Fiber Bundle Size Research Articles

Fiber-Specific White Matter Alterations in Parkinson's Disease Patients with GBA Gene Mutations.

Patients with Parkinson's disease (PD) carrying GBA gene mutations (GBA-PD) have a more aggressive disease course than those with idiopathic PD (iPD). The objective of this study was to investigate fiber-specific white matter (WM) differences in nonmedicated patients with early-stage GBA-PD and iPD using fixel-based analysis, a novel technique to assess tract-specific WM microstructural and macrostructural features comprehensively. Fixel-based metrics, including microstructural fiber density (FD), macrostructural fiber-bundle cross section (FC), and a combination of FD and FC (FDC), were compared among 30 healthy control subjects, 16 patients with GBA-PD, and 35 patients with iPD. Associations between FDC and clinical evaluations were also explored using multiple linear regression analyses. Patients with GBA-PD showed significantly lower FD in the fornix and superior longitudinal fasciculus than healthy control subjects, and lower FC in the corticospinal tract (CST) and lower FDC in the CST, middle cerebellar peduncle, and striatal-thalamo-cortical pathways than patients with iPD. Contrarily, patients with iPD showed significantly higher FC and FDC in the CST and striatal-thalamo-cortical pathways than healthy control subjects. In addition, lower FDC in patients with GBA-PD was associated with reduced glucocerebrosidase enzyme activity, lower cerebrospinal fluid total α-synuclein levels, lower Montreal Cognitive Assessment scores, lower striatal binding ratio, and higher Unified Parkinson's Disease Rating Scale Part III scores. We report reduced fiber-specific WM density and bundle cross-sectional size in patients with GBA-PD, suggesting neurodegeneration linked to glucocerebrosidase deficiency, α-synuclein accumulation, and poorer cognition and motor functions. Conversely, patients with iPD showed increased fiber bundle size, likely because of WM reorganization. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The Relationship Between Fiber Bundle Size and Mechanical Performance of Additively Manufactured Continuous Carbon Fiber Reinforced Thermoplastic Composites.

Additively manufactured continuous fiber-reinforced thermoplastic (CFRTP) composites are still in the early stages of reaching competitive mechanical properties compared with conventional composites. The main reason for this is that their mechanical properties are limited due to weak interlayer strength, porosity, and low fiber fraction. Therefore, the effects of many parameters, such as layer thickness, temperature, printing speed, and fiber fraction, have been extensively studied to improve mechanical properties. With a different perspective on these parameters, this study aimed to investigate the effect of fiber bundle size on the mechanical properties of CFRTP composites. For this purpose, 3K and 6K fiber bundle filaments with the same fiber volume fractions (∼41%) were produced utilizing a polymer impregnation setup. CFRTP samples were printed using fused deposition modeling with polylactic acid as the matrix. The mechanical properties were investigated via three-point bending, interlaminar shear strength (ILSS), and tensile tests. The results showed that fiber bundle size does not particularly influence tensile strength but dominates flexural and ILSS performance. Although increased flexural strength and modulus were observed, the bundle size effect was much more dominant in ILSS tests, and 6K bundle size samples with the same fiber fraction showed much higher strength.

Structure-function relationships of TMJ lateral capsule-ligament complex

The human temporomandibular joint (TMJ) lateral capsule ligament (LCL) complex is debated as a fibrous capsule with distinct ligaments or ligamentous thickening, necessitating further evaluation of the complex and its role in TMJ anatomy and mechanics. This study explores the ultrastructural arrangement, biomechanical tensile properties, and biochemical composition of the human LCL complex including region-specific differences to explore the presence of a distinct temporomandibular ligament and sex-specific differences to inform evaluations of potential etiological mechanisms. LCL complex ultrastructural arrangement, biomechanical properties, and biochemical composition were determined using cadaveric samples. Statistical modeling assessed sex- and region-specific effects on LCL complex tissue properties. Collagen fiber coherency, collagen fiber bundle size, and elastin fiber count did not differ between sexes, but females trended higher in elastin fiber count. LCL complex water and sGAG content did not differ between sexes or regions, but collagen content was higher in the anterior region (311.0 ± 185.6 μg/mg) compared to the posterior region (221.0 ± 124.9 μg/mg) (p = 0.045) across sexes and in males (339.6 ± 170.6 μg/mg) compared to females (204.5 ± 130.7 μg/mg) (p = 0.006) across regions. Anterior failure stress (1.1 ± 0.7 MPa) was larger than posterior failure stress (0.6 ± 0.4 MPa) (p = 0.024). Regional differences confirm the presence of a mechanically and compositionally distinct temporomandibular ligament. Baseline sex-specific differences are critical for etiological investigations of sex disparities in TMJ disorders. These results have important biomechanical and clinical ramifications, providing critical baseline tissue material properties, informing the development of TMJ musculoskeletal models, and identifying new areas for etiologic investigations for temporomandibular disorders.

Fiber-specific white matter alterations in early-stage tremor-dominant Parkinson\u2019s disease

Using a fixel-based analysis (FBA), we assessed the fiber-specific white matter (WM) alterations in nonmedicated patients with early-stage Parkinson’s disease (PD) with tremor-dominant (TD; n = 53; mean age, 61.7 ± 8.7 years) and postural instability and gait disorder (PIGD; n = 27; mean age, 57.8 ± 8.1 years) motor subtypes and age- and sex-matched healthy controls (HC; n = 43; mean age, 61.6 ± 9.2 years) from Parkinson’s Progression Markers Initiative dataset. FBA revealed significantly increased macrostructural fiber cross section and a combination of fiber density and cross section metrics within the corticospinal tract in patients with TD-PD compared with HC. Nonetheless, no significant changes in FBA-derived metrics were found in patients with PIGD-PD compared with HC or patients with TD-PD. Our results may provide evidence of WM neural compensation mechanisms in patients with TD-PD marked by increases in fiber bundle size and the ability to relay information between brain regions.

Early childhood development of white matter fiber density and morphology

Early childhood is an important period for cognitive and brain development, though white matter changes specific to this period remain understudied. Here we utilize a novel analytic approach to quantify and track developmental changes in white matter micro- and macro-structure, calculated from individually oriented fiber-bundle populations, termed “fixels”. Fixel-based analysis and mixed-effects models were used to assess tract-wise changes in fiber density and bundle morphology in 73 girls scanned at baseline (ages 4.09–7.02, mean ​= ​5.47, SD ​= ​0.81), 6-month (N ​= ​7), and one-year follow-up (N ​= ​42). For comparison, we also assessed changes in commonly utilized diffusion tensor metrics: fractional anisotropy (FA), and mean, radial and axial diffusivity (MD, RD, AD). Maturational increases in fixel-metrics were seen in most major white matter tracts, with the most rapid increases in the corticospinal tract and slowest or non-significant increases in the genu of the corpus callosum and uncinate fasciculi. As expected, we observed developmental increases in FA and decreases in MD, RD and AD, though percent changes were smaller relative to fixel-metrics. The majority of tracts showed more substantial morphological than microstructural changes. These findings highlight early childhood as a period of dynamic white matter maturation, characterized by large increases in macroscopic fiber bundle size, mild changes in axonal density, and parallel, albeit less substantial, changes in diffusion tensor metrics.

Micromechanical study on the origin of fiber bridging under interlaminar and intralaminar mode I failure

Fiber reinforced polymers (FRPs) subjected to mode I fracture show important toughening due to the development of large scale bridging (LSB). Experimental studies of this phenomenon in unidirectional carbon/epoxy laminates using double cantilever beam specimens, demonstrate important differences in R-curve response for inter- and intralaminar fracture. Post fracture observation of composite’s cross-section pointed out dissimilar fiber bundle size and shape, as the main origin of their differences. In the present paper, representative volume elements with the composite’s constituents, based on the actual material microstructure, and homogenized 2D finite element models were developed to study the effects of microstructure on the first stage of damage leading to LSB development in carbon/epoxy composites under mode I fracture. The differences between inter- and intralaminar fracture were investigated along with the influence of fiber dispersion and the presence of interply and intraply resin-rich zones. The numerical simulations captured different microcrack morphologies for inter- and intralaminar fracture, supporting the experimental observations, while parametric studies showed the influence of the microstructure in the formation of LSB. In particular, fiber dispersion within a ply and resin rich zone between plies play significant roles in mode I fracture and can be used to control toughening mechanisms in FRPs.

Effects of Set Curvature and Fiber Bundle Size on the Printed Radius of Curvature by a Continuous Carbon Fiber Composite 3D Printer

The present study investigated the effects of set radius of curvature and fiber bundle size on the precision of the radius of curvature during continuous carbon fiber three-dimensional (3D) printing. First, individual circles with various radii using various sizes of fiber bundles were printed with a 3D printer. It was demonstrated that with a larger fiber bundle size or a smaller set radius, the printed radius would be lower than the set value. Based on the printing experiments, twist and path length difference models were constructed to predict the actual printed radius. Comparison between the models and experimental values verified that the twist model provides the upper bound on the printed radius and the path length difference model provides the lower bound.

Influence of Fiber Bundle Morphology on the Mechanical and Bonding Properties of Cotton Stalk and Mulberry Branch Reconstituted Square Lumber

The mechanical properties of natural fiber composites can be strengthened in the longitudinal direction if the fiber is formed in a parallel manner. Reconstituted cotton stalk lumber and mulberry branch lumber were fabricated using hot-press technology, and the effects of fiber morphology on their mechanical and bonding properties were investigated. The fiber bundle size had a great influence on the mechanical and bonding properties of the final products. The maximum specific modulus of rupture (MOR) and specific modulus of elasticity (MOE) of the reconstituted lumber were obtained for medium-size fiber bundles, and the maximum MOR and MOE of reconstituted cotton stalk lumber was 130.3 MPa·g-1·cm-3 and 12.9 GPa·g-1·cm-3, respectively. The maximum MOR and MOE of the mulberry branch lumber was 147.2 MPa·g-1·cm-3 and 14.7 GPa·g-1·cm-3, respectively. Mechanical interlocking structures in the lumber were observed via fluorescence microscopy, showing that phenol-formaldehyde adhesive had penetrated into several cell layers of the fiber bundle under heating and pressure. The adhesive penetration capacity was stronger when the fiber bundles were smaller in size and density. The reconstituted lumber fabricated from both materials exhibited excellent mechanical performance in the parallel direction. Therefore, reconstituted cotton stalk and mulberry branch lumber are attractive potential materials for the construction industry.

Effects of fiber bundle size and weave density on stiffness degradation and final failure of fabric laminates

The mechanical behavior of twill-weave carbon fabric laminates under tensile loading is experimentally studied in this work. The focus is on the effect of the fiber bundle size and weave density of the fabric. The twill-weave carbon fabrics are woven from two different fiber bundles, 3 K and 12 K, with three different weave densities. The carbon fabrics are thus of three types having areal densities between 200 and 600 g/m2, and crimp ratios from 0.049 to 0.12. The laminates are manufactured through vacuum infusion process to minimize the effect of voids and poor resin regions. Tensile tests show serious differences in the behavior of the low and high areal density fabrics although the crimp ratio is about the same in some of the laminates. The low density fabric laminates show a linear stress–strain curve up to a sudden rupture of the laminate. The higher density fabric laminates present a stiffness degradation observed in their stress–strain curve which occurs after a plateau region or just a knee behavior. These high density fabric laminates encounter a severe delamination before the final failure. Digital image correlations (DIC) performed in this work show novel changes of the strain distribution before and after the stiffness degradation in the laminates.

Gas Transfer of an Implatable Artificial Lung

The water flow characteristics in the implantable artificial lung (IAL) were evaluated by in vitro experiments. The 50-fiber modules were of different lengths but contained well-spaced fibers; and the 300-fiber module had a volume fraction of 0.9. A lower number of tired hollow fibers produce a higher water-side film coefficient of oxygen transfer at a constant velocity of water-side flow. The area of the water flow decreases with increasing hollow fiber packing density, thus if water is induced to flow uniformly in the IAL module, the oxygen transfer rate should monotonously increase with the packing density. The water flow in the IAL is not uniform and depends on the hollow fiber packing density. The stagnation of the water flow occurs in the bundle of the hollow fibers at the water inlet. Intravascular oxygenation represents an attractive, alternative support modality for patients with ARDS. The concept of intravascular oxygenation as an alternative ARDS therapy originated with Mortensen (7), who developed an intravenous oxygenator (IVOX) consisting of a bundle of crimped hollow fiber positioned in the vena cava. In phase I clinical trials, the IVOX provided an average of 28% of basal gas exchange requirements for patients with severe ARDS (8-14). The clinical study, however, concluded that more gas exchange was needed for intravascular oxygenation to be clinically effective in ARDS treatment. We are developing an intravenous membrane oxygenator (IMO) with a design goal of 50% of basal oxygen and carbon dioxide exchange requirements for end-stage ARDS patients. Like the IVOX, the IMO consists of a bundle of manifolded hollow fiber, and is intended for intravenous placement within the superior and inferior vena cava. The target level of gas exchange in the IVOX, and consequently, the IMO, incorporates a polyurethane balloon concentric with the fiber bundle, which rhythmically inflates and deflates to provide active blood mixing, and thus enhances gas exchange. Our current efforts focus on device improvements intended to provide the target levels of gas exchange, given the constraints imposed by intravenous placement on fiber bundle size and hence fiber area for gas exchange. Although critical care techniques have been improved, the high mortality of severe ARDS has not significantly changed (10-15). In an implantable artificial lung (IAL), the greater part of the oxygen transfer resistance is located in the blood-side laminar film (16), and various methods have been attempted to make the laminar film thin and improve the oxygen transfer rate (17, 18). In the present study, the water flow characteristics in the IAL were evaluated by in vitro experiments. The effect of hollow fiber packing fraction on water flow condition was evaluated to produce effective constant of water with the hollow fibers. Oxygen transfer rates were evaluated, and the optimum hollow fiber packing fraction was determined at an outside diameter of hollow fibers of 380 μm. II. THEORYT The Reynolds number (NRe =Lv/υ) characterizes the flow regime and is the ratio of inertial force to viscous force. The Schmidt number (NSc=υ/D), analogous to the Prandtl number in heat transfer, characterizes the fluid properties and is the ratio of momentum transport to diffusive transport. The Peclet number (NPe=Lv/D), which is the product of NRe, characterizes the relative importance of convective and diffusive processes and is the ratio of bulk mass transport to diffusive mass transport. The Sherwood number (NSh=KL/D), also known as the mass transfer Nusselt number, likewise characterizes the relative importance of convective and diffusive transport; it is the ratio of total transport to diffusive transport. The mass transfer Stanton number (NSt=K/v) is proportional to the ratio of the actual mass flux to the mass flux capacity of the flow, i.e. the amount of mass potentially transferable per unit time and cross-sectional area.

Effect of the timing of posthatch feed restrictions on broiler breast muscle development and muscle transcriptional regulatory factor gene expression

The effect of the timing of an immediate posthatch feed restriction on broiler pectoralis major muscle development was studied by applying a 20% feed restriction either the first or second week after hatch. Pectoralis major muscle morphological structure and the expression of the myogenic transcriptional regulatory factors, myogenic determination factor 1 (MyoD), myogenic regulatory factor 4 (MRF4), and myogenin, were measured. Broiler chicks at hatch were divided into a full-fed (control) group and a 20% feed restriction treatment administered either the first or second week posthatch. At the end of the feed restriction, the chicks were placed on a full feed ad libitum diet with no further restrictions. Muscle fiber diameter and fiber bundle size of the pectoralis major muscle were smaller in the wk 1 restricted group than the control group by 7 d of age. By 15 d of age through the duration of the study, d 43, both endomysial and perimysial connective tissue spacing were diminished in the wk 1 feed-restricted group. The expression of MyoD, MRF4, and myogenin was affected by the wk 1 feed restriction. The expression of MyoD and MRF4 was significantly increased during the first week posthatch. Both of the genes have been shown to be expressed during proliferation especially MyoD, which is required for muscle cell proliferation. In contrast, myogenin expression was significantly decreased. Myogenin expression is required for differentiation to occur. The morphological changes and gene expression changes observed with the wk 1 feed restriction were eliminated by moving the 20% feed restriction to wk 2, which is after the period of maximal myogenic satellite cell mitotic activity. Taken together, these results demonstrate that the timing of early posthatch feed restrictions to chicks is critical for the morphological development of the pectoralis major muscle and the expression of genes required for muscle satellite cell proliferation and differentiation.

Complex Collagen Fiber and Membrane Morphologies of the Whole Porcine Aortic Valve

ObjectivesReplacement aortic valves endeavor to mimic native valve function at the organ, tissue, and in the case of bioprosthetic valves, the cellular levels. There is a wealth of information about valve macro and micro structure; however, there presently is limited information on the morphology of the whole valve fiber architecture. The objective of this study was to provide qualitative and quantitative analyses of whole valve and leaflet fiber bundle branching patterns using a novel imaging system.MethodsWe developed a custom automated microscope system with motor and imaging control. Whole leaflets (n = 25) were imaged at high resolution (e.g. 30,000×20,000 pixels) using elliptically polarized light to enhance contrast between structures without the need for staining or other methods. Key morphologies such as fiber bundle size and branching were measured for analyses.ResultsThe left coronary leaflet displayed large asymmetry in fiber bundle organization relative to the right coronary and non-coronary leaflets. We observed and analyzed three main patterns of fiber branching; tree-like, fan-like, and pinnate structures. High resolution images and quantitative metrics are presented such as fiber bundle sizes, positions, and branching morphological parameters.SignificanceTo our knowledge there are currently no high resolution images of whole fresh leaflets available in the literature. The images of fiber/membrane structures and analyses presented here could be highly valuable for improving the design and development of more advanced bioprosthetic and/or bio-mimetic synthetic valve replacements.

Abstract 18657: Fibulin-4 Deficiency Alters Collagen Regulation in the Aortic Wall

Thoracic aortic aneurysms/dissections (TAAD) are a major cause of mortality each year in the U.S. Disruption of fibulin-4 (fbln4), an extracellular matrix component, leads to TAAD in human and mouse models. Fbln4 plays an essential role in elastic fiber assembly: our recent data suggest a role for proliferation in the aortic wall that may be independent of elastic fiber defects. Roles for Fbln4 beyond elastic fiber assembly have been suggested but not previously investigated. We hypothesize that Fbln4 loss alters the aortic wall microenvironment to promote localized cell proliferation, in part through altered collagen synthesis and maturation. Smooth muscle-specific Fbln4 deficient (SMKO) ascending aortas show increased BrdU+ cells at P30 (p<.05) localized throughout the aortic wall but mainly near the medial/adventitial border, irrespective of elastic fiber disruption. Smooth muscle actin inducible Cre mice show intact elastic fibers but a similar pattern of BrdU+ cells. Fbln4 loss also alters synthesis of collagen isoforms, leading to increased Type VIII mRNA (p<.05) and Type I protein expression. Electron microscopy, second harmonic generation images, and molecular analysis of collagen cross-linking revealed highly irregular collagen fiber bundle size, collagen fiber disorganization, and decreased mature cross-links (p<.05). Our data demonstrate a proliferative phenotype and previously uncharacterized collagen defect in Fbln4 deficient mice. Altered collagen isoforms and maturity are known to influence cell proliferation: future work will determine the precise identity of the proliferating cells and specific mechanisms by which collagen defects drive the proliferative phenotype. Increased understanding of the molecular mechanisms driving TAAD will ultimately lead to more effective treatments to delay or prevent onset of disease.

Evaluation of a Respiratory Assist Catheter that Uses an Impeller Within a Hollow Fiber Membrane Bundle

Respiratory assist using an intravenous catheter may be a potential treatment for patients suffering from acute or acute-on-chronic lung failure. The objective of this study was to evaluate a novel respiratory catheter that uses an impeller within the fiber bundle to enhance gas exchange efficiency, thus requiring a smaller fiber bundle and insertional size (25 Fr) and permitting simple percutaneous insertion. Bench testing of gas exchange in deionized water was used to evaluate eight impeller designs. The three best performing impeller designs were evaluated in acute studies in four calves (122 + or - 10 kg). Gas exchange increased significantly with increasing impeller rotation rate. The degree of enhancement varied with impeller geometry. The maximum gas exchange efficiency (exchange per unit surface area) for the catheter with the best performing impeller was 529 + or - 20 ml CO(2)/min/m(2) and 513 + or - 21 ml CO(2)/min/m(2) for bench and animal studies, respectively, at a rotation rate of 20,000 rpm. Absolute CO(2) exchange was 37 and 36 ml CO(2)/min, respectively. Active mixing by rotating impellers produced 70% higher gas exchange efficiency than pulsating balloon catheters. The sensitivity of gas exchange to impeller design suggests that further improvements can be made by computational fluid dynamics-based optimization of the impeller.

Studies for the design of the Wendelstein 7-X Thomson Scattering polychromators

The aim of the Thomson scattering system is the measurement of electron temperature and density profiles with high time and spatial resolution. The whole Thomson scattering optical system is optimized to minimize losses of scattered light with wavelengths from 700 nm up to 1064 nm. A five-channel polychromator serves as spectral analyzer of the scattered light. The light is carried to the polychromator input via fiber bundles of 3 mm diameter. High performance dielectric interference filters will be used for spectral analyzing. Their transmission curves will be chosen according to the range of electron temperature that is supposed during W7-X operation (from 10 eV up to 10 keV). The design of the polychromator must be optimized for a high throughput and size compactness. The article describes three possible polychromator setups. The main difference between these designs is the usage of relay and field lenses. The optical properties of the designs will be derived both by measurements and by simulations. Limitations considering high Numerical Aperture (N.A.) and fiber bundle size are discussed.

Spunlaced Cotton and Cotton Blend Cosmetic Pads and Bed Sheets: Study of Fiber Entanglement

Nonwoven webs containing five different blends of bleached cotton with Lyocell rayon, bicomponent core/sheath polyester/polyethylene, or cotton comber noil were prepared by either light needlepunching, or light needlepunching followed by spunlacing (hydroentanglement). We optically acquired fiber bundle size measurements to learn about the pre-needling process, the hydroentangling process and the influence of fiber blend composition on fiber entanglement. Fiber entanglement measurements were compared to basis weight uniformity measurements. One of the bed sheet developments utilized a combination of bonding technologies (spunlacing and thermal bonding) that used low energy. Results from this work indicate that spunlacing produced high quality cosmetic pads and economical short-life bed sheeting.

Influence of Processing Conditions on Melt Blown Web Structure. Part III — Water Quench

The overall goal of our recent research has been to quantitatively measure the influence of commercial processing variables on the structure of polypropylene melt blown webs. In this paper, we applied a cool water quench spray to fibers to increase their thermal quenching rate. Then, we collected webs and measured single fiber diameter, shot content, fiber bundle size, basis weight uniformity and pore structure. The structure of webs produced with and without quenching was compared to access the influence of quenching on webs.

Effect of fiber geometry on the elastic constants of the plain woven fabric reinforced aluminum matrix composites

The geometric and elastic models based on the unit cell have been proposed to predict the geometric characteristics and the elastic constants of plain woven carbon fabric reinforced metal matrix composites. In the geometric model, the inclined angle of the yarn crimp and the fiber volume fraction of woven composites have been predicted. In the elastic model, the coordinate transformation has been utilized to determine the elastic constants of the yarn crimp. The effective elastic constants have been obtained from the volume averaging of the elastic constants for constituent materials in composites. In order to verify the proposed model, plain woven carbon fabric reinforced Al matrix composites were fabricated using the vacuum assisted pressure infiltration casting process. Resonant ultrasound spectroscopy was performed to measure the effective elastic constants of the composites. Good correlation between the model predictions and the experimental results has been observed. Parametric study has been conducted to investigate the effect of various geometric parameters of plain weaves on the elastic constants of the composites. The yarn crimp angle, the gap length, fiber bundle size, the shape of yarn section, and the constituent materials have been examined in this study. Based on the proposed model, the effect of various geometric parameters and constituent materials on the three-dimensional elastic properties of woven fabric reinforced composites can be reasonably predicted.

Ultrasonic assessment of skin and surgical wounds utilizing backscatter acoustic techniques to estimate attenuation

Backscatter acoustic techniques at high ultrasonic frequencies (10–40 MHz) were utilized to investigate the ultrasonic attenuation coefficient of normal skin and the relationship between attenuation and the healing of surgical wounds ranging in age from 9 to 49 days. The attenuation coefficient was calculated with measurements from depths of 0.5 and 1.0 mm, primarily in the reticular dermis. The values for control skin ranged from 6.0 Np cm −1 at 10 MHz to 19.6 Np cm −1 at 40 MHz and a corresponding slope of 0.45 Np cm −1 MHz −1. Wound attenuation initially increased with wound age from approximately 15% of control at day 9 to 30% of control at day 34 but did not continue to increase through day 49. During the same period, however, total collagen (as a percentage of wet weight) increased at a constant rate from approximately 45% of control at day 9 to 70% of control at day 49. Thus the attenuation coefficient in healing wounds over the time period studied may be sensitive to more than total collagen content in the tissue. It may be affected by other competing factors as wounds mature such as intermolecular cross-linking, collagen fiber bundle size, and structural arrangement of fiber bundles or other tissue constituents such as proteoglycans and elastin. The observations that wound integrated attenuation using backscatter techniques over the range of 10–40 MHz substantially increased in early wounds, did not increase beyond day 34, and remained significantly lower than control values over the entire healing period studied are in agreement with the results of an independent study of the same tissue using transmission techniques at 100 MHz.