The Role of Three-dimensional Printed Models in Women's Health

Three-dimensional (3D) printing—also known as additive manufacturing—has emerged as a revolutionary technology that has received attention over recent years. In general, it is a process in which materials are deposited meticulously in a layer-by-layer fashion by a specialized printer to produce a 3D object from an original 3D digital image. 1 , 2 In the medical field, the 3D digital image can be obtained from the patient’s 3D ultrasound images, magnetic resonance imaging (MRI), and computerized tomography (CT) scans. This process allows the printing of detailed anatomical structures of body organs into an identical 3D model. 3 The 3D printing technology has been widely applied in various biomedical fields ( Figure 1 ). 4 Several medical specialties utilize 3D printing technologies, in particular neurosurgery, cardiology, orthopedics, and pediatric surgery. 5 – 7 Recently, 3D printing technology has been also utilized to provide novel solutions for several medico-technological challenges during the COVID-19 pandemic. 8 The applications of 3D printing technology in the medical field: Educational; Presurgical planning; and Implants and Prosthetics. Source: Educational, adapted from Bartellas et al. 9 (CC-BY 3.0). Presurgical planning, adapted from Flaxman et al. 1 (CC-BY 4.0). Implants and Prosthetics, adapted from Xia et al. 10 (CC-BY). The ability of the 3D printing technology to provide patient-tailored anatomical models with such a degree of feasibility can be of significant clinical impact. 11 , 12 For example, improving patients’ understanding of their body anatomy in both health and disease can provide a powerful tool in health education. Likewise, access of health professionals to such models is seen as a novel tool to enhance patient counseling and enforce patients in their decision-making process and their ability to give well-informed consent about their treatment options. 13 , 14 Relative to the traditional manufacturing methods of anatomical models, 3D printing technology offers multiple advantages such as accessibility, cost-effectiveness, rapid production, diversity of model material, and increasing feasibility. 15 While 3D printing technology has made significant progress in several medical specialties, its application in the field of obstetrics and gynecology (OBGYN) is relatively limited. 16 The factors behind this limitation are not well understood from the current evidence; however, we believe this might be due to the fact that OBGYN has not received the same level of attention in terms of 3D printing research and development, leading to fewer established applications. The sensitive nature of gynecologic disorders and the vulnerability of pregnant women may contribute to such research limitations. 17 Furthermore, although MRI scans could potentially be a useful add-on diagnostic method, ultrasound remains the imaging modality of choice in the OBGYN field. 18 Hence we believe this could be another reason for the lack of use of 3D printed models in OBGYN, as an ultrasound alone does not suffice for use in 3D printing and may have artifacts, and an MRI would only be obtained if the result of the ultrasound is inconclusive. 18 In the field of OBGYN, this technology remains uncommon and minimally utilized in comparison to other medical specialties. This is due to the complexity of dynamic structures such as the uterus, ovaries, fallopian tubes, and placenta, which undergo significant changes during pregnancy and menstrual cycles. In addition, the variability in patient anatomy poses challenges in creating standardized models. Furthermore, while ultrasound plays a crucial role in obstetrics, its two-dimensional (2D) images lack the necessary depth and spatial data for accurate 3D printing. In this review, we provide an overview of 3D printing applications in the medical field highlighting the current applications in obstetrics and gynecology, including therapeutics, patient counseling, and educational training. We also discuss the limitations and the potential future applications of 3D printing technology in the field of women’s health.

The use of 3D printing technology in the medical field, including OBGYN, presents both challenges and opportunities for improvement. For a clinician, creating a customized 3D model for a patient could be inconvenient as it requires the expertise of highly skilled technicians and specific software for the conversion process from radiological images to 3D printable formats. 4 , 92 We believe this can potentially be simplified through the development of user-friendly software and tools, reducing the reliance on skilled technicians, and streamlining the workflow for clinicians. Moreover, the choices of soft materials that can be used to closely represent human tissues are quite limited and require specific printer resolutions. These are particularly needed to meet the required dynamic nature of the designed models representing the female pelvic organs such as during the stages of pregnancy or genital prolapse. In addition, 3D printed models used in training and educating medical professionals are usually white, when in fact real human organs are multi-colored. Hence, the color of the materials plays an equal role alongside texture. 4 Therefore, new materials that closely mimic human tissues should be explored and developed, to improve the realism of 3D printed models. The investment in high-quality printers and materials comes at a cost; however, as this technology advances, the cost of the machines decreases 15 as there are emerging companies that provide this service on demand which is expected to significantly reduce this cost. 93 , 94

3D printing is also known as additive manufacturing, where successive layers of materials are printed on top of each other, in contrast to removing material through traditional methods such as milling. 19 It is a process to create 3D objects from digital files. Several methods can be used to create digital files, such as 3D modeling and 3D scanning. For patient-oriented 3D-printing applications, creating an accurate medical model is a crucial step. The initial model is created using a Digital Imaging and Communications in Medicine (DICOM) file from a radiological image. 20 Segmentation is then utilized to separate the required anatomical structure and avoid unwanted overlapping during the 3D printing process. It is a must to segment to extract the points used to create a contour of the structure to be printed. 21 The model is refined using 3D modeling software to remove unwanted details and reduce noise. This process ensures that the model can be printed correctly. The digital file is then exported as a stereolithography (STL) object (or any other compatible file format for 3D printing); this format describes only the surface geometry of a 3D object without representing color, texture, or other common model attributes. 22 The STL file is then uploaded to the 3D printer slicer, where the slicer converts the digital model to a set of G-code commands, which are then uploaded to the 3D printer and are used to control the various function of the 3D printer. 23 After printing the required object, the model is sanded using various grits of sandpaper to ensure a smooth finish. The model is then sprayed with several layers of primer and painted to achieve a durable and uniform finish 22 , 24 ( Figure 2 ). General overview of 3D printing workflow with segmentation of MRI using images of a multi-fibroid uterus as an example. Source: Adapted from Flaxman et al 1 (CC-BY 4.0). Several types of 3D printing techniques are available; Alexander et al. have reviewed the most updated ISO/ASTM guidelines for terminology used to describe 3D printing in biomedical applications. Several types of 3D printing technologies have been adopted in the medical field. The six most common types implemented by the ISO/ASTM standard for medical applications are discussed below and summarized in Table 1 . 53 An overview of the 3D printing technologies currently used in the medical field. 25 – 28 UV: ultraviolet; PPE: personal protective equipment. Binder jetting is a 3D printing technique that first lays a thin layer of powdered material across a build platform. Then, a liquid binding agent or glue is deposited in specific locations using a printhead. Once the binder contacts the powdered material, it fuses the various layers to create the required object. 54 Similar technology to binder jetting is material jetting, which deposits a photopolymer material stored in air-excluding tanks instead of the binding agent; the photopolymer is then cured using ultraviolet (UV) light to harden the photopolymer. 55 Moreover, material extrusion (ME) is an affordable additive manufacturing technique relative to the other available technologies. Furthermore, ME is known for rapidly producing prototypes by dispensing material from a filament spool through a nozzle or orifice. The nozzle melts the filament before dispensing it at the specified location, where it cools and bonds with the filament from the layer below. 56 Powder bed fusion (PBF) utilizes a heat source, typically a laser, to fuse powdered particles in precise locations either by total melting, which results in selective laser melting (SLM), or partial melting, which results in selective laser sintering (SLS). 57 Sheet lamination is another 3D printing technology that utilizes sheets of material, which are layered on top of each other and bonded together using an adhesive. The sheets are then cut into the required shape using a carbon dioxide laser or a computer numerical control (CNC) machine. 58 Finally, vat photopolymerization uses a vat filled with a liquid photopolymer resin; the resin is then cured on a build plate using a screen that partially blocks a UV light, causing the exposed resin layer to harden. After the first layer is cured, the build plate is lowered, and a new layer of liquid resin covers the cured layer. The above process is repeated until the entire object is created. 59 Other methods of 3D printing include laser scanning and photogrammetry. Laser scanning involves using a laser scanner to capture the shape and contour of an object with high precision to generate 3D models for different medical applications. Photogrammetry relies on capturing multiple images of an object from different angles, followed by using specialized software to analyze the images and construct a 3D model for printing. After printing the required object, the model is sanded using various grits of sandpaper to ensure a smooth finish. The model is then sprayed with several layers of primer and painted to achieve a durable and uniform finish. 24 Table 2 summarizes the most common materials used in the various 3D printing technologies and their properties. 21 Most common materials used in the various 3D printing technologies and their properties.

The integration of 3D printing in the field of OBGYN presents unique opportunities to revolutionize the field. Although 3D printing has been used extensively in various medical specialties, its utilization in the OBGYN field remains limited due to certain challenges. By overcoming limitations such as converting radiological images, improving the precision of 3D models, expanding the range of materials, and decreasing their cost, 3D printing can then further contribute to the advancements in this field. Hence, by actively working toward optimizing the 3D printing technology from various aspects, it can help improve patient outcomes, educate medical professionals, optimize treatment strategies, and altogether reinforce innovative healthcare practices in the OBGYN field.

Since it is not a systematic review, this article does not cover all the published literature relevant to the topic. As is the nature of any narrative review, selection bias is a possibility.

The use of 3D printing technology has been recently introduced in OBGYN for patient management and professional training purposes. In the following sections, we review the reported utilization of 3D printing models in the field of OBGYN in pre-operative surgical planning, drug delivery and implants, training purposes, and patient counseling. In the fetomaternal specialty, the use of 3D printed models together with prenatal ultrasound reduced the misdiagnosis of fetal abnormalities from 5% to 0.4%. 74 It has also been used in the training of OBGYN residents in simulation settings, 9 including practicing communication in sensitive situations such as examining patients of sexual assault. 75 Moreover, a 3D printed model was generated using ultrasound images of a fetus with meningomyelocele in preparation for intrauterine surgical intervention. The model provided an excellent opportunity for the surgical team to practice the surgical repair of meningomyelocele beforehand. 76 Using 3D printed technology for the pre-planning of complex OBGYN surgeries for uterine abnormalities is found to be a useful complementary tool in conventional 2D imaging. 77 It has been applied in surgeries for uterine fibroids, including myomectomies and hysterectomies ( Figure 5 ). 1 , 78 , 79 In addition, 3D-printed models of the gravid uterus with multiple uterine fibroids provided precise identification of the myoma’s location to plan a safe cesarean section incision. 80 Sagittal plane views of 3D digital fibrosed uterus model (top-left) and 3D printed model (top-right). The model was printed in two pieces (bottom), with the mid-sagittal plane as the dissecting line. Fibroids were printed in translucent red, endometrium in opaque blue, and non-neoplastic myometrium and cervical tissue in clear material. Magnets (gray dots) are used to hold the two pieces together. Source: Adapted from Flaxman et al 1 (CC-BY 4.0). Surgical management of advanced endometriosis is often challenging and carries the risk of multiple complications. 1 , 81 One case report has demonstrated the value of using 3D printing in patients with severe endometriosis. A 3D pelvic model was generated from the patient’s pre-operative MRI, which was then compared with the intraoperative findings. The authors reported the accuracy of the model in visualizing the anatomy, location, and extent of the infiltrative endometriotic nodules and endorsed the value of using 3D-printed personalized models to enhance the safety and success of surgery for patients with deep infiltrative endometriosis. 82 , 83 In the management of gynecologic tumors, a 3D- printed stent loaded with localized cytotoxic drugs (cisplatin-polymer compound stent) was used in mice models of ovarian cancer. Such a promising strategy can reduce the systemic side effects compared with the use of systemic cytotoxic drugs. 84 Likewise, 3D-printed hormone-eluted constructs were developed to provide personalized biodegradable implants for indicated hormonal therapies. 85 In uterine and cervical cancer, brachytherapy can be suboptimal in large tumors with extensive paravaginal or parametrial involvement. Laan et al. developed patient-tailored 3D-printed applicators based on MR images. This strategy could improve the target coverage and lead to an effective brachytherapy procedure with fewer side effects, and better quality of life post-treatment. 86 The use of a synthetic mesh in the surgical management of pelvic organ prolapse (POP) has been recently restricted or banned in several countries due to long-term postoperative complications. This has necessitated the need for a new class of mesh-based repair that is safe and effective. Paul et al. discussed the potential of the 3D printing technology to improve the outcome of POP surgeries by producing a patient-personalized mesh that allows control over the pore size, geometry, and interconnectivity of the designed mesh. In addition, they presented the possibility of applying the technology of 3D bioprinting in producing a safer and more biocompatible mesh with less risk of foreign body response. In bioprinting, natural compounds (polysaccharides and synthetic polymers) are integrated with cells to produce an extracellular-like material that supports the growth of cells and their functionality. 87 – 89 A study of patient education incorporated the use of personalized 3D-printed models of endometrial cancer to educate patients about their illnesses. Based on the feedback, patients expressed higher satisfaction with the 3D models during the explanation by the surgeons in comparison to only using the 2D MRI images. Patients reported an excellent understanding of their disease, surgical procedures, and risk of complications. In addition, when used in presurgical planning, surgeons indicated better experience with pre-operative patient counseling and understanding of the positional relationship between the tumor and the uterus. 79 3D models of cleft lip and palate were used for patient education. A study by Chou et al. used 3D-printed models from normal and abnormal anatomy CT scans. The models were used to educate expecting parents with a prenatal diagnosis of cleft lip and palate. There was a high level of parent satisfaction in terms of understanding the condition and the proposed corrective surgery. 90 , 91 One study demonstrated the application of 3D-printed cervical cancer models for OBGYN residents’ training purposes ( Figure 6(a) ). This study aimed to create a low-cost model that looks and feels realistic ( Figure 6(b) ). The cervical neoplasm was adjusted to induce bleeding from the cervical os and the mass itself. It was presented to a group of OBGYN residents during a hybrid simulation session. They were tasked with taking a medical history and performing a physical examination on a printed model. During the pelvic examination, the residents successfully visualized the abnormality and observed the bleeding using a speculum. They also attempted to suture the bleeding sites. The majority of the residents reported a positive learning experience. However, there were suggestions for future improvement to enhance the realism and accuracy of the cervical model. These suggestions included securely fixing the cervix to the pelvic model for more stable and comfortable usage, as well as using various colors to simulate a more realistic experience. 9 (a) 3D design of the cervical model: normal (left), with tumor (right). (b) Final printed cervical model with tumor (top), and cervical models with different presentations of cervical cancer (bottom). Source: (a) and (b) are adapted from Bartellas et al. 9 (CC-BY 3.0).