Essen%al  Biomaterials  Science:  Professor  David  Williams    

Biocompa(bility  Pathways  Overview  of  defini4ons  of  biocompa4bility  and  basic  ground  

rules  Overarching  biocompa4bility  paradigm  

 Biocompa4bility  scenarios:  

A:  Mechanisms  that  do  not  rely  on  chemical  interac4ons  B:  Mechanisms  that  do  rely  on  chemical  interac4ons  at  macroscale  

C:  Microscale  biocompa4bility  D:  Nanoscale  biocompa4bility  

E:  Mechanisms  influenced  by  pharmacological  agents  

 

The  Williams  Defini4on  of  Biocompa4bility  

‘The  ability  of  a  material  to  perform  with  an  appropriate  host  response  in  

a  specific  applica6on’    

The  Williams  Dic4onary  of  Biomaterials  Liverpool  University  Press,  1999  

 Williams  D.F.  On  the  mechanisms  of  biocompa4bility  

Biomaterials,  2008,  29,  2941    

The  Consequences  of  Biocompa(bility  Failures    Death  of  the  Pa4ent      Thromboembolic  complica4ons  

       Anaphylac4c  shock          Organ  failure  

   Major  Disease      Cancer  

       Central  nervous  system  damage          Autoimmunity          Incon4nence          Peripheral  nerve  damage          Reproduc4ve  errors          Loss  of  sensory  func4on          Viral  disease  transmission  

   Minor  –  major    Complaints    Allergy  

       Inflamma4on  /  edema          Hyperplasia          Hypoplasia  /  resorp4on  

   Failure  to  Achieve  Desired    Osteolysis  Outcome        Loss  of  patency  of  vessel  

       Infec4on                    

Intensity

Injury 1 Day 1 Week 1 Month

A

B1 C1 D1

B2 C2 D2

Phases  of  wound  healing  

Hemostasis    Acute  Inflamma4on  Chronic  inflamma4on  Repair  /  scar  

Fibrosis Blood biocompatibility -thrombosis -embolus -endocarditis

Microtoxicology Nanotoxicology

Ocular biocompatibility - cornea - lens -retina

Bioreactor biocompatibility

Problems  with  Conven4onal  Treatment  of  Biocompa4bility  Mechanisms  

•  Biocompa4bility  of  biomaterials  has  usually  been  discussed  as  a  perturba4on  of  wound  healing,  which  is  based  on  inflamma4on,  repair  and  remodelling,  but  most  biomaterials  are  not  placed  in  

contact  with  cells  /  4ssues  by  surgical  implanta4on.  Biocompa4bility  mechanisms  and  tes4ng  procedures  have  been  based  on  experiences  

with  implantable  devices  •  Blood  compa4bility  has  been  treated  separately  to  all  other  aspects  of  

biocompa4bility.  In  fact,  we  have  wrongly  tried  to  compartmentalize  different  aspects  of  biocompa4bility  instead  of  considering  them  as  

parts  of  an  over-­‐arching  phenomenological  system.  •  There  has  been  an  over-­‐reliance  on  in  vitro,  non-­‐physiological,  protein  

adsorp4on  and  cell  adhesion  data.    •  There  are  been  major  misunderstandings  of  the  roles  of  innate  and  

adap4ve  immunity  in  biocompa4bility.  •  ESPECIALLY,  BIOCOMPATIBILITY  HAS  WRONGLY  BEEN  CONSIDERED  AS  

A  PROPERTY  OF  A  MATERIAL;  IT  IS  A  PROPERTY  OF  A  BIOMATERIAL-­‐HOST  SYSTEM  

 

The  Basic  Ground  Rules  of  Biocompa(bility    The  introduc4on  of  a  biomaterial  into  the  human  body  represents  a  physiologically  

stressful  event  and  we  must  expect  the  body  to  present  some  adap4ve  response.      

The  default  posi4on  is  that  there  is  inherent  incompa4bility  between  foreign  materials  and  the  4ssues  of  the  body.  

   Biocompa4bility  is  not  a  property  of  a  material;  it  is  a  characteris4c  of  a  material  –  

4ssue  system.      

In  biocompa4bility,  an  event  may  be  triggered  spontaneously,  at  any  4me,  the  effect  of  which  can  be  powerfully  amplified  by  one  or  more  mechanisms,  changing  

the  whole  nature  of  the  response  in  a  short  space  of  4me.  Mechanisms  of  biocompa4bility  do  not  necessarily  show  a  linear  progression  with  4me.  

   The  consequences  of  interac4ons  may  be  localized  to  the  vicinity  of  the  material,  

oben  referred  to  as  the  foreign  body  response,  or  they  may  be  seen  at  some  distant  site,  or  they  may  be  truly  systemic.  

   Biocompa4bility  phenomena  vary  from  pa4ent  to  pa4ent  and  may  vary  with  the  

techniques  used  to  administer  the  biomaterial  to  the  pa4ent.        

T

NN

BiomaterialSolid, Immobile

Chemically unreactiveUnchanging with time

Tissue EnvironmentSolid, or fluid, or collection of cells +/- ECMDynamic environment, changing with time

The conceptual starting point is that biocompatibility concerns the effect of the physical presence of the material on the dynamic

response of the tissue.

Potential factors to be superimposed on the basic concept

Adsorption

Mechanical forces

Effects of topography

Systems approach to biocompatibility

The essential biocompatibility paradigm

§  Resolution of response§  Clinically acceptable§  Tolerable to patient

Mechanical forcesProtein adsorption

Cell adhesionPolymer degradation

InflammationHyperplasia

Tissue resorptionThrombus formation

Surgical implantationInfusion / injection

Extracorporeal circuitIn vitro bioreactor

§  Inadequate resolution§  Clinically relevant effects§  Not tolerable

Causative event

Material and tissue come into contact

Progression of host response

Generic Biocompatibility Pathways

Essen(al  Cells  in  Biocompa(bility  Phenomena    

Cells  of  inflamma6on  and  the  Immune  Response    Basophils,  Eosinophils,  Monocytes,  Mast  cells  Polymorphonuclear  leukocytes  (neutrophils)  

B-­‐lymphocytes,  T-­‐lymphocytes,  Plasma  cells,  Dendri4c  cells  Macrophages,  Foreign  body  giant  cells  

NK  cells  Platelets  

 Cells  of  Repara6ve  and  Hyperplas6c  responses  

Epithelial  cells  Endothelial  cells  

Fibroblasts  Myoblasts,  Myofibroblasts  

Odontoblasts  Osteoblasts  

Smooth  muscle  cells    

Cells  of  Tissue  Resorp6on  Chondroclasts  Odontoclasts  Osteoclasts  

           

 

Biocompa4bility  Scenarios    

Scenario  A;  Mechanisms  of  biocompa(bility  that  do  not  rely  on  direct  chemical  interac(ons  

Scenario  B;  Mechanisms  of  biocompa(bility  involving  chemical  reac(ons  between  macroscale  biomaterials  and  their  soluble  

deriva(ves  with  the  host  Scenario  C;  Mechanisms  of  biocompa(bility  involving  microscale  

biomaterials  and  micropar(cles  Scenario  D;  Mechanisms  of  biocompa(bility  involving  nanoscale  

biomaterials  and  nanopar(cles  Scenario  E;  Mechanisms  of  biocompa(bility  involving  delivery  of  pharmaceu(cal  agents  from  macroscale  biomaterial  to  the  host  

 

     

 

Scenario  A    Mechanisms  of  biocompa(bility  that  do  not  rely  on  direct  

chemical  interac(ons    

•  This  does  not  mean  that  chemical  reac4ons  do  not  take  place,  but  chemistry  is  not  the  driving  force  

•  The  first  involves  the  effects  of  mechanical  forces  and  the  phenomenon  of  mechanotransduc4on  

Moshayedi  P  et  al  “The  rela4onship  between  glial  cell  mechanosensi4vity  and  foreign  body  reac4ons  in  the  central  nervous  system”  Biomaterials  2014;35:3919  

•  The  second  involves  the  biophysical  forces  associated  with  macromolecular  adsorp4on  and  cell  ac4va4on  on  biomaterials  surfaces.  

Wilson  C  J  et  al    “Media4on  of  biomaterial-­‐cell  interac4ons  by  adsorbed  proteins;  a  review”  Tissue  Engineering  2005;11:1-­‐18.    

Nucleusgene expression

I. Force transmission

II. Force transduction

Mechanosensitive ion channels

Force-induced exposure of molecular

recognition sites

Force regulation of protein activity

Effect of strain on integrin adhesions

III. Signal propagation

Intermediate filaments

Signaling molecules in cytoskeleton, changes to protein conformation, protein recruitment, cytoskeletal contraction, calcium signaling

Cell membrane IV. Cell responseECM production, change of phenotype, altered motility and shape

Actin filaments

Microtubules

Cell shape dynamics as a regulator of cell fate. Regulation of cell shape is a complex and dynamic process. Classically, in vitro cell shape was thought to be the output of variables such as adhesive ligands or more recently substrate stiffness..

Evangelia Bellas, Christopher S Chen

Forms, forces, and stem cell fate

Current Opinion in Cell Biology, Volume 31, 2014, 92–97

http://dx.doi.org/10.1016/j.ceb.2014.09.006

Forces on bone

Forces on soft tissue

Shear stressesin fluids in vivo

Shear stressesin fluids in vitro

Forces on cells

at surfaces

Signal propagation

Compressive forces Tensile forces

Fluid shear stresses

Fibrosis

Phenotype change

Intimal hyperplasia

Osteoporosis

Hemolysis

Exposure of peptide sequences

Regulation of proteinsChanges to ion channels

Cytoskeletal filaments

Signaling molecules

Force transduction

Force transmission

Gene expression – cell responses

The  essence  of  mechanotransduc4on-­‐mediated  biocompa4bility    

BloodExtra-

cellular fluidCulture mediumCytoplasm CSF

Molecular re-arrangement

Molecular activationCell interactions

Coagulationcascade

ComplementcascadeActivationAdhesion Proliferation Phenotype

change

Cross-talk

Physiological / pathological outcomes

HydrodynamicsFluid characteristics

HydrophilicityTopographyElasticityFunctional groups

Macromolecular adsorption

The  essence  of  surface  biocompa4bility  mechanisms  

Extrinsic Pathway Intrinsic Pathway

Tissue factor Foreign surface

TF + Factor VII → TF-VIIa (extrinsic tenase)

Factor X → Factor Xa

Factor XII → Factor XIIa

Kallikrein

Factor XI → Factor XIa

Prekallikrein

Factor IX → Factor IXa

Factor II (Prothrombin ) → Thrombin

Factor Va

Fibrinogen → Fibrin monomer

Fibrin polymer

Factor XIII

Factor XIIIa

Cross-linked blood clot

Factor VIIIa

Coagula4on  cascade  

Alternative Pathway

Foreign surface

C3

C5b

Terminal Complement Complex (TCC)

C4

C4b2a (C3 convertase)

C4b

C3a (An*)

C3b

C5

C5a (An*)

C6 C7

C8 C9

C3b C3

C3a

C3bBb(C3 convertase)

fD

fB

C2

C1

Classical Pathway

Antigen-antibody complex

C1q / C1r / C1s

Complement  ac4va4on  

•    

Cell membrane with receptors, GPIb and GPIIb/IIIa

Microtubules

Surface connected

canalicular system

Mitochondrion

Glycogen

Dense granule

Lysosomal granule

Dense tubular system

Dense bodyα-granules

Platelet  

�  

Endothelial cell / subendothelium / collagen

vWF

GP Ib

Thrombin

Thrombin receptor

GP IIb-IIIa of other platelet

GP IIb-IIIa

Fibrinogen

α degranulation

Platelet Factor 4,β thromboglobulin,other soluble factors, platelet microparticles

Serotonin, ADP, Factor V,Thromboxane A, etc.

Gorbet  and  Sebon,  “Biomaterials-­‐associated  thrombosis;  roles  of  coagula4on  factors,  complement,  platelets  and  leukocytes:  Biomaterials  2004;25:5681  

Scenario  B;  Mechanisms  of  biocompa(bility  involving  chemical  reac(ons  between  macroscale  biomaterials  and  their  soluble  

deriva(ves  with  the  host  

•  Recognizes  that  virtually  all  monolithic  biomaterials  have  chemically-­‐reac4ve  surfaces  and  /  or  release  chemically-­‐reac4ve  moie4es  into  an  aqueous  biological  environment  

•  The  human  body  has  well-­‐developed  mechanisms  to  deal  with  many  foreign  substances.  These  mechanisms  are  based  on  the  immune  system  that  has  evolved  to  provide  defense  to  micro-­‐organisms  

•  There  are  two  types  of  immune  response  •  Innate  immunity  is  non-­‐specific,  involving  leukocytes  (including  natural  killer  cells,  

mast  cells,  eosinophils,  basophils)  and  phagocy4c  cells  (including  macrophages  and  neutrophils)  

•  Adap4ve  immunity  is  an4gen-­‐specific,  laregly  mediated  by  lymphocytes.  B  cells  are  ac4vated  to  secrete  an4bodies  (  immunoglobulins)  which  bind  specifically  to  the  foreign  an4gen  that  s4mulated  their  produc4on  

•  Biomaterials  are  generally  considered  to  evoke  innate  immunity  but  adap4ve  immunity  may  also  be  involved  

C

Gene expression

Ligand

Receptor

Cell membrane

Signal initiation

Signal transduction A cascade of events such as phosphorylation

ProliferationDifferentiation

ApoptosisEtc.

A

B

The  essence  of  cell  signaling  pathways  and  mechanisms  of  biocompa4bility  concerned  with  biomaterial-­‐released  molecules  

Rounding-up of cell, reduction of cell volume, chromatin condensation, nuclear fragmentation, retraction of pseudopodia

Increase in cell volume swelling of organelles, plasma membrane rupture, loss on intracellular content

Appearance of multiple-membrane enclosed vesicles, engulfment and loss of organelles

≅≅≈ ≈. ≅ ≈ ≈ + ≈ ≈ = ≈

NECROSIS APOPTOSIS AUTOPHAGY

Macrophage derived from monocytes or other progenitor cells

Exposure to cytokines such as Interferon γ and Tumor Necrosis Factor α

M1 macrophage Macrophage phenotypes : M2a M2b M2c

IL-4, IL-13 IC IL-1R IL-10

Pathogen killing Th2 response Th2 response ImmunosuppressionAntigen presentation Macrophage fusion ECM remodelingMatrix destructionTissue reorganization

IL-12

Macrophage  polariza4on  

TIME ZERO ; BIOMATERIAL-HOST CONTACT

RELEASE OF CHEMICALLY ACTIVE AGENTS FROM BIOMATERIAL

INITIATION OF CELL SIGNALING

Metal ions Monomers

ECM components Oligomers

Free radicals

Endotoxins

Additives Catalysts Impurities

CELL SIGNALING PATHWAYS

CELL DESTRUCTION

TISSUE GROWTH

DIRECTION CHANGE

Fibrosis Hyperplasia (Cancer)

Differentiation Phenotype shift

Granulation Necrosis Osteolysis

� �  

� �  

� �  

Apoptosis Necrosis Autophagy

Innate immunity Inflammation Wound healing Adaptive immunity

Varia

ble

influ

ence

of t

ime

Intensity of host response

Time

Acute phase

Acute / sub-chronic destructive responses, e.g. thrombus, necrosis, hyperplasia, granuloma

Minor chronic inflammation and fibrosis

Equilibrium:  The  Foreign  

Body  Response  

The Metastable Pathway

The Chronic Quiescent Pathway ofBenign Acceptance

The Chronic Anti-inflammatory Pathway

Chemically-­‐driven  biocompa4bility  phenomena  

The  most  chemically  inert  biomaterials  are  associated  with  minimal  inflamma4on:  PTFE,  Titanium  and  Pla4num,  Alumina  

Degrada4on  products  of  some  polyesters  produce  late  inflamma4on  (pH,  catalysts  etc.)  

Quantum  dots  may  ini4ate  toxicity  because  of  metal  ion  (Cd)  release  Adap4ve  immune  response  to  some  metallic  nanopar4cles  (e.g.  Co-­‐Cr  

wear  debris)  Adap4ve  immune  response  seen  to  some  collagen  products  

Anaphylac4c  response  seen  with  some  hemodialysis  membranes  Hydroxyl  groups  in  some  hydrogels  ac4vate  complement  by  alterna4ve  

pathway  

Scenario  C;  Mechanisms  of  biocompa(bility  involving  microscale  biomaterials  and  micropar(cles  

 •  Micropar4cles  u Wear  par4cles,  corrosion  products,  degrada4on  products,  drug  

delivery  vehicles,  porous  coa4ngs  u Mechanisms  based  on  phagocytosis  of  bacteria  (few  micron  

diameter)  u Clinical  experience  with  pneumoconiosis  (esp  asbestos)  u No  clear  correla4on  between  biomaterial  parameters  and  host  

response    Sheikh  Z  et  al,  Macrophages,  foreign  body  giant  cells  and  their  response  to  implanted  biomaterials,  Materials  2015;8:5671    

•  Microtopography  v Manufactured  surface  finish  v Deliberate  surface  paoerning  v Most  interested  in  bone  contact  

Scenario  D;  Mechanisms  of  biocompa(bility  involving  nanoscale  biomaterials  and  nanopar(cles  

 •  Nanopar4cles  Deliberate  introduc4on  of  nanopar4cles  into  medical  

technology,  in  drug  and  gene  delivery  systems  and  imaging  contrast  agents  

Oh  N,  Endocytosis  and  exocytosis  of  nanopar4cles  in  mammalian  cells,  Int  J  Nanomedicine  2014;9(Suppl  1):  S1  

 •  Nanotopography  

Possible  effects  on  bone  biocompa4bility  Probable  influence  on  stem  cell  differen4a4on  

Toxicological  effects  of  nanopar4cles        This  list  represents  the  possible  effects  of  nanopar4cles  on  the  human  body.    There  is  clear  experimental  and  clinical  evidence  for  

some  of  them;  in  other  cases  the  effects  are  theore4cal  and  not  necessarily  proven.      

Genera4on  of  reac4ve  oxygen  species,  leading  to  oxida4ve  stress      

Pro-­‐inflammatory  responses,  including  granuloma  forma4on  and  acute  phase  protein  expression      

Effects  on  phagocy4c  func4on,  especially  prolonga4on  of  chronic  inflamma4on  and  inhibi4on  of  clearance  of  microorganisms  and  4ssue  debris  

   Effects  on  proteins,  denatura4on  and  loss  of  enzyme  ac4vity  

   Effects  on  mitochondria,  including  disrup4on  of  energy  processes    

   Uptake  by  re4culo-­‐endothelial  system,  sequestra4on  in  liver  and  spleen  

   Nuclear  uptake,  leading  to  DNA  damage  and  mutagenesis  

   Uptake  in  neuronal  4ssue,  damage  to  central  and  peripheral  nerve  systems  

   Cardiovascular  effects,  including  thrombosis,  myocardial  infarc4on  and  stroke  

   Effects  on  cell  cycle,  including  prolifera4on,  senescence  and  apoptosis  

     

Intensity of host response

Time

Acute phase

Acute / sub-chronic destructive responses, e.g. thrombus, necrosis, hyperplasia, granuloma

Minor chronic inflammation and fibrosis

Equilibrium:  The  Foreign  

Body  Response  

The Metastable Pathway

The Chronic Quiescent Pathway ofBenign Acceptance

The Chronic Anti-inflammatory Pathway

Scenario  E;      

Mechanisms  of  biocompa(bility  involving  delivery  of  pharmaceu(cal  agents  from  macroscale  biomaterial  to  host      

 

An4bio4c  bone  cements  Drug  elu4ng  intravascular  stents  

Bone  morphogene4c  proteins  in  spinal  fusion  Bisphosphonates  in  bone  

Drug  elu4ng  intraocular  lenses  

Without drug

With drug

Without drug

With drug

Acuteinflammation

Acute inflammation

Example 1 Intravascular stent

Acute Endothelial Smooth Stenosis inflammation response muscle cell response

Minimal endothelial response, anti-proliferativeeffect, delayed / minimal stenosis

Example 2 Bone fusion

Acute Chronic Fibrosis Delayed inflammation inflammation bone union

Reduced chronic inflammation, minimalfibrosis, accelerated, superior bone union

                             Pharmacologically-­‐mediated  biocompa4bility  

Diagnosis of clinical condition êDecision to use procedure involving biomaterial ê Presentation of biomaterial to tissues

BIOCOMPATIBILITY PATHWAY

Adverse Neutral Idealoutcome outcome outcome

Summary  of  Biocompa4bility  Pathways  

Biomaterial

Molecular adsorption, mechanical or biophysical factors and chemical agents

Defensive

Cells Target

Interfering

No effects GOOD OUTCOME

Adverse effects ADVERSE OUTCOME

No interaction NEUTRAL

Required interaction GOOD OUTCOME

No interference GOOD OUTCOME

Interference POOR OUTCOME

Effects within cell

• Material destruction by cell environment

• Generation of reactive oxygen species and cell damage

• Alteration of organelle function• Interference with apoptotic and

necrotic pathways• Passage into nucleus affecting gene

expression• Passage into nucleus with gene

damage

Biomaterial components : metal ions, polymer additives, corrosion products, nanoparticle contrast agents, degradation products, contaminants etc

Internalization mechanisms : phagocytosis, endocytosis, pinocytosis

Mechanical and biophysicalmediators of interactionswith cells; forces, Electromagnetic fields etc

Material mediators of reactions: chemical structure, elasticity, shape and volume, topography etc

                                               Summary  of  the  control  of  biocompa4bility  

Special  Considera4ons  

q  Carcinogenicity  q  Reproduc4ve  toxicity  

q  Infec4on    

Biocompa4bility  Tes4ng  

Remember  BIOCOMPATIBILITY  HAS  WRONGLY  BEEN  CONSIDERED  AS  A  PROPERTY  OF  A  MATERIAL;  IT  IS  A  PROPERTY  OF  A  BIOMATERIAL-­‐HOST  SYSTEM  

 Williams  D  F  

Leading  Opinion  Paper  There  is  no  such  thing  as  a  biocompa4ble  material  

Biomaterials  2014,  35(38),  10009-­‐14