Tissue Engineering

biomaterial

any substance other than drugs, synthetic or natural, that can be used as a system or part of a system that treats, augments, or replaces any tissue, organ, or function of the body

biocompatibility

the ability of a material to perform with an appropriate host response in a specific application. no synthetic material is bioinert

ISO 10993

Which standard is used for the biological evaluation of medical devices?

medical device

any instrument, apparatus, implement, machine, appliance, implant, reagent for in vitro use, software, material or other similar or related article, intended by the manufacturer to be used, alone or in combination for a medical purpose

bioactive

elicits a specific biological response at the interface of the material that results in the formation of a bond between between tissues and the material

biodegradable

A biomaterial that degrades under physiological conditions, ideally degrading at the rate the tissue heals

bioresorbable

A material that will be completely broken down in time

simulated body fluid

SBF

in vitro

in the lab

in vivo

in the body

in silico

in the computer

half a day

How long does SBF take to make from scratch?

none

what cells does SBF contain?

5 mins

How long does SBF take to make from a tablet?

osteoconduction

ability of a material to support new bone formation

osteoinduction

ability of a material to stimulate cells to differentiate into osteoblasts, essential to the formation of bone at an implant site

osteointegration

direct contact at the microscopic level between living bone and implant

tissue engineering

an interdisciplinary field which applies the princpals of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function

cells, scaffold, environment

what are the three main components of tissue engineering?

replacement tissue, research models

what are the two main uses of tissue engineering?

cell isolation, seeding on a scaffold, bioreactor stimulation, implantation

what are the four steps of tissue engineering?

understand requirements, design scaffold, design bioreactor, select chemical signal, select cell source

what are the five steps of tissue modelling?

regenerative medicine

the process of repairing, replacing, or regenerating human cells, tissues or organs to restore or establish normal function.

tissue repair

healing in which lost tissue is replaced by a fibrous scar, which is produced from granulation tissue

congenital defects, burns, sports injuries, accidents, war injuries, cancer

what can tissue engineering be used in the repair of?

polymers, ceramics, metals, composites

what synthetic materials can scaffolds be made of?

autografts, allografts, xenografts, decellularised tissue

what natural materials can scaffolds be made of?

porous

what structure must scaffolds have?

decellularisation

a process used to disrupt and/or remove cells and cellular components from a biological material, while maintaining key structural and/or compositional properties of the extracellular matrix material

physical, chemical, enzymatic

what are the three types of methods for decellularisation?

freeze-thawing, supercritical CO2, hydrostatic pressure

what are the three types of physical decellularisation?

detergents, acids, bases

what are the three types of chemical decellularisation?

proteases, nucleases

what are the two types of enzymatic decellularisation?

RNase

ribonuclease

DNase

deoxyribonuclease

crushed or powdered

how can scaffolds be modified to fit into small or oddly shaped cavities?

nude mouse

animal genetically modified to have no hair and more skin

bioreactor

a dynamic cell environment that maintains cells/tissue in a controlled environment, while mimicking a living organism

temperature, pH, oxygen, mechanical stimulation, nutrients

What controls can be found in a bioreactor?

Spinner, rotating wall, perfusion

What are common types of mechanical stimulation in a bioreactor for bone TE?

Scaffolds suspended in medium, small turbulent flow

What does a spinner flask bioreactor look like?

scaffolds free to move, walls rotate causing scaffolds to be suspended

what does a rotating wall bioreactor look like?

fluid pumped through scaffold

what does a perfusion bioreactor look like?

patient’s own body, or animal

what is a natural bioreactor?

stem cell

undifferentiated cell that can replicate into different cell types with stimulation

embryonic stem cell

stem cells that can differentiate into anything, but has significant ethical concerns

adult stem cell

any non-embryonic stem cell, including placental and umbilical cells

totipotent

can differentiate into any type of cell

pluripotent

can differentiate into any type of stem cell except placental and embryonic

multipotent

can differentiate into tissue-specific cell types

any cells, proliferate continuously, easy to use

advantage of embryonic stem cells

requires destruction of an embryo

disadvantage of embryonic stem cells

harder to use, limited proliferation, switch off irrelevant DNA

disadvantages of adult stem cells

induced pluripotent stem cell

iPSCs

virus

what is used to make iPSCs?

potential carcinogen (teratoma), unwanted tissue growth

what is a risk of stem cells?

hematopoietic (blood) and stromal (bone)

what are the two types of bone marrow stem cells?

mesenchymal stem cells (MSCs)

what is another name for bone marrow stromal stem cells?

Very slowly - no vascularisation

How does cartilage heal?

It doesn’t - no innervation

How does cartilage sense pain

60-80% water

How does cartilage withstand compression and cyclical loading?

Through the water in the synovial fluid

How do chondrocytes get fed?

horizontally, to resist tension and shear

how are collagen fibres aligned at the outer edge of the cartilage, and why?

vertically, to resist compression

how are collagen fibres aligned at the inner edge of the cartilage, and why?

water, chondrocytes, tensile strength

what decreases as you get further into the cartilage?

compressive strength, proteoglycans (GAG)

what increases as you get further into cartilages?

osteoarthritis

erosion of cartilage due to loading, bone injury

rheumatoid arthritis

immune attack on the synovial membrane, reduced joint space

autologous chondrocyte implantation

ACI

microfracture

the process of clearing out damaged cartilage, punching spaced-out holes into the trabecular bone to cause blood and MSCs to invade

defects <20mm

when is microfracture used?

helathy biopsy taken from non-loadbearing region, chondrocytes isolates and multiplied, defect debrided and grafted over, chondrocytes reinjected under graft

how is ACI done?

articular cartilage, tidemark, calcified cartilage, cement line, subchondral bone, trabecular bone

what order to the tissues go from the cartilage to the bone?

no defect

what is a grade 0 cartilage defect?

swollen and soft cartilage

what is a grade 1 cartilage defect?

partial thickness cartilage defect

what is a grade 2 cartilage defect?

full thickness cartilage defect

what is a grade 3 cartilage defect?

full thickness OC defect

what is a grade 4 cartilage defect?

mosaicplasty

what is the name for an operation where osteochondral plugs from healthy tissue are implanted into a cartilage defect?

monophasic, biphasic, multiphasic

what three types of osteochondral plugs are available?

PGA-PLA, PVA hydrogel

what are synthetic osteochondral scaffolds made of?

autologous blood extraxct

what are allograft osteochondral scaffolds mixed with?

radiolucent

is cartilage radiolucent or radiopaque?

painkiller

what is an analgesic

analgesics or joint replacement

what are current OA treatments?

age, gender, menopause, genetics, nutrition, bone density

what are systemic factors in OA development?

obesity, injury, surgery, elite athletics, joint deformity

what are mechanical factors in OA?

Trichostatin A

what drug can be used to prevent OA progression?

cells within the matrix secrete ECM molecules, along iwth proteases that digest the matrix

how is a healthy ECM maintained?

bone ECM broken down faster than it’s made

what is osteoporosis?

Gly-X-Y (truple repeat of amino acids starting with glycine)

what is the structure of collagen?

glycine-proline-hydroxyproline

what is the most common amino acid chain for collagen?

attracts water to form a hydrated gel for structure

what does aggrecan do for collagen structure?

irreversible step in collagen destruction, done by specific enzymes

what is collagen cleavage?

cartilage model, from the middle outward, endcaps develop separately, joined together with growth plates

how do bones develop?

in columns

how are chondrocytes arranged?

transcription factors

what controls gene expression?

young active patients

for whom is ACI better than microfracture?

placebo effect

what is a difficulty in analysing the effects of MSK treatments?

lacunae for osteocytes

what is the point of micropores in a bone scaffold?