It was recognized quite early that rapid prototyping could bring great improvements to the fields of prosthetics and implantation. Previously, hip replacements and other similar surgeries were carried out using standard sized replacement parts selected from a range provided by manufacturers based on anthropomorphic data. This works satisfactorily for some types of procedures, but not all, and not all cases of any given procedure. There are always patients outside the standard range, between sizes, or with special requirements caused by disease or genetics. Rapid prototyping makes it possible to manufacture a custom prosthesis that precisely fits a patient at reasonable cost.

Fortuitously, rapid prototyping and computed tomography (CT) measurement techniques, using X-rays or NMRI, are both layer-based methodologies. This enables relatively straightforward transfer of measurement data generated using these imaging methods to be used as input data for a rapid prototyping system. Much work has been done over the years to improve the interpretation, translation and accuracy of the CT measurement data, and to study the accuracy of the models generated by it from rapid prototyping systems. There are now routine methodologies for many medical procedures.

No single rapid prototyping technology is dominant in medical applications. Many of the technologies have been applied over a large range of prosthetic and implant applications. There are specific procedures which have achieved a significant level of maturity, however. One well-developed example is the case of a hip replacement, mentioned above. In this application, CT scan data from the patient, is combined with engineering data such as standard geometries to connect to the bone, and quickly turned into a plastic model of an optimally fitting joint implant for a patient. The fused deposition modeling process is frequently used as the rapid prototyping technology component. The plastic model is then used as a casting pattern to manufacture a custom titanium implant.

An interesting example of an external prosthetic device is the fabrication of a missing ear for a patient. The remaining ear is scanned in three dimensions and the resultant data is mirror-imaged to create the data for the missing organ. The molding pattern for the missing ear is then generated by a rapid prototyping system and the final object is molded in flesh-like polymer from the pattern.

These are but sparse examples drawn from a range of applications that span nearly every facet of human anatomy.

Rapid prototyping is being used by surgeons to plan and explain complex operations, especially craniofacial and maxillofacial surgeries. As with any manual art requiring great precision and dexterity, much of the knowledge resides in the surgeon's hands. There's no substitute for practicing on a precise model to educate the hands and determine the course of progress of a complicated operation. Models are frequently present in the operating room where they are used as templates and guides. Stereolithography is often the rapid prototyping method of choice for such applications. The transparency of the model and recent developments in color resins allow distinct visualization of tumors or other anomalies within the surrounding tissue or bone. Cost is a factor and rapid prototyping has been used in the past instead of CNC modeling techniques only when there is an advantage that justifies the extra expense. However, the advent of lower-cost RP systems and full color capability in recent years, as well as more awareness in the medical community is likely to lead to greatly increased usage for such models.

Surgeons aren't the only people interested in bones. Anthropologists, paleontologists and forensic specialists are, too. RP and the related technologies have enabled these scientists to put a recognizable face on skeletons, share precise replicas of rare finds and build museum exhibits.

The direct manufacture of biologically active implants is also being investigated, especially bone that might be missing or otherwise malformed due to disease. These applications, often using selective laser sintering of ceramics as the rapid prototyping component, can be expected to yield results over the next few years.

More exciting yet is carrying this process to its logical conclusion. There's a good possibility that any organ, no matter how complex, may be generated using additive fabrication technology. Early experiments have been carried out that are quite encouraging and the nascent field of tissue engineering is moving ahead rapidly. Stem cells are undifferentiated progenitor cells from which an organ develops into its fully functional and complex maturity. While the processes are as yet far from completely understood, stem cells may be able to express all the necessary proteins to create a complex organ such as a heart or a liver if they are held in the correct geometric structure. Such structures, called scaffolds, can be created in a variety of ways using rapid prototyping. The engineering problems associated with generating scaffolds concern fine resolution and materials. The stem cells must be held in close proximity in a controlled geometric relationship, and the materials of the scaffold must "melt away" or metabolize in some way as the organ develops.

The geometric requirements are at the performance limit of today's rapid prototyping systems. However, special purpose systems could likely be built using existing technology to meet these requirements. The existing chemistry holds a lot of promise, as well. Some possibilities are offered by biodegradable polymers such as polylactic acid and the caprolactones. These materials are used at present for dissolvable sutures and their chemistry is well understood. However, such materials might require the development of specialized rapid prototyping processes before they can be utilized in a way that meets the geometric requirements. There are also some interesting biodegradable photopolymers under investigation that might be used in a specialized stereolithography process which might provide a more direct development path.

Rapid prototyping is one of the primary means by which computational advances will become physically melded with humanity. The prospect for greatly improved health and the conquest of mortality are visible on a distant horizon.