Current Nanoscience - Volume 2, Issue 3, 2006

Bio-nanohybrid materials constitute an emerging interdisciplinary field in the frontier between Life Sciences, Material Sciences and Nanotechnology. Since the last few years, special attention is being devoted to bio-nanohybrids due to their incidence in significant areas from regenerative medicine to new materials showing improved functional and structural properties. This issue of CNANO introduces some selected works showing recent research focused on the synthesis and properties of bio-hybrid materials, which are based on the assembly at the nanometric scale of compounds derived from natural sources with different inorganic solids. Among these nanostructured materials, the structural and functional bio-hybrids resulting from the combination of natural polymers, such as polysaccharides, polyesters, RNA and DNA, polypeptides, fibrous and globular proteins and enzymes, with inorganic substrates, such as silica and phyllosilicates, layered double hydroxides (LDHs), phosphates and metal oxides, are significant examples illustrating new insights in this multidisciplinary area. Nowadays, there is an increasing interest in the preparation of bio-inspired or biomimetic materials following the examples found in Nature, developing bio-nanohybrids of enhanced mechanical resistance mimicking the exceptional features of native materials. Illustrating these features, studies on bio-nanohybrids that mimic the hierarchical structural bone organization are presented in this Issue by Senna's and Vallet's Groups. These authors report about the bio-nanohybrids based on the assembling of nanosized hydroxyapatite and other inorganic substrates with collagen and other proteins as key materials for artificial bones. In this context, the review by Vohra and co-workers highlights the preparation of nanostructured biomaterials for tissue engineering. Recent advances on fabrication of nanofibrous matrices of biopolymers for tissue engineering scaffold applications attained by the Vohra's Group are reported and discussed by these authors. Despite the great number of publications within this topic, this key contribution signals that this type of bio-nanohybrids can still be considered in its infancy regarding their possibilities for application in regenerative medicine. Bio-nanohybrids derived from the assembly of silica and silicate particles with biomolecules constitute one of the major topics in relation with the scope of this Special Issue. In this context, Ariga and co-workers introduce an overview on organicinorganic hybrids derived from the immobilization of biomolecules on nanosized inorganic substrates. These authors have developed a new concept of multicellular mimicking systems named cerasomes, which are based on hybrid vesicles. Bioencapsulation of enzymes and other biological molecules in mesoporous silica gives bio-nanohybrids in which their stability is increased allowing future applications as catalysts, membranes or energy conversion devices, as reviewed by Fukushima and co-workers at the Toyota Central R&D Laboratory. Combination at the molecular level of biopolymers such as polysaccharides and structural proteins with inorganic silica and other inorganic substrates leads to an emerging research field in the so-called bio-nanocomposite materials. In this way, the contribution by Livage's Group refers to sol-gel processes giving silica based bio-nanocomposites, which show resemblance with native biomineral systems. The contribution by Ruiz-Hitzky's Group reviews different bio-nanocomposites based on gelatin, in particular those related to inorganic layered solids, such as clay minerals (smectites) and metal mixed-oxides (perovskites). On the other hand, nanoscale systems based on porous membranes offer the possibility to synthesize materials within nanopores, which also constitutes an improved way for advanced separation techniques and sensing purposes. This important aspect has been reviewed by Martin's Group at the University of Florida based on their own experience, discussing in their contribution various synthetic strategies, as well as recent advances on nanotube membranes for biotechnological applications. The Group of Choy, in Korea (Center for Intelligent Nano-Bio Materials, CINBM) contributes with a review emphasizing on DNA based hybrids with multipurpose applications, from drug delivery systems to gene therapy. In addition, two contributions, related to the sensing ability of bio-nanohybrids have been elaborated by Briones & Martín-Gago as well as by Forano's Group, the former centered on the development of DNA microarrays and the last one dealing with enzyme-based bio-nanohybrids useful for bio-sensing devices......

An ideal 3D-scaffold for tissue regeneration should have similarity to native ECM in terms of both chemical composition and physical nanostructure. Recently, nanostructured biomaterials having physical nanofeatures such as nanocrystals, nanofibers nanosurfaces, nanocomposites, etc. gained much interest in regenerative medicine. This is mainly because of their resemblance of physical nanofeatures to natural extra cellular matrices. This review mainly focuses on nanocrystalline bioresrobable bioceramic scaffolds and nanofibrous polymeric scaffolds for tissue regeneration. Fabrication of porous bioceramics based on HA and other calcium phosphates with interconnected pore structure can be done by the replication of polymer foam. The advantage of this technique is the control over porosity, pore geometry and pore size of the fabricated scaffolds. Therefore, the first part of the review focused on porous nanocrystalline bioceramics for bone tissue engineering. Electrospinning is a versatile technique to fabricate nanofibrous polymeric matrices for use in regenerative medicine. The recent developments in electrospun scaffolds with a special emphasis on FDA approved biodegradable polymers such as PCL, PLA, PLGA, collagens, etc are presented in the second part. A special attention has been made to review the mechanical properties and cell interaction of the electrospun mats. Electrostatic co-spinning of polymers with nanohydroxyapatite to fabricate hybrid nanocomposite scaffolds as potential scaffolds mimicking the complex nanostructured architecture of bone has been suggested for hard tissue regeneration.

The study of materials for bone tissue repair is one of the most important subjects in the field of materials research for biomedical applications. Bone can be considered as a biological hybrid material composed of an organic component, collagen, and an inorganic one, nanocrystalline carbonate hydroxyapatite (CHA). Both phases integrate each other into a nano-metrical scale in such a way that the crystallite size, nanofibers orientation, short range order between both components, etc. determine its nanostructure and therefore the function and mechanical properties of each kind of bone. On the basis of bone regeneration, new biomaterials have been developed. These materials stimulate the bone tissue formation by promoting the osteoblast proliferation and differentiation. One of the most promising alternatives is to apply materials with similar nanostructure to that of natural bone tissue. In this sense, the nanotechnology and the development of organic-inorganic hybrid materials provide excellent possibilities for improving the conventional bone implants. The present article reviews the advances in silicate - containing hybrids for bone tissue repair, as well as the chemical methodologies that allow to control the material nanostructure. Special attention is paid to bioactive hybrid materials, which are able to produce biological apatites on their surfaces when they are in contact with physiological fluids.

Biocompatible nano-composite sol (NCS) comprising nano-crystalline hydroxyapatite (HAp, Ca 10(PO4)6(OH)2) and hyaluronic acid (HYA) was prepared. By varying the relative content of HAp in NCS, strongest network structure was obtained at 10wt% HAp in NCS, as confirmed from a number of circumstance evidences obtained by rheological, thermoanalytical, crystallographical measurements as well as FT-IR spectra. Interaction of NCS with natural bones and gut strings made from gut collagen was then examined in vitro. Adhesion of the collagen fibers with NCS was observed at the fracture surface of natural bones. Gut collagen was disentangled to the fragments of about 10 nm thick, where no NCS was observed, thus, confirming the fact that the adhesive strength between NCS and bone surface is stronger than that among collagen fibers.

This review presents a comprehensive overview of the recent advances in the field of bio-inorganic nanohybrids. In the first part of this review, examples on hybridization of biomembrane mimics with inorganic backbone are described. Silane-bearing amphiphile was used for the preparation of Langmuir-Blodgett films that are mechanically stable and capable of permeation controls and electrode modification with vitamin function. The similar amphiphiles were utilized to form organic-inorganic hybrid vesicle "Cerasome", which can be assembled in layer-by-layer manner to construct multi-cellular mimic. Furthermore, the potential applications of the above materials are reviewed and proposed. The second part of this review provides the methodology of immobilizing various biomolecules into nanosized inorganic structures including clay minerals and layer-by-layer (LBL) assemblies. Films and hollow capsules prepared through the LBL techniques offer sophisticated designs of the bio-inorganic nanohybrids that can be applied to biomaterial entrapment and bio-reactors. Examples on hybridization of biomolecules with mesoporous inorganic structure are also introduced in the last part. A controlled release of biochemical drugs and immobilization of bio-assemblies on the materials with welldefined pore structures in nanometer ranges are briefly examined, discussed and summarized.

The incorporation of bio-molecules and proteins into inorganic host materials has been given great attention recently. The present paper deals with the preparation, structures and properties of conjugates of mesoporous silica: folded sheet mesoporous materials (FSM), with chlorophyll (Mg-porphyrin) and heme (ferriprotoporphyrin). Horseradish peroxidase, light harvesting protein and myoglobin were also adsorbed in mesoporous silica of adequate pore size. The molecules and proteins adsorbed in the mesopores were stabilized according to temperature change, oxidation and/or light irradiation. The porphyrin/FSM conjugates showed characteristic performance resembling that of the light harvest system in natural leaves, myoglobin or catalase. The stabilized proteins in FSM also maintained their own functions. These results suggested that bio-inspired assembly technologies in nanospaces are valuable tools for the design and preparation of catalysts, adsorbents, membranes and energy conversion devices.

Bioencapsulation in silica gels has become a very popular field of research, leading to the design of biosensors and bioreactors. If pure silica gels appear suitable to maintain the biological activity of entrapped enzymes, there are many cases where hybrid materials are necessary to reach the long-term preservation of biomolecular or cellular species and/or to provide new functionalities. This review focuses on the design of such nanocomposite materials combining silica with biopolymers. In the first part, the synthesis and characterization of these bio-hybrid materials are described, emphasizing the importance of the polymer influence on the reactivity of silica precursors. In the second part, the benefits of biopolymer incorporation in silica gels are illustrated in the context of biotechnological devices. As a conclusion, a parallel is drawn between biohybrids and biominerals, opening new perspectives for the design of multi-component biologically-active materials.

An emerging group of hybrid materials is the so-called bio-nanocomposites, which are bio-hybrid nanostructured materials based on the combination of natural polymers (polysaccharides, proteins, enzymes, nucleic acids) and inorganic solids (clays, double layered hydroxides, phosphates, metal oxides, etc.). Bio-nanocomposites are interesting because, among other properties, the use of biopolymers provides biocompatibility, non-toxicity and biodegradability to the resulting nanohybrid materials. An example of this type of natural polymers is gelatin, a polypeptide derived from the structural protein collagen, that is able to form transparent, elastic and thermoreversible gels. This paper will review the role of inorganic solids, such as montmorillonite or perovskite, in combination with gelatin, on the characteristics and final properties of different type of bio-nanocomposites based on this protein. With these examples, we will show the influence of the solids on the gelatin gel-transition temperature, film formation ability and rheological, mechanical and dielectric properties.

We have developed techniques and methods based on porous membranes for applications in bionanotechnology. There are three general membrane-based strategies we have used to prepare our nanoscale systems. In the first method, namely, template synthesis, nanometer scale pores are used to synthesize and modify materials. We have shown that template synthesis is highly adept at producing biomaterials with at least one dimension that is nanometer in scale. In the second strategy, we describe chemical and biochemical sensors based on nanotube membranes. These sensors function largely by monitoring variations in the ionic currents through the pores of the membranes that develop under an applied transmembrane potential. In the third approach, nanometer scale pores are used to separate species that translocate a nanotube membrane. The selectivity and flux of species that translocate the nanotube membrane can be further controlled through chemical modification of the nanotube walls. In this review, we will discuss these three uses of nanotube membranes (template synthesis, sensing and separation) in the context of biotechnology and biomaterials. We will briefly review the materials and methods of nanotube membrane technology and then discuss our most recent biooriented research of these interesting systems.

Nucleic acids are natural biopolymers that store the genetic information of organisms. This makes the detection and characterization of DNA and RNA a relevant task in biotechnology, with applications ranging from medicine to environmental control. During the last decades, a large effort has been focused on the development of biosensors, among them those devoted to the detection of nucleic acids in natural samples and those that include nucleic acids as nanosized capture probes for different biomolecules. DNA microarray technology has been successfully used in biotechnological applications including genotyping and gene expression studies. Nevertheless, the performance of DNA microarrays has a limitation imposed by the need of a previous fluorescent labeling of the target molecule to be analyzed. This encouraged the use of alternative detection methods, such as optical and electrochemical ones, and recently others based on surface characterization techniques. New trends in nanotechnology point towards new tools for manipulating molecules and macromolecules that could be developed as high performance biosensors. This interdisciplinary approach towards the integration of novel biosensors can benefit from the capability of certain polymers to form self-assembled monolayers (SAMs) on different surfaces. Thiol-modified DNA can form SAMs on gold surfaces with reduced efficiency, and the biological activity of the probe is decreased upon adsorption. Therefore, thiolated DNA has a very limited use in biosensor development. These constraints have been successfully by-passed using uncharged, artificial analogs of natural nucleic acids, such as peptide nucleic acids (PNAs), as molecular probes. This contribution reviews the state of the art in the use of nucleic acids and their analogs as biosensor nanomaterials, and summarizes the novel approach towards the development of biosensors based on SAMs of PNAs. Finally, we present the current trends in this promising aspect of nanobiotechnology.

Layered double hydroxides (LDHs) with high anion exchange capacity have attracted particular attention in the fields of bio-hybrid nanomaterials due to their unique properties such as excellent biocompatibility, high affinity to carbonate anion, pH-dependent stability and high availability. To date, a variety of negatively charged biomolecules have been hybridized with LDHs to evolve into bio-LDH nanohybrids, including vitamins, drugs and DNA strands as well as simple organic acids. Bio-LDH nanohybrids can be readily prepared in a mild condition by coprecipitation, anion exchange or reconstruction. Their applications can be found in a wide range from the controlled release and delivery systems to biosensors and genetic molecular code system. In this review, special emphasis has been placed on DNA-LDH nanohybrids because DNA molecules are of great importance in many sciences and industrial fields. Their synthesis methods, characteristics and application potentials are reviewed briefly.

Bioinorganic hybrid materials constitute a new generation of materials at the interface of biology and material science, able to display functionalities as complex as that of natural systems such as drug vectorization and delivery, molecular machinery functions or sensing properties. Among these bioinorganic structures, enzyme-clay nanohybrid compounds are under investigations for applications as biosensors or for biosynthesis applications. Due to their anionic exchange properties, wide range of chemical composition and versatile structural and textural properties, layered double hydroxides are very appropriate materials for the immobilization of biomolecules, which often bear an overall negative charge. This review focuses on the strategy of elaboration procedures of new active bioinorganic LDH-enzyme materials with potential applications in biocatalysis and for the elaboration of biosensors. Various soft chemistry processes such as adsorption, delamination/restacking and coprecipitation methods are examined. Structural and textural characterizations of the bioinorganic materials are described in order to understand the interactions between biomolecules and host structure. Bioactivity of immobilized enzymes and electrochemical performance of biosensors are also discussed in relation with the immobilization state of the enzyme.