3 - Skin reconstruction & dermal equivalents Flashcards
Epithelial layer
- Keratinocytes (90%)
- Melanocytes (pigmentation)
- Immune cells
Dermal layer
- Fibroblasts (matrix)
- Endothelial cells (vascular supply)
- Hair follicle cells
Merkel’s cells
Touch
Hair receptor
Movement
Pacinian corpuscles
Rapid vibration
Ruffini’s corpuscles
Lateral stretch
Meissner’s corpuscles
Vibration
Importance of treating skin injuries
- Sepsis and death
- Delayed healing increases scar risk
- Infection leads to delay in healing
- Oedema increases risk of infection
- Inflammation increases oedema
Response to injury
- Clotting
- Vascular response
- Inflammation
- Scar formation
- Epithelial healing
- Contraction
- Scar remodelling
Ctritical burn injury treatment factors
Depth and surface area
Epidermolysis Bullosa
- 40% die before adolescence
- Entire epidermis regenerated using transgenic stem cells
- Transgenic cells have selective advantage (don’t detach)
How many deaths from fire related burns each year worlidwide
~300,000
Wound debridement
- 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
Wound debridement using Rapid Evaporative Ionisation- Mass Spectrometry (REIMS)
- 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
Skin grafts
- 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
Xenografts
- From animals
- Usually not cultured
- Vigorous rejection, limited to temporary biological dressing
Allografts
- *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
Cell types and therapeutic approaches
- 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)
Cultured Epithelial Autograft (CEA) sheets
- 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
Time and scar risk
- 10 days to heal –> 4% scar risk
- > 21 days to heal –> 78% scar risk
- Early treatment decreases risk and level of scarring
Spray on skin (ReCell)
- 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)
Importance of ECM and dermal scaffold use
- Physical characteristics (strength and stress)
- Biological characteristics (secreted factors and glycosylation)
- Can affect cells and determine phenotype
Use of matrices
- 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
Integra
- Porous, biological collagen based matrix
- Biodegradable so can be left in wound
- Add integrae to wound then ReCell
Matriderm guided tissue regeneration and cell activation
- 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
Biodegradable Temporizing Matrix (BTM)
- 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
Bilayered replacements (Apligraf)
- 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
Examples of difficult to treat burn cases
- Deep, highly pigmented and vascularised scars
- Hands due to curves
- Joints
Laser scar amelioration
- 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
Adult multipotent stem cells
Hematopoietic stem cells
- fibrocytes
- Mesenchymal stem cells
- Adipose derived stem cells
Reprogrammed stem cells
- Somatic cell nuclear transfer
- Cell fusion
- Induced pluripotent stem cells
Possible functions of cultured MSC
- Immunomodulation
- Anti apoptosis
- Angiogenesis
- Support of growth and differentiation of stem and progenitor cells
- Anti scarring (anti fibrosis)
- Chemoattraction
Too much vs too little vascularisation
- Too much = scarring
- Too little = inefficient scar healing
3D bioprinting
- Drop-on-demand printhead
- Bioinks and cells suspended in activators in the printhead
- Printing layering of bioink and activator
Split Thickness Skin Graft (STSG)
- A graft that contains the epidermis and a portion of the dermis,
- Still widely used
