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Wound Healing Models in Research: Scratch Assays, Splinted Wounds and Tendon Injury
Healing research looks simple on the surface: make an injury, apply a compound, measure how fast it closes. In practice, the model you choose decides what you can conclude. A scratch in a cell dish and a surgical wound in a mouse measure very different things.
Key takeaways
- The scratch assay measures cell migration in two dimensions.
- Mouse skin heals mainly by contraction, so splinted models are used to mimic human healing.
- Tendon and muscle injury models test mechanical recovery.
- Closure speed is only one of several readouts.
The scratch assay
Cells are grown to a confluent layer, a gap is scraped across it with a pipette tip, and the gap is imaged over 12 to 48 hours. The remaining open area gives percent closure. It is cheap and quick, but closure comes from both migration and cell division. To isolate migration, labs often lower serum or add a proliferation blocker such as mitomycin C. Edges scraped unevenly or with damaged cells add noise, so automated scratching tools and ring-barrier inserts are used.
Excisional wounds in mice
A circle of skin is removed, commonly with a punch biopsy. A key problem is that loose mouse skin heals largely by contraction of the surrounding tissue, whereas human skin heals mainly by new tissue formation and re-epithelialization. The splinted wound model addresses this by sewing a silicone ring around the wound to hold the edges open, forcing healing through granulation and epithelial growth. Without a splint, a compound can appear to speed healing just by affecting contraction.
Other injury models
- Incisional wounds test tensile strength of a healed cut.
- Burn models examine deeper tissue injury and scarring.
- Tendon transection or Achilles models cut the tendon and measure mechanical strength and collagen organization later.
- Muscle injury models such as cardiotoxin injection test regeneration.
- Diabetic and aged animal models assess impaired healing.
What gets measured
- Wound closure rate from photographs with a ruler for scale.
- Histology. Re-epithelialization, granulation tissue thickness, collagen deposition with Masson trichrome or picrosirius red.
- Vessel density by CD31 staining (see angiogenesis assays).
- Inflammation markers such as immune cell counts and cytokines.
- Mechanical testing of strength for tendons and incisions.
- Scar quality and function, rather than closure alone.
Pitfalls to watch for
- Unblinded scoring of photographs.
- Wounds of unequal size at the start, which should be normalized.
- Animals housed together can chew or reopen each other’s wounds.
- Time-of-day and stress effects, which alter healing hormones.
- Only a single time point, which can mean the treatment is faster, or simply earlier.
Reading the literature
When a paper reports faster healing, check the model, whether it was splinted, who scored it and whether it was blinded. Our guide to the evidence ladder covers where animal healing studies sit among types of evidence, and our post on self-experiments explains why anecdotes about healing are especially prone to regression to the mean.
The bottom line
Healing is a multistage process of inflammation, new tissue and remodeling. A good model matches the question: migration, closure, strength or scar. Mixing them leads to conclusions the data cannot support.
Related reading
- How Angiogenesis Is Measured: Tube Formation, Aortic Ring and CAM Assays
- The Evidence Ladder: How to Read Peptide Research Without Being Fooled
- Why Self-Experiments Mislead: Placebo, Regression to the Mean and the n-of-1
- Browse the full Research Library
For laboratory research use only. Not for human or veterinary use, and not intended to diagnose, treat, cure or prevent any condition. This article is educational and is not medical advice.