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PubMed2005

Preparation of a chemically anchored phospholipid monolayer on an acrylated polymer substrate.

This paper describes a strategy for designing a chemically anchored phospholipid monolayer that could be used as coating materials for biomedical implants. To make a chemically anchored phospholipid monolayer on the polymer substrate, we prepared the mono-acrylated phospholipid (1-palmitoyl-2-[12-(acryloyloxy)-dodecanoyl]-sn-glycero-3-phosphocholine; acryloyl-PC) and the acrylated polymer (poly(octadecylacrylate-co-4-acryloyloxy butylacrylate)), which was synthesized by the acrylation of poly(octadecyl acrylate-co-hydroxybutyl acrylate, poly(OA-co-HA)) with acryloyl chloride. The chemically anchored phospholipid monolayer was prepared by using in situ photopolymerization of a pre-assembled phospholipid monolayer, produced by lipid vesicle fusion, onto the acrylated polymer coated silicon wafer. Optimal condition of vesicle fusion and irradiation time was determined from the degree of hydrophilicity rendered by the polymerized phospholipid surface. The physicochemical properties of polymerized phospholipid monolayer on the substrate were evaluated using water contact angle, field-emission scanning electron micrograph (FE-SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). These results confirmed that the polymerized phospholipid monolayer was chemically anchored on the acrylated polymer substrate. The chemically anchored phospholipid monolayer was stable in aqueous condition for 2 weeks, but the physically adsorbed phospholipid monolayer got removed within 1 day. Moreover, the polymerized phospholipid monolayer also suppressed albumin absorption and platelet adhesion, in vitro. This polymerized phospholipid monolayer provides a new biomimetic system for coating medical devises.

Acrylates↗

PubMed2005

The effect of the surface modification of titanium using a recombinant fragment of fibronectin and vitronectin on cell behavior.

The surface of titanium implants is in direct contact with host tissue and plays a critical role in determining biocompatibility. Fibronectin (FN) and vitronectin (VN) are major cell adhesive proteins found in the extracellular matrix (ECM) of various tissues, and in circulating blood. The aim of this study was to evaluate the engineered biomimetic surface of titanium by using recombinant fragment of FN(8-10) and VN(NTD) that contains the binding site for integrins. MC3T3-E1 cells seeded upon the FN(8-10)-coated titanium showed a marked increase in cell adhesion, proliferation, and differentiation over VN(NTD)-coated titanium. In addition, we confirmed that the surface properties of titanium prefer for FN(8-10) over VN(NTD) (p<0.05) in protein adhesion. These results suggest that the FN(8-10)-modified titanium surface can be used to improve the osseointegration of titanium implants by enhancing bone formation.

3T3 Cells↗

PubMed2005

Electrospun protein fibers as matrices for tissue engineering.

Electrospinning has recently emerged as a leading technique for generating biomimetic scaffolds made of synthetic and natural polymers for tissue engineering applications. In this study, we compared collagen, gelatin (denatured collagen), solubilized alpha-elastin, and, as a first, recombinant human tropoelastin as biopolymeric materials for fabricating tissue engineered scaffolds by electrospinning. In extending previous studies, we optimized the shape and size (diameter or width) of the ensuing electrospun fibers by varying important parameters of the electrospinning process, such as solute concentration and delivery rate of the polymers. Our results indicate that the average diameter of gelatin and collagen fibers could be scaled down to 200-500 nm without any beads, while the alpha-elastin and tropoelastin fibers were several microns in width. Importantly, and contrary to any hitherto reported structures of electrospun polymers, fibers composed of alpha-elastin, especially tropoelastin, exhibited "quasi-elastic" wave-like patterns at increased solution delivery rates. The periodicity of these wave-like tropoelastin fibers was partly affected by the delivery rate. Atomic force microscopy was utilized to profile the topography of individual electrospun fibers and microtensile testing was performed to measure their mechanical properties. Cell culture studies confirmed that the electrospun engineered protein scaffolds support attachment and growth of human embryonic palatal mesenchymal (HEPM) cells.

Animals↗

PubMed2005

Soluble osteogenic molecular signals and the induction of bone formation.

The induction of bone formation starts by erecting scaffolds of smart biomimetic matrices acting as insoluble signals affecting the release of soluble osteogenic molecular signals. The cascade of bone differentiation by induction develops as a mosaic structure singly initiated by the osteogenic proteins of the transforming growth factor-beta (TGF-beta) supergene family. The osteogenic signals when combined with an insoluble signal or substratum initiate de novo bone formation by induction and are deployed singly, synergistically and synchronously to sculpt the architecture of the mineralized bone/bone marrow organ. The osteogenic proteins of the TGF-beta superfamily are the common molecular initiators deployed for embryonic development and the induction of bone in postnatal osteogenesis, whereby molecules exploited in embryonic development are re-deployed in postnatal tissue morphogenesis as a recapitulation of embryonic development. The pleiotropy of the osteogenic proteins of the TGF-beta superfamily is highlighted by the apparent redundancy of molecular signals initiating bone formation by induction including the TGF-beta isoforms per se, powerful inducers of endochondral bone but in the primate only. Bone induction by the TGF-beta isoforms in the primate is site and tissue specific with substantial endochondral bone induction in heterotopic sites but with absent osteoinductivity in orthotopic calvarial sites on day 30 and only limited osteogenesis pericranially on day 90. Ebaf/Lefty-A, a novel member of the TGF-beta superfamily, induces chondrogenesis in calvarial defects of Papio ursinus and bone regeneration across the defect on day 30 and 90, respectively. The strikingly pleiotropic effects of the bone morphogenetic and osteogenic proteins (BMPs/OPs) spring from amino acid sequence variations in the carboxy-terminal domain and in the transduction of distinct signalling pathways by individual Smad proteins after transmembrane serine/threonine kinase complexes of type I and II receptors. Predictable bone regeneration in clinical contexts requires information concerning the expression and cross regulation of gene products of the TGF-beta superfamily. OP-1, BMP-3, TGF-beta1 and type IV collagen mRNAs expression correlates to the morphological induction and maintenance of engineered ossicles by the hOP-1 osteogenic devices in the non-human primate P. ursinus. Amino-acid sequence variations amongst BMPs/OPs in the carboxy terminal domain confer the structure/activity profile responsible for the pleiotropic activity that controls tissue induction and morphogenesis of a variety of tissues and organs by different BMPs/OPs which are helping to engineer skeletal tissue regeneration in molecular terms.

Animals↗

PubMed2005

The effect of structural alterations of PEG-fibrinogen hydrogel scaffolds on 3-D cellular morphology and cellular migration.

The need for alternative scaffolds in tissue engineering has motivated the establishment of advanced biomaterial technologies based on biosynthetic polymers. Networks of synthetic and biologic building blocks are created into a biomimetic environment for enhanced tissue compatibility with precise structural properties. The current investigation describes a unique biosynthetic hybrid scaffold comprised of synthetic polyethylene glycol (PEG) and endogenous fibrinogen precursor molecules. The PEGylated fibrinogen is cross-linked using photoinitation in the presence of cells to form a dense cellularized hydrogel network. The fibrin-like scaffold material maintains its biofunctionality through the fibrinogen backbone, while changes in the molecular architecture of the synthetic precursor are used to alter the nanostructrual properties of the scaffold, including mesh size and permeability. The structural properties of 6- and 10-kDa PEG-fibrinogen hydrogels are characterized by measuring the swelling properties and relating them to the degradation kinetics of the scaffold. Increased concentrations of the synthetic PEG are used to further alter the network structure of the PEG-fibrinogen hydrogel. Experiments using smooth muscle cells cultured inside the PEG-fibrinogen scaffold demonstrates a qualitative relationship between the molecular architecture of the matrix and the cellular morphology. A quantitative assessment of cell migration into the hydrogel network demonstrates a strong correlation between rate of cellular invasion and the network structure of the matrix. The ability to regulate cellular characteristics using structural modifications to the PEG-fibrinogen scaffold can be a valuable tool in tissue engineering and tissue regeneration.

Animals↗

PubMed2006

The development and characterization of a glutathione-sensitive cross-linked polyethylenimine gene vector.

A glutathione-sensitive cross-linked polyethylenimine gene vector CLPEI(50%) was specially designed via the cross-linking reaction between the low molecular weight polyethylenimine (PEI(1800)) and dimethyl 3.3'-dithiopropionimidate dihydrochloride (DTBP). The acid-base titration test indicated that CLPEI(50%) still possessed efficient proton sponge effect. The property of CLPEI(50%)-DNA complexes were investigated by atomic force microscopy (AFM) and dynamic light scattering (DLS). CLPEI(50%) induced DNA condensation and formed spherical nanoparticles. The diameter of polyplexes prepared at pH value of 6.0 and 7.4 was about 150 and 260 nm, respectively. It was interesting to find the polyplexes were sensitive to the reductive glutathione (GSH). The CLPEI(50%)-DNA polyplexes prepared at N/P ratio of 10 were unpacked at GSH concentration of 3mm, which was comparable to the intracellular environment. The in vitro cytotoxicity of CLPEI(50%) was also significantly reduced comparing with PEI(25k). The biomimetic CLPEI(50%)-DNA polyplexes with the low cytotoxicity and GSH-sensitive property could be a good candidate for gene delivery.

Animals↗

PubMed2004

Biomaterials in total joint replacement.

The current state of materials systems used in total hip replacement is presented in this paper. An overview of the various material systems used in total hip replacement reported in literature is presented in this paper. Metals, polymers, ceramics and composites are used in the design of the different components of hip replacement implants. The merits and demerits of these material systems are evaluated in the context of mechanical properties most suitable for total joint replacement such as a hip implant. Current research on advanced polymeric nanocomposites and biomimetic composites as novel materials systems for bone replacement is also discussed. This paper examines the current research in the materials science and the critical issues and challenges in these materials systems that require further research before application in biomedical industry.

Alloys↗

PubMed2005

Magnetic field induced synthesis and self-assembly of super paramagnetic particles in a protein matrix.

Aqueous solution of a globular protein named bovine serum albumin was homogeneously mixed with ferrous and ferric ions and allowed to gel at ambient conditions. Gels were then oxidized using sodium hydroxide, in the presence of magnetic field of magnitude 0.13 T. The effect of magnetic field on the above biomimetic synthesis was a reduction in particle size and a directional assembly of synthesized super paramagnetic particles into a regular pattern in the protein film. The microstructural revelation was complimentary to Mossbauer results and magnetic measurement studies, i.e., an interesting variation in the magnetic behaviour of self-assembled super paramagnetic particles as a function of dc magnetic field induced ordering.

Biomimetic Materials↗

PubMed2006

Protein-mediated nanoscale biotemplating.

Biomimetics--the concept of taking ideas from nature and implementing them in technology--has found particular use for the development of nanoscale materials. One such approach employs protein-mediated biotemplating for the nanostructuring of inorganic material. Recently, two key advances have been witnessed in this field. Firstly, the number of successfully employed biotemplates, including feasibility demonstrations of using three-dimensional crystalline structures, has been expanded. Secondly, the introduction of site-directed mutations on the protein template, or the display of peptides that exhibit effective biorecognition sequences for inorganic structures, has led to substantial improvements in our ability to control protein-mediated biotemplating. Taken together, these achievements will pave the way for the successful application of protein-mediated biotemplating in the future.

Binding Sites↗

PubMed2006

Assessing the aquatic hazard of commercial hydrocarbon resins.

Hydrocarbon resins are used to modify polymer products to achieve desired functional properties for a diverse range of products. These complex hydrocarbon-based mixtures are typically poorly soluble in water. However, resins may leach lower-molecular-weight monomers or impurities upon contact with water, thus posing a potential hazard to the aquatic environment. The bioavailability and toxicity of leachable constituents of four solid and three liquid resins were evaluated by analyzing water-accommodated fractions prepared with each resin, using biomimetic solid phase microextraction (SPME) techniques. Liquid resins exhibited concentrations of bioavailable constituents that were sufficiently elevated to cause acute toxicity to the aquatic organism Daphnia magna. All solid resins exhibited lower bioavailable concentrations of leachable constituents that were unlikely to pose an aquatic toxicity concern. Since observed toxicity of both resin types was generally consistent with bioavailable concentrations determined using SPME fiber measurements, it is concluded that this approach provides a convenient in vitro screening tool that can help reduce the use of animal testing in environmental hazard assessment of complex hydrocarbon-based substances.

Animal Testing Alternatives↗

PubMed2005

Oxidative metabolism of 5-o-caffeoylquinic acid (chlorogenic acid), a bioactive natural product, by metalloporphyrin and rat liver mitochondria.

Synthetic metalloporphyrins, in the presence of monooxygen donors, are known to mimic the various reactions of cytochrome P450 enzymes systems in the oxidation and oxygenation of various drugs and biologically active compounds. This paper reports an HPLC-MS-MS investigation of chlorogenic acid (CGA) oxidation by iodosylbenzene using iron(III) tetraphenylporphyrin chloride as catalyst. The oxidation products have been detected by sequential MS analyses. In addition, CGA was submitted to an in vitro metabolism assay employing isolated rat liver mitochondria. The single oxidized product obtained from mitochondrial metabolism corresponds to the major product formed by the metalloporphyrin-catalyzed reaction. These results indicate that biomimetic oxidation reactions, in addition to in vitro metabolism assays employing isolated organs/organelles, could replace some in vivo metabolism studies, thus minimizing the problems related to the use of a large number of living animals in experimental research.

Animals↗

PubMed2004

A novel method for biomaterial scaffold internal architecture design to match bone elastic properties with desired porosity.

An often-proposed tissue engineering design hypothesis is that the scaffold should provide a biomimetic mechanical environment for initial function and appropriate remodeling of regenerating tissue while concurrently providing sufficient porosity for cell migration and cell/gene delivery. To provide a systematic study of this hypothesis, the ability to precisely design and manufacture biomaterial scaffolds is needed. Traditional methods for scaffold design and fabrication cannot provide the control over scaffold architecture design to achieve specified properties within fixed limits on porosity. The purpose of this paper was to develop a general design optimization scheme for 3D internal scaffold architecture to match desired elastic properties and porosity simultaneously, by introducing the homogenization-based topology optimization algorithm (also known as general layout optimization). With an initial target for bone tissue engineering, we demonstrate that the method can produce highly porous structures that match human trabecular bone anisotropic stiffness using accepted biomaterials. In addition, we show that anisotropic bone stiffness may be matched with scaffolds of widely different porosity. Finally, we also demonstrate that prototypes of the designed structures can be fabricated using solid free-form fabrication (SFF) techniques.

Animals↗

PubMed2005

Sulfur ligation in copper enzymes and models.

Biological copper-sulfur entities display versatile and unusual coordination chemistry. The role of the sulfur ligation is briefly reviewed through examples from selected copper enzymes and relevant biomimetic models. Copper thiolate complexes are of particular interest because of their key roles in a number of ubiquitous metalloenzymes such as Type I (blue copper proteins) or in the binuclear Cu(A) electrons transfer site found in both cytochrome c oxidase (CcO) and nitrous oxide reductase (N2OR). The possible roles of the S(Met) ligand in monoxygenases are described in relation to recently proposed pathways. Some prospective regarding the biological relevance of disulfide copper ligation and possible radical copper bonds in catalytic cycle are also discussed.

Biomimetic Materials↗

PubMed2006

Spectroscopy and electronic structures of mono- and binuclear high-valent non-heme iron-oxo systems.

High-valent iron-oxo intermediates are known or believed to be key oxidizing species in the catalytic mechanisms of many mononuclear and binuclear non-heme iron enzymes. So far only limited experimental data on their electronic structures are available. In this study we extend knowledge from the experimentally well characterized mononuclear Fe(IV)=O (S=1) biomimetic model system to computational insight into the spectroscopy and electronic structures of mono-and binuclear high-valent iron-oxo enzyme intermediates. In the mononuclear Fe(IV)=O complexes, we predict the spectroscopy and energies of the electronic transitions to be very different for the S=1 and S=2 spin states, but the iron-oxo bonding for both spin states to be very similar. A comparison of the S=2 mono- and binuclear high-valent iron-sites predicts similar electronic transitions. However, the bent iron-oxo bridge and interactions with the second iron-center in the dimer shift the transitions to higher energies and splits the d(xz/yz) orbital set. These electronic structure and TD-DFT results provide a basis for understanding the spectroscopy and electronic structures of high-valent intermediates in mono- and binuclear non-heme iron enzymes.

Biomimetic Materials↗

PubMed2005

Deconstructing the design of a biological material.

By identifying the functional conflicts in its design, the cuticle of arthropods can be shown to cope with IR and UV irradiation in the same manner as our technology-by controlling spectral properties (transmission and reflection). However, the skeletal properties of cuticle are integrated with demands for sensory transmission, movement, etc, by controlling the local properties of the material rather than by changing global parameters (which would be the technical solution). On the basis of this study, the biomimetic similarity of cuticle with technology is only about 20%, suggesting that we can learn from the design of arthropod cuticle.

Animals↗

PubMed2006

Schwarz meets Schwann: design and fabrication of biomorphic and durataxic tissue engineering scaffolds.

Tissue engineering is a discipline at the leading edge of the field of computer assisted intervention. This multidisciplinary engineering science attempts to meet the reparative and regenerative needs of tissues and organs based on the notion of design and fabrication of scaffolds- porous, three-dimensional "trellis-like" biomimetic structures that, on implantation, provide a viable environment to recuperate and regenerate damaged cells. Existing scaffold fabrication strategies produce sub-optimal porous labyrinths with contra-naturam straight edges. The biomorphic geometry that mimics the secundam-naturam substrate would be one that is continuous through all space, partitioned into two not-necessarily-equal sub-spaces by a non-intersecting, two-sided surface. Minimal surface geometry is not only ideal to describe such a space but is also the preferentially assumed geometry in natural and pathological or manipulated cells. We present results on the premier attempt in computer-controlled fabrication, modulation, and mechanical characterization of tissue engineering scaffolds based on triply periodic minimal surfaces (TPMS). We also present novel strategies to realize coterminous seeding-feeding networks thereby guaranteeing blood/nutrient supply to the proliferating cells at close proximity. This initiative of linking Schwann's 1838 cell theory with Schwarz's 1865 discovery of TPMS is a significant step to fabricate the previously elusive optimal biomorphic tissue analogs.

Animals↗

PubMed2004

Lessons from seashells: silica mineralization via protein templating.

Silica, the most abundant compound in the earth's crust, is also widespread in biological systems. Silica has many functions, including support and protection in single-celled organisms and in higher plants and animals alike. Despite this widespread occurrence and importance of function, little is known about biosilica and the mechanisms that produce controlled microscopic and macroscopic silica structures with nanoscale precision, exceeding present synthetic technological approaches. Here we highlight recent progress in identifying proteins, genes and the various environmental factors responsible for the controlled synthesis of silica by marine organisms. Examples of biomimetic approaches to biosilica formation using model peptides to control the formation of structures through manipulation of the processing environment are discussed.

Animals↗

PubMed2003

Sound velocity determination in gel-based emulsions.

Sound velocity is a main parameter in non destructive characterization, closely related to the elastic properties and to the microstructure of heterogeneous materials. The accurate determination of the sound velocity using pulse-echo technique relies on the ability to reduce pulse distortion and to measure specimen dimensions with a high precision. In the field of bio-mimetic materials and biological tissues, the nature of the specimen makes this last requirement highly difficult or inappropriate. The present work, using a through-transmission configuration, allows, in a stress free environment, to access the sound velocity in soft, low acoustic contrast materials without requiring the specimen dimensions. The specimen sound velocity is obtained from the echo time-of-flights through a Z-scan process providing the absolute medium sound velocity as reference. The technique uses an excitation burst at a frequency below the transducer resonance to ensure a significantly reduction in pulse distortions and improve signal-to-noise ratio. The accurate determination of the echo time-of-flight relies on a highly efficient cross-correlation/Hilbert transform signal processing. The method has been applied to gel-based emulsions of different microstructures considered as biomimetic phantoms, as well as to their constituents: pure gelatin and vegetable oil.

Biomimetic Materials↗