Mechanics of Biological Systems and Materials, Volume 4

Frontmatter

Chapter 1. Study of the Transient Response of Tympanic Membranes Under Acoustic Excitation

Abstract

Characterization of the transient response of the human Tympanic Membrane (TM) subjected to impulse acoustic excitation is important in order to further understand the mechanics of hearing. In this paper, we present results of our initial investigations of the transient response of an artificial fully-constrained circular membrane as a simplified model of the TM. Two different optical methods used in our investigations are Laser Doppler Vibrometery (LDV) and Pulsed Double-Exposure Digital Holography (PDEDH) for single-point and full-field-of-view measurements of displacements, respectively. Applying Hilbert Transformation methods to the measured displacements allows determination of the transient characteristics of the membrane, including damping ratios and time constants, which are also computed and compared with corresponding FEM models. We expect to use this method in the investigation of the transient response of TM of specific species.

Morteza Khaleghi, Ivo Dobrev, Ellery Harrington, Cosme Furlong, John J. Rosowski

Chapter 2. Directional Failure of Tendons in the Presence of a Notch Defect

Abstract

Ligaments and tendons have been hypothesized to be highly resistant to tear propagation. However, alterations to ligament material response in the presence of tears have yet to be reported. The purpose of this research was to identify the variation in mechanical behavior at distinct fiber angles in tendon both with and without an intentional notch defect (mode I fracture toughness). Seventy two porcine tendon specimens were tested in uniaxial tension. Twety four specimens were pulled along the fiber direction (90°), 24 specimens along the matrix direction (0°), and 24 specimens had a fiber orientation of approximately 45°. In each group of specimens, half (12) were notched approximately 1/4 of the dimension transverse to the loading direction. Tendon tissues containing defects demonstrated a phenomenal resistance to tear propagation, regardless of loading direction. No observable crack propagation occurred in any of the specimens. Also, no significant differences were found in the strength and stiffness of specimens between the groups that had the defects and the ones that didn’t.

Gregory A. Von Forell, Peter S. Hyoung, Anton E. Bowden

Chapter 3. Age and Regional Dependence of Collagen Crimp in Heart Valves

Abstract

The hierarchical structure and organization of collagen plays an integral role in the mechanical behavior of heart valve tissues, but with few exceptions the degree of collagen fiber crimp has not been extensively quantified. Given our recent demonstration of age-dependent and region-dependent variations in mechanical behavior of heart valves, this study quantified crimp period and amplitude in all four heart valves as a function of orientation (circumferential vs. radial), age (6 week, 6 month, and 6 year old pigs), and region (mitral anterior leaflet center vs. free edge). Polarized light microscopy of picrosirius red stained sections revealed that collagen crimp was generally consistent between the circumferential and radial directions, although for the pulmonary valve there was a greater crimp period circumferentially than radially. Comparing all valves and orientations showed that the crimp period was greatest circumferentially in the center of the mitral anterior leaflet. With respect to age, crimp period was lowest in the 6 month old aortic valve (matching previously reported patterns of aortic valve leaflet extensibility) and highest in the 6 month old mitral anterior leaflet center. Interestingly, the differences in magnitudes of crimp amplitude mimicked the crimp period data, suggesting a scaling phenomenon in collagen fiber crimping.

Jennifer M. Kreuz, Kendra N. Erskine, Alicia A. Blancas, K. Jane Grande-Allen

Chapter 4. The Cohesive Law and Toughness of Engineering and Natural Adhesives

Abstract

Polymeric adhesives play a critical role in engineering applications, whether it is to bond components together or to serve as matrix for composite materials. Likewise, adhesives play a critical role in natural materials where adhesion is needed (e.g. mussel byssus) or to simply preserve the integrity of natural composite materials by holding fibers together (e.g. extra-collagenous proteins in bone). In this work we use a newly developed technique to measure the cohesive law and toughness of adhesives which is similar to a standard double cantilever beam configuration, but in which the beams are replaced by two rigid blocks. We originally developed this method for extracting the cohesive law of soft and weak biological adhesives, and we here show that it can be modified to include high strength of engineering adhesives. Using this method, the cohesive law of the adhesive is directly computed from the load-deflection curve of the experiment, without making initial assumption on its shape. The cohesive law reveals the strength and extensibility of the adhesives, which is richer in information than the toughness (which is the area under the cohesive law). We also define a non-dimensional parameter which can be used to quantitatively investigate whether the assumption of rigid substrates is valid. For values of the parameter close to unity, the RDCB rigidity assumption is valid and the method directly yields the cohesive law of the adhesive. The engineering and natural adhesives we tested showed a wide range of strength, toughness and extensibility, and revealed new pathways which can be exploited in the design and fabrication of biomimetic materials.

Ahmad Khayer Dastjerdi, Elton Tan, François Barthelat

Chapter 5. Comparing the Passive Biomechanics of Tension-Pressure Loading of Porcine Renal Artery and Its First Branch

Abstract

Renal arteries provide blood and nutrients to the kidneys, which are high demand organs. It is important to determine how these arteries behave under physiological loadings and their stress/strain response to increasing pressure and tension. To determine the passive mechanical behavior of both the porcine renal artery and its first branch, we performed simultaneous pressurization and axial loading on porcine artery specimens. Biomechanical experimental studies of soft-tissue are highlighted in this paper. The measurements will be used to identify parameters in the Holzapfel soft-tissue constitutive formulation describing the mechanical behavior of these arteries, a model that is widely used to describe the mechanical behavior of arteries Holzapfel GA, Gasser TC, Ogden RW (J Elast 61:1–48, 2000). Preliminary data from the experiments show that there is a difference in mechanical response behavior between the renal artery and its branch.

Mohamed G. Gabr, Michael A. Sutton, Susan M. Lessner, Stephane Avril, Pierre Badel

Chapter 6. Indentation Measurements on Soft Materials Using Optical Surface Deformation Measurements

Abstract

Instrumented indentation is a common technique for measuring the elastic properties of bulk materials as well as thin films on substrates. However, in traditional indentation, it can be difficult to determine the true deformation of a specimen due to the effects of machine compliance and thermal drift. In the present work, a method is developed to track the in-plane and out-of-plane deformation of a specimen during indentation tests using fluorescent microparticles. Bead tracking and quantitative defocusing methods are used to track the in-plane and out-of-plane displacements of the beads, respectively. Here, we describe the calibration of the system and assess the effects of particle size and magnification on the accuracy and resolution of the system. In addition, results from preliminary indentation tests performed on bulk polydimethylsiloxane specimens are reported. An analysis algorithm was developed to extract the elastic properties by measuring the displacements on the surface as a function of applied indentation force. Results are compared to traditional indentation measurements in which load and displacement are only measured at the indenter.

M. J. Wald, J. M. Considine, K. T. Turner

Chapter 7. Cadaveric Femoral Fractures in a Fall on the Hip Configuration

Abstract

We fractured 100 cadaveric femora with different areal bone mineral density (aBMD) (normal, osteopenic, and osteoporotic) in a fall on the hip loading configuration using a mechanical testing system. Two single-axis and one multi-axis load cells measured the forces and moments in the femoral head, shaft, and the greater trochanter. Two high-speed video cameras recorded the events leading to fracture from the anterior and posterior directions.

Force-displacement curve of a typical experiment showed a linear elastic region followed by post-yielding associated with sinking of the superior neck region into greater trochanter (73 of the tested femora). Fatal crack initiated in tension on the inferior region of the neck or medial shaft. Femoral strength (peak trochanteric force) exhibited strong correlation with aBMD. One-way analysis of variance showed significantly lower values for means of fracture forces and moments of osteoporotic femora compared to those of osteopenic and normal femora. Fracture forces showed very weak correlation with the femoral geometric parameters measured from CT scans. Using post-fracture CT scans and with the help of an orthopedist, the femoral fractures were classified into subcapital, transcervical, intertrochanteric and pertrochanteric. One-way analysis of variance indicated that femora with intertrocanteric fracture had significantly lower neck aBMD than femora with pertrochanteric and transcervical fractures.

S. Javid, V. Kushvaha, G. Karami, S. McEligot, D. Dragomir-Daescu

Chapter 8. Correlation of Multi-scale Modeling and Experimental Results for the Elastic Modulus of Trabecular Bone

Abstract

Trabecular bone is a porous nanocomposite material with a hierarchical structure. In this study, a multi-scale modeling approach, addressing scales spanning from the nanometer (collagen-mineral) to mesoscale (trabecular bone) levels, was developed to determine the elastic moduli of trabecular bone. Then, the predicted modeling results were compared with experimental data obtained by compression testing of bovine femur trabecular bone samples loaded in two different directions; parallel to the femur neck axis and perpendicular to that. Optical microscopy, scanning electron microscopy and micro-computed tomography techniques were employed to characterize the structure and composition of the samples at different length scales and provide the inputs needed for the modeling. To obtain more insights on the structure of bone, especially on the interaction of its main constituents (collagen and mineral phases), trabecular bone samples were deproteinized or demineralized and, afterwards, tested mechanically in compression. The experimental observations were used, in turn, to fine-tune the multi-scale model of bone as an interpenetrating composite material. Good agreement was found between the theoretical and experimental results for elastic moduli of untreated, deproteinized, and demineralized trabecular bones.

Elham Hamed, Ekaterina Novitskaya, Jun Li, Alexander Setters, Woowon Lee, Joanna McKittrick, Iwona Jasiuk

Chapter 9. Analysis of Stress Distribution Caused by Orthodontic Correctional Devices

Abstract

This investigation has been carried out to support the empirical studies conducted by dentists in orthodontic correction using brackets. Both numerical and experimental methods have been implemented in order to give a clear indication of the intrinsic stress distribution throughout a tooth and its surrounding periodontum when a load is applied to the tooth in its initial translation stage. For optimal accuracy, the tooth and surrounding periodontum in both cases are assigned different values proportional to those present in actuality. From the numerical model developed using Ansys Workbench 12, the possible stress patterns are determined. These are validated by the use of 3-dimensional photoelasticity. Tooth models manufactured from polymethyl-methacrylate are stress-frozen with a known loading configuration and sectioned in order to determine the internal stress pattern. These results are then compared with the finite element model. The choice of material was due to its ability to be manufactured without residual stresses, and its birefringent properties. This investigation will be effective in the improvement of orthodontic correctional procedures, especially with the emergence of more aesthetic bracket designs.

A. N. Okioga, R. J. Greene, D. G. Patrick, R. A. Tomlinson

Chapter 10. Hierarchical Bionanomaterials Under the Hammer: High-Rate Response of Silks

Abstract

Silks are of significant interest to scientists and the public due to their high specific strength and unsurpassed toughness. The study of their properties and formulation of physically-based models is ongoing in the biomaterials community. Interesting models and simulation data are appearing in the literature but there is a paucity of experimental data at high strain-rate or high frequency. To remedy this, high strain-rate characterisation has been undertaken alongside conventional low-rate tests, under a range of conditions. The methods reported here represent large-strain, high-rate, i.e. transverse impact; and small-strain, high-rate, i.e. vibration. Both have relevance to the use of silk in nature by organisms (protection, predation and communication) and the application/imitation of silk by materials scientists. Here we report the methodology and results to date in our investigations on silkworm and orb weaver silks.

D. R. Drodge, B. Mortimer, C. R. Siviour, C. Holland

Chapter 11. A Novel Dental Restorative Composite Fabricated with Nanostructured Poly(KAMPS)/Aragonite Filler

Abstract

A nanostructured dental restorative composite has been fabricated with a new poly(KAMPS)/aragonite filler to investigate the use of bioinspired materials in dental applications. The composite is fabricated with a common dental light activated resin and a poly(KAMPS)/aragonite filler created by biomimetic pathways and formed entirely from dilute aqueous solutions. The aragonite nanorod filler has a nanostructure with rod widths of 120 nm and polymer-filled spacings of 10–20 nm. Nanoindentation is used to characterize the mechanical properties of the novel composite. The new bioinspired composite has application as a dental restorative material.

Chad S. Korach, Matvey Sirotkin, Ranjith Krishna Pai

Chapter 12. The Effect of Dilution in Natural and Bio-inspired Staggered Composites

Abstract

The staggered structure is prominent in high-performance biological materials such as nacre, spider silk or bone. It consists of stiff and strong elongated inclusions aligned with the direction of loading. This structure leads to useful combinations of stiffness, strength and toughness, and it is therefore increasingly mimicked in bio-inspired composites. The modulus and strength of natural and bio-inspired composites are typically predicted using the shear lag model, where inclusions carry tensile stress and interfaces carry shear stresses. In this work, we have used a simple doctor blade technique to make thin film of nacre-like materials, which we tested in tension. Strength and modulus increase up to 10–15 % volume concentration of mineral reinforcement after which they degrade. Finite element analyses of staggered microstructure over a wide range of arrangement and concentrations revealed new trends which can explain the experimental results. For example the stiffness of the material can degrade in higher mineral concentrations if the tablets lack interface in the matrix. The results show that materials with combination of stiffness, strength and energy absorption can be achieved when there is an overlap between the tablets the distance between them is small in the transverse direction. This is identical with the microstructure of nacre where mineral tablets are divided by a very thin organic layer. The results suggest new approaches to simultaneously optimize modulus, strength and toughness in this class of composites.

Seyed Mohammad Mirkhalaf Valashani, François Barthelat

Chapter 13. New Insight into the Toughening Mechanisms of Nacre

Abstract

Many biogenic composites possess excellent mechanical properties in comparison to their abiogenic architectures (Nacre from Abalone is on the order of 3,000 times greater), which make them attractive for mechanically protective applications. The Nacre architecture has been well studied the past decade, however little work has focused on the fact that the Nacre composite is also itself a component of another composite architecture in the shells. In between thick layers of Nacre is a thin layer of an organic matrix that marks the seasonal growth patterns of the shells, analogous to tree rings. No work has focused on how these two layers interact to determine mechanical properties, which are likely as important as the tablet sliding itself. This work presents the first results in characterizing these layers.

MariAnne Sullivan, Barton C. Prorok

Chapter 14. Heterogeneity in Microscopic Residual Stress in the Aortic Wall

Abstract

Aortic wall has a concentric layered structure which is a pair of relatively stiff elastic lamina (EL) and a relatively soft smooth muscle cell (SMC)-rich layer. If soft and stiff layers bear the same stress in a loaded state, tensile and compressive residual stress should appear in the soft and stiff layer, respectively, in an unloaded state. In fact, ELs are corrugated and SMCs remain stretched in an unloaded aortic wall, and ELs become straight and SMCs shrink upon isolation from the surrounding tissues. As an index of compressive residual stress, a waviness W, defined as the length along its corrugation divided by its straight length, was calculated in the sections of porcine thoracic aortas. The waviness varied widely, ranging from 1.00 to 1.35. The variation of the waviness caused wide variation of the stress borne by the ELs. For example, estimated stress was as high as 150 kPa for the ELs with W = 1.00, and was 0 kPa for the ELs with W = 1.35. The reason for the large difference in the stress in the ELs is unclear at this stage. This may be caused by local activities of the smooth muscle cells such as wall remodeling and cell division.

Takeo Matsumoto, Akihisa Fukunaga, Kengo Narita, Yohei Uno, Kazuaki Nagayama

Chapter 15. Measuring and Modeling Morphogenetic Stress in Developing Embryos

Abstract

The biological tissues of a developing organism are built and reshaped by intra-embryonic forces. Such morphogenetic forces can be assessed and measured similarly to residual stresses. We will discuss in vivo measurements of morphogenetic stress using two quantitative laser-microsurgery techniques. The first uses a laser to drill a sub-cellular hole in a sheet of epithelial cells. The subsequent dynamic retraction of surrounding cells allows one to infer the local mechanical stress. The second uses a laser to isolate a single cell from the rest of a cell sheet. Isolation is accomplished on a microsecond time scale by holographically shaping a single laser pulse. The subsequent retraction (or expansion) of the isolated cell allows one to separate and quantify the effects of cell-internal and cell-external stresses in the determination of cell shape. Both types of experiment are strongly supported by cell-level finite element models. We will discuss application of these techniques and models to the time-dependent biomechanics of epithelial tissues during early fruit fly embryogenesis – specifically during the processes of germband retraction and dorsal closure.

M. S. Hutson, G. W. Brodland, X. Ma, H. E. Lynch, A. K. Jayasinghe, J. Veldhuis

Chapter 16. Residual Stress and Structural Anisotropy of Cortical Bone

Abstract

The concept of residual stress and strain does not have long history for biological tissues. In the case of cortical bone, during remodeling process the old tissue is replaced by the new tissue with construction of osteons. Since the new tissue is generated under in vivo loadings as a non-deformed state, an indeterminate structure may be generated as a result of difference between the deformations of the old and new phases. Further, the mechanical properties (e.g. elastic modulus) are also different in these phases. Because of such non-uniform structures in cortical bone, residual stress/strain will remain in the replaced region even without external loading being applied. Tadano and co-workers initiated efforts to estimate residual stress/strain in cortical bone. In a very few applications with bone, the authors have successfully applied X-ray diffraction to quantify residual stresses at the bone surface. In this work, site-specific residual strain characteristics in relation with the mineral crystal orientation were studied and the sin² ψ method was applied to measure residual stresses in bovine and rabbit extremities. The relationship between residual stress and osteon population density on the respective sites has also been obtained. Thus the knowledge about residual stress/strain in cortical bone, related with mineral crystal distribution and osteon population density, might play an important role in the biomechanical aspects of bone healing and remodeling.

Shigeru Tadano, Satoshi Yamada

Chapter 17. Microcracking Morphology and Structure Optimization of Compact Bovine Bone Under Impact Loading

Abstract

Deterioration of bone is a progress of damage accumulation in the form of microcracking spanning a wide range of dimensional scales. To examine the microcracking morphology of compact bone subjected to impact loading, non-notched beam specimens of compact bovine femur were loaded with an instrumented Charpy impact system under various impact energy levels. The middle sections of the tested specimens was examined the by Frost’s basic funsion technique by Frost (Med Bull 8:25–35, 1960) to investigate the microcracking morphology. The effects of size of osteon on the mechanical integrity of ostoen structure were also investigated by using of a finite element modeling (FEM), micromechanics, and constrained optimization method. The damage mechanism and energy dissipation were analyzed.

Wei Zhang, Srinivasan Arjun Tekalur, Ziwei Zhong

Chapter 18. Biomechanical Response of Blast Loading to the Head Using 2D-3D Cineradiographic Registration

Abstract

This paper details a method for tracking 3D kinematics of the skull and brain deformation in post-mortem human subjects (PMHS) using 2D cineradiographic images during a high-rate loading event. Brain displacement and resulting strain due to blast loading is a metric for Traumatic Brain Injury (TBI), however physically measuring brain motion experimentally is a significant challenge. A shock tube, used to simulate blast exposure, created skull and brain motion tracked using implanted radio-opaque markers and high-speed X-ray images. These images were registered to a computed tomography (CT) scan using intensity-based 2D-3D registration techniques. To register the 2D images to the 3D scan, digitally reconstructed radiographs were generated from the CT scan, and then compared to the recorded x-ray frames by maximizing similarity metrics between the images using a Covariance Matrix Adaptation Evolution Strategy. As compared to pure 2D tracking, 2D-3D registration provides out-of-plane kinematics by fully leveraging information in the x-ray projection image and prior information from the 3D CT scan. Data generated with these techniques are critical for physically understanding the mechanisms associated with blast exposure that may lead to TBI, and can be used for human computational model validation.

R. S. Armiger, Y. Otake, A. S. Iwaskiw, A. C. Wickwire, K. A. Ott, L. M. Voo, M. Armand, A. C. Merkle

Chapter 19. Dynamic Analysis of a Spread Cell Using Finite Element Method

Abstract

The dynamic analysis of a cultured cell using Finite Element Analysis is presented to understand the effect of vibration on a cell structure. The model of a spread cell on a culturing plate has been developed as a continuum model and a cellular tensegrity model. Using Finite Element modal analysis, natural frequencies and mode shapes of both models were obtained and compared with each other. Finite Element harmonic response analysis was carried out to investigate the dynamic response of a spread cell exposed to vibration in the frequency range of 1–60 Hz with 1 G acceleration. Both continuum model and tensegrity model showed that the first three natural frequencies appeared in range of 18 ~ 27 Hz and they were in the effective vibration frequency range for bone cell growth. In mode 1–3 the major oscillation was observed in horizontal direction and the resonance occurred when the base vibration frequency was closed to the calculated natural frequency. It is presumed that the optimal frequency for bone cell growth is closely related the natural frequency of cell structures and associated with the resonance of cellular structures. For better understanding resonance of cell structure future studies will consider the damping capability of cell structures.

Hwabok Wee, Arkady Voloshin

Chapter 20. Imaging Targets to Identify Chromosomal Abnormalities in Cells

Abstract

Ensuring genetic stability in pluripotent stem cell (PSC) cultures is essential for the development of successful cell therapies. Many laboratories have found the emergence of genetic abnormalities in PSCs when cultured in vitro for prolonged amounts of time. These cells are mostly cultured in non-physiological stiff substrates like tissue culture polystyrene which produces the suspicion that the cause of these abnormalities may be influenced by substrate mechanics. In order to verify this, it is important to be able to determine and image, using fluorescence microscopy, potential targets within the cells that are indicative of genetic abnormalities. These genetic abnormalities are most likely to occur during cell division. Microtubules, comprised of the cytoskeletal protein tubulin, organize and separate chromosomes during cell division, thus it has been our main imaging target. We have been able to detect chromosomal abnormalities in human embryonic stem cells by fluorescence microscopy.

S. Acevedo-Acevedo, B. Napiwocki, W. C. Crone

Chapter 21. 3D Neutrophil Tractions in Changing Microenvironments

Abstract

The mechanical properties and geometry of the surrounding microenvironment play a significant role in regulating cellular behavior including cell adhesion, migration and generation of traction forces. In many 3D tissue culture scenarios, changing the local matrix geometry, or cellular confinement simultaneously alters matrix stiffness, which makes the two physical factors coupled. In this study we design an interchangeable 2D-3D sandwich gel structure system with tunable mechanical properties capable of changing matrix stiffness and cellular confinement independently. Using a double-hydrogel system and our previously developed 3D TFM technique we investigate neutrophil migration and traction forces as a function of varying matrix stiffness and confinement.

Jennet Toyjanova, Estefany Flores-Cortez, Jonathan S. Reichner, Christian Franck

Chapter 22. Correlations Between Quantitative MR Imaging Properties and Viscoelastic Material Properties of Agarose Gel

Abstract

This study determines and assesses correlations between quantitative magnetic resonance imaging (qMRI) parameters (proton density, diffusion, T1 and T2 relaxation) and viscoelastic material properties (storage modulus) for various low concentrations (0.5–3.0 % weight/volume) of agarose gel. MR imaging was done using a 3T (Philips Achieva) scanner. Dynamic mechanical analysis (DMA) was used to characterize the viscoelastic properties of the gels. The repeatability and accuracy of the DMA measurements have some dependence on various geometric sample and measurement parameters. An optimal set of parameters (for compression mode testing) that would produce reliable and repeatable measurements was identified for ranges of sample geometry. Higher concentrations of agarose were associated with higher storage moduli and lower relaxation times, diffusion coefficients, and proton densities. Of the qMRI parameters, T2 relaxation is the most sensitive to changes in concentration.

Erica D. Chin, Jenny Ma, Christopher L. Lee, Hernan J. Jara

Chapter 23. Electrostatic Actuation Based Modulation of Interaction Between Protein and DNA Aptamer

Abstract

The need to design nanoscale, sensitive and flexible biotic-abiotic interface keeps increasing. The essential issue is how to facilitate biological signal transmission and modulation through controllable external stimuli. This requires a thorough understanding of the binding and dissociation process between bio-molecules under the stimuli. The purpose of this study is to demonstrate the binding and dissociation behavior between the anti-coagulation protein thrombin and single-stranded DNA aptamer with application of electrical fields. Micro-contact printing was utilized to prepare compositionally patterned gold specimen with adjacent regions covered with alkanethiol and DNA aptamer molecules, then thrombin molecules were injected into the system to form the binding pair with aptamer. Different electrical field potentials were applied to the nanoscale structure by a three-electrode electrochemical cell. Due to the negatively charged nature of aptamer DNA strands, positive electrical field can trigger a large bending-down conformational transition of the aptamer, thus can break the bonds between binding pair. Through Atomic Force Microscopy, height of the pattern was measured and the difference of height under different potentials can show the binding state of the pair. We can propose a method to actuate and modulate the dissociation behavior between thrombin and aptamer through the external electrostatic stimuli.

Xiao Ma, Pranav Shrotriya

Chapter 24. The Relation Between Crispness and Texture Properties of Wax Apple

Abstract

In this study, the relations between the well-like sensory properties, crispness and firmness, of wax apple (Syzygium samarangense) and the texture properties were investigated by using double-bite tests. The strains of wax apples used in this study are Black Pearl and Tubtimchan. By comparing the sensory judgment and the TPA test results, the sensory judgment of crispness could be related to the TPA parameter fracturability. The wax apple with higher fracturability is considered to be crispier. However the sensory judgment of firmness cannot be direct correlated to any single TPA parameter. The sensory feeling of firmness could be related to the difference between hardness and fracturability.

S. Topaiboul, C.-C. Guo, R.-H. Gao, N.-S. Liou

Chapter 25. Fabrication and Mechanical Characterization of Jute Fiber/Epoxy Laminar Composites

Abstract

Alkali and Silane surface treatments based off of work published previously (J Appl Polym Sci 71(4):623–629, 1999; Polym Eng Sci 49(7):1253–1272, 2009; Mater Sci Eng A 508(1–2):247–252, 2009) were applied to plain weave and unidirectional jute fabric to improve epoxy compatibility and reduce moisture affinity. Efficacy of treatments was proven with the use of wicking tests. Studies performed on the hand-layup method showed unacceptable void content. Laminated jute/epoxy composites were fabricated using Vacuum Infusion to create void-free samples. This process was improved through optimization for use with jute and the addition of a pre-compaction step to increase fiber volume fraction from 25 % to a maximum of 40 %. Mechanical testing on composites fabricated with raw and treated jute fabrics showed a 300 % increase in elastic modulus for treated jute fabric over neat epoxy resin. Moisture absorption testing (ASTM D570) showed a significant improvement in moisture resistance for silane-treated fabrics.

M. Pinto, Y. K. Kim, A. F. Lewis, V. Chalivendra

Chapter 26. A Fractional Pressure-Volume Model of Cerebrospinal Fluid Dynamics in Hydrocephalus

Abstract

Hydrocephalus is a serious neurological disorder characterized by abnormalities in the cerebrospinal fluid (CSF) circulation, resulting in an excessive accumulation of CSF in the ventricles of the brain, brain compression and sometimes an increase in the intracranial pressure. It is believed that hydrocephalus may be caused by increased CSF production, or by obstruction of CSF circulation or of the venous outflow system. Therefore, the treatment is based on CSF flow diversion. Given that the response of patients who have been treated continues to be poor, there is an urgent need to design better therapy protocols for hydrocephalus. An important step in this direction is the development of predictive mathematical models that better explain the fundamental science behind this clinical condition. One of the first mathematical models of CSF pressure-volume compensation introduced by Marmarou in the 1970s provides a theoretical basis for studying hydrocephalus. However, the model fails to fully capture the complex CSF dynamics. In this paper we propose a generalization of Marmarou’s model using fractional calculus. We use a modified Adomian decomposition method to solve analytically the proposed fractional order nonlinear differential equation. Our results show temporal multi-scaling behavior of the CSF dynamics.

Justin Kauffman, Corina S. Drapaca

Chapter 27. Site-Specific Diagnostic Evaluation of Hard Biological Tissues Using Solitary Waves

Abstract

We perform site-specific diagnostic evaluation of hard biological tissues via highly nonlinear solitary waves. Solitary waves are compact-supported tunable pulses with extremely high energy density, which can be efficiently formed in a chain of ordered granular particles defined as 1D granular crystals. We transmit a single pulse of solitary waves into specific areas of artificial biological systems via direct mechanical contact with a granular crystal sensor. We then record the solitary waves backscattered from a targeted bone area to assess its mechanical stiffness. By taking advantage of the coupling between nonlinear granular media and biological systems, we demonstrate that reflected solitary waves are highly sensitive to site-specific mechanical properties of hard biological tissues. The efficacy of the diagnostic approach is investigated by comparing the stiffness measurements with nominal elastic moduli of polyurethane foams that mimic osteoporotic bone. We also perform numerical investigations via a discrete element (DE) model, simulating propagation and attenuation of solitary waves at the interfaces. The site-specific evaluation technique via solitary waves has the potential for clinical applications, such as assisting appropriate intraoperative decision during joint replacement or spinal surgery for better surgical outcome.

Jinkyu Yang, Sophia N. Sangiorgio, Sean L. Borkowski, Edward Ebramzadeh, Chiara Daraio