22721
Amorphous mesoporous silica nanoparticles ( ' protocells ' ) that support surface lipid bilayers recently characterized in vitro as carrier constructs for small drug and DNA delivery are reported here as highly biocompatible both in vitro and in vivo , involving the brain and spinal cord following spinal delivery into the lumbosacral subarachnoid space ( intrathecal ; i . t . ) .
 Chemical: silica
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: silica