4 research outputs found
DEVELOPMENT OF A PATIENT-SPECIFIC OCULAR MODEL FOR RISK ASSESSMENT OF GLAUCOMA DEVELOPMENT AND PROGRESSION
No full textGlaucoma is the leading cause of blindness worldwide. Once the retinal ganglion cell axons are lost they cannot be cured. Therefore, preventative risk assessment measures are important. To be able to perform these tasks, one needs to understand the mechanism behind the axonal blockage that leads to glaucoma. Biomechanical factors are thought to play a role in glaucoma, but the specific mechanism is not explored. In a Finite Element (FE) ocular model, the complex shape of the optic nerve components can be modeled and relevant mechanical quantities, such as stresses and strains due to intraocular (IOP) and/or intracranial (ICP) pressure, can be estimated and their effects assessed. Furthermore, optic nerve head (ONH) morphology and especially lamina cribrosa shape and properties, which are tightly linked to Glaucoma onset and development, vary greatly between individuals. This consequently suggests the development of patient-specific FE ocular models.
A method to generate patient-specific ocular models was contrived based on the geometry extracted from Optical Coherence Tomography (OCT) scans. Specifically, retinal layers were segmented using intensity and graph-based algorithms and the segmented layers were then reconstructed with a thin plate spline method. Finally, solid models were created from the reconstructed surfaces and meshed with tetrahedral elements. The geometric details of the generated ONH model correlate well with those of generic models from pertinent literature and special attention was paid to meshing so that the optic nerve region of the ocular model exhibits analysis-suitable element quality. The suggested reconstruction method is semiautomatic and although we aimed to fully capture the complete ONH region, some anatomical structures, which are generally considered relevant and important, could not be extracted from OCT images in vivo. These include the pia arachnoid complex (dura mater and pia mater) that contains cerebrospinal fluid material and is considered to exert ICP. These were handled by carrying out a parametric analysis, using generic models with linear elastic material properties, to establish the degree of importance of the pia arachnoid complex. It was found that pia and dura mater properties can affect post laminar neural tissue and lamina cribrosa biomechanics. As it is currently infeasible to obtain high-quality patient-specific geometries for the pia arachnoid complex in vivo, we embed generic models of the pia and dura mater in our patient-specific ONH model. Viscoelastic material properties of dura mater and sclera were additionally retrieved from physical unidimensional tensile stress-relaxation tests. The influence of viscoelastic material properties at certain levels of ICP/IOP with a generic ocular model was examined, and results indicated, as expected, the importance of viscoelastic properties. Parametric analysis of patient-specific models was performed via the principal component analysis method deriving statistical shape models (SSM). Qualitative, quantitative and biomechanical assessments were performed with the aid of the generated SSM. For the biomechanical assessment, finite element modeling was employed and several patient-specific models, based on SSM shape modes, were generated and tested. We anticipate further enhancements and developments for this approach in the future. Based on the so far obtained results, we find evidence that patient-specific, anatomically detailed 3D ocular models allow for a better understanding of employed biomechanics and can benefit glaucoma risk assessment
Brillouin Biosensing of Viscoelasticity across Phase Transitions in Ovine Cornea
No full textNoninvasive in situ monitoring of viscoelastic characteristics of corneal tissue at elevated temperatures is pivotal for mechanical property-informed refractive surgery techniques, including thermokeratoplasty and photorefractive keratectomy, requiring precise thermal modifications of the corneal structure during these surgical procedures. This study harnesses Brillouin light scattering spectroscopy as a biosensing platform to noninvasively probe the viscoelastic properties of ovine corneas across a temperature range of 25–64 °C. By submerging the tissue samples in silicone oil, consistent hydration and immiscibility are maintained, allowing for their accurate sensing of temperature-dependent mechanical behaviors. We identify significant phase transitions in the corneal tissue, particularly beyond 40 °C, likely due to collagen unfolding, marking the beginning of thermal destabilization. A subsequent transition, observed beyond 60 °C, correlates with collagen denaturation. These phase transformations highlight the cornea’s sensitivity to both physiologically reversible and irreversible viscoelastic changes induced by mild to high temperatures. Our findings underscore the potential of the Brillouin biosensing technique for real-time diagnostics of corneal biomechanics during refractive surgeries to attain optimized therapeutic outcomes
Critical Assessment on the Stability and Convergence of the Conventional Gear Tooth Contact Analysis
No full textMathematical modeling of gear engagement is crucial during design to ensure optimal performance in manufacturing. This study reproduces the conventional tooth contact analysis (TCA) model, highlighting convergence issues in parallel-axis gears and limitations in local synthesis methods. The research critically analyzes the TCA method, which solves five nonlinear equations to assess performance and accuracy. Simulations replicate the conditions of previous studies to ensure valid comparisons. Initial guess values are randomly generated within a specific range to guide the iterative process toward convergence, with this range progressively narrowed to improve computational efficiency and accuracy. Results indicate that the TCA approach is highly sensitive to initial guess values, particularly the starting angular position. Convergence issues arise from the complexity of nonlinear equations and multiple roots. This can lead to divergence or reverting to the initial guess when values deviate significantly from the true solution
Mechano-Chemistry across Phase Transitions in Heated Albumin Protein Solutions
No full textThe presence of certain proteins in biofluids such as synovial fluid, blood plasma, and saliva gives these fluids non-Newtonian viscoelastic properties. The amount of these protein macromolecules in biofluids is an important biomarker for the diagnosis of various health conditions, including Alzheimer’s disease, cardiovascular disorders, and joint quality. However, existing technologies for measuring the behavior of macromolecules in biofluids have limitations, such as long turnaround times, complex protocols, and insufficient sensitivity. To address these issues, we propose non-contact, optical Brillouin and Raman spectroscopy to assess the viscoelasticity and chemistry of non-Newtonian solutions, respectively, at different temperatures in several minutes. In this work, bovine and human serum albumin solution-based biopolymers were studied to obtain both their collective dynamics and molecular chemical evolution across heat-driven phase transitions at various protein concentrations. The observed phase transitions at elevated temperatures could be fully delayed in heated biopolymers by appropriately raising the level of protein concentration. The non-contact optical monitoring of viscoelastic and chemical property evolution could represent novel potential mechano-chemical biomarkers for disease diagnosis and subsequent treatment applications, including hyperthermia
