The use of polymer-based additive manufacturing in medicine has gained traction over the past 10-15 years. However, the printers are not robust enough for non-skilled professionals to obtain optimal results. Furthermore, the technology is not a single-step process. A series of careful steps are required to fabricate an additively constructed object. Therefore, skilled professionals are required with proper training in materials science and engineering, polymer chemistry and chemical engineering fundamentals to handle the production of dental and medical objects that fulfill the needs of the medical professionals. Over the past eight years we have been working on the implementation of ChemE and polymer chemistry fundamentals to the fabrication of anatomical phantoms (replicas) to be used in cardiovascular medicine. We have tested in the field the use of anatomical models in a range of polymers for preprocedural planning in more than 20 surgeries. We have field tested our models for the simulation and testing of novel stent grafts. In addition, our models have been utilized in cardiovascular research for the visualization of fluid flow with lasers and ultrasound. In this talk, we cover the developments we have been over the years in the improvement of the materials and the processes based on the requirements established for each medical application by the physicians and health practitioners. We highlight two cases: 1) the use of soft materials for dual particle image velocimetry in the study of cardiovascular pathologies associated with cronical anatomical alterations to the endovascular system, and 2) the use of anatomical phantoms in the adjustment of medical protocols for the surgical treatment of aneurysms and related complications.
Case I
The fabrication of arterial flow phantoms for fluid dynamics studies suitable for particle image velocimetry (PIV) techniques has presented challenges. Current 3D-printed blood flow phantoms with suitable transparency for optical PIV (laserPIV) are restricted to rigid materials far from those of arterial properties. Conversely, while soft 3D-printed phantoms demonstrate promise for sufficient acoustical transparency for ultrasound PIV (echoPIV), their optical translucency challenges the use of laserPIV. The possibility of a dual-modality approach would leverage the high spatial resolution of laserPIV for in-vitro applications and the ability of echoPIV to quantify flow in both in-vivo and in-vitro application (i.e., inside stents), providing a comprehensive understanding of flow dynamics. We present a series of coated thin-walled 3D-printed compliant phantoms suitable for dual-modality PIV flow imaging (i.e., laserPIV & echoPIV) methods, overcoming current 3D-printable material limitations. Vat photopolymerization was used to fabricate pipe flow phantoms from a set of commercial soft resins (flexible and elastic) as vascular tissue surrogates. To overcome low transparency and poor surface finish of soft resins, we coated the 3D-printed flow phantoms with a soft, optically transparent, photo-activated polymeric coating. The feasibility of performing dual-modality PIV was tested in an in-vitro flow setup. We show that the average normalized root mean square errors obtained from comparing laserPIV and echoPIV velocity profiles against the analytical solutions were 3.2% and 5.1%, and 3.3% and 5.3% for the flexible and elastic phantoms, respectively. These results indicate that dual-modality PIV flow imaging is feasible in the 3D-printed coated phantoms, promoting its use in fabricating clinically-relevant flow phantoms.
Case II
When treating aortic aneurysm patients with complex anatomical features, preprocedural planning aided by 3D-printed models offers valuable insights for endovascular intervention. We studied the use of vat photopolymerization to fabricate a phantom of a challenging aortic arch aneurysm with a complex neck anatomy. As an exemplary case from the several cases performed in Mexico, a 75-year-old female presented with a 58 mm descending thoracic aortic aneurysm (TAA) extending to the distal arch, involving the left subclavian artery (LSA) and the left common carotid artery (LCCA). The computed tomography (CT) scans underwent scrutiny by radiology and vascular teams. Nevertheless, the precise spatial relationships of the ostial origins proved to be challenging to ascertain. To address this, a patient-specific phantom of the aortic arch was fabricated utilizing an SLA printer and a biomedical resin. The thoracic endovascular aortic repair (TEVAR) procedure was simulated using fluoroscopy on the phantom to enhance procedural preparedness. Subsequently, the patient underwent a right carotid-left carotid bypass and a right carotid-left subclavian bypass. After a 24-hour interval, the patient underwent the TEVAR procedure, during which a 37 mm × 150 mm and a 40 mm × 200 mm stent graft were deployed, effectively covering the LSA and LCCA. Notably, the aneurysm exhibited complete sealing, with no indications of endoleaks or graft infoldings. At the 12-month follow-up, the patient remains in good health, with no evidence of endoleaks or any other surgery-related complication. This report showcases the successful use of endovascular phantoms fabricated by vat photopolymerization in guiding the decision-making process during the preparation for a TEVAR procedure. The simulation played a pivotal role in selecting the appropriate stent graft, ensuring an intervention protocol optimized based on the patient-specific anatomy. The analysis of all cases is summarized at the end with the goal of providing additional information supporting the benefits of employing anatomical phantoms in preprocedural planning in terms of lower mortality rates, time in the OR, and overall surgical costs.
Through these cases, we discuss the avenues for the involvement of chemical engineers in the fabrication process of patient-specific anatomical models that require several paradigm changes form the standard ChemE mindset of mass production to on-demand low to mid-scale production of high-value products in the medical field.
