Dr. Locksley E. McGann

Natural and engineered tissues are increasingly being used as effective and cost-effective approaches a wide variety of applications in transplantation medicine, other medical applications, toxicology testing, agriculture, and food engineering. Cryopreservation is often the only method for preserving physiological structure, viability and function in living tissues for long periods of time, so our research efforts are now exploring methods for cryopreservation of viability and function in complex cellular and tissue systems.

Members of the Biopreservation Research Group at the University of Alberta include Dr. Janet Elliott (Chemical and Materials Engineering), Dr. Jason Acker (Canadian Blood Services) and Dr. Nadr Jomha (Surgery). Research in the Biopreservation Research Group aims to understand the responses of living cells and tissues to freezing and desiccation. This Group has a significant history in the science of cryobiology and its applications in medicine, with research ranging from fundamental aspects of osmotic transport to clinical applications in transplantation. These studies involve developing and testing concepts on the nature and mechanisms of injury sustained during preservation, and applying these concepts to the development of strategies in the preservation of viability and function.

Fundamental Aspects of Low-Temperature Biology:
We have been applying fundamental concepts to extending our understanding of osmotic transport across cell membranes, diffusion in tissue systems, and freezing in complex aqueous solutions. Our transport equations are implemented in mathematical models that are applied to enhance our understanding of living systems at low temperatures.

Osmotic Effects:
Experimental measurements of cell volume change during osmotic excursions are tracked using electronic or optical measurements, and used to test and validate theoretical descriptions of osmotic transport. Osmotic parameters from measurements on a variety of cell types (including spermatozoa, hematopoietic stem cells, endothelial cells, and a variety of other normal and malignant cells) have been used to simulate osmotic responses during cryopreservation and cryosurgery. These simulations are used practically to optimize protocols for the addition and removal of cryoprotectants in a variety of living cells.

Modeling and Simulation of Low-Temperature Responses:
We developed a thermodynamic approach to the prediction of phase diagrams for non-dilute aqueous solutions containing many solutes, including the cytoplasm of living cells. Coupled with our transport equations that do not make simplifyng assumptions, are have created analytical tools for predicting the conditions inside and outside cells during cooling and warming.This approach is being used to model osmotic and low-temperature responses in cells and tissues for comparison to experimental measurements.

Injury and Protection at Low Temperatures:
Our research in this area explores multiple facets of cryoinjury, including damage related to osmotic stresses, intracellular ice, and cellular interactions with their environment. Our theoretical descriptions have contributed to the development of concepts related to the mechanisms of cryoinjury and cryoprotection.

Cellular systems:
Studies on cellular systems use a wide variety of primary and cultured cells, including hematopoietic stem cells from bone marrow, peripheral blood, and the umbilical cord, spermatozoa from a variety of species, endothelial cells from various tissues, and isolated cells from the liver and pancreas. Some are used purely for experimental purposes, and others are target cells for cryopreservation.

The Cryobiology of Tissue Systems:
Information on osmotic properties of cells in suspension, the incidence of intracellular freezing, and limits for toxicity have been used to design and optimize strategies for cryopreservation for a wide variety of cells. This approach, however, is not directly applicable to tissues, because the structure of tissues and the interactions between cells and the extracellular matrix add dimensions not present in cell suspensions.

While significant advances are being made in biosynthetic constructs for a wide variety of applications in medical, agricultural, and food industries, our ability to preserve these constructs has lagged significantly. Our current focus is to extend understanding of preservation sciences for applications to systems where there is a demonstrated need, by consolidating a variety of disciplines to focus on the preservation of living systems.

The purpose of these studies is to investigate fundamental low-temperature responses of tissues, and correlate these responses with subsequent biological outcomes. A goal is to bridge fundamental and applied aspects by addressing some of the outstanding questions in the cryobiology of tissue systems, so that the results of these studies may be applied to the banking of natural and engineered tissues for transplantation and other uses in society.

Experimental Approaches:
The experimental model tissues being used to investigate low-temperature responses include:
1. confluent monolayers of cells forming a 2-dimensional tissue, to study consequences of cell adhesions to other cells and to substrates (this system also models the corneal endothelium, a sensitive site for cryoinjury)
2. 3-D experimental model systems consisting of various cell types in a matrix, similar to many engineered tissues being developed for clinical use
3. engineered tissues
4. natural tissues, including articular cartilage, heart valves, corneas, islets of Langerhans, skin, arteries

Consequences of osmotic and low-temperature exposures are investigated using in situ assessments of cell integrity and function. Complementing mathematical modeling of responses, experimental assessments of morphological and quantitative biophysical and physiological assessments are used. These include cryomicroscopy with fluorescent markers to monitor low-temperature responses, confocal microscopy to examine responses as a function of location within tissues, mechanical and optical properties of tissues such as cartilage and cornea, and physiological responses such as insulin production in islets of Langerhans, metabolic activity in skin. Electron microscopy is used to assess structural consequences, and MRI to track diffusion, ice formation, and in vivo performance of transplanted tissues.

Applications in Medicine:
These research efforts have contributed to the development of significant medical applications in Edmonton - the bone marrow and stem cell transplantation program; the Alberta Cord Blood bank for banking umbilical cord blood; and the Comprehensive Tissue Centre, a major Canadian tissue bank.

Other applications:
We have also been involved in applying concepts and techniques to the conservation of biological diversity in endangered species, the freeze-texturization of food materials, and the management of human remains frozen in a glacier for centuries.

The reproductive biology of many species is now central to the production of food in plants, fish, birds and animals. Preservation of reproductive tissues in these species is becoming increasingly critical to ensure the food supply keeps pace with the demand. In many cases, research is required to bring our ability to cryopreserve reproductive cells and tissues up to a standard that maximizes benefit to this industry.

Human stem cells are currently being altered and used in a variety of ways that include medical applications. Some stem cells have very low recovery after cryopreservation, and others, where the numbers are limited, could be far more effectively utilized with higher post-thaw recovery.

Bioengineered tissues are being developed for transplantation and for toxicology testing. Effective utilization of these engineered tissue products will require preservation at least for distribution. Cryopreservation would uncouple the production of these living tissues from the utilization.