Claire Acevedo

University of California, San Diego | UCSD · Department of Mechanical and Aerospace Engineering (MAE)

Adults with type 2 diabetes (T2D) have a higher fracture risk for a given bone quantity, but the mechanisms remain unclear. Using a rat model of polygenic obese T2D, we demonstrate that diabetes significantly reduces whole-bone strength for a given bone mass (micro-CT-derived BMC), and we quantify the roles of T2D-induced deficits in material prope...

The prevention of fragility fractures in bone—pathologic fractures resulting from daily activity and mostly occurring in the elderly population—has been a long-term clinical quest. Recent research indicating that falls in the elderly might be the consequence of fracture rather than its cause has raised fundamental questions about the origin of frag...

All levels of the unique, hierarchical structure of bone consisting of collagen and hydroxyapatite crystals at the nanoscale to osteon/lamellae structures at the microscale contribute to its characteristic toughness and material properties. Elements of bone's density and size contribute to bone quantity (or bone mass), whereas elements of bone's ma...

When studying bone fragility diseases, it is difficult to identify which factors reduce bone’s resistance to fracture because these diseases alter bone at many length scales. Here, we investigate the contribution of nanoscale collagen behavior on macroscale toughness and microscale toughening mechanisms using a bovine heat-treatment fragility model...

Understanding the biomechanical behavior of the intervertebral disc is crucial for studying disease mechanisms and developing tissue engineering strategies for managing low back pain. We used synchrotron small-angle x-ray scattering (SAXS) to investigate how changes in collagen behavior contribute to alterations in the disc’s ability to resist comp...

The mineralized collagen fibril is the main building block of hard tissues and it directly affects the macroscopic mechanics of biological tissues such as bone. The mechanical behavior of the fibril itself is determined by its structure: the content of collagen molecules, minerals, and cross-links, and the mechanical interactions and properties of...

The primary clinical indicator of fracture risk among the elderly is low bone mass, yet it accounts for less than half of fractures in individuals over 50 years. Age is recognized to influence bone quality, affecting bone structure and properties. Previous research indicates that age diminishes tissue plasticity and toughness conferred by collagen,...

The osteon is the primary structural component of bone, contributing significantly to its unique toughness and strength. Despite extensive research on osteonal structure, the properties of osteons have not been fully investigated, particularly within the context of bone fragility diseases like type 2 diabetes mellitus (T2DM). This study aims to iso...

Osteocytes locally remodel their surrounding tissue through perilacunar canalicular remodeling (PLR). During lactation, osteocytes remove minerals to satisfy the metabolic demand, resulting in increased lacunar volume, quantifiable with synchrotron X-ray radiation micro-tomography (SRµCT). Although the effects of lactation on PLR are well-studied,...

The mineralized collagen fibril is the main building block of hard tissues and it directly affects the macroscopic mechanics of biological tissues such as bone. The mechanical behavior of the fibril itself is determined by its structure: the content of collagen molecules, minerals, and cross-links, and the mechanical interactions and properties of...

Advanced-Glycation-Endproducts (AGEs) are known to be a major cause of impaired tissue material properties. In collagen fibrils, the main building component of human tissue, these AGEs appear as fibrillar cross-links. When AGEs accumulate in collagen fibrils, a process often caused by diabetes and aging, the mechanical properties of the collagen fi...

Advanced-Glycation-Endproducts (AGEs) are known to be a major cause of impaired tissue material properties. In collagen fibrils, the main building component of human tissue, these AGEs appear as fibrillar cross-links. When AGEs accumulate in collagen fibrils, a process often caused by diabetes and aging, the mechanical properties of the collagen fi...

Age and diabetes have long been known to induce an oxidative reaction between glucose and collagen, leading to the accumulation of advanced glycation end-products (AGEs) cross-links in collagenous tissues. More recently, AGEs content has been related to loss of bone quality, independent of bone mass, and increased fracture risk with aging and diabe...

Type 2 diabetes mellitus (T2DM) is associated with an increased fracture risk independent of bone mass. The exact origin of this increased fracture remains to be fully understood. Using a polygenic diabetic Zucker Diabetic Sprague Dawley (ZDSD) rat model, synchrotron radiation micro-computed tomography imaging (SRµCT), and in situ scanning electron...

The denaturation of collagen at the molecular level in bone and dentin can impact their structure and properties, leading to increased brittleness in pathological diseases such as osteogenesis imperfecta, dentinogenesis imperfecta, diabetes, and cancer. This study investigates the relationship between collagen denaturation and the macroscale resist...

Type 2 diabetes mellitus (T2DM) is associated with an increased fracture risk independent of bone mass. The exact origin of this increased fracture risk still needs to be better understood. Using a polygenic diabetic ZDSD rat model, synchrotron radiation micro-computed tomography imaging (SRuCT), and in situ scanning electron microscope (SEM) fract...

Cross-links are considered to be a key component of collagen fibrils as they can change the fibrillar behavior in various ways. Advanced-Glycation Endproducts (AGEs), one particular type of cross-links, have been shown to accumulate and impair the mechanical properties of collageneous tissues, whereas enzymatic cross-links (ECLs) are known for stab...

Cross-links are considered to be a key component of collagen fibrils as they can change the fibrillar behavior in various ways. Advanced-Glycation Endproducts (AGEs), one particular type of cross-links, have been shown to accumulate and impair the mechanical properties of collageneous tissues, whereas enzymatic cross-links (ECLs) are known for stab...

The fracture resistance of bone has been attributed to a competition of sub-micron lengthscale intrinsic mechanisms, including plasticity conferred by collagen stretching and intermolecular sliding and much larger lengthscale extrinsic mechanisms such as crack deflection and bridging. In this study, the contribution of intrinsic toughening mechanis...

This research aims to further the understanding of the structure and mechanical properties of the dermal armor of the boxfish (Lactoria cornuta). Structural differences between collagen regions underlying the hexagonal scutes were observed with confocal microscopy and microcomputed tomography (μ-CT). μ-CT revealed a tapering of the mineral plate fr...

Some natural materials, such as the dactyl club of the mantis shrimp, have impressive mechanical properties (e.g. strength) due to their microstructure that consists of periodic layers of high and low density material, which prevent crack propagation. Although such layered structures have the potential to increase the strength of engineered epoxy-c...

Bone fragility is the product of defects in bone mass and bone quality, both of which show sex‐specific differences. Despite this, the cellular and molecular mechanisms underpinning the sexually dimorphic control of bone quality remain unclear, limiting our ability to effectively prevent fractures, especially in postmenopausal osteoporosis. Recentl...

Osteoarthritis (OA), long considered a primary disorder of articular cartilage, is commonly associated with subchondral bone sclerosis. However, the cellular mechanisms responsible for changes to subchondral bone in OA, and the extent to which these changes are drivers of or a secondary reaction to cartilage degeneration, remain unclear. In knee jo...

Bone fragility is the product of defects in bone mass and bone quality, both of which show sex-specific differences. Despite this, the cellular and molecular mechanisms underpinning the sexually dimorphic control of bone quality remain unclear, limiting our ability to effectively prevent fractures, especially in postmenopausal osteoporosis. Recentl...

Chronic kidney disease (CKD) is a common disease of aging and increases fracture risk over advanced age alone. Aging and CKD differently impair bone turnover and mineralization. We thus hypothesize that the loss of bone quality would be greatest with the combination of advanced age and CKD. We evaluated bone from young adult (6 mo.), middle-age (18...

Osteoarthritis (OA), long considered a primary disorder of articular cartilage, is commonly associated with subchondral bone sclerosis. However, the cellular mechanisms responsible for changes to subchondral bone in OA, and the extent to which these changes are drivers of or a secondary reaction to cartilage degeneration, remain unclear. In knee jo...

Poor bone quality contributes to bone fragility in diabetes, aging, and osteogenesis imperfecta. However, the mechanisms controlling bone quality are not well understood, contributing to the current lack of strategies to diagnose or treat bone quality deficits. Transforming growth factor beta (TGF-β) signaling is a crucial mechanism known to regula...

At the Advanced Light Source (ALS), Beamline 8.3.2 performs hard X-ray micro-tomography under conditions of high temperature, pressure, mechanical loading, and other realistic conditions using environmental test cells. With scan times of 10s–100s of seconds, the microstructural evolution of materials can be directly observed over multiple time step...

Through a process called perilacunar remodeling, bone-embedded osteocytes dynamically resorb and replace the surrounding perilacunar bone matrix to maintain mineral homeostasis. The vital canalicular networks required for osteocyte nourishment and communication, as well as the exquisitely organized bone extracellular matrix, also depend upon perila...

There is increasing demand for 3D micro-scale time-resolved imaging of samples in realistic - and in many cases extreme environments. The data is used to understand material response, validate and refine computational models which, in turn, can be used to reduce development time for new materials and processes. Here we present the results of high t...

Bisphosphonates are a common treatment to reduce osteoporotic fractures. This treatment induces osseous structural and compositional changes accompanied by positive effects on osteoblasts and osteocytes. Here, we test the hypothesis that restored osseous cell behavior, which resembles characteristics of younger, healthy cortical bone, leads to impr...

Bisphosphonates are widely used to treat osteoporosis, but have been associated with atypical femoral fractures (AFFs) in the long term, which raises a critical health problem for the aging population. Several clinical studies have suggested that the occurrence of AFFs may be related to the bisphosphonate-induced changes of bone turnover, but large...

Real behavior of existing structures is usually associated with large uncertainty that is often covered by the use of conservative models and code practices for the evaluation of remaining fatigue lives. In order to make better decisions related to retrofit and replacement of existing bridges, new techniques that are able to quantify fatigue reserv...

Conservative models and code practices are usually employed for fatigue-damage predictions of existing structures. Direct in-service behavior measurements are able to provide more accurate estimations of remaining-fatigue-life predictions. However, these estimations are often accurate only for measured locations and measured load conditions. Behavi...

This paper is devoted to the experimental and numerical assessment of residual stresses created by welding in the region surrounding the weld toe of tubular K-shaped joints (i.e. region most sensitive to fatigue cracking). Neutron-diffraction measurements were carried out on K-joints cut from large-scale truss beams previously subjected to high cyc...

This paper presents a 3D thermo-mechanical model of arc-welding applied to tubular K-joints susceptible to fatigue cracking. The 3D torch trajectory is reproduced to simulate both temperatures and stresses during welding and ultimately the 3D residual stress distribution after cooling. The influence of latent heat, of the increase of thermal conduc...

Theweld-induced residual stresses in a tubular planar K-shaped connection made of construction steel grades S355J2H and S690QH is evaluated using three-dimensional finite element models in thermomechanical simulation of welding process. Both lumped single-pass and multi-pass simulation alternatives are examined. The transversal component is the lar...

This paper describes the numerical analysis method used to estimate welding induced residual stresses in K-shape tubular bridge joints. The knowledge of residual stress distribution is required to design the geometry of K-joints loaded under fatigue stresses. Numerical simulations are focused on the arc welding MAG process, generally used to weld j...

Tubular bridge design has to deal with fatigue issues. The fatigue susceptibility of these bridges, composed of circular hollow section profiles welded together in K-joints, is mainly due to stress concentrations, to welding imperfections and to tensile residual stresses induced by the welding process. Since these residual stresses are unknown for...

Seeking light and transparent bridge designs, engineers and architects have found an efficient and artistic way to fulfill their requirements: steel tubular bridges. In these modern tubular truss bridges, welded K-joints have been shown to be critically susceptible to fatigue failure induced by repeated traffic loads. Despite the research devoted t...

The fabrication procedure changes when changing the size of the structural components. For the weldments, the change of the welding procedure leads to the change in residual stresses which consequently affects the fatigue life of the structure. The weld size and number of welding passes are important factors which have considerable impact on the va...

Tubular bridge design has to deal with fatigue issues. The fatigue susceptibility of these bridges, composed of circular hollow section profiles welded together in K-joints, is mainly due to stress concentrations, to welding imperfections and to tensile residual stresses induced by the welding process. Since these residual stresses are unknown for...

Seeking light and transparent bridge designs, engineers and architects have found an efficient and artistic way to fulfill their requirements: steel tubular bridges. Like any other welded structure, the joints of this kind of bridge suffer from high tensile weld residual stresses. Combined with high stress concentrations, tensile residual stress is...

Large scale tubular truss beams, approximately of 9 m long and 2 m high, were tested under constant amplitude fatigue loading. The beams were made out of circular hollow sections of steel S355, welded to form a uni-planar truss with K-joints, in a shape common to bridge construction. The main goal of these tests was to focus on the fatigue behavior...

In tubular joints, the hot spot stress concept is used to characterize the stress field at potential fatigue crack locations. The combination of determining stresses using the hot spot concept, with a reduction factor on fatigue strength is however not a satisfactory solution. In this paper, an overview of a on-going research project in which the o...