KEY NOTES CHAPTER 1: GENERAL PRINCIPLES (F) Transplantation, tissue engineering, alloplastic implantation. Flashcards
What is transplantation?
Movement of tissue from one body location to another - Orthotopic → transplant to an anatomically similar site - Heterotopic → different site
What are the different types of transplants?
Autograft - from 1 location to another within the same individual o Includes all flaps and grafts o Flaps have some intrinsic blood supply grafts don’t Isograft - between genetically identical twins Allograft (Homograft) between same species Xenograft (Heterografts) - between different species
What is the 2nd set phenomenon?
Gibson and Medawar (1940s). First set reaction → when skin allograft is applied to an individual for the first time. Second set phenomenon → accelerated rejection of allogenic tissue due to presence of humoral antibodies from prior exposure to the same allogenic source.
Allograft - 1st and 2nd set phenomena
First set o Days 1–3 allograft behaves as autograft → develop dilated capillaries with no blood flow o Days 4–7 grafts infiltrated by leucocytes and thrombi, punctate haemorrhages appear within vessels o Days 7–8 blood flow ceases and skin graft necrose Second set → occurs if individual has already been exposed to same allograft material o Immediate → hyperacute rejection, graft never undergoes any revascularisation → ‘white graft’
What happens when grafts are rejected?
Rejection occurs when the host immune system recognizes foreign antigens - Direct destruction – Cell mediated → CD4 and CD8 cytotoxic T cells cause damage to the graft - Indirect destruction – Antibody mediated → humoral system (stimulated B cells) produce antibody that binds with antigen and stimulates tissue destruction via complement system
What are the different types of immunosuppression?
Non-specific - Radiation (graft) ↓ antigenicity- Drugs - Biological agents Specific - monoclonal anti T- lymphocyte antibodies
Another classification of immunosuppressive drugs
Antibody mediated (biologic) 1. Antilymphocyte - antilymphocyte Ig, antithymocyte Ig, OKT3 2. Anti IL2 Non-biologic 1. Calcineurin inhibitors - cyclosporin, tacrolimus 2. Antiproliferative agents - azathioprine 3. Corticosteroids 4. Macrolide Inhibitors - sirolimus
What are the ideal properties of an implant?
- Impervious to tissue fluid - Chemically inert - Non irritant (causing no inflammatory or foreign body reaction) - Noncarcinogenic - Nonallergenic - Resistant to mechanical strains - Capable of being fabricated to the desired form - Sterilisable - Readily available, cheap - Radiolucent - Resistant to reabsorption, corrosion or deformation - Non-supportive of growth of micro-organisms
How do you classify them?
Liquids → silicone , collagen preparations, hyaluronic acid preparations Solids → metals, polymers, ceramics
What is silicone?
- Silicon = element, silica = silicone oxide (sand) - Silicone = polydimethyl siloxane - interlinked silicon and oxygen molecules with methyl, vinyl or phenol side groups - Short polymer chains → viscous liquid, long chains → firmer cohesive gel - Cross linking of chains → solid silicone. - biologically inert but elicits a mild foreign body reaction → capsule formation - Synovitis can occur in silicone joint arthroplasty
What collagen preps do you know?
Zyderm 1 o sterilised fibrillar bovine collagen o Used to inject fine superficial wrinkles Zyderm 2 o coarser wrinkles. Both Zyderms will ↓ as lose water component so over do by 30% initially. Zyplast o Cross linked collagen with glutaraldehyde o Firmer than Zyderm 1 or 2 o Treat deep dermal defects and coarse wrinkles, little resorption so DON’T overcorrect
What hyaluronic acid preps do you know?
Hyaluronic Acid Preparations - Restylane and Perlane (Nufill!) - Synthetic hyaluronic acid - Absorption 20-50% of original volume by 6 months - Injected superficially to treat wrinkles or ↑ lip definition - HIV lipoatrophy
What metals are used ?
Stainless Steel - alloy of iron, chromium and nickel - corrosion, implant failure, galvanic currents Vittalium - alloy of chromium, cobalt and molybdenum - higher tensile strength than titanium Titanium - pure metal, more malleable, less corrosion - less artefact on MRI CT Gold - resistant to corrosion, low tensile strength - eyelid weight to facilitate eye closure in facial palsy
What polymers are there?
Polyurethane - Produces an intense foreign body reaction then tissue adhesion - Breast implants covered with polyurethane foam have a low rate of capsule contracture, but breakdown products → toluene-diamine dimers → ?carcinogenesis → implants withdrawn Fluorocarbons - Gortex polytetrafluoroethylene (PTFE) Polyethylene - Low density - High density → Medpore (facial augment) Methylmethacrylate - bone cement Cyanoacrylate - Superglue
What ceramics are available?
Hydroxyapatite - major inorganic constituent of bone (the major organic constituent is osteoid) - in corals, available in block, granule or cement - osseoconductive → allows creeping substitution - not osseoinductive or osteogenic - calvarial remodelling (inlay and onlay), facial augmentation - Inlay = replacement of full thickness defect - Onlay = outer table replacement Other ceramics - Calcium sulphate (plaster of Paris) - Calcium phosphate
