Renewable Natural Polymer Research Articles

Amidoximated graphene/konjac glucomannan composite gel for uranium extraction from saline lake brine

To overcome the separation defect of amidoximated graphene oxide (rGO-PAO) in uranium sorption from water solutions, the renewable natural polymer material konjac glucomannan (KGM) is selected as the immobilization reagent, since KGM can easily form gel structure and very cheap. A rationally designed strategy is developed to synthesize the new composite gel sorbent denoted as rGO-PAO/KGM. The acquired sorbents are characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and BET specific surface area analyses. All the results prove that rGO-PAO is successfully immobilized by KGM and composite gels with three dimensional (3D) sponge-like architectures are obtained. Batch uranium sorption experiments are conducted and the effects of initial solution pH, ion strength, time, uranium concentration and coexisting ions on uranium sorption are investigated. Blank KGM is found to have low uranium sorption capacity and most of uranium ions are sorbed by rGO-PAO. The maximum experimental sorption capacities are determined to be 52.6 ± 0.5 mg/g for 20-rGO-PAO/KGM. Furthermore, the sorption mechanism of uranium by rGO-PAO/KGM are revealed by using different analytical methods. Amidoxime groups are found to play the major role in uranium sorption. Uranium extraction from natural saline lake brine sample by rGO-PAO/KGM is conducted. Although the sorption capacity is not very high, rGO-PAO/KGM can be regarded as potential sorbents for uranium extraction from natural complicated waters, considering some of their superior properties.

Chitosan strengthened and multiple hydrogen bonds crosslinked styrene-acrylate coatings as conductive substrate with excellent mechanical performance

In this work, styrene-acrylate (SA) coatings were strengthened with renewable natural polymers (carboxymethyl chitosan, CMCS) and crosslinked by multiple hydrogen bonds, which improved the mechanical performance and endowed the self-healing properties. SA latex was synthesized by styrene (St), butyl acrylate (BA), glycidyl methacrylate (GMA) and acrylamide (AM) with semi continuous seed emulsion polymerization. SA coatings were obtained after drying the mixture of SA latex and CMCS. The rigid skeleton of CMCS and hydrogen bonds cross-linked network improved the mechanical properties of SA coatings. The stress and strain improved from 12.3 to 17.9 MPa and 1765% to 2148%. The reversible hydrogen bonding interactions between SA and CMCS made the films had a self-healing efficiency of 68.7%. Moreover, the hardness of SA coatings reached 80.6. Combined with the spraying technique, SA conductive coatings were prepared by spraying carbon nanotubes aqueous dispersions (CNTs) on the surface. The conductivity and sensing ability of the SA conductive coatings were examined by an electrochemical workstation. The results demonstrated that SA conductive coatings had the signal sensing ability for tiny movements, which was of potential applications in the field of sensors.

Starch Grafted Water Resistant Polyvinyl Acetate-Based Wood Adhesive: A Review

Global energy issues and the reliance on hydrocarbon resources have resulted in the reduction of petroleum sources, and the focus of the chemical industries has shifted to substitute raw material sources. The major raw materials used in wood adhesives, such as hydrocarbons like polyvinyl acetate, would be gradually replaced by renewable natural polymers. Currently, polyvinyl alcohol has the limitation of petroleum origin, which is non-economical and it will be replaced by biopolymers. Conventionally available wood adhesive emulsions are colloid-like polyvinyl alcohol stabilized. Starch, being a naturally available polymer, has gained interest from researchers for replacing polyvinyl alcohol as a stabilizer. New research on sustainable, economical, biodegradable, renewable, and environmentally friendly starch grafted polyvinyl acetate emulsion that was synthesized by the graft polymerization of vinyl acetate monomer onto starch. However, starch grafted polyvinyl acetate emulsion-based adhesive’s properties, such as poor water resistance, weak adhesion, delayed drying rate and delayed setting speed, have resulted in limitations in its application as a wood adhesive. A detailed review of starch grafting on vinyl acetate and comonomers like acrylamides, and acrylic acid, and the addition of nano-fillers to enhance the water resistance and performance properties of sustainable adhesives has been explained.

Polytetrahydrofuran from renewable natural raw materials and polymers based on it

A review of the works devoted to the synthesis and investigation of the properties of block copolymers containing fragments of polytetrahydrofuran obtained from renewable natural raw materials is presented. It is shown that the presence of chemically bonded blocks of elastic polytetrahydrofuran in rigid-chain polymer matrices increases their impact resistance and elongation at break, reduces the viscosity of the melt, and improves miscibility with other polymers. It is expected that a similar positive effect of polytetrahydrofuran elastic blocks will be observed in polymer composites filled with dispersed and continuous fibers.

Jin Shofu Starch Nanoparticles for the Consolidation of Modern Paintings

Matte, porous, and weakly bound paint layers, typically found in modern/contemporary art, represent an unsolved conservation challenge. Current conservation practice relies on synthetic or natural adhesives that can alter dramatically the optical properties of paints. Alternatively, we propose a novel nanostructured consolidant based on starch, a renewable natural polymer. We synthesized starch nanoparticles (SNPs) to boost their penetration into the porous painted layers; upon solvent evaporation, the particles were expected to adhere to the pigments thanks to their large surface area and abundant -OH groups. The SNPs were formulated through a bottom-up approach, where gluten-removed Jin Shofu wheat starch was gelatinized and then precipitated in a nonsolvent. The low gelatinization temperature of wheat starch is likely key to favor disassembly in alkali and reassembly in the nonsolvent. The synthesis conditions can be tuned to obtain amorphous SNPs of ca. 50 nm with acceptable polydispersity. The particles swell in water to form nanosized gel-like fractal domains (as observed with cryogenic electron microscopy), formed by the organization of smaller units in polymer-rich and -deficient regions. Aqueous and hydroalcoholic particles' dispersions were assessed on aged ultramarine blue mock-ups that mimic degraded modern/contemporary paints. The consolidation effectiveness was evaluated with a specifically designed in-house protocol: the SNPs distribute across the paint section and strongly increase pigments' cohesion while preserving the original optical properties of the painted layer, as opposed to dispersions of bulk starch that simply accumulate on the paint surface, forming superficial glossy films. The Jin Shofu SNPS proved to be a new promising tool for the consolidation of weakened paintings, opening perspectives in the formulation and application of consolidants for modern and contemporary art.

Confined Chemical Transitions for Direct Extraction of Conductive Cellulose Nanofibers with Graphitized Carbon Shell at Low Temperature and Pressure.

Cellulose is the most abundant renewable natural polymer on earth, but it does not conduct electricity, which limits its application expansion. The existing methods of making cellulose conductive are combined with another conductive material or high-temperature/high-pressure carbonization of the cellulose itself, while in the traditional method of sulfuric acid hydrolysis to extract nanocellulose, it is usually believed that a too high temperature will destroy cellulose and lead to experimental failure. Now, based on a new research perspective, by controlling the continuous reaction process and isolating oxygen, we directly extracted intrinsically conductive cellulose nanofiber (CNF) from biomass, where the confined range molecular chains of CNF were converted to highly graphitized carbon at only 90 °C and atmospheric pressure, while large-scale twisted graphene films can be synthesized bottom-up from CNFene suspensions, called CNFene (cellulose nanofiber-graphene). The conductivity of the best CNFene can be as high as 1.099 S/cm, and the generality of this synthetic route has been verified from multiple biomass cellulose sources. By comparing the conventional high-pressure hydrothermal and high-temperature pyrolysis methods, this study avoided the dangerous high-pressure environment and saved 86.16% in energy. These findings break through the conventional notion that nanocellulose cannot conduct electricity by itself and are expected to extend the application potential of pure nanocellulose to energy storage, catalysis, and sensing.

Mesoporous cellulose-chitosan composite hydrogel fabricated via the co-dissolution-regeneration process as biosorbent of heavy metals

Developing low-cost and high-performance biosorbent for water purification continues drawing more and more attention. In this study, cellulose-chitosan composite hydrogels were fabricated via a co-dissolution and regeneration process using a molten salt hydrate (a 60 wt% aqueous solution of LiBr) as a solvent. The addition of chitosan not only introduced functionality for metal adsorption but also increased the specific surface area and improved the mechanical strength of the composite hydrogel, compared to pure cellulose hydrogel. Batch adsorption experiments indicated that the composite hydrogel with 37% cellulose and 63% chitosan exhibited an adsorption capacity of 94.3 mg/g (1.49 mmol/g) toward Cu2+ at 23 °C, pH 5, and initial metal concentration of 1500 mg/L, which was 10 times greater than the adsorption capacity of pure cellulose hydrogel. Competitive adsorption from a mixed metals solution revealed that the cellulose-chitosan composite hydrogel exhibited selective adsorption of the metals in the order of Cu2+ > Zn2+ > Co2+. This study successfully demonstrated an innovative method to fabricate biosorbents from abundant and renewable natural polymers (cellulose and chitosan) for removing metal ions from water.

Characterization of Chitosan from the Haliling Snail (Filopaludina javanica) Shell in South Kalimantan

Chitosan is a renewable natural polymer derived from chitin which can be found in many invertebrate animals. Chitosan has non-toxic properties, is easily broken down (biodegradable and bioresorbable), and is able to adapt to its environment (biocompatibility). This study aims to characterize chitosan produced from haliling (Filopaludina javanica) shell waste originating from South Kalimantan. Haliling meat is consumed as a side dish by the people of South Kalimantan so that the shell becomes a waste that can be used as raw material for chitosan. Chitosan characterization included determination of yield, solubility test, calculation of the degree of deacetylation with Fourier Transform Infra Red (FTIR), as well as observing the crystallinity and morphology of the yield compounds by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM). The yield of chitosan obtained was 8.890% with the best solubility at 0.1 N HNO 3 N. The FTIR analysis of chitosan obtained a degree of deacetylation of 60.581%. XRD and SEM data showed a crystallinity index of 52.945% with a granular surface.

The Mass Production of Lignin Fibres by Means of Needleless Electrospinning

Lignin, a cheap renewable natural polymer, can be used as a precursor for the production of carbon fibres, its conversion into which is significantly faster than that of polyacrylonitrile. Lignin can be fractionated in various solvents via dissolution to decrease its polydispersity. Fractions with a higher molecular weight distribution can then be used in solvent-based spinning technologies such as electrospinning. We selected several solvent systems according to the Hansen solubility theory and subsequently tested them for solubility and electro-spinability. The selected solvent systems were then successfully tested for use in the needleless electrospinning process due to their potential for mass production. The solutions used in the electrospinning process needed high concentrations of lignin, which led to a high degree of viscosity. Therefore, we measured the relaxation times and viskosity for selected solutions, a factor that plays a pivotal role in terms of the production of smooth fibres. Finally, these solutions were tested for electrospinning using alternating current. This technology brings a new possibility in mass production of lignin fibres due to its high productivity and ease of use. Such materials can be used in a number of applications such as batteries, supercapacitors or for the production of composite materials. They provide a cheap and renewable natural polymer source which can easily be transformed into a carbon nanofibrous layer.

Synthesis and Characterization of Hydroxyethyl Starch from Chips Wastes Under Microwave Irradiation

This article focuses on the synthesis of hydroxyethyl potato starch (HEPS) for liquid hand soap by evaluating waste potato starch (WPS), a byproduct in potato chips production. It is a cheap, biodegradable, non-toxic and renewable natural polymer, available in great quantities on a global level. In a factory producing potato chips, WPS, which remained in the aqueous medium during peeling, slicing, and washing the potatoes, was purified at the desired temperature with H2O2 and NaOH. HEPSs with the molar substitution (MS) in the range from 0.298 to 0.670, were synthesized under microwave irradiation in isopropanol (IPA) and NaOH solution by adding ethylene oxide (EO) to WPS. The selected reaction parameters were the concentration of NaOH, the proportion of EO, and reaction time in an attempt to understand their effects on the reaction. Considering all the studied conditions, the highest viscosity was reached at 250 cP for the highest MS in the sample of HEPS-4 when 15 g EO was used in 20 mL solution of 40% NaOH at 40 °C for 40 min under microwave irradiation. The structure of synthesized HEPSs has been characterized by FT-IR, XRD, 1H(13C)-NMR spectroscopic methods, and the degree of molar substitution was calculated from 1H-NMR spectra. In addition, thermal stability and surface morphology of characterized HEPSs were studied by DTG-TG and SEM, respectively. The thickener effect of hydroxyethyl starch in liquid hand soap was investigated. In this way, it has been understood that in the production of liquid hand soaps, hydroxyethyl potato starch can be used instead of coco diethanolamide (CDEA).

Enhancement of Versatile Extracellular Cellulolytic and Hemicellulolytic Enzyme Productions by Lactobacillus plantarum RI 11 Isolated from Malaysian Food Using Renewable Natural Polymers.

Lactobacillus plantarum RI 11 was reported recently to be a potential lignocellulosic biomass degrader since it has the capability of producing versatile extracellular cellulolytic and hemicellulolytic enzymes. Thus, this study was conducted to evaluate further the effects of various renewable natural polymers on the growth and production of extracellular cellulolytic and hemicellulolytic enzymes by this novel isolate. Basal medium supplemented with molasses and yeast extract produced the highest cell biomass (log 10.51 CFU/mL) and extracellular endoglucanase (11.70 µg/min/mg), exoglucanase (9.99 µg/min/mg), β-glucosidase (10.43 nmol/min/mg), and mannanase (8.03 µg/min/mg), respectively. Subsequently, a statistical optimization approach was employed for the enhancement of cell biomass, and cellulolytic and hemicellulolytic enzyme productions. Basal medium that supplemented with glucose, molasses and soybean pulp (F5 medium) or with rice straw, yeast extract and soybean pulp (F6 medium) produced the highest cell population of log 11.76 CFU/mL, respectively. However, formulated F12 medium supplemented with glucose, molasses and palm kernel cake enhanced extracellular endoglucanase (4 folds), exoglucanase (2.6 folds) and mannanase (2.6 folds) specific activities significantly, indicating that the F12 medium could induce the highest production of extracellular cellulolytic and hemicellulolytic enzymes concomitantly. In conclusion, L. plantarum RI 11 is a promising and versatile bio-transformation agent for lignocellulolytic biomass.

Coating phosphorus fertilizer with renewable natural polymers

Low phosphorus use efficiency (PUE) is one of the major reasons of poor production worldwide. Among the various approaches used to enhance PUE, polymer coated fertilizers are relatively a new concept. Its main advantages are that they dissolve slowly and release nutrients to plants gradually during the growing season. Keeping this in view, a study was performed in the laboratory to evaluate polymers coated monoammonium phosphate (MAP) to enhance PUE. Commercial MAP and MAP coated with biodegradable polymers with Krafit black liquor (BL) and cellulose acetate (CA) in the concentration (0.5, 1.0, 2.0 wt % coating). The effectiveness of these coatings was assessed by the electrical conductivity (EC) and phosphorus release (PR) in a kinetic experiment. The kinetic study was carried out in a controlled environment (± 25 °C), following the release pattern of P from 1.5 g of fertilizer in 50 mL of H2O, with and without the coatings. The objective of this work was to study different lignin-based coatings and the phosphorus release behavior of the resulting fertilizer. EC showed to be an effective method of indirect analysis of P releasing from coated MAP. The BL coating presented better results than the CA in terms of controlling the release of P, and the higher the coating ratio (1.0 and 2.0 %) the slower the release of P.

Production and characterization of PVA/alginate composite filament with cellulose from oil palm empty fruit bunches

Cellulose is a renewable natural polymer that has abundant availability in the Earth and found in oil palm empty fruit bunches (OPEFBs). OPEFBs is one of the biomass produced from the crude palm oil industry. Cellulose fibers were isolated by alkaline treatment and bleaching. Cellulose from OPEFBs can be utilized as filament material by mixing it with polyvinyl alcohol (PVA) and alginate. In this work, OPEFBs cellulose/PVA/alginate composite filaments were produced by the wet spinning method with 9 wt% CaCl2 as a coagulant solvent and characterized. The effect of composite formulation on mechanical, morphological, crystallinity, and thermal properties of filaments was observed. The observed result shows that the increasing cellulose concentration had excellent thermal stability, higher crystallinity, with the morphology of the surface became rougher than 0% cellulose filament. The addition of cellulose had a significant effect on the mechanical properties of filaments, increasing the tensile strength and decreasing the elongation of filaments.

Lignin modified by deep eutectic solvents as green, reusable, and bio-based catalysts for efficient chemical fixation of CO2

Lignin is a biodegradable, abundant and renewable natural polymer on earth. In this study, deep eutectic solvents (DESs)-modified lignin heterogeneous catalysts were prepared for the first time via a facile acid-base interaction between choline chloride (ChCl) and p-aminobenzoic acid (PABA) or its derivatives, which were used to efficiently catalyze the cycloaddition of CO2 and terminal epoxides under green and mild conditions. Among them, lignin-ChCl-PABA was found to exhibit the highest catalytic activity for the cycloaddition of epoxides in the presence of 1.0 MPa of CO2 while retaining high selectivity, which far outperformed those achieved on the homogeneous EDSs catalytic system. A series of cyclic carbonates could be obtained in high yields (90–99%), and lignin-ChCl-PABA was stable and reusable for the cycloaddition reaction (84% yield after 5 recycles). The attaching DES of ChCl/PABA onto the functional lignin increased the catalytic activity and also made the catalyst easier to recycle from the reaction mixture. The OH and NH2 groups on the surface of lignin-ChCl-PABA played a very important role in the acceleration of the cycloaddition reaction under solvent free conditions.

Novel porous oil-water separation material with super-hydrophobicity and super-oleophilicity prepared from beeswax, lignin, and cotton

The traditional fluorinated porous material with super-hydrophobicity and super-oleophilicity is an effective strategy for oil-water separation. However, in recent years, fluorinated materials have been classified as “Emerging Environmental Pollutants” by U. S. Environmental Protection Agency because of difficult degradation and bio-accumulation. It is unacceptable to introduce new pollutants while solving environmental disasters. Therefore, it is great requirement to explore a low-cost, environmentally friendly, and renewable technique for the fabrication of novel porous materials with super-hydrophobicity and super-oleophilicity to separate oil-water mixtures. In this work, renewable beeswax, lignin, and cotton have been chosen to prepare the biomass-based porous materials with super-hydrophobicity and super-oleophilicity for oil-water separation. The mixture of beeswax and lignin is modified on the surface of cotton to obtain the biomass-based porous materials with super-hydrophobicity and super-oleophilicity. The beeswax and lignin provide low surface energy and micro/nanoscale structures, respectively. The introduction of lignin effectively improves the thermal stability of the porous materials. The apparent contact angle still remains to be above 150° after a long-time heating. The porous materials effectively separate oil-water mixtures and have good absorption effect for heavy oil (density greater than water). Moreover, the porous materials are easily recyclable after reactivation. This strategy of preparing oil-water separation materials from renewable natural polymers not only helps to clean the environment, but also helps to recover valuable oil.

Nanocellulose-based Hydrogels for Biomedical Applications

Hydrogels are three-dimensional polymer networks capable of absorbing and holding a large amount of water. They have a wide range of biomedical applications including drug carriers, biosensors, tissue scaffolds and wound dressings owning to their innate resemblance to the living tissue. Recently biodegradable and renewable natural polymers, especially nanocellulose, have gained immense attention in the development of hydrogels for biomedical applications. This review provides a brief analysis of the various nanocellulosic materials used in the fabrication of hydrogels for various biomedical applications. Recent developments in high performance hydrogels based on nanocellulose, including self-healing, highly tough and/or stretchable and 3D printable hydrogels will also be covered in this review.

Cellulose Aerogels: Synthesis, Applications, and Prospects.

Due to its excellent performance, aerogel is considered to be an especially promising new material. Cellulose is a renewable and biodegradable natural polymer. Aerogel prepared using cellulose has the renewability, biocompatibility, and biodegradability of cellulose, while also having other advantages, such as low density, high porosity, and a large specific surface area. Thus, it can be applied for many purposes in the areas of adsorption and oil/water separation, thermal insulation, and biomedical applications, as well as many other fields. There are three types of cellulose aerogels: natural cellulose aerogels (nanocellulose aerogels and bacterial cellulose aerogels), regenerated cellulose aerogels, and aerogels made from cellulose derivatives. In this paper, more than 200 articles were reviewed to summarize the properties of these three types of cellulose aerogels, as well as the technologies used in their preparation, such as the sol–gel process and gel drying. In addition, the applications of different types of cellulose aerogels were also introduced.

High Ionic Conductivity, Mechanically Strong Ion Gels for All Solid State Supercapacitor Applications

Electrochemical double layer capacitors (EDLCs) have many advantages compared with batteries and fuel cells because of their cycle life and power density. The limitation for use of EDLCs in major applications such as electric vehicles and grid storage is their low energy density. One way to increase energy density of EDLCs is to increase the stability window of the electrolytes. Room temperature ionic liquids (RTILs), which are salts with low temperature melting points, have been investigated as electrolytes in electrochemical devices, since they have useful (i.e. large) electrochemical stability windows (> 4V), are nonvolatile (and as a result often non-flammable), and are therefore safer than conventional aprotic liquid electrolytes. The utility of a EDLC device increases if it is developed in the form of a thin, solid film since it avoids leakage problems and the use of casings that decrease energy density. One method to make these films is to form iongels, which are ion conducting liquids (such as RTILs) immobilized in a polymer matrix, forming a solid polymer electrolyte (SPE). Since RTILs are typically more viscous (30-200 cP vs ~ 1 cP) than conventional aprotic or aqueous solvents, and therefore less conductive (0.1 to 18 mS/cm), it becomes important to decrease the amount of polymer required to solidify the iongel. Immobilization of the RTIL can be achieved using gelators that participate in chemical crosslinking reactions or form physical crosslinks. Gelators further increase viscosity and decrease conductivity of RTIL, which decreases the conductivity and increases the equivalent series resistance (ESR) in EDLCs. Therefore, the requirements of iongels in EDLC applications are minimum wt% of gelator, low ESR, good chemical and electrochemical stability with the electrodes and good mechanical properties (to prevent shorting the electrodes under pressure). In our previous work, we have shown that renewable, environmentally friendly, abundant and inexpensive natural polymers such as methyl cellulose (MC), (as gel former), when combined with an ionic liquid, form tough, temperature stable ion gels1,2. In this work, we developed an iongel with 5% MC as gelator and 95% 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as the ionic liquid, for all solid state supercapacitor applications. The formed iongels have temperature dependent ionic conductivities only 1.5 to 1.8 times lower than the pure RTILs, high thermal stability up to 350oC, solid like behavior over a frequency range of 1 Hz to 100 Hz, at 25oC and a storage modulus of 5 MPa at 25oC, as shown in Figure 1. The iongel was incorporated into 3-D porous interconnected network of free standing porous carbon nanofibers prepared by an electrospinning technique and further chemically activated, yielding a high surface area of 2282 m2/g as shown in Figure 2.A specific capacitance of 137 F g-1 at 20 mV s-1was obtained for the cell corresponding to a specific energy density of 56 Wh/kg (based on total electrode mass) for a 3.5V window. At the same scan rate 163 F/g was obtained for liquid based cell. In this talk, the performance, stability and postmortem studies of the supercapacitor will be discussed. In summary we have developed novel iongels that have been solidified with only 5% methylcellulose as gelator, with excellent ionic conductivities (1.5 to 1.8 times lower than the RTIL) and mechanical properties (5MPa at 25oC) as electrolytes for all solid state supercapacitor applications. Figure 1: Comparison of liquid IL and gel IL; Log σ vs 1000/T (a) 2ndheating DSC thermograms (b) TGA thermograms (c) and storage and loss moduli as a function of frequency for gel IL at 25 °C (d). Figure 2 top left. SEM micrographs: a-CNFs and right; a-CNFs filled with iongel; bottom left. EIS of liquid- and solid-based cells and right; corresponding CVs Figure 1

Synthesis and Characterization of Water-Soluble Dendronized Chitosan Using Newkome-Type Dendrons

With increasing emphasis on environmental care and use of renewable resources, simple and effective dendronization processes were performed to obtain chitosan derivatives. We present different alternatives for the modification of chitosan: dendronization with a biocompatible dendron; a quaternization process with an ammonium salt, which confers a permanent positive charge to the polymer; and a combination of methodologies allowing amphiphilic polymers. This process confers unique multivalent properties to the native chitosan, and further modifications reach multivalent water-soluble polymers. Hence, the most important highlight of this work is the use of renewable natural polymers and the different methodologies applied to nontoxic solvents with low temperatures. The process described in this paper represents a sustainable alternative for obtaining a functionalized material with properties suitable for application in different areas, such as biomedicine or environmental remediation.

Application of natural and semi-synthetic polymers for the delivery of sensitive drugs

This review summarises recent developments in the application of natural and semi-synthetic polymers for the delivery of sensitive drugs. Peptides, proteins and nucleic acids are drugs of increasing relevance potentially offering treatment options in indications with high unmet medical need. However, these drugs are characterised by high molecular weight, high sensitivity to enzymatic degradation, unfavourable pharmacokinetics and often require targetting to specific cell types or cellular compartments. To successfully transform these drug molecules into efficacious therapies, advanced drug delivery systems must be developed that protect the drug, control drug release to improve pharmacokinetics and allow efficient targetting. Synthetic, semi-synthetic or natural polymers or inorganic materials are frequently used for the development of drug delivery systems. Considering factors such as biocompatibility, biodegradability, solvent-free processing and availability from renewable resources, natural and semi-synthetic polymers are often advantageous compared to synthetic alternatives. On the other hand, material heterogeneity and purity of natural materials are concerns that need to be addressed. In this review, authors focus on frequently used biopolymers such as polysaccharides like chitosan and hyaluronan and proteins like silk fibroin (SF) and collagen and their semi-synthetic derivatives. Special emphasis will be put on material properties of such polymers rendering them suitable for drug delivery purposes and allow tight control to assure product quality and proper release characteristics. Natural polymers are frequently synthetically modified to alter or improve their characteristics. Such semi-synthetic derivatives and their advantages and disadvantages are critically discussed. Furthermore, the biocompatibility of natural materials and their derivatives is discussed.