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PubMed2006

Tuning peptoid secondary structure with pentafluoroaromatic functionality: a new design paradigm for the construction of discretely folded peptoid structures.

Peptoids, or oligomers of N-substituted glycine, are an important class of non-native polymers whose close structural similarity to natural alpha-peptides and ease of synthesis offer significant advantages for the study of biomolecular interactions and the development of biomimetics. Peptoids that are N-substituted with alpha-chiral aromatic side chains have been shown to adopt either helical or "threaded loop" conformations, depending upon solvent and oligomer length. Elucidation of the factors that impact peptoid conformation is essential for the development of general rules for the design of peptoids with discrete and novel structures. Here, we report the first study of the effects of pentafluoroaromatic functionality on the conformational profiles of peptoids. This work was enabled by the synthesis of a new, alpha-chiral amine building block, (S)-1-(pentafluorophenyl)ethylamine (S-2), which was found to be highly compatible with peptoid synthesis (delivering (S)-N-(1-(pentafluorophenyl)ethyl)glycine oligomers). The incorporation of this fluorinated monomer unit allowed us to probe both the potential for pi-stacking interactions along the faces of peptoid helices and the role of side chain electrostatics in peptoid folding. A series of homo- and heteropeptoids derived from S-2 and non-fluorinated, alpha-chiral aromatic amide side chains were synthesized and characterized by circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy. Enhancement of pi-stacking by quadrupolar interactions did not appear to play a significant role in stabilizing the conformations of heteropeptoids with alternating fluorinated and non-fluorinated side chains. However, incorporation of (S)-N-(1-(pentafluorophenyl)ethyl)glycine monomers enforced helicity in peptoids that typically exhibit threaded loop conformations. Moreover, we found that the incorporation of a single (S)-N-(1-(pentafluorophenyl)ethyl)glycine monomer could be used to selectively promote looped or helical structure in this important peptoid class by tuning the electronics of nearby heteroatoms. The strategic installation of this monomer unit represents a new approach for the manipulation of canonical peptoid structure and the construction of novel peptoid architectures.

Amides↗

PubMed2007

Synthetic control over magnetic moment and exchange bias in all-oxide materials encapsulated within a spherical protein cage.

This work focuses on the synthetic control of magnetic properties of mixed oxide magnetic nanoparticles of the general formula Fe(3-x)Co(x)O(4) (x < or = 0.33) in the protein cage ferritin. In this biomimetic approach, variations in the chemical synthesis result in the formation of single-phase Fe(3-x)Co(x)O(4) alloys or intimately mixed binary phase Fe/Co oxides, modifying the chemical structure and magnetic behavior of these particles, as characterized by static and dynamic magnetization measurements and X-ray absorption spectroscopy.

Alloys↗

PubMed2006

Design of a novel fibronectin-mimetic peptide-amphiphile for functionalized biomaterials.

The interaction of the alpha5beta1 integrin with its ligand, fibronectin, supports numerous adhesive functions and has an important role in health and disease. In recent years, there has been a considerable effort in designing fibronectin-mimetic peptides to target the integrin. However, to date, the therapeutic use of these peptides has been limited, as they cannot accurately mimic fibronectin's binding affinity for alpha5beta1. A peptide-amphiphile (PR_b) was synthesized with a peptide headgroup composed of four building blocks: a spacer; RGDSP, the primary recognition site for alpha5beta1; PHSRN, the synergy binding site; and a linker. The linker was designed to mimic two important criteria: the distance and the hydrophobicity/hydrophilicity between PHSRN and RGD in fibronectin. Human umbilical vein endothelial cells were seeded on different substrates and evaluated in terms of adhesion, spreading, specificity, cytoskeleton organization, focal adhesions, and secretion of extracellular fibronectin. This peptide was shown to perform comparably to fibronectin, indicating that a biomimetic approach can result in the design of novel peptides with therapeutic potential for biomaterial functionalization.

Biomimetic Materials↗

PubMed2006

Engineered wettability in tree capillaries.

The water-conducting network of capillaries in plants has evolved to cope with the frequent occurrence of cavitation, which leads to air-filled capillaries that are unable to function in water transport. However, the material from which the capillaries are constructed is not perfectly wetted by water, contrary to what is often assumed and to what one might expect in an optimal design. I demonstrate that nature is able to overcome this deficiency by engineering the roughness of the capillary walls to achieve near complete wetting, a strategy analogous to that used in the natural engineering of the wettability of plant leaves and insect wings. The results provide an appealing answer to the long-standing debate on the function of wall sculpturing in plant capillaries, and may provide biomimetic clues for the engineering of wettability in technological applications such as microfluidics.

Biomimetics↗

PubMed2003

Fibronectin fragment promotes osteoblast-associated gene expression and biological activity of human osteoblast-like cell.

A fibronectin fragment, which spans from the ninth to tenth type III domain, showed > 95% biological activity in promoting osteoblast adhesion, proliferation and differentiation level compared with those of native fibronectin (FN) molecule. This suggests that the FN type III ninth-tenth domain fragment serves a good substitute for native FN in biomimetic application for osteogenesis.

Biomimetics↗

PubMed2004

Pre-mineralisation of starch/polycrapolactone bone tissue engineering scaffolds by a calcium-silicate-based process.

This work describes a new methodology to produce bioactive coatings on the surface of starch-based biodegradable polymers or other degradable polymeric biomaterials. As an alternative to the more typical bioactive glass precursors, a calcium silicate gel is being employed as a nucleating agent, for inducing the biomimetic formation of a calcium-phosphate (Ca-P) layer. The method has the advantage of being able to coat efficiently both compact materials and porous 3-D architectures aimed at being used on tissue replacement applications and as bone tissue engineering scaffolds. This treatment is also very effective in reducing the incubation periods, being possible to observe the formation of an apatite-like layer, only after 12 h of immersion in a simulated body fluid (SBF). The apatite coatings formed on the compact surfaces or along the fibres of a fibre mesh scaffold structure made from a starch/polycrapolactone blend (SPCL) were analysed and compared in terms of morphology, chemical composition and structure. After the first days of SBF immersion, the apatite-like films exhibit the typical cauliflower like morphology. With increasing immersion times, these films exhibited a partially amorphous nature and the Ca/P ratios became very closer to the value attributed to hydroxyapatite (1.67). It was possible to fully pre-mineralise the SPCL scaffolds and simultaneously to keep the porous morphology of the fibre-bonded scaffold.

Absorption↗

PubMed2003

Fabrication of microfluidic mixers and artificial vasculatures using a high-brightness diode-pumped Nd:YAG laser direct write method.

This paper describes a direct write laser technology, which is fast and flexible, for fabricating multiple-level microfluidic channels. A high brightness diode-pumped Nd-YAG laser with slab geometry was used for its excellent beam quality. Channels with flat walls and staggered herringbone ridges on the floor have been successfully fabricated and their ability to perform passive mixing of liquid is discussed. Also, a multi-width multi-depth microchannel has been fabricated to generate biomimetic vasculatures whose channel diameters change according to Murray's law, which states that the cube of the radius of a parent vessel equals the sum of the cubes of the radii of the daughters. The multi-depth architecture allows for flow patterns to resemble physiological vascular systems with lower overall resistance and more uniform flow velocities throughout the network compared to planar patterning techniques which generate uniformly thin channels. The ability to directly fabricate multiple level structures using relatively straightforward laser technology enhances our ability to rapidly prototype complex lab-on-a-chip systems and to develop physiological microfluidic structures for tissue engineering and investigations in biomedical fluidics problems.

Biomimetics↗

PubMed2006

Can an ancillary ligand lead to a thermodynamically stable end-on 1 : 1 Cu-O2 adduct supported by a beta-diketiminate ligand?

The finding that dioxygen binds end-on to the Cu(B) site in the crystal structure of a precatalytic complex of peptidylglycine alpha-hydroxylating monooxygenase has spurred the search for biomimetic model complexes exhibiting the same dioxygen coordination. Recent work has not only indicated that sterically hindered beta-diketiminate ligands (L(1)) could support side-on 1 : 1 Cu-O(2) adducts, but also that an end-on L(1)Cu(THF)O(2) structure occurs as an unstable intermediate in the oxygenation mechanism of the Cu(I) complex. In this work, density functional theory and multireference methods are used to determine the potential of ancillary ligands, X, other than THF to yield thermodynamically stable end-on L(1)CuXO(2) species. A diverse set of ligands X, comprising phosphines, thiophene, cyclic ethers, acetonitrile, para-substituted pyridines, N-heterocyclic carbenes, and ligands bearing hydrogen bond donors, has been considered in order to identify ligand characteristics which energetically favor end-on L(1)CuXO(2) over: a) reversion to the Cu(I) complex and dioxygen, b) isomerization to side-on L(1)CuXO(2), and c) decay to L(1)CuO(2) and X. Ancillary ligands with judiciously chosen degrees and orientation of steric bulk and which bear potential hydrogen bond donors to an end-on bound dioxygen moiety most favor oxygenation of L(1)CuX to yield end-on L(1)CuXO(2). Conversion to the side-on isomer can be deterred through the use of a sufficiently bulky ligand X, such as one that is at least the size of a 5-membered ring. Loss of X to give L(1)CuO(2) can be made prohibitively endergonic by employing ligands X which are highly electron donating and which backbond strongly with and sigma-donate significantly to copper.

Binding Sites↗

PubMed2006

The microwave spectrum of a two-top peptide mimetic: the N-acetyl alanine methyl ester molecule.

The rotational spectrum of N-acetyl alanine methyl ester, a derivative of the biomimetic, N-acetyl alanine N'-methyl amide or alanine dipeptide, has been measured using a mini Fourier transform spectrometer between 9 and 25 GHz as part of a project undertaken to determine the conformational structures of various peptide mimetics from the torsion-rotation parameters of low-barrier methyl tops. Torsion-rotation splittings from two of the three methyl tops capping the acetyl end of the -NH-C(=O)- and the methoxy end of -C(=O)-O- groups account for most of the observed lines. In addition to the AA state, two E states have been assigned and include an AE state having a torsional barrier of 396.45(7) cm(-1) (methoxy rotor) and an EA state having a barrier of 64.96(4) cm(-1) (acetyl rotor). The observed torsional barriers and rotational constants of alanine dipeptide and its methyl ester are compared with predictions from Möller-Plesset second-order perturbation theory (MP2) and density functional theory (DFT) in an effort to explore systematic errors at the two levels of theory. After accounting for zero-point energy differences, the torsional barriers at the MP2/cc-pVTZ level are in excellent agreement with experiment for the acetyl and methoxy groups while DFT predictions range from 8% to 80% too high or low. DFT is found to consistently overestimate the overall molecular size while MP2 methods give structures that are undersized. Structural discrepancies of similar magnitude are evident in previous DFT results of crystalline peptides.

Alanine↗

PubMed2006

Clotrimazole inhibits the Ca2+-ATPase (SERCA) by interfering with Ca2+ binding and favoring the E2 conformation.

Clotrimazole (CLT) is an antimycotic imidazole derivative that is known to inhibit cytochrome P-450, ergosterol biosynthesis and proliferation of cells in culture, and to interfere with cellular Ca(2+) homeostasis. We found that CLT inhibits the Ca(2+)-ATPase of rabbit fast-twitch skeletal muscle (SERCA1), and we characterized in detail the effect of CLT on this calcium transport ATPase. We used biochemical methods for characterization of the ATPase and its partial reactions, and we also performed measurements of charge movements following adsorption of sarcoplasmic reticulum vesicles containing the ATPase onto a gold-supported biomimetic membrane. CLT inhibits Ca(2+)-ATPase and Ca(2+) transport with a K(I) of 35 mum. Ca(2+) binding in the absence of ATP and phosphoenzyme formation by the utilization of ATP in the presence of Ca(2+) are also inhibited within the same CLT concentration range. On the other hand, phosphoenzyme formation by utilization of P(i) in the absence of Ca(2+) is only minimally inhibited. It is concluded that CLT inhibits primarily Ca(2+) binding and, consequently, the Ca(2+)-dependent reactions of the SERCA cycle. It is suggested that CLT resides within the membrane-bound region of the transport ATPase, thereby interfering with binding and the conformational effects of the activating cation.

Adsorption↗

PubMed2006

Melanin and Glycera jaws: emerging dark side of a robust biocomposite structure.

Defining the design principles guiding the fabrication of superior biocomposite structures from an assemblage of ordinary molecules is a key goal of biomimetics. Considering their low degree of mineralization, Glycera jaws have been shown to be extraordinarily resistant to abrasion based on the metric hardness3/Young's modulus2. The jaws also exhibit an impressive chemical inertness withstanding boiling concentrated hydrochloric acid as well as boiling concentrated sodium hydroxide. A major organic component largely responsible for the chemical inertness of the jaws has been characterized using a spectrophotometric assay for melanin content, 13C solid state nuclear magnetic resonance, IR spectroscopy, and laser desorption ionization-time of flight mass spectrometry and is identified here as a melanin-like network. Although melanin is widely distributed as a pigment in tissues and other structural biomaterials, to our knowledge, Glycera jaws represent the first known integument to exploit melanin as a cohesive load- and shape-bearing material.

Animals↗

PubMedDate not supplied

Human osteoprogenitor bone formation using encapsulated bone morphogenetic protein 2 in porous polymer scaffolds.

The ability to deliver, over time, biologically active osteogenic growth factors by means of designed scaffolds to sites of tissue regeneration offers tremendous therapeutic opportunities in a variety of musculoskeletal diseases. The aims of this study were to generate porous biodegradable scaffolds encapsulating an osteogenic protein, bone morphogenetic protein 2 (BMP-2), and to examine the ability of the scaffolds to promote human osteoprogenitor differentiation and bone formation in vitro and in vivo. BMP-2-encapsulated poly(DL-lactic acid) (PLA) scaffolds were generated by an innovative supercritical fluid process developed for solvent-sensitive and thermolabile growth factors. BMP-2 released from encapsulated constructs promoted adhesion, migration, expansion, and differentiation of human osteoprogenitor cells on three-dimensional scaffolds. Enhanced matrix synthesis and cell differentiation on growth factor-encapsulated scaffolds was observed after culture in an ex vivo model of bone formation developed on the basis of the chick chorioallantoic membrane model. BMP-2-encapsulated polymer scaffolds showed morphologic evidence of new bone matrix and cartilage formation after subcutaneous implantation and within diffusion chambers implanted into athymic mice as assessed by X-ray analysis and immunocytochemistry. The generation of three-dimensional biomimetic structures incorporating osteoinductive factors such as BMP-2 indicates their potential for de novo bone formation that exploits cell-matrix interactions and, significantly, realistic delivery protocols for growth factors in musculoskeletal tissue engineering.

Adolescent↗

PubMed2006

Review: bioprinting: a beginning.

An increasing demand for directed assembly of biologically relevant materials, with prescribed three-dimensional hierarchical organizations, is stimulating technology developments with the ultimate goal of re-creating multicellular tissues and organs de novo. Existing techniques, mostly adapted from other applications or fields of research, are capable of independently meeting partial requirements for engineering biological or biomimetic structures, but their integration toward organ engineering is proving difficult. Inspired by recent developments in material transfer processes operating at all relevant length scales--from nano to macro--which are amenable to biological elements, a new research field of bioprinting and biopatterning has emerged. Here we present a short review regarding the framework, state of the art, and perspectives of this new field, based on the findings presented at a recent international workshop.

Biomimetics↗

PubMed2006

Calcium-binding phospholipids as a coating material for implant osteointegration.

Among the many biomolecules involved in the bone mineralization processes, anionic phospholipids play an important role because of their ability to bind calcium. In particular, phosphatidylserine is a natural component of the plasmalemma and of the matrix vesicles generated from the osteoblast membrane to create nucleation centres for calcium phosphate crystal precipitation. In the present work, we demonstrate that calcium-binding phospholipids can be used as biomimetic coating materials for improving the osteointegration of metal implants. Relatively thick phosphatidylserine-based coatings were deposited on titanium coupons by dip-coating. Upon dehydration in a simulated body fluid phospholipids were quickly crosslinked by calcium and re-arranged into a three-dimensional matrix able to induce rapid formation of a calcium phosphate mineral phase. The rate of mineralization was shown to be dependent on the adopted coating formulation. In the attempt to closely mimic the cell membrane composition, heterogeneous formulations based on the mixing of anionic phospholipids (either phosphatidylserine or phosphatidylinositol) with phosphatidylcholine and cholesterol were synthesized. However, surface plasmon resonance studies as well as scanning electron microscopy and elemental analysis demonstrated that the homogeneous phosphatidylserine coating was a more effective calcification environment than the heterogeneous formulations.

Biomimetic Materials↗

PubMed2003

Bio-inspired solutions for locomotion in the gastrointestinal tract: background and perspectives.

This paper illustrates a bio-inspired approach to effective, smooth and safe navigation in the human body and, in particular, in the gastrointestinal tract. This idea originates from the medical need to develop more powerful tools for microendoscopy, which is one of the most challenging frontiers of modern medicine. Understanding motion and perception systems of lower animal forms, such as parasites, worms, insects and snakes, can help to design and fabricate bio-inspired robots able to navigate in tortuous, slippery and difficult-to-access cavities of the human body. A preliminary study of a biomimetic adhesion system for the human tissues is presented in this work and some technological implementations are illustrated and discussed. Finally, some issues concerning the goals of smart and reactive locomotion are considered and the most promising and relevant enabling technologies are discussed.

Animals↗

PubMed2005

Synthesizing bird song.

In this work we present an electronic syrinx: an analogical integrator of the equations describing a model for sound production by oscine birds. The model depends on time varying parameters with clear biological interpretation: the air sac pressure and the tension of ventral syringeal muscles. We test the hypothesis that these physiological parameters can be reconstructed from the song. In order to do so, we built two transducers. The input for these transducers is an acoustic signal. The first transducer generates an electric signal that we use to reconstruct the bronchial pressure. The second transducer allows us to reconstruct the syringeal tension (in both cases, for the time intervals where phonation takes place). By driving the electronic syrinx with the output of the transducers we generate synthetic song. Important qualitative features of the acoustic input signal are reproduced by the synthetic song. These devices are especially useful to carry out altered feedback experiences, and applications as biomimetic resources are discussed.

Animals↗

PubMed2003

Concentration-independent spontaneously forming biomimetric vesicles.

In this Letter we present small-angle neutron scattering data from a biomimetic system composed of the phospholipids dimyristoyl and dihexanoyl phosphorylcholine (DMPC and DHPC, respectively). Doping DMPC-DHPC multilamellar vesicles with either the negatively charged lipid dimyristoyl phosphorylglycerol (DMPG, net charge -1) or the divalent cation, calcium (Ca2+), leads to the spontaneous formation of energetically stabilized monodisperse unilamellar vesicles whose radii are concentration independent and in contrast with previous experimental observations.

Biomimetic Materials↗

PubMed2006

Complementary control by additives of the kinetics of amorphous CaCO3 mineralization at an organic interface: in-situ synchrotron x-ray observations.

The kinetics of biomimetic mineralization at a fatty acid monolayer interface have been measured in situ by synchrotron x-ray reflectivity. The formation of biologically relevant amorphous calcium carbonate films is affected by soluble macromolecules, supersaturation rate of change, and Mg cations. We find that these solution conditions influence mineral film formation in a complementary fashion. Poly(sodium acrylate) extends the lifetime of metastable amorphous calcium carbonate, solution saturation controls the mineral film growth rate, and Mg cations create a longer induction time. This is the first quantification of potentially competitive biomineralization mechanisms that addresses nucleation and growth of the amorphous mineral phases, which are important in biomineralization.

Biomimetic Materials↗