3 - Skin reconstruction & dermal equivalents

Question 1

Epithelial layer

Answer 1

• Keratinocytes (90%)
• Melanocytes (pigmentation)
• Immune cells

Question 2

Dermal layer

Answer 2

• Fibroblasts (matrix)
• Endothelial cells (vascular supply)
• Hair follicle cells

Question 3

Merkel’s cells

Answer 3

Touch

Question 4

Hair receptor

Answer 4

Movement

Question 5

Pacinian corpuscles

Answer 5

Rapid vibration

Question 6

Ruffini’s corpuscles

Answer 6

Lateral stretch

Question 7

Meissner’s corpuscles

Answer 7

Vibration

Question 8

Importance of treating skin injuries

Answer 8

• Sepsis and death
• Delayed healing increases scar risk
• Infection leads to delay in healing
• Oedema increases risk of infection
• Inflammation increases oedema

Question 9

Response to injury

Answer 9

1. Clotting
2. Vascular response
3. Inflammation
4. Scar formation
5. Epithelial healing
6. Contraction
7. Scar remodelling

Question 10

Ctritical burn injury treatment factors

Answer 10

Depth and surface area

Question 11

Epidermolysis Bullosa

Answer 11

• 40% die before adolescence
• Entire epidermis regenerated using transgenic stem cells
• Transgenic cells have selective advantage (don’t detach)

Question 12

How many deaths from fire related burns each year worlidwide

Answer 12

~300,000

Question 13

Wound debridement

Answer 13

• Removal of dead tissue
• Cut by surgeon or use of bromelain (pineapple enzymes)
• Too much tissue cut off leads to slow healing, too little leads to infection

Question 14

Wound debridement using Rapid Evaporative Ionisation- Mass Spectrometry (REIMS)

Answer 14

• Diathermy knife used to cut necrotic tissue
• Smoke extracted and sent to mass spectrometer
• Profile of healthy and dead tissue is different, can help guide surgeon in what to cut out and what to leave

Question 15

Skin grafts

Answer 15

• Graft taken from patient’s healthy skin
• Skin is meshed to cover large wound
• Limited size (1:3 expansion)
• Mesh pattern of healed skin
• Donor site morbidity

Question 16

Xenografts

Answer 16

• From animals
• Usually not cultured
• Vigorous rejection, limited to temporary biological dressing

Question 17

Allografts

Answer 17

• *From humans, typically cadaveric or neonatal donors
• May or may not be cultured
• Eventual rejection due to HLA-DR antigens
• Immunosuppressive therapy must be given to prevent early rejection
• Risk of cross-contamination

Question 18

Cell types and therapeutic approaches

Answer 18

• Keratinocytes (epithelial cover)
• Fibroblasts (dermal matrix)
• Melanocytes (appropriate pigmentation)
• Endothelial cells (revascularisation)
• Cultured or non-cultured (time to application)
• Combined therapies (with dermal matrices/scaffolds)

Question 19

Cultured Epithelial Autograft (CEA) sheets

Answer 19

• Cultured using a large, full-thickness biopsy
• Cultured as confluent sheets in the laboratory
• Generally 3 to 10 cell layers thick
• Clipped to a petrolatum gauze backing

Question 20

Time and scar risk

Answer 20

• 10 days to heal –> 4% scar risk
• > 21 days to heal –> 78% scar risk
• Early treatment decreases risk and level of scarring

Question 21

Spray on skin (ReCell)

Answer 21

• Stamp size piece of skin taken
• Subject skin piece to enzymatic digestion to break down cells to individual cell suspension
• Sprayed onto wound (greater coverage)

Question 22

Importance of ECM and dermal scaffold use

Answer 22

• Physical characteristics (strength and stress)
• Biological characteristics (secreted factors and glycosylation)
• Can affect cells and determine phenotype

Question 23

Use of matrices

Answer 23

• With deep/extensive burns, rapid replacement of dermal template can enhance recovery
• Limited by angiogenesis into new template to achieve epidermal coverage
• E.g. integra

Question 24

Integra

Answer 24

• Porous, biological collagen based matrix
• Biodegradable so can be left in wound
• Add integrae to wound then ReCell

Question 25

Matriderm guided tissue regeneration and cell activation

Answer 25

• Invading cells use the fibers as guiding ridges for structured healing
• The cells recognise binding sites on the native collagen fiber and get activated by binding to them
• Activated fibroblasts start to produce the body’s own collagen

Question 26

Biodegradable Temporizing Matrix (BTM)

Answer 26

• Porous, synthetic polymer
• Top layer non-biodegradable, bottom layer biodegradable
• BTM applied to wound bed, limiting water loss
• After 2-3 weeks, cells have integrated and blood vessels have formed
• Once integrated, sealing membrane removed

Question 27

Bilayered replacements (Apligraf)

Answer 27

• Cultured allogeneic graft that contains both epidermal and dermal layers
• Contains all layers of skin
• Does not contain blood vessels, hair follicles, or sweat glands or
  other cell types such as Langerhans’ cells, melanocytes, macrophages, or lymphocytes

Question 28

Examples of difficult to treat burn cases

Answer 28

• Deep, highly pigmented and vascularised scars
• Hands due to curves
• Joints

Question 29

Laser scar amelioration

Answer 29

• Adjunct therapy
• Laser burns small holes in skin (re-injuring)
• Resulting re healing of the scar with less inflammation and stress improves scar outcome
• Also affacts vascularisation

Question 30

Adult multipotent stem cells

Answer 30

Hematopoietic stem cells
- fibrocytes
- Mesenchymal stem cells
- Adipose derived stem cells

Question 31

Reprogrammed stem cells

Answer 31

• Somatic cell nuclear transfer
• Cell fusion
• Induced pluripotent stem cells

Question 32

Possible functions of cultured MSC

Answer 32

• Immunomodulation
• Anti apoptosis
• Angiogenesis
• Support of growth and differentiation of stem and progenitor cells
• Anti scarring (anti fibrosis)
• Chemoattraction

Question 33

Too much vs too little vascularisation

Answer 33

• Too much = scarring
• Too little = inefficient scar healing

Question 34

3D bioprinting

Answer 34

• Drop-on-demand printhead
• Bioinks and cells suspended in activators in the printhead
• Printing layering of bioink and activator

Question 35

Split Thickness Skin Graft (STSG)

Answer 35

• A graft that contains the epidermis and a portion of the dermis,
• Still widely used