title: Automated AFM force curve analysis for determining elastic modulus of biomaterials and biological samples.
abstract: The analysis of atomic force microscopy (AFM) force data requires the selection of a contact point (CP) and is often time consuming and subjective due to influence from intermolecular forces and low signal-to-noise ratios (SNR). In this report, we present an automated algorithm for the selection of CPs in AFM force data and the evaluation of elastic moduli. We propose that CP may be algorithmically easier to detect by identifying a linear elastic indentation region of data (high SNR) rather than the contact point itself (low SNR). Utilizing Hertzian mechanics, the data are fitted for the CP. We first detail the algorithm and then evaluate it on sample polymeric and biological materials. As a demonstration of automation, 64 × 64 force maps were analyzed to yield spatially varying topographical and mechanical information of cells. Finally, we compared manually selected CPs to automatically identified CPs and demonstrated that our automated approach is both accurate (< 10nm difference between manual and automatic) and precise for non-interacting polymeric materials. Our data show that the algorithm is useful for analysis of both biomaterials and biological samples.
authors.affiliation: Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, California 95616, USA.
authors.forename: Yow-Ren
authors.initials: YR
authors.lastname: Chang
authors.affiliation: Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, California 95616, USA.
authors.forename: Vijay Krishna
authors.initials: VK
authors.lastname: Raghunathan
authors.affiliation: Department of Biomedical Engineering, University of California Davis, Davis, California 95616, USA.
authors.forename: Shaun P
authors.initials: SP
authors.lastname: Garland
authors.affiliation: Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, California 95616, USA.
authors.forename: Joshua T
authors.initials: JT
authors.lastname: Morgan
authors.affiliation: Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, California 95616, USA.
authors.forename: Paul
authors.initials: P
authors.lastname: Russell
authors.affiliation: Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California Davis, Davis, California 95616, USA; Department of Ophthalmology and Vision Science, School of Medicine, University of California Davis, Davis, California 95616, USA. Electronic address: cjmurphy@ucdavis.edu.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Murphy
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000465:Algorithms; D000818:Animals; D001331:Automation; D001672:Biocompatible Materials; D001696:Biomechanical Phenomena; D003315:Cornea / Q000166:cytology; D004285:Dogs; D055119:Elastic Modulus; D007498:Iris / Q000166:cytology; D018625:Microscopy, Atomic Force / Q000379:methods*; D011092:Polyethylene Glycols / Q000737:chemistry; D000099166:Polyacrylamides
chemical_list: D000180:Acrylic Resins; D001672:Biocompatible Materials; D011092:Polyethylene Glycols; D000099166:Polyacrylamides
keywords: Atomic force microscopy; Biomechanics; Contact point; Elastic modulus; Nano-indentation