Aims

Osteosarcoma is the most common primary bone malignancy among children and adolescents. We investigated whether benzamil, an amiloride analogue and sodium-calcium exchange blocker, may exhibit therapeutic potential for osteosarcoma in vitro.

Side-effects associated to the use of bone morphogenetic proteins into scaffold-based devices for bone repair highlight the necessity for identifying new therapeutic targets that potentially improve bone healing in adults. In this sense, we recently demonstrated the age-associated decrease in the mechanosensitivity of bone marrow mesenchymal stromal/stem cells (MSCs) and identified c-Jun N-terminal kinase 3 (JNK3) as a mechanically-activated modulator of the superior osteogenic potential of MSCs derived from children (C-MSCs) in comparison to adults (A-MSCs). Building on this work, the aim of this study was to design a JNK3-activated collagen-nanohydroxyapatite (coll-nHA) scaffold that restore the child bone healing capacity in adults. Results revealed that JNK3 activator (JNK3*) enhanced A-MSC’ alkaline phosphatase (ALP) activity to the same extent of C-MSCs by facilitating the activation of JNK3. Moreover, A-MSCs cultured on the coll-JNK3* scaffold (collagen-scaffold containing JNK3*) showed positive uptake of the JNK3*, upregulation of early osteogenic markers as well as increased ALP activity and mineralization. More importantly, rat critical calvarial defects treated with coll-JNK3* for 28 days showed a significantly higher 18.07 % bone volume fraction in comparison to rats treated with Coll-nHA −6.04%- and empty defects −2.58%. Which correlated with the presence of a larger amount of blood vessels and mineralized tissue in samples treated with coll-JNK3* when compared with coll-nHA and empty defects. In conclusion, the coll-JNK3* capacity to enhance osteogenesis and bone healing by activating JNK3 highlights how by understanding the stem cell mechanobiology we can improve the development of next generation therapeutics for tissue repair.

Introduction

Although tension band wiring fixation of patellar fracture has been the most widely used technique, the metal implants related complications including implant loosening, postoperative pain are very common and additional surgeries are often necessary.

Introduction

Long bone surgery and marrow instrumentation represent significant surgical insults, and may cause severe local and systemic sequelae following both planned and emergent surgery. Preconditioning is a highly conserved evolutionary endogenous protective mechanism, but finding a clinically safe and acceptable method of induction has proven difficult. Glutamine, a known inducer of the heat shock protein (HSP) response, offers pharmacological modulation of injury through clinically acceptable preconditioning. This effect has not been previously demonstrated in an orthopaedic model.

Successful treatment of bone fractures requires a balance between stability, to restore functional anatomy and allow early mobilisation (and thus avoid dystrophy). The healing occurs through complex interactions of inducing, enabling and inhibitory factors. The mechanical environment (e.g. stress and strain) in/around the fracture site regulates tissue changes throughout the healing process, including the formation of a fibro-cartilaginous callus and its progressive replacement by bone. The mechanical and biological environment is controlled substantially by the selection of the fracture stabilisation method achieving either absolute stability (mostly achieved with compression plating technique) or relative stability allowing a limited amount of dynamic fracture displacement across the fracture gap. A number of treatments may be used to accomplish these conditions, ranging from splinting with a plaster cast, external fixator or an intramedullary nail to rigid internal fixation using plates affixed to the bone fragments. Fixation methods are presently selected on the basis of general guidelines, but nevertheless the optimal stability/instability remains unclear and relies heavily on the surgeon’s experience. With the recently more and more widely used locking plates the question of the optimal fixation technique and applied stability to the fracture zone especially in simple fractures have raised again.

To fill this knowledge gap, an interdisciplinary approach with in vitro and in vivo experiments seems to be essential. Analysing clinical situations and the healing course with mathematical modelling and computational simulations can further aid to understand the healing conditions in respect to stability.

This presentation will give an overview on the role of the mechanical environment in fracture healing, and demonstrating clinical examples that highlight the relevance of this research.

Bilateral mandibular lengthening is widely accepted during mandibular distraction osteogenesis. However, distraction osteogenesis are sometimes associated with clinical complications such as open bite deformity, lateral displacement of temporo-mandibular joint, premature consolidation and pin loosening. Although distraction osteogenesis aims to develop pure tensile strain on the regenerate tissue however, in real life situation due to differences in device orientation, materials and misalignment it is often subjected to complex stress and strain regimes.

The objective of this study was to characterise the mechanical environment (stress and strain) in the Finite Element Models (FEM) of regenerate tissue during two different device orientations:

(a) device placed parallel to the mandibular body

Furthermore, the influence of misalignment from above two idealised orientations was also investigated.

The distraction protocol in this study was similar to previous study of Loboa et al (2005). FE models were developed at four stages: end of latency, distraction day two, distraction day five and distraction day eight. At each time period a distraction of 1mm was applied to the model as it is most widely used distraction rate. In these models two primary distraction vectors were simulated; first when the device is parallel to the body of the mandible and second when the device is parallel to the axis of distraction.

Results indicate that when the device is placed parallel to the mandible the effect of distraction vector variation due to misalignment in transverse plane (±150 at an interval of 50 ; + indicate lateral and indicates medial) is symmetric and variation in the stress and strain regimes on regenerative tissue are less than 3%. However, when the device is placed parallel to axis of distraction the corresponding change is asymmetric and almost double in magnitude. The greatest differences were seen when misalignment is towards lateral side (+150). Similarly in the sagittal plane variations up to 17% were developed due to 0- 400 change in the distraction vector orientation. Thus the orientation of device which determines the distraction vector plays an important role in determining the mechanical environment around regenerative tissue. The results suggest that implications of misalignment of the device and its sensitivity from the ideal situation should be well understood during clinical planning.

Bone fluid flow transports nutrients to, and carries waste from, the bone cells embedded in the bony matrix. In long bones, it is driven by the blood pressure differentials between the medullary cavity and the periosteal surface and it is enhanced by mechanical loading. Loading of bone tissue deforms the bone matrix and changes the volume of the medullary cavity. Both mechanisms alter the interstitial fluid flow in the bone cortex. The former changes the volume of the fluid cavities in the cortex, while the latter modifies the intramedullary pressure (IMP). This study aims to investigate and compare, for the first time, the effects of these two mechanisms combined on the interstitial fluid flow in the bone cortex.

A hydraulic-fluid method is proposed to investigate the enhancement of IMP induced by the external loading. An intact sheep tibia is represented by a hollow cylinder, with the bone marrow being completely constrained in the cavity and assumed to behave as an icompressible liquid. The cortex is supposed to be a purely elastic material, and its permeability is ignored at this stage. The numerical results show that an axial compressive load of 500 N increases the IMP from 4000 Pa to 48900 Pa.

The influence of the enhanced IMP on the interstitial fluid flow is examined in a subsequent poroelastic analysis. At this stage, the cortex is assumed to be a biphasic material that permits fluid perfusion. The poroelastic analyses were conducted for both initial and enhanced IMPs. The results of the simulations demonstrate that the external load induces very high interstitial pressure. The highest pressure could be 25 times higher than the initial marrow pressure, but its magnitude decreases quickly. Furthermore, the influence of the IMP on the interstitial pressure is limited to the inner half of the cortical wall adjacent to the endosteal surface. However, the influence becomes more significant with decreasing load-induced interstitial pressure.

In conclusion, these simulations suggest that the increase in IMP during mechanical loading further enhances interstitial fluid movements in cortical bone, which highlights the importance of mechanical loading for the maintenance of healthy bones.

Biodegradable porous scaffolds play an important role in tissue engineering as the temporary templates for transplanted cells to guide the formation of the new organs. The most commonly used porous scaffolds are constructed from two classes of biomaterials. One class consists of synthetic biodegradable polymers such as poly (α-hydroxy acids), poly(glycolic acid), poly(lactic acid), and their copolymer of poly(DL-lactic-co-glycolic acid) (PLGA). The other class consists of naturally derived polymers such as collagen. These biomaterials have their respective advantages and drawbacks. Therefore, hybridization of these biomaterials has been expected to combine their advantages to provide excellent three-dimensional porous biomaterials for tissue engineering. Our group developed one such kind of hybrid biodegradable porous scaffolds by hybridizing synthetic poly (α-hydroxy acids) with collagen. Collagen microsponges were nested in the pores of poly (α-hydroxy acids) sponge to construct the poly (α-hydroxy acids)-collagen hybrid sponge.

Observation by scanning electron microscopy (SEM) showed that microsponges of collagen with interconnected pore structures were formed in the pores of poly (α-hydroxy acids) sponge. The mechanical strength of the hybrid sponge was higher than those of either poly (α-hydroxy acids) or collagen sponges both in dry and wet states. The wettability with water was improved by hybridization with collagen, which facilitated cell seeding in the hybrid sponge. Use of the poly (α-hydroxy acids) sponge as a skeleton facilitated formation of the hybrid sponge into the desired shapes with high mechanical strength, while collagen microsponges contributed good cell interaction and hydrophilicity. One of such kind of hybrids. Additionally, our group developed a hydrostatic pressure bioreactor for chondrocyte culture. And our study showed that hydrostatic pressure (0–3 MPa) had promotional effects on the production of proteoglycan and type II collagen by cultured chondrocytes. Therefore, it would be a promising pathway for reconstructing cartilage-like tissue to culture chondrocytes in this three-dimensional hybrid sponge under physiological hydrostatic pressure.