Successful application of patient derived cells to engineer vascularized bone grafts is often hampered by low cell numbers and lengthy in vitro expansion. With sound induced morphogenesis (SIM), local cell density enhancement was shown to improve microvasculature formation at lower cell concentration than conventional methods [1]. SIM takes advantage of hydrodynamic forces that act on cells to arrange them within a hydrogel. Following, we are evaluating the potential of cell-hydrogel biografts with high local cell density to improve the therapeutic efficacy in clinical scenarios such as anastomosis or bone formation within non-union fractures.

To assess anastomosis, human umbilical vein endothelial cells (HUVEC) and human mesenchymal stromal cells (MSC) were mixed at a 1:1 ratio in PEG-based or Dextran-based hydrogels at a final concentration of 2×10⁶ cells×mL^-1. For ectopic bone formation, MSC were resuspended in PEG-based hydrogels at 2×10⁶ or 5×10⁶ cells×mL^-1, with or without BMP-2. Cells were assembled into distinct patterns at a frequency of 60 Hz. Four biografts of 4 × 9 mm² were implanted at the back of nude mice (total of 7 animals) and harvested after 2 or 8 weeks. Explants were fixed and imaged as whole constructs or embedded in paraffin for histological analysis.

Upon explantation, microscopic evaluation indicated that HUVEC were retained within the PEG-hydrogel after 2 weeks and formed a pre-vascular network. In the second study, ectopic bone formation was more pronounced in areas of higher local cell density based on visual inspection. Ongoing experiments are further characterizing bone formation by micro-CT and histological evaluation.

Our results indicate that local cell density enhancement by sound requires a lower initial cell concentration than conventional, static seeding methods to achieve comparable microvasculature structures or local osteogenesis.

Introduction and Objectives: The disadvantages attributed to unreamed intramedullary nails in fractures of the femoral diaphysis include delayed fracture consolidation and fatigue of the material. The aim of our study is to describe the low incidence of these complications.

Materials and Methods: We present a series of 25 patients treated by means of 26 unreamed femoral nails (Synthes) and static locking in all cases and follow up until the time of bone healing (6 months). Mean age of the patients was 43 years (range 18–86 years). The most common cause of injury was automobile accident. All treated fractures were located in the diaphysis (32-A in 9 cases, 32-B in 15 cases, and 32-C in 2 cases) and were closed fractures, except in 4 cases (2 Gustillo type II and 2 of type IIIa). In only 6 patients was the femoral fracture the sole lesion. In the rest of the patients, it was accompanied by other skeletal (multiple fractures) or visceral (polytraumatic) lesions.

Results: We were able to achieve fracture consolidation within a period ranging from 2 to 6 months (mean 4.2 months). We did not experience any problems with material fatigue in any of the cases. In one case it was necessary to remove the static lock to allow for bone healing due to diastasis of the fracture site.

Discussion and Conclusions: Unreamed intramedullary nails allow for consolidation of fractures of the femoral diaphysis in a period of time of about 4 months, which we consider to be accurate. Furthermore, the absence of reaming is associated with a less severe local reaction, which we consider to be preferable.