Hw5 BME

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School

University of Mississippi *

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Course

222

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Mechanical Engineering

Date

Apr 3, 2024

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Uploaded by LieutenantDolphin2660

BME 222 Homework 5 Total Points: 100 1. (20 pts ) Below you can see contact angle measurements of water on two surfaces (surface 1 and surface 2). a. (10 points) Assuming that one of these materials is PTFE (Polytetrafluoroethylene) and the other is PTFE with covalently-tethered PEG (Polyethylene glycol), which surface is which? How do you know? (3 sentences or less) b. (10 points) The following is a plot of contact angle (θ 2 ) vs. liquid- vapor surface tension (γ LV ) for surface 2 as it interacts with several different liquids. Determine the critical surface tension (γ c ) and calculate the γ LV for the system in which surface 2 interacts with water. 2. ( 30 pts ) You have developed a self-assembled monolayer (SAM) to modify the surface of a new polymer for facial reconstruction with an aldehyde group. The chemical structure is shown below: 1 2 = 100° = 40° Surface 1 Surface 2 0 20 40 60 80 100 120 0 10 20 30 40 50 60 70 80 90 θ = 2.2*γ LV – 70.4 γ LV (dynes/cm) θ (degrees) Surface 1 is PTFE and Surface 2 is PTFE with PEG. The reason why I believe this is because peg is a hydrophilic material so it would cause more water to come in contact with the material thus having a smaller angle. - r 4C -32 324k ¥ 40--2.2 - X - 70.4 50.18

A. (10 points) Identify the 3 key regions of the SAM molecule in the previous structure, and explain each region’s functional significance. B. (10 points) Why is it important for SAMs to be amphiphilic? What would you expect to happen if you have a SAM with a shorter hydrophobic chain, as seen below? Explain both answers from a molecular perspective. (6 sentences or less) C. (10 points) Your attachment group is found to have insufficient bonding with the polymer surface. Explain the theory behind plasma treatment and how plasma treatment may be used to improve SAM attachment. (6 sentences or less) 3. (30 points) You are a recent hire to a biomaterials consulting company, and you are tasked with redesigning the polymer housing of a pacemaker. Currently, the pacemaker housing is made from a material with many of the desired bulk properties, then coated with a material that improves biocompatibility. However, reducing the fabrication process to one manufacturing step (instead of the current two-step process) will minimize the production cost, which will surely please your supervisor. a. (10 points) Which surface modification technique would you propose to your supervisor and why? b. (10 points) You conduct dynamic secondary ion mass spectrometry (SIMS) on samples of your new material to explore the material composition at different depths, with the following results. Based on a positive control sample, you have determined that with your current dynamic SIMS settings, the material is removed at a rate of 20 nm/sec. Approximately how far into the depth of the material does your surface modification extend? Be sure to explain how you determined this based on the data. The functional group, aldehyde, is polar so it can interact with aqueous environments. The hydrocarbon chain acts as support due to the van der wal interactions with the non polar and SAMs region (make it stronger and more stable). The attachment group is saline and it can covalently bond with the surface of polymers to aid in self assembly. Amphiphilic means that the molecule is both hydrophobic and hydrophilic. These two qualities help in aqueous environments with the hydrophobic region interacting with non polar regions (van dear waals). Additionally the hydrophilic portion allows the molecule to interact with the aqueous part on the outside of the molecule. A shorter chain will decrease the stability of the molecule. This is because long carbon chains allow for lateral interactions and shortening it will lower these interactions. Plasma treatment is used to alter or modified surface of a molecule to have more OH groups. These OH groups can help will increase bonding due its ability to covalently bond. This factor will help attaching with the saline group thus improving sam attachment. The method that I would choose is surface modifying additive. The reason why I would choose this method is because it has to be done in one step and it still has the ability to affect the surface of the molecule. Surface modifying additive can can turn the multi step process into one by polymer melt. Carbon Chain Aldehyde Attachment Group ( functional Group I

c. (10 points) How is it possible to achieve depth profiling with secondary ion mass spectrometry? Be sure to discuss the instrumentation of SIMS and how the different parts of the instrumentation work together to produce plots like those seen in part b. 4. (20 points- 5 points each ) For the following biomaterials and/or applications, pick and justify which surface characterization technique would be best. a. To determine if you have achieved peptide coated silicon nanoparticles b. Size characterization of polymeric microspheres c. To visualize cellular uptake of fluorescent nano/microparticles d. To determine the strength of synthetic nano-spun collagen fibers vs. natural collagen fibers I would use Fluorescent microscopy because it can allow the cellular uptake to be visualize AFM Cana be used to pull on fibers thus testing strength SEM can be used because it can help visualize the surface of the a particle and help find the size/diameter I would use TEM because it tells information about the chemical makeup At 10 seconds you can see a change in material composition. This means that at 20nm/sec the surface modification will be over 200nm into the dept of the material SIMS is an ion micro probes that uses an internally generated beam of positive or negatively charged ions focused on a sample surface to generate ions that are then transferred into a mass spectrometer across a high electrostatic potential. First a primary ion is emitted to strip away the surfaces, then secondary atoms pass through the mass spectrometer where they are separated by mass. This separations is then read by a computer and is graphed at specific locations at different times.

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