Pectin Aerogels Research Articles

Hydrophobic Modification of Pectin Aerogels via Chemical Vapor Deposition.

Pectin aerogels, with very low density (around 0.1 g cm-3) and high specific surface area (up to 600 m2 g-1), are excellent thermal insulation materials since their thermal conductivity is below that of air at ambient conditions (0.025 W m-1 K-1). However, due to their intrinsic hydrophilicity, pectin aerogels collapse when in contact with water vapor, losing superinsulating properties. In this work, first, pectin aerogels were made, and the influence of the different process parameters on the materials' structure and properties were studied. All neat pectin aerogels had a low density (0.04-0.11 g cm-1), high specific surface area (308-567 m2 g-1), and very low thermal conductivity (0.015-0.023 W m-1 K-1). Then, pectin aerogels were hydrophobized via the chemical vapor deposition of methyltrimethoxysilane using different reaction durations (2 to 24 h). The influence of hydrophobization on material properties, especially on thermal conductivity, was recorded by conditioning in a climate chamber (25 °C, 80% relative humidity). Hydrophobization resulted in the increase in thermal conductivity compared to that of neat pectin aerogels. MTMS deposition for 16 h was efficient for hydrophobizing pectin aerogels in moist environment (contact angle 115°) and stabilizing material properties with no fluctuation in thermal conductivity (0.030 W m-1 K-1) and density for the testing period of 8 months.

Fabrication and characterization of porous pectin-based aerogels for drug delivery

Aerogels are renowned for their exceptional characteristics such as high porosity and ultra-low density. Among these, pectin aerogels, offering biodegradability, low toxicity, and versatility, are prominent candidates for innovative biomedical materials. This study focused on synthesizing pectin-based aerogels as carriers for ibuprofen and diclofenac sodium. Hydrogels were formed by combining a low methoxy pectin with calcium chloride solution, followed by dehydration and drying using either supercritical carbon dioxide (scCO2) or freeze–drying. Comparative analysis showed scCO2-dried aerogels exhibited slightly less shrinkage (0.27 %) than freeze–dried counterparts. Both types showed high porosity and mesoporous characteristics. However, scCO2-dried aerogels demonstrated higher specific surface area, pore volume, and smaller pore diameter. FTIR spectra indicated no interaction between the drugs and pectin-based aerogels. The loading of ibuprofen in scCO2-dried, pectin-based aerogels at 90, 95, and 100 bar were 60.0 %, 59.9 %, and 52.1 %, respectively, and the solution loading of diclofenac sodium was 38.37 %. At 90, 95, and 100 bar, ibuprofen-loaded pectin-based aerogels were released at 90.0 %, 84.0 %, and 75.5 %, respectively. The release of diclofenac sodium-loaded, pectin-based aerogels was at 88.4 %. The Korsmeyer–Peppas model was fitted for both ibuprofen and diclofenac sodium, indicating the release is mainly driven by diffusion.

Pectin-based aerogel particles for drug delivery: Effect of pectin composition on aerogel structure and release properties

In this work, nanostructured pectin aerogels were prepared via a sol-gel process and subsequent drying under supercritical conditions. To this end, three commercially available citrus pectins and an in-house produced and enzymatically modified watermelon rind pectin (WRP) were compared. Then, the effect of pectin's structure and composition on the aerogel properties were analysed and its potential application as a delivery system was explored by impregnating them with vanillin. Results showed that the molecular weight, degree of esterification and branching degree of the pectin samples played a main role in the production of hydrogels and subsequent aerogels. The developed aerogel particles showed high specific surface areas (468–584 m2/g) and low bulk density (0.025–0.10 g/cm3). The shrinkage effect during aerogel formation was significantly affected by the pectin concentration and structure, while vanillin loading in aerogels and its release profile was also seen to be influenced by the affinity between pectin and vanillin. Furthermore, the results highlight the interest of WRP as a carrier of active compounds which might have potential application in food and biomedical areas, among others.

Hybrid Polylactic-Acid–Pectin Aerogels: Synthesis, Structural Properties, and Drug Release

Wound-dressing materials often include other materials stimulating wound healing. This research describes the first formulation of biodegradable hybrid aerogels composed of polylactic acid and pectin. The prepared hybrid material showed a highly porous structure with a surface area of 166 ± 22.6 m2·g-1. The addition of polylactic acid may have decreased the surface area of the pure pectin aerogel, but it improved the stability of the material in simulated body fluid (SBF). The pure pectin aerogel showed a high swelling and degradation ratio after 3 h. The addition of the polylactic acid prolonged its stability in the simulated body fluid from 24 h to more than one week, depending on the amount of polylactic acid. Biodegradable aerogels were loaded with indomethacin and diclofenac sodium as model drugs. The entrapment efficiencies were 63.4% and 62.6% for indomethacin and diclofenac sodium, respectively. Dissolution of both drugs was prolonged up to 2 days. Finally, sodium percarbonate and calcium peroxide were incorporated into the bioaerogels as chemical oxygen sources, to evaluate oxygen generation for potential wound healing applications.

Influence of the Impregnation Technique on the Release of Esomeprazole from Various Bioaerogels.

The presented study shows the possibility of using bioaerogels, namely neat alginate, pectin, chitosan aerogels, and alginate and pectin aerogels coated with chitosan, as drug delivery systems for esomeprazole. Two different techniques were used for the impregnation of esomeprazole: Supercritical impregnation, and diffusion via ethanol during the sol-gel synthesis. The prepared samples were characterized by employing N2 adsorption-desorption analysis, TGA/DSC, and FTIR. The achieved loadings were satisfactory for all the tested samples and showed to be dependent on the technique used for impregnation. In all cases, higher loadings were achieved when impregnation via diffusion from ethanol was used. Extensive release studies were performed for all impregnated samples. The in vitro dissolution profiles were found to be dependent on the carrier and impregnation method used. Most importantly, in all cases more controlled and delayed release was achieved with the bioaerogels compared to using pure esomeprazole.

Tuning bio-aerogel properties for controlling theophylline delivery. Part 1: Pectin aerogels

A comprehensive study of release kinetics of a hydrophilic drug from bio-aerogels based on pectin was performed. Pectin aerogels were made by polymer dissolution, gelation (in some cases this step was omitted), solvent exchange and drying with supercritical CO2. Theophylline was loaded and its release was studied in the simulated gastric fluid during 1 h followed by the release in the simulated intestinal fluid. Pectin concentration, initial solution pH and concentration of calcium were varied to tune the properties of aerogel. The kinetics of theophylline release was monitored and correlated with aerogel density, specific surface area, and aerogel swelling and erosion. Various kinetic models were tested to identify the main physical mechanisms governing the release.

Preparation and Characterization of Chitosan-Coated Pectin Aerogels: Curcumin Case Study.

The following study describes the preparation of pectin aerogels and pectin aerogels coated with an external layer of chitosan. For the preparation of chitosan-coated pectin aerogels, a modified coating procedure was employed. Since pectin as well as pectin aerogels are highly water soluble, a function of chitosan coating is to slow down the dissolution of pectin and consequently the release of the active substances. Textural properties, surface morphologies, thermal properties, and functional groups of prepared aerogels were determined. Results indicated that the coating procedure affected the textural properties of pectin aerogels, resulting in smaller specific surface areas of 276 m2/g, compared to 441 m2/g. However, chitosan-coated pectin aerogels still retained favorable properties for carriers of active substances. The case study for prepared aerogels was conducted with curcumin. Prior to in-vitro release studies, swelling studies were performed. Curcumin’s dissolution from both aerogels showed to be successful. Pectin aerogels released curcumin in 3 h showing a burst release profile. Chitosan-coated pectin aerogels prolonged curcumin release up to 24 h, thus showing a controlled release profile.

Pectin-assisted dispersion of exfoliated boron nitride nanosheets for assembled bio-composite aerogels

Boron nitride nanosheets (BNNSs) were prepared via the exfoliation of hexagonal boron nitride in isopropyl alcohol. Extremely stable BNNSs dispersions were obtained after the ultrasonication in pectin aqueous suspensions, and the bio-composite aerogels were fabricated via the freeze-drying process. The digital photographs of pectin/BNNSs aqueous suspensions and Fourier-transform infrared spectroscopy results showed that there was a strong interfacial interaction between BNNSs and pectin macromolecular chains. Owing to the excellent dispersion and intensive interaction, the thermal stability, compressive strength and flame retardant properties of pectin/BNNSs bio-composite aerogels were significantly improved. Compared to neat pectin aerogel, pectin/BNNSs-2 (mass ratio of pectin and BNNSs, 10/1) possessed improved onset thermal decomposition temperature (by 9 °C), enhanced compressive strength (by 119%), reduced peak heat release rate (by 45%) and peak CO2 production (by 53%) at cone radiation intensity of 60 kW/m2. Residue analysis indicated that the presence of BNNSs promoted the carbonization of pectin aerogels.

Tuning structure and properties of pectin aerogels

Highly porous and nanostructured pectin aerogels were synthesized via dissolution-solvent exchange-drying with supercritical CO2. The goal was to show why and how aerogel morphology and properties vary as a function of external conditions. Polymer concentration, pH and concentration of mono- and divalent metal salts were varied. The way of structure stabilization, i.e. gelation or direct non-solvent induced phase separation (in other words, the state of the matter before solvent exchange, gel or solution) turned out to be one of the key parameters influencing aerogel morphology and density. When strong gels were formed via calcium-induced gelation at pH around pKa, the corresponding aerogels presented large pores, the lowest density (0.04–0.05 g/cm3) and lowest specific surface area (around 270–350 m2/g). On the contrary, when pectin network was formed via non-solvent induced phase separation from non-gelled pectin solutions during solvent exchange step, the resulting aerogels were mesoporous, with highest density (0.12–0.15 g/cm3) and highest specific surface area (around 600 m2/g). The results obtained provide the guidelines for making aerogel matrices with fully controlled morphology and properties.

Thermal conductivity/structure correlations in thermal super-insulating pectin aerogels

Pectin aerogels were synthesized via dissolution-solvent exchange-drying with supercritical CO2. The goal was to correlate thermal conductivity with aerogel morphology and properties in order to understand how to obtain a thermal super-insulating material with the lowest possible conductivity. Polymer concentration, solution pH and presence of bivalent ions were varied to tune pectin gelation mechanism and the state of matter, solution or gel. For the first time for bio-aerogels, a U-shape curve of thermal conductivity as a function of aerogel density was obtained. It shows that to reach the lowest conductivity values, a compromise between density and pore sizes is needed to optimize the inputs from the conduction of solid and gaseous phases. The lowest value of conductivity, 0.015 W/m K, was for aerogels from non-gelled pectin solutions. Calcium-induced gelation leads to pectin aerogels with very low density, around 0.05 g/cm3, but with many macropores, thus reducing the contribution of Knudsen effect.

Pectin-based nanocomposite aerogels for potential insulated food packaging application

Environmental-friendly pectin-TiO2 nanocomposite aerogels were prepared via sol-gel process and subsequent drying under supercritical conditions. The first step includes dissolution of pectin in water, addition of proper amount of TiO2 colloid and crosslinking reaction induced in the presence of tert-butanol and zinc ions. Then, the gels are subjected to the solvent exchange and supercritical CO2 drying. The influence of TiO2 nanoparticles on the textural, mechanical, thermal and antibacterial properties of aerogels was investigated. Results indicate that in the presence of TiO2 nanoparticles (NPs) mechanical, thermal and antimicrobial properties of pectin-based aerogels are improved in comparison to the control pectin aerogels. It should be emphasized that the thermal conductivity of pectin-based aerogels (0.022–0.025 W m−1 K−1) is lower than the thermal conductivity of air. Generally, the results propose that the pectin-TiO2 nanocomposite aerogels, as bio-based material, might have potential application for the storage of temperature-sensitive food.

Encapsulation and drug release of poorly water soluble nifedipine from bio-carriers

Controlled drug delivery is one of the most intruding field in pharmaceutical research. It is desired for most of the drugs due to safety and efficacy reasons. Another emerging field is improving the bioavailability of poorly water-soluble drugs. By encapsulating such drugs into biodegradable polysaccharide materials both, improved bioavailability and controlled drug release is readily expected. Nifedipine, used as a model drug, was encapsulated within polysaccharide gels by the novel ethanol induced gelation method. Wet materials were processed by supercritical technology to retain its form and structure. Swelling and in-vitro dissolution tests were performed to investigate the swelling of aerogels and release behavior of nifedipine within body fluids. It was observed that guar and xanthan are not the best candidates for oral delivery of nifedipine, since the release was prolonged to 14days. Oppositely, pectin and alginate are both suitable for nifedipine encapsulation as they released 100% of nifedipine within the first 5h. Higher drug loading was achieved by pectin aerogels most likely due to their higher surface area.

PH sensitive mesoporous materials for immediate or controlled release of NSAID

The aim of this research was to investigate novel mesoporous materials, polysaccharide aerogels, as drug delivery carries in order to achieve controlled release of a model drug, diclofenac sodium. Pectin, alginate and composite pectin–alginate aerogels were prepared by cross-linking with three different ions, zinc, strontium and calcium. Calcium ions are not the best cross-linkers when controlled release is desired, since the release of a model drug was achieved in initial 1 h. Oppositely, zinc cross-linking provided more controlled release of diclofenac sodium. Therefore, zinc cross-linked pectin aerogels were used as the final drug delivery carriers in order to compare the release profile with two commercially available drugs. Pectin–zinc aerogel capsule degraded completely within the 24 h, oppositely both commercial drugs did not degrade even after 72 h. Moreover, the release profiles of all three tested drugs were dissimilar. Pectin–zinc aerogel capsule released 80% of the model drugs in 7 h, first commercial drug around 60% and second commercial drug nearly 100%.

Fast production of high-methoxyl pectin aerogels for enhancing the bioavailability of low-soluble drugs

Aerogels are outstanding materials with high porosities, low densities and large surface areas. Moreover, polysaccharide aerogels e.g. pectin aerogels, are gaining interest due to their biodegradability and biocompatibility, which makes them interesting materials for medical, pharmaceutical or food applications. In this research we propose a new method for the gelation of high-methoxyl pectin. In later continuation those aerogels will be proposed as carriers to enhance the dissolution of poorly soluble drugs. Nifedipine was used as model drug. The aim of the research was to investigate two methods for the drug loading; first by adding the drug during the sol–gel process and second by supercritical adsorption. By the novel gelation method, the overall aerogel production time was shorter. In addition, prepared aerogels possessed highest yet reported surface area for high-methoxyl pectin monolithic aerogels, namely around 390m2g−1. Drug loading during the sol–gel process was higher (22%), however also supercritical adsorption gave comparably good results (13%) according to the low solubility of nifedipine. Nifedipine release was controlled over 12h and 100% (60mg) drug release was achieved in this period.

Encapsulation of pharmaceuticals into pectin aerogels for controlled drug release

For this paper pectin aerogels were obtained by the sol-gel process and further supercritical drying with CO2. The materials were first characterised by nitrogen adsorption and scanning electron microscopy in order to investigate their structures. The highest yet reported surface area on pectin aerogels was achieved during this research (590m2/g). Then the drug loading was performed as the first step of the sol-gel process. Nicotinic acid was used as a model drug. Membranes were added to the pectin microsphere to control the release of nicotinic acid. The release of the model drug was investigated regarding triple and five membrane-aerogels. It was observed that the triple-membrane aerogel was unable to control the release. By adding the 5-membrane, the release decreased. 50% of the drug was released during the first hour followed by the slow first-order release up to 7h. The results clearly indicate that the addition of membranes on pectin aerogel has a significant impact on the drug release kinetics. The 5-membrane pectin aerogel showed potential to be a suitable carrier of the nicotinic acid after further research.

Characterisation of biodegradable pectin aerogels and their potential use as drug carriers

The purpose of this work was to prepare stable citrus (CF) and apple (AF) pectin aerogels for potential pharmaceutical applications. Different shapes of low ester pectin aerogels were prepared by two fundamental methods of ionic cross-linking. Pectins’ spherical and multi-membrane gels were first formed by the diffusion method using 0.2M CaCl2 solution as an ionic cross-linker. The highest specific surface area (593m2/g) that had so far been reported for pectin aerogels was achieved using this method. Monolithic pectin gels were formed by the internal setting method. Pectin gels were further converted into aerogels by supercritical drying using CO2. As surface area/volume is one of the key parameters in controlling drug release, multi-membrane pectin aerogels were further used as drug delivery carriers. Theophylline and nicotinic acid were used as model drugs for the dissolution study. CF aerogels showed more controlled release behaviour than AF pectin aerogels. Moreover a higher release rate (100%) was observed with CF aerogels.

Aeropectin: fully biomass-based mechanically strong and thermal superinsulating aerogel.

Monolithic pectin aerogels, aeropectins, were prepared via dissolution-gelation-coagulation and subsequent drying with supercritical CO2. Aeropectin had pore sizes that varied from mesopores to small macropores and compression moduli in the range from 4 to 18 MPa. Aeropectins show plastic deformation up to 60% strain before the pore walls collapse. Pectin aerogels have a thermal conductivity below that of air in ambient conditions, making them new thermal superinsulating fully biomass-based materials. The contribution of gas and solid conduction plus radiative heat transfer were determined and discussed.

Biodegradable Pectin/Clay Aerogels

Biodegradable, foamlike materials based on renewable pectin and sodium montmorillonite clay were fabricated through a simple, environmentally friendly freeze-drying process. The addition of multivalent cations (Ca(2+) and Al(3+)) resulted in apparent cross-linking of the polymer and enhancement of aerogel properties. The compressive properties increased as the solid contents (both pectin and clay) increased; moduli in the range of 0.04-114 MPa were obtained for materials with bulk densities ranging from 0.03 g/cm(3) to 0.19 g/cm(3), accompanied by microstructural changes from a lamellar structure to a cellular structure. Biodegradability of the aerogels was investigated by detecting CO2 release for 4 weeks in compost media. The results revealed that pectin aerogels possess higher biodegradation rates than wheat starch, which is often used as a standard for effective biodegradation. The addition of clay and multivalent cations surprisingly increased the biodegradation rates.

Design of biocompatible magnetic pectin aerogel monoliths and microspheres

Novel material formulations for biomedical uses containing magnetic nanoparticles are currently being explored. The synergistic combination of a polymeric matrix and a filler with magnetic properties in hybrid nanoporous materials (aerogels) will confer versatility to the product. In this work, the use of pectin aerogels as a biodegradable matrix containing maghemite nanoparticles (γ-Fe2O3 NPs) is studied. The γ-Fe2O3 NPs-loaded pectin aerogels are developed in two different morphologies (cylindrical monoliths and microspheres) prepared by a combination of sol–gel and supercritical drying methods. In the case of the aerogel microspheres, the sol–gel method was substituted by the emulsion-gelation procedure. The obtained aerogel-based materials were evaluated regarding their physical appearance and stability and their textural and magnetic properties. The particle size distribution and morphology of the aerogel microspheres were additionally analyzed by laser dispersion spectrometry, static image analysis and scanning electron microscopy. Process parameters influenced the distribution of the γ-Fe2O3 NPs within the material. Whereas the γ-Fe2O3 NPs were homogeneously distributed throughout the aerogel monoliths, γ-Fe2O3 NPs were mostly deposited on the outer surface of the aerogel microspheres. The magnetic properties of maghemite were preserved in the end material after overall processing.