Microcracks　are　present　in　bone　and　can　result　from　fatigue　damage　due　to　repeated,　cyclically　applied　stresses.　From　a　mechanical　point,　microcracks　can　dissipate　strain　energy　at　the　advancing　tip　of　a　crack　to　improve　overall　bone　toughness.　Physiologically,　microcracks　are　thought　to　trigger　bone　remodeling.　Here,　we　examine　the　effect　of　microcracks　specifically　on　osteoblasts,　which　are　bone-forming　cells,　by　comparing　cell　responses　on　microcracked　versus　non-microcracked　hydroxyapatite　(HA)　specimens.　Osteoblast　attachment　was　found　to　be　greater　on　microcracked　HA　specimens　(p　＜　0.05).　More　importantly,　we　identified　the　preferential　alignment　of　osteoblasts　in　the　direction　of　the　microcracks　on　HA　Cells　also　displayed　a　preferential　attachment　that　was　75　to　90　mu　m　away　from　the　microcrack　indent.　After　21　days　of　culture,　osteoblast　maturation　was　notably　enhanced　on　the　HA　with　microcracks,　as　indicated　by　increased　alkaline　phosphatase　activity　and　gene　expression.　Furthermore,　examination　of　bone　deposition　by　confocal　laser　scanning　microscopy　indicated　preferential　mineralization　at　microcrack　indentation　sites.　Dissolution　studies　indicate　that　the　microcracks　increase　calcium　release,　which　could　contribute　to　osteoblast　responses.　Our　findings　suggest　that　microcracks　signal　osteoblast　attachment　and　bone　formation/healing.　(C)　2014　Elsevier　B.V.　All　rights　reserved.