3P10: Chronicles 1 Flashcards
Define medical device
A medical device is any instrument or apparatus for diagnosis, cure, treatment or prevention of diseases or conditions.
- Not a drug or pharmaceutical agent
What type of devices does medical device cover?
Accessories – intended to be used with the device
In-vitro diagnostics – vials for samples
Custom-made devices – personalised device
Active medical devices – rely on source of power
Implantable medical devices – stay in human body
What are the two key European regulations that cover medical devices?
- Medical Devices Regulation 2017/745
- In vitro Medical Device Regulation 2017/746
Give examples of the 4 different classifications in EU regulation
- I – corrective glasses and frames, walking aids, non-sterile dressings, stethoscopes
- IIa – Devices to manage micro-environment of a wound short term corrective contact lenses, arterial blood filter, hearing, aids, antistatic tubing for anaesthesia
- IIb – Insulin pens, contact lens solution, machines for haemodialysis
- III – total hip and knee replacements, cardiovascular catheters, vascular stents
Why have a classification system? (I-III)
- The greater the risk, the greater the reassurance that needs to be given
- Manufacturers and their cost/controls – allows manufacturers which products to focus efforts on keep most sterilised.
What major changes were made to EU regulations in May 2017?
- The Active Implantable Medical Devices Directive (AIMDD) & Medical Devices Directive (MDD) where combined to make the Medical Devices Regulation (MDR)
- The IVD Directive (IVDD) was updated to In Vitro Medical Device Regulation (IVDR)
Explain the difference between the EU and US MD approval systems
- EU has centralized and decentralized agencies throughout its member states
- US the process is centralized through the FDA
- EU system requires a lot more work for approval but is more flexible
- US classification is easier to get but more rigid
What is the simple definition of a biomaterial?
A material intended to interface with biological systems to evaluate, treat, augment or replace any tissue, organ or function in the body
List the different categories of materials in medical devices/implants:
Bio-inert
- Has no cells or living components
Hybrid
- Implants with both cellular and materials components
Biological
- Transplants
- Can have a cost in terms of immune reaction
Give the simple definition of biocompatibility (in terms of bio-functionality)
The ability of a material to perform with an appropriate host response in a specific application
- Appropriate host response: resistance to clotting, antibacterial
- Specific application: hip joint replacement
Give the simple definition of biocompatibility (in terms of biosafety)
The exclusion of severe deleterious effects of a biomaterial on an organism
- Includes cytotoxicity and mutagenicity, carcinogenity, pyrogenicity, irritation, etc.
Explain Polymethylmethacrylate, PMMA in making contact lenses
- Used in rigid contact lenses: must be tough, stable and have excellent light transmittance
- A hydrophobic, linear, amorphous polymer
- One potential disadvantage is the lack of oxygen permeability
- Melt processing, compression moulding and casting can be used.
Explain UltraHigh Molecular Weight PolyEthylene, UHMWPE
- Used in low-friction inserts for bearing surfaces in Total Joint Arthroplasty
- Must be tough, with a high impact strength and low coefficient of friction
- Disadvantage: wear rate of 1mm/year
What are the different polymers that can be used in implants?
- “Permanent”
- Bioelimiable, i.e. excreted in urine
- Bioresorbable/bioerodable i.e broken down by hydrolysis and metabolised
Describe PLA and PGA and explain their roles in allowing tuneable hydrolysis rates
PLA:
- Amorphous or semi-crystalline
- High strength and thermoplastic properties
PGA:
- Very crystalline
- Excellent mechanical properties
PLA/PGA copolymers have tuneable hydrolysis rates
Explain Hydrolysis
- Water enters the polymer
- A chemical reaction causes the bonds to break
- Crosslinks cleaved – water soluble molecules
- Side chains transformed/cleaved – water soluble
- Backbone covalent bonds cleaved
- This causes the pore size to increase – more water can enter
- All polymers undergo some hydrolysis
What are the factors affecting hydrolysis reaction rate
- Basic chemistry
- Side chains
- Crystallinity
- Geometry
- Porosity
- Glass vs. rubbery state (rubbery means faster)
Explain Titanium-based Alloys in Femoral Implants
- Lower moduli and ductility than steel
- Allows load to be transferred to the femur
- Improved tensile and yield strength
- Improved corrosion resistance
- Significantly lower density