Enigmatic functions of amorphous calcium carbonates (ACC) are explored by inducing the formation and the stabilization of spherulitic ACC particles on self-assembled monolayers (SAM) of hydroxy-terminated alkanethiols on Au surface. We demonstrate that the stabilized ACC particles can be induced to crystallize on command to form oriented calcite crystals by introducing a nucleating surface by a means of a secondary SAM surface with carboxylate functionality.

Diatoms are a large group of unicellular microalgae encased by silica cell walls that exhibit species-specific, mostly porous micro-and nanopatterns. Previously, from the diatom Cylindrotheca fusiformis unique phosphoproteins (termed silaffins) and unusually long polyamine chains (termed LCPA) have been identified and implicated in silica formation. However, analysis of the general role of silaffins in species-specific silica morphogenesis has been hampered by lack of data about silaffins from other diatom species. Recently, we have isolated the five major silaffins from the diatom Thalassiosira pseudonana and aided by the genome data available from this organisms we were able structurally und functionally characterize these molecules. These data clearly support the hypothesis that silaffins play an important role in the nanofabrication of diatom biosilica. The basic insights into the mechanism of biomineral morphogenesis by silaffins and LCPA suggest future pathways for the fabrication of nanostructured minerals by synthetically available polymers.

A new crystallization device, based on a constant-composition double-diffusion setup, was constructed to study biomineralization in vitro. The device was tested with poly(aspartic acid) as a model additive in the precipitation of calcium carbonate, showing a complete crystal growth inhibition.

This paper reports the development of a biodegradable porous scaffold made from naturally derived chitosan and alginate polymers for bone tissue engineering. The scaffold has a 3-D interconnected porous structure and was fabricated through thermally induced phase separation. The mechanical test showed that the scaffold has compressive strength of 0.46 ± 0.02 MPa — about 4 times that of the pure chitosan scaffold. The cell-material interaction study indicated that osteoblast cells seeded on the chitosan-alginate scaffold attach and proliferate well. The mineral deposition occurred after 3 days of culture and formed large chunks after 7 days. The chitosan-alginate scaffold was also found to have desirable swelling property and was structurally stable in solutions of different pH. The chitosan-alginate scaffold can be prepared from solutions of neutral pH allowing growth factors to be incorporated homogeneously into the scaffold for sustained release. This research demonstrated a technique by which a polymer-based biodegradable scaffold can be made to have high porosity up to 92% and excellent mechanical and biological properties.

Bone substitutes are often required to replace damaged tissue due to injuries, diseases and genetic malformations. Traditional bone substitutes, such as autografts, allografts, xenografts and metal implants, are far from ideal as each have their own specific problems and limitations. Bone tissue engineering offers a promising opportunity for bone regeneration in a natural way. However, currently the scientific challenges of bone tissue engineering lie in the development of suitable scaffold materials that can improve bone cell adhesion, proliferation and differentiation. The design of nanophase titania/polymer composites offers an exciting approach to combine the advantages of a degradable polymer with nano-size ceramic grains that optimize biological properties for bone regeneration. Importantly, nanophase titania mimics the size scale of constituent components of bone since bone itself is a nanostructured composite composed of nanometer hydroxyapatite crystals well-dispersed in a mostly collagen matrix. Previous studies have shown significant improvement in protein adsorption, osteoblast (bone-forming cell) adhesion and long-term functions on nano-grain ceramic materials compared to traditional micron-grain ceramic materials. This study used nanometer grain size titania dispersed in a model polymer (PLGA or poly-lactic-co-glycolic acid) matrix by using various sonication powers to increase osteoblast adhesion. The surface characteristics of the composites, such as topography, titania surface area coverage and surface roughness, were studied by scanning electron microscopy and atomic force microscopy. Of all the composites formulated in this study, osteoblast adhesion was the greatest on nanophase titania/PLGA (30/70 wt.%) sonicated at 118.75 for 10 minutes; this composite was the closest in terms of nanometer surface roughness compared to bone of all the composites formulated. In this manner, this study suggests that nanophase titania sonicated in PLGA under these conditions should be further studied for orthopedic applications.

To understand the inelastic response of bone, a two-part investigation has been conducted. In the first, a flexural test protocol has been designed and implemented that monitors the axial and transverse strains on both the tensile and compressive surfaces of cortical bone. The results are used to assess the relative contributions of dilatation and shear to the inelastic deformation. Unload/reload tests have characterized the hysteresis and provided insight about the mechanisms causing the strain. These tests reveal strain healing attributed to sacrificial bonds. The second part devises a model for the stress/strain response, based on a recent assessment of the nano-scale organization of the collagen fibrils and mineral platelets. The model rationalizes the inelastic deformation in tension, as well as the permanent strain and hysteresis.

A Polymer-Induced Liquid-Precursor (PILP) process for mineralization of calcium carbonate has been studied in-situ by laser light scattering. Static and dynamic light scattering data were obtained from CaCl2 solutions containing poly(aspartic acid). Under these conditions calcium carbonate mineralizes through a liquid droplet precursor phase when the solution is exposed to the decomposition products of ammonium carbonate. Our measurements probe the integrated scatterer mass and the apparent hydrodynamic radius Rh,app of the droplets as they nucleate and coalesce. The data reveal three stages in the formation of the PILP phase: an early stage of droplet growth to Rh,app ≈ 250 nm; a mid-time stage of fluctuations and polydispersity in particle size; and a final growth period where Rh,app increases from 350 nm to the micron scale. Aggregation of precursor droplets, rather than atom-by-atom growth, is the dominant mechanism of mineral formation under these conditions. With respect to biomineralization, this first observation of 100-nm-scale droplets is significant, implying a possibility to mineralize from the liquid phase within the nanoscale compartments in which many biominerals form.

The coccoliths that form the outer cell covering of the unicellular coccolithophores are assembled in a coccolith vesicle. The coccolith vesicle maintains the conditions and protein carriers sufficient to import the raw materials (Ca2+ and CO32-) for calcite formation and, furthermore, to initiate and sustain mineralization. We have isolated the coccolith vesicle membrane on which a proton-pumping, vacuolar ATPase has been localized. The V-ATPase has been characterized and its membrane-spanning subunit c has been cloned and sequenced. We used the highly conserved sequence for designing and constructing probes and primers that allowed us to analyze expression patterns to show a direct relationship between expression of the gene and calcification. Our collaborative work has now turned to a genomics approach that will lead us to additional calcification-specific genes.

Sol-gel derived silane hybrid films composing of (3-aminopropyl)trimethoxysilane–tetramethoxysilane (APTMS-TMOS) have been shown to have properties that make the films suitable for DNA microarray applications. The ability of the films to bind DNA was studied using aminated 25-mer oligonucleotide DNA and 1, 4-phenylenediisothiocyanate linker. The binding of DNA onto the films was shown to depend on films' composition i.e. the binding rate decreased with the decrease of APTMS content in the film. The arrayed primer extension (APEX) analysis showed reversed tendency – fluorescence signals of bound probes increased with the decrease of APTMS content in the film. The background noise was low and the fluorescent probes were clearly outlined. The density of functional amino groups on the films was estimated by fluorescence spectroscopy.

In order to achieve multiple intracellular stimulation and recording devices with high electrode density and low manufacturing cost, we have fabricated and characterized an active matrix thin film transistor array with integrated vertically aligned carbon nanofibers. This device has the potential for cell probing and screening that provides great potential to execute direct cell sensing/probing and recording with a high electrode density. Each unit pixel in the array is individually addressed by a thin film transistor (TFT) and the vertically aligned carbon nanofibers (VACNF) used to impale the cell are fabricated on the drain electrode of the TFT. The VACNF is grown by direct current plasma enhanced chemical vapor deposition (DCPECVD) using a nickel catalyst. Electroanalysis or impedance differences between the cell probing site and a reference electrode are recorded with a potentiostat or a semiconductor analyzer connected to the output terminals. Additionally, the impedance change with frequency of the intracellular probe can be measured by applying a frame signal input and the signal can be recorded in storage capacitors after the frame scan of the TFTs. Consequently, actively addressed nanofiber arrays enable bidirectional interfacing with tissue matrices in a format that provides intercellular positioning of electrode elements as well as the potential for intracellular residence of probes within individual cells. In our research, we exploit these non-planar electrode systems for efficient coupling with excitable cell matrices as well as for intracellular biochemical manipulation and sensing of and delivery to single cells. In this paper, we will discuss the fabrication sequence of the inverted metal-oxide-semiconductor (MOS) TFT, and will elaborate the materials issues related to integrating the carbon nanofibers with the TFT.

In an effort to decrease the number of problems associated with osteoporosis, the long-term goal of the present study is to design calcium phosphate-based nanoparticles that specifically attach to areas of low bone density and once attached, allow for the targeted release of bioactive agents that can quickly increase bone formation. Efforts are focused on nanoparticles of calcium phosphate-based materials since they are similar in size and chemistry to the major inorganic components of bone. As a first step in this research, the objective of the present study was to synthesize nanoparticles of crystalline hydroxyapatite (or HA) and amorphous calcium phosphate. Crystalline HA is stable under physiological fluids and, thus, will release embedded bioactive agents slowly. Alternatively, amorphous calcium phosphate is highly biodegradable and will, thus, release embedded bioactive agents quickly. A further objective of the present study was to functionalize such inorganic biodegradable materials with amino groups which would allow for the subsequent attachment of entities to direct such nanoparticles to osteoporotic bone and increased bone formation once attached. One promising approach to direct the nanoparticles to osteoporotic bone is to attach antibodies to pentosidine on the nanoparticles since pentosidine is present in higher amounts in osteoporotic compared to healthy bone. A promising approach to increase bone growth once nanoparticles attach to osteoporotic bone, is to embed nanoparticles with regions of the bone growth factor: bone morphogenic protein-2 (or BMP-2). Results of this study demonstrated the successful synthesis of both crystalline HA and amorphous calcium phosphate nanoparticles. Furthermore, results showed that these nanoparticles can be functionalized with versatile amino groups. In this manner, this study takes the first steps toward utilizing calcium phosphate based nanoparticles to reverse bone loss associated with osteoporosis.

Marine diatoms are a class of microalgae that possess cell walls composed of silica nanoparticles. These organisms actively assimilate silicic acid Si(OH)4 from seawater, polymerize silicic acid to silica nanoparticles by a protein-mediated precipitation process, then assemble the silica nanoparticles into intricate patterns that constitute the cell wall microarchitecture of the diatom frustule. The biomineralization capacity of marine diatoms, Nitzschia frustulum, was harnessed to biologically manufacture silicon oxide / germanium oxide nanocomposite materials. Germanium was incorporated into living diatom cell mass by a two-stage cultivation process. The micro- and nanostructures of biogenic oxide nanocomposite were characterized by TEM with EDS, and XRD. Furthermore, photoluminescence (PL) measurements were performed on these biogenic nanocomposites with different post processing to study their optoelectronic properties. Strong blue photoluminescence was observed from samples treated with H2O2 and oxygen plasma. A clear blueshift was observed from the biogenic oxides with the addition of germanium. It is believed that self-trapped exciton affected by quantum confinement effect is responsible for the PL from these biogenic oxide nanocomposites.

Self-organized hydroxyapatite /collagen (HAp/Col) nanocomposite was synthesized by a co-precipitated method. The porous HAp/Col nanocomposites with unidirectional and interconnected pores with approximately 20μm in size were prepared by a facile method. The ice crystals were grown up at a cooling brass bottom in the paste which kneaded the HAp/Col nanocomposite with a sodium phosphate buffer. The freeze-drying technique produced the replica of ice structures, and the porous composites showed the anisotropic compressive strengths. The nanostructure and micropore structure are of great importance for developing the novel artificial bone filling materials; attachment and migration of cells and blood vessels, and early regeneration of bone tissues.

Hydroxyapatite (HAp) is widely used as bioceramics for bone and dental tissue reconstructions due to its excellent biocompatibility with hard tissues and high osteoconductivity. Although it is well known that HAp has the high adsorbed ability, its ability is decreased in high ionic solution. To immobilize protein on the HAp surface, this study demonstrates that Collagen (Col) and fibronectin (Fnt) were immobilized on the surface of hydroxyapatite (HAp) sintered body with and without the silane coupling agent of aminopropyltriethoxysilane (APS). The proteins immobilized on the HAp and APS/HAp surfaces were investigated by atomic force microprobe (AFM, Simadzu; SPM 9500) analyses and Ζ potential measurements. The stability of protein/APS/HAp and protein/HAp composites was evaluated after immersion in phosphate buffer and NaCl solutions with various concentrations. AFM analyses and Ζ potential measurements revealed that proteins immobilized on the APS/HAp are more stable than those immobilized on the HAp in high ionic solutions.

Controlled-shape BaTiO3-based microparticles were synthesized with the use of diatom microshells (frustules) as templates. The SiO2-based frustules of Aulacoseira diatoms were first converted into MgO-based replicas via a gas/solid displacement reaction at 900°C. A BaTiO3 coating was then applied to the MgO-bearing frustules by a sol-gel process. After firing at 700°C for 1.5 h, a conformal nanocrystalline coating of BaTiO3was generated on the surfaces of the MgO-bearing frustules. The underlying MgO scaffolds were then selectively dissolved away to yield freestanding 3-D BaTiO3-based replicas of the original Aulacoseira diatom frustules. This work demonstrates that microparticles with well-controlled 3-D morphologies and non-natural multicomponent ceramic compositions can be produced by merging the self-assembly ability of biomineralizing micro-organisms with synthetic chemical tailoring.

Within this paper the suitability of amino acids and dipeptides as structure-directing agents is discussed. According to that bio-inspired approach these biomolecules were investigated with respect to the evolution of zinc oxide-based architectures. Those small molecules are able to trigger the morphology of these materials ranging from grain-like via two up to three dimensional features. Besides morphological aspects the structural characterization of these solids by means of electron and atomic force microscopy as well as by photoelectron spectroscopy and X-ray diffraction are discussed in order to extract the function of the biomolecules with regard to the formation of the inorganic phases.

Glassy Polymeric Carbon (GPC) is completely biocompatible and is widely used as a material for artificial heart valves and in other biomedical applications. Although it is ideally suited for fluid flow in the blood stream, collagenous tissue that normally forms around the moving parts of a GPC heart valve sometimes loses adhesion and creates embolisms downstream. We have shown that moderate fluence of MeV ions, especially oxygen ions, increases the surface roughness of GPC on a scale appropriate for enhancing tissue adhesion. Silver ion implantation is shown to inhibit cell growth on GPC. Ion bombardment also increases the surface hardness of GPC, already an extremely hard material. In vitro biocompatibility tests have been carried out with model cell lines to demonstrate that MeV ion bombardment can favorably influence the surface of GPC for biomedical applications.

In the present work, novel hybrid nanostructured composites were produced to be used in many potential applications such as biomedical, drug delivery systems, tri-dimensional scaffolds for biomaterials and tissue engineering, biomembranes and optical devices among others. Hybrids were synthesized by reacting poly (vinyl alcohol) (PVA) in aqueous acid solution with silicon alcoxide tetraethoxysilane (TEOS). PVA/TEOS hybrids were also modified in the nanometer-scale by crosslinking with glutaraldehyde (GA) during the synthesis involving hydrolysis and policondensation of PVA/TEOS. The hybrids were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Small Angle X-ray Scattering (SAXS) and Scanning Electron Microscopy (SEM). FTIR spectra have shown major vibration bands associated with organic-inorganic chemical groups present in the hybrid composite PVA/TEOS. Also, typical absorption bands related to glutaraldehyde alkyl chain have indicated the crosslinking reaction of the hybrid network with glutaraldehyde (PVA/TEOS/GA). SAXS results have indicated different nano-ordered disperse phases for PVA, PVA/TEOS hybrid and PVA/TEOS/GA chemically crosslinked hybrid. SEM micrographs have shown morphology difference between PVA and PVA hybrid samples.

Native load-bearing proteins, such as the muscle protein titin, exhibit a remarkable degree of combined toughness, strength, and elasticity which have yet to be matched by synthetic materials.Single molecule nanomechanical studies on titin and other modular proteins suggest that these exceptional properties arise from a modular elongation mechanism. The sequential unfolding allows modular biopolymers to sustain a large force over the whole extension of the chain, which makes the polymer strong, along with a large area under the force-extension curve, making it tough as well. In addition, when the external force is removed, the unfolded domains of modular proteins will refold automatically, making them elastic. Inspired by nature, one research effort in my group is aimed at designing synthetic macromolecules that form high order structures by programming non-covalent interactions into polymer chain. The goal is to achieve synthetic biomaterials with combined strength, toughness and elasticity. Three classes of well-defined modular polymers have been synthesized in our laboratory: (1) using quadruple hydrogen-bonding motif 2-ureidon-4-pyrimidone (Upy) to direct the formation loops along a polymer chain (J. Am. Chem. Soc.2004, 126, 2058); (2) using a peptidomimetic beta-sheet based double-closed loop (DCL) as module (J. Am. Chem. Soc.2004, 126, 14328); and (3) an engineered protein G domain III as module. Single molecule force-extension experiments revealed the sequential unfolding of the loops or domains as these modular polymers are stretched, resulting in sawtooth-patterned curves similar to those seen in titin and other biopolymers. In this paper, we will discuss our designs, syntheses and single-molecule studies of polymers having modular domain structures.

Environmentally friendly organic-inorganic hybrid materials with repellent activity against marine fouling organisms have been developed using interpenetrating polymer networks (IPNs), composed of a three-dimensional silica matrix of tetraethoxysilane (TEOS) and chain-like polymers, such as poly(methylmethacrylate) (PMMA) and poly(vinylacetate) (PVAc). The repellent activity of the IPNs reached a maximum of approximately 90% relative to that of tetrabutyl tin oxide (TBTO). Simple bioassays using blue mussels and algae were used to screen out the adequate proportions of those components.