Design and application of an oscillatory compression device for cell constructs

The design and development of a high-throughput magneto-mechanostimulation device for cartilage tissue engineering

To recapitulate the in vivo environment and create neo-organoids that replace lost or damaged tissue requires the engineering of devices, which provide appropriate biophysical cues. To date, bioreactors for cartilage tissue engineering have focused primarily on biomechanical stimulation. There is a significant need for improved devices for articular cartilage tissue engineering capable of simultaneously applying multiple biophysical (electrokinetic and mechanical) stimuli. We have developed a novel high-throughput magneto-mechanostimulation bioreactor, capable of applying static and time-varying magnetic fields, as well as multiple and independently adjustable mechanical loading regimens. The device consists of an array of 18 individual stations, each of which uses contactless magnetic actuation and has an integrated Hall Effect sensing system, enabling the real-time measurements of applied field, force, and construct thickness, and hence, the indirect measurement of construct mechanical properties. Validation tests showed precise measurements of thickness, within 14 μm of gold standard calliper measurements; further, applied force was measured to be within 0.04 N of desired force over a half hour dynamic loading, which was repeatable over a 3-week test period. Finally, construct material properties measured using the bioreactor were not significantly different (p=0.97) from those measured using a standard materials testing machine. We present a new method for articular cartilage-specific bioreactor design, integrating combinatorial magneto-mechanostimulation, which is very attractive from functional and cost viewpoints.

Primary cilia modulate Ihh signal transduction in response to hydrostatic loading of growth plate chondrocytes

Indian hedgehog (Ihh) is a key component of the regulatory apparatus governing chondrocyte proliferation and differentiation in the growth plate. Recent studies have demonstrated that the primary cilium is the site of Ihh signaling within the cell, and that primary cilia are essential for bone and cartilage formation. Primary cilia are also postulated to act as mechanosensory organelles that transduce mechanical forces acting on the cell into biological signals. In this study, we used a hydrostatic compression system to examine Ihh signal transduction under the influence of mechanical load. Our results demonstrate that hydrostatic compression increased both Ihh gene expression and Ihh-responsive Gli-luciferase activity. These increases were aborted by disrupting the primary cilia structure with chloral hydrate. These results suggest that growth plate chondrocytes respond to hydrostatic loading by increasing Ihh signaling, and that the primary cilium is required for this mechano-biological signal transduction to occur.

Design, construction and validation of a computer controlled system for functional loading of soft tissue

Osteoarthritis is a chronic degenerative disease affecting body joints. Abnormal mechanical loading could be an initiating factor of cartilage damage, by influencing chondrocytes activity. To date, devices performing mechanical studies of viable tissues are mostly uniaxial. In this work, we developed and validated a multi-axial device for static and dynamic mechanical testing of viable soft tissues. The system, named RPETS, is composed of a motor driven indenter, moving vertically and horizontally along the bottom of a tank containing tissue samples and it can apply combined compression, sliding, and rolling on viable samples. Validation studies were performed with standard rubber and bovine nasal cartilage tissue. Static tests demonstrated that the system is comparable to existing uniaxial devices, with a maximum force control error smaller than 0.5N and a positioning resolution of 5 μm. Dynamic tests performed with different motion profiles showed that the system can exert a load of 100N with a maximum velocity of 100mm/s maintaining the force control error within 10% of the desired value. Sinusoidal motion frequency can vary between 0.05 and 0.5Hz. In practical tests, viability staining of dynamically loaded cartilage slices showed extents of cell death to depend on the indenter velocity.

A novel bioreactor for the dynamic stimulation and mechanical evaluation of multiple tissue-engineered constructs

Systematic advancements in the field of musculoskeletal tissue engineering require clear communication about the mechanical environments that promote functional tissue growth. To support the rapid discovery of effective mechanostimulation protocols, this study developed and validated a mechanoactive transduction and evaluation bioreactor (MATE). The MATE provides independent and consistent mechanical loading of six specimens with minimal hardware. The six individual chambers accurately applied static and dynamic loads (1 and 10 Hz) in unconfined compression from 0.1 to 10 N. The material properties of poly(ethylene glycol) diacrylate hydrogels and bovine cartilage were measured by the bioreactor, and these values were within 10% of the values obtained from a standard single-chamber material testing system. The bioreactor was able to detect a 1-day 12% reduction (2 kPa) in equilibrium modulus after collagenase was added to six collagenase sensitive poly(ethylene glycol) diacrylate hydrogels (p = 0.03). By integrating dynamic stimulation and mechanical evaluation into a single batch-testing research platform, the MATE can efficiently map the biomechanical development of tissue-engineered constructs during long-term culture.

An integrated instrument for rapidly deforming living cells using rapid pressure pulses and simultaneously monitoring applied strain in near real time

Because many types of living cells are sensitive to applied strain, different in vitro models have been designed to elucidate the cellular and subcellular processes that respond to mechanical deformation at both the cell and tissue level. Our focus was to improve upon an already established strain system to make it capable of independently monitoring the deflection and applied pressure delivered to specific wells of a commercially available, deformable multiwell culture plate. To accomplish this, we devised a custom frame that was capable of mounting deformable 6 or 24 well plates, a pressurization system that could load wells within the plates, and a camera-based imaging system which was capable of capturing strain responses at a sufficiently high frame rate. The system used a user defined program constructed in Labview(®) to trigger plate pressurization while simultaneously allowing the deflection of the silicone elastomeric plate bottoms to be imaged in near real time. With this system, up to six wells could be pulsed simultaneously using compressed air or nitrogen. Digital image capture allowed near-real time monitoring of applied strain, strain rate, and the cell loading profiles. Although our ultimate goal is to determine how different strain rates applied to neurons modulates their intrinsic biochemical cascades, the same platform technology could be readily applied to other systems. Combining commercially available, deformable multiwell plates with a simple instrument having the monitoring capabilities described here should permit near real time calculations of stretch-induced membrane strain in multiple wells in real time for a wide variety of applications, including high throughput drug screening.

Development of a micromanipulator-based loading device for mechanoregulation study of human mesenchymal stem cells in three-dimensional collagen constructs

Mechanical signal is important for regulating cellular activities, including proliferation, metabolism, matrix production, and orientation. Bioreactors with loading functions can be used to precondition cells in three-dimensional (3D) constructs so as to study the cellular responses to mechanical stimulation. However, full-scale bioreactor is not always an affordable option considering the high cost of equipment and the liter-sized medium with serum and growth factor supplements. In this study, a custom-built loading system was developed by coupling a conventional camera-equipped inverted research microscope with two micromanipulators. The system was programmed to deliver either cyclic compressive loading with different frequencies or static compressive loading for 1 week to investigate the cellular responses of human mesenchymal stem cells (hMSCs) entrapped in a 3D construct consists of reconstituted collagen fibers. Cellular properties, including their alignment, cytoskeleton, and cell metabolism, and properties of matrix molecules, such as collagen fiber alignment and glycosaminoglycan deposition, were evaluated. Using a MatLab-based image analysis program, reorientation of the entrapped cells from a random distribution to a preferred alignment along the loading direction in constructs with both static and cyclic compression has been demonstrated, but no such alignment was found in the free-floating controls. Fluorescent staining on filamentous actin cytoskeleton also confirmed the finding. Nevertheless, the collagen fiber meshwork entrapping the hMSCs remained randomly distributed, and no change in cellular metabolism and glycosaminoglycans production was noted. The current study provides a simple and affordable option toward setting up a mechanoregulation facility based on existing laboratory equipment and sheds new insights on the effect of mechanical loading on the alignment of hMSCs in 3D collagen constructs.

Modulation of gene expression of rabbit chondrocytes by dynamic compression in polyurethane scaffolds with collagen gel encapsulation

Chondrocytes have been demonstrated to be sensitive to mechanical stimuli, such as compression, tension, shear force, and hydrostatic pressure. The responses of chondrocytes to mechanical compression have been often studied in vitro with cartilage and chondrocyte/hydrogel systems. The aim of this study was to investigate the effects of dynamic compression on gene expression of rabbit chondrocytes which were seeded in elastic polyurethane scaffolds with or without collagen gel encapsulation. Dynamic compression of 20% or 30% strain with 0.1 Hz frequency was applied to the cell-seeded scaffolds for 4, 8, 12, or 24 h, and then the expression of the three genes related to chondrogenic phenotype, type I and II collagens and aggrecan, was analyzed by RT-PCR. We also investigated the gene expression of the compressed chondrocytes, which had experienced 12-h 30% strain dynamic loading, during the post-compression resting period. We found that the expression of type II collagen did not seem to respond to cyclic compression. On the other hand, aggrecan gene was stimulated by dynamic compression. The stimulatory effect disappeared gradually after the dynamic compression was ceased. Furthermore, the mechano-response of the chondrocytes to aggrecan expression was delayed by collagen gel encapsulation. The expression of type I collagen was enhanced by collagen gel. We found that collagen gel encapsulation prolonged the expression of aggrecan and type I collagen during post-compression resting period. We demonstrated that mechanical and biochemical stimuli modulate the gene expression of chondrocytes.