Starch-based Polymers Research Articles

Preparation, characterization and sorption properties of crosslinked starch-based exchangers

Starch-based polymers were prepared by a crosslinking reaction of starch-enriched flour using epichlorohydrin as a crosslinking agent in the presence of NH 4OH. Yield, mobility and structural properties of crosslinked starch materials with various compositions were investigated by elemental analysis, electrophoretic mobility and NMR spectroscopy. In particular cross-polarization magic angle spinning (CPMAS) and magic angle spinning (MAS) techniques were used, as well as relaxation time measurements. The homogeneity and the molecular mobility of these polymers were analyzed in terms of cross-relaxation time between protons and carbons ( T CH), 1H spin–lattice relaxation in the rotating frame ( T 1 ρ 1H) and 1H longitudinal spin–lattice relaxation time ( T 1 1H). A correlation was found between the structure, mobility and degree of crosslinking of these sorbents. This correlation was discussed. Finally, these crosslinked starch-based materials, containing tertiary amine groups have been used for the recovery of various dyes from aqueous solutions. Sorption studies are presented, focusing on the polymer and dye structures. The results showed that these polymers exhibited interesting sorption properties and that the sorption mechanism was correlated to the structure of the polymer.

Cytokine secretion from mononuclear cells cultured in vitro with starch‐based polymers and poly‐L‐lactide

The cytokine network is one of the major controlling systems of the inflammatory process, driving the magnitude and duration of the host response against invading microorganisms, foreign materials, or altered internal stimuli. Pro- and antiinflammatory cytokines were quantified after in vitro culture of a mixed population of monocytes/macrophages and lymphocytes with biodegradable polymers. Different blends of starch-based polymers and their composites filled with hydroxyapatite were studied and compared with poly-L-lactide. Interleukin (IL)-1beta, IL-6, and tumour necrosis factor-alpha were investigated as the markers of immunological reactivity because they are known to act at the early stages of injury/invasion. Interferon-gamma, recognized as a proinflammatory cytokine, although not present during early responses was also investigated. Contrarily, IL-4 derived from T lymphocytes, was investigated because it is an immunoregulator that counteracts some aspects of inflammation. T lymphocyte activation was also determined by quantifying IL-2. The results support the hypothesis that different biodegradable polymers can affect mononuclear cell activation and the production of several cytokines associated with the inflammatory process. No IL-2 or interferon-gamma was found in the culture supernatants after 3, 7, and 14 days in the presence of any of the materials. IL-6 was detected in the highest amounts, for all the conditions, followed by tumour necrosis factor-alpha. IL-1beta was produced in very low amounts, being undetectable with some of the starch-based materials. IL-4 was the only cytokine that did not demonstrate any significant difference within this group of materials. Starch-based polymers and composites induced lower production of proinflammatory cytokines in comparison to poly-L-lactide.

In vitro assessment of the enzymatic degradation of several starch based biomaterials.

The susceptibility of starch-based biomaterials to enzymatic degradation by amylolytic enzymes (glucoamylase and alpha-amylase) was investigated by means of incubating the materials with a buffer solution, containing enzymes at different concentrations and combinations, at 37 degrees C for 6 weeks. Two polymeric blends of corn starch with poly(ethylene-vinyl alcohol) copolymer and poly(epsilon-caprolactone), designated by SEVA-C and SPCL, respectively, were studied. The material degradation was characterized by gravimetry measurements, tensile mechanical testing, scanning electron microscopy (SEM), and Fourrier transform infrared-attenuated total reflectance (FTIR-ATR). The degradation liquors were analyzed for determination of reducing sugars, as a result of enzyme activity, and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was used to identify the degradation products. All of the analysis performed showed that starch polymeric blends are susceptible to enzymatic degradation, as detected by increased weight loss and reducing sugars in solution. alpha-Amylase caused significant changes on the overall mechanical properties of the materials, with a decrease of about 65% and 58% being observed in the moduli for SEVA-C and SPCL, respectively, when compared with the control (samples incubated in buffer only). SEM analysis detected the presence of fractures and pores at the material's surface as a result of starch degradation by amylolytic enzymes. FTIR spectra confirmed a decrease on the band corresponding to glycosidic linkage (-C-O-C-) of starch after incubation of the materials with alpha-amylase. In contrast, the incubation of the polymers in buffer only, did not cause significant changes on the material's properties and morphology. Comparing the two materials, SEVA-C exhibited a higher degradability, which is related to the physicochemical structure of the materials and also to the fact that the starch concentration is higher in SEVA-C. The identification of the degradation products by HPAEC-PAD revealed that glucose was the major product of the enzymatic degradation of starch-based polymers. alpha-Amylase, as expected, is the key enzyme involved in the starch degradation, contributing to major changes on the physicochemical properties of the materials. Nevertheless, it was also found that starch-based polymers can also be degraded by other amylolytic enzymes but in a smaller extent.

Evaluation of the potential of starch-based biodegradable polymers in the activation of human inflammatory cells.

The inflammatory response resulting from the implantation of a medical device may compromise its performance and efficiency leading, in certain cases, to the failure of the implant. Thus, the assessment of the behavior of inflammatory cells in vitro, constitutes a key feature in the evaluation of the adverse potential, or not, of new promising biomaterials. The objectives of this study were to determine whether starch-based polymers and composites activated human neutrophils. Blends of starch with ethylene-vinyl alcohol, with cellulose acetate and polycaprolactone, as well as composites based on all these materials filled with hydroxyapatite have been studied. A lysozyme assay was adapted to examine enzyme secretion from human neutrophils incubated with different starch-based materials. Changes in the free radical and degranulation activity of the neutrophil were also determined by measuring the luminescent response of Pholasin, a photoprotein that emits light after excitation by reactive oxygen species. The amount of lysozyme secreted by neutrophils incubated with the polymers did not exhibit significant differences between the tested materials. Results were in all cases similar to those obtained for the control (polypropylene) except for one of the starch blends (corn starch with polycaprolactone reinforced with 30% (w/w) of HA). The chemiluminescence experiments showed that polymers reduce the signal produced by activated neutrophils. Furthermore, for some polymers it was demonstrated that the phenomenon was due to an effect of the surface of the materials in cell adhesion or a simultaneous competition for the photoprotein in solution, which results in the decrease of the intensity of light emitted and detected.

APPROXIMATE MODEL OF THERMAL RESIDUAL STRESS IN AN INJECTION MOLDED PART

A description and model of the thermally induced residual stress that forms in a ''platelike'' injected molded polymer part is outlined. A linear heat balance integral (LHBI) temperature profile approximation and the concept of a virtual adjunct mold (VAM) is used to arrive at an approximate algebraic model that, upon providing material properties and processing conditions, gives an immediate evaluation of the residual stress through the plate thickness. Results obtained with this model are in very close agreement with a full numerical solution and agree closely with experimental measurements made on a range of starch-based biodegradable polymer samples.

Scaffold development using 3D printing with a starch-based polymer

Rapid prototyping (RP) techniques have been utilised by tissue engineers to produce three-dimensional (3D) porous scaffolds. RP technologies allow the design and fabrication of complex scaffold geometries with a fully interconnected pore network. Three-dimensional printing (3DP) technique was used to fabricate scaffolds with a novel micro- and macro-architecture. In this study, a unique blend of starch-based polymer powders (cornstarch, dextran and gelatin) was developed for the 3DP process. Cylindrical scaffolds of five different designs were fabricated and post-processed to enhance the mechanical and chemical properties. The scaffold properties were characterised by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), porosity analysis and compression tests.

Alternative tissue engineering scaffolds based on starch: processing methodologies, morphology, degradation and mechanical properties

An ideal tissue engineering scaffold must be designed from a polymer with an adequate degradation rate. The processing technique must allow for the preparation of 3-D scaffolds with controlled porosity and adequate pore sizes, as well as tissue matching mechanical properties and an appropriate biological response. This communication revises recent work that has been developed in our laboratories with the aim of producing 3-D polymeric structures (from starch-based blends) with adequate properties to be used as scaffolds for bone tissue engineering applications. Several processing methodologies were originally developed and optimised. Some of these methodologies were based on conventional melt-based processing routes, such as extrusion using blowing agents (BA) and compression moulding (combined with particulate leaching). Other developed technologies included solvent casting and particle leaching and an innovative in situ polymerization method. By means of using the described methodologies, it is possible to tailor the properties of the different scaffolds, namely their degradation, morphology and mechanical properties, for several applications in tissue engineering. Furthermore, the processing methodologies (including the blowing agents used in the melt-based technologies) described above do not affect the biocompatible behaviour of starch-based polymers. Therefore, scaffolds obtained from these materials by means of using one of the described methodologies may constitute an important alternative to the materials currently used in tissue engineering.

The biocompatibility of novel starch-based polymers and composites: in vitro studies

Studies with biodegradable starch-based polymers have recently demonstrated that these materials have a range of properties, which make them suitable for use in several biomedical applications, ranging from bone plates and screws to drug delivery carriers and tissue engineering scaffolds. The aim of this study was to screen the cytotoxicity and evaluate starch-based polymers and composites as potential biomaterials. The biocompatibility of two different blends of corn-starch, starch/ethylene vinyl alcohol (SEVA-C) and starch/cellulose acetate (SCA) and their respective composites with hydroxyapatite (HA) was assessed by cytotoxicity and cell adhesion tests. The MTT assay was performed with the extracts of the materials in order to evaluate the short-term effect of the degradation products. The cell morphology of L929 mouse fibroblast cell line was also analysed after direct contact with polymers and composites for different time periods and the number of cells adhered to the surface of the polymers was determined by quantification of the cytosolic lactate dehydrogenase (LDH) activity. Both types of starch-based polymers exhibit a cytocompatibility that might allow for their use as biomaterials. SEVA-C blends were found to be the less cytotoxic for the tested cell line, although cells adhere better to SCA surface. The cytotoxicity test also revealed that SCA and SEVA-C composites have a similar response to the one obtained for SCA polymer. Scanning electron microscopy (SEM) analysis showed that cells were much more spread on the SCA polymer and LDH measurements showed a higher number of cells on this surface.

Developing Biodegradable Mulch Films from Starch-Based Polymers

This paper examines the development of starch-based plastics for use as biodegradable mulch film. A variety of starch-based polymers are blended with high performance biodegradable polyester polymers in order to determine the applicability of films to be processed on a film blowing line and to perform well in mulch film field trials. The process of material formulation, film blowing processing and scale-up and performance properties are highlighted for a successful material. Insights into future developments of starch-derived biodegradable polymers are given.

Cytocompatibility and response of osteoblastic-like cells to starch-based polymers: effect of several additives and processing conditions

This work reports on the biocompatibility evaluation of new biodegradable starch-based polymers that are under consideration for use in orthopaedic temporary applications and as tissue engineering scaffolds. It has been shown in previous works that by using these polymers it is both possible to produce polymer/hydroxyapatite (HA) composites (with or without the use of coupling agents) with mechanical properties matching those of the human bone, and to obtain 3D structures generated by solid blowing agents, that are suitable for tissue engineering applications. This study was focused on establishing the influence of several additives (ceramic fillers, blowing agents and coupling agents) and processing methods/conditions on the biocompatibility of the materials described above. The cytotoxicity of the materials was evaluated using cell culture methods, according to ISO/EN 109935 guidelines. A cell suspension of human osteosarcoma cells (HOS) was also seeded on a blend of corn starch with ethylene vinyl alcohol (SEVA-C) and on SEVA-C/HA composites, in order to have a preliminary indication on cell adhesion and proliferation on the materials surface. In general, the obtained results show that all the different materials based on SEVA-C, (which are being investigated for use in several biomedical applications), as well as all the additives (including the novel coupling agents) and different processing methods required to obtain the different properties/products, can be used without inducing a cytotoxic behaviour to the developed biomaterials.

Starch-Based Polymers in Extrusion Coating

The starch-based polymers exhibited shear thinning and elastic nature in rheological characterizations. Thin coatings with narrow neck-in could be produced at fairly high extrusion coating line speeds. Adhesion between the starch-based polymers and paperboard was typically weak. Water vapor barrier of starches was very poor. Soft starch grades had a good pinhole resistance and a good heat sealing performance. Brittle nature of starch caused cracking as the coated paperboards were creased.

Injection molding of a starch/EVOH blend aimed as an alternative biomaterial for temporary applications

Biodegradable polymers show great potential to be used as materials for temporary implants and bone replacement applications in orthopedics. However, its use in high load-bearing applications will depend on the successful development of biode- gradable implants with a mechanical performance matching that of human bone. This article describes the optimization of the injection molding process of an alternative biodegradable starch-based polymer aimed at biomedical applications. A blend of starch with a copolymer of ethylene-vinyl alcohol (SEVA-C) was studied. Both conventional injection molding and shear controlled orientation (SCORIM) were optimized with the support of design of experiments and analysis of variance techniques. The mechanical characterization was performed by tensile testing. The structure developed within the moldings was assessed by wide-angle X-ray diffraction and differential scanning calo- rimetry. Increases up to 30% in the tangent modulus and 20% in the ultimate tensile strength compared with conventional molding were achieved with the application of SCORIM. The holding pressure and the frequency of the shear applied have the strongest influence on the morphology development and consequently on the mechan- ical performance. The solidification of SEVA-C at high cavity pressures enhances stiffness for long durations of the shearing stage in SCORIM. However, the effect of viscous heating of SEVA-C is important and ought to be considered. A decrease of the material phase miscibility in SEVA-C occurs as result of the shear fields imposed. The microstructure evaluation suggests that the mechanical properties enhancement in SCORIM molded SEVA-C is attributable to preferred orientation developed during processing. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1303-1315, 2000

Surface modification tailors the characteristics of biomimetic coatings nucleated on starch-based polymers.

This work describes the influence of surface pretreatments over the nucleation and growth of an apatite layer, formed by a biomimetic process, on which a bioactive glass is used as a precursor of the calcium-phosphate (Ca-P) formation on the materials surface. SEVA-C, a corn starch-based biodegradable blend, was used as substrate. The surfaces were pretreated during various periods by: (i) physical methods, namely ultraviolet radiation (u.v.), and over exposure to ethylene oxide sterilization (EtO); and (ii) chemical methods, namely potassium hydroxide (KOH) and acetic anhydride (CH3CO)2 etchings. The surface modifications, performed before the production of the biomimetic coatings, resulted in a faster formation of Ca-P nuclei during the first stages of SBF immersion, particularly in the case of the KOH etching. In this case, it was possible to observe a decrease in the average surface roughness, as measured by laser profilometry, and an increase of the hydrophilicity of the material, which was evident from a clear increment in the water-uptake ability and quantified by contact angle measurements. With this treatment it was possible not only to reduce the induction period for the formation of a well defined and dense apatite-like layer, as observed by scanning electron microscopy (SEM), but also to improve the adhesion of the Ca-P layer to the substrate, as confirmed by the adhesion strength tests. For all the studied pre-treatments, the composition of the films, analyzed by energy dispersive spectroscopy (EDS) and identified by thin-film X-ray diffraction (TF-XRD), seems to be very similar to that of human bone apatites.

Structure development and control of injection‐molded hydroxylapatite‐reinforced starch/EVOH composites

This article reports on the development of novel composites of starch-based polymers reinforced with hydroxylapatite (HA). Two different grades of blends of starch and ethylene vinyl alcohol copolymers were reinforced with up to 30% (wt) of sintered and nonsintered HA. The initial compounding stage was carried out either in a rotating drum or by twin-screw extrusion (TSE). Compounds were injection molded using both conventional molding and a shear-controlled orientation in injection molding (Scorim) technique. It was possible to obtain composites with very good mechanical properties, approaching those of cortical bone. The best results were achieved for 30% sintered HA composites processed by TSE and Scorim, due to the in situ formation of HA fibers, and the development of molecular orientation and more compact microstructures in the moldings. This was confirmed by SEM analysis of the fracture surfaces, x-ray diffraction, and Raman spectroscopy. The biodegradability of the composites was also assessed and was found to be faster than that of the matrix. © 1997 John Wiley & Sons, Inc. Adv Polym Techn 16: 263–277, 1997

Mechanical Behavior of Injection-molded Starch-based Polymers

This work evaluates the mechanical performance of injection-molded starch-based copolymers, 60/40 (mol/mol) starch/poly(ethylene vinyl alcohol), and the possibility of improving material properties through deliberately induced anisotropy during processing. Different types of samples were produced by conventional and shear-controlled injection molding (Scorim) and tested under tensile and impact loading. The behavior of three distinct grades is discussed in terms of the respective fracture morphology (evaluated by scanning electron microscopy). A comparison is made between the behavior of conventional and Scorim samples. The results show that the mechanical properties of the materials used were significantly improved by the employment of the Scorim process. The stiffness values of the conventional moldings were doubled, without reducing the ductility of the polymer. The impact data showed a material sensitivity, and consequent loss of properties, to the localized shear imposed to the melt during processing. This situation is attributed to very narrow mold gates (in the case of pingated systems) and leads to much reduced impact performance.

Solid-phase extraction and subsequent gas chromatography-mass spectrometry analysis for identification of complex mixtures of degradation products in starch-based polymers

A solid-phase extraction (SPE) method, using silica bonded with aminopropyl groups, was developed to separate highly complex mixtures of degradation products into three fractions. The SPE allowed the subsequent GC-MS identification of nearly 140 thermo-oxidation products of starch-based polymer blends, consisting of 70% starch and either ethylene maleic anhydride (EMA) or ethylene vinyl acetate maleic anhydride (EVAMA). It was thus possible to identify several homologous series of degradation products such as n-alkanes and 1-alkenes, 1-alcohols, 2-ketones, aldehydes, carboxylic acids and dicarboxylic acids. The homologous series of dicarboxylic acids ranged from butanedioic acid (C 4) to nonadecanedionic acid (C 19) and was for the first time identified in thermo-oxidized starch-based blends with polyethylene (PE). Hydrocarbons of even carbon number were formed to a larger extent than those with an uneven carbon number in the starch-EMA blend and the ratio n-alkane to 1-alkene increased (i.e. relatively more alkane is formed) under more severe thermo-oxidation conditions. The same phenomenon was not observed in the starch-EVAMA blend. Formic acid, acetic acid and γ-butyrolactone were the most predominant degradation products in both materials. Typical starch degradation products were difficult to resolve but we identified 2-hexanone, formic acid and acetic acid, which also have been reported previously to be degradation products of starch. The molecular mass measurements showed that the starch-EVAMA blend starts to degrade earlier than the starch-EMA, but on the other hand, at a lower rate. A good correlation between the decrease in M n and the amount of degradation products formed was observed. A higher degree of cross-linking occurred in the starch-EVAMA blend in comparison with the starch-EMA blend and, in parallel, qualitatively and quantitatively more degradation products are formed in the starch-EMA blend.

A carbon-13 method for evaluating degradation of starch-based polymers

A new method for evaluating biodegradability of starch-based and certain other polymer blends uses the pre- and postexposure stable carbon isotope composition of material coupled with weight loss data to determine which components have degraded. The naturally occurring stable isotope of carbon.13C, is enriched in corn starch (δ13C, approx. −11‰) compared to petroleum-derived synthetic polymers (δ13C, approx. −32‰). Results on starch-synthetic polymer blends indicate that the δ13C signatures of these blends are near-linear mixtures of their component δ13C. Values of a δ13C for starch-synthetic polymer blends exposed to biologically active laboratory soil and artificial seawater conditions are depleted in13C compared to unexposed samples, suggesting loss of the starch component. Combined with weight loss data for the exposed samples, the δ13C values are statistically consistent with models requiring loss of the soluble component glycerin, followed by loss of starch, then petrochemical polymer, or simultaneous loss of starch and petrochemical polymer. Replicate δ13C analyses of starch-synthetic polymer blends increase the statistical power of this relatively inexpensive, accessible technique to discriminate between degrading components.

Liquid-Mix Synthesis of Oxide Powders and Thin Films Using A Starch-Based Polymer

ABSTRACTA commercially available water-soluble starch derivative was used as the sole organic precursor in the Liquid-Mix synthesis of mixed-cation oxide powders and thin films. The acidified polymer (by nitric acid) was able to complex metal ions through the carboxylate ligands. Loosely agglomerated fine powders as well as dense thin films of complex oxides have been prepared using the same type of polymer. Oxide powders of Cr-doped lanthanum aluminate and yttrium aluminum garnet both crystallized in a single step, without forming any intermediate or second phases, when the amorphous resin intermediates were calcined at 650°C and 750°C for 2 hours, respectively. It was demonstrated that nitric acid could effectively reduce the viscosity of the polymer-nitrate solution to make it suitable for spin coating process. Dense thin films of Y(8 mol%)-doped ZrO2 were formed on Si and A12O3 substrates by spin coating the polymeric solution and heating at temperatures below 1000°C.

Microstructure and melt flow behavior of a starch-based polymer

Results on some physical properties and on melt processing of a starch-based polymer under steady-state shearing are presented. A peculiar microstructure involving a strong pseudoplastic behavior at high shear rates as well as yield stress at lower ones is discussed. A model is proposed to explain the characteristic viscoelastic behavior of this material based on hydrophylic and hydrophobic interactions between starch and vinyl-alcohol copolymers.

Hydrophilic Polymers—Their Response to Soil Amendments and Effect on Properties of a Soilless Potting Mix

The levels of hydration of several hydrophilic polymers (hydrogels) varied greatly. Starch-based polymers had the fastest rate of hydration (<2 hours), followed by a propenoate-propenamide copolymer. Polyacrylamide materials required 4 to 8 hours to become fully hydrated. Maximum water retention in distilled water varied from 400 to 57 g of water per gram of dry material. All hydrogels retained less water in the presence of metal ions or fertilizers in the soaking solution, with substances releasing Fe+2 being the most detrimental. After exposure to fertilizers and ions, the water-holding capacity of a polyacrylamide with a high degree of cross linkage, but not that of hydrogels of the other structures, was fully recovered by subsequently soaking in distilled water. Pots amended with a polyacrylamide polymer but without Micromax (a micronutrient source) reached maximum water retention after six irrigations, while those with Micromax required 10 irrigations to reach peak water retention. The amounts of water being held in pots decreased after repeated fertilization. Medium volume increased with increasing levels of the polyacrylamide Supersorb C (0, 2, 4, or 6 g/pot). Micromax incorporated in medium amended with Supersorb C caused a depression in volume. Medium bulk density, total water retention, and water retention per unit volume of medium were increased by the incorporation of the hydrogel, regardless of the presence of Micromax. Noncapillary porosity measured at container capacity in medium amended with Micromax progressively decreased as the amount of hydrogel increased, but remained unchanged in medium without Micromax. Repeated drying and dehydration of the medium resulted in reduced water retention and increased noncapillary pore space.