Repeatability, Reproducibility, and Calibration of the MyotonPro® on Tissue Mimicking Phantoms

The MyotonPro® (Myoton AS, Tallinn, Estonia) is commonly used to quantify stiffness properties of living tissues in situ. Current studies quantify the dynamic stiffness properties of living tissues, but do not validate or compare these measurements to a standardized method. Additionally, living tissue, being dynamic in nature, presents much variability in data collection. To address these issues this study focuses on the repeatability and reproducibility of the MyotonPro® on polymeric gel-based tissue phantoms. In addition, a correlation study is also performed to translate dynamic stiffness to a more standardized property, Young’s modulus. Such studies help to confirm the reliability of the measurements obtained in situ.

An Efficient Preconditioner for Linear System Solution in Multi-Domain Modeling of the Circulatory System

A closed-loop lumped parameter network (LPN) coupled to a 3D domain is a powerful tool that can be used to model the global dynamics of the circulatory system. Coupling a 0D LPN to a 3D CFD domain is a numerically challenging problem, often associated with instabilities, extra computational cost, and loss of modularity. A computationally efficient finite element framework has been recently proposed that achieves numerical stability without sacrificing modularity [1]. This type of coupling introduces new challenges in the linear algebraic equation solver (LS), producing an strong coupling between flow and pressure that leads to an ill-conditioned tangent matrix. In this paper we exploit this strong coupling to obtain a novel and efficient algorithm for the linear solver (LS). We illustrate the efficiency of this method on several large-scale cardiovascular blood flow simulation problems.

Effects of Body Weight Modification on Internal Knee Contact Forces During Gait

Obesity is commonly considered a risk factor for the development of knee osteoarthritis [1]. Previous studies have shown that reductions in body weight correspond to reductions in total knee joint compressive forces (as calculated by inverse dynamics) [2–4]. A recent study showed that external knee load measurements are not strong predictors of internal knee contact forces [5]. Therefore, direct measurement of knee contact force is important for understanding how body weight changes impact knee joint loading. Force-measuring knee implants can directly measure internal knee contact forces [6].

Age Dependent and Anisotropic Material Properties of Immature Porcine Sclera

Current finite element (FE) models of the pediatric eye are based on adult material properties [2,3]. To date, there are no data characterizing the age dependent material properties of ocular tissues. The sclera is a major load bearing tissue and an essential component to most computational models of the eye. In preparation for the development of a pediatric FE model, age-dependent and anisotropic properties of sclera were evaluated in newborn (3–5 days) and toddler (4 weeks) pigs. Data from this study will guide future testing protocols for human pediatric specimens.

Region-Specific Medial Fiber Micro-Architecture in the Longitudinal-Radial and Circumferential-Radial Planes of Ascending Thoracic Aortic Aneurysm Among Bicuspid and Tricuspid Aortic Valve Patients

Aortic dissection is a life-threatening cardiovascular emergency with a high potential for death. It usually begins with an intimal tear which permits blood to enter the wall, split the media and create a false lumen, which can reenter the true lumen or exit through the adventitia causing complete rupture. A possible mechanism for dissection of ascending thoracic aortic aneurysm (ATAA) can be the occurrence of blood pressure-induced wall stresses in excess to the adhesive strength between the degenerated aortic wall layers.

Nycthemeral Rhythm of the Frequency and Biomechanical Energy of High Frequency Intraocular Pressure Fluctuations

The optic nerve head (ONH) is the site of insult in glaucoma, the second leading cause of blindness worldwide. Intraocular pressure (IOP) is commonly regarded as a major factor in the onset and progression of the disease1 and lowering IOP is the only clinical treatment that has been shown to retard the onset and progression of glaucoma2. However, many patients continue to progress even at an epidemiologically-determined normal level of IOP3. This suggests that in addition to the mean value of IOP, IOP fluctuations could be a factor in glaucomatous pathophysiology. The importance of low frequency fluctuations of clinically-measured mean IOP remains controversial. These studies all rely on snapshot measurements of mean IOP at each time point, and those measurements are taken at relatively infrequent intervals (hourly at the most frequent, but usually monthly or longer). Recently however, there has been some interest in ocular pulse amplitude, or the fluctuation in IOP associated with the cardiac cycle, which can be measured by Dynamic Contour Tonometry (DCT). DCT provides continuous measurement of IOP, but only for a period of tens of seconds in which a patient can tolerate corneal contact without blinking or eye movement, which ironically are two of the most common sources of large high frequency IOP fluctuations according to our telemetric data collected from monkeys4 and previous human studies. In a recent report, continuous IOP telemetry was used in three nonhuman primates to characterize IOP dynamics at multiple time scales for multiple 24-hour periods5.

Skin Perfusion, Arterial and Venous Blood Flow, and Soft Tissue Thickness in Relation to Pressure Ulcers

Pressure ulcers have been a concern in healthcare settings, with more than 50% of bedridden or wheelchair-bound patients being affected [1]. Pressure ulcers typically occur on a region of the body that experiences forces from an external structure (e.g. bed, wheelchair). Researchers believe that such forces cause a decrease in blood flow, which results in tissue necrosis, causing pressure ulcers [2].

Uvula Dynamic Characteristics

The airway binary fluid layer and the structural characteristics of the upper airways have significant influence on the activity of the airway muscles by changing airway compliance and collapsibility during obstructive sleep apnea trauma. The uvula plays an important role in the collapse process. Using MRI scans, this paper develops a structural model for the uvula and determines its dynamic characteristics in terms of natural frequencies and mode shapes as a preliminary process to determine optimum conditions to therapeutically relieve upper airway obstruction. The effect of the variation of tissue elasticity due to water content is elaborated on.

Constitutive Modeling of Biaxial Mechanical Response of Arteries Subjected to Gradual Elastin Degradation

The passive mechanical response of arteries is believed to be mainly dominated by elastin and collagen fibers. Many arterial diseases are accompanied by significant changes in quantity and as well as the microstructure of these constituents due to the mechanical and biological adaptive processes. In this study we focus on the biaxial tensile test data of elastase-treated porcine aortic tissues [1]. We study the mechanical behavior of aortic tissues under gradual elastin degradation through constitutive modeling and associate the mechanical response with the microstructure of collagen observed in the microscopic images of fresh and digested tissues.

Fabrication of Hybrid Cell-Microbead Constructs Using Laser Direct-Write of Alginate Microbeads and Adherent Breast Cancer Cells

Microbeads are becoming popular tools in tissue engineering as 3D microstructure hydrogels. The gel nature of microbeads enables them to sequester soluble factors and mammalian cells, and their high surface area-to-volume ratio allows diffusion between the bead and the environment [1,2]. Microbeads are thus good systems for drug delivery and can serve as 3D microenvironments for cells. To fully maximize their potential as delivery systems and microenvironments, it is highly desirable to create spatially-precise hybrid cultures of microbeads and mammalian cells. Precise placement of microbeads in proximity to patterned cells will allow the study of spatial cellular interactions, paracrine signaling, and drug delivery.