Response to Implantation

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Response to Implantation

• The implantation/injection/insertion of any
  device into the body will evoke a host tissue
  response to the injury.
• OBJECTIVES
• to provide an overview of the bodys normal
  response to an injury
• to overview the body response to the implantation
  of a device

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Normal Wound Healing

• wound healing is a dynamic cascade of events
  initiated by injury
• it may be divided into phases characterized by
  both cellular population and cellular function
• blood clotting
• inflammation
• cellular invasion and remodeling
• before reviewing wound healing, it is necessary
  to introduce some of the main players
• cells of the blood stream
• fibroblasts

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Fibroblasts
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Intravascular Cells
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Intravascular Cells

• red blood cells

erythrocytes, thrombocytes
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Clotting or Thrombosis

• blood coagulation or clotting is the blood
  response to damaged blood vessels
• objective is to form a patch that isolates the
  leak and stops blood loss

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Coagulation Pathways
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Inflammation

• Inflammation is the reaction of vascularized
  tissue to local injury.
• ACUTE INFLAMMATION
• implantation causes disruption of
  microvasculature
• initial response is vasodilation and increased
  permeabilty of capillaries
• fluid and proteins and leukocytes exude into
  injured tissue (extravasation)
• CHRONIC INFLAMMATION
• characterized by the presence of macrophages,
  monocytes, and lymphocytes with the proliferation
  of blood vessels and connective tissue

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Leukocyte Invasion at Wound Site
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Granulation Tissue Deposition - Remodeling

• Due to death of cells following injury, and their
  removal, there is a local decreased tissue mass
• fibroblasts and vascular endothelial cells are
  recruited to site
• Begin to form granulation tissue (ECM and new
  blood vessels)

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Wound Healing
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Foreign Body Reaction

• The presence of the implant changes the healing
  response, and this is called the Foreign Body
  Reaction.
• FBR consists of
• macrophages
• multinucleated foreign body giant cells
• form upon coalescence of macrophages
• fibroblasts
• capillaries

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Fibrosis and Fibrous Encapsulation

• End stage of healing response
• Usually four or more weeks after implantation
• A relatively acellular fibrous capsule
• spindle shaped fibroblasts
• small number of macrophages
• Presence of neutrophils suggests persisting
  inflammatory challenge
• Presence of foreign body giant cell suggests
  production of small particles by corrosion,
  depolymerization, dissolution or wear

14
Foreign Body Response - Resolution

• continuing presence of an implant may result in
  the attainment of a final steady-state condition
  called resolution
• there are 3 possible outcomes for the implant
• resorption
• integration
• encapsulation (fibrosis)

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Cell Regeneration After Injury

• Possible outcomes for the injured tissue
• replacement of injured tissue with parenchymal
  cells of the same type
• replacement by connective tissue that constitutes
  the fibrous capsule
• The regeneration of cells in the body is tightly
  controlled
• There are essentially 3 categories of cell
  populations
• Renewing or labile
• Expanding or stable
• Static or permanent

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Fibrosis and Fibrous Encapsulation

• 78-week PMMA histology (sheep) illustrates soft
  tissue encapsulation of prepolymerized PMMA

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Experimental Results
5050 CLLA 18 000 g/mol sterilized with
25kGy rat femur