Effects of cyclic compression on the mechanical properties and calcification process of immature chick bone tissue in culture

Integration of clinical perspective into biomimetic bioreactor design for orthopedics

The challenges to accommodate multiple tissue formation metrics in conventional bioreactors have resulted in an increased interest to explore novel bioreactor designs. Bioreactors allow researchers to isolate variables in controlled environments to quantify cell response. While current bioreactor designs can effectively provide either mechanical, electrical, or chemical stimuli to the controlled environment, these systems lack the ability to combine all these stimuli simultaneously to better recapitulate the physiological environment. Introducing a dynamic and systematic combination of biomimetic stimuli bioreactor systems could tremendously enhance its clinical relevance in research. Thus, cues from different tissue responses should be studied collectively and included in the design of a biomimetic bioreactor platform. This review begins by providing a summary on the progression of bioreactors from simple to complex designs, focusing on the major advances in bioreactor technology and the approaches employed to better simulate in vivo conditions. The current state of bioreactors in terms of their clinical relevance is also analyzed. Finally, this review provides a comprehensive overview of individual biophysical stimuli and their role in establishing a biomimetic microenvironment for tissue engineering. To date, the most advanced bioreactor designs only incorporate one or two stimuli. Thus, the cell response measured is likely unrelated to the actual clinical performance. Integrating clinically relevant stimuli in bioreactor designs to study cell response can further advance the understanding of physical phenomenon naturally occurring in the body. In the future, the clinically informed biomimetic bioreactor could yield more efficiently translatable results for improved patient care.

A standalone bioreactor system to deliver compressive load under perfusion flow to hBMSC-seeded 3D chitosan-graphene templates

The availability of engineered biological tissues holds great potential for both clinical applications and basic research in a life science laboratory. A prototype standalone perfusion/compression bioreactor system was proposed to address the osteogenic commitment of stem cells seeded onboard of 3D chitosan-graphene (CHT/G) templates. Testing involved the coordinated administration of a 1 mL/min medium flow rate together with dynamic compression (1% strain at 1 Hz; applied twice daily for 30 min) for one week. When compared to traditional static culture conditions, the application of perfusion and compression stimuli to human bone marrow stem cells using the 3D CHT/G template scaffold induced a sizable effect. After using the dynamic culture protocol, there was evidence of a larger number of viable cells within the inner core of the scaffold and of enhanced extracellular matrix mineralization. These observations show that our novel device would be suitable for addressing and investigating the osteogenic phenotype commitment of stem cells, for both potential clinical applications and basic research.

Mechanical behaviour of alginate film with embedded voids under compression-decompression cycles

Voids of 300 µm diameter were embedded uniformly as monolayer in alginate gel film using a fluidic device. Voids of these dimensions in biopolymer gel film are desired for better transport of bioactive species and cell colonization in engineered tissues. In this article, the role of embedded voids in reducing compressive stress, hysteresis, and time scale of reheal vis-a-vis expulsion of pore fluid and its reabsorption upon reversal of load are reviewed. The cyclic loading was conducted with varying amplitude and frequency. The irreversible changes, if any in the gel structure under extreme compression were analyzed. The rate of expulsion of aqueous phase directly relates to the permeability of the gel film that is estimated here using simplified momentum and volumetric balance equations. The decrease in permeability with deformation is analyzed further, and the contribution of voids in this regard is discussed.

Metallic ion doped tri-calcium phosphate ceramics: Effect of dynamic loading on in vivo bone regeneration

The present study was carried out to evaluate the effect of dynamic loading on bone regeneration performance of different doped β-tri-calcium phosphate ceramics. We have developed porous beta tri-calcium phosphate (β-TCP), 5%zinc doped, 5% magnesium doped and 5% titanium doped β-TCP by aqueous solution combustion technique. All the synthesized β-TCP powders showed pore size of 21-146 μm (pure β-TCP), 16-142 μm (Zn-β-TCP), 28-156 μm (Mg- β-TCP) and 14-173 μm (Ti-β-TCP) while their apparent porosity 17.89%, 28.09%, 26.54% and 25.87% respectively. The pure and doped samples were implanted in femoral bone defect model (rabbit) to assess bone regeneration under dynamic loading. Bone regeneration was assessed after 1 and 2 month post-implantation on the basis of clinical radiological, histological, fluorochrome labelling, micro computed tomography (μ-CT) and scanning electron microscopy (SEM). Radiological and fluorochrome labelling study showed reduced size of 5%Ti-β-TCPimplant vis-à-vis more new bone formation as compared to other groups. Micro-CT of the implanted bone sample showed a significant amount of newly formed bony tissue surrounding the Ti-β-TCP implant as compared to other samples. Similar findings of less interfacial gap between the implant and bone were also observed in SEM study. However, all the doped materials are suitable as bone grafting material and have potential for application in bone tissue engineering.

Finite-Element Syntheses of Callus and Bone Remodeling: Biomechanical Study of Fracture Healing in Long Bones

Computational simulations of fracture healing are a valuable tool to improve fracture treatment and implants. Several finite-element models have been established to predict callus formation due to mechanobiological rules. This work provides a comprehensive simulation for virtual implantation through the combination of callus simulation and finite-element structural synthesis (FESS) of (re-)modeling during and after healing based on Pauwel's theory of histogenesis and Wolff's law. The simulation is based on a linear elastic material model and includes generation of fracture hematoma and initial mesenchymal stem cell concentration out of an unspecified solid, cell proliferation, migration, and differentiation due to mechanical stimuli and time-dependent axial loading. Three nondisplaced femoral shaft fractures with initial interfragmentary movement of 0.2, 0.6, and 1 mm and one fracture with 4 mm translation are modeled. The predictions of interfragmentary movement during fracture healing, healing success, and healing time agree with observed clinical outcome, animal models, and other numerical models. Initial interfragmentary movement between 0.2 and 1 mm leads to healing success, with the fastest healing occurring at 0.2 mm. The model of the dislocated fractures shows no further bending after remodeling and is loaded with physiological stress of -13 MPa. Ideal load-time graphs may give insight into the bone's ability to withstand loads as healing time progresses, and thus holds potential for applications in rehabilitation planning. Better knowledge of the forces present during fracture healing is needed to deploy simulations for surgical planning and manufacturing of patient individualized implants. Anat Rec, 301:2112-2121, 2018. © 2018 Wiley Periodicals, Inc.

Ex-vivo observation of calcification process in chick tibia slice: Augmented calcification along collagen fiber orientation in specimens subjected to static stretch

Bone formation through matrix synthesis and calcification in response to mechanical loading is an essential process of the maturation in immature animals, although how mechanical loading applied to the tissue increases the calcification and improves mechanical properties, and which directions the calcification progresses within the tissue are largely unknown. To address these issues, we investigated the calcification of immature chick bone under static tensile stretch using a newly developed real-time observation bioreactor system. Bone slices perpendicular to the longitudinal axis obtained from the tibia in 2- to 4-day-old chick legs were cultured in the system mounted on a microscope, and their calcification was observed up to 24 h while they were stretched in the direction parallel to the slice. Increase in the calcified area, traveling distance and the direction of the calcification and collagen fiber orientation in the newly calcified region were analyzed. There was a significant increase in calcified area in the bone explant subjected to tensile strain over ∼3%, which corresponds to the threshold strain for collagen fibers showing alignment in the direction of stretch, indicating that the fiber alignment may enhance tissue calcification. The calcification progressed to a greater distance to the stretching direction in the presence of the loading. Moreover, collagen fiber orientation in the calcified area in the loaded samples was coincided with the progression angle of the calcification. These results clearly show that the application of static tensile strain enhanced tissue calcification, which progresses along collagen fibers aligned to the loading direction.