title: Building, testing and validating a set of home-made von Frey filaments: a precise, accurate and cost effective alternative for nociception assessment.
abstract: BACKGROUND
  A von Frey filament (vFF) is a type of aesthesiometer usually made of nylon perpendicularly held in a base. It can be used in paw withdrawal pain threshold assessment, one of the most popular tests for pain evaluation using animal models. For this test, a set of filaments, each able to exert a different force, is applied to the animal paw, from the weakest to the strongest, until the paw is withdrawn.
  
  
  METHODS
  We made 20 low cost vFF using nylon filaments of different lengths and constant diameter glued perpendicularly to the ends of popsicle sticks. They were calibrated using a laboratory balance scale. Building and calibrating took around 4h and confirmed the theoretical prediction that the force exerted is inversely proportional to the length and directly proportional to the width of the filament.
  
  
  RESULTS
  The calibration showed that they were precise and accurate. We analyzed the paw withdrawal threshold assessed with the set of home-made vFF and with a high quality commercial set of 5 monofilaments vFF (Stoelting, Wood Dale, USA) in two groups (n=5) of healthy mice.
  
  
  METHODS
  The home-made vFF precisely and accurately measured the hind paw withdrawal threshold (20.3±0.9 g). The commercial vFF have different diameters while our set has the same diameter avoiding the problem of lower sensitivity to larger diameter filaments.
  
  
  CONCLUSIONS
  Building a set of vFF is easy, cost effective, and depending on the kind of tests, can increase precision and accuracy of animal nociception evaluation.
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA 02114, USA; Laboratory of Radiation Dosimetry and Medical Physics, Institute of Physics, São Paulo University, São Paulo, Brazil. Electronic address: marcelovictor@usp.br.
authors.forename: Marcelo Victor Pires
authors.initials: MV
authors.lastname: de Sousa
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA 02114, USA; Laboratory of Electro-thermo-phototherapy, Department of Physical Therapy, Federal University of São Carlos, São Paulo, Brazil; Post-Graduation Program in Biotechnology, Federal University of São Carlos, São Paulo, Brazil; Optics Group, Physics Institute of Sao Carlos, University of São Paulo, São Carlos, Brazil.
authors.forename: Cleber
authors.initials: C
authors.lastname: Ferraresi
authors.affiliation: Laboratory of Radiation Dosimetry and Medical Physics, Institute of Physics, São Paulo University, São Paulo, Brazil.
authors.forename: Ana Carolina
authors.initials: AC
authors.lastname: de Magalhães
authors.affiliation: Laboratory of Radiation Dosimetry and Medical Physics, Institute of Physics, São Paulo University, São Paulo, Brazil.
authors.forename: Elisabeth Mateus
authors.initials: EM
authors.lastname: Yoshimura
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA 02114, USA; Harvard Medical School, Department of Dermatology, Boston, MA 02115, USA; Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA 02139, USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hamblin
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D059225:Nociception / Q000502:physiology*; D010146:Pain / Q000175:diagnosis* / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods*; D010812:Physical Stimulation; D011601:Psychophysics; D015203:Reproducibility of Results
keywords: Home-made von Frey filament; Pain evaluation; Validation; von Frey filament