Sentence:  Similar studies of rats have employed four different intracranial resorbable, slow sustained release systems&mdash;nb.... Such a slow-release device containing angiogenic factors could be placed on the pia mater <WSD>covering</WSD> the cerebral cortex and tested in persons with senile dementia in long term studies. 
Meaning of the word marked with <WSD> tags:  To be over or upon, as to conceal or protect.