Differentiation of mesenchymal stem cells for cartilage tissue engineering: Individual and synergetic effects of three-dimensional environment and mechanical loading.

Chondrogenesis of dedifferentiated chondrocytes and mesenchymal stem cells is influenced not only by soluble molecules like growth factors, but also by the cell environment itself. The latter is achieved through both mechanical cues - which act as stimulation factor and influences nutrient transport - and adhesion to extracellular matrix cues - which determine cell shape. Although the effects of soluble molecules and cell environment have been intensively addressed, few observations and conclusions about the interaction between the two have been achieved. In this work, we review the state of the art on the single effects between mechanical and biochemical cues, as well as on the combination of the two. Furthermore, we provide a discussion on the techniques currently used to determine the mechanical properties of materials and tissues generated in vitro, their limitations and the future research needs to properly address the identified problems. STATEMENT OF SIGNIFICANCE: The importance of biomechanical cues in chondrogenesis is well known. This paper reviews the existing literature on the effect of mechanical stimulation on chondrogenic differentiation of mesenchymal stem cells in order to regenerate hyaline cartilage. Contradictory results found with respect to the effect of different modes of external loading can be explained by the different properties of the scaffolding system that holds the cells, which determine cell adhesion and morphology and spatial distribution of cells, as well as the stress transmission to the cells. Thus, this review seeks to provide an insight into the interplay between external loading program and scaffold properties during chondrogenic differentiation. The review of the literature reveals an important gap in the knowledge in this field and encourages new experimental studies. The main issue is that in each of the few cases in which the interplay is investigated, just two groups of scaffolds are compared, leaving intermediate adhesion conditions out of study. The authors propose broader studies implementing new high-throughput techniques for mechanical characterization of tissue engineering constructs and the inclusion of fatigue analysis as support methodology to more exhaustive mechanical characterization.

Design and validation of a biomechanical bioreactor for cartilage tissue culture.

Specific tissues, such as cartilage, undergo mechanical solicitation under their normal performance in human body. In this sense, it seems necessary that proper tissue engineering strategies of these tissues should incorporate mechanical solicitations during cell culture, in order to properly evaluate the influence of the mechanical stimulus. This work reports on a user-friendly bioreactor suitable for applying controlled mechanical stimulation--amplitude and frequency--to three-dimensional scaffolds. Its design and main components are described, as well as its operation characteristics. The modular design allows easy cleaning and operating under laminar hood. Different protocols for the sterilization of the hermetic enclosure are tested and ensure lack of observable contaminations, complying with the requirements to be used for cell culture. The cell viability study was performed with KUM5 cells.

In vitro mechanical fatigue behavior of poly-ɛ-caprolactone macroporous scaffolds for cartilage tissue engineering: Influence of pore filling by a poly(vinyl alcohol) gel.

Polymeric scaffolds used in regenerative therapies are implanted in the damaged tissue and submitted to repeated loading cycles. In the case of articular cartilage engineering, an implanted scaffold is typically subjected to long-term dynamic compression. The evolution of the mechanical properties of the scaffold during bioresorption has been deeply studied in the past, but the possibility of failure due to mechanical fatigue has not been properly addressed. Nevertheless, the macroporous scaffold is susceptible to failure after repeated loading-unloading cycles. In this work fatigue studies of polycaprolactone scaffolds were carried by subjecting the scaffold to repeated compression cycles in conditions simulating the scaffold implanted in the articular cartilage. The behavior of the polycaprolactone sponge with the pores filled with a poly(vinyl alcohol) gel simulating the new formed tissue within the pores was compared with that of the material immersed in water. Results were analyzed with Morrow's criteria for failure and accurate fittings are obtained just up to 200 loading cycles. It is also shown that the presence of poly(vinyl alcohol) increases the elastic modulus of the scaffolds, the effect being more pronounced with increasing the number of freeze/thawing cycles.

Fatigue prediction in fibrin poly-ε-caprolactone macroporous scaffolds.

Tissue engineering applications rely on scaffolds that during its service life, either for in-vivo or in vitro applications, are under loading. The variation of the mechanical condition of the scaffold is strongly relevant for cell culture and has scarcely been addressed. The fatigue life cycle of poly-ε-caprolactone, PCL, scaffolds with and without fibrin as filler of the pore structure were characterized both dry and immersed in liquid water. It is observed that the there is a strong increase from 100 to 500 in the number of loading cycles before collapse in the samples tested in immersed conditions due to the more uniform stress distributions within the samples, the fibrin loading playing a minor role in the mechanical performance of the scaffolds.

Fibronectin adsorption and cell response on electroactive poly(vinylidene fluoride) films.

Due to the large potential of electroactive materials in novel tissue engineering strategies, the aim of this work is to determine if the crystalline phase and/or the surface electrical charge of electroactive poly(vinylidene fluoride), PVDF, have influence on the biological response in monolayer cell culture. Non-polar α-PVDF and electroactive ß-PVDF were prepared. The ß-PVDF films were poled by corona discharge to show negative or positive electrical surface charge density. It has been concluded that hydrophilicity of the PVDF substrates depends significantly on crystalline phase and polarity. Furthermore, by means of atomic force microscopy and an enzyme-linked immunosorbent assay test, it has been shown that positive or negative poling strongly influences the behavior of ß-PVDF supports with respect to fibronectin (FN) adsorption, varying the exhibition of adhesion ligands of adsorbed FN. Culture of MC3T3-E1 pre-osteoeblasts proved that cell proliferation depends on surface polarity as well. These results open the viability of cell culture stimulation by mechanical deformation of a piezoelectric substrate that results in varying electrical charge densities on the substrate surface.

Ventilación mecánica no invasiva. Utilidad clínica enurgencias y emergencias / Non-invasive mechanical ventilation. Clinical utility in urgencias and emergencias

La ventilación mecánica no invasiva (VMNI) es una modalidad ventilatoria en la cual la interfase entre el ventilador y el paciente es una máscara nasal o facial. Esto evita muchas de las complicaciones de la ventilación mecánica convencional ligadas fundamentalmente a la intubación endotraqueal y la sedorrelajación del enfermo. Con VMNI el paciente mantiene intactos los mecanismos de defensa de la vía aérea, el habla y la deglución. La forma de administrar VMNI suele ser mediante presión de soporte durante la inspiración y presión positiva (PEEP) en la espiración (ésta es la modalidad conocida con las siglas BIPAP), o mediante presión positiva continua en la vía aérea (CPAP).Otras formas, como la ventilación con presión positiva intermitente con máscara facial o nasal se puede también emplear, aunque se utiliza menos. La principal indicación la constituye la insuficiencia respiratoria aguda con hipercapnia, aunque también puede ser utilizada en el fracaso respiratorio hipoxémico. En los pacientes con autoPEEP proporciona descanso a la musculatura respiratoria y mejora notablemente el intercambio de gases. Esta forma de ventilación mecánica se está empezando a utilizar en los servicios de urgencia y emergencia, evitando en muchos casos el ingreso del paciente en la unidad de cuidados intensivos y acortando la estancia en el hospital. El médico de urgencias debe conocer esta técnica de terapia respiratoria y administrarla precozmente al paciente en insuficiencia respiratoria, y no esperar a una situación de preintubación (AU)