Understanding factors affecting cell invasion influences the design of engineered constructs for tissue regeneration. The objective of this work was to investigate the effect of matrix stiffness on invasion of tumor cells through a synthetic hydrogel with well-defined properties. A novel star acrylate-functionalized polyethylene glycol-co-lactide (SPELA) macromer was synthesized to produce hydrogels with well-defined water content, elastic modulus, degree of crosslinking and hydrophilicity. The hydrogel was formed by photo-polymerization of the macromer with or without integrin-binding cell adhesive RGD peptide. Cell invasion experiments were carried out in a transwell with SPELA hydrogel as the invading matrix and 4T1 mouse breast cancer cells. The invading cells on the lower membrane side were counted with an inverted fluorescent microscope. The concentration of SPELA macromer ranged 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 Pa to 25 kPa as the SPELA concentration increased from 10 to 25 wt%. Cell invasion slightly increased with increasing RGD concentration. However, RGD concentration >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 kPa the 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 in invasion rate for matrix stiffness greater than 10 kPa. Results demonstrate that matrix stiffness plays a major role in invasion of tumor cell through a gelatinous matrix.

Inkjet printing of alternate layers of anionic and cationic polyelectrolytes allows organized gels to form with structures similar to those made by layer--by-layer dipping methods but very much faster. Structures of gels formed using slow and fast inkjet printing systems are compared using elemental analysis, swelling and diffusion kinetics as characterization methods. After printing and washing, most sodium or chloride counter-ions are last from the gel, leave only the polymer complex. The swelling properties of the printed and washed gel depend on the deposition rate and on the ratio of the two polymers as originally printed. The synthetic polyelectrolytes reported here can be compared with biological polyelectrolytes reported earlier by us.

To date, there are a strikingly growing number of patients who need various orthopedic implants. However, traditional orthopedic implants face many complications such as infection and implant loosening which may lead to implant failures. Conventional metal implants such as titanium were chosen for orthopedic applications mainly based on their excellent mechanical properties and biological inertness. Since natural bone matrix is nanometer in dimension, it is desirable to design a biologically inspired nanostructured coating that can turn conventional inert titanium surfaces into biomimetic active interfaces, thus enhance bone cell adhesion and osseointegration. For this purpose, we designed a biomimetic nanostructured coating based on nanocrystalline hydroxyapatites (nHA) and single wall carbon nanotubes (SWCNTs). Specifically, nHA with good crystallinity and biomimetic dimensions were prepared via a wet chemistry method and hydrothermal treatment; and the SWCNTs were synthesized via an arc plasma method with or without magnetic fields. TEM images showed that the hydrothermally treated nHA possessed regular rod-like nanocrystals and biomimetic nanostructure. In addition, the length of SWCNTs can be significantly increased under external magnetic fields when compared to nanotubes produced without magnetic fields. More importantly, our results showed that the above nHA and SWCNTs nanomaterials can greatly promote osteoblast (bone-forming cell) adhesion on titanium in vitro, thus holding great promise to improve osseointegration and lengthen the lifetime of current orthopedic implants.

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

In this study, Ag doped hydroxyapatite (HA) samples prepared by EDTA chelate decomposition method were characterized with X-Ray Diffraction Spectroscopy (XRD), Scanning Electron Microscopy (SEM) and antimicrobial sensitivity test. Hydroxyapatite (Ca10(PO)6(OH)2) and NaCaPO4 (rhenanite) phases were observed while Ag was present in the form of Ag2O. Results showed that microstructurally controlled HA-based composites with NaCaPO4 interphase can be prepared, which significantly enhances sinterability of hydroxyapatite at 1100° C without formation of any undesired second phases, such as tricalcium phosphate (TCP) known to decrease the stability of HA. The antibacterial sensitivity was tested with E.Coli gram-negative bacteria. The radius of circle enclosing the sample increases with increasing Ag content in the structure as an indication of the region of non-bacterial activity.

Articular cartilage is a low-friction, load-bearing tissue located at joint surfaces. It experiences static and dynamic forces including shear, compression and tension. We investigate the relationship between structure and function by measuring the osmotic and mechanical properties in cartilage layers as a function of the distance from the articular surface. Atomic force microscopy is used to probe the mechanical properties at high spatial resolution. The mechanical measurements are complemented by osmotic swelling pressure observations made on the same samples using a novel tissue osmometer. The results show that the osmotic modulus significantly depends on the distance from the articular surface. Its value is highest in the deep zone and lowest in the middle zone.

Photoembossing is a technique used to create relief structures using a patterned contact photo-mask exposure and a thermal development step. Typically, the photopolymer consists of a polymer binder and a monomer in a 1/1 ratio together with a photo-initiator which results in a solid and non-tacky material at room temperature. Here, new mixtures for photoembossing are presented which are potentially biocompatible. A polymer binder such as poly (methyl methacrylate) with triacrylate monomer and biocompatible photo-initiator Irgacure 369 is used. Photopolymer films produced are successfully embossed with height of relief structures controlled by UV dosage and developing temperature. Furthermore, the photopolymer blend is electrospun to form fibres with diameters of 5 μm which are then photoembossed. The photoembossed fibres showed homogenous reproducible surface textures. Biocompatibility is evaluated by culturing human umbilical vein endothelial cells (HUVECs) on films of this photopolymer blend. The study shows that photoembossing is a feasible method of producing surface texturing on both films and electrospun fibres for tissue engineering applications.

Collagen fibril membranes (CFMs) with a high mechanical property were fabricated with a lateral face evaporation method, in which type I atelocollagen extracted from tilapia scales was used. The density and thickness of the CFM obtained were 0.51 ± 0.04 mg/cm3 and 50 ± 5 μm. The collagen fibrils in the CFM had a similar periodic stripped pattern of 67 nm with native collagen fibrils. The CFM was crosslinked in gaseous glutaraldehyde for different duration in order to increase the mechanical property. The crosslinking degrees of the CFMs analyzed by free amino groups gradually increased to 70.3 % against the exposure duration until 6 hours, and reached a plateau. The denaturation temperatures of the CFMs with the crosslinking degrees at 20.4 % to 43% were linearly increased from 49°C to 75°C. The tensile strength of the CFMs was slightly improved until the crosslinking degree at 33.3 % and then the tensile strength rapidly increased to be 68 MPa. It was suggested that a percolation phenomenon took place in the CFMs by crosslinking of collagen fibrils with polymerized GA molecules.

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

By systematically altering the number and position of phenylalanine and carboxylate groups on a series of hydrogelators containing a naphthalene motif, we evaluated the correlation of molecular structures, self-assembly, and the rheological properties of the hydrogels. The storage moduli of the hydrogels decrease with the increase of the number of phenylalanine or with the insertion of a cysteine residue, and the effect of the carboxylic group on the rheological properties depends on the backbone of the hydrogelators. Transmission electron microscopy shows that these hydrogelators self-assemble in water to form nanofibers and result in threedimensional networks. Circular dichroism experiment indicates the hydrogelators self-assemble to form β-sheet-like structure within the nanofibers. This work suggests that control of the synergy of hydrogen bonding and aromatic-aromatic interactions may offer a feasible way to modulate the rheological properties of molecular hydrogels consisting of small molecules.

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

Ventilator associated pneumonia (VAP) is a serious and costly clinical problem. Specifically, receiving mechanical ventilation for over 24 hours increases the risk of VAP and is associated with high morbidity, mortality and medical costs. Cost effective endotracheal tubes (ETTs) that are resistant to bacterial infection could help prevent this problem. The objective of this study was to determine differences in the growth of Staphylococcus aureus (S. aureus) on nanomodified and unmodified polyvinyl chloride (PVC) ETTs under dynamic airway conditions. PVC ETTs were modified to have nanometer surface features by soaking them in Rhizopus arrhisus, a fungal lipase. Twenty-four hour experiments (supported by computational models) showed that air flow conditions within the ETT influenced both the location and concentration of bacterial growth on the ETTs especially within areas of tube curvature. More importantly, experiments revealed a 1.5 log reduction in the total number of S. aureus on the novel nanomodified ETTs compared to the conventional ETTs after 24 hours of air flow. This dynamic study showed that lipase etching can create nano-rough surface features on PVC ETTs that suppress S. aureus growth and, thus, may provide clinicians with an effective and inexpensive tool to combat VAP.

A fluid lubrication model for articular cartilage was put forward by Mc Cutchen, in which a high percentage of the load is supported by fluid pressurization in the interface region separating the two cartilage coated surfaces as the cartilage is compressed under load. This reduces the friction by reducing the percentage of the load which is carried by solid material in the cartilage. For two bones which are in contact in a healthy joint, which are each coated by a layer of cartilage whose thickness is much smaller than its lateral dimensions, it will be argued that since the bone is impervious to fluid flow in healthy joints, almost all of the fluid that is expressed from the cartilage under load flows through the interface region, where it supports part of the load. This is in contrast to previous theoretical and in vitro experimental studies of this problem, in which most of the fluid does not flow into the interface. It is shown that for mean asperity height small compared to a length scale (which depends on the cartilage or hydrogel permeability, the fluid viscosity and the dimensions of the cartilage or hydrogel) a large percentage of the load is supported by fluid pressurization.

Titanium and its alloys have been employed in bone plates/screws, and these are often designed to be removed after recovery. Bone is known to bond to the surface of Ti alloys. This can lead to re-fracture of newly repaired bone during operations to remove the implants, however bone does not bond to Zr-based alloys. The inhibition of bone conduction on the surface of Zr-based alloys is thought to be due to the presence of a thin layer of zirconia (ZrO2) on the surface. The purpose of the present study was to synthesize bioinert films, including ZrO2 on pure Ti surfaces. In vitro apatite (HAp) formation and in vivo bone conduction in the tibiae of rats on the films were also investigated.

Commercial purity Ti was chemically treated with aqueous H2O2/HNO3 at 353 K for 20 min. The disks were 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 with a TiO2–ZrO2 composite film though the amount of ZrO2 was very small. HAp began to form on the non-modified Ti and TiO2 surfaces after 6 days and 4 days immersion in Hank’s solution, respectively. On the surfaces of TiO2–ZrO2, the presence of precipitates was confirmed after 6-8 days. The HAp formation was suppressed on the surfaces of TiO2–ZrO2.The present TiO2-ZrO2 surface also showed significantly lower bone-implant contact ratio in cortical bone compared with TiO2.