▁cell ▁cult uring ▁purposes ▁and ▁can ▁be ▁used ▁to ▁control ▁cell ▁growth ▁pattern . ▁ ▁Non - to xic ▁waste ▁product ▁ ▁Another ▁positive ▁attribute ▁of ▁por ous ▁sil icon ▁is ▁the ▁de grad ation ▁of ▁por ous ▁sil icon ▁into ▁mon omer ic ▁sil ic ic ▁acid ▁( Si OH 4 ). ▁Sil ic ic ▁acid ▁is ▁re put ed ▁to ▁be ▁the ▁most ▁natural ▁form ▁of ▁element ▁in ▁the ▁environment ▁and ▁is ▁readily ▁removed ▁by ▁kid ne ys . ▁ ▁The ▁human ▁blood ▁pl asma ▁contains ▁mon omer ic ▁sil ic ic ▁acid ▁at ▁levels ▁of ▁less ▁than ▁ 1   m g ▁Si / l , ▁corresponding ▁to ▁the ▁average ▁di et ary ▁int ake ▁of ▁ 2 0 – 5 0   m g / day . ▁It ▁was ▁proposed ▁that ▁the ▁small ▁thick ness ▁of ▁sil icon ▁coat ings ▁presents ▁minimal ▁risk ▁to ▁a ▁to xic ▁concentration ▁being ▁reached . ▁The ▁proposal ▁was ▁supported ▁by ▁an ▁experiment ▁involving ▁volunte ers ▁and ▁sil ic ic - ac id ▁drink s . ▁It ▁was ▁found ▁that ▁concentration ▁of ▁the ▁acid ▁rose ▁only ▁briefly ▁above ▁the ▁normal ▁ 1   m g ▁Si / l ▁level ▁and ▁was ▁efficiently ▁exp elled ▁by ▁ur ine ▁ex cret ion . ▁ ▁Super h ydro ph ob icity ▁ ▁The ▁simple ▁adjust ment ▁of ▁p ore ▁morph ology ▁and ▁geometry ▁of ▁por ous ▁sil icon ▁also ▁offers ▁a ▁convenient ▁way ▁to ▁control ▁its ▁wet ting ▁behavior . ▁St able ▁ult ra - ▁and ▁super