Understanding factors affecting cell invasion influences the design ofengineered constructs for tissue regeneration. The objective of this workwas to investigate the effect of matrix stiffness on invasion of tumor cellsthrough a synthetic hydrogel with well-defined properties. A novel staracrylate-functionalized polyethylene glycol-co-lactide (SPELA) macromer wassynthesized to produce hydrogels with well-defined water content, elasticmodulus, degree of crosslinking and hydrophilicity. The hydrogel was formedby photo-polymerization of the macromer with or without integrin-bindingcell adhesive RGD peptide. Cell invasion experiments were carried out in atranswell with SPELA hydrogel as the invading matrix and 4T1 mouse breastcancer cells. The invading cells on the lower membrane side were countedwith an inverted fluorescent microscope. The concentration of SPELA macromerranged from 10-25 wt% and that of RGD ranged from 1x10-4 to 1x10-2 M. The shear modulus of the hydrogel varied from 200 Pato 25 kPa as the SPELA concentration increased from 10 to 25 wt%. Cellinvasion slightly increased with increasing RGD concentration. However, RGDconcentration >1% resulted in a significant decrease in cell migration.As the matrix stiffness increased from 0.15 to 0.4, 3, 5, 6, 14, and 25 kPathe invasion rate decreased from 18.0 to 5.5, 6, 5.7, 5.2, 1.5, and 1.0 cells/mm2/h, respectively. There was a sharp decrease ininvasion rate for matrix stiffness greater than 10 kPa. Results demonstratethat matrix stiffness plays a major role in invasion of tumor cell through agelatinous matrix.

Inkjet printing of alternate layers of anionic and cationic polyelectrolytesallows organized gels to form with structures similar to those made bylayer--by-layer dipping methods but very much faster. Structures of gelsformed using slow and fast inkjet printing systems are compared usingelemental analysis, swelling and diffusion kinetics as characterizationmethods. After printing and washing, most sodium or chloride counter-ionsare last from the gel, leave only the polymer complex. The swellingproperties of the printed and washed gel depend on the deposition rate andon the ratio of the two polymers as originally printed. The syntheticpolyelectrolytes reported here can be compared with biologicalpolyelectrolytes reported earlier by us.

To date, there are a strikingly growing number of patients who need variousorthopedic implants. However, traditional orthopedic implants face manycomplications such as infection and implant loosening which may lead toimplant failures. Conventional metal implants such as titanium were chosenfor orthopedic applications mainly based on their excellent mechanicalproperties and biological inertness. Since natural bone matrix is nanometerin dimension, it is desirable to design a biologically inspirednanostructured coating that can turn conventional inert titanium surfacesinto biomimetic active interfaces, thus enhance bone cell adhesion andosseointegration. For this purpose, we designed a biomimetic nanostructuredcoating based on nanocrystalline hydroxyapatites (nHA) and single wallcarbon nanotubes (SWCNTs). Specifically, nHA with good crystallinity andbiomimetic dimensions were prepared via a wet chemistry method andhydrothermal treatment; and the SWCNTs were synthesized via an arc plasmamethod with or without magnetic fields. TEM images showed that thehydrothermally treated nHA possessed regular rod-like nanocrystals andbiomimetic nanostructure. In addition, the length of SWCNTs can besignificantly increased under external magnetic fields when compared tonanotubes produced without magnetic fields. More importantly, our resultsshowed that the above nHA and SWCNTs nanomaterials can greatly promoteosteoblast (bone-forming cell) adhesion on titanium in vitro, thus holding great promise to improve osseointegrationand lengthen the lifetime of current orthopedic implants.

The shear stress relaxation of a thermally reversible, physicallyassociating solution formed from a triblock copolymer in solvent selectivefor the mid-block was found to be well described over a broad temperaturerange by a stretched exponential function with a temperature independent‘stretching exponent’, β ≈ 1/3. This same exponent valuehas been suggested to have particular significance in describing structuralrelaxation in a wide range of disordered viscoelastic materials ranging fromassociating polymer materials (‘gels’) to glass-forming liquids. We quantifythe temperature dependence of the high frequency, or short time, shearmodulus as function of temperature and find that this property also followsa variation often observed in gels and glass-forming materials.

In this study, Ag doped hydroxyapatite (HA) samples prepared by EDTA chelatedecomposition method were characterized with X-Ray Diffraction Spectroscopy(XRD), Scanning Electron Microscopy (SEM) and antimicrobial sensitivitytest. Hydroxyapatite (Ca10(PO)6(OH)2) and NaCaPO4 (rhenanite) phases were observed while Ag was presentin the form of Ag2O. Results showed that microstructurallycontrolled HA-based composites with NaCaPO4 interphase can beprepared, which significantly enhances sinterability of hydroxyapatite at1100° C without formation of any undesired second phases, such as tricalciumphosphate (TCP) known to decrease the stability of HA. The antibacterialsensitivity was tested with E.Coli gram-negative bacteria. The radius ofcircle enclosing the sample increases with increasing Ag content in thestructure as an indication of the region of non-bacterial activity.

Articular cartilage is a low-friction, load-bearing tissue located at jointsurfaces. It experiences static and dynamic forces including shear,compression and tension. We investigate the relationship between structureand function by measuring the osmotic and mechanical properties in cartilagelayers as a function of the distance from the articular surface. Atomicforce microscopy is used to probe the mechanical properties at high spatialresolution. The mechanical measurements are complemented by osmotic swellingpressure observations made on the same samples using a novel tissueosmometer. The results show that the osmotic modulus significantly dependson the distance from the articular surface. Its value is highest in the deepzone and lowest in the middle zone.

Photoembossing is a technique used to create relief structures using apatterned contact photo-mask exposure and a thermal development step.Typically, the photopolymer consists of a polymer binder and a monomer in a1/1 ratio together with a photo-initiator which results in a solid andnon-tacky material at room temperature. Here, new mixtures forphotoembossing are presented which are potentially biocompatible. A polymerbinder such as poly (methyl methacrylate) with triacrylate monomer andbiocompatible photo-initiator Irgacure 369 is used. Photopolymer filmsproduced are successfully embossed with height of relief structurescontrolled by UV dosage and developing temperature. Furthermore, thephotopolymer blend is electrospun to form fibres with diameters of 5 μmwhich are then photoembossed. The photoembossed fibres showed homogenousreproducible surface textures. Biocompatibility is evaluated by culturinghuman umbilical vein endothelial cells (HUVECs) on films of thisphotopolymer blend. The study shows that photoembossing is a feasible methodof producing surface texturing on both films and electrospun fibres fortissue engineering applications.

Collagen fibril membranes (CFMs) with a high mechanical property werefabricated with a lateral face evaporation method, in which type Iatelocollagen extracted from tilapia scales was used. The density andthickness of the CFM obtained were 0.51 ± 0.04 mg/cm3 and 50 ± 5μm. The collagen fibrils in the CFM had a similar periodic stripped patternof 67 nm with native collagen fibrils. The CFM was crosslinked in gaseousglutaraldehyde for different duration in order to increase the mechanicalproperty. The crosslinking degrees of the CFMs analyzed by free amino groupsgradually increased to 70.3 % against the exposure duration until 6 hours,and reached a plateau. The denaturation temperatures of the CFMs with thecrosslinking degrees at 20.4 % to 43% were linearly increased from 49°C to75°C. The tensile strength of the CFMs was slightly improved until thecrosslinking degree at 33.3 % and then the tensile strength rapidlyincreased to be 68 MPa. It was suggested that a percolation phenomenon tookplace in the CFMs by crosslinking of collagen fibrils with polymerized GAmolecules.

Gold nanorods (NRs) were fixed on an ITO plate and used for theSurface-Assisted Laser Desorption/Ionization Time-of-Flight MassSpectrometry (SALDI-MS) of oligopeptides (angiotensin I). The SALDI-MSmeasurements had a high sensitivity to the angiotensin on the ITO plate onwhich isolated NRs were deposited. Angiotensin molecules in a very dilutedsolution (1 × 10-11 M) could be detected at m/z = 1297 with agood signal/noise ratio (S/N = 18). In contrast, alternatively deposited NRan ITO plate, which present broad surface plasmon bands, was found to beinactive for SALDI measurements.

By systematically altering the number and position of phenylalanine andcarboxylate groups on a series of hydrogelators containing a naphthalenemotif, we evaluated the correlation of molecular structures, self-assembly,and the rheological properties of the hydrogels. The storage moduli of thehydrogels decrease with the increase of the number of phenylalanine or withthe insertion of a cysteine residue, and the effect of the carboxylic groupon the rheological properties depends on the backbone of the hydrogelators.Transmission electron microscopy shows that these hydrogelatorsself-assemble in water to form nanofibers and result in threedimensionalnetworks. Circular dichroism experiment indicates the hydrogelatorsself-assemble to form β-sheet-like structure within the nanofibers. Thiswork suggests that control of the synergy of hydrogen bonding andaromatic-aromatic interactions may offer a feasible way to modulate therheological properties of molecular hydrogels consisting of smallmolecules.

Gold nanoparticles (AuNp) formed using alkoxysilane precursors are utilizedin the development of thin organically modified silicates (ormosil) films.The resulting films are optically transparent thereby retaining the opticalproperties of AuNp. Surface morphology shows that the in situ generated AuNp retained their nanogeometry in the ormosilfilms. An application of the AuNp encapsulated ormosils is shown inelectrocatalytic determination of hydrogen peroxide. For this purpose,potassium ferricyanide is chosen as electron transfer mediator and isencapsulated in the films. Results show that the presence of AuNp in theormosil matrix dramatically improves the electrochemical behavior ofpotassium ferricyanide. The ormosil films are utilized for electrocatalyticdetermination of hydrogen peroxide. In order to investigate thebiocompatibility of the ormosil film, horseradish peroxidase (HRP) isincorporated resulting in improvement in oxidation and reduction ofperoxide.

Ventilator associated pneumonia (VAP) is a serious and costly clinicalproblem. Specifically, receiving mechanical ventilation for over 24 hoursincreases the risk of VAP and is associated with high morbidity, mortalityand medical costs. Cost effective endotracheal tubes (ETTs) that areresistant to bacterial infection could help prevent this problem. Theobjective of this study was to determine differences in the growth of Staphylococcus aureus (S. aureus) onnanomodified and unmodified polyvinyl chloride (PVC) ETTs under dynamicairway conditions. PVC ETTs were modified to have nanometer surface featuresby soaking them in Rhizopus arrhisus, a fungal lipase.Twenty-four hour experiments (supported by computational models) showed thatair flow conditions within the ETT influenced both the location andconcentration of bacterial growth on the ETTs especially within areas oftube curvature. More importantly, experiments revealed a 1.5 log reductionin the total number of S. aureus on the novel nanomodifiedETTs compared to the conventional ETTs after 24 hours of air flow. Thisdynamic study showed that lipase etching can create nano-rough surfacefeatures on PVC ETTs that suppress S. aureus growth and,thus, may provide clinicians with an effective and inexpensive tool tocombat VAP.

A fluid lubrication model for articular cartilage was put forward by McCutchen, in which a high percentage of the load is supported by fluidpressurization in the interface region separating the two cartilage coatedsurfaces as the cartilage is compressed under load. This reduces thefriction by reducing the percentage of the load which is carried by solidmaterial in the cartilage. For two bones which are in contact in a healthyjoint, which are each coated by a layer of cartilage whose thickness is muchsmaller than its lateral dimensions, it will be argued that since the boneis impervious to fluid flow in healthy joints, almost all of the fluid thatis expressed from the cartilage under load flows through the interfaceregion, where it supports part of the load. This is in contrast to previoustheoretical and in vitro experimental studies of this problem, in which mostof the fluid does not flow into the interface. It is shown that for meanasperity height small compared to a length scale (which depends on thecartilage or hydrogel permeability, the fluid viscosity and the dimensionsof the cartilage or hydrogel) a large percentage of the load is supported byfluid pressurization.

Titanium and its alloys have been employed in bone plates/screws, and theseare often designed to be removed after recovery. Bone is known to bond tothe surface of Ti alloys. This can lead to re-fracture of newly repairedbone during operations to remove the implants, however bone does not bond toZr-based alloys. The inhibition of bone conduction on the surface ofZr-based alloys is thought to be due to the presence of a thin layer ofzirconia (ZrO2) on the surface. The purpose of the present studywas to synthesize bioinert films, including ZrO2 on pure Tisurfaces. In vitro apatite (HAp) formation and in vivo bone conduction in the tibiae of rats on the films werealso investigated.

Commercial purity Ti was chemically treated with aqueous H2O2/HNO3 at 353 K for 20 min. The diskswere hydrothermally treated with aqueous ZrOCl2/NH3/C6H8O7(citric acid) in an autoclave at 453 K for 12 h. Simulated body fluid (SBF)immersion test and implantation into tibiae of rats were carried out.

In the hydrothermal treatment with aqueous ZrOCl2/NH3,the surface product was anatase-type TiO2. On the other hand,when citric acid was added the surface of Ti was covered homogeneously witha TiO2–ZrO2 composite film though the amount of ZrO2 was very small. HAp began to form on the non-modified Tiand TiO2 surfaces after 6 days and 4 days immersion in Hank’ssolution, respectively. On the surfaces of TiO2–ZrO2,the presence of precipitates was confirmed after 6-8 days. The HAp formationwas suppressed on the surfaces of TiO2–ZrO2.Thepresent TiO2-ZrO2 surface also showed significantlylower bone-implant contact ratio in cortical bone compared with TiO2.