BIOE 2010 Week 6 Notes
BIOE 2010 Week 6 Notes BIOE 2010
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This 4 page Class Notes was uploaded by Sara Littlejohn on Thursday September 29, 2016. The Class Notes belongs to BIOE 2010 at Clemson University taught by Dr. Alexis and Dr. Webb in Fall 2016. Since its upload, it has received 5 views. For similar materials see Intro to Biomedical Engineering in Bioengineering at Clemson University.
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Date Created: 09/29/16
Implant Sterilization Cleaning Implants Contaminant removal o Lubricating oils used during fabrication process o Metal shavings o Solvents Methods: o Ultrasonic cleaning o Detergents (that will not interfere with materials) o Drying under vacuum / temperature-inert or air- clean Ultrasonic Cleaning Tank containing ultrasound conducting fluid o Aqueous or organic solvent o Surfactant to break down surface tension High frequency transducer generates ultrasonic waves in fluid Cleaning mechanism: o energy release from alternating high-low pressure sounds waves in fluid creates cavities o Microscopic cavitation bubbles break up & lift off surface contaminants o Higher frequencysmaller cavitation nodesmore precise cleaning Detergents/Soaps Based on Surfactants-Surface Active Agents o Two types: Soap Biological origin Detergents Synthetic Amphiphilic (hydrophobic and hydrophilic ends) How Soap/Detergents Work Soapy water effectively holds particles in suspension so entire contaminated solution can be rinsed off with clean water Surfactants are useful for cleaning because the molecules attach readily to: o Non-polar molecules (such as grease or oil) o Polar molecules (such as water) Hydrocarbon (“fatty”) portion dissolves dirt and oils while the ionic end makes it soluble in water Allows water to move normally insoluble matter by emulsification Emulsification: the mixing of two immiscible materials enhanced by emulsifiers Sterilizing Implants Sterile: absence of living organisms Sterilization: the physical of chemical destruction of micro-organisms including those in the sporing state Disinfection: the destruction of bacteria in the vegetable state, and usually implies the use of chemical agents SAL Sterility Assurance level: probability that given implant will remain non- sterile during a given sterilization process o Generally acceptable minimum SAL is a probability of no more than 1 in a million Sterility Testing How to test: o Immerse sample in microbiological culture media to see of anything grows o Viral detection is extremely difficult Determine “Bioburden” o Wash shake or sonicate implant to remove micro-organisms into sterile fluid o Count number of micro-organisms in fluid o Run fractional sterilization studies to determine lethality of a proposed sterilization process Device-Centered Infection Formation of biofilm layer of adherent micro-organisms colonizing the implant surface embedded in mixture of polysaccharides / proteins derived from blood Extremely resistant to antibiotic treatment o Physical protection of film limits antibiotic availability Typically results in implant removal/ revision surgery / infection treatment Sterilization Method Selection Goal: to achieve sterility with minimal impact on physical, chemical, or biological properties of the material There is no ideal sterilization process but in general: o For liquid products: Where possible, utilize variation of steam sterilization Small volume liquids sometimes compatible with radiation sterilization Avoid aseptic filtration unless absolutely dictated by product compatibility o For non-liquid products: Steam, dry heat, and radiation sterilization are much preferred over EtO These processes are relatively simple and do not leave toxic residues Mechanisms Physical methods (dry/moist heat) o Destruction of metabolic and structural components essential for survival and replication (proteins) Chemical methods (gas) o Alkylation of amine groups in proteins Chemical methods (radiation) o Ionization and cleavage of cellular components (DNA & RNA) Filtration o Physical separation based on filter pore size Selection Criteria Penetration Residuals Expense Compatibility with material Dry Heat Relatively simple process that involves exposure of the product to hot air in an appropriate sized chamber Typical products that are sterilized by dry heat are: o Glass vials o Other products that are heat stable Autoclave First method applied to biomedical implants Expose implant to saturated steam o 15 minutes at 121 C (15 PSI) o 10 minutes at 126 C (20 PSI) o 3 minutes at 135 C (30 PSI) Destroys microbial proteins Very cost effective Only effective if the steam reaches all parts of the implant Heat alters the mechanical properties of some polymers can induce considerable distortion to water absorption Good for metals Advantages: o Efficacy o Speed o Simplicity o Lack of toxic residues Disadvantages: o high temperature o pressure o moisture o limit range of implant and packaging that can be used Chemical Agents Chemical sterilants are often used especially gases such as ethylene oxide
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