Textured/Porous Materials, Medical Fibers, and Biotextiles

Question 1

Why are textured surfaces more successful in implants?

Answer 1

• improves tissue ingrowth at the implant interface, with thinner foreign body fibrosis capsules
• reduces micromotion via interlocking to reduce chronic inflammation
• disorganizes collagen, makes it more susceptible to degradation (increases macrophage presence to help this)
• more surface area means more cell attachment
• macrotopography or microscale texturing

Question 2

Porous Materials

Answer 2

• helps facilitate tissue ingrowth/integration with increased vascularization (needs pore size of about 100-400 micrometers)
• small enough to prevent fibrotic tissue formation
• vascular grafts and subcutaneous implants

Question 3

Manufacturing porous materials

Answer 3

• modifying metals, ceramics, natural/synthetic polymers with variety of coating and processing techniques
• polymers: salt/particle leaching, gas foaming, freeze drying/lyophilization

Question 4

Bone implants

Answer 4

• need similar mechanical properties and proper biocompatibility and biodegradation rates
• texture fixation layers used to minimize loosening
• using porous materials helps elicit osteointegration, which reduces stress shielding
• minimum 100 micrometers required for continuous ingrowth (although as small as 50 help with blood vessels)

Question 5

Downsides of porosity

Answer 5

• if fibrous ingrowth of tissue happens first, osteointegration won’t occur
• porous metals applied in load bearing applications, but porosity decreases mechanical properties

Question 6

Biotextiles

Answer 6

• non-viable fibrous textile structures created from synthetic or natural materials used in biological environments
• provide thin/strong/flexible structures with excellent fatigue resistance and large surface area for drug delivery and cell attachment
• usually have intermediate to high-molecular weight (20-250 KDa)
• linear polymer chains without bulky side groups, cross links or side chains, can form crystalline structures when solid, and can have favorable interchain interactions for alignment

Question 7

Textile processing

Answer 7

• can be continuous monofilament or multifilament of various lengths
• yarn linear density expressed in decitex (dtex) or denier in North America
• (Filament number) x (fabric density) x (length) x (cross section) = (# textile unit)

Question 8

Melt spinning

Answer 8

• heating a resin to melting temperature and extruding through a spinneret
• number and shape of holes defines the count and cross-sectional shape
• then lubricated, drawn, and twisted

Question 9

Wet/gel spinning

Answer 9

• for polymers that degrade at high temperatures, like natural materials
• dissolved in a solvent then extruded through a spinneret into a non-solvent spin bath
• 10 micrometer diameter for multifilament yarns (up to 500 micrometer diameter), or thicker for monofilament

Question 10

Bi-component spinning

Answer 10

• multiple polymer components are brought together at the spinneret hole, creating filaments with all the polymer components in separate parts of cross-section
• takes advantage of the properties of more than one fiber
• can then split/separate further