Margarita Darder

Advances in biomimetic and nanostructured biohybrid materials.

The rapid increase of interest in the field of biohybrid and biomimetic materials that exhibit improved structural and functional properties is attracting more and more researchers from life science, materials science, and nanoscience. Concomitant results offer valuable opportunities for applications that involve disciplines dealing with engineering, biotechnology, medicine and pharmacy, agriculture, nanotechnology, and others. In the current contribution we collect recent illustrative examples of assemblies between materials of biological origin and inorganic solids of different characteristics (texture, structure, and particle size). We introduce here a general overview on strategies for the preparation and conformation of biohybrids, the synergistic effects that determine the final properties of these materials, and their diverse applications, which cover areas as different as tissue engineering, drug delivery systems, biosensing devices, biocatalysis, green nanocomposites, etc.

Hybrid materials based on clays for environmental and biomedical applications

Nanostructured hybrids derived from clays are materials of increasing interest based on both structural characteristics and functional applications, including environmental and biomedical uses. This review introduces some recent examples of nanostructured clay derivatives (organoclays) useful as adsorbents or photocatalysts for environmental applications such as the removal of pollutants or development of environmentally oriented pesticide formulations. The second group of nanostructured materials considered here are related to the so-called bio-nanohybrids, formed by combination of an inorganic solid (clay mineral) with organic entities from biological origin at the nanometric scale. Bionanocomposites are an emerging group of nanomaterials resulting from the assembly of different clay minerals and biopolymers. Among the proposed applications, the development of novel hybrid materials for scaffolds and regenerative medicine, as well as new substrates to immobilize biological species from enzymes to viruses, is notable. Hybrid materials based on layered double hydroxides are receiving special attention in view of the possible applications as drug delivery systems.

Functional biopolymer nanocomposites based on layered solids

Bio-nanocomposites are an emerging group of hybrid materials derived from natural polymers and inorganic solids interacting at the nanometric scale. These nanostructured organic–inorganic materials could be designed and prepared using a wide type of biopolymers and also inorganic solids with different compositions and topologies. Among these last solids, special attention is devoted to layered materials that show the ability to intercalate biopolymers giving hybrids with functional properties. This novel research topic envisages the future development of biomimetic materials to provide novel bio-nanocomposites as multicomponent and multifunctional materials.

Bionanocomposites based on alginate–zein/layered double hydroxide materials as drug delivery systems

The present work introduces new hybrid materials based on the combination of layered double hydroxides (LDH) and two biopolymers (a protein and a polysaccharide) to produce LDH–biopolymer nanocomposites, able to act as effective drug delivery systems (DDS) in comparison to the LDH or the biopolymers alone. Ibuprofen (IBU) has been chosen as a model drug, being intercalated in a Mg–Al LDH matrix. The resulting hybrid is used to prepare bionanocomposite materials by association with two biopolymers: (i) zein, a highly hydrophobic protein, and (ii) alginate, a polysaccharide widely applied for encapsulating drugs. Characterization of the IBU/Mg–Al LDH intercalation compound and the bionanocomposites resulting from its incorporation into alginate–zein matrices of different composition was carried out by means of different experimental techniques: X-ray diffraction, infrared spectroscopy, chemical and thermal analysis, as well as optical and scanning electron microscopies. Preliminary kinetic studies of IBU liberation from bionanocomposites processed as beads show a better protection against drug release at the stomach pH and a controlled liberation in the intestinal tract conditions. This effect can be attributed to the hydrophobic nature of zein, which limits the passage of water and swelling of biocomposite beads prepared with such systems, delaying the release of the drug.

Pectin-coated chitosan-LDH bionanocomposite beads as potential systems for colon-targeted drug delivery.

This work introduces results on a new drug delivery system (DDS) based on the use of chitosan/layered double hydroxide (LDH) biohybrid beads coated with pectin for controlled release in the treatment of colon diseases. Thus, the 5-aminosalicylic acid (5ASA), the most used non-steroid-anti-inflammatory drug (NSAID) in the treatment of ulcerative colitis and Crohns disease, was chosen as model drug aiming to a controlled and selective delivery in the colon. The pure 5ASA drug and the hybrid material prepared by intercalation in a layered double hydroxide of Mg2Al using the co-precipitation method, were incorporated in a chitosan matrix in order to profit from its mucoadhesiveness. These compounds processed as beads were further treated with the polysaccharide pectin to create a protective coating that ensures the stability of both chitosan and layered double hydroxide at the acid pH of the gastric fluid. The resulting composite beads presenting the pectin coating are stable to water swelling and procure a controlled release of the drug along their passage through the simulated gastrointestinal tract in in vitro experiments, due to their resistance to pH changes. Based on these results, the pectin@chitosan/LDH-5ASA bionanocomposite beads could be proposed as promising candidates for the colon-targeted delivery of 5ASA, with the aim of acting only in the focus of the disease and minimizing side effects.

Bio-organoclays based on phospholipids as immobilization hosts for biological species.

A new type of hybrid biomaterials based on the clay minerals montmorillonite and sepiolite as well as phosphatidylcholine, acting as environment-friendly biomodifier, was prepared. The biohybrids were characterized by sampling of adsorption isotherms in different organic solvents. The results suggest bilayer formation both on the external sepiolite surface as well as in the intracrystalline space of the montmorillonite. The obtained supported lipid membranes were further investigated by X-ray diffraction, multinuclear solid state NMR, Fourier transformed IR spectroscopy and thermal analysis. From these results an adsorption model based on electrostatic interaction between the polar phospholipid headgroups and the silicate surface could be postulated. The versatility of bio-organoclays as immobilization host for biological species was demonstrated in a mycotoxin retention study.

Caramel–clay nanocomposites

Novel nanocomposite materials have been prepared following a microwave assisted reaction of sucrose with 2 : 1 phyllosilicates belonging to the clay minerals family. In this way, sucrose gives macromolecular intercalation compounds (referred to as “caramel–clay nanocomposites”) when mixtures of this disaccharide with Na–montmorillonite are heated in a monomodal microwave furnace. The starting, intermediate and final materials were characterized by XRD, FTIR, DTA-TG, 13C NMR, SEM, N2 adsorption (BET) and in situ EIS. It is proposed that a rapid intercalative polycondensation of sucrose forms conventional caramel under these experimental conditions. The most interesting feature of these compounds is their excellent behaviour as precursors of carbon–clay nanocomposites, presenting attractive characteristics as environmental friendly porous materials of low cost provided with electrical conductivity.

Phospholipid–Sepiolite Biomimetic Interfaces for the Immobilization of Enzymes

Biomimetic interfaces based on phosphatidylcholine (PC) assembled to the natural silicate sepiolite were prepared for the stable immobilization of the urease and cholesterol oxidase enzymes. This is an important issue in practical advanced applications such as biocatalysis or biosensing. The supported lipid bilayer (BL-PC), prepared from PC adsorption, was used for immobilization of enzymes and the resulting biomimetic systems were compared to several other supported layers including a lipid monolayer (ML-PC), a mixed phosphatidylcholine/octyl-galactoside layer (PC-OGal), a cetyltrimethylammonium monolayer (CTA), and also to the bare sepiolite surface. Interfacial characteristics of these layers were investigated with a focus on layer packing density, hydrophilicity/hydrophobicity, and surface charge, which are being considered as key points for enzyme immobilization and stabilization of their biological activity. Cytoplasmic urease and membrane-bound cholesterol oxidase, which served as model enzymes, were immobilized on the different PC-based hybrid materials to probe their biomimetic character. Enzymatic activity was assessed by cyclic voltammetry and UV-vis spectrophotometry. The resulting enzyme/bio-organoclay hybrids were applied as active phase of a voltammetric urea biosensor and cholesterol bioreactor, respectively. Urease supported on sepiolite/BL-PC proved to maintain its enzymatic activity over several months while immobilized cholesterol oxidase demonstrated high reusability as biocatalyst. The results emphasize the good preservation of bioactivity due to the accommodation of the enzymatic system within the biomimetic lipid interface on sepiolite.

Multifunctional Porous Materials Through Ferrofluids

Authors thank funding from CICYT (Spain), project MAT2009-09960 and NAN2007-31173-E. FMF and BW acknowledge the Ministerio de Ciencia e Innovacion (Spain) and the Comunidad de Madrid, respectively, their graduate fellowships.

Algae–silica systems as functional hybrid materials

Microalgal cells were entrapped within two different sol–gel silica matrices with the aim of carrying out viability studies and developing active phases for sensor development. The first sol–gel system, based on methacryloxypropyltrimethoxysilane (MAPTS) and tetramethoxysilane (TMOS) monomers, was able to entrap lyophilized Chlorella vulgaris and Anabaena sp. PCC7120, but its rather non-porous nature limited the algal viability to the surface and fractures of the resulting hybrid material. However, this sol–gel material prepared with Chlorella tissue successfully performed as an active phase in the development of sensors for heavy-metal ions (e.g. Pb2+, Cu2+ and Cd2+) in water solution. The second sol–gel system was obtained using methyltrimethoxysilane (MTMOS), phenyltrimethoxysilane (PhTMOS) and TMOS monomers. Here, entrapped algae appeared to weakly interact with the resulting matrix probably due to its high hydrophobicity and also very low porosity. In this context, SEM and AFM studies carried out with the Anabaena-sol–gel material showed that algae could be removed from the polymeric network leaving traces having the algae’s peculiar three-dimensional shape. This opens the way to prepare imprinted materials using a soft lithographic approach, which could be potentially used as artificial receptors for electrochemical sensing of algae target species.