Skin Banking – short notes

Need for skin banking –

Large burn areas.

Donor sites not available.

Homografts can work as temporary dressing.

 

Methods of skin storage –

1. Refrigeration
2. Deep freezing or cryopreservation

 

Refrigeration –

Most common method of storage.

Skin kept at 4 ° C.

Preservation maximum up to 3 weeks.

But, best used within 1 week.

Cryoprotective medium can prolong life of the grafts. Eg. –

Dilute homologus serum,

Tissue culture medium,

Balanced salt solution

Grafts is kept in a sterile bottle after wrapping in a Vaseline gauze (epidermal side on the gauze) followed by saline soaked gauze.

 

Deep freezing or cryopreservation

Cooling of tissue to ultra-low temperature.

Cryoprotective agents are used.

Storage temperature can be -80°C to -196°C

Stored in deep freezer or liquid nitrogen

Liquid nitrogen is used for cooling.

Cryoprotective agents are used to protect cells from disintegrating.

Cryoprotective agents used are –

1. Glycerol,
2. Ethylene glycol,
3. Dimethylsulfoxide (DMS)

Grafts stored at -80°C can be stored – for up to 6 months

Grafts stored at -196°C can be stored – for indefinite period.

 

Freeze drying or lyophilization

Grafts is rapidly cooled and then

Water is removed by sublimation

Tissue is then vacuum sealed

Sterilized by gamma radiation

Stored at room temperature

Tissue is non-viable and used as biological dressing

 

Cadaveric skin banking

SSG harvested from refrigerated cadavers within 24 hours of death.

Consent is taken

Age limit – 12-60 yrs

No h/o – malignancy, hepatitis, jaundice, skin disease or veneral disease

Following markers should be negative – HIV, HBsAg, HCV, VDRL

Skin harvested using dermatome

Strips between 0.25mm – 0.35mm is harvested.

Skin tissue sample sent for streptococcus, pseudomonas, staphylococcus culture

Graft with more than 10 organism is discarded.

 

Cryo-preservation :

Harvested grafts is spread on meshed Vaseline gauze with epidermal side on gauze.

Rolled up and then immediately immersed in sterile solution of 15% glycerol and RL at 4°C for 2-4 hours

(Other cryopreservative used are – dimethylsulphoxide, ethanediol, propane-diol)

After 4 hours – solution is poured off and skin graft strips transferred to heat stable polyester plastic envelope.

It is then properly labelled with patient name and size of grafts.

If grafts are planned to be used within days then its stored @ 4°C in refrigerator.

Otherwise, it is deep freezed.

Freezing can be –

Controlled – with gradual cooling 1°C/ min to reach  -80°C to -100°C

Direct – where grafts is directly kept in liquid nitrogen vapor (with temperature reaching -100°C) or directly to refrigerator @ -70°C

Controlled cooling is better than direct cooling, with better skin cell viability.

 

Increasing the cell viability –

After harvest, skin cell viability decreases due to –

1. Lack of nitrogen and oxygen
2. Build of toxic material
3. Generation of free radicals causing lipid peroxidation
4. Osmotic changes
5. Uncoupling of biological pathways

 

1. 1. Addition of 10-35% concentration of homologus serum –
      1. Provides nutrition
      2. Dilutes and buffers acid produced during metabolism
   2. Tissue culture medium –
      1. Provides nutrition
      2. Neutralizes harmful metabolites
   3. Reducing temperature –
      1. At 0°C oxygen requirement is zero.
   4. Balanced salt solution
   5. University of Wisconsin solution

 

Rewarming

For use of stored grafts, it is rewarmed

Rewarming is done @ 50-70°C per minute

Microwave @ lowest setting

Hot saline bath @ 42°C

After rewarming – graft is to be used within 2 hours

Skin stored in flat pockets are rewarmed faster than ones stored in cylinder.

Faster rewarming is better.

 

[During preservation slower cooling is better]

[During rewarming faster is better]

 

Future –

Improving the homograft “take”

1. Removing the epidermis and covering with keratinocyte culture
2. Immunosuppression – cyclosporin A has good safety profile (Given for 120 days can keep grafts alive for 2 yrs)