The scratch assay is an in vitro laboratory method that measures cell migration by creating a gap in a confluent cell monolayer and imaging how that gap closes over time. It is one of the simplest and most widely used models for studying migration behavior in cultured cells. This guide explains the method, how it is quantified, and how researchers keep the data reliable.
What is a scratch assay?
A scratch assay (also called an in vitro wound-healing assay) begins with a confluent layer of cells grown in a dish or multi-well plate. A thin gap is introduced across the monolayer, and the cells at the edges of that gap migrate inward over the following hours. By imaging the gap at set time points, a researcher can quantify the rate of migration. The term describes a cell-culture technique; it measures cellular behavior in a dish, not any process in a living organism.
How is the gap created?
The classic approach draws a sterile pipette tip across the monolayer to displace cells in a straight line, leaving a defined gap. Alternatives include removable culture inserts that create a gap of fixed width when lifted, or masks that keep a region cell-free during seeding. Insert-based methods trade a small amount of setup for a more consistent, reproducible gap width.
How is migration quantified?
Images are captured at the start (time zero) and at defined intervals afterward. Analysis software measures the open area at each time point, and the reduction in open area is expressed as a percentage of gap closure or as a migration rate. Reporting closure relative to the starting gap, rather than as an absolute distance, keeps results comparable across replicates with slightly different starting widths.
What controls make the assay reliable?
Three factors drive data quality: a consistent gap width across wells, a vehicle (untreated) control run alongside every test condition, and fixed imaging time points. Because the readout can reflect both migration and a degree of proliferation, serum-reduced conditions or a proliferation inhibitor are sometimes used so the measurement reflects migration more specifically. Every condition should be run in replicate.
What compounds are studied this way?
The assay is a common in vitro screen for research compounds whose mechanisms involve cell migration or extracellular-matrix interaction. In laboratory studies, matrix-associated research peptides such as BPC-157 and TB-500 and the copper-binding tripeptide GHK-Cu are examples of materials examined in migration and matrix-interaction models. In every case the assay characterizes behavior in cultured cells, not an outcome in a person or animal.
Common pitfalls
- Inconsistent gap widths from freehand scratching, which widen the error bars between wells.
- Debris or detached cells left in the gap after scratching; a gentle rinse before imaging removes them.
- Imaging different regions of the gap at each time point rather than reference-marked positions.
- Confounding migration with proliferation when the measurement window is long.
Related research guides
- What are research peptides? A laboratory primer
- How to reconstitute lyophilized peptides
- How to verify research peptide purity
Research-use note
All materials discussed are supplied for in vitro laboratory research use only, and are not for human or animal use. This article describes a cell-culture technique, not any therapeutic process.
