described herein is a novel drug delivery assembly having particular applicability to the field of orthopedic and surgical medicine . the devices and assemblies described herein enable the efficient application and retention of potentially expensive therapeutic materials to very specific locations , particularly those associated with voids in bone and tissue . one particularly unique aspect of the present invention involves the introduction of constructs which promote the retention of therapeutic material in the target area of application for beneficial use , for example by forming a proximal barrier that prevents leakage of the therapeutic material out of the target area . additionally , the present invention provides unique devices and methods for surgical introduction of such constructs . the present invention finds particular application in connection with introduction of stem and progenitor cells , bioactive molecules and bone scaffold materials in conjunction with bone voids and with the use of cannulated implants , such as bone screws and pins . the present invention also has beneficial use in the delivery of cancer drugs , antimicrobials , bone cements and other therapeutic materials .