Brittany Coats

Potential for head injuries in infants from low-height falls: Laboratory investigation

OBJECT Falls are the most common accident scenario in young children as well as the most common history provided in child abuse cases. Understanding the biomechanics of falls provides clinicians with objective data to aid in their diagnosis of accidental or inflicted trauma. The objective of this study was to determine impact forces and angular accelerations associated with low-height falls in infants. METHODS An instrumented anthropomorphic infant surrogate was created to measure the forces and 3D angular accelerations associated with falls from low heights (0.3-0.9 m) onto a mattress, carpet pad, or concrete. RESULTS Although height significantly increased peak angular acceleration (alpha(p)), change in peak-to-peak angular velocity, time duration associated with the change in velocity, and peak impact force (F(p)) for head-first drops onto a carpet pad or concrete, none of these variables were significantly affected by height when dropped onto a mattress. The alpha(p) was not significantly different for drops onto a carpet pad and concrete from 0.6 or 0.9 m due to compression of the carpet pad. Surprisingly, sagittal alpha(p) was equaled or surpassed by axial alpha(p). CONCLUSIONS These are the first 3D angular acceleration and impact force data available for head impact in infants from low-height falls. A future study involving a computational model of the infant head will use the loads measured in this study to predict the probability of occipital skull fracture on impact from head-first low-height falls. Together, these studies will provide data that will aid clinicians in the evaluation of accidental and inflicted head injuries, and will contribute to the design of safer environments for children.

Characterization and evaluation of tissue-mimicking gelatin phantoms for use with MRgFUS

BackgroundA tissue-mimicking phantom that accurately represents human-tissue properties is important for safety testing and for validating new imaging techniques. To achieve a variety of desired human-tissue properties, we have fabricated and tested several variations of gelatin phantoms. These phantoms are simple to manufacture and have properties in the same order of magnitude as those of soft tissues. This is important for quality-assurance verification as well as validation of magnetic resonance-guided focused ultrasound (MRgFUS) treatment techniques.MethodsThe phantoms presented in this work were constructed from gelatin powders with three different bloom values (125, 175, and 250), each one allowing for a different mechanical stiffness of the phantom. Evaporated milk was used to replace half of the water in the recipe for the gelatin phantoms in order to achieve attenuation and speed of sound values in soft tissue ranges. These acoustic properties, along with MR (T1 and T2*), mechanical (density and Young’s modulus), and thermal properties (thermal diffusivity and specific heat capacity), were obtained through independent measurements for all three bloom types to characterize the gelatin phantoms. Thermal repeatability of the phantoms was also assessed using MRgFUS and MR thermometry.ResultsAll the measured values fell within the literature-reported ranges of soft tissues. In heating tests using low-power (6.6 W) sonications, interleaved with high-power (up to 22.0 W) sonications, each of the three different bloom phantoms demonstrated repeatable temperature increases (10.4 ± 0.3 °C for 125-bloom, 10.2 ± 0.3 °C for 175-bloom, and 10.8 ± 0.2 °C for 250-bloom for all 6.6-W sonications) for heating durations of 18.1 s.ConclusionThese evaporated milk-modified gelatin phantoms should serve as reliable, general soft tissue-mimicking MRgFUS phantoms.

Finite Element Model Predictions of Intracranial Hemorrhage from Non-Impact, Rapid Head Rotations in the Piglet

Clinicians are charged with the significant task of distinguishing between accidental and inflicted head trauma. Oftentimes this distinction is straightforward, but many times probabilities of injuries from accidental scenarios are unknown making the differential diagnosis difficult. For example, it is unknown whether intracranial hemorrhage (IH) can occur at a location other than a focal contact site following a low height fall. To create a foundation for predicting regional IH in infants, we sought to identify the biomechanical response and injury threshold best able to predict IH in 3–5 day old piglets. First, finite element (FE) model simulations of in situ animal studies were performed to ascertain the optimal representation of the pia‐arachnoid complex, cerebrospinal fluid and cortical vasculature (PCC) for predicting brain strain and brain/skull displacement. Second, rapid head rotations resulting in various degrees of IH were simulated (n = 24) to determine the biomechanical predictor and injury threshold most closely correlated with IH. FE models representing the PCC with either spring connectors or solid elements between the brain and skull resulted in peak brain strain and brain/skull displacement similar to measured values in situ. However, when predicting IH, the spring connector representation of the PCC had the best predictive capability for IH with a sensitivity of 80% and a specificity of 85% when ≥1% of all spring connectors had at least a peak strain of 0.31 mm/mm. These findings and reported methodology will be used in the development of a human infant FE model to simulate real‐world falls and identify injury thresholds for predicting IH in infants.

Ocular Hemorrhages in Neonatal Porcine Eyes from Single, Rapid Rotational Events

PURPOSE To characterize ocular hemorrhages from single, rapid head rotations in the neonatal pig. METHODS Three- to 5-day-old anesthetized piglets (n=51) underwent a single, rapid (117-266 rad/s) head rotation in the sagittal (n=13), coronal (n=7), or axial (n=31) planes. Six hours after injury, the animals were euthanatized and perfusion fixed, and the brain and eyes were harvested for gross and histopathologic examination by masked neuro- and ocular pathologists. RESULTS Ocular hemorrhage was found in 73% of animals (51% bilateral). Intraocular hemorrhage was primarily located near the vitreous base (70% of injured animals had ciliary body hemorrhage, and 11% had peripheral retinal hemorrhage). Hemorrhages were also found in the anterior chamber (11%), vitreous (5%), and optic nerve (disc, 8%; nerve sheath, 57%). Rapid axial head rotations resulted in a higher incidence of intraocular hemorrhage than coronal or sagittal head rotations, but the difference did not reach statistical significance (P=0.06). Control eyes had no injuries. CONCLUSIONS Optic nerve sheath and ciliary body hemorrhages were common in piglets that experienced a single, rapid head rotation. Retinal hemorrhage was present in a smaller number of animals. Most intraocular hemorrhages were located in regions of strong vitreous attachment, suggesting that this animal model will be useful in investigating the effect of vitreoretinal adhesion on ocular hemorrhage caused by inertial head rotations. Extrapolation of this model to the human infant should not be made until the effect of anatomic differences between the human and pig on the occurrence and patterns of ocular injuries is further investigated.

In situ deformations in the immature brain during rapid rotations.

Head trauma is the leading cause of death and debilitating injury in children. Computational models are important tools used to understand head injury mechanisms but they must be validated with experimental data. In this communication we present in situ measurements of brain deformation during rapid, nonimpact head rotation in juvenile pigs of different ages. These data will be used to validate computational models identifying age-dependent thresholds of axonal injury. Fresh 5 days (n=3) and 4 weeks (n=2) old piglet heads were transected horizontally and secured in a container. The cut surface of each brain was marked and covered with a transparent, lubricated plate that allowed the brain to move freely in the plane of rotation. For each brain, a rapid (20-28 ms) 65 deg rotation was applied sequentially at 50 rad/s, 75 rad/s, and 75 rad/s. Each rotation was digitally captured at 2500 frames/s (480x320 pixels) and mark locations were tracked and used to compute strain using an in-house program in MATLAB. Peak values of principal strain (E(peak)) were significantly larger during deceleration than during acceleration of the head rotation (p<0.05), and doubled with a 50% increase in velocity. E(peak) was also significantly higher during the second 75 rad/s rotation than during the first 75 rad/s rotation (p<0.0001), suggesting structural alteration at 75 rad/s and the possibility that similar changes may have occurred at 50 rad/s. Analyzing only lower velocity (50 rad/s) rotations, E(peak) significantly increased with age (16.5% versus 12.4%, p<0.003), which was likely due to the larger brain mass and smaller viscoelastic modulus of the 4 weeks old pig brain compared with those of the 5 days old. Strain measurement error for the overall methodology was estimated to be 1%. Brain tissue strain during rapid, nonimpact head rotation in the juvenile pig varies significantly with age. The empirical data presented will be used to validate computational model predictions of brain motion under similar loading conditions and to assist in the development of age-specific thresholds for axonal injury. Future studies will examine the brain-skull displacement and will be used to validate brain-skull interactions in computational models.

Biological Sample Preparation for SEM Imaging of Porcine Retina

Introduction Sample preparation is a critical step in scanning electron microscopy (SEM) imaging. This is especially true for biological samples because of charge build-up and sensitivity to vacuum and electron beam damage. In terms of ultrastructure imaging, a variety of advancements in detectors and approaches have improved biological imaging such that fewer steps are required for sample preparation. However, the conventional approach incorporating osmium tetroxide fixing, ethanol dehydrating, critical-point drying, and coating still finds useful application. This paper evaluates three biological sample-preparation methodologies for imaging the ultrastructure of immature porcine retina. The three preparation methods examined are critical-point drying (CPD), hexamethyldisilazane (HMDS) dehydration, and direct imaging by environmental scanning electron microscopy (ESEM). Preparation methodologies were evaluated based on resulting image quality and reduced potential for artifacts.

Molded polymer-coated composite bone void filler improves tobramycin controlled release kinetics

Infection remains a significant problem associated with biomedical implants and orthopedic surgeries, especially in revision total joint replacements. Recent advances in antibiotic-releasing bone void fillers (BVF) provide new opportunities to address these types of device-related orthopedic infections that often lead to substantial economic burdens and reduced quality of life. We report improvements made in fabrication and scalability of an antibiotic-releasing polycaprolactone-calcium carbonate/phosphate ceramic composite BVF using a new solvent-free, molten-cast fabrication process. This strategy provides the ability to tailor drug release kinetics from the BVF composite based on modifications of the inorganic substrate and/or the polymeric component, allowing extended tobramycin release at bactericidal concentrations. The mechanical properties of the new BVF composite are comparable to many reported BVFs and validate the relative homogeneity of fabrication. Most importantly, fabrication quality controls are correlated with favorable drug release kinetics, providing bactericidal activity to 10 weeks in vitro when the polycaprolactone component exceeds 98% w/w of the total polymer fraction. Furthermore, in a time kill study, tobramycin-releasing composite fragments inhibited S. aureus growth over 48 h at inoculums as high as 10(9) CFU/mL. This customizable antibiotic-releasing BVF polymer-inorganic biomaterial should provide osseointegrative and osteoconductive properties while contributing antimicrobial protection to orthopedic sites requiring the use of bone void fillers.

Stress profile of infant rib in the setting of child abuse: A finite element parametric study

The primary goal of this study is to advance our current understanding of infant rib injuries in the setting of child abuse. To this end, we employed finite element model simulations to determine the sensitivity of an infant ribs stress response to varying material properties and under varying degrees of anterior-posterior chest compression. Using high-resolution chest CT images obtained from a 6-day-old infant, we constructed a simplified geometric model consisting of bone and cartilage structures. To simulate the lateral gripping of an infant in child abuse, an anterior-posterior chest compression load was applied to cause increased stresses along the costovertebral articulation, a classic site for inflicted rib fractures. A sensitivity analysis was conducted to quantify the effects of varying Youngs modulus and Poissons ratio of the bones and cartilages. In addition, we varied the amount of anterior-posterior chest displacement to assess the sensitivity of this parameter to the ribs stress profile. We found that varying Youngs modulus of the bone and cartilage not only changed the magnitude but also the shape profile of the ribs stress response. In contrast, varying the degree of chest compression only changed the magnitude of the stress response and not the shape profile. We also discovered that by varying Poissons ratio of the bone and cartilage, no appreciable change was seen in the magnitude or the shape profile of the ribs stress response. Finite element modeling shows promise as a tool to elucidate the mechanisms of rib fractures in abused infants.

Microstructural Characterization of the Pia-Arachnoid Complex Using Optical Coherence Tomography

Traumatic brain injury (TBI) is one of the leading causes of death and disability in the world, and is often identified by the presence of subdural and/or subarachnoid hemorrhages that develop from ruptured cortical vessels during brain-skull displacement. The pia-arachnoid complex (PAC), also known as the leptomeninges, is the major mechanical connection between the brain and skull, and influences cortical vessel deformation and rupture following brain trauma. This complex consists of cerebrospinal fluid, arachnoid trabeculae, and subarachnoid vasculature sandwiched between the arachnoid and pia mater membranes. Remarkably, studies of the tissues in the PAC are largely qualitative and do not provide numerical metrics of population density and variability of the arachnoid trabeculae and subarachnoid vasculature. In this study, microstructural imaging was performed on the PAC to numerically quantify these metrics. Five porcine brains were perfusion-fixed and imaged in situ using optical coherence tomography with micrometer resolution. Image processing was performed to estimate the volume fraction (VF) of the arachnoid trabeculae and subarachnoid vasculature in 12 regions of the brain. High regional variability was found within each brain, with individual brains exhibiting up to a 38.4 percentage-point range in VF. Regions with high VF were often next to regions with low VF. This suggests that some areas of the brain may be mechanically weaker, increasing their susceptibility to hemorrhage during TBI events. This study provides the first quantifiable data of arachnoid trabeculae and subarachnoid vasculature distribution within the PAC and will be valuable to understanding brain biomechanics during head trauma.

Experimental Injury Biomechanics of the Pediatric Head and Brain

Traumatic brain injury (TBI) is a leading cause of death and disability among children and young adults in the United States and results in over 2,500 childhood deaths, 37,000 hospitalizations, and 435,000 emergency department visits each year (Langlois et al. 2004). Computational models of the head have proven to be powerful tools to help us understand mechanisms of adult TBI and to determine load thresholds for injuries specific to adult TBI. Similar models need to be developed for children and young adults to identify age-specific mechanisms and injury tolerances appropriate for children and young adults. The reliability of these tools, however, depends heavily on the availability of pediatric tissue material property data. To date the majority of material and structural properties used in pediatric computer models have been scaled from adult human data. Studies have shown significant age-related differences in brain and skull properties (Prange and Margulies 2002; Coats and Margulies 2006a, b), indicating that the pediatric head cannot be modeled as a miniature adult head, and pediatric computer models incorporating age-specific data are necessary to accurately mimic the pediatric head response to impact or rotation. This chapter details the developmental changes of the pediatric head and summarizes human pediatric properties currently available in the literature. Because there is a paucity of human pediatric data, material properties derived from animal tissue are also presented to demonstrate possible age-related differences in the heterogeneity and rate dependence of tissue properties. The chapter is divided into three main sections: (1) brain, meninges, and cerebral spinal fluid (CSF); (2) skull; and (3) scalp.