
Cited by 108 | PDF Full-text (1102 KB) | HTML Full-text | XML Full-text
Abstract
Natural polymers such as collagens, elastin, and fibrinogen make up much of the body’s native extracellular matrix (ECM). This ECM provides structure and mechanical integrity to tissues, as well as communicating with the cellular components it supports to help facilitate and regulate [...] Read more.
Natural polymers such as collagens, elastin, and fibrinogen make up much of the body’s native extracellular matrix (ECM). This ECM provides structure and mechanical integrity to tissues, as well as communicating with the cellular components it supports to help facilitate and regulate daily cellular processes and wound healing. An ideal tissue engineering scaffold would not only replicate the structure of this ECM, but would also replicate the many functions that the ECM performs. In the past decade, the process of electrospinning has proven effective in creating non-woven ECM analogue scaffolds of micro to nanoscale diameter fibers from an array of synthetic and natural polymers. The ability of this fabrication technique to utilize the aforementioned natural polymers to create tissue engineering scaffolds has yielded promising results, both in vitro and in vivo, due in part to the enhanced bioactivity afforded by materials normally found within the human body. This review will present the process of electrospinning and describe the use of natural polymers in the creation of bioactive ECM analogues in tissue engineering. Full article
(This article belongs to the Special Issue Natural Polymers)
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Open AccessReview Oleic and Undecylenic Acids as Renewable Feedstocks in the Synthesis of Polyols and Polyurethanes
Polymers 2010, 2(4), 440-453; doi:10.3390/polym2040440
Received: 3 September 2010 / Revised: 11 October 2010 / Accepted: 12 October 2010 / Published: 14 October 2010
Cited by 38 | PDF Full-text (428 KB) | HTML Full-text | XML Full-text
Abstract
Nowadays, the utilization of raw materials derived from renewable feedstock is in the spotlight of the chemical industry, as vegetable oils are one of the most important platform chemicals due to their universal availability, inherent biodegradability and low price. Taking into account [...] Read more.
Nowadays, the utilization of raw materials derived from renewable feedstock is in the spotlight of the chemical industry, as vegetable oils are one of the most important platform chemicals due to their universal availability, inherent biodegradability and low price. Taking into account that polyurethanes are one of the most important industrial products exhibiting versatile properties suitable for use in many fields, our research is focused on exploiting fatty acids in the preparation of biobased polyols and polyurethanes. This review is organized as a function of the nature of the final polyurethane systems; hence we describe the preparation of linear thermoplastic and crosslinked polyurethanes derived from oleic and undecylenic acids-based diols and polyols, respectively. Full article
(This article belongs to the Special Issue Natural Polymers)
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