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Abstract
Devices implanted into the body become encapsulated due to a foreign body reaction.
In the central nervous system (CNS), this can lead to loss of functionality in electrodes
used to treat disorders. Around CNS implants, glial cells are activated, undergo gliosis
and ultimately encapsulate the electrodes. The primary cause of this reaction is unknown.
Here we show that the mechanical mismatch between nervous tissue and electrodes activates
glial cells. Both primary rat microglial cells and astrocytes responded to increasing
the contact stiffness from physiological values (G' ∼ 100 Pa) to shear moduli G' ≥
10 kPa by changes in morphology and upregulation of inflammatory genes and proteins.
Upon implantation of composite foreign bodies into rat brains, foreign body reactions
were significantly enhanced around their stiff portions in vivo. Our results indicate
that CNS glial cells respond to mechanical cues, and suggest that adapting the surface
stiffness of neural implants to that of nervous tissue could minimize adverse reactions
and improve biocompatibility.