Weekly Updates

Week 1

During the first week, very little was achieved. The first class did not meet until Friday, thus we were unable to form a group and develop a project idea until then.

That weekend, the first group meeting was held where we discussed how we would approach the problem.

Week 2

We have developed a project proposal outlining the aims of and necessities of our project.

Due to expenses of stent material, it has been decided that all tests will be performed on less expensive student produced large scale models. We will be performing experiments with a cardio-vascular simulation device to test various heart conditions on our implant.

A few crude drafts have been produced in Fusion 360 and should be available below.

In the above images, the metal sleeve represents a stent. The fabric cylinder is a mesh sleeve containing the alginate-medication capsule. The design of the stent, with a partial wall on the end, prevents the capsule from being mobile in the direction of blood flow while being removable through re-catheterization.

Week 3 

The original design proposal has been replaced with a more practical design. The previous design was more complicated than it needed to be, thus a simpler design was thought of. Applying principles of fluid mechanics rather than theories of materials science would make the most sense to regulate the medication release rate. Fluid mechanical properties would most closely mimic the movement of blood within a human body. 


This week the stent design was changed. The idea of lining the inside of the stent with a semi-permeable mesh material was too complicated. As previously stated, fluid mechanical theories such as the natural way blood moves through veins will be used to the project’s advantage. Although stent is still lined with alginate gel, is now a conic shape. When the right mixture of alginate is discovered, the stent will allow for the appropriate release of medication based on blood flow rate. A very viscous concentration is crucial in the design. This is necessary so the gel is not too soft and doesn't fall apart in the vein, which can cause a plethora of disastrous implications. 

Week 4

This week the team met to build a presentation to explain the project idea to the class. The presentation began by highlighting the problems that are there in current medication delivery systems. Then the group explained the technical details of the idea and the challenges that the group faced in making this idea a reality, thus far. For example, current medication delivery systems are expensive, invasive, and require manual monitoring by healthcare professionals. Ideally, this implant will be used for patients who have just undergone MI surgery because it will offer them the maximum amount of patient mobility because they won't have to be attached to bulky machinery and the implant will be more sensitive to when the patient needs medication so that they won't need to be monitored as closely by hospital staff. The following image shows one of the slides explaining the technical details of the system. The graphic below shows how the shape of the stent and the alginate gel cast inside of it contributes to it's release rate. Specifically, as blood flow rate increases, the medication will be released at a faster rate, but it will not cause the alginate-medication matrix to break apart and cause blood clotting.

During this lab period, the team was also exposed to the other uses of alginate gel that were presented by other groups.

Week 5

After speaking with Professor Cheng it came to the group's attention that specific details needed to be mentioned in our experimental proposal. Specifically the group came up with different concentrations of alginate mixture to be created in order to determine the desired viscosity of the gel. These concentrations were as follows: 

• Concentration A: 3.75:1 water to alginate ratio (by weight)

• Concentration B: 4:1 water to alginate ratio (by weight)

• Concentration C: 3.5:1 water to alginate ratio (by weight)

In addition, the group decided to create a sheet of gel using a moderately inclined plane, this sheet would be cut into tiny rectangles that could be wrapped around the circumference of the stent. This gel will then be rolled into a cardiod shape in order for it to be placed inside the compressed stent that would be inflated by a balloon for proper placement within the vein. Each concentration of the gel will hold 14 doses of simulated beta-blockers. The simulated medication is acidic and thus pH will represent release of medication. 

The group will be creating a cast for the gel on Monday in the machine shop. This involve working with the lab technicians in order to properly construct the 3-D design for cast.

Week 6

In week 6, the group planned attempted to print a cast to form the gel into the proper shape to fit in the stent. The printer was unable to print the required resolution and the slope in the cast was inaccurately printed. The group decided to alter the design of the file to compensate for the error in the printer.

The group ordered a Universal Solid State Electric Fuel Pump to simulate the heart and the blood flow within the vessels. This equipment will be used to control the independent variable of the heart rate simulation.

Week 7

This week, the group received all the items that were ordered. The PVC pipe was cut in the Drexel Machine Shop. These sections will be combined together to form the exterior skeleton of the intravenous blood flow simulation. The PVC caps will be drilled to fit the pressure pump as required. The following computer drawings show the final version of the stent that will be used inside the simulation. This is a modified version of the stent that the machine shop was unable to print initially.

Week 8

During week 8, the entirety of the experiments was completed because we were granted lab space. Once the simulated vascular system was created, the same experiments were completed at different speeds. The simulated vascular system was created using PVC pipes, which were cut and fit together with the help of the machinery and staff at the machine shop. Then, the alginate hydrogel was created, with crushed Aspirin tablets added to the mixture as well. The alginate gel had to be cast in the molds that were previously 3-D printed so that they would fit perfectly around the inside of the model stent, which was also created using the 3-D printers available at Drexel. Once the alginate hydrogel was cast, it was rolled up and placed inside the stent. The stent, in turn, was placed inside the PVC pipe of the simulated vascular system. Then, the simulated vascular system was filled with a glycerine and water mixture, whose viscosity most accurately matched that of blood. The volume and mass of the mixture was measured before being run through the machine. Then, the simulated vascular system was run on the low speed and the mixture’s volume and mass was measured again. The same process was completed, but with the pump of the simulated vascular system on a higher speed. The following video and pictures shows the simulation.

                               



                                                 


                                                 

                                                 

Week 9

In week 9, the group worked together on the final report and the final presentation. The data gathered during the experiment were used in the report to interpret and draw our conclusions. 

Week 10 

This week the group worked on the alternative method recommended by Dr.Cheng instead of using the change in weight. We performed a basic spectroscopy experiment to see if spectroscopy would be a good measuring system for low concentrations of medications in blood. For the spectroscopy we took the liberty upon the advice of Dr. Cheng to test light absorption in UV light for aspirin medication at various concentrations as would be seen in future stent testing. The medication range in our testing varied from concentrations of 0.001% all the way up to 0.009%. We used a spectrophotometer to test various concentrations within that range and were able to plot a curve upon which we could do some comparison work with spectroscopy to define the concentration of aspirin within blood very accurately. Although this is a bit rudimentary, in future experiments we would create a far more complete scale. The following two graphs shows the interpretation of this data.

The group finally presented the project in front of a live audience on the last day of the course.