In vitro metal ion release and biocompatibility of amorphous Mg67Zn28Ca5 alloy with/without gelatin coating.

Amorphous zinc-rich Mg-Zn-Ca alloys have exhibited good tissue compatibility and low hydrogen evolution in vivo. However, suboptimal cell-surface interaction on magnesium alloy surface observed in vitro could lead to reduced integration with host tissue for regenerative purpose. This study aims to improve cell-surface interaction of amorphous Mg67Zn28Ca5 alloy by coating a gelatin layer by electrospinning. Coated/uncoated alloys were immersed and extracted for 3 days under different CO2. The immersion results showed that pH and metal ion release in the alloy extracts were affected by gelatin coating and CO2, suggesting their roles in alloy biocorrosion and a mechanism has been proposed for the alloy-CO2 system with/without coating. Cytotoxicity results are evident that gelatin-coated alloy with 2-day crosslinking not only exhibited no indirect cytotoxicity, but also supported attachment of L929 and MG63 cell lines around/on the alloy with high viability. Therefore, amorphous Mg67Zn28Ca5 alloy coated with gelatin by electrospinning technique provides a useful method to improve alloy biocompatibility.

Esophageal tissue engineering: an in-depth review on scaffold design.

Treatment of esophageal cancer often requires surgical procedures that involve removal. The current approaches to restore esophageal continuity however, are known to have limitations which may not result in full functional recovery. In theory, using a tissue engineered esophagus developed from the patient's own cells to replace the removed esophageal segment can be the ideal method of reconstruction. One of the key elements involved in the tissue engineering process is the scaffold which acts as a template for organization of cells and tissue development. While a number of scaffolds range from traditional non-biodegradable tubing to bioactive decellularized matrix have been proposed to engineer the esophagus in the past decade, results are still not yet favorable with many challenges relating to tissue quality need to be met improvements. The success of new esophageal tissue formation will ultimately depend on the success of the scaffold being able to meet the essential requirements specific to the esophageal tissue. Here, the design of the scaffold and its fabrication approaches are reviewed. In this paper, we review the current state of development in bioengineering the esophagus with particular emphasis on scaffold design.

Dependence of alignment direction on magnitude of strain in esophageal smooth muscle cells.

The response of cells in vitro to mechanical forces has been the subject of much research using devices to exert controlled mechanical stimulation on cultured cells or isolated tissue. In this study, esophageal smooth muscle cells were seeded on flexible polyurethane membranes to form a confluent cell layer. The cells were then subjected to uniform cyclic stretch of varying magnitudes at a frequency of approximately five cycles per minute in a custom made mechatronic bioreactor, providing similar strains experienced in the in vivo mechanical environment of the esophagus. The results show that the orientation response is dependent on the magnitude of cyclic stretch applied. Smooth muscle cells showed parallel alignment to the force direction at low cyclic strains (2%) compared to the hill-valley morphology of static controls. At higher strains (5% and 10% magnitude), the cells exhibited a consistent alignment perpendicular to the strain. To our knowledge, this is the first time that the alignment direction's dependence on strain magnitude has been demonstrated. MTS analysis indicated that cell metabolism was reduced when mechanical strain was applied, and proliferation was inhibited by mechanical strain. Protein expression indicates a decrease in smooth muscle alpha-actin, indicative of changes in cell phenotype, an increase in vimentin, which is associated with increased cell motility, and an increase in desmin, indicating differentiation in stimulated cells.

Three-dimensional finite element model of the two-layered oesophagus, including the effects of residual strains and buckling of mucosa.

This study was carried out to develop a two-layered finite element model of the oesophagus. The outer muscle and inner mucosal layer were constructed individually with different mechanical properties and zero-stress opening angles. With the model, two simulations were performed. First, the distention of oesophageal wall under the pressurized state was investigated, from which the effects of residual strains on the stress distribution were evaluated. Second, the buckling modes were determined using a linear eigenvalue analysis. The self-contact capability in ABAQUS was applied to simulate the folding of mucosa under the muscle contraction. The first simulation indicated that, by taking the residual strains into account, the mucosa undertook a very small portion of stress and the luminal pressure almost transmitted completely to the outer muscle layer. On the other hand, the folding of mucosa was shown to be able to reduce the contractile force of circular muscle to maintain the lumen closure. In conclusion, the preliminary study demonstrated the feasibility of simulating the oesophageal peristaltic transport using finite element analysis.

Instability of the two-layered thick-walled esophageal model under the external pressure and circular outer boundary condition.

The mucosal folding is a phenomenon observed for some biological tissues, including the pulmonary airway and gastrointestinal tract. In order to understand the mechanism of the formation of mucosal folding, a thick-walled two-layered cylindrical mathematical model was developed to investigate the buckling behavior under the external pressure and circular outer boundary condition. With the finite element method, the validity and accuracy of the proposed model was verified. The results showed that the fold number was in the range of 4-6, which was agreed with the experimental observation for the mucosal folding of a porcine esophagus. The fold number was found to decrease with the increase in the ratio of the inner to outer material stiffness. The increase in the thickness of inner layer also caused a slight declination of the fold number. Since the effects of both the material and geometrical nonlinearities have been accounted for, this model is more general to be used for the prediction of the buckling behavior of the layered structure with a wide range of thickness ratios and/or stiffness ratios.

3D Mechanical properties of the layered esophagus: experiment and constitutive model.

The identification of a three dimensional constitutive model is useful for describing the complex mechanical behavior of a nonlinear and anisotropic biological tissue such as the esophagus. The inflation tests at the fixed axial extension of 1, 1.125, and 1.25 were conducted on the muscle and mucosa layer of a porcine esophagus separately and the pressure-radius-axial force was recorded. The experimental data were fitted with the constitutive model to obtain the structure-related parameters, including the collagen amount and fiber orientation. Results showed that a bilinear strain energy function (SEF) with four parameters could fit the inflation data at an individual extension very well while a six-parameter model had to be used to capture the inflation behaviors at all three extensions simultaneously. It was found that the collagen distribution was axial preferred in both layers and the mucosa contained more collagen, which were in agreement with the findings through a pair of uniaxial tensile test in our previous study. The model was expected to be used for the prediction of stress distribution within the esophageal wall under the physiological state and provide some useful information in the clinical studies of the esophageal diseases.

Viscoelasticity of esophageal tissue and application of a QLV model.

The time-dependent mechanical properties of the porcine esophagus were investigated experimentally and theoretically. It was hypothesized that the viscoelasticity was quasilinear, i.e., the time and strain effects were independent. In order to verify the separability of time and strain effects, the stress-relaxation test was conducted at various strains and the data were fitted with the Fung's quasilinear viscoelastic (QLV) model. By using the material parameters obtained from the stress relaxation test, the cyclic peak stress and hysteresis were predicted. Results showed that the stress relaxed by 20-30% of the peak stress within the first 10 s and stabilized at approximately 50% at the time of 300 s. The relative stress relaxation R(2) (i.e., the difference of stress at a particular time to the final equilibrium stress normalized by the total difference of the peak and final stress) was not different significantly for various strains. It was also found that, by using the stress-time data during both the ramp and relaxation phases, the correlation between parameters was substantially reduced. The model could also predict the cyclic peak stress and hysteresis except for the underestimate of valley stress. We conclude that the QLV model could be used as the material characterization of the esophageal tissue.

Novel biophysical techniques for investigating long-term cell adhesion dynamics on biomaterial surfaces.

Cell adhesion on biomaterial surface is crucial for the regeneration and function of clinically viable cell and tissues. In turn, the cellular phenotypes, following the mechanochemical transduction of adherent cells on biomaterials, are directly correlated to the biophysical responses of cells. However, the lack of an integrated bio-analytical system for probing the cell-substrate interface poses significant obstacles to understanding the behavior of cells on biomaterial surface. We have developed a novel method, based on the principle of confocal reflectance interference contrast microscopy (C-RICM) that has enabled us to study the biomechanical deformation of cells on biomaterial surfaces. In this article, we would like to describe our recent development of the C-RICM system that integrates a confocal fluorescence microscope, phase contrast microscope and GFP expression system. We shall demonstrate the system by determining the adhesion contact kinetics, initial deformation rate, cytoskeleton structures of adherent cells on extracellular matrices (e.g., collagen and fibronectin) and biodegradable polymer (e.g., poly(lactic acid)) during long-term culture. We shall demonstrate that this unique approach could provide valuable biophysical information necessary for designing optimized biomaterial surfaces for cell/tissue regeneration applications.

Directional, regional, and layer variations of mechanical properties of esophageal tissue and its interpretation using a structure-based constitutive model.

The esophagus, like other soft tissues, exhibits nonlinear and anisotropic mechanical properties. As a composite structure, the properties of the outer muscle and inner mucosal layer are different. It is expected that the complex mechanical properties will induce nonhomogeneous stress distributions in the wall and nonuniform tissue remodeling. Both are important factors which influence the function of mechanosensitive receptor located in various layers of the wall. Hence, the characterization of the mechanical properties is essential to understand the neuromuscular motion of the esophagus. In this study, the uniaxial tensile tests were conducted along two mutually orthogonal directions of porcine esophageal tissue to identify the directional (circumferential and axial), regional (abdominal, thoracic, and cervical), and layer (muscle and mucosa) variations of the mechanical properties. A structure-based constitutive model, which took the architectures of the tissue's microstructures into account, was applied to describe the mechanical behavior of the esophagus. Results showed that the constitutive model successfully described the mechanical behavior and provided robust estimates of the material parameters. In conclusion, the model was demonstrated to be a good descriptor of the mechanical properties of the esophagus and it was able to facilitate the directional, layer, and regional comparisons of the mechanical properties in terms of the associated material parameters.

Osteoblast cell adhesion on a laser modified zirconia based bioceramic.

Due to their attractive mechanical properties, bioinert zirconia bioceramics are frequently used in the high load-bearing sites such as orthopaedic and dental implants, but they are chemically inert and do not naturally form a direct bond with bone and thus do not provide osseointegration. A CO2 laser was used to modify the surface properties with the aim to achieve osseointegration between bioinert zirconia and bone. The surface characterisation revealed that the surface roughness decreased and solidified microstructure occurred after laser treatment. Higher wettability characteristics generated by the CO2 laser treatment was primarily due to the enhancement of the surface energy, particularly the polar component, determined by microstructural changes. An in vitro test using human fetal osteoblast cells (hFOB) revealed that osteoblast cells adhere better on the laser treated sample than the untreated sample. The change in the wettability characteristics could be the main mechanism governing the osteoblast cell adhesion on the YPSZ.

Enhanced human osteoblast cell adhesion and proliferation on 316 LS stainless steel by means of CO2 laser surface treatment.

An effective and novel technique for improving the biocompatibility of a biograde 316 LS stainless steel through the application of CO(2) laser treatment to modify the surface properties of the material is described herein. Different surface properties, such as surface roughness, surface oxygen content, and surface energy for CO(2) laser-treated 316 LS stainless steel, untreated, and mechanically roughened samples were analyzed, and their effects on the wettability characteristics of the material were studied. It was found that modification of the wettability characteristics of the 316 LS stainless steel following CO(2) laser treatment was achieved. This improvement was identified as being mainly due to the change in the polar component of the surface energy. One-day cell adhesion tests showed that cells not only adhered and spread better, but also grew faster on the CO(2) laser-treated sample than on either the untreated or mechanically roughened sample. Further, compared with the untreated sample, MTT cell proliferation analysis revealed that the mechanically roughed surface resulted in a slight enhancement, and CO(2) laser treatment brought about a significant increase in cell proliferation. An increase in the wettability of the 316 LS stainless steel was observed to positively correlate with the cell proliferation.

The formation of a hydroxyl bond and the effects thereof on bone-like apatite formation on a magnesia partially stabilized zirconia (MgO-PSZ) bioceramic following CO2 laser irradiation.

For the purpose of improving the bioactivity of a magnesia partially stabilized zirconia (MgO-PSZ) and to explore a new technique for inducing OH group and apatite formation, a CO(2) laser has been used to modified the surface properties. The bioactivity of the CO(2) laser modified MgO-PSZ has been investigated in stimulated human fluids (SBF) with ion concentrations almost equal to those in human blood plasma. Some hydroxyl groups were found on the MgO-PSZ following CO(2) laser treatment with selected power densities. The surface melting on the MgO-PSZ induced by CO(2) laser processing provides the Zr(4+) ion and OH(-) ion, in turn, the incorporation of the Zr(4+) ion and the OH(-) ion creates the Zr-OH group on the surface. After 14 days of SBF soaking, the apatites formed on the MgO-PSZ with relatively high amount of hydroxyl groups generated by the CO(2) laser treatment, while no apatite was observed on the untreated with few hydroxyl groups. It exhibits that the Zr-OH groups on the MgO-PSZ surface is the functional groups to facilitate the apatite formation. The increased surface roughness provides more active sites, meantime, increased surface energy benefits to the adsorption and reaction on the surface.

Effects of CO2 laser irradiation on the surface properties of magnesia-partially stabilised zirconia (MgO-PSZ) bioceramic and the subsequent improvements in human osteoblast cell adhesion.

In order to acquire the surface properties favouring osseo-integration at the implant and bone interface, human foetal osteoblast cells (hFOB) were used in an in vitro test to examine changes in cell adhesion on a magnesia-partially stabilised zirconia (MgO-PSZ) bioceramic after CO(2) laser treatment. The surface roughness, microstructure, crystal size and surface energy of untreated and CO(2) laser-treated MgO-PSZ were fully characterised. The in vitro cell evaluation revealed a more favourable cell response on the CO(2) laser-treated MgO-PSZ than on the untreated sample. After 24-h cell incubation, no cell was observed on the MgO-PSZ, whereas a few cells attached on the CO(2) laser-treated MgO-PSZandshowedwellspreadandgood attachment. Moreover, the cell coverage density indicating cell proliferation generally increases with CO(2) laser power densities applied in the experiments. The enhancement of the surface energy of the MgO-PSZ, especially its polar component caused by the CO(2) laser treatment, was found to play a significant role in the initial cell attaching, thus enhancing the cell growth. Moreover, the change in topography induced by the CO(2) laser treatment was identified as one of the factors influencing the hFOB cell response.

Hybrid biomaterials based on the interaction of polyurethane oligomers with porcine pericardium.

Hybrid biomaterials have been produced by the interaction of polyurethane oligomers with both fresh and glutaraldehyde-fixed porcine pericardium. The hybrid biomaterials so formed were translucent with occasional white streaks and/or spots, had increased stiffness (to touch) but remained pliable. No shrinkage temperature was detected for fresh porcine pericardium hybrid up to 100 degrees C compared to porcine pericardium (approximately 67 degrees C) and glutaraldehyde-fixed porcine pericardium (approximately 87 degrees C). Amino acid analysis of the fresh porcine pericardium hybrid showed a reduction in lysine content after active isocyanate-terminated polyurethane oligomers exposure, indicating cross-linking between the polymer and tissue. Histological examination of the hybrid material shows a thin grey coating on both surfaces of the tissue, implying at least surface cross-linking of the tissue with polyurethane. The results suggest that fresh porcine pericardium can be reacted with active isocyanate-terminated polyurethane oligomers to produce hybrid biomaterials with covalent bonding.