desired to simulate the tendency of the device to penetrate the artery then penetration resistance or shear strength of the shell (a related mechanical property) would be included in the list as well. Any number of properties may be added to this list. However, as the number of modeled properties grows it becomes progressively more difficult to simultaneously satisfy all of the design requirements. In fact, if a particular tissue or organ must mimic more than three mechanical properties it will typically be necessary to employ multiple analogs to meet design requirements.
The data source which will form the design basis for the new tissue analogs must also be defined. First of all, it must be decided if the analogs will be formulated to mimic the properties of human tissues or animal tissues (either living or dead). Once this question is answered, the relevant data may either be drawn from the literature or generated directly by performing the appropriate tests on tissue samples. However, it should be noted that vastly superior results will always be achieved by performing the relevant tests directly. The results of mechanical-physical tests are highly dependent on test conditions, and controlling the test gives the designer control over such conditions. More importantly however, it allows the candidate tissue analogs to be tested and subsequently validated under exactly the same conditions as the target tissue.
Model and Tissue Design
SynDaver™ and SynTissue™ brand products are designed to mimic specific human tissues and organs. The chemical, physical, mechanical, electrical, and optical properties these tissues mimic are based on data derived from testing LIVING human and non-human animal tissues. For the past decade we have performed relevant tests on live human lumenal (mouth, anus, vagina, etc) and skin tissues as well as living internal tissue from porcine models. The inclusion of porcine data in this data set is justified by the similarity between human and porcine tissues on the most basic level. For example, heart valves, arteries, fascia, and brain matter are similar in structure and function whether they are sourced from a human or porcine model, and this similarity is underscored by the established practice of porcine tissue transplantation into humans.
The drawbacks to using live animal data in this application are limited. The alternative (using live human tissue on a large scale) is not feasible for a number of reasons. First of all, the logistical and regulatory issues associated with testing live human tissues make collecting that type of data extremely difficult. While living human tissues are difficult to obtain in small quantities, they are impossible to obtain in statistically useful quantities, and there are very high regulatory hurdles that must be overcome in order to gain access to even a single live human subject. In addition, since the properties of any living tissue generally begin to change immediately after death, any samples harvested would need to be tested at the patient's death bed to minimize the lapse between harvest and data collection. This would would be impractical and prohibitively expensive given the high volume of testing required.
Of course, a great deal of information on the physical properties of human cadaveric tissue is available in the literature, and this data is one potential source for the design of tissue analogs. However, we do not use this type of data as design criteria unless specifically requested to do so by a client. First of all, the properties of living and dead tissues are different, with the discrepancy increasing with time elapsed after death and even more so after freezing or chemical preservation. In addition, employing data from literature would preclude control of tissue harvest, sample preparation, test design, and test method. This in turn would prevent validation of the resulting
