Reverse engineering in medical application: literature review, proof of concept and future perspectives

The human body is a very complicated piece of engineering. As previously stated, reverse engineering can be regarded as a means of gaining knowledge in situations where there is a lack of data pertaining to an object. The human body can serve as a mechanism for the reinvention of its components, such as body parts and organs, through reverse engineering. This approach can be particularly useful in situations where there is an absence of design data, and it can facilitate a deeper understanding of the body.

Internal body components can be scanned using medical imaging, while external body parts can be scanned using 3D scanners. These tools facilitate the collection of information from a human subject, an attached device, or a model. When used in a medical setting, the steps depicted in Fig. 2can begin with a 3D scanning or medical imaging to learn more about a patient’s interior anatomy. Patient-specific preoperative 3D medical imaging data can be used in a wide variety of 3D bio-modeling and imaging applications, including the manufacture of implants, saw guides, and drill guides²⁸.

Haleem et al²⁹. conducted bibliometric analysis that displayed the increasing trend of researching 3D scanning applications in the medical field. This study’s main findings are:

• 3D scanning and printing are highly compatible and make a great medical support technology.

• 3D scanning offers insight into the external anatomy, while medical imaging explores more deeply the internal workings of the human body.

• All medical fields can benefit from the 3D scanning technologies.

• 3D scanning tools are reliable and helpful for carrying patient information electronically rather than physically (e.g., molds), provided that basic training is provided.

• For applications such as orthosis, prosthesis, and dentistry, 3D scanning offers a convenient replacement for the time-consuming process of making a plaster cast³⁰.

The above research (Haleem et al²⁹.) was driven by the demand for 3D scanning data for external body parts. RE is used in the medical field for a variety of medical applications, such as implants, patient shape, size, surface area, and body part information, as well as digital models for virtual reality and holographic applications. Implant manufacture is fast with a 3D scanner and post-process software. Additive Manufacturing (AM) is a method frequently used in RE. When integrated with AM technologies, RE has a wide range of potential uses^4,15,31, including in dentistry, tissue engineering, and medical devices – all of which are further discussed.

Dentistry

It appears that 3D scanners and printers are becoming increasingly commonplace in dental offices, although the intra-oral scanner is used to determine the amount of a damaged tooth in the most common routine check-ups. A variety of dental specialties, including prosthodontics, oral and maxillofacial surgery, oral implantology, and orthodontics, make use of RE and 3D scanners.

3D scanners provide surface information for dental preparations that are possible either in vivo or in vitro. The scanned data is used for implants or restorations. Recent applications of RE in dentistry include dental implants^32,33, medical devices³⁴, dental restorations³⁵, and finite element method (FEM) on dental implants³⁶. Dental impressions were traditionally taken using plaster models. However, the use of 3D scanners has made it possible to acquire digital impressions. The digital model’s dimensional precision and likeness match the plaster model³⁷. RE dental devices include prostheses, implants, and surgical guides^33,34,35.

RE has been implemented as a new method for comparing medical models produced by various 3D scanning techniques. This process was illustrated by Martorelli et al.‘s³⁸research, in which Cone Beam Computed Tomography (CBCT) was used to scan the 3D model of simulated human dentition. Afterwards, the same 3D model was laser-scanned to make a comparison of the CBCT model with the laser-scanned model. Zhou et al³⁹. conducted a study with a similar objective, analyzing and measuring dental casts and testing 3D scanning as a replacement for gypsum casts. Pereira et al⁴⁰. and Liu et al⁴¹. conducted experiments examining the viability of digital casts, as well as the angle and distance between dental implants. These studies demonstrate the viability of using non-contact laser 3D scanning as an alternative to CT scanning for dimension verification, as well as deviation analyses based on the reconstructed implant cylinder. Figure 6displays the protocol for evaluating the accuracy of guided implant surgery by using digital casts⁴⁰.

Procedures for evaluating the accuracy of guided implant surgery by using digital casts⁴⁰.

Additionally, RE has been incorporated into dental analysis. For instance, Martorelli et al ⁴². utilized 3D models of the human mandible that were generated through RE. The objective was to recreate 3D models with the same or relatively similar mechanical properties as a human mandible. To ascertain the load-displacement relationship, the 3D model was then subjected to experimentation under suitable loading conditions as part of the validation procedure. In essence, RE was used in this study to ascertain the design information of the human mandible’s surface layout and strength. Additionally, finite element analysis (FEA) and fatigue analysis^43,44were conducted for the same purpose. These studies demonstrate that non-contact laser 3D scanning can be used to obtain geometric data for analysis purposes. On the other hand, Giudice et al⁴⁵. show that using the mirroring process and best-fit alignment algorithm, the differences between anatomical sides of the patient (left-to-right and right-to-left) can be obtained from the surface analysis and color map visualizations, as seen in Fig. 7.

Computer-assisted analysis of maxillary asymmetry of a 7-year-old girl, using reverse engineering. (A) Pre-treatment frontal view, (B) Pre-treatment occlusal view, (C) Pre-treatment deviation analysis between original maxillary scan and mirrored scan, (D) Post-treatment frontal view, (E) Post-treatment occlusal view, (F) Post-treatment deviation analysis between original maxillary scan and mirrored scan.

The development of material science has led to the incorporation of composite materials into dental devices. RE has made it possible to analyze these composite materials. This is evident in the research conducted by Ilie⁴⁶, which suggests that, through its analysis of clinically tested materials, RE is a viable method for future design. In this investigation, the materials analyzed were composites based on resin. In dentistry, RE tools enable kinematic analysis and virtual design in conjunction with CAD tools. This allows for the creation of a virtual articulator. A virtual articulator reduces the need for a mechanical physical articulator while allowing practitioners to simulate actual patient data and conduct analysis^47,48.

The digital planning of skeletal anchoring systems is another way that RE is used in dentistry to overcome the constraints of traditional therapy. While a free-hand technique can safely implant mini-screws in this area, digital planning and the creation of surgical guides are recommended for the following reasons: The three main aspects of miniscrew management are as follows: (1) regulating miniscrew inclination and parallelism, to prevent undercuts and facilitate orthodontic appliance placement; (2) controlling miniscrew insertion depth, to prevent bone trauma during insertion; and (3) precisely planning the relationship between the miniscrew and the cortical palatal and nasal bone, which is essential for applying orthopedic forces⁴⁹. Figure 8 describes a clinical example of miniscrew placement with 3D-printed guided systems developed from a reverse-engineered 3D model.

Clinical example of miniscrews’ placement with 3D printed guided systems. (A) Digital guide in the digital 3D printing plate, (B) 3D printed surgical guide, (C) Clinical procedure of miniscrew insertion, (D) Miniscrews placed in the palatal paramedian region, (E) Scan bodies for intra-oral scan, (F) Appliance fixed to the miniscrews.

Tissue engineering

Tissue engineering is a solution for regenerative medicine problems associated with tissue repair and organ replacement. 3D cellular structures (also known as scaffolds) provide an effective platform for the development of novel tissues, primarily by providing mechanical support during the development phase⁵⁰. Scaffolds have an intricate structural composition. In this regard, RE plays a significant role as structural information for modeling, and it can be extracted using scanning techniques. In the research conducted by Pina et al⁵¹., multiple strategies that could be utilized to develop scaffold designs for tissue engineering and regenerative medicine for various organs and tissues are explained. The work describes the diverse applications of 3D scanning and RE for 3D printing hydrogel scaffolds. For instance, Li et al⁵². proposed 3D printed hydrogels as osteochondral (OC) defect fillers using alginate and hyaluronic acid as photopolymerized bioinks. The OC tissue was restored by reverse engineering, using high-resolution 3D scanning to obtain models of sample defects and the corresponding parts after regeneration. Wang et al⁵³. distinguished between parametric design and the RE-based generation of vascular scaffold models. Due to the complexity of vascular scaffolds, it is said that parametric design without AI and machine learning is nearly impossible. However, parametric design in conjunction with AI and machine learning is said to be applicable for the bulk processing of models that are quite similar.

The use of reverse-engineered models is applicable for patient-specific vascular scaffolds but is typically not employed for extensive quantity modeling where structural similarity exists. Figure 9depicts the workflow of 3D model reconstruction for these models, where MRI or CT images are used to acquire DICOM images. The general conclusion is that parametric design is more expedient, whereas RE models are more personalized and offer high anatomical compatibility⁵³.

Workflow for creating 3D models from DICOM images.

RE has also been applied to bone tissue engineering^54,55. Again, RE is advantageous in the design and construction of scaffolds, in this case bone tissue scaffolds. After CT data of a bone is obtained, it is transferred to CAD software for design and analysis purposes. According to Yao et al⁵⁶., animal (rabbit) spinal specimens were utilized to investigate design and construction procedures using RE, as seen in Fig. 10. Fucile et al⁵⁷. demonstrated another application in this regard, where RE was used to create nanocomposite structures. In the work by Wang et al. ⁵⁸, the RE process was implemented for bone tissue engineering, and the models were ultimately incorporated for computational fluid dynamics (CFD) to determine the flow field surrounding a cell.

Designs of anatomical femoral and vertebral plate-fused scaffolds. (A) Design of rabbit femoral scaffold, (B) CT data-based rabbit femoral scaffold.

Medical devices

When the majority of a country’s debt is attributable to the import of medical devices, as was the case in the study by Asmaria et al⁵⁹., the widespread adoption of RE can be an effective national strategy for debt relief. The research took place in Indonesia and involved the backwards engineering of an aneurysm clip (a highly sought-after medical device in that country). There have also been attempts to use RE in place of importing costly medical equipment in South Africa, another country with severe resource limitations⁶⁰.

Recently, the use of RE during the COVID-19 pandemic has been quite prevalent. As the demand for personal protective equipment (PPE), ventilators, and other vital medical devices skyrocketed, supply chains began to break down. RE was proposed as a solution to these shortages, and numerous instances of hospitals developing equipment in-house to satisfy the high demand have been reported^61,62,63,64.

These applications relate more to supply chain processes; nonetheless, they demonstrate the applicability of RE in the medical context. In the medical industry, RE can be said to have both direct and indirect applications. The aid RE provides in prosthetics and implants, surgical planning, customized medical devices, and anatomical modeling is among the direct applications of RE in the medical industry, whereas quality control, regulatory compliance, data integration, as well as research and development activities, can be categorized as indirect applications.

Surgical guides are important dental tools because they improve numerous aspects of the surgical procedure⁶⁵. A CAD model produced with intra-oral 3D scanners is used to design and fabricate these devices. 3D scanning is used to collect intra-oral surface information. The accuracy of the surgical guide has been determined with the aid of RE and 3D scanning. One such instance is the work of Giordano et al²⁰., in which RE was used to assess the precision of surgery guides in dental implants. In this way, RE is found to be a useful instrument for accuracy evaluation and quality control. Liang et al⁶⁶. and Russo et al⁶⁷. discussed additional applications of RE to ascertain the accuracy.

As previously stated, one of the opportunities provided by RE in the medical sector is the development of customized healthcare products. This enables customized implants and prosthetics for each patient. In their study, Noor et al⁶⁸. demonstrated how a customized bone fracture implant developed from RE reduces the stress and movement between the fractured bone and the implant, in comparison to the implant constructed from a generic model. In addition to design and construction, RE has also been utilized in verification processes. In one instance described by Kloesel et al⁶⁹., the RE procedure was used to verify the suitability of a medical device for a patient. Other uses for RE include hand orthotics⁷⁰and soles⁷¹, as seen in Fig. 11.

Design and production of orthotic insole shoes for diabetic patients⁷¹.

Having gone through the various literature, some of the typical medical applications of RE are identified and summarized in Fig. 12.

Summarized medical and biomedical application of RE.

The following section is a proof of concept on one of the above-mentioned applications of RE in the medical field, i.e., reconstruction (solid modeling). In this proof of concept, the protocol to reconstruct the human femur 3D model is provided. Additionally, the reconstructed model is compared to the reference model.