June 20, 2024

Bioabsorbable Polymers ( alpha polyesters or poly alpha hydroxyl acids) have been studied and used recently in orthopedics for multiple causes. Some are used in managing bone defects in chronic osteomyelitis. With recent advances in medical practice, these polymers are getting more space in different fields of medicine.

  1. Polylactic acids (PLA)
  2. Poly glycolic acids (PGA)
  3. Poly di dioxanone (PDS)
  4. Combinations of these materials

Properties of bioabsorbable polymers

Important three properties of bioabsorbable polymers are:

  1. Semi crystalline
    • Both amorphous and crystalline
    • Plays a role in strength and absorption both
  2. Visco-elastic
    • Physical properties change in rate of load application
  3. Low Tg ( Glass-transition temperature)
    • Glass Transition Temperature (Tg) is the point at which a material alters state – going from a glass-like rigid solid to a more flexible, rubbery compound
Bioabsorbable polymers

Advantages of using bioabsorbable polymers

  1. Limit stress shielding of bone (as they degrade)
  2. Eliminate the need of hardware removal
  3. Radiolucency

Role of degradation depends upon:

  1. Starting molecular weight of polymers
  2. Crystalline
  3. Composition
  4. Porosity of implant
  5. Loading characteristics
  6. Local vascularity

Principle of degradation

The degradation of the polymers occurs by two mechanisms; Chemical and Biological

Early phase of degradation:-

Chemical degradation

The early phase of degradation is basically chemical in nature.

Water molecules enters the implanted material and initiate degradation by hydrolysis. Cleavage of the monomers molecular bands occurs with scissoring of long polymer chains into shorter chains ( Decrease overall molecular weight)

Depends upon porosity i.e.

Low porosity is associated with slow cleareance of the degradation process which enhances autocatalysis of implants. It increases acidity which further causes fast molecular scissoring and shortened functional life

Biological Degradation

After implant loses intregity and fragments biological removal of these polymers takes place by:

  1. Foreign body reactions
  2. Activation of compliments
  3. Synovities

Complications using bioabsorbable Polymers

Complications are seen in around 40% of cases of using these polymers. Some common complications are:

  1. Sterile sinus tract formation
  2. Hypertrophic fibrous encapsulation
  3. Osteolysis