Wound healing assay

The wound healing assay, also known as the in vitro scratch assay, is a widely used method to measure cell migration and wound closure in cultured cell monolayers. This protocol involves creating a “wound” or gap in a confluent cell monolayer and monitoring the movement of cells into the cleared area over time. It is a simple, cost-effective method that provides quantitative data on cell motility, making it ideal for evaluating the effects of drugs, growth factors, or genetic modifications. The assay enables analysis of whole cell masses for collective migration as well as individual cell migration, depending on the experimental setup. Abcam’s standardized wound healing assay protocol ensures reproducibility and clarity, supporting researchers in cancer biology, regenerative medicine, and drug discovery. The assay is compatible with imaging software like ImageJ for precise wound closure analysis.

Introduction

Cell migration plays a critical role in numerous physiological and pathological processes, including development, immune response, and cancer metastasis. The wound healing assay offers a straightforward approach to assess this behavior in vitro. By simulating a wound in a cell monolayer, researchers can observe how cells respond to injury-like conditions. This assay is particularly valuable in screening compounds that influence cell motility or in studying the molecular mechanisms underlying tissue regeneration. Abcam’s protocol provides a reliable framework for conducting this assay with consistency, making it a go-to method for labs investigating cellular dynamics and therapeutic interventions.

Background and principles

The wound healing assay is grounded in the principle of collective cell migration. It is one of several cell migration assays used in research. A scratch is introduced into a confluent monolayer of adherent cells, creating a cell-free zone. Over time, cells migrate into this gap, mimicking the natural wound healing process. The rate and extent of wound closure are indicative of the cells’ migratory capacity. This assay does not require specialized equipment and can be performed using standard cell culture tools and imaging systems. Quantitative analysis is typically done using software like ImageJ, which measures the reduction in wound width over time, providing insights into cellular behavior under various experimental conditions.

Compared to Transwell migration or Boyden chamber assays, the wound healing assay is simpler and more visually intuitive. The wound healing assay is a type of cell migration assay and is particularly suited for measuring collective migration of whole cell masses, while other assays may focus on individual cell migration. While transwell assays measure chemotactic migration through a membrane, the scratch assay focuses on collective lateral movement across a surface. Unlike 3D invasion assays, which assess movement through extracellular matrices, the wound healing assay is strictly two-dimensional. Its main advantages are ease of setup, low cost, and real-time visualization. However, it may be less suitable for studying single-cell migration or invasive behavior in complex environments. For high-throughput needs, specialized kits or automated imaging systems may offer enhanced scalability.

Stage 1 - Method

Materials required

• A confluent flask or plate of cells
• 12 well culture plates
• Appropriate growth medium (containing any serum, growth factors or small molecules required for your specific cell type)
• Enzymatic or chemical cell detachment agent (for adherent or semi-adherent cells)
• Standard cell culture consumables (serological pipettes, pipette tips, centrifuge tubes, 70% ethanol, sterile PBS, etc.)
• Any treatments you are assessing
• Standard cell culture equipment (pipette boy, pipettes, containment facilities, centrifuge, light microscope, cell counter/hemocytometer etc.)
• Light microscope with an attached digital camera
• Thin tipped permanent marker

Steps

Wash cells and culture without growth serum

• Using a confluent plate or flask of cells, aspirate the media and dispose.
• Add an appropriate volume of PBS, ensuring the cells are covered.
• Gently swirl the plate, then aspirate and discard PBS.
• Add an appropriate amount of serum-free media (10-12 mL) and culture the cells for 24 h.

Wash and collect cells

• Aspirate media and dispose.
• Add an appropriate volume of PBS, ensuring the cells are covered.
• Gently swirl the plate, then aspirate and discard PBS.
• Add appropriate detachment reagent and incubate at 37°C until cells are detached.
• Add fresh culture media and transfer cell suspension to a centrifuge tube.
• Centrifuge at 200-250 x g for 5 min.
• Remove media and resuspend the cell pellet in an appropriate volume of PBS.
• Centrifuge at 200-250 x g for 5 min.
• Aspirate and discard PBS.
• Resuspend cell pellet in fresh growth medium.

Seed cells into a 12-well plate in fresh supplemented culture medium

• Transfer the required volume of cells to each well of the 12-well plate such that the cells would be ~80% confluent after 24 h.
• Add serum-free media to the required volume (1-2 mL) and culture the cells for 24 h. Label flasks as required.
  • At this point, add any treatments you are assessing, if they require a pre-treatment period.

Wound the monolayer of cells

• Using a 200 µL pipette tip, scratch the monolayer of confluent cells in the center and along the entirety of the well's diameter.

Wash cells

• Aspirate the media from each well and dispose.
• Gently add an appropriate volume of PBS, ensuring the cells are covered.
• Gently swirl the plate, then aspirate and discard PBS. Ensure any detached cells and debris are removed.
• Add an appropriate amount of serum-free culture media (1-2 mL).
• At this point, add any treatments you are assessing – assuming they do not require a pre-treatment period.

Image the wound at several points

• Using a light microscope with an attached digital camera, focus on the wound area.
• Ensuring a suitable area of the monolayer of cells is visible on either side of the wound with the wound in the center, obtain an image of the cells.
• Using a thin-tipped permanent marker, carefully mark on the bottom or top of the culture plate where the image was taken.
• Repeat this for each well.
• Return cells to a culture incubator and culture for 24 h.

Re-image the wound at the same points

• Using a light microscope with an attached digital camera, focus on the wound areas marked previously.
• Ensuring a suitable area of the monolayer of cells is visible on either side of the wound with the wound in the center, obtain an image of the cells.
• Repeat this for each well.
• If you are observing wound closure for longer than 24 h, replace media/treatments if required and return cells to a culture incubator and culture for your designated time period.
  • Repeat the imaging steps as required.
• Once your assessment is complete, discard of the cells as required by local guidelines and regulations.

Measure wound closure

• Ensure the digital images obtained are named appropriately and filed accordingly.
• Using a tool like ImageJ, measure the width of the wound in the images taken after scratching (a).
• Using the image from the same well after allowing for wound closure, measure the width of the wound following closure (b).
• The percentage of wound closure can be calculated as follows:
  • % wound closure = (a-b)/a x 100

Applications

The wound healing assay is extensively used in cancer research to evaluate the metastatic potential of tumor cells. It also serves as a model for studying the effects of pharmacological agents on cell motility. Researchers use it to investigate signaling pathways involved in migration, such as those mediated by growth factors, cytokines, or matrix metalloproteinases. In regenerative medicine, it helps assess the healing potential of stem cells or biomaterials. The assay is also valuable in toxicology for evaluating how environmental agents affect cellular dynamics. Its versatility makes it a staple in both academic and pharmaceutical research settings.

Limitations

Despite its utility, the wound healing assay has several limitations. It lacks the complexity of in vivo environments, such as extracellular matrix interactions and three-dimensional architecture. The manual creation of the wound can introduce variability, and cell proliferation may confound migration measurements if not properly controlled. Additionally, the assay is not ideal for non-adherent or weakly adherent cell types. Imaging and analysis can be subjective without standardized protocols or automated tools. To mitigate these issues, researchers often use serum starvation, mitotic inhibitors, or commercial inserts to improve reproducibility and isolate migratory behavior from proliferative effects.

Troubleshooting

Common issues in the wound healing assay include inconsistent scratch width, poor cell adherence, and unclear imaging. To ensure uniform scratches, use a consistent pipette tip angle and pressure. If cells detach excessively, verify that the monolayer is fully confluent and that the scratch is not too aggressive. For blurry images, ensure the microscope is properly calibrated and that the wound area is centered. If wound closure is too rapid or too slow, adjust serum levels or treatment concentrations. Always include controls and replicate wells to account for variability. Using image analysis software like ImageJ can help standardize measurements and improve data reliability.