Design and Evaluation of an Osteogenesis-on-a-Chip Microfluidic Device Incorporating 3D Cell Culture.

Microfluidic-based tissue-on-a-chip devices have generated significant research interest for biomedical applications, such as pharmaceutical development, as they can be used for small volume, high throughput studies on the effects of therapeutics on tissue-mimics. Tissue-on-a-chip devices are evolving from basic 2D cell cultures incorporated into microfluidic devices to complex 3D approaches, with modern designs aimed at recapitulating the dynamic and mechanical environment of the native tissue. Thus far, most tissue-on-a-chip research has concentrated on organs involved with drug uptake, metabolism and removal (e.g., lung, skin, liver, and kidney); however, models of the drug metabolite target organs will be essential to provide information on therapeutic efficacy. Here, we develop an osteogenesis-on-a-chip device that comprises a 3D environment and fluid shear stresses, both important features of bone. This inexpensive, easy-to-fabricate system based on a polymerized High Internal Phase Emulsion (polyHIPE) supports proliferation, differentiation and extracellular matrix production of human embryonic stem cell-derived mesenchymal progenitor cells (hES-MPs) over extended time periods (up to 21 days). Cells respond positively to both chemical and mechanical stimulation of osteogenesis, with an intermittent flow profile containing rest periods strongly promoting differentiation and matrix formation in comparison to static and continuous flow. Flow and shear stresses were modeled using computational fluid dynamics. Primary cilia were detectable on cells within the device channels demonstrating that this mechanosensory organelle is present in the complex 3D culture environment. In summary, this device aids the development of 'next-generation' tools for investigating novel therapeutics for bone in comparison with standard laboratory and animal testing.

Multiscale hierarchical bioresorbable scaffolds for the regeneration of tendons and ligaments.

Lesions of tendons and ligaments account for over 40% of the musculoskeletal lesions. Surgical techniques and materials for repair and regeneration are currently not satisfactory. The high rate of post-operative complications and failures mainly relates to the technical difficulties in replicating the complex multiscale hierarchical structure and the mechanical properties of the native tendons and ligaments. With the aim of overcoming the limitations of non-biomimetic devices, we developed a hierarchical structure replicating the organization of tendons and ligaments. The scaffold consists of multiple bundles made of resorbable electrospun nanofibers of Poly-L-Lactic acid (PLLA) having tailored dimensions, wrapped in a sheath of nanofibers able to compact the construct. The bundles in turn consist of electrospun nanofibers with a preferential direction. High-resolution x-ray tomographic investigation at nanometer resolution confirmed that the morphology of the single bundles and of the entire scaffold replicated the hierarchical arrangement in the natural tendons and ligaments. To confirm that these structures could adequately restore tendons and ligaments, we measured the tensile stiffness, strength and toughness. The mechanical properties were in the range required to replace and repair tendons and ligaments. Furthermore, human fibroblasts were able to attach to the scaffolds and showed an increase in cell number, indicated by an increase in metabolic activity over time. Fibroblasts were preferentially aligned along the electrospun nanofibers. These encouraging in vitro results open the way for the next steps towards in vivo regeneration of tendons and ligaments.

Tendon Fascicle-Inspired Nanofibrous Scaffold of Polylactic acid/Collagen with Enhanced 3D-Structure and Biomechanical Properties.

Surgical treatment of tendon lesions still yields unsatisfactory clinical outcomes. The use of bioresorbable scaffolds represents a way forward to improve tissue repair. Scaffolds for tendon reconstruction should have a structure mimicking that of the natural tendon, while providing adequate mechanical strength and stiffness. In this paper, electrospun nanofibers of two crosslinked PLLA/Collagen blends (PLLA/Coll-75/25, PLLA/Coll-50/50) were developed and then wrapped in bundles, where the nanofibers are predominantly aligned along the bundles. Bundle morphology was assessed via SEM and high-resolution x-ray computed tomography (XCT). The 0.4-micron resolution in XCT demonstrated a biomimetic morphology of the bundles for all compositions, with a predominant nanofiber alignment and some scatter (50-60% were within 12° from the axis of the bundle), similar to the tendon microstructure. Human fibroblasts seeded on the bundles had increased metabolic activity from day 7 to day 21 of culture. The stiffness, strength and toughness of the bundles are comparable to tendon fascicles, both in the as-spun condition and after crosslinking, with moderate loss of mechanical properties after ageing in PBS (7 and 14 days). PLLA/Coll-75/25 has more desirable mechanical properties such as stiffness and ductility, compared to the PLLA/Coll-50/50. This study confirms the potential to bioengineer tendon fascicles with enhanced 3D structure and biomechanical properties.

An in vitro evaluation of resonant frequency analysis to measure fixed bridge stability.

OBJECTIVES/AIMS: To determine whether a clinically available resonance frequency analysis (RFA) device (Osstell Mentor), designed to assess implant integration, could identify a single uncemented retainer on fixed-fixed bridges, in vitro. MATERIALS AND METHODS: All-metal fixed-fixed bridges were cemented to acrylic tooth analogue abutments with simulated periodontal ligaments. Dental stone bases provided 100 or 50% 'bone support' groups (n = 50 in each). Control groups had both retainers cemented, whereas the test groups had the 'premolar' uncemented, mimicking clinical failure. A RFA device was used to measure bridge stability, expressed as a modified Implant Stability Quotient (Bridge Stability Quotient-BSQ) from a Smartpeg temporarily affixed to the bridge via composite. RESULTS: The BSQ recorded at the premolar site in both 100 and 50% support models demonstrated highly statistically significant differences (P <0.003) between the control and test groups. Sensitivity and specificity, area under the curve (receiver operating characteristic), analyses showed moderate test accuracy (0.735) for the 100% support group and good accuracy (0.96) for the 50% support group. CONCLUSION: The investigation suggests that RFA measurements were able to identify, reliably and non-destructively, in vitro, fixed-fixed bridges where the anterior retainer was uncemented. Further clinical research is required to determine whether this technique may allow early diagnosis of failing bridgework.