Research Tools

A Review:Additive fabrication technologies applied to medicine and health careJ. Giannatsis & V. Dedoussis

International Journal of Advanced Manufacturing Technology (2009) Vol. 40- pages 116127Contents:Introduction.Fabrication of RP models based on medical data.RP biomodels for surgical planning.Tools for intra-operation guidance and testing.Patient-specific implants.

2Contents:Tissue and organism manufacturing engineering.Drug delivery and microscale devices.Discussion and concluding remarks.

31. Introduction

Additive fabrication (AF) and rapid prototyping (RP) technologies are mostly associated with applications in the product development and the design process as well as with small batch manufacturing. 1. IntroductionWhat makes RP particularly appealing for all applications is the fact that compared to alternative manufacturing technologies, like CNC machining, RP systems can fabricate parts of almost any geometrical complexity in relatively lower time and with reduced cost and without high technical expertise.1. IntroductionRP technologies are even more appealing for medical applications as they utilize medical imaging data (obtained by techniques like computed tomography - CT or magnetic resonance imaging - MRI), almost directly, for the production of customized patient specific parts.Medical applications of RP technologies:Biomodelling, which is the fabrication of physical models of parts of the human anatomy for surgery planning or testing.Design and fabrication of customized implants for prosthetic operations, and plastic surgery.Fabrication of porous implants (scaffolds) and tissue engineering.Fabrication of specific surgical aids and tools.Drug delivery and micron-scale medical devices .

1. Introduction RP technologies have not yet been widely adopted in the medical and health-care sectors because of:

High cost and time required for the fabrication of corresponding models. The accuracy of RP systems, which is not sufficient for some applications, due mainly to poor or inaccurate medical imaging data.Materials and their properties, i.e., flexibility, strength and biocompatibility.1. IntroductionFirst, obtain the data of the patients area of interest with the use of (CT, MRI, etc.), which provides a representation of the patients anatomy through a series of 2D images.The images are next manipulated using special software, which converts the 2D image information to a 3D representation. Finally, the biomodel is fabricated via an RP system.

2. Fabrication of RP models based on medical dataChoi et al. analyzed the possible sources of error in biomodeling and identified the main sources of error in the translation of 2D data to a 3D virtual model. This has led to the development of special software tools like Mimics from Materialise Inc. and Biobuild that have simplified and enhanced the accuracy of the 2D- 3D data transformation process. 2. Fabrication of RP models based on medical data3. RP biomodels for surgical planningSince every patient is unique, the surgeon must fully understand the anatomy of the patient before operation. In complex surgical operations, RP biomodels facilitate diagnosis and treatment planning, and decrease the risk of the surgery. Furthermore, the study of a biomodel allows a detailed evaluation of the operation, without the time pressure present during actual operation, and also possible problem prediction. 3. RP biomodels for surgical planningMuller et al. investigated the usefulness of RP models of the skull in craniofacial and neurosurgical practice. RP biomodels of 52 patients, whose treatment required corrective/reconstructive cranioplasty were fabricated. They report that SL models help increase operation accuracy, support accurate fabrication of implants, facilitate pre-surgical simulation and improve education of trainees.4. Tools for intra-operation guidance and testingDUrso et al. investigated the possibility of using accurate SL biomodels of the patient neurosurgical stereotactic surgery. The method of stereotaxy is a minimally invasive form of surgical intervention which uses 3D coordinates in order to locate specific targets and perform on them an operation like removal, implantation or injection. 4. Tools for intra-operation guidance and testingThe location of the target is based on MRI/CT data and is determined with respect to a reference frame that is attached to the patients body. They report that biomodel-guided stereotaxy is advantageous in terms of speed, simplicity, accuracy, and versatility but with the extra cost and time required for biomodel fabrication.4. Tools for intra-operation guidance and testingStarly et al. used the SL model as a medium for the transfer of the anticipated skull geometry in a surgical guidance system. In this approach, the 3D virtual model of the patients skull is constructed first using CT data. The virtual model is then split in two parts, the undamaged half and the defective half that contains the trauma.Next, the defective part is discarded and replaced by the mirror image of the other half. 4. Tools for intra-operation guidance and testingSLS have been employed for the construction of protective patient-specific shielding masks that may be used as protective shields during cancer treatment. The fabrication procedure proposed by De Beer et al. comprises of three phases:First the face geometry for the mask is captured by 3D photography.5. Patient-specific implantsTruscott et al. used SLS models in the design process of customized titanium elbow implants which greatly improved the accuracy and reduced the cost of the implant design process.Winder et al. present ten clinical cases in which the required titanium implants for the reconstruction of skull defects were created using RP models as masters for casting.They report reduced operating time and excellent results at a reasonable cost.5. Patient-specific implantsBens et al. developed a flexible (meth) acrylate based resin for SL that could be useful in various biomedical applications.Hunt et al. employed SLS for the fabrication of moulds for the production of wax investment casting patterns. According to their findings, the bone growth in implants fabricated this way is less than in porous implants directly fabricated with SLS.6. Tissue and organism manufacturing engineeringRP technologies are also ideal for the fabrication of implants with special geometry, like scaffolds for the restoration of tissues.Scaffolds are porous supporting structures that are used as a vessel for the transplantation of tissue cells into the body of the patient. They serve as the platform for the guided growth of new tissue in damaged or defective bones or even organs of the human body.6. Tissue and organism manufacturing engineeringChen et al. presented a case where an SL mould of the intended scaffold geometry was used to cast an artificial bone through injection of calcium phosphate cement (CPC), which is a non-toxic soluble material and bone morphogenic protein. Tests performed on animals showed that the artificial bone scaffold accelerated the growth of the actual bone.6. Tissue and organism manufacturing engineering3D scaffold modeling is a tradeoff design process (porosity versus structural strength) that requires considerable time and effort employing standard mechanical design software. Chua et al. suggested utilizing libraries of application-specific polyhedral shapes that are used as constructing elements of the scaffolds. 6. Tissue and organism manufacturing engineeringYan et al. proposed a new process called (low-temperature deposition manufacturing LDM) employs the layer manufacturing principle and an extrusion-type system for the construction of composite scaffolds.Compared to established AF methods, the LDM process is reported to preserve bio-activities of scaffold materials because of its non-heating liquefying processing of materials.7. Drug delivery and microscale devicesRP technologies are expected to prove very useful in the fabrication of customized micro-systems and devices for controlled drug delivery. Such devices involve complex micron-scale networks of fluidic and electronic components capable of operating in an integrated manner.8. Discussion and concluding remarksThe review of the international specialized literature showed that custom biomodels fabricated with RP technologies are quite useful for planning and the rehearsal of complex surgical operations.Among the RP technologies applied to medicine, SL seems to have attracted the attention of most researchers.8. Discussion and concluding remarksSL is not only relatively more accurate but also SL resins provide the advantage of biomodel transparency that can be quite useful in surgery rehearsal.However, they are not biocompatible and require special handling; a fact that makes adoption of SL systems in the hospital environment difficult.The accuracy and the low surface roughness of SL biomodels makes them ideal as casting patterns for the fabrication of custom implants.8. Discussion and concluding remarksFabrication of custom-made scaffolds is another application in which RP can be quite useful. Two approaches have been identified:Direct Methods they employ a RP system for the fabrication of the actual scaffold itself.Indirect Methods they employ RP for the fabrication of the tool (pattern or mould) that will be used for the production of the actual scaffold.8. Discussion and concluding remarksMicro- and nano- AF technologies are expected to make possible the fabrication of controllable drug-delivery units or implants in the micron or the submicron level. Fabrication of artificial organ substitutes is a very interesting area of research, that enables controlled assembly of living cells and supporting material in order to construct the organ substitute.