Tracheobronchial Stent
Design Researcher -Thesis Project
THE CHALLENGE
Create a prototype for a tracheobronchial stent tailored to latin American patients.
THE OUTCOME
Developed a first prototype.
MY ROLE
Researcher and developer intern.
SKILLS
Biomedical research
Product design
Material selection
Anatomy analysis
Context
For my undergraduate thesis, I worked with NovaCrealt to develop a tracheobronchial stent prototype specifically tailored for Latin American populations. Many existing medical devices are designed based on American and European anatomical models, leaving gaps in accessibility for other ethnic groups.
As a researcher and developer intern, I conducted extensive research on materials, existing products, and human anatomy. I designed the prototype using engineering software and collaborated with NovaCrealt to explore its feasibility.
Currently, tracheobronchial stents available on the market are designed for American and European anatomical characteristics, making them unsuitable for Latin American patients. This mismatch leads to complications such as stent displacement, granulation, fractures, and patient discomfort, often requiring additional surgical interventions. Despite the growing market for these stents and the presence of international patents, Mexico lacks a patented, locally designed option. Additionally, as of October 2022, no manufacturer has an authorized sanitary registration under COFEPRIS for distributing these stents in Mexican hospitals. Developing a standardized stent tailored to Latin American anatomy would not only improve patient outcomes but also reduce import costs and enable affordable local manufacturing.
Goals
General Goal
Develop a design strategy for a customizable tracheobronchial stent tailored to Latin American patients.
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Collect and document data to identify patient needs and explore potential design solutions.
Select and analyze suitable materials for the stent design.
Utilize CAD and CAE methodologies to develop the stent model.
Define a manufacturing process to produce a physical prototype.
Establish testing protocols for mechanical and functional evaluations to meet FDA and COFEPRIS regulatory standards.
Conduct initial mechanical and development tests on the prototype.
Constraints and limitations
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The number of active weeks during the semester was insufficient to produce a fully developed prototype that meets regulatory approval. As a result, the project was delivered at a testing stage, with protocols in place to continue further research.
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The unique properties of the nitinol alloy are complex to replicate and integrate into the finite element analysis (FEA) software used for testing. However, prior research conducted by the client allowed for manual incorporation of the material’s behavior, enabling the necessary simulations.
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Tracheobronchial stents remain an emerging innovation in medical research, leading to a scarcity of scientific literature on the subject. To address this, the project relied on existing bibliographic resources and expert insights from specialists in the field.
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Since the manufacturing process is largely manual, acquiring the necessary materials and tools according to the selected method could exceed the planned timeline. Therefore, available materials and tools were used during the research phase to ensure progress.
Design Process
1. Initial Research
A comprehensive literature review on tracheobronchial stents was conducted to analyze key design factors, materials, complications, and dimensions.
There is no universally ideal stent; however, essential characteristics include:
Biocompatibility: Made from inert materials.
Flexibility: Adapts to the tracheobronchial surface.
Strength: Withstands uniform pressure, compression, and microbial invasion.
Stable Placement: Prevents migration.
Easy Insertion & Removal: Allows precise positioning and repositioning.
Affordability: Cost-effective production.
Based on these factors and existing stent dimensions, the new design must ensure material biocompatibility, durability, and secure fixation to withstand natural neck movements. It should also facilitate surgical handling and be economically viable. Once an optimal model is developed, finite element simulations will assess structural integrity.
2. Material Selection
Given the need for biocompatible materials with the necessary structure, strength, and flexibility for stent insertion and function, we selected materials based on their mechanical properties and cost-effectiveness:
Nitinol: A nickel-titanium alloy with shape memory and superelasticity, allowing the stent to compress for insertion and expand to exert outward force, keeping the trachea open (Stoeckel et al., 2004).
Medical-Grade Silicone: Chosen for its flexibility, hypoallergenic properties, and low viscosity, making it ideal for long-term use without promoting mucus formation. It can stay inside the body for over 10 years.
The combination of these materials ensures biocompatibility, durability, and adaptability, supporting the forces exerted by the tracheobronchial tract.
3. CAD Design
After selecting materials, a customizable structure was designed, focusing on patient-specific height variations. Standard diameters of 17mm and 20mm were chosen to create a tubular design that could be cut or extended as needed. The selected manufacturing method is a cost-effective ring-braiding technique using nitinol rings.
Design Parameters:
Rings with variable height, cell count, and wire thickness were analyzed.
The experiment design uses finite element analysis (FEA) to evaluate the ideal parameters for material behavior.
Ring Design: The diameter of the trachea minus the nitinol diameter defines the geometry. Experimental data will assess the optimal wire thickness (0.381mm and 0.50mm), cell count, and other variables for the final design.
4. Finite Element Method Testing
Stress points were assessed at the
In this phase, the number of cells for the rings was determined. Existing designs with fewer than six cells were discarded as they were uncommon in the market, and their simulations failed when applying the evaluation parameters.
After selecting a 12-cell ring, the design of one cell was transferred to finite element analysis for compression and extension tests. This simulated the force required to compress the stent and insert it into the cartridge before surgery, as well as the force required for the stent to expand inside the trachea and remain in place.
The highest stress was observed at the cell radius, so simulations were conducted with variations in the radius.
Stress points were assessed at the
5. Manufacturing Process Development
The innovative structure was created in steps, dividing the process by materials and parts that needed to be assembled to form the final tracheobronchial stent.
Nitinol Structure Formation:
Ring Formation: Nitinol wire is cut and shaped using a mold with calibrated pins.
Braiding: The rings are interwoven to form the required tube length.
Clamping: The rings are pressed together to distribute force, using clamps and another metal, though this process is only a hypothesis, as compression forces in the trachea are not excessively high.
Silicone Structure Formation:
Tracheal Model: A 3D model of the silicone part is created based on the patient’s measurements, designed as a tubular structure with hollow external protrusions.
Mold Printing: The CAD model is 3D-printed in PLA, with the mold featuring a top section for connecting the nitinol structure.
6. Protocols
Manufacturing Protocol (Annex A):
This protocol does not differentiate between nitinol and medical-grade silicone testing, as both are subject to industry standards for medical material approval (ASTM and ISO standards).
Development Protocol (Annex B):
The development protocol outlines tests for the fully assembled stent prototype, based on ISO and ASTM standards that ensure the proper functionality of the prototype.
7. Mechanical and Development Testing
Stress points were assessed at the
Stress points were assessed at the
Annex A
Stress points were assessed at the
Stress points were assessed at the central and lateral points of the cell (where the cell joins with the rest of the ring), which are crucial for CAD analysis.
Structure Joining:
Mold Placement: The nitinol ring is placed at the bottom of the mold to provide structure at the distal end of the stent. Additional nitinol rings are placed in the mold, centered between the inner and outer diameters.
Silicone Injection: Silicone is injected into the mold, covering the rings and joining the pieces.
Polishing: After the silicone solidifies, it is polished to stabilize the stent.
Along with mechanical testing, development protocols were created for documenting material and prototype testing. These protocols ensure that the stent prototype is viable and can eventually be commercialized.
Annexes C and D outline the mechanical and development testing protocols, based on standards from the American Society for Testing and Materials (ASTM) and the International Organization for Standardization (ISO).
Annex B
To physically create the tracheobronchial stent model, each of its two materials—nitinol wire and solidified medical-grade silicone—was subjected to mechanical testing. Although these materials were sourced from health suppliers with the necessary regulatory approvals, testing was required to confirm their expected behavior.
Following the selection of manufacturing parameters and material testing, the fully assembled prototype underwent development testing as outlined in the protocol. Once these tests were approved and the prototype met the required technical specifications, it was designated as Prototype Zero and prepared for animal testing.
Long-term project outlook
Medical device development requires a long-term approach due to extensive research, prototyping, and testing.
The process includes:
Gathering and analyzing medical needs.
Developing the initial prototype.
Conducting material and product development tests.
Iteratively refining the prototype for optimization.
Future steps:
Validate a fully functional prototype through development testing.
Conduct preclinical animal trials once the prototype meets performance standards.
Progress to clinical trials with regulatory evaluations.
Seek FDA and COFEPRIS approval for commercialization.