Sample size considerations in soft tissue biomechanics

Niels Hammer; Benjamin Ondruschka; Andrea Berghold; Thomas Kuenzer; Gudrun Pregartner; Mario Scholze; Gundula Gesine Schulze-Tanzil; Johann Zwirner

doi:10.1016/j.actbio.2023.07.036

Sample size considerations in soft tissue biomechanics

Acta Biomater. 2023 Oct 1:169:168-178. doi: 10.1016/j.actbio.2023.07.036. Epub 2023 Jul 29.

Authors

Niels Hammer¹, Benjamin Ondruschka², Andrea Berghold³, Thomas Kuenzer³, Gudrun Pregartner³, Mario Scholze⁴, Gundula Gesine Schulze-Tanzil⁵, Johann Zwirner⁶

Affiliations

¹ Division of Macroscopic and Clinical Anatomy, Gottfried Schatz Research Center, Medical University of Graz, Graz, Austria; Department of Orthopedic and Trauma Surgery, University of Leipzig, Leipzig, Germany; Division of Biomechatronics, Fraunhofer Institute for Machine Tools and Forming Technology Dresden, Germany. Electronic address: niels.hammer@medunigraz.at.
² Institute of Legal Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
³ Institute for Medical Informatics, Statistics and Documentation, Medical University of Graz, Graz, Austria.
⁴ Institute of Materials Science and Engineering, Chemnitz University of Technology, Chemnitz, Germany.
⁵ Institute of Anatomy and Cell Biology, Paracelsus Medical University, Nuremberg and Salzburg, Nuremberg, Germany.
⁶ Institute of Legal Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany; Department of Oral Sciences, University of Otago, Dunedin, New Zealand.

PMID: 37517620
DOI: 10.1016/j.actbio.2023.07.036

Abstract

Biomechanical experiments help link tissue morphology with load-deformation characteristics. A tissue-dependent minimum sample number is indispensable to obtain accurate material properties. Stress-strain properties were retrieved from human dura mater and scalp skin, exemplifying two distinct soft tissues. Minimum sample sizes necessary for a stable estimation of material properties were obtained in a simulation study. One-thousand random samples were sequentially drawn for calculating the point at which a majority of the estimators settled within a corridor of stability at given tolerance levels around a 'complete' reference for the mean, median and coefficient of variation. Stable estimations of means and medians can be achieved below sample sizes of 30 at a ± 20%-tolerance within 80%-conformity for scalp skin and dura. Lower tolerance levels or higher conformity dramatically increase the required sample size. Conformity was barely ever reached for the coefficient of variation. The parameter type appears decisive for achieving conformity. STATEMENT OF SIGNIFICANCE: Biomechanical trials utilizing human tissues are needed to obtain material properties for surgical repair, tissue engineering and modeling purposes. Linking tissue mechanics with morphology helps elucidate form-function relationships, the 'morpho-mechanical link'. For material properties to be accurate, it is vital to examine a minimum number of samples. This number may vary between tissues, and the effects of intrinsic tissue characteristics on data accuracy are unclear to date. This study used data obtained from human dura and skin to compute minimum sample sizes required for estimating material properties at a stable level. It was shown that stable estimations are possible at a ± 20%-tolerance within 80%-conformity below sample sizes of 30. Higher accuracy warrants much higher sample sizes for most material properties.

Keywords: Biomechanical property; Conformity; Corridor of stability; Dura mater; Head; Human scalp skin; Morpho-mechanical parameter; Neurocranium; Sample size estimation; Tolerance level; Variation.

MeSH terms

Biomechanical Phenomena
Dura Mater*
Humans
Sample Size
Skin*