Biomedical Engineering Reference
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Fig. 1 Bare MWCNTs are a permissive substrate for neuronal growth. Both polyethyleneimine
(PEI; left column images ) and as-prepared MWCNTs (AP-MWCNTs; right column images ) allow
neuronal viability and neurite outgrowth. ( a, b ) SEM images of hippocampal neurons grown on
PEI ( a ) and AP-MWCNTs ( b ). ( c, d ) Fluorescence images showing live neurons, which accumu-
late a vital stain, calcein. Arrows indicate growth cones. Scale bar: 20 mm, except 10 mm in b .
( e ) Drawing summarizing the effects of MWCNT charges on the neurite outgrowth and branching.
Neurons grown on positively charged MWCNTs have longer and more branched neurites than
neurons grown on negative or zwitterionic MWCNTs. Modifi ed from (Hu et al. 2004 )
comparable typology but, due to dissociation constants of attached groups, with
different charges, negatively (MWCNT-COOH), zwitterionic (MWCNT-PABS),
or positively charged (MWCNT-EN) at the physiological extracellular pH of 7.35.
Indeed, the authors used mid-infrared (IR) spectroscopy of MWCNTs to confi rm
the success of covalent modifi cations. Each of these three functionalized MWCNTs
was deposited onto glass coverslips precoated with PEI and used as scaffolds/
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