Narrow Results

Late stent edge restenosis (SER) following percutaneous coronary intervention (PCI) remains a significant complication with unclear etiology. This study aims to investigate the transient edge vascular response (EVR) using virtual stenting technology. Methods: Six finite element analysis (FEA) models were constructed to simulate stenting procedures. Profiles of lumen diameter, ellipticity, and maximum principal stress (MPS) distribution of the vascular wall were calculated and analyzed at four typical time points: the initial state, post-balloon pre-dilation analysis, maximum stent expansion, and final configuration. Results: Balloon pre-dilation significantly increased lumen diameters in the stented segments but had a minimal impact on the nonstented segments. At maximum stent expansion, the diameter of the stented segments showed a substantial increase compared to the post-balloon pre-dilation phase. Subsequently, a reduction in diameter was observed the following recoil of the vascular wall. The ellipticity of stenotic segments decreased markedly at maximum stent expansion. Following balloon pre-dilation, the stress within the artery wall was relatively low and did not differ significantly between stented and nonstented segments. At maximum stent expansion, MPS was elevated in both the stented and nonstented segments, particularly near the stent end. In the final configuration, there was a significant reduction in MPS, especially in the stented sections. Conclusion: The virtual stenting method allows for the simulation of transient EVR and facilitates the analysis of geometric and biomechanical changes. This approach aids in understanding the mechanical factors involved in late SER.

Articular cartilage is an hydrated tissue that withstands and distributes mechanical stresses. The chondrocytes respond to mechanical signals by regulating their metabolic activity through complex biological and biophysical interactions with the extracellular matrix (ECM). The objective of this work was to compare, under mechanical stress, the ECMs synthesized by rat chondrocytes seeded onto biosystems based on alginate (Alg), hyaluronic acid (HA) and a HA amphiphilic derivative. The mechanical stress simulates the traumatisms resulting from accidental shocks or intensive physical exercise by knocking the biosystems together. The investigation of ECMs neosynthesized by chondrocytes was carried out according to various criteria: proliferation, proteoglycans synthesis activity, expression of type I and type II collagens and the expression of α5/β1 integrin.

The results obtained for the stress applied on neosynthesized matrixes of 3, 10, 17 and 24 days evidenced a high proliferation and proteoglycans synthesis activity for cells submitted to a knocking process. For all biosystems, the neosynthesized matrix contained an important level of collagen, which was in part of type II, whatever the biosystems.

Finally, the chemical modification of HA by long hydrophobic alkyl chains, affords an amphiphilic derivative with viscoelastic properties perfectly mimicking those of matricial environment of chondrocytes. This study showed that the HA amphiphilic derivative induced biological effects similar to those of parent HA containing no hydrophobic modifications.

Nowadays, because of great biomedical applications of state-of-the art prototyping (bio-printing), many studies have been conducted in this field with focus on three-dimensional prototyping. There are several mechanisms for bio-printing of live cells such as piezoelectric and thermal and pneumatic inkjeting systems. Cell viability should be preserved during the bio-printing process. Lots of researches have been carried out to investigate and compare cell viability through different prototyping mechanisms. In order to quantify percentage of the cells that are killed during the proto-typing process, applied stresses on the cell and consequently its deformation should be calculated. A maximum strain energy density that the cell can tolerate is reported in the range of 25 Kj ⋅ m^-3 to 100 Kj ⋅ m^-3. This can be considered as a criteria to find the percentage of the damaged cells during the bio-printing processes. In this study, the bio-printing of the cell has been modeled and the cell viability have been investigated. Firstly, it is shown that in modeling of the bio-printing process, the effects of dynamic flow on calculating the applied stress on the cell is not negligible and must be considered. In the next step, the percentage of damaged endothelial cell aggregate under 80 kPa applied pressure (64 MPa/m) and 200 micron nozzle diameter is reported. Based on findings of this study, the percentage of endothelial cells viability under mentioned condition is reported 76%. The proposed method of this study can be utilized to examine the cell viability and performance of each prototyping systems.

BiFeO₃ (BFO) is usually considered as a multiferroic material, which shows both ferroelectric and antiferromagnetic properties at room temperature. It is an important material having potential applications in various spintronics devices. Many studies have been done to understand the ferroelectric and magnetic responses of BFO; therefore, this work is focused on characterizing the coupling effects of electric, magnetic and mechanical field on the ferroelectric properties and surface potential of the BFO thin films. A polycrystalline BFO film (~200 nm) is deposited on the Si substrate by the Pulse Laser Deposition techniques. The Vertical Piezoresponse Force Microscopy (PFM) is used to study the ferroelectric domain structure and the hysteresis loop of as-deposited BFO film as well as the effects of the mechanical stress and magnetic field on those properties. Kelvin Probe Force Microscopy (KPFM) is used to measure the surface potential of the samples. To apply the mechanical stress on the film, micro-indentations were made on the surface of the film with two different loads (1.96 N, 2.94 N). Then the ferroelectric domain structure, strain amplitude, domain switching (hysteresis response) behavior and surface potential are measured at the locations near the side of the indentation cavity and cracks. This way, the coupling effects of electric, magnetic and stress field on BFO film are studied at nanoscale.

The replacement of the "flat biology" of the Petri dish with three-dimensional (3D) cell cultures has shown to narrow the gap between cell behaviours and function in vitro and at the physiological settings. A fundamental challenge to realise the potential of the 3D cell culture is the design and application of "smart" bioreactor systems. These systems should provide homogenous mass transport into the internal volume of the cultured cell constructs as well as to efficiently propagate physical and mechanical stimuli. Herein, we describe the design principles of various bioreactors, starting with the conventional spinner flasks, the rotary wall vessels and up to the latest perfusion vessels. In particular, the key role of perfusion bioreactors in regenerating the dynamic 3D cell microenvironment is demonstrated by providing a few successful examples of engineering thick functional tissues, such as the cardiac muscle tissue. In closing this chapter, we envision future innovations in bioreactors.