Osteoporosis is a pervasive issue in the old, and potential methods for reversing its effects are welcome: scientists have "developed a novel technique to enhance bone growth by using a molecule which, when injected into the bloodstream, directs the body's stem cells to travel to the surface of bones. Once these cells are guided to the bone surface by this molecule, the stem cells differentiate into bone-forming cells and synthesize proteins to enhance bone growth. ... There are many stem cells, even in elderly people, but they do not readily migrate to bone. Finding a molecule that attaches to stem cells and guides them to the targets we need is a real breakthrough. ... The researchers made use of a unique hybrid molecule, LLP2A-alendronate ... The researchers' hybrid molecule consists of two parts: the LLP2A part that attaches to mesenchymal stem cells in the bone marrow, and a second part that consists of the bone-homing drug alendronate. After the hybrid molecule was injected into the bloodstream, it picked up mesenchymal stem cells in the bone marrow and directed those cells to the surfaces of bone, where the stem cells carried out their natural bone-formation and repair functions. ... Twelve weeks after the hybrid molecule was injected into mice, bone mass in the femur (thigh bone) and vertebrae (in the spine) increased and bone strength improved compared to control mice who did not receive the hybrid molecule. Treated mice that were normally of an age when bone loss would occur also had improved bone formation, as did those that were models for menopause." This is an example of the future of stem cell medicine - more about directing and altering stem cells in the body to create in-situ effects than providing new cells or growing tissue for transplant.