Ayman Grada, MD, Joshua Mervis BS, Vincent Falanga, MD, FACP Research Techniques Made Simple Animal Models of Wound Healing in Disease Ayman Grada, MD, Joshua Mervis BS, Vincent Falanga, MD, FACP

What is an Animal Model? An animal model is a living, non-human organism used to study human biological processes under controlled conditions, for the purpose of better understanding, and to enable predictions about these processes, without the added risk of harming an actual human being during the process.

Purpose of Animal Models in Wound Healing Better understanding of the healing process Development of biological therapeutics pertinent to wound healing Test the efficacy and safety of a particular therapy in a living model prior to its use in humans

Proliferation Migration Acute Wound Chronic Wound Time Coagulation Coagulation Day 1 Inflammation Remodeling Time Inflammation Proliferation Migration Days 3-5 Proliferation Migration Weeks Months Remodeling

Choice of Animal Species in Wound Models Mouse Rat Rabbit Pig Guinea pig Greyhound Zebrafish Cost Size Ease of handling Physical space Degree of similarity to human skin Genetic tractability Experimental objectives Expertise

Animal Models of Acute Healing Excisional wounds Partial-thickness model Full-thickness model Incisional wounds Burn wounds

Animal Models of Impaired Healing Diabetes-associated wounds Drug induced models Genetic models Pressure wound Rat magnet ischemia-reperfusion model Fuzzy rat model Ischemic wounds Rabbit ear model Pig flap ischemic model Skin banding model Infected-biofilm wounds Pig wound infection Rabbit ear, wound biofilm model

Ischemic rabbit ear model Clinically relevant to ischemic ulcers Suturing of blood vessels generates an ischemic zone within which wounds can be made Benefits: accessible/suitable for pharmacological testing Drawbacks: does not fully replicate human hypoxic wounds and not genetically tractable

Diabetic mouse wound model Clinically relevant to diabetic ulcers Diabetic mice are chemically or genetically induced Benefits: enable testing of pharmacological agents/multiple wounds per animal Drawbacks: mouse diabetes does not fully reflect human diabetic complications. variability between different diabetic models Diabetic ulcer

Excision wound splinting model in mouse Clinically relevant to acute and chronic wounds Splinting ring tightly placed on the skin around the excisional wound Benefits: splinting minimizes contraction Drawbacks: anatomical differences between rodent and human skin; splinting materials may detach and move into the wound site

Rat magnet ischemic-reperfusion Clinically relevant to pressure ulcers A steel plate is inserted beneath the dorsal skin A magnet is applied over a number of cycles to generate chronic skin wound Benefits: can vary in degree of blood perfusion to skin and thus grade of ulcer Drawbacks: anatomical differences between rodent and human skin

Pig wound infection Clinically relevant to infected ulcers Wounds are seeded with bacteria that produce a biofilm Benefits: skin anatomically and physiologically similar to humans Drawbacks: expensive and not genetically tractable

Pig flap ischemia Clinically relevant to ischemic ulcers Surgical incisions severs blood flow to specific regions of skin, creating hypoxic zones Benefits: skin anatomically and physiologically similar to humans Drawbacks: expensive and not genetically tractable

Mouse tail full-thickness wound model Clinically relevant to delayed wound healing Rectangular full-thickness excision on the dorsum of the tail Benefits: delayed healing (up to 21 days), minimal contraction, and can be used in wild-type animal Drawbacks: anatomical differences between rodent and human skin

Limitations of Animal Wound Models Anatomical and physiological differences among and within animal species, including humans No one model can recapitulate the heterogeneity and complexity of chronic wounds in humans Lack of standardization in design, procedure, and evaluation