Application of Rapid Prototyping in the Medical Field

After the emergence of modern rapid prototyping technology in the late 1980s, Rapid prototyping has been used to produce prototype implants, monitoring systems, and many other medical device prototypes.

Using physiological data, using SLA, LOM, SLS, FDM and other technologies to quickly make physical models can be very useful for researchers, implant designers and surgeons who want to see the bone structure of patients without surgery help.

These techniques have been widely used in craniocerebral surgery, neurosurgery, oral surgery, plastic surgery, and head and neck surgery to help surgeons in surgical planning.

Design and manufacture implantable prostheses

Rapid prototyping has been used in implant design for a long time. Engineers can design a product quickly using CAD software, and the rapidity of Rapid Prototyping equipment allows designers to verify and modify it many times in a short period of time. Design, which saves time and cost in the design process.

Using Rapid Prototyping technology, designers can design and fabricate implants based on CT or MR data of a specific patient instead of standard anatomical and geometric data, as shown in the figure. This greatly reduces the error space of implant design, and this kind of implant suitable for each patient’s anatomical structure can indeed design a better operation paired patient anesthesia time, and can also reduce the overall operation cost.

From CT data to bone 3D model
From CT data to bone 3D model

Surgical planning

Complex surgical operations often require rehearsals on three-dimensional models to ensure the success of the operation. Rapid prototyping technology can meet this requirement. Thanks to the anatomical model, the doctor can effectively communicate with the patient. With the aid of the patient’s own anatomical model, the doctor can point out key areas, thereby increasing the patient’s understanding.

The model increases the patient’s understanding of treatment, which is much easier to understand than obscure two-dimensional X-ray photos. The model also allows the doctor to see at a glance the patient’s previous surgical experience. In addition, the model can also allow the doctor to plan surgery on the model before the operation, as shown in the figure. The time saving alone makes model making very important and necessary in many complex operations.

RP model aids in surgical planning
RP model aids in surgical planning

Jaw Bone Repair Surgery

At present, many countries attach great importance to the application of rapid prototyping in the medical field. Dental surgery, facial correction surgery, cranial surgery, jaw repair surgery, all rely on rapid prototyping technology, and achieved obvious results.

Human maxillofacial defect repair surgery based on CT technology and rapid prototyping technology is a valuable clinical application of rapid prototyping technology in the medical field. Into the patient’s head
Spiral CT scan is performed to obtain two-dimensional CT data with the smallest spacing. By setting the gray threshold of the bone, extract the bone contour in the CT image to obtain the head of the patient’s diseased area
The model is shown in the figure. The left side of the image was excised due to tumor lesions. The purpose of the operation is to repair the defect of the left mandible by cutting the leg bones from the patient. In data processing
Shi also carried out the extraction and mirroring of the right mandible, which was used to make rapid prototypes to assist the operation.

Input the above-mentioned processed data file into the rapid prototyping system for processing and production in the required format. The picture below shows the SLA model of the patient’s skull with defect, the SLA model of the patient’s calf, and the mirrored jaw SLA model of the mandible model on the left side of the patient.

CT model to SLA Model
CT model to SLA Model

production of prosthetic ear

Total auricle defect is a relatively common disease in clinical practice. The loss of the outer ear not only affects the beauty, but also the hearing. There are generally two repair methods for total ear defects: surgery and prosthetic ear. The appearance of surgically reconstructed ears is not ideal, and there are disadvantages such as high cost, high risk, long cycle, and unsatisfactory results. With the development of computer technology, the rapid development of CT image processing and three-dimensional reconstruction technology, along with the maturity of rapid prototyping technology, the combination of the two provides a new process for the production of prosthetic ears.

The prosthetic ear shape production has always had the problem of low degree of simulation. Based on the medical CT three-dimensional reconstruction technology, data processing is performed to obtain the three-dimensional model of the prosthetic ear and the injection mold, and the rapid prototyping technology is used for rapid production of the prosthetic ear injection mold. At the same time, match the color of the cast silicone rubber material, and then use the prosthetic ear injection mold made by rapid prototyping to perform vacuum injection of the prosthetic ear to obtain a prosthetic ear with satisfactory geometric shape simulation.

The process of constructing a prosthetic ear model based on spiral CT images is shown in the figure. Scan the patient’s normal side of the ear and store the CT data in DICOM format, as shown in the figure; Use special 3D reconstruction software to reconstruct the CT data of the patient’s ear, and the generated 3D model, as shown in the figure; Smooth the 3D model, and Convert the data format to the STL file format accepted by the rapid prototyping system, as shown in the figure; mirror the 3D data model of the patient’s prosthetic ear, as shown in the figure.

CT Image
CT Image
3D reconstruction
3D reconstruction
3D model
3D Model

When the 3D model of the prosthetic ear is obtained, the upper and lower molds of the prosthetic ear injection are obtained according to the requirements of vacuum injection molding process, and the sprue and mold clamping positioning head are set according to the requirements of Wang type process. The upper and lower molds of prosthetic ear injection type are shown in the figure. The picture below is a prosthetic ear mold for silicone rubber casting made by curing rapid prototyping technology.

Molds of Prosthetic Ear
Molds of Prosthetic Ear
Prosthetic ear mold made by SLA
Prosthetic Ear Mold made by SLA

The prosthetic ear injection mold made by SLA rapid prototyping technology uses medical silicone rubber materials to perform vacuum injection of the ear. However, before injection, it is necessary to avoid color matching of the silicone rubber material according to the individual skin color. The color of the implant should be able to coordinate with the facial tissue as a whole, which needs to be accurately matched with the patient’s skin color. Medical technicians perform color matching according to the patient’s skin color record according to experience.

However, the difference in the ability of the operator to distinguish colors and the color change after curing of the material has always affected the accuracy of the color of the artificial ear. The latest research is based on colorimetry, and establishes the mathematical relationship between the skin color value of the bean, the pigment ratio value, the color chroma value of the ear and the color difference. Scientific color matching method with more precise skin tone. The picture below shows the use of SLA rapid prototyping molds to obtain artificial ears through vacuum injection technology after color matching of silicone materials.

Prosthetic Ear
Prosthetic Ear

Cardiovascular model making

The cardiovascular system is composed of the heart, arteries, veins, capillaries, etc. It accurately replicates the soft tissue structures of the heart, blood vessels, hemangioma, trachea, etc., and can provide personalized soft tissue models that can be used for diagnosis, treatment, surgery, and medical education.
Science and other fields are of great significance. The figure below is the 3D structure of the left and right halves of the cardiovascular system extracted from the CT data of the heart organ.

3D Structure of Left and Right Cardiovascular
3D Structure of Left and Right Cardiovascular
Right Cardiovascular SLS Model
Right Cardiovascular SLS Model

Biological Engineering

The application of rapid prototyping technology in bioengineering has just started, but gratifying results have also been achieved. According to the specific structure of the bone, CAD modeling is carried out, and then the internal micro-structure bionic modeling technology and layered manufacturing are used. The cell carrier frame structure made by rapid prototyping technology using biodegradable materials while adding bioactive factors and seed cells to create a micro-environment at room temperature. In order to facilitate the adhesion, proliferation and function of cells, in order to achieve the parallel growth of tissue engineering bone, and accelerate the degradation of materials and the process of bone formation.
In addition, the related literature also reported the use of a method called soft lithography combining surfactants and particle templates to form functional nanostructures, and its research has reached the molecular level. In summary, the current medical applications of rapid prototyping are shown in the figure.

Medical Applications of Rapid Prototyping

Each Rapid Prototyping model for medical applications requires a special combination of prototype equipment and materials to produce the desired effect. One situation may require semi-transparent hard plastics, while another situation may require soft biocompatible materials. Sometimes sterilizing materials are needed, and sometimes they are not. For the selection of equipment and materials in Rapid Prototyping medical applications, please refer to the table below. USPVI grade materials are materials that have passed safety tests and can be sterilized. At present, there are only a few RP materials that meet this requirement. There is one type of SLA, one type of FDM, two types of SLS, and several types of LOM. The other type of material in the table is implantable materials, which are still weak. It is expected that this type of materials will grow rapidly in the future. Rapid Prototyping technologies such as 3DP and SLS have great advantages in this respect.

Selection of equipment and materials in rapid prototyping medical applications
Category USP Level VI Disinfected Translucent Be Implanted Suitable RP Method
Implant prototype Y/N Y/N N N FDM, SLA, SLS
Biological model  Y/N  Y/N Y/N N SLS, FDM, SLS, 3DP
Clinical biological model Y Y Y/N N FDM
Tissue and organ development Y Y N Y 3DP, SLA, LOM
Medical products Y Y N Y 3DP, SLS
Bone replacement Y Y N Y SLS, LOM

Anatomical models obtained from medical images have a series of requirements. Some models are best for making translucent materials, and some are best for making opaque materials to better observe the surface. In most cases, these models are used before surgery, and under certain circumstances, the models need to be sterilized for reference during surgery. With the development of knowledge of biomaterials, the clinical applications of rapid prototyping products in the medical field will continue to grow, ranging from bone regeneration implants to organ replacements, with a wide range of applications.
The artificial bone production currently under study is a very promising application field of RP technology. There are currently two methods for manufacturing bone implants. One method is to use a process of selective deposition of calcium phosphate powder to make porous implants. Animal experiments show that these porous implants have excellent performance in terms of new bone growth performance. After a certain period of time, these porous implants will become part of the animal skeleton. When the relative density of these porous implants is 50%, the strength is reduced to 70MPa. Therefore, their use is limited to non-carrying parts, such as the face and skull. The second process is to prepare a carbon mold with SLS, and the molten calcium phosphate is poured into the mold at a melting temperature of H00°C. The full-density glassy part obtained in this way can be annealed to obtain a semi-crystalline composite with a compressive strength of more than 170 MPa. These can be used to carry implants such as teeth, bone screws and vertebrae.

Customized bone implant

There are 206 bones in the human body, and the size and shape of these bones vary from person to person. In reconstruction and plastic surgery, it is very useful if the patient can economically customize the bone implant through the medical CT scan. If possible, a CT scan of the injured part before the accident is required, or a mirror image of the uninjured bone on the other side of the body should be used. The implant customized according to the actual size can reduce the process of medical cultivation steps and reduce the risk of the patient. The use of rapid prototyping technology to make bone implants generally uses a polymer material system of a glass phase powder mixture of hydroxyapatite (HA) and phosphate. This material is biocompatible with the human body and can be made into a LOM process The thin layer of material. The process of using the LOM process to make hydroxyapatite custom bone implants is shown in the figure.

This composite system includes hydroxyl particles and a glass phase of calcium phosphate, as shown in the figure. The glass phase calcium phosphate is used as a binder. When sintered, the glass phase melts and fuse the hydroxyapatite together. The proper proportion of glass additives enables the HA sintering process to be performed at a lower temperature (equal to or slightly higher than the melting temperature of the glass), thereby reducing the tendency of HA to lose hydroxyl groups and decompose. In addition, the shrinkage rate after sintering is also significantly lower than that of pure solid sintering.

Production of PCL porous scaffold

The repair and reconstruction of complex joints such as jaw joints poses a great challenge to bone tissue engineering. The malignant reaction of the patient’s body to allogeneic and non-biological materials greatly compromises the results of the treatment.
Bone grafting in other parts of the patient will cause complications in other parts of the patient. To this end, the stent must be consistent with anatomical defects, have mechanical properties that can withstand living body loads, strengthen tissue growth, and produce biocompatible degradation products.

PCL is a biodissolvable polymer with potential application value in bone and cartilage repair. PCL stents can be made by a variety of rapid prototyping technologies, including fused deposition technology, light curing molding technology, precision
Extrusion deposition, three-dimensional printing, etc., and the use of SLS technology to produce PCL scaffolds with a variety of internal structures and porosities can be easily achieved.

Figure a shows the cylindrical porous scaffold (diameter 12.7mm, height 25.4mm) designed on the UG three-dimensional modeling software. Figure b shows the SLS scaffold model made with PCL powder on the Sinterstation2000TM equipment.

Porous Scaffold STL Model
Porous Scaffold STL Model
SLS PCL Scaffold Model
SLS PCL Scaffold Model
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