An osteoimplant comprising an expandable, biocompatible material. The expandable material may be demineralized bone particles such as demineralized cancellous chips or demineralized cortical fibers or may be another material such as a polymer. The osteoimplant has a first state and a second expanded state. The osteoimplant may be used with another device or on its own. The osteoimplant may be inserted into a device such as an intervertebral body fusion device in the compressed state. The osteoimplant may be rehydrated to expand to an increased size, for example as far as permitted by the confines of the intervertebral body fusion device and spinal endplates, thereby aiding in greater vertebral endplate contact and conformity in spinal surgery.