Ectopic bone formation in bone marrow stem cell seeded calcium phosphate scaffolds as compared to autograft and (cell seeded) allograft

Improvements to current therapeutic strategies are needed for the treatment of skeletal defects. Bone tissue engineering offers potential advantages to these strategies. In this study, ectopic bone formation in a range of scaffolds was assessed. Vital autograft and devitalised allograft served as controls and the experimental groups comprised autologous bone marrow derived stem cell seeded allograft, biphasic calcium phosphate (BCP) and tricalcium phosphate (TCP), respectively. All implants were implanted in the back muscle of adult Dutch milk goats for 12 weeks. Micro-computed tomography (µCT) analysis and histomorphometry was performed to evaluate and quantify ectopic bone formation. In good agreement, both µCT and histomorphometric analysis demonstrated a significant increase in bone formation by cell-seeded calcium phosphate scaffolds as compared to the autograft, allograft and cell-seeded allograft implants. An extensive resorption of the autograft, allograft and cell-seeded allograft implants was observed by histology and confirmed by histomorphometry. Cell-seeded TCP implants also showed distinct signs of degradation with histomorphometry and µCT, while the degradation of the cell-seeded BCP implants was negligible. These results indicate that cell-seeded calcium phosphate scaffolds are superior to autograft, allograft or cell-seeded allograft in terms of bone formation at ectopic implantation sites. In addition, the usefulness of µCT for the efficient and non-destructive analysis of mineralised bone and calcium phosphate scaffold was demonstrated

Ppia and ywhaz constitute a stable pair of reference genes during electrical stimulation in mesenchymal stem cells

YesMesenchymal stem cells (MSCs) are multipotent adult stem cells with great potential in regenerative medicine. One method for stimulating proliferation and differentiation of MSCs is via electrical stimulation (ES). A valuable approach for evaluating the response of MSCs to ES is to assess changes in gene expression, relative to one or more reference genes. In a survey of 25 publications that used ES on cells, 70% selected GAPDH as the reference gene. We conducted a study to assess the suitability of six potential reference genes on an immortalized human MSC line following direct current ES at seeding densities of 5000 and 10,000 cells/cm2 . We employed three methods to validate the most stable reference genes from qRT-PCR data. Our findings show that GAPDH and ACTB exhibit reduced stability when seeded at 5000 cell/cm2 . In contrast, we found that the most stable genes across both plating densities and stimulation regimes were PPIA and YWHAZ. Thus, in ES gene expression studies in MSCs, we support the use of PPIA and YWHAZ as an optimal reference gene pair, and discourage the use of ACTB and GAPDH at lower seeding densities. However, it is strongly recommended that similar verification studies are carried out based on cell type and different ES conditions

A generalized frequency detuning method for multidegree-of-freedom oscillators with nonlinear stiffness

In this paper, we derive a frequency detuning method for multi-degree-of-freedom oscillators with nonlinear stiffness. This approach includes a matrix of detuning parameters, which are used to model the amplitude dependent variation in resonant frequencies for the system. As a result, we compare three different approximations for modeling the affect of the nonlinear stiffness on the linearized frequency of the system. In each case, the response of the primary resonances can be captured with the same level of accuracy. However, harmonic and subharmonic responses away from the primary response are captured with significant differences in accuracy. The detuning analysis is carried out using a normal form technique, and the analytical results are compared with numerical simulations of the response. Two examples are considered, the second of which is a two degree-of-freedom oscillator with cubic stiffnesses

State of the art composites comprising electrospun fibres coupled with hydrogels: a review

Research into scaffolds tailored for specific tissue engineering and biomaterial applications continues to develop as these structures are commonly impeded by their limitations. For example, electrospun fibres and hydrogels are commonly exploited because of their ability to mimic natural tissues; however, their clinical use remains restricted due to negligible cellular infiltration and poor mechanical properties, respectively. A small number of research groups are beginning to investigate composite scaffolds based on electrospun fibres and hydrogels in an attempt to overcome their individual shortcomings. This review paper discusses the various methodologies and approaches currently undertaken to create these novel composite structures and their intended applications. The combination of these two commonly used scaffold architectures to create synergistically superior structures is showing potential with regards to therapeutic use within the tissue engineering community

Vibration suppression of a principal parametric resonance

In this paper, a control method that combines linear and nonlinear-velocity feedback control is proposed to suppress the principal parametric resonance in a flexible cantilever beam structure. Linear-velocity feedback is employed for bifurcation control, and cubic-velocity feedback is employed to suppress high-amplitude vibration. A unified bifurcation parameter 2 that includes both the excitation frequency and amplitude is defined for the stability analysis, so that bifurcations under quasi-stationary frequency-response and quasi-stationary force-response can be treated uniformly when 2 is quasi-statically varied. This unified bifurcation parameter simplifies the system stability analysis as well as the controller design procedure. Numerical simulation and experimental results show that the combined bifurcation control and nonlinear feedback control strategy performs better than linear-velocity or cubic-velocity feedback control alone, and is less susceptible to actuator saturation.L. Chen, F. He and K. Sammu