Timothy Deville

 Introduction.  MSCs obtained from bone marrow, adipose tissue, and blood are important components of bone tissue engineering, because they have the potential for acting as progenitor cells and also have the capacity of self‐renewal¹. In order to implant to stem cells, it requires a porous scaffold to serve as support and guide vascularization². Atrophic nonunion fractures could benefit the most from proper bone repair using mesenchymal stem cells, allowing for the return of biological healing to the damaged bone. There is need for research into better stem cell isolation and building a better osteogenic scaffold. Advancements in these areas could result in more efficient bone healing treatments. Methods. MSCs were removed from a growing fetal femur and through surface receptor gating, skeletal stem cells were isolated and placed onto a mouse kidney. SSCs were then isolated from the transplant and placed into a second mouse³. Scaffolds made of chitosan variants (hydroxyapatite, tricalcium phosphate, bioactive glass) were implanted with SSCs and placed into mice to observe which combination was most inducive for osteogenesis⁴. Lanthanum was also used as an osteogenic promotor on chitosan scaffolds⁵. Finally, VEGF was also used as a promoter of vascularization in SSC trasnplants⁶. Growth promotion was visualized via alizarin red stains and fluorescent F-actin observation. Results.  SSCs were able to be isolated from MSCs by screening for CD45⁺CD235⁺TIE2⁺CD31⁺ and demonstrated the ability to form bone in the original transplant as well as the secondary transplant, showing that these stem cells have more specificity for osteogenesis³. The chitosan-bioactive glass variant proved to be the best promotor of osteogenesis, visualized by F-actin fluorescence⁴. Lanthanum also proved to be a promotor for osteogenesis⁵. The osteogenesis promotion is believed to be caused by the activation of the WNT/beta-catenin pathway⁵. VEGF was shown to allow more vascularization compared to a non-VEGF scaffold control and is visualized via alizarin red stain⁶.  Conclusions.  In order for proper bone formation to take place, there must be mesenchymal stem cells, growth factors, a supportive bioactive scaffold, and stimulation of angiogenesis. Improved stem cell isolation methods and scaffolds that promote vascularization and bone growth were shown to improve bone formation in these experiments. Therapeutic application of these experiments pave the way for a more effective method of healing non-union bone fractures.

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