Feature

Plastic Brains

First take one brain...

Peter Cook

Hi-tech plastics are taking over from formaldehyde-filled jars in the anatomy labs of Auckland's School of Medicine, providing perfectly preserved specimens for the teaching of gross anatomy.

An understanding of the structure of the human body is the very foundation of medicine. No amount of lectures, textbooks or computers can replace the actual examination of the human body. Traditional methods of teaching anatomy involve using embalmed, bequeathed cadavers for dissection and specially prosected, preserved specimens immersed in formaldehyde-filled glass jars.

The process of plastination of human tissue provides a valuable method of maintaining the specimens in an odourless, dry form indefinitely. Plastination is a technique developed in Germany in 1982 by Dr Gunther von Hagens at Heidelberg University, and it allows any perishable biological tissue to be permanently preserved in a lifelike state.

First the specimen is saturated in a dehydration medium such as acetone or ethanol and then immersed in any one of a number of reactive polymers inside a special reinforced chamber where a vacuum is gradually applied. This causes the solvent to be drawn out of the specimen in a gaseous form and replaced by the polymer. The vacuum process may take anything from 24 hours to four weeks to complete, depending on the size and weight of the specimen.

Following the forced impregnation vacuum process, the specimen is cured either by gas vapour, heat or UVA light depending on the class of reactive polymer used for impregnation. The finished plastinated specimen is dry, odourless, durable and safe to handle without gloves.

Thus plastination is not a mere coating or encapsulation of a specimen with resin -- it is the complete infiltration down to the cellular level creating a finished product with all moisture replaced by a selected resin. Most importantly, shrinkage is virtually nonexistent, and (unlike specimens in jars of preservative liquid) no distortion or magnification of structures occurs. When carried out slowly and carefully there is no distinguishable difference between the wet, embalmed tissue and the fully cured plastinated end product.

New Applications

Since the technique was first introduced in the Anatomy Department in 1984, the basic method has developed to correlate with a number of exciting new fields in clinical medicine.

Serially sectioned cadavers have been prepared in this way to assist in understanding the modern clinical radiographic diagnostic tools such as CT (computed tomography), MRI (magnetic resonance imaging) and ultrasound.

A most successful example of this technology produced in the Department of Anatomy is 25 serially sectioned specimens of the human head, cut in the coronal or frontal plane which relates directly to MRI imaging planes.

Ready-Sliced Frozen Brains

Through the application of the method known as sheet plastination, a cadaver or a specific section is deep frozen to -80C and carefully cut into very thin transparent 2.5-mm slices which correspond exactly with radiographic images. The sliced, frozen sections are then placed in fibreglass mesh grids and quickly immersed in -25C acetone for dehydration. After two or three changes of acetone, the residual water within the specimen is determined with a calibrated acetonometer to establish complete dehydration.

A crucial stage in the success of producing clear, finely detailed slices is the extraction of fatty lipids from the tissue, using methylene chloride as the "degreasing" medium.

Following degreasing, the thin sections are carefully immersed in the bath of reactive polymer specifically designed for this aspect of plastination (an epoxy resin). The solvent-saturated specimens are vacuum impregnated for up to 48 hours, at which time a vacuum pressure of one atmosphere is reached. This ensures total extraction of all solvent, and the resulting volume deficit is filled with the reactive polymer. Once the tissue sections are fully impregnated with resin, the next, and most potentially difficult, step is to encapsulate the thin, resin-impregnated sections within a crystal clear mould.

Each individual slice is sandwiched between two sheets of tempered glass which is then sealed around three of the four outer edges to create a flat, narrow filling chamber for the resin to be poured into, thus filling the glass chamber. The resin-filled chamber is cured by low heat for around seven days and finally the glass chamber is disassembled and the smooth, clear cured resin plate containing the specimen is removed.

The visual qualities of the completed specimen are quite spectacular. Detail such as nerves, blood vessels, bone marrow and even individual muscle fibres can be identified with the naked eye. Over 150 such specimens have already been produced and are displayed in the department, along with annotations. Tissue sections can be taken in any plane to illustrate certain crucial features of anatomical relationships.

Transparent body slices offer an insight into the intricate structure of the human body not clearly identifiable on traditionally dissected cadavers. They also offer the student of anatomy a vivid and comprehensive basis for understanding the modern clinical diagnostic imaging methods later to be encountered in their medical training. Perhaps, most importantly, these specimens are long lasting and virtually indestructible.

The applications of plastination to anatomy, pathology, zoology, structural biology and botany are almost limitless and offer an exciting addition to the resources available to students of medicine, health-related sciences and biological sciences.

Peter Cook is a senior technician in the Department of Anatomy at Auckland University's School of Medicine.