Key points
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Point-of-care (POC) manufacturing is the just-in-time creation of anatomic models, surgical instruments, prosthetics, scaffolds, and other three-dimensional printed applications either at the place of patient care, such as a hospital, or in a centralized facility owned by the health care organization based on the patient’s medical imaging data.
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POC manufacturing provides a cost-effective use of the available computer-aided design/computer-assisted manufacturing technologies for patient care or education.
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The type of POC manufacturing program depends on the local needs.
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A high level of personnel competence and internal quality control programs is important to maintain patient safety.
Introduction
A successful outcome in craniomaxillofacial surgery and reconstruction entails formulation of a plan centered, among other factors, on disease biology, an understanding of the complex anatomy and close proximity of vital structures in the region, the type and extent of the anticipated defect, and a treatment outcome that achieves functional and esthetic results. Virtual surgical planning (VSP) and three-dimensional (3D) printing have been transformative in craniomaxillofacial surgery where preoperative planning and the fabrication of patient-specific cutting guides and implants have led to a more accurate and efficient reconstruction of geometrically complex anatomic defects with a decrease in intraoperative decision making and reduction of surgery time. The exponential utility of 3D printing with its ability to create different product designs without the need for process modification and its capability of creating complex anatomic models and devices have led to its widespread use in patient care, patient education, and surgical training. ,
3D printing, also known as additive manufacturing or rapid prototyping, references a process by which different technologies are used to build complex models layer by layer directly from a computer-assisted design (CAD). Additive manufacturing , as it relates to patient-specific devices, is used more commonly in surgery compared with subtractive processes where the removal of material through milling, drilling, or machining achieves the planned shape of a particular device. 3D printing offers a greater advantage in material choice and the degree of complexity of the objects manufactured. In VSP, the volumetric imaging data are segmented, processed in a CAD program, and may be further modified; for example, using normal mirror imaging for digital planning a surgical procedure. The transfer of this surgical plan to patient care is facilitated by the digital creation and 3D printing of personalized templates or models.
As 3D printing and VSP are rapidly changing the landscape of research, education, and clinical practice in medicine, it has also facilitated the increase in point-of-care (POC) manufacturing in hospitals and the development of institutional multidisciplinary collaborations to provide these services. POC manufacturing is defined as the just-in-time creation of anatomic models, surgical instruments, prosthetics, scaffolds, and other 3D printed applications either at the place of patient care, such as a hospital, or in a centralized facility owned by the health care organization based on the patient’s medical imaging data. The increased accessibility of this technology at the POC allows the implementation of a cost-effective, iterative process for translation of a concept to clinical application of ideas, technology, and patient-specific devices. The long-established relationship between hospitals, medical device manufacturers, the Radiological Society of North America (RSNA) 3D printing Special Interest Group (3DSIG), and the US Food and Drug Administration (FDA) has provided the necessary framework in 3D printing for the fabrication of safe and effective personalized devices through the establishment of regulatory guidelines in parallel with the acceleration of innovation. POC manufacturing requires maintaining this partnership in order to solve in unison the increasingly complex biomedical problems and advance therapeutic discoveries while safeguarding quality and patient safety.
Different types of in-house VSP or POC CAD and computer-assisted manufacturing (CAM) examples have been described in the literature. These examples provide a cost-effective use of the available CAD/CAM technologies in the delivery of services that otherwise would not be feasible because of availability or the added cost of a third-party digital planning and manufacturer. This article discusses the general principles and steps of the 3D printing process, considerations in each of the steps, and our institution’s experience in the development and use of a centralized POC program with the cross-disciplinary collaboration of radiology, biomedical engineering, and surgical/medical disciplines.
Funding
The origin of the POC program at Mayo Clinic was rooted in finding an answer to a complex medical problem through a multidisciplinary approach. In 2006, a 70-member multidisciplinary care team used in-house 3D printed anatomic models of the complex anatomy of conjoined twins to facilitate the planning of the complex 12-hour surgery to separate them ( Fig. 1 ). Cross-disciplinary institutional collaborations also developed in time with the Division of Engineering, which led to clinical applications of an in-house CAD/CAM program with the use of 3D printed models to aid in the management of congenital scoliosis in children and the fabrication of patient-specific custom fossa implants for the treatment of temporomandibular joint disorders. As the applications and benefits of additive manufacturing and VSP in patient care continued to expand, institutional grants to the Department of Radiology provided the initial capital investment for the start of a centralized POC manufacturing program tasked with the design, production, quality control, and safety of additive manufacturing based in the hospital for patient care.
The Department of Radiology’s foundation as the image acquisition, processing, interpretation, and storage unit within the institution allowed it to be well positioned to administer and refine a centralized POC manufacturing program. This centralization has allowed the support of the clinical practice across multiple disciplines and provided a volume of 3D models, digital planning, and other technologies that offer cost justification because of the significant savings in clinical care with the decrease in surgical time, return to the operating room, need for revisions, improved patient consent, and in some instances reduced length of stay. , A centralized POC program has also led to the establishment of universal protocols and a centralized quality assurance and control mechanism to ensure quality while also limiting the inefficiencies that might arise with multiple specialties attempting to simultaneously implement their own 3D printing program in silos.
The capital investment of establishing a POC program can vary widely depending on need. This range can extend from a full good manufacturing practice manufacturing facility with multiple employees, industrial 3D printers, and postprocessing in a hospital to a centralized health care facility producing anatomic models, sterilizable guides, and custom patient-specific medical devices, all the way to a small surgical practice with a part-time computed tomography (CT) technologist, a dedicated radiologist or surgeon, FDA-approved software, a robust quality control program, and a small single-material prosumer printer. Whichever POC solution is needed, a comprehensive program should include the following components: personnel, space, software, medical imaging capabilities/equipment, 3D printers, postprocessing equipment, and an internal quality control program.
In our program creation, some of the essential personnel (radiologists, radiology segmenters, information technologist) for the POC manufacturing program were integrated from existing work units within the institution/hospital system as either a part-time or full-time allocation depending on their need and responsibilities. This personnel cross-assignment has helped in cost containment and maintains a level of flexibility when making process changes and adopting new technologies and services. There are full-time biomedical engineers with expertise in CAD/CAM technologies that help surgeons through the digital planning, design, and manufacturing process. This interaction also provides an opportunity for exchange of ideas and clinical questions, thus facilitating brainstorming, iterative creativity, and refinement of concepts and designs. Continued education in established and emerging technologies in additive manufacturing and digital planning is important in order to maintain their safe and efficient clinical application.
A POC manufacturing program needs to be financially sustainable. The combined effects of reduced operative time and reoperations, improved outcomes, and the newly created reimbursement for 3D-printed models and patient-specific guides and templates is integral for the program’s longevity and ability to expand and use new technologies as they become available. The Current Procedural Terminology (CPT) codes, which are published and maintained by the American Medical Association, allow for third-party reimbursement of 3D printed anatomic models and personalized 3D printed cutting guides or drilling tools. They are currently classified as American College of Radiology category III codes: 0559T, 0560T, 0561T, and 0562T. Codes 0559T and 0560T are for the fabrication of patient-specific 3D printed anatomic models, and codes 0561T and 0562T are for patient-specific 3D printed anatomic guides. The category III CPT codes are temporary codes for use in data collection of emerging technologies, services, and procedures. They provide evidence of the use of 3D printing in medicine and could help direct health care policy in the future. In order for them to be considered category I codes in the future, they would need to be used by health care providers and have FDA approval. Category I CPT codes are often tied to Medicare reimbursement, which private payers typically follow. Category III procedures/services are often excluded by private payers; however, the current tendency is for insurance companies to cover some of these codes before category I designation. It depends on how often the new technology/services are being provided, thus highlighting the need to document the specific use of 3D printing with the designated CPT codes and continue to provide the scientific evidence to support their clinical efficacy. At this time, there are no clear guidelines for FDA approval of POC manufacturing.
Physical space
The components of the POC program can be centralized or in different locations across the institution, depending on the physical space availability and specific requirements for each of its elements. In our experience, a centralized location for Mayo Clinic’s anatomic laboratory for image processing, digital planning, and 3D printing collocated where the surgeons are predominantly has been advantageous. It facilitates communication between providers and personnel and direct oversight of its components. Collocation of multidisciplinary teams has been proved to be more effective in several other industries to date. Its hospital location offers convenient access and the ability for surgeons to be part of the VSP while working around their clinical commitments. The safe and efficient transport of the patient-specific guides and 3D models to the surgical suites for sterilization is also facilitated by the hospital location.
Information technology support, electronic health record
Information technology support is instrumental in a POC manufacturing program. Its involvement early in the process allows the 3D printing process to be integrated with the existing clinical workflow and electronic health record. The data storage and hardware requirements for software performance have to be carefully considered so that all functionalities are available. It is important to ensure that patient health information is accessible only to those involved in the care of the patient and that patient confidentiality is maintained. Security considerations with new equipment, software, technical updates, and maintenance need to be well thought out and discussed from the outset. At our institution, any new technology goes through the security, privacy, architecture, and data review process to help identify and diminish any potential risks to the electronic environment with the use of equipment or software. A robust and indexed data management program was created to store within the institutional firewall the data related to the image segmentation, CAD/CAM, and documentation of the models and guides.
Three-dimensional applications and process
The process of generating 3D objects and/or VSP from a digital blueprint is as follows: (1) image acquisition, (2) extraction of the regions of interest (segmentation), (3) transformation of the data from volumetric to a 3D triangular mesh, (4) digital planning of surgical intervention, (4) conversion of data into one of many files (Standard Tessellation Language [STL], OBJ, VRML, or 3MF file), (5) transfer of the data to a 3D printer for production, (6) cleaning and inspection of the models and/or devices, and (7) quality control of the models ( Fig. 2 ). The Radiological Society of North America (RSNA) 3D printing Special Interest Group (SIG) has provided consensus recommendations for each of the steps in POC 3D printing.
The common applications of 3D printing in medicine are (1) anatomic models, (2) modified anatomic models, and (3) VSP with templates. An anatomic model is classified as a 3D representation of the scanned and unaltered anatomy ( Fig. 3 ). These models are used for patient care, education, and aids during the informed consent process before treatment. A modified anatomic model represents the altered anatomy after digital planning is performed ( Fig. 4 ). During VSP, a complex surgical plan is performed digitally and 3D printed cutting guides and templates facilitate the execution of the plan in the operating room ( Fig. 5 ). There is an increase in process complexity and specific quality and safety considerations when the use of the anatomic data goes from diagnosis to VSP and 3D printing of patient-specific devices. ,
Image acquisition
The most common imaging modalities used for digital planning and 3D printing in craniomaxillofacial surgery are CT and MRI. The standard format for these files is Digital Imaging and Communications in Medicine (DICOM). The image type and its individual requirements depend on the intended use of the files. The decision needs to be made at the time of ordering the study as to whether the images are for diagnostic purposes only, VSP, or the fabrication of devices and implants. The more detailed and precise the clinical application is (eg, 3D printing), the more detailed the radiographic information needs to be. Defining the optimal cross-sectional imaging parameters for the intended data use is important in order to ensure that the appropriate image properties are obtained initially and prevent the fabrication of an inaccurate anatomic model or patient-specific device, and to eliminate the need for additional imaging and radiation exposure.
A high-spatial-resolution image absent of artifacts is ideal for digital planning and fabrication of patient-specific devices. Obtrusive metal artifacts are seen in approximately 25% of head and neck CT scans from orthodontic brackets or dental restorations, which can hide or mimic disorders. They also affect the fabrication of 3D models and custom devices and become time consuming in the additive manufacturing process because of the additional segmentation steps required to eliminate them. Image acquisition techniques such as higher x-ray tube voltage, gantry/head tilting, dual energy scanning, and dedicated metal artifact reduction algorithms aid in artifact reduction and improve the quality of the imaging and subsequent CAD. Gantry tilt allows better tumor detection because it redistributes the metal artifacts outside of the tumor location. The use of a jaw spacer during scanning decreases the amount of overlapping artifacts and allows the segmentation of the maxilla and mandible separately, which is at times necessary for digital planning and 3D printing. It also provides a more accurate representation of the dentition during the segmentation process. In dual energy CT scanning, 2 energy levels are used to acquire images. The material composition of the objects can be analyzed based on their attenuation profiles at the different energy levels. Depending on the material composition, there might be small or large differences in attenuation between the high and low photon energies. Additional datasets can be generated with this technique that facilitate digital planning and 3D printing. When a scan is used for both 3D printing and diagnosis, the patient is preferably scanned with a mouth spacer, in a gantry tilt and in a dual energy CT scan with an iterative metal artifact reduction (iMAR) algorithm for imaging postprocessing.
Image segmentation
The accurate manipulation of the DICOM images is necessary for generating a high-fidelity anatomic mesh. Segmentation divides an image into regions of similar properties and helps to delineate anatomic structures and regions of interest (ROIs). , Segmentation can be performed automatically, manually, or with a combination of the two. Algorithms exist for segmentation but the presence of artifacts or complex anatomy may require expertise and familiarity with the regional anatomy. Manual segmentation or a combination of manual and automated segmentation is required in these circumstances in order for it to be accurate. The most common algorithms for image segmentation are thresholding, edge detection, and region growing. The STL file is created by interpolating the ROIs from each imaging slice, and the STLs generated can be displayed over the original DICOM images to verify the accuracy of the file.
There are various segmentation software options available, both commercial and open source. Mimics Medical (Materialise, Leuven, Belgium) is 510(k) cleared by the FDA and is used by our laboratory and other hospitals. Other 510(k)-cleared segmentation software for the specific purposes of creating a diagnostic anatomic model are OsiriX Professional (Pixmeo SARL, Bernex, Switzerland) and D2P (3D Systems, SC). There are several open-source segmentation applications that are not cleared but are widely used in research and in some POC facilities
Three-dimensional representation and data conversion
After segmentation takes place, a 3D STL model is generated from the segmented DICOM data for CAD/CAM purposes. During this step, the CAD file is further manipulated, which may include placing cylinders to hold parts of the model together, smoothing the surface, fixing the triangular mesh, 3D removal of additional shells or unwanted data such as metal artifact, mirror imaging of perfected anatomy, and splitting the model for the placement of magnet casings. The surface contours of the 3D STL file are then placed back over the DICOM axial data to ensure it retains the originally segmented patient data. VSP takes place with the use of ProPlan CMF or SurgiCase (Materialise, Leuven, Belgium), and the fabrication of the surgical guides takes place with the use of 3-matic (Materialise, Leuven, Belgium). Input from the surgeon and surgical team is paramount when designing models and guides. CAD expertise from the engineering team is used to ensure precise and consistent elements are included in a model. For example, anatomies such as connective struts are placed in order to maintain accurate 3D relationships, and appropriate clearance between the surgical guide and segmented bone is established during the design process. Screw casings and holes for drilling are matched to custom implants if needed.
Three-dimensional printers and printing process
A 3D printer must be reliable, accurate, easily accessible, and properly qualified through installation, operation, and performance to ensure the highest-quality output. There is no single 3D printer that fits all the needs of a POC manufacturing program. Different 3D printing technologies exist and they are divided into 7 main additive technologies often described by their respective liquid-based, powder-based, and solid-based feedstock or input materials. , The 5 most commonly used 3D printer technologies in medicine are binder jetting (powder based), powder bed fusion (powder based), vat photopolymerization (liquid based), material jetting (liquid based), and material extrusion (solid based). Powder bed fusion and vat photopolymerization may be used for fabrication of models, surgical tools, patient-specific implants (PSIs), and tissue engineering scaffolds. Material extrusion may be used for 3D printing of porous custom implants for craniofacial reconstructions.
3D printer capabilities vary depending on programmable slice thickness, color (unicolor vs multicolor print), and build volume. Among the considerations given when selecting a printer are its technology, output color capabilities and material properties, and cost of both the capital equipment and the consumables. The requirement of material properties and size of parts dictates the 3D printing technology used, which influences the transparency, biocompatibility, moisture resistance, and sterilization capability of the patient-specific 3D model and patient-specific device. The group of materials with the largest versatility in 3D printing is the polymer-based materials. They can be used in the fabrication of bioengineering scaffolds and surgical guides, and the design of drug delivery vehicles. ,
3D printers also have different accuracy levels. For a 3D printed anatomic model, a layer thickness less than or equal to 0.125 mm is recommended. In addition to the layer thickness, the in-plane resolution should be less than 0.25 mm. The model should include a patient identifier or an internal unique identifying number. The 3D anatomic models are presumed to be of anatomic size unless otherwise specified.
Cleaning, sterilization, and inspection
The cleaning and sterilization of the anatomic model or patient-specific devices before their clinical use is important. Support material and any residual manufacturing materials should be removed as completely as possible after 3D printing. This removal should be done carefully in order not to damage the model or devices and alter their accuracy. The manufacturer recommendations for cleaning and postprocessing need to be followed during this process. Additional postprocessing elements to take cleaning and part verification to a higher level of quality assurance are often added to the standard operating procedures.
There are several available sterilization techniques, such as steam sterilization, hydrogen peroxide, gas plasma, and ethylene oxide gas. Steam sterilization is nontoxic, uses steam under pressure at a high temperature, and is one of the most common sterilization means used in surgery. It can damage devices printed with polymeric materials that have a low melting point. If an inadequate material is selected, this can have an impact on the accuracy of the final delivered device. Sterilization and handling instructions are provided with each 3D printed model and custom devices in the instructions for use . This document must be followed in order for the product to be used safely in the operating room.
Three-dimensional printing process quality assurance in point-of-care manufacturing and regulation
Each step in the 3D printing process is a potential source of error and multiple errors can compound, thus affecting the final model or guide. It should be emphasized that the quality of the initial images affects the accuracy of the models and devices created. The intended use of the 3D printed model or digital surgical planning dictates the level of tolerated dimensional inaccuracy. It might be acceptable to have larger inaccuracies in 3D models used only for training purposes, preliminary decision making, or VSP for simulation. Communication between the radiologist, biomedical engineer, and surgeon about the case-specific 3D applications and associated diagnostic parameters is imperative in order to mitigate delays or inefficiencies that could affect patient care.
The creation of in-house verification and validation protocols is important for a POC manufacturing program in order to monitor the fabrication process with checkpoints to safeguard product safety. The verification process refers to ensuring that the model or device created is made to the predefined specifications, and validation certifies that the printing and postprocessing of the model or device is accurate and fulfills its intended purpose, meeting the clinical need. The printed anatomic model needs to match the interpretation of the cross-sectional images during segmentation. The segmentation process represents one of the most common areas of error in 3D printing. A 3D printer’s inconsistencies and reliability, especially in the prosumer and lower-end models, is another commonplace, which is one of the reasons for validation of every printed object.
The verification process in 3D printing is demanding. Establishing the accurate dimensions of anatomic structures for model verification is difficult because the measurement of organic structures is challenging. There are several techniques available for measurement of models and devices. These techniques are manual measurements, digital photographic measurements, 3D scanning, photogrammetry, and CT scanning. This process verification can be performed for individual parts or for the entire model or device printed. 3D printers should undergo regular accuracy testing, preventive maintenance, and recalibration. The printing and verification of a phantom regularly ensures that appropriate quality standards for the printers are maintained.
The verification of material biocompatibility and sterilization is vitally important. The biocompatibility of materials depends on the base material, the 3D printing process, postprocessing techniques, and the cleaning and sterilization methods used. The FDA does not give 510(k) approval of raw base materials such as resin for the manufacturing of an end part, which is an often-misunderstood point in 3D printing. A company selling raw materials can list or clear a specific raw material. Most resins used in dentistry are FDA 510(k)-exempt biocompatible class I resins, which means that they have been tested by the manufacturer to be biocompatible using cytotoxicity testing and other ISO (International Organization for Standardization) 10993 testing. The company has to have an establishment registration with the FDA that allows them to be audited. FDA cleared refers to a product that was cleared because of a claim by the manufacturer that the product is substantially equivalent to another device. FDA 501(k) approved indicates that specific testing has been performed and specific instructions for every step of manufacturing and sterilization have been approved for a narrow use of the end product. Most resins or powders are either listed or cleared and none are in the approved category. Thus, it is up to POC manufacturers producing sterilizable class II devices, such as an osteotomy guide, to perform independent testing of the end products for biocompatibility and cytotoxicity following the standard operating procedure (SOP) in each facility. The authors have independently verified, through Nelsons laboratories (Sotera Health Company, Salt Lake City, UT) that surgical resin from Formlabs (Somerville, MA) used on our printers, with our SOP and in our facility, produces biocompatible autoclavable parts as defined by ISO 10993 and class VI testing.
Modified anatomic models and cutting guides and templates are categorized as medical devices. The regulatory considerations differ for a commercial manufacturer of a medical device compared with those for a hospital or academic health center. The FDA Center for Devices and Radiological Health is responsible for regulating commercial manufacturers of medical devices in the United States. For a commercial manufacturer to legally market and sell these devices, it must be (1) registered with the FDA, (2) have product clearance, (3) have an FDA-compliant quality system, and (4) list the product with the FDA. Health care providers or hospitals involved in 3D printing are not under the purview of the FDA. It is the Joint Commission that accredits and certifies hospitals and health care organizations in the United States. As the application of 3D printing continues to expand in POC manufacturing and the regulatory guidelines are being conceived, clinicians need to ensure that a high level of personnel training and competence exists and robust quality control systems are in place to maintain patient safety.
Point-of-care manufacturing in craniomaxillofacial surgery experience
The digital planning and 3D printing process at our institution is similar to that already described in the literature. Modifications have been implemented in order to integrate the 3D printing process with the electronic health record and direct clinical care ( Fig. 6 ). The workflow is initiated when an internal referring physician places an order through the electronic medical record that triggers the correct radiology protocols and the specific destination for the transfer of these images for segmentation. The anatomic modeling order has the following items in place: anatomic region (eg, head/craniofacial, heart), purpose of 3D model, type of 3D application needed (eg, 3D model, patient-specific guides and templates, fixation tray), intended use, and anticipated surgical date.
