Ruptured tendons. Our semiquantitative immunoistochemical evaluation showed that the expression of versican protein was not influenced by hMSC implantation. Collagen II positivity, Alcian blue and Alizarin red staining were used to investigate the formation of cartilage and bone at the site of injury. In three rats from the salinetreated group (30 ) and eight rats from the hMSC-treated group (73 ), the presence of newly formed cartilage at the site of injury was detected. It is probable that the cartilage was developing towards the bone that was present in 20 of controls PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/28128382 and 55 of hMSC-treated tendons. The low vascularity of the tendon and the very denseMachova Urdzikova et al. BioMedical Engineering OnLine 2014, 13:42 http://www.biomedical-engineering-online.com/content/13/1/Page 13 ofsuspension of hMSCs implanted into the lesion site established hypoxic conditions for the cells. hMSCs cultured under hypoxic conditions expressed higher levels of osteoblastic and adipocytic differentiation markers than normoxic controls [28]. Different protocols for increasing tenogenic differentiation and decreasing the risk of ectopic cartilage and bone formation using, e.g., growth and differentiation factors 5 and 6, have been developed [29,30]; however, before translation of the protocols to the clinical environment, their safety should be well documented. Biomechanical testing of stiffness and load to failure did not result in differences between the groups. However, the stiffness of the 5-BrdU price tendons improved after the application of hMSC treatment at the 90 confidence level (27-85 taking into Deslorelin side effects account the lower and upper quartiles, 18 taking into account the medians). From the point of view of the mechanical testing of biological materials, we can consider the 90 confidence level as a sufficient result; however, more in vivo experimental work is needed to clarify this. While lower than the widely used 95 and 99 confidence levels, the 90 confidence level in statistical hypothesis testing theory can indicate useful experimental effects. According to previous publications [31,32], we decided to test the biomechanical properties of the tendons 4 weeks after injury. However, as was shown in our results, the reorganization of the extracellular matrix and the healing processes still continued for another two weeks. Also, the vascularity of the tendon tissue was very high 4 weeks after injury and then decreased. Neovascularization is an important part of the healing process and ultimately enhances tendon regeneration, but it actually could change the mechanical properties of the tendon and affect the results between groups.Conclusions Human multipotent mesenchymal stromal cells, when implanted into artificially induced tendinitis, promote neovascularization and tissue organization. The implantation may increase the stiffness of the tendons; however, more experiments are needed to clarify this point. The treatment procedure is safe, no tumor formation or excessive inflammatory reaction were detected; nonetheless, cartilage formation at the implantation site occurred in a few cases, and this should be taken into account when planning subsequent in vivo and clinical trials as an expected adverse event.Abbreviations hMSCs: Human mesenchymal stromal cells; IQR: Interquartile range; CI: Confidence intervals; RECA: Anti-endothelial cell antibody; MTCO2: Anti-cytochrome c oxidase subunit II antibody; GMP: Good manufacturing practice; BBB: BassoBeattie-Bresna.Ruptured tendons. Our semiquantitative immunoistochemical evaluation showed that the expression of versican protein was not influenced by hMSC implantation. Collagen II positivity, Alcian blue and Alizarin red staining were used to investigate the formation of cartilage and bone at the site of injury. In three rats from the salinetreated group (30 ) and eight rats from the hMSC-treated group (73 ), the presence of newly formed cartilage at the site of injury was detected. It is probable that the cartilage was developing towards the bone that was present in 20 of controls PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/28128382 and 55 of hMSC-treated tendons. The low vascularity of the tendon and the very denseMachova Urdzikova et al. BioMedical Engineering OnLine 2014, 13:42 http://www.biomedical-engineering-online.com/content/13/1/Page 13 ofsuspension of hMSCs implanted into the lesion site established hypoxic conditions for the cells. hMSCs cultured under hypoxic conditions expressed higher levels of osteoblastic and adipocytic differentiation markers than normoxic controls [28]. Different protocols for increasing tenogenic differentiation and decreasing the risk of ectopic cartilage and bone formation using, e.g., growth and differentiation factors 5 and 6, have been developed [29,30]; however, before translation of the protocols to the clinical environment, their safety should be well documented. Biomechanical testing of stiffness and load to failure did not result in differences between the groups. However, the stiffness of the tendons improved after the application of hMSC treatment at the 90 confidence level (27-85 taking into account the lower and upper quartiles, 18 taking into account the medians). From the point of view of the mechanical testing of biological materials, we can consider the 90 confidence level as a sufficient result; however, more in vivo experimental work is needed to clarify this. While lower than the widely used 95 and 99 confidence levels, the 90 confidence level in statistical hypothesis testing theory can indicate useful experimental effects. According to previous publications [31,32], we decided to test the biomechanical properties of the tendons 4 weeks after injury. However, as was shown in our results, the reorganization of the extracellular matrix and the healing processes still continued for another two weeks. Also, the vascularity of the tendon tissue was very high 4 weeks after injury and then decreased. Neovascularization is an important part of the healing process and ultimately enhances tendon regeneration, but it actually could change the mechanical properties of the tendon and affect the results between groups.Conclusions Human multipotent mesenchymal stromal cells, when implanted into artificially induced tendinitis, promote neovascularization and tissue organization. The implantation may increase the stiffness of the tendons; however, more experiments are needed to clarify this point. The treatment procedure is safe, no tumor formation or excessive inflammatory reaction were detected; nonetheless, cartilage formation at the implantation site occurred in a few cases, and this should be taken into account when planning subsequent in vivo and clinical trials as an expected adverse event.Abbreviations hMSCs: Human mesenchymal stromal cells; IQR: Interquartile range; CI: Confidence intervals; RECA: Anti-endothelial cell antibody; MTCO2: Anti-cytochrome c oxidase subunit II antibody; GMP: Good manufacturing practice; BBB: BassoBeattie-Bresna.