The tribological behavior of crosslinked ultra-high molecular weight polyethylene (UHMWPE) was compared to that of non-crosslinked UHMWPE, used as control sample. A reciprocating pin-on-disk tribometer was used to determine the effects of countersurface roughness and conformity on wear mechanisms occurring during the initial stage of sliding. Pin samples of two different radii of curvature were slid against medical-grade Co-Cr alloy disks with surface roughness ranging from 0.005 to 0.04 μm in a lubricant of bovine serum. Normal loads were chosen to provide physiological contact stresses. The focus of this study was on the dependence of early wear mechanisms on surface roughness and conformity. Although a correlation between coefficient of friction data and dominant wear mechanisms was not observed, different wear mechanisms were found between control and crosslinked UHMWPE. The results of this study provide insight into the differences of the initial wear behavior of noncrosslinked and crosslinked UHMWPE used in total joint replacements.

Bone is the substantial unit of human skeletal system, which supports the body and its movement. At the ultra-structure level, the bone matrix is a composite material consisting of bone mineral particles, which are mainly substituted, calcium-deficient hydroxyapatite, and collagen, which is a natural polymer. Bone serves as the template for developing bone replacement materials. Research on biomaterials analogous to bone was started in the early 1980s by incorporating bioactive particles into biocompatible polymers so as to produce bone substitutes. Over the last two decades, a variety of bioactive polymer matrix composites have been developed for tissue substitution and tissue regeneration. The bioactive phases in these composites are normally one of the calcium phosphates, especially synthetic hydroxyapatite (HA, Ca10(PO4)6(OH)2) which closely resembles bone apatite and exhibits osteoconductivity. If enhanced bioactivity is required, bioceramics having higher bioactivity such as Bioglass® and A-W glass-ceramic can be used as the bioactive phase in the composites. For tissue replacement, bio-stable polymers such as polyethylene (PE) and polysulfone (PSU) are used as the matrix polymer. For tissue regeneration, natural, biodegradable polymers such as polyhydroxybutyrate (PHB) and chitin are used as matrices. Furthermore, mechanical as well as biological performance of a particular composite can be controlled by varying the amount of the bioactive phase in the composite, thus meeting specific clinical requirements. For bioactive ceramic-polymer composites, major influencing factors such as shape, size and size distribution of bioactive particles, mechanical properties and volume percentage of the bioactive phase, properties of the matrix polymer, distribution of bioactive particles in the matrix and the particle-matrix interfacial state should be controlled in order to obtain materials of desirable properties. Various techniques are used to evaluate the composites.

Supramolecular assemblies of vesicles composed of natural lipids embedded in a matrix of polydiacetylene are shown to undergo blue-to-red color changes related to specific interactions between the lipids or recognition elements and biomolecules. The colorimetric transitions observed in the vesicles are due to structural modifications within the conjugated PDA polymer backbone. This colorimetric assay could serve as a membrane-mimicking environment for detection of interfacial processes, such as peptide-membrane interactions, antibody-antigen binding, enzymatic catalysis, and detection of physiological ions. The lipid/PDA mixed vesicles are robust and can be readily applied to diagnosis of physiological molecules and rapid screening of biological and chemical libraries.

Textures of calcite crystals from ostrich (Struthio camelus) eggshells were examined with X ray diffractometry (XRD), transmission and scanning electron microscopy (TEM, SEM), and the thermal stability by thermal expansion analysis (TEA). Results showed that textures vary through the thickness of the eggshell and that expansion properties and thermal behaviour are unusual. Crystals from ostrich eggshell are arranged in two main configurations or layers; the outer layer with the c-axis of crystals oriented perpendicular to the eggshell surface and the inner layer with the c-axes of the crystals arranged almost parallel to eggshell surface; thermal expansion analysis show high stability through a wide range of temperatures until a steep growth near 450-460°C. These results show that the manipulation of crystal texture and properties is under biological control and a better understanding of this biological phenomenon will provide more and better data for improving new synthetic composite materials.

The research about the structural stability of bone, as a composite material, compromises a complete understanding of the interaction between the mineral and organic phases. The thermal stability of human bone and type I collagen extracted from human bone by different methods was studied in order to understand the interactions between the mineral and organic phases when is affected by a degradation/combustion process. The experimental techniques employed were calorimetry and infrared spectroscopy (FTIR) techniques. The extracted type I collagens result to have a bigger thermal stability with a Tmax at 500 and 530 Celsius degrees compared with the collagen present in bone with Tmax at 350 Celsius degrees. The enthalpy value for the complete degradation/combustion process were similar for all the samples, being 8.4 +- 0.11 kJ/g for recent bones diminishing with the antiquity, while for extracted collagens were 8.9 +- 0.07 and 7.9 +-1.01 kJ/g. These findings demonstrate that the stability loss of type I collagen is due to its interactions with the mineral phase, namely carbonate hydroxyapatite. This cause a change in the molecular properties of the collagen during mineralization, specifically in its cross-links and other chemical interactions, which have a global effect over the fibers elasticity, but gaining tensile strength in bone as a whole tissue. We are applying this characterization to analyze the diagenetic process of bones with archaeological interest in order to identify how the environmental factors affect the molecular structure of type I collagen. In bone samples that proceed from an specific region with the same environmental conditions, the enthalpy value per unit mass was found to diminish exponentially with respect to the bone antiquity.

Rat Basophilic Leukemia (RBL) cells are immobilized and stimulated on micro- and nanometer scale patterns of supported lipid bilayers. The patterns are realized as the photolithographically patterned polymer is mechanically peeled away in one contiguous piece in solution. The 0.36 μm2 to 4, 489 μm2 patches can contain both fluorescent lipids and lipid-linked antigen and provide a synthetic biological substrate for analysis of cell surface receptor-mediated events. 100-nm unilamellar lipid vesicles spread to form a supported lipid bilayer on a thermally oxidized silicon surface as confirmed by fluorescence recovery after photobleaching (FRAP). Aggregation of fluorescently labeled receptors is observed as their coincidence with the patterned antigen. Cell morphology is analyzed with scanning electron microscopy (SEM). Thus, a novel method has been developed for patterning antigen, capturing and immobilizing cells via specific receptors, and spatially controlling antigenic stimulus on the nanoscale.

Our biomimetic approach for patterned crystallization is based on the combination of the Micro-Contact Printing technique and a novel mineralization process, called the Polymer-Induced-Liquid-Precursor (PILP) process, which enables the deposition of mineral films under low-temperature and aqueous-based conditions. We demonstrate that a liquid-phase mineral precursor is deposited onto specific areas templated with self-assembled monolayers of alkanethiolate on gold, and then the patterned calcitic films grow under constrained conditions via transformation of the PILP phase, leading to control over the location and morphology of calcitic films.

We have developed polymers, which borrowing from biology, assemble into networks. The self-assembly regions of fibrinogen were cloned to form a scaffolding that either interacts with fibrin or assembles independently. Peptides consisting of a binding pocket (BP), ligand (L), and/or a Factor XIIIa substrate were synthesized and conjugated to methacroylated dextran or acrylated poly(ethylene glycol). Peptide-conjugated dextran was added to polymerizing fibrin, and the resulting hydrogels were evaluated rheologically. These conjugates significantly affected the mechanical properties of fibrin while the addition of unconjugated dextran did not. The BP and L peptides were conjugated to PEG star polymer. Mixtures of conjugated PEG-BP and PEG-L were found to assemble. This work shows that peptides directing assembly can be designed using motifs found in proteins. The peptides in this study not only alter the mechanical properties of fibrin, but also allow a mechanism for creating a self-assembling network.

Honeybees are the most studied insects in the magnetic orientation research field. Experiments on the magnetic remanence of honeybees have shown the presence of magnetite nanoparticles, aligned transversely to the body axis on the anterodorsal abdomen horizontal plane. These results support the hypothesis of ferromagnetic sensors for the magnetoreception mechanism. An Electron Paramagnetic Resonance (EPR) study identified isolated magnetite nanoparticles and aggregates of these particles with a low temperature transition (52 K – 91 K). Hysteresis curves of Apis mellifera abdomens organized parallel and perpendicular to the applied magnetic field were obtained from 5K to 310K. At low temperatures, the hysteresis curves indicate a preferential orientation of the magnetic easy axis parallel to the body axis. The saturation (Js) and remanent (Jr) magnetizations, coercive field (Hc) and initial susceptibility (Ψ) were obtained. Results were interpreted based on the presence of magnetite nanoparticles with 50 K and 120 K mean blocking temperatures.

This paper briefly reviews our recent studies, which aimed to investigate the effects of 1) the Ca2+ and PO43- ions flow and 2) amelogenins on the lengthwise growth of octacalcium phosphate (OCP), which is a potent precursor of enamel apatite crystal. OCP crystals were grown at 37°C in a dual membrane system under various amount of ionic inflow into a reaction space, using 1) 5-30mM Ca and PO4 solutions as ionic sources and 2) extracted bovine amelogenin and recombinant murine amelogenins (rM179, rM166). With an increase in the amount of Ca2+ and/or PO43- ions flow, the length of OCP crystal increased, while the width decreased. As a result, the length to width (L/W) ratio of crystal changed from 3 to 95, while the width to thickness (W/T) ratio from 32 to 9. The effect of amelogenins was unique, regardless of the type of amelogenins: Rod-like and prism-like OCP crystals with large L/W (61∼107) and small W/T (1.3∼2.2) ratios were formed in 10% amelogenin gels. In contrast, characteristic ribbon-like OCP crystals grew without protein and with gelatin, albumin, polyacrylamide gel and agarose gel. Specific interaction of amelogenins with OCP crystal was ascribed to the self-assembly property of amelogenin molecules and their hydrophobic nature. It was suggested that ionic flow and amelogenins play some critical roles in the elongated growth of enamel crystals.

Triblock copolymers have traditionally been synthesized with conventional organic components. However, triblock copolymers could be synthesized by the incorporation of two incompatible protein-based polymers. The polypeptides would differ in their hydrophobicity and confer unique physiochemical properties to the resultant materials. One protein-based polymer, based on a sequence of native elastin, that has been utilized in the synthesis of biomaterials is poly (Valine-Proline-Glycine-ValineGlycine) or poly(VPGVG) [1]. This polypeptide has been shown to have an inverse temperature transition that can be adjusted by non-conservative amino acid substitutions in the fourth position [2]. By combining polypeptide blocks with different inverse temperature transition values due to hydrophobicity differences, we expect to produce amphiphilic polypeptides capable of self-assembly into hydrogels. Our research examines the design, synthesis and characterization of elastin-mimetic block copolymers as functional biomaterials. The methods that are used for the characterization include variable temperature 1D and 2D High-Resolution-NMR, cryo-High Resolutions Scanning Electron Microscopy and Differential Scanning Calorimetry.

Biodegradable polymers have significant potential in biotechnology and bioengineering. However, for some applications, they are limited by their inferior mechanical properties and unsatisfactory compatibility with cells and tissues. A strong, biodegradable, and biocompatible elastomer could be useful for fields such as tissue engineering, drug delivery, and in vivo sensing [1, 2]. We designed, synthesized, and characterized a tough biodegradable elastomer from biocompatible monomers. This elastomer forms a covalently crosslinked three-dimensional network of random coils with hydroxyl groups attached to its backbone. Both crosslinking and the hydrogen bonding interactions between the hydroxyl groups likely contributes to the unique properties of the elastomer. In vitro and in vivo studies show the polymer has good biocompatibility. Subcutaneous (SC) polymer implants are absorbed completely within 60 days with restoration of the implantation sites to their normal architecture.