Lectures Flashcards
(126 cards)
1
Q
Describe biocompability
A
Between material and body; a measure on how well the material can integrate. Can’t give any harming effects. Also about the ability to perform its desired function.
2
Q
What is the usage of biomaterials in the body? (5 ex)
A
- Internal fracture fixation
- Joint replacements
- Bone fillers
- Scaffolds
- Carriers for drug delivery
3
Q
What is the structure of polymers?
A
Monomers linked together by primary covalent bonds
4
Q
Attractive features of polymers?
A
- Greatest versability in chemistry and processing
- Lighter than metals
- Used as composite materials with ceramics
5
Q
Requirements for polymers?
A
- Chemical biocompability
- Sterilization stability
- Low friction coefficient
- Wear resistant
- Creep resistance
6
Q
Usage for polymers?
A
- Total joint replacements
- Fixation parts for bone fracture
- Tissue engineering (bone, cartilage)
- Local drug delivery (coatings, micro-/nanospheres- drug carriage)
- Bone filler/cement
7
Q
Define biocompability:
A
The ability of a biomaterial to perform its desired function, without eliciting any undesirable local or systemic effects.
8
Q
Steps to assure biocompability:
A
Research on biomaterials => Engineering to develop a medical device => Preclinical and clinical testing => Regulatory approval => Commercialization and clinical application
9
Q
Name different available “off the shelf”-materials (9 st)
A
- Fe (Iron)
- Au (gold)
- Ag (Silver)
- Pt (Platinum)
- Steel (Nickel, Vanadium)
- CoCrMo (Cobalt Chromium Molybdenum)
- Stainless steel
- PMMA (Poly(methyl methacrylate))
- Ti (Titanium) alloys
10
Q
Name different “designed” biomaterials.
A
- Polymers (acrylic cements, silicones)
- UHMWPE (Ultra-high-molecular-weight polyethylene)
- Polylactic acid
- Hydroxyapatite, bioglass
- Porous Ta (trabecular metal)
- Oxidized Zr-Nb (Oxinium)
11
Q
Describe the first generation of biomaterials
A
Goal: Bioinertness
Minimal reactions/interaction
12
Q
Describe the second generation of biomaterials
A
Goal: Bioactivity
Resorbable materials; controlled reaction with the physiological environment (e.g bone bonding, drug release)
13
Q
Describe the third generation of biomaterials
A
Goal: Regenerate functional tissue
Biointeractive, integrative, resorbable materials; stimulate specific cell responses (e.g proliferation, differentiation, ECM production, organization)
14
Q
What are the concerns about using polymers?
A
- Long term chemical biocompability
- Wear debris (osteolysis)
15
Q
What is osteolysis?
A
the pathological destruction or disappearance of bone tissue.
16
Q
Describe the usage of PMMA:
A
- Bone filler/cement
- Immediate fixation of a total joint implant within the medullary canal
- Minimizes the need for perfect fit between bone and implant
- Used for patients with poor bone cement
17
Q
Describe the liquid chemical composition of PMMA bone cement:
A
- Monomer (methyl methacrylate)
- Curing accelerator (N, N-dimethyl-p-toluidine)
- Polymerization inhibitor (hydroquinone)
18
Q
Describe the solid chemical composition of PMMA bone cement:
A
- PMMA powder
- Initiator (benzoyl peroxide)
- Radio-opaque additive (BaSO_4)
19
Q
What are the sideeffects of PMMA?
A
- Exothermic in-situ polymerization (80 - 124 degrees celsius) - PMMA particle size, polumer/monomer ratio
- Produces debris through fatique and biological processes as osteolysis (bone loss) and third-body wear of the acetabular cup and/or femoral head.
- Extra interface (bone-cement-implant), reduce implant life span by loosening.
Implant may be hard to remove in case of revision surgery
20
Q
What is an alternative implant fixation instead of PMMA?
A
Osseointegration
21
Q
How is UHMWPE used in orthopedics?
A
- Bearing material in Total Joint Replacement
- Hip, knee, shoulder, wrist, finger, toe joints
22
Q
What is the physiological role of cartilage?
A
Low-friction bearing surface of the articular joints (hip, knee, shoulder)
23
Q
What does articular cartilage mean?
A
Articular cartilage is the smooth, white tissue that covers the ends of bones where they come together to form joints.
24
Q
What does hyaline cartilage mean?
A
a translucent bluish-white type of cartilage present in the joints, the respiratory tract, and the immature skeleton.
25
What are the components of cartilage?
- Extracellular matrix: proteoglycans, collagen
- Cells: chondocytes
- Water: 60-80 %
26
What is the role for polymeric biomaterials in tissue engineering?
- Temporary support for cellular infiltration and growth
| - Carrier for the release of bioactives in a controlled manner (doses and kinetics)
27
What are the pros and cons of synthetic polymers?
+ Good processing characteristics
+ Off-the-shelf availability
+ Reproducable mechanical and physical properties
- Long-term biocompability issues (persistent inflammatory reactions, toxic/acid degradation products, not fully integrated in the host tissue)
- Not sufficient mechanical integrity (collapse of scaffolds)
28
What are the pros and cons of natural polymers?
+ Chemically biocompatible
+ Support cell viability and tissue formation to various degrees
- Potential risk in transmitting animal-originated pathogens
- Difficulty in processing
- Poor load bearing properties
- Variable physical and mechanical properties
29
What are the structural components of bone tissue?
- Collagen matrix
- Hydroxyapatite crystals
- Hierarchical structure
30
What are the cellular components of bone?
- Osteoblasts: secrets the substance of bone
- Osteoclasts: a large multinucleate bone cell which absorbs bone tissue during growth and healing.
- Osteocytes: formed when an osteoblast becomes embedded in the material it has secreted.
31
What are the attractive properties of ceramic biomaterials?
- Dense and hard materials (scratch resistant)
- Ability to be polished to an ultra smooth finish
- Wear resistance and low friction
- Inert/bioactive
32
What are the limitations of ceramic biomaterials?
- Brittle
- Low tensile and bending strength
- Low fracture strength
- Difficult processing control
33
Name some applications of ceramic biomaterials:
- Total joint replacements (bearing surfaces)
- Coatings for implant fixation
- Bone filler
- Vehicles for drug delivery
34
What are the applications for aluminium?
- Total hip replacements (THR)
| - Total knee replacements (TKR)
35
Name an alternative material to aluminia:
Zirconia (ZrO_2)
36
What advantages do Zirconia have compared to Aluminia?
- Lower young's modulus
- Lower wear rates (grain size, roughness, residual compressive stresses)
- Increased fracture toughness
37
Bioactive ceramics: Name two Ca-based cheramics:
- Ca_3 (PO_4)_2, Tricalcium phosphates (TCP)
| - Ca_10 (PO_4)_6(OH)_2, Hydroxyapatite (HA, OHAp)
38
Name some applications of bioactive ceramics:
- Synthetic bone substitutes (bulk)
- Coatings on metallic devices - improved fixation
- Composites with bioglass, polymers
39
What makes metals unique?
- High stiffness
- High strength (similar in tension/compression)
- High fracture toughness
- Low strength/weight ratio
- Low corrosion resistance
40
Name some metals used in Biomaterials
- Stainless steels
- Cobalt based alloys
- Titanium (Ti) & its alloys
- Porous Tantalum (Tu)
- Zirconium-Niobium (Zr-Nb)
- (Magnesium)
- (Iron)
() = Degradable metals (under development)
41
What are the required combination of properties for metallic biomaterials?
- Chemical biocompability
- Corrosion resistance
- Yield and ultimate strength
- (Low) young's modulus
- Fatique strength
- Ductility
- Wear resistance
- Manufacturing - high quality at low cost
42
What does osteopenia mean?
Reduction in bone density as a consequence of removal of normal stress from the bone by an implant
43
Describe the implant associated infection regarding Biofilm:
- Biofilm forms within hours following implantation
| - Requires > 1000x normal antiobiotic dose => Impossible to treat by systemic antibiotic therapy
44
Name some advantages with Porous Tantalum:
- Minimum tissue response
- High density (166 g/cm^3) - good X-ray imaging
- High E-modulus (190 GPa)
- Ability to form it into porous forms
45
Name applications of Porous Tantalum:
- In clinical use since 1995
- Backing of acetabular cups
- Tibial knee components
- Patella components
- Glenoid fixation
46
Name some properties about Oxidized zirconium - niobium alloy (Oxinium):
- Zr is a chemically biocompatible metal
- Zr-2.5Nb alloy has improved mechanical properties
- Heating in air at 535 celsius for 3-4 hours => oxide layer of about 5 µm thickness
- Scratch resistant
47
Name two applications of Oxidized zirconium - niobium alloy (Oxinium):
- Femoral head prostheses
| - Femoral knee prostheses
48
What are the advantages of using Mg alloys as a degradable metallic biomaterial?
- Attractive mechanical properties (better strength than polymers, better fatique than ceramics, closer E to bone than other metallic materials)
- Biodegradable under physiological conditions
- Non-toxic degradation products
- Light weight
49
Name some unsolved issues with Mg alloys which contributes to it not yet being in clinical use:
- Uncontrolled and high degradation rates
- Biocompability of alloying elements and of degradation products
- Mechanical integrity during biodegradation
50
What are the possible physiological effects of corrosion?
- Release of magnesium ions, Mg^2+
- Local increase in pH
- Hydrogen evolution
- Too high corrosion rates
51
Titanium and its alloys: How is titanium used in bone conduction hearing aids?
They are anchored with a Ti device that connects to the middle ear
52
Titanium and its alloys: What are Ti pegs and Ti grid implants used for?
Ti pegs: Used to attach false eyes
| Ti grid implants: Provide fixation for interorbital fractures
53
Titanium and its alloys: What are maxillofacial prosthesis used for?
Made of Ti-Ti alloys, implants stabilizes soft tissue prosthesis.
54
Titanium and its alloys: Describe expandable rib cages:
Made of Ti, allows a child's cage to 'grow' with the patient
55
Titanium and its alloys: Describe spinal fusion cages implants:
One of the most frequent uses of Ti. Used for correction parts and fixation
56
Titanium and its alloys: Which is the most common use of Ti?
```
Most common use is in Hip replacements
Other:
Spinal fusion cages
Shoulder and elbow joint implants
Toe and finger implants
```
57
Titanium and its alloys: How is Ti plates and meshes used?
Used in cranioplasticy and neurosurgery to speed up operations and recovery and reduce chances of infection
58
Titanium and its alloys: Describe Ti dental implants:
They act as artificial roots, providing a secure base of a full arch of teeth or a single tooth: orthodontic braces of Ti are stronger, lighter and more biocompatible than steel.
59
Titanium and its alloys: Describe the use of Ti in the heart:
Ti heart valves compete with those made of tissue; pacemaker cases and vascular access ports are Ti
60
Titanium and its alloys: Describe how TiNi shape memory alloys are used:
Used in medication mini-pumps that flex due to an electric current that creates a heating/cooling cycle that changes shape of chamber
61
Titanium and its alloys: Describe the use of urethal stents
Ti is used for urethral stents to treat urethral structures
62
Titanium and its alloys: Describe the use of tibia nails:
Tibia nails made of Ti are used for reinforcement in lower leg fractures
63
Titanium and its alloys: Describe the use of Ti bone plates and mesh:
Reconstructive Ti bone plates and mesh support broken bones
64
Titanium and its alloys: Name a few Ti fixation devices:
- Bone screws
- Plates
- Rods
- Hooks
- Cable
- Staples
65
Titanium and its alloys: Name some instruments made of Ti:
- Surgical devices
- Dental drills
- Laser electrodes
- Marker bands
- Optical procedure devices
- Vena capa clip
- Needles
- Staples
- Blades and forcepts
66
Describe the properties regarding wear resistance of Ti biomaterials:
- When compared to CoCr alloys and stainless steel or ceramic materials, Ti and its alloys are not appropriate for bearing applications due to low wear resistance.
- Wear resistance of Ti alloys can be improved by suitable surface modification (coating) techniques.
67
Describe Ti-Ni (Nitinol) alloys:
- Most attractive shape memory alloy (SMA) for biomedical applications because of its unique mechanical characteristics, such as superelasticity (SE), shape memory effect (SME), good resistance to fatique and wear and relatively good biocompability.
68
Describe the Shape Memory Effect (SME):
SME: Restoring the original shape of a plastically deformed sample by heating it up. This is a result of a crystalline phase change known as a thermoelastic martensitic transformation
69
Describe the thermoelastic martensitic transformation for an SMA (shape memory alloy):
- A SMA undergoes a martensitic transformation when it is cooled below a martensite start point M_s
- The transformation is completed at a lower martensite finish temperature, M_f
- When martensite is deformed below M_f, it undergoes a strain which is completely recoverable upon heating.
- Shape recovery begins at an austerite start temperature A_s, and is completed at a higher austerite finish temp A_f (Called thermal shape memory effect)
- SME can be devided into one-way or two-way.
70
Name some applications of Nitinol in orthopedics and medical instruments:
Orthopedics: A wide variety of bone plates, U-, Omega- and spiral shaped wires, rings, tubings, etc
Medical instruments: Spatulas, forcepts, scissors on wires, laparoscopy tools
71
Orthopedic materials: Name the advantages and disadvantages of Stainless steel:
+ Strength
+ Ease of manufacturing
+ Availability
+ Cost
- Propensity to corrosion
- High E modulus
72
Orthopedic materials: Name the advantages and disadvantages of Co-Cr based alloys:
+ Strength
+ Relative wear resistant
+ Fatique strength
- High E modulus
73
Orthopedic materials: Name the advantages and disadvantages of Ti and its alloys:
+ Strength
+ Low E modulus
+ Corrosion resistance
- Poor wear resistance
74
Orthopedic materials: Name the advantages and disadvantages of Ta porous coating:
+ Excellent bone in-growth
+ Corrosion resistance
- High manufacturing cost
75
Orthopedic materials: Name the advantages and disadvantages of Oxinium:
+ Scratch resistance
+ Low E modulus
+ Corrosion resistance
- High manufacturing cost
- Fracture?
76
Name the immune reactions to biomaterials:
- Foreign body response
- Cells
- Inflammatory mediators
- Biomaterial characteristics
Incision => Tissue removal => Insertion of implant
Result: Bleeding, tissue damage. Response of body is wound heeling process. Complication: non-removable foreign body
77
Name the two "sides" of the immune system:
Innate immunity and adaptive immunity
78
Name the properties of the innate immune system:
- Immidiate protection
- Primitive/ evolutionary old
- Not adaptive
- No memory
Is the initial response to biomaterials
79
Name the properties of the adaptive immune system:
- Repeated protection
- Adapting to challenge: recognition
- Antibodies, T-cells
- Memory
80
Which are the major players in foreign body response (FBR):
- Coagulation cascade: fibrin deposition
- Blood platelets: activate, wound closing, signalling
- Complement pathway: Cover foreing material with C3b opsonin. Recruit leucocytes
- Immune cells
81
What are polymorphonuclear leucocytes?
Agressive phagocytes: cells that ingest harmfull foreign particles
82
What are mononuclear cells/macrophages?
Garbage collectors
83
Name the signalling molecules:
Cytokines and chemokines
84
Name the characteristics influencing FBR (foreign body response):
- Site/tissue of implantation
- Physio-chemical composition of biomaterial surface
- Condition of tissue: primary or secondary implantation
- Presence of bacteria or bacterial components
85
Describe the procedure of initial fixation (first months) of an implant:
- Cementing with PMMA cement
- Porous implant surface for bone ingrowth
- Stimulating bone opposition with bioactive coatings such as hydroxyapatite
86
Describe the process om prosthetic hip loosening:
- After 15 years 3-10 % aseptic loosening:
Inflammation, reactivation FBR => Recruitment/activation of osteoclasts/osteoblasts => Bone resorbtion => Loosening
87
Describe infection vs inflammation
Infection: caused by micro-organisms such as bacteria, yeast, fungi, parasites, viruses. Infection will provoke an inflammatory response
Inflammation also from other stimuli: Wounds, foreign body materials, dead cells by own body
88
Site of application: Describe External:
- No surgical wound, port d' entrée
Ex:
- Urinary catheters
- Endotracheal tubes
89
Site of application: Describe Transcutaneous
```
- Surgical wound and port d'entrée
Ex:
- Intravenous catheters, shunts
- CAPD catheters
- External fixation devices
```
90
Site of application: Describe Implanted:
```
Surgical wound, no port d'entrée
Ex:
- Prosthetic joints like hips and knees
- Prostethic heart valves, prosthetic hearts
- Pacemakers
- Hydrocephalus shunts
```
91
Prevention: Antiseptic coatings should...
- Prevent adherence/kill adherent micro-organisms
- Be non-toxic
- Allow proper tissue regeneration/ingrowth
- Have activity for a relevant time period
- Implants: Prevent colonization during/shortly after surgery
- External and transcutaneous devices: Prevent colonization during application period
- Not select for resistant micro-organisms
92
What is the function of cartilage?
Painfree movements and shock absorbing
93
What does arthroplasty mean?
Human joint replacement by an artificial joint
94
Name the most frequent location of arthrotic joints:
- Cervical spine
- Fingers
- Lumbal spine
- Knee joint
- Hip joint
- Shoulder joint
- Ankle joint
- Foot joints and great toe
- Elbow joint
- Wrist joint
95
Describe Wolffs Law: Stress shielding
- Wolffs law: Bone will remodel in response to the load
- With a prosthesis the bone has to share the load, therefore stress shielding of bone by prosthesis
- Consequence: progressive periprosthetic bone loss, reduction of bone, disuse osteoporosis
- Progressive femoral bone loss induces stem loosening and migration
- Distal fixation and prox loosening of prosthesis promotes fracture prosthesis stem and bone
- Stress shielding induces bad quality bone for revision
96
Describe cemented and cementless fixation of total hip arthroplasty to bone:
Cemented:
- With bone cement
- Chromium cobalt alloy
- Smooth finished surface
Cementless:
- Press fit
- Biological bone ingrowth
- Osseointegration
- Rough surface, texture, coating
- Titanium, Ti-6AI-4V, Ti-6AI-7Nb
- Tantalum
97
Name an alternative to cemented or cementless fixation of total hip arthroplasty:
Powder coatings, with titanium or hydroxyapatite.
98
Describe the bone preparation for bone cement:
- High pressure puls lavage for cleaning bone
- Good cement penetration into bone
- Improved micro interlock, interdigitation
- Increasing cement strength
- Reducing loosening implant
- Reduced risk fat embolism
99
Why do we need bone and cartilage replacement therapies?
Need for replacement of tissue/organs at various sites of the body.
100
Name different tissue/organs that could need replacement therapy:
- Lenses/retina
- Brains
- Cochlear implants/external ear
- Heart/heart valves
- Blood vessels
- Hand
- Nerves
- Skin
- Hip
- Liver
- Bone
- Finger joints
- Bladder
- Pancreas
- Breast implants
101
Where is bone graft usually harvested from?
The hip bone
102
What are the drawbacks to current bone repair approaches when it comes to autologous bone graft (from same individual):
- 2nd site morbidity
- Increased patient recovery time
- Limited availability
- Cost
103
What are the drawbacks to current bone repair approaches when it comes to Allogeneic bone graft (from separate individual):
- Increased risk of infection
| - Poorer integration
104
What is the definition of tissue engineering?
The development of biological substitutes for implantation into the body and/or the fostering of tissue regeneration and remodelling, with the purpose being to replace, repair, maintain, or enhance function.
105
Describe scaffolding in people:
- Allow cell attachment and migration
- Deliver and retain cells and biochemical factors
- Enable diffusion of vital cell nutrients and expressed products
- Exert certain mechanical and biological influences to modify the behavior of the cell phase
- Provide a 3D framework
106
What are the considerations that need to be done when it comes to scaffolding?
- Biologically active/inert
- Endogenous/exogenous
- Biodegradable/Permanent
- Degradation rate
- Biocompability
- Pore size
- Surface treatment
- Growth factors
- Nutrient delivery/waste removal
107
Compare scaffolding materials from natural and synthetic/metal materials:
Natural:
- Biocompatible
- Biodegradable
- Risk of disease transmission
Synthetic/metal:
- No risk of disease transmission
- Chemical and mechanical properties can be controlled very well.
108
Name the combinations of mechanical stresses that are developed during joint motion:
- Cell/tissue deformation
- Compressive and shear force
- Fluid flow
- Changes in hydrostatic pressure
109
What is the purpose of bioreactors?
Bioreactors aim to replicate the in vivo physiological environment via application of mechanical stimuli in vitro
110
Name the tissues of the musculoskeletal system (5 st):
- Bone
- Cartilage
- Tendon
- Ligament
- Muscle
111
What is connective tissue?
Tissues of the body with varying functions, typically they support, bind, transport, insulate, or provide storage. They are characterized by widely spaced cells.
112
Name the different types of bone:
- Long bones
- Short bones
- Flat bones
- Irregular bones
- Sesamoid bones (embedded in tendon/muscle)
113
What is the composition of bone?
- Organic component: Primarily collagen and cells
| - Inorganic component: Primarily calcium phosphate in the form of hydroxyapatite
114
What kind of cells are present in bone?
- Osteoblasts: cells with a single nucleus that synthesize bone
- Osteoclasts: type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodelling of bones
- Osteocytes: a cell that lies within the substance of fully formed bone
- Chondrocytes: the only cells found in healthy cartilage. They produce and maintain the cartilaginous matrix
- Bone marrow cells
115
What is the different roles of bone in the body?
- Protection
- Movement/articulation
- Shape
- Mineral storage
- Acid-base balance/homeostasis
- Production of blood/cells
- Detoxification
- Sound conduction
116
Describe bone formation by intramembranous ossification:
1. Increased vascularity of tissue
2. Active proliferation of mesenchymal cells (The mesenchymal cells give rise to osteogenic cells, which develop into osteoblasts)
3. Osteoblasts begin to lay down osteoid (Osteoid is the organic part of bone without the inorganic constituent)
4. Osteoblasts either retreat or become entrapped as osteocytes in the osteoid
5. The osteoid calcifies to form spicules of spongey bone (The spicules unite to form trabeculae. The inorganic salts carried in by the blood vessels supposedly bring about calcification. The salts are deposited in an orderly fashion as fine crystals (hydroxyapatite crystals) intimately associated with the collagenous fibers. These crystals are only visible with the electron microscope)
6. Bone remodelling occurs (Periosteum and compact bone are formed)
117
What are the current approaches to bone repair?
- Autografting (same individual): 80% success rate. Two surgeries. Pain, cost, infection.
- Allografting (different individual): Less successfull, possibly due to immunogenicity, Disease transmission
- Man made materials (plastics, ceramics, metals): High failure rate. No remodelling.
118
What are the prerequisites for successfull bone tissue engineering?
1. Sufficient number of cells with osteogenic capacity
2. An appropriate scaffold to seed the cells
3. Factors to stimulate osteogenic differentiation in vivo
4. Sufficient vascular supply
119
What is the problem of cartilage wound healing?
Cartilage has no bloodvessels
120
What is the functions of articular cartilage?
- Bear mechanical load
- Shock absorbtion
- Unique "friction and lubrication properties"
121
What is the composition of cartilage?
- Water (65-80%), important for mechanical properties
- Matrix (proteoglycan & collagen network)
- Chondrocytes (<5% volume), maintain matrix
122
Describe the function and properties of cartilage:
- Water can move freely through cartilage
- Upon deformation (mechanical load) => water is squeezed out
- Upon removal of loading => water attracted => proteoglycan
- Matrix strength, shape and elasticity => collagen
123
What is a stem cell?
A cell that has the ability to self replicate indefinitely, can give rise to many (all) different tissue types.
Pluropotency: Give rise to different new cells
Self-renewal: Give rise to a new version of same cell
124
What are embryonic stem cells?
Cells that can give rise to all the cells in the body
125
Describe the advantages and prerequisites for scaffold-free tissue engineering procedures:
Advantages:
- Cells implanted without scaffolds
- No adverse reactions to material or degradation products (immuno system)
Prerequisites:
- Load-bearing properties
- Mechanical stability
- Predictability of size and amount of tissue generated
126
Describe the advantages and prerequisites for cell-free tissue engineering procedures:
Advantages:
- No cell culture involved
- Off the shelf product
- Reduced infection risk
- Reduced cost
Prerequisites:
- Cells attracted from surrounding tissues
- Cells grow in material
- Material properties very important
