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PubMed2007

In vivo response to starch-based scaffolds designed for bone tissue engineering applications.

Our purpose was to evaluate the in vivo endosseous response to three starch-based scaffolds implanted in rats (n = 54). We implanted the three scaffold groups; a 50/50 (wt %) blend of corn starch and ethylene-vinyl alcohol (SEVA-C), the same composition coated with a biomimetic calcium phosphate (Ca-P) layer (SEVA-C/CaP), and a 50/50 (wt %) blend of corn starch and cellulose acetate (SCA), all produced by extrusion with blowing agents, into distal femurs proximal to the epiphyseal plate, for 1, 3, or 6 weeks. Our results showed that at 1 week considerable reparative bone formed around all scaffold groups, although the bone was separated from the scaffold by an intervening soft tissue interfacial zone that comprised two distinct compartments: the surface of the scaffold was occupied by multinucleate giant cells and the compartment between these cells and the surrounding bone was occupied by a streaming fibrous-like tissue. The extracellular matrix of the latter was continuous with the extracellular bone matrix itself, labeled positively for osteocalcin and appeared mineralized by back-scattered electron imaging. All three scaffolds showed a similar tissue response, with the soft tissue interface diminishing with time. No bone contact was observed with SEVA-C at any time point, only transitory bone contact was observed with SEVA-C/CaP at 3 weeks, but SCA exhibited direct bone contact at 6 weeks where 56.23 +/- 6.46% of the scaffold surface was occupied by bone. We conclude that all materials exhibited a favorable bony response and that the rapidly forming initial "connective tissue" seen around all scaffolds was a very early form of bone formation.

Animals↗

PubMed2007

Bio-mimetic composite matrix that promotes endothelial cell growth for modification of biomaterial surface.

The incidence of thrombogenesis and occlusion of cardiovascular implants is likely to be reduced by endothelial cell (EC) growth promotion on biomaterials used for device fabrication. However, proper signaling between the matrix proteins deposited on the device surface and the cells grown on it is a prime requirement for growth and function. It was demonstrated earlier that a composition of matrix proteins that include fibrin, fibronectin, gelatin, and growth factors maintain a steady proliferation potential and prolong the survival of endothelial cells in vitro. In this study, assessment of the same matrix to prevent EC from dedifferentiation during in vitro culture and to promote endothelialization of biomaterials used for fabrication of cardiovascular implants is carried out. Up/down regulation of m-RNA expression for a prothrombotic molecule-plasminogen activator inhibitor (PAI), and two antithrombotic molecules- nitric oxide synthetase (eNOS) and tissue plasminogen activator (t-PA) are chosen as the indicators of cell dedifferentiation during cell culture and passaging. Immunostaining for vinculin and actin demonstrated that composite coating on biomaterials improves focal adhesion and cytoskeletal organization that increases the quality of EC grown on it. EC proliferation, measured by (3)H-thymidine uptake, on all bare materials was poor and high incidence of cell apoptosis was noticed within 72 h in culture, whereas once coated with composite all materials showed good proliferation and survival. The results suggest that the designed composition of biomimetic adhesive proteins and growth factors is suitable for EC growth, survival, and functional integrity, thus making it suitable for cardiovascular tissue engineering that requires in vitro EC culture.

Biocompatible Materials↗

PubMed2005

In vitro response of MC3T3-E1 pre-osteoblasts within three-dimensional apatite-coated PLGA scaffolds.

Biomimetic apatites have been reported to promote osteogenic activities in numerous in vivo and in vitro models, but the precise mechanism by which the apatite microenvironment promotes such activities is not well understood. Such mechanistic studies require reproducible model systems that are relevant to tissue engineering practices. Although two-dimensional (2D) apatite-coated polystyrene culture dishes provide practicality and reproducibility, they do not simulate the effects of the three-dimensional (3D) microenvironment and degrading polymeric substrates. A simple 3D model system to address these relevant effects, and its utilization in the investigation of apatite-promoted osteoblastic differentiation in vitro is reported in this paper. Apatite coating was achieved by sequentially immersing poly(lactide-co-glycolide) (PLGA) scaffolds into different simulated body fluids (SBF). SEM, EDX, FTIR, TEM electron diffraction confirmed the apatite coating to comprise of calcium-deficient carbonated hydroxyapatite crystals. While both apatite-coated and non-coated PLGA scaffolds supported MC3T3-E1 attachment, spreading, and proliferation, significant differences in osteoblastic differentiation were observed. Relative to non-coated controls, quantitative real-time PCR revealed significant apatite-associated suppression of alkaline phosphatase (ALP), early upregulation of osteopontin (OPN) at 3 days, and upregulation of osteocalcin (OCN) and bone sialoprotein (BSP) at 4 weeks. In summary, apatite-promoted osteoblastic differentiation can be observed in a 3D model system that is relevant to tissue engineering.

Animals↗

PubMedDate not supplied

An artificial receptor for glycoproteins.

We describe the rational design, synthesis and development of a sterilizable biomimetic ligand for the affinity purification of glycoproteins. Based on mimicking the principles of natural carbohydrate recognition, a putative library of 196 glycoprotein-binding synthetic ligands was designed and synthesized on a polymeric support. Ligand 11/11, based on a triazine scaffold and immobilized on a hydrophilic support, was identified as the "lead" ligand. The carbohydrate recognizing the potential of the "lead" ligand was revealed by reduced binding of a periodate oxidized model glycoprotein, and by "sharp" elution profiles achieved with borate buffer eluents. Specific elution and competitive binding experiments determined the monosaccharide specificity of 11/11 in the order mannoside > glucoside > galactoside. The diastereo-selective performance of ligand 11/11 was quantified and reaffirmed by analytical affinity chromatography and (1)H-NMR, in the order galactoside < glucoside < mannoside with binding affinities (K(a), M(-1)) in the 63-214 and 20-83 M(-1) range, respectively. Partition coefficient analysis revealed binding constants towards glycoproteins in the 10(4) M(-1) range, that compared favourably with the affinities of carbohydrate binding lectins for glycoproteins, such as concanavalin A. Molecular modelling studies of ligand 11/11 revealed the formation of a pre-organized apolar "tweezer-like" cavity, containing complementary nitrogenous hydrogen bond donor and acceptor groups that formed selective interactions with the equatorial 3- and 4-hydroxyl groups of saccharides.

Binding Sites↗

PubMed2007

Nanobiomaterial applications in orthopedics.

Advancements in nanobiotechnology are revolutionizing our capability to understand biological intricacies and resolve biological and medical problems by developing subtle biomimetic techniques. Nanocomposites and nanostructured materials are believed to play a pivotal role in orthopedic research since bone itself is a typical example of a nanocomposite. This article reviews current strategies using nanobiomaterials to improve current orthopedic materials and examines their applications in bone tissue engineering. Preliminary investigations support the potential of nanobiomaterials in orthopedic applications; however, significant advancements are necessary to achieve clinical use. Overall, current trends in nanobiotechnology foreshadow a bright future through the use of nanobiomaterials in the orthopedic domain.

Biocompatible Materials↗

PubMed2004

Extracellular matrix-like surfactant polymers containing arginine-glycine-aspartic acid (RGD) peptides.

We report on a novel series of biomimetic polymers exhibiting interfacial properties similar to the extracellular matrix. A series of well-defined surfactant polymers were synthesized by simultaneously incorporating arginine-glycine-aspartic acid (RGD) peptide, dextran oligosaccharide, and hexyl ligands with controlled feed ratios onto a poly(vinyl amine) (PVAm) backbone. The peptide sequence was H-GSSSGRGDSPA-NH(2) (Pep) having a hydrophilic extender at the amino terminus and capped carboxy terminus. The peptide-to-dextran (Pep:Dex) ratios were varied to create surfactants having 0, 25, 50, 75, and 100 mol-% peptide relative to dextran. The surfactants were characterized by IR, NMR and atomic force microscopy (AFM) for composition and surface active properties. AFM confirmed full surface coverage of PVAm(Pep)(100%) on graphite, and supported the mechanism of interdigitation of hexyl ligands between surfactant molecules within a specified range of hexyl chain densities. the attachment and growth of human pulmonary artery endothelial cells on the PVAm(Pep)(100%) surface was identical to the fibronectin positive control. Cell adhesion decreased dramatically with decreasing peptide density on the surfactant polymers. Molecular model of a peptide surfactant polymer, consisting of poly(vinyl amine) backbone with peptide, dextran oligosaccharide and hexyl branches coupled to the polymer chain.

Absorption↗

PubMed2006

Materials for peripheral nerve regeneration.

Recent efforts in scientific research in the field of peripheral nerve regeneration have been directed towards the development of artificial nerve guides. We have studied various materials with the aim of obtaining a biocompatible and biodegradable two layer guide for nerve repair. The candidate materials for use as an external layer for the nerve guides were poly(caprolactone) (PCL), a biosynthetic blend between PCL and chitosan (CS) and a synthesised poly(ester-urethane) (PU). Blending PCL, which is a biocompatible synthetic polymer, with a natural polymer enhanced the system biocompatibility and biomimetics, fastened the degradation rates and reduced the production costs. Various novel block poly(ester-urethane)s are being synthesised by our group with tailored properties for specific tissue engineering applications. One of these poly(ester-urethane)s, based on a low molecular weight poly(caprolactone) as the macrodiol, cycloesandimethanol as the chain extender and hexamethylene diisocyanate as the chain linker, was investigated for the production of melt extruded nerve guides. We studied natural polymers such as gelatin (G), poly(L-lysine) (PL) and blends between chitosan and gelatin (CS/G) as internal coatings for nerve guides. In vitro and in vivo tests were performed on PCL guides internally coated either with G or PL to determine the differences in the quality of nerve regeneration associated with the type of adhesion protein. CS/G natural blends combined the good cell adhesion properties of the protein phase with the ability to promote nerve regeneration of the polysaccharide phase. Natural blends were crosslinked both by physical and chemical crosslinking methods. In vitro neuroblast adhesion tests were performed on CS/G film samples, PCL/CS and PU guides internally coated with G to evaluate the ability of such materials towards nerve repair.

Absorbable Implants↗

PubMed2007

Customized PEG-derived copolymers for tissue-engineering applications.

PEG-containing copolymers play a prominent role as biomaterials for different applications ranging from drug delivery to tissue engineering. These custom-designed materials offer enormous possibilities to change the overall characteristics of biomaterials by improving their biocompatibility and solubility, as well as their ability to crystallize in polymer blends and to resist protein adsorption. This article demonstrates various principles of PEG-based material design that are applied to fine tune the properties of biomaterials for different tissue engineering applications. More specifically, strategies are described to develop PEG copolymers with various block compositions and specific bulk properties, including low melting points and improved surface hydrophilicity. Highly hydrated polymer gel networks for promoting cellular growth or suppressing protein adsorption and cell adhesion are introduced. By incorporating selectively cleavable cross-links, these hydrophilic polymers can also serve as smart hydrogel scaffolds, mimicking the natural extracellular matrix for cell cultivation and tissue growth. Ultimately, these developments lead to the creation of biomimetic materials to immobilize bioactive compounds, allowing precise control of cellular adhesion and tissue growth. [image: see text]

Biocompatible Materials↗

PubMed2005

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

Tissue engineering is a discipline at the leading edge of the field of computer assisted intervention. This multidisciplinary engineering science is 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 CAD-based approaches produce 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 surfaces are ideal to describe such a space. We present results on the premier attempt in computer controlled fabrication and mechanical characterization of Triply Periodic Minimal Surfaces [TPMS]. This initiative is a significant step to link Schwann's 1838 cell theory with Schwarz's discovery of TPMS in 1865 to fabricate the previously elusive optimal biomorphic tissue analogs.

Biocompatible Materials↗

PubMed2006

The use of hydroxyl-radical-generating systems for the treatment of olive mill wastewaters.

Three hydroxyl-radical producing biomimetic systems, composed of CuII, hydrogen peroxide and pyridine, glucaric or succinic acid, were able to perform decolorization of olive mill wastewaters (OMW) >85 % within 3 d combined with a significant removal of total phenols (>75 %). The systems consisting of 50 mmol/L succinic acid, 5-10 mmol/L CuSO4 and 100 mmol/L H2O2 were the most effective at OMW treatment, and led to the reduction of phenol contents to <1 % along with high decolorization (>88 %) and acceptable values of chemical oxygen demand.

Bacteria↗

PubMed2006

Theoretical modelling of tripodal CuN3 and CuN4 cuprous complexes interacting with O2, CO or CH3CN.

Dioxygen binding at copper enzymatic sites is a fundamental aspect of the catalytic activity observed in many biological systems such as the monooxygenases, especially peptidylglycine alpha-hydroxylating monooxygenase (PHM), in which two mononuclear Cu(I) sites are involved. Biomimetic models have been developed: dipods, tripods, and, more recently, functionalized calixarenes. The modelling of calixarene systems, although not unreachable for theory yet, requires, however, a number of preliminary investigations to ensure proper calibrations if relevant description of the metal-ligand interaction at the hybrid quantum mechanical/molecular mechanics levels of theory is the aim. In this paper, we report quantum chemistry investigations on a coherent series of representative cuprous tripodal species characterized by (1) monodentate ligands [Cu(ImH)3]+ (where ImH is imidazole), [Cu(MeNH2)3]+ and [Cu(MeNH2)4]+ , (2) neutral tripodal ligands [CuCH(ImH)3]+, [Cu(tren)]+ [where tren is tris(2-aminoethyl)amine], and [Cu(trenMe3)]+ [where trenMe3 is tris(2-methylaminoethyl)amine] and (3) a hydrido-tris(pyrazolyl)borate [CuBH(Pyra)3]. The structures of these complexes, the coordination mode (eta(2) side-on or eta(1) end-on) of O2 to Cu(I) and the charge transfer from the metal to dioxygen have been computed. For some systems, the coordination by CH3CN and CO is also reported. Beyond results relative to structural properties, an interesting feature is that it is possible to build from computational results only a set of abacuses linking the nu(16O-16O) vibrational frequency of the coordinated O2 molecule to the O-O bond length or to the net charge of the O2 moiety. Such abacuses may help experimentalists in distinguishing between the four possible ways of binding O2 to CuN3 and CuN4 cuprous centres, namely (1) end-on triplet states, (2) side-on triplet states, (3) end-on singlet states and (4) side-on singlet states. These abacuses are extended to three tripods obtained by the substitution of one nitrogen atom by either a phosphorus or a sulphur atom. Moreover, it is shown that any factor favouring pyramidalization at copper favours charge transfer and thus coordination of the incoming O2 moiety. All these allow insight into the coordination mode of O2 and into the charge transfer from Cu(I) in site Cu(M) of PHM.

Acetonitriles↗

PubMed2005

Enhancement of the adhesion of fibroblasts by peptide containing an Arg-Gly-Asp sequence with poly(ethylene glycol) into a thermo-reversible hydrogel as a synthetic extracellular matrix.

In an effort to regulate the behavior of mammalian cell entrapped in a gel, the gels were functionalized with the putative cell-binding (-Arg-Gly-Asp-) (RGD) domain. The adhesion molecules composed of Gly-Arg-Gly-Asp-Ser (GRGDS) peptides and the cell recognition ligands were inculcated into the thermo-reversible hydrogel composed of N-isopropylacrylamide, with a small amount of succinyl poly(ethylene glycol) (PEG) acrylate (MW 2000) used as the biomimetic extracellular matrix (ECM). The GRGDS-containing p(NiPAAm-co-PEG) copolymer gel was examined in vitro for its ability to promote cell spreading and to increase the viability of the cells by introducing PEG spacers. ECM poorly adhered to hydrogel lacking adhesion molecules permitting only a 20% spread of the seeded cells after 10 days. When the PEG spacer arms, which were immobilized by a peptide linkage, had been integrated into the hydrogel, the conjugation of RGD improved cell spreading by 600% in a 10-day trial.

3T3-L1 Cells↗

PubMed2005

Osteogenic differentiation of mesenchymal progenitor cells in computer designed fibrin-polymer-ceramic scaffolds manufactured by fused deposition modeling.

Biomimetic scaffolds offer great potentials in the development of bone analogs for tissue engineering. The studies presented in this paper focus specifically on the osteogenic potential of the novel PCL/CaP matrices and its degradation behavior. Biodegradable Polymer-ceramic Scaffolds were fabricated using the solid free form fabrication technology: Fused Deposition Modeling (FDM). The scaffold architecture was characterized by a honeycomb-like design and a complete interconnectivity of the pores. Human mesenchymal stem cells (MSCs) were seeded together with fibrin glue into PCL/CaP scaffolds and cultured in vitro for periods of up to eight weeks. Cellular adhesion, proliferation and osteogenic differentiation were assessed in these constructs using a range of histological and microscopic techniques. In additional experiments, degradation was assessed by measuring mass loss, diameter change, molecular weight change and by scanning electron micrographs. MSCs were able to adhere, migrate, and differentiate along the osteogenic lineage with in these scaffolds. The PCL/CaP scaffolds showed up to 27 fold increased degradation of compared to PCL scaffolds.

Biodegradation, Environmental↗

PubMed2006

Calcium phosphate fibres synthesized from a simulated body fluid.

The biomimetic coating method was used for fabricating calcium phosphate fibres for biomedical applications such as bone defect fillers. Natural cotton substrate was pre-treated with phosphorylation and a Ca(OH)2 saturated solution. The pre-treated samples were then soaked in simulated body fluid (SBF) of two different concentrations, 1.5 times and 5.0 times the ion concentration of blood plasma. The cotton was then burnt out via sintering of the ceramic coating at 950 degrees C, 1050 degrees C, 1150 degrees C, and 1250 degrees C. The results demonstrated that osteoblastic cells were able to cover the entire surface cotton fibres, and the cell coverage appeared to be independent of surface roughness and Ca/P ratio of fibres.

Biocompatible Materials↗

PubMed2006

Orthodontic materials research and applications: part 1. Current status and projected future developments in bonding and adhesives.

The purpose of this opinion article, to be presented in 2 parts, is to project immediate future developments expected in orthodontic materials research and applications. Analysis of the material is structured around 2axes: presentation of evidence summarizing the current status in various fields, and formulation of a hypothesis for short-term future developments. This first part of the article deals with advances and developments in bonding to enamel. Projected adhesive developments include greater use of high-energy lamps for polymerization in light-cured systems, universal application of molar tube bonding, widespread use of self-etching primers, broader acceptance of glass ionomers in their conventional and modified modes, and elimination of 2-phase adhesives in favor of no-mix and light-cured adhesives. Long-term future adhesive applications might also include biomimetic approaches, adopting mechanisms used by living organisms to adhere to surfaces.

Biomimetic Materials↗

PubMed2003

Enhanced cell attachment and osteoblastic activity by P-15 peptide-coated matrix in hydrogels.

The cells in bone grow on a composite matrix made up of mineral and organic (mainly type-I collagen) components. In this study, anorganic bone mineral (ABM) particles were coated with a cell-binding domain of type-I collagen (P-15 peptide) to mimic the bone matrix components and suspended in injectable hyaluronate (Hy) hydrogels. The ABM/P-15/Hy was compared to ABM/Hy-the same matrix without P-15 peptide. Osteoblast-like HOS cells migrated through the hydrogels around ABM/P-15 or ABM particles; however, more cells adhered to ABM/P-15/Hy particles, and the cells formed better surface coverage and had more stress fibers on ABM/P-15/Hy. HOS cells cultured on ABM/P-15/Hy had increased osteogenic gene expression for alkaline phosphatase and bone morphogenetic proteins, and deposited more mineralized matrix. Studies with two different hydrogels (carboxymethylcellulose and sodium alginate) showed similar enhanced cell attachment and mineralization. The studies suggest that the ABM/P-15 in hydrogels can be used as an injectable biomimetic matrix to facilitate bone repair.

Biomimetic Materials↗

PubMed2004

Tethered bilayer lipid membranes self-assembled on mercury electrodes.

In order to incorporate integral proteins in a functionally active state, metal-supported lipid bilayers must have a hydrophilic region interposed between the bilayer and the metal. This region is realized with a hydrophilic molecule terminating at one end with a sulfhydryl or disulfide group that anchors this "hydrophilic spacer" to the surface of a metal, such as gold or mercury. The other end of the hydrophilic spacer may be covalently linked to the polar head of a phospholipid molecule, giving rise to a supramolecule called "thiolipid" (TL). With respect to gold, mercury has the advantage of providing a defect-free and fluid surface to the self-assembling spacer. Hydrophilic spacers consisting of a polyethyleneoxy or a hexapeptide chain, as well as thiolipids derived from these spacers, were employed to fabricate mercury-supported lipid bilayers. The formation of a lipid bilayer on top of a self-assembled monolayer of a hydrophilic spacer, or of a single-lipid monolayer on top of a self-assembled monolayer of a thiolipid, was realized by simply immersing the coated mercury electrode into an aqueous solution across a lipid film previously spread on its surface at its spreading pressure. Particularly stable mercury-supported lipid bilayers were obtained by using thiolipids. The biomimetic properties of these lipid bilayers were tested by incorporating channel-forming polypeptides (gramicidin and melittin) and proteins (OmpF porin). The effect of the transmembrane potential on the function of these channels was estimated by using a simple electrostatic model of the mercury-solution interphase.

Biomimetic Materials↗

PubMed2006

Probing organization and communication at layered interfaces.

We have investigated the local organization intrinsic to a variety of interfacial structures, by both electrochemical and spectroscopic means. Our focus has been on the design and construction of biomimetic interfaces, where a lipid bilayer or a hybrid bilayer membrane can be bound to an interface. The goal of this work is ultimately to create an interface on a transducer surface that can support an enzyme in its active form. To this point, we have examined the extent of organization that is achievable in monolayers that will be used to bind bilayer structures to a transducer surface. Our electrochemical data point to the important role of the substrate surface in determining adlayer organization. We have also investigated the fluidity and structural heterogeneity of lipid bilayers using time-resolved and steady state fluorescence spectroscopy. Our data point to the highly interactive nature of lipid bilayer constituents, where perturbations introduced to one region have significant consequences on other regions of the bilayer. Such information is directly relevant to the existence and properties of lipid raft structures in both model and biological bilayers.

Biomimetic Materials↗