Vascularization of Natural and Synthetic Bone Scaffolds.

Vascularization of engineered bone tissue is critical for ensuring its survival after implantation. In vitro pre-vascularization of bone grafts with endothelial cells is a promising strategy to improve implant survival. In this study, we pre-cultured human smooth muscle cells (hSMCs) on bone scaffolds for 3 weeks followed by seeding of human umbilical vein endothelial cells (HUVECs), which produced a desirable environment for microvasculature formation. The sequential cell-seeding protocol was successfully applied to both natural (decellularized native bone, or DB) and synthetic (3D-printed Hyperelastic "Bone" scaffolds, or HB) scaffolds, demonstrating a comprehensive platform for developing natural and synthetic-based in vitro vascularized bone grafts. Using this sequential cell-seeding process, the HUVECs formed lumen structures throughout the DB scaffolds as well as vascular tissue bridging 3D-printed fibers within the HB. The pre-cultured hSMCs were essential for endothelial cell (EC) lumen formation within DB scaffolds, as well as for upregulating EC-specific gene expression of HUVECs grown on HB scaffolds. We further applied this co-culture protocol to DB scaffolds using a perfusion bioreactor, to overcome the limitations of diffusive mass transport into the interiors of the scaffolds. Compared with static culture, panoramic histological sections of DB scaffolds cultured in bioreactors showed improved cellular density, as well as a nominal increase in the number of lumen structures formed by ECs in the interior regions of the scaffolds. In conclusion, we have demonstrated that the sequential seeding of hSMCs and HUVECs can serve to generate early microvascular networks that could further support the in vitro tissue engineering of naturally or synthetically derived bone grafts and in both random (DB) and ordered (HB) pore networks. Combined with the preliminary bioreactor study, this process also shows potential to generate clinically sized, vascularized bone scaffolds for tissue and regenerative engineering.

El reto de las transferencias de colgajos libres en pacientes quemados ¿Cuál es el mejor momento para la cirugía? / The challenge of free flap transfers in burn patients. What is the best timing of surgery?

La transferencia de colgajos libres es una herramienta fundamental dentro del arsenal reconstructivo para el tratamiento quirúrgico del gran quemado. Durante años ha existido controversia sobre la influencia del momento de la cirugía sobre la tasa de complicaciones, así como el alto riesgo de complicaciones al realizar reconstrucciones con colgajos libres en pacientes quemados. Diseñamos un estudio retrospectivo de las reconstrucciones quirúrgicas mediante colgajos libres realizadas en nuestra Unidad de Quemados del Hospital Universitari y Politecnic La Fe, de Valencia (España) en el periodo comprendido entre 2001 y 2013, recogiendo todos los datos relativos al paciente, a la lesión, al procedimiento reconstructivo, a los resultados y relacionando todo ello con el momento en el cual se realizó la cirugía. Para el análisis de los datos y asociaciones entre distintas variables usamos tablas de contingencia y aplicamos el test de independencia de Chi-cuadrado. Exponemos además 2 casos clínicos representativos de la cirugía reconstructiva practicada en pacientes quemados. Recogimos en total datos de 21 procedimientos de reconstrucción mediante colgajo libre en pacientes quemados. En ninguno se realizó reconstrucción primaria inmediata (en los primeros 5 días), mientras que la reconstrucción primaria temprana (entre el día 5 y el 21) se realizó en el 28,57% de los casos, la primaria intermedia (entre el día 21 y las 6 semanas) en el 28,57%, la secundaria (más de 6 semanas) en el 9,5%, y la cirugía de secuelas en el 33,33% de los casos. Las tasas de complicaciones mayores y menores fueron respectivamente 19,05% y 9,5%. El 50% de complicaciones mayores ocurrieron en el periodo de reconstrucción primaria temprana, mientras que no registramos ninguna en el periodo primario intermedio. El resto de complicaciones se repartió a partes iguales entre el periodo secundario y la cirugía de secuelas (ambas con el 25%). No encontramos asociación estadísticamente significativa entre las variables en ninguna de las comparaciones realizadas. En conclusión, creemos que la reconstrucción mediante colgajos libres en pacientes quemados presenta un riesgo más elevado de complicaciones mayores cuando se realiza en el periodo primario temprano (entre los días 5 y 21 tras la quemadura) (AU)

Free flap transfer is an essential tool within the reconstructive repertoire for the surgical treatment of major burn patients. For a long time there has been controversy about the influence of the timing over the complication rate, as well as the increased complication risk when we perform reconstruction by means of free flaps in burn patients. We designed a retrospective study about free flap reconstructions performed in our Burns Unit at the Hospital Universitari y Politecnic La Fe, Valencia (Spain), in the period from 2001 to 2013, collecting data related to the patient, the lesion, the reconstructive procedure, the results, and all this data related to timing. For the data analysis and associations between the different variables we used contingency tables and applied the Chi-square independence test. In addition we present 2 representative clinical reports about burn reconstructive surgery. Data from 21 reconstructive procedures with free flaps in burn patients were collected. Immediate primary reconstruction (in the first 5 days) is not performed in any patient, while early primary reconstruction (from day 5 to 21) was performed in 28,57% of cases; the intermediate primary reconstruction (from day 21 to 6th week) was performed in 28,57%, the secondary reconstruction (more than 6 weeks) in 9,5% and sequelae surgery in 33,33% of the cases. Major and minor complication rate were 19,05% and 9,5% respectively; 50% of major complications happened in early primary reconstruction period, whereas no complication is registered in intermediate primary period, the rest of complications are equally divided between secondary reconstruction period and sequelae surgery (both of them 25%). No statistically significant association between the variables is found in any of the comparisons performed. In conclusion, we think that reconstruction with free flaps applied to burn patients presents a higher major complication rate when performed in the early primary period (from day 5 to day 21 after the burn) (AU)