Characterizing the free volume of ultrahigh molecular weight polyethylene to predict diffusion coefficients in orthopedic liners

Kyle B. Ludwig, Vaishnavi Chandrasekar, David M. Saylor, Douglas W. Van Citters, Steven D. Reinitz, Christopher Forrey, Martin K. McDermott, Samanthi Wickramasekara, Dustin W. Janes

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Liners used in orthopedic devices are often made from ultrahigh molecular weight polyethylene (UHMWPE). A general predictive capability for transport coefficients of small molecules in UHMWPE does not exist, making it difficult to assess properties associated with leaching or uptake of small molecules. To address this gap, we describe here how a form of the Vrentas–Duda free volume model can be used to predict upper-bound diffusion coefficients (D) of arbitrary molecules within UHMWPE on the basis of their size and shape. Within this framework, the free-volume microstructure of UHMWPE is defined by analysis of a curated set of model diffusants. We determined an upper limit on D for vitamin E, a common antioxidant added to UHMWPE, to be 7.1 × 10−12 cm2 s−1. This means that a liner that contains 0.1 wt % or less Vitamin E and has <120 cm2 patient contacting surface area would elute <100 µg/day of vitamin E. Additionally, the model predicts that squalene and cholesterol—two pro-oxidizing biological compounds—do not penetrate over 820 µm into UHMWPE liners over the course of 5 years because their (Formula presented.) is ≤7.1 × 10−12 cm2 s−1.

Original languageEnglish (US)
Pages (from-to)2393-2402
Number of pages10
JournalJournal of Biomedical Materials Research - Part B Applied Biomaterials
Issue number6
StatePublished - Aug 2018

Bibliographical note

Funding Information:
The findings and conclusions in this article are the views of the authors, have not been formally disseminated by the Food and Drug Administration, and should not be construed to represent any agency determination or policy. The mention of commercial products, their sources, or their use in connection with material reported herein is not to be construed as either an actual or implied endorsement of such products by the Department of Health and Human Services. This research was supported by the CDRH Critical Path program, DBCMS program funding, and in part by appointments to the Research Participation Program administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and FDA. The authors thank Berk Oktem, Brendan Casey, Michael Owens, Antonio Toledo, and Laura Espinal for their time and assistance.

Funding Information:
Additional Supporting Information may be found in the online version of this article. Correspondence to: D. W. Janes; e-mail: Contract grant sponsor: CDRH Critical Path Program Contract grant sponsor: DBCMS Program Funding FIGURE 1. Graphical representation of cholesterol and squalene penetrating into a Vitamin E doped orthopedic device liner and Vitamin E and its photoproducts leaching out, which provide practical motivations for the present work. The rate at which Vitamin E and pro-oxidant lipids diffuse within UHMWPE acetabular liners may be related to the biocompatibility and long-term biostability of the liners.

Publisher Copyright:
© 2017 Wiley Periodicals, Inc.


  • diffusion
  • free volume
  • medical devices
  • orthopedic liners
  • polymer


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