Cryo-Induced Thermal Wounds: A Human Acute Wound Model

July 2015 | Volume 14 | Issue 7 | Original Article | 734 | Copyright © 2015

Alejandra Vivas MD,a Joshua D. Fox BS,a Katherine L. Baquerizo Nole MD,a Andrea D. Maderal MD,a Evangelos Badiavas MD PhD,a D. Innes Cargill PhD,b Herbert B. Slade MD,b Steven R. Feldman MD PhD,c Robert S. Kirsner MD PhDa

aDepartment of Dermatology and Cutaneous Surgery, University of Miami Miller School of Medicine, Miami, FL
bSmith and Nephew, plc. Fort Worth, TX
cDepartment of Dermatology, Wake Forest University, Winston Salem, NC

Abstract

INTRODUCTION: Clinical models are invaluable in studying wound healing. Challenges in studying human wounds include heterogeneity of patients and wounds, as well as prolonged study time, resulting in high costs. Animal models are an efficient method to study wound healing, but often lack correlation with human acute wound healing. Human wound models can be created using sharp instruments, suction, acids, heat and cold. In this observational study, we propose a practical human acute wound model where partial thickness wounds are induced by cryosurgery to create wounds that could facilitate wound healing research and development.
METHODS: On forearms of 8 healthy adult volunteers, freeze injuries were induced using liquid nitrogen spray delivered onto a target area of a 1 cm circular opening at a distance from the cryo-device to the skin of 0.5-1 cm. Several freeze-thaw time cycles were implemented by administering pulses ranging from 3 to 12 seconds. Clinical evaluation was performed at a 24-hour follow-up period. Blister roofs were histologically analyzed by a blinded dermatophathologist. Clinical assessment of time to heal was determined.
RESULTS: Freeze-times greater than 5 seconds caused a majority of subjects to develop blisters, and freeze-times greater than 8 seconds resulted in uniform blister formation. Consistent histology of full thickness necrotic epidermis with intact detached basement membrane with minimal acute neutrophilic inflammatory infiltrate was observed in all blister specimens examined. The 8-second freeze-time group had a time to heal of 13-14 days, while the 12-second freeze-time group required 3 weeks to heal. After healing, an area of hypopigmented skin and slightly hypertrophic scarring remained.
DISCUSSION: This novel cryo-induced wound model is a potential simple, efficient and reliable model for studying the dynamic processes involved in acute wound healing and to aid in the development of new wound healing therapies.
Clinicaltrials.gov identifier: NCT01253135.

J Drugs Dermatol. 2015;14(7):734-738.

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INTRODUCTION

Wound healing is a multifaceted highly synchronized process that involves interaction between several cell types, pathways, processes and mechanical forces that influence gene expression, synthesis of growth factors and inflammatory products and proliferation of cells.1 Wound healing research, both at macroscopic and molecular levels, continues to expand our understanding the pathophysiology of healing and the basis of non-healing wounds. Interventional human trials are conducted to evaluate potential new treatments of chronic cutaneous ulcers (CCU) related to underlying conditions such as diabetes mellitus, venous or arterial insufficiency, or immobility resulting in prolonged, excessive localized pressure. Problematic issues in studying these wounds are the heterogeneity of both patients and wounds and the prolonged study period, resulting in high investigational costs. Intrinsic to the controlled trial methodology, is an assumption that the matched placebo or vehicle control will not exert any negative influence on healing- an assumption, which cannot be tested within the interventional trial. To more efficiently study healing, in vitro and in vivo animal models have been developed addressing some of the issues related to studying CCU. However, while approaches such as the use of splints, ligation of arteries, introduction of bacteria and/or use of diabetic animals can be internally validated, these models do not fully reproduce the dynamics of human chronic wounds.2 Even well established animal models using porcine partial thickness wounds show less than 80% concordance with human acute wounds and require housing and other related associated costs of dealing with and studying large animals.3-6 Alternatively, surgically created human wounds such as partial thickness skin graft donor sites 7,8 and full thickness wounds using punch biopsy techniques9 have been used to study healing and the various effects of therapies. Additional models include wounds created using scalpels or suction, by heat using lasers, by cold using liquid nitrogen and by acids.10,11

Cryo-wounding models have been described using a contact cryosurgery probe (Kryomed, MediUmtech, Germany) placed

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