Heterogeneity in calcium nephrolithiasis: A materials perspective
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Ling Chen and Feifei Yang Division of Biomaterials and Bioengineering, Department of Preventive and Restorative Dental Sciences, School of Dentistry, University of California San Francisco, San Francisco, CA 94143
Krishna Ramaswamy Department of Urology, University of California San Francisco, San Francisco, CA 94143
David W. Killilea Children’s Hospital Oakland Research Institute, Oakland, CA 94609
Ryan S. Hsi Department of Urologic Surgery, Vanderbilt University Medical Center, Nashville, TN 37232
Marshall L. Stoller Department of Urology, University of California San Francisco, San Francisco, CA 94143
Sunita P. Hoa) Division of Biomaterials and Bioengineering, Department of Preventive and Restorative Dental Sciences, School of Dentistry, University of California San Francisco, San Francisco, CA 94143 (Received 21 November 2016; accepted 3 April 2017)
Calcium-based renal calculi demonstrated significant heterogeneity in the structure, density, mineral composition, and material hardness not elucidated by routine clinical testing. Mineral density distributions within calcium oxalate stones revealed differential areas of low (590680 mg/cc), medium (8406140 mg/cc), and high (11006200 mg/cc) densities. Apatite stones also contained regions of low (7006200 mg/cc), medium (11006200 mg/cc), and high (14006140 mg/cc) densities within layers extending from single or multiple nucleation sites. Despite having lower average mineral density, calcium oxalate (CaOx) stones demonstrated higher material hardness compared to apatite stones, suggesting other chemical components might be involved in determining stone hardness properties. Carbon concentrated sites were identified between morphologic layers in CaOx stones and in stratified layers of apatite stones. Elemental analyses revealed numerous additional trace elements in both stone types. Despite the widespread assumption that stone mineral density is an indicator of susceptibility to lithotripsy, calcium stone mineral density estimates do not directly correlate with actual ex vivo stone hardness. Underlying stone heterogeneity in both structure and mineral density could explain why historical approaches have failed in accurately predicting response of stones to lithotripsy.
I. INTRODUCTION
The historical approach to physicochemical analyses of stones embraced the assumption that individual calcium kidney stones can be routinely segregated into meaningful categories based on the identification of two predominant minerals, namely, calcium oxalates (CaOx) or calcium phosphates. Unfortunately, traditional methods of clinical stone analytics have been unable to provide reliable parameters that can predict or direct prophylactic treatment to help reduce recurrent nephrolithiasis. Stone recurrence rates for calcium stone formers remain high (.50% at 10 years), despite a variety of preventive efforts.1 Contributing Editor: Adrian B. Mann a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.153
Based on similarities in stone appearance on
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