|Vol. 19, No. 19||October 15, 1997|
TMC Institutions, Rice
by KRISTINA VAN ARSDEL
Texas Medical Center News
Clinicians, scientists, and engineers are combining their efforts in a new area of science that could change the way burn, orthopaedic, and cancer patients, among others, are treated. With the Texas Medical Center and Rice University in collaboration, Houston is poised to be one of the hubs for such activity in the field known as tissue engineering.
Michael J. Miller, M.D., (left) and Charles W. Patrick, Jr., Ph.D.,
examine a polymer in the Laboratory of Reparative Biology and
Bioengineering at M. D. Anderson Cancer Center.
Tissue engineering involves the clinician's knowledge of what patients need, the life scientist's understanding of how cells interact, and the engineer's development of biomaterials that can function with cells in the body to form new tissue. When these three disciplines come together, the objective is to develop new ways of replacing tissue using biodegradable materials that interact with the cells in the body to spark tissue growth.
"Tissue engineering is very exciting. It's unique and it's going to change the way we do medicine," says Michael J. Miller, M.D., who is currently working on tissue engineering applications for cancer patients with other members of the plastic surgery department at The University of Texas M. D. Anderson Cancer Center. Dr. Miller, associate professor in the department of plastic surgery, was one of several presenters at the annual "Advances in Tissue Engineering" continuing education short course held at Rice University in August.
"The classical approaches of replacing function with synthetic materials, such as in the case of bone where substances like titanium or ceramic are used, often work for only a limited time," says Larry V. McIntire, Ph.D., chair of the Institute of Biosciences and Bioengineering at Rice University and chair of the newly created bioengineering department. "There is a need for a true biological substitute."
According to Antonios G. Mikos, Ph.D., an associate professor of bioengineering and chemical engineering at Rice University and organizer of the annual short course, the FDA has approved three products for skin and cartilage replacement in the last year - good news for patients with such problems as burn wounds and damage to knees. While researchers continue to study and refine the areas of skin and cartilage replacement, Dr. Mikos and Dr. Miller, in collaboration with Alan W. Yasko, M.D., associate professor of orthopaedic surgical oncology at M. D. Anderson Cancer Center, have set their sights on developing bone tissue.
Bone is a complex structure, made up of a multi-cell, three-dimensional system which requires extensive blood supply. In contrast, skin is a two-dimensional cellular system, which makes it easier for vascularization to occur. Cartilage, like bone, is three-dimensional but has fewer cells to maintain, so development of a blood vessel network is not necessary, says Dr. McIntire.
Maintaining adequate blood supply to bone cells is one of the major challenges scientists face in growing bone tissue. Another problem is size. Studies have been conducted using small animals, but the same principles do not always apply to larger animals or humans, says Dr. Mikos.
"When one scales up in larger animals or humans, there are major problems such as diffusion limitations for transplant cells, or vascularization of implants," Dr. Mikos says.
"We can grow bone cells and we can grow limited amounts of bone-like tissue outside the body, but because bone requires a blood supply, the amount that can grow outside the body is very limited," says Dr. Miller. "One approach is to grow bone tissue in the body, using the body as a bioreactor to grow tissues and blood cells together." Dr. Miller and Dr. Mikos have already made advances in the area of in vivo tissue growth in a large animal by developing vascularized bone tissue on a scaffold in the rib cage of a sheep.
Though it may be several years before engineered bone tissue is available in a clinical setting, the plastic surgery team at M. D. Anderson has already begun to explore its practical applications. In the field of plastic surgery, engineered bone tissue would allow for the replacement of bone in the face, hands, and other limbs without taking the bone tissue from another part of the body.
"When Dr. Miller rebuilds a jaw bone now, frequently he has to take bone from the leg. That leaves some potential problems from the donor area," says Gregory R. D. Evans, M.D., associate professor of plastic surgery at M. D. Anderson Cancer Center, whose research involves the engineering of peripheral nerves. Dr. Evans and Dr. Mikos are currently working to develop synthetic biodegradable polymer materials for peripheral nerve regeneration.
Gregory R.D. Evans, M.D., in the Laboratory of
Reparative Biology and Bioengineering at
M. D. Anderson Cancer Center.
The plastic surgery team is also developing a program in which fat cell tissues are engineered for such applications as breast reconstruction following a mastectomy. In this procedure, plastic surgeons would remove a small amount of adipose tissue from the patient following the mastectomy and expand it ex vivo, according to Charles W. Patrick, Jr., Ph.D., research director in the department of plastic surgery at M. D. Anderson Cancer Center. The expanded tissue would then be attached to a biodegradable polymer that matches the shape of the patient's other breast and then re-implanted inside the breast envelope while being neovascularized. The fat tissue would then continue to grow while the scaffold dissolves, says Dr. Patrick, who has recently edited a book with Dr. McIntire and Dr. Mikos due out this month called Frontiers in Tissue Engineering.
"Our hope is to have a comprehensive program where we're looking at the whole spectrum of tissues," says Dr. Miller. "We could get a long way to solving problems in this field with the collaboration of the whole medical center, local academic institutions and the biotechnological industry in the region."
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