Hypertrophic scarring is an abnormal process of wound healing that results in excessive scar tissue formation. Creating human-like fibrotic models can help develop therapies to prevent scarring and promote regeneration. Over the past decade, we have demonstrated that mechanical transduction, in which mechanical stimuli is converted into cellular responses, drives excessive scar formation.
We have inhibited mechanical stimuli and found that it promotes healing and regeneration in large animal models, and also identified its importance in the foreign body response to biomedical implants. After injury, mice form fewer scars than humans due to their looser and thinner skin, as well as the underlying muscle layer, the musculus panniculus carnosus, that contracts the wound. We've developed a mouse model that applies human levels of mechanical strain over a healing wound to create a human-like hypertrophic scarring model.
Our protocol is notable for its simplicity, reproducibility, and biomimicry. By applying mechanical tension to wounds, we reliably induce more human-like hypertrophic scarring, harnessing physiological mechanical transduction pathways rather than relying on burn or chemical injury models. This reliably mirrors how hypertrophic scarring forms in the body, making it highly translatable.
Overall, our lab is investigating how to pharmacologically target mechanical signaling to reduce fibrosis across organ systems. Specifically, using this model, we'll explore other anti-scarring therapies, such as tissue regenerative scaffold, wound dressings, and steroids. To begin, place the anesthetized mouse on the operating surface.
Insert the mouse nose into the nose cone opening for anesthesia maintenance. Confirm the depth of anesthesia by the lack of response to a toe pinch. Using a 21 gauge needle, inject 0.05 milligrams per kilogram of buprenorphine subcutaneously into the shoulder for post-surgical pain treatment.
Disinfect the mouse's dorsum with three alternating rounds of iodine or chlorhexidine-based scrub and alcohol swab. Now, using a scalpel, make a full thickness dorsal midline incision along the marked area. Close the incision with 5-0 sutures in a simple interrupted pattern by bisecting the wound.
Cut a Telfa gauze into a three centimeter by one centimeter piece. Place the gauze piece in the center of a film adhesive dressing and apply it to the dorsum, ensuring the gauze covers the incision. Then, place a halved dressing on the abdomen and wrap it circumferentially until it meets the dorsal dressing.
After dressing the wound, place the mouse in a separate sterile cage and monitor it until it fully recovers from the anesthetic. Four days after creating the dorsal midline incision, anesthetize the mouse and place it on a working platform. Use forceps to separate the dressing from the mouse's abdomen by working the tool side to side against the ventral side.
Leave the tool between the wrap and the skin to elevate the dressing off the skin. Then, use scissors to cut the dressing off. Clean the dorsum with an alcohol swab.
Examine the incision for wound dehiscence or signs of infection. Next, lightly coat the arms of the hypertrophic scarring, or HTS device, with medical glue. With one hand, render the skin on the mouse dorsum slightly taut in the transverse direction.
Then, with the help of the other hand, place the HTS device on the dorsum, ensuring that the incision is equidistant from each arm and the skin is uniformly taut between the arms. After drying, secure four sutures around each arm of the device and through the skin, ensuring the needle exits towards the incision. Now, place three skin staples around the arms of the device, securing it to the skin.
Then, place the Telfa gauze piece in the center of a film adhesive dressing and apply it to the dorsum of the mouse, ensuring the gauze covers the incision. Place a halved dressing on the abdomen and wrap it circumferentially until it meets the dorsal dressing. The next day, remove the sutures from the wound using dissection scissors.
For the initial stretch of the HTS device, insert the HTS device key into the device and turn it to expand the device until the skin is taut, but not at risk of tearing. Finally, bandage the mouse as demonstrated previously. The stretch group mice exhibited significantly wider scars compared to the control group, with a peak scar width of 0.99 millimeters at postoperative day nine, which remained significantly wider at postoperative 15 and 19 days.
