The zonal organization of articular cartilage is crucial in providing the tissue with mechanical properties to withstand compression and shearing force. Current treatments available for articular cartilage injury are not able to restore the hierarchically organized architecture of the tissue. Implantation of zonal chondrocyte as a multilayer tissue construct could overcome the limitation of current treatments. However, it is impeded by the lack of efficient zonal chondrocyte isolation protocol and dedifferentiation of chondrocytes during expansion on tissue culture plate (TCP). This study aims to develop a protocol to produce an adequate number of high-quality zonal chondrocytes for clinical application via size-based zonal chondrocyte separation using inertial spiral microchannel device and expansion under dynamic microcarrier culture.

Full thickness (FT) chondrocytes isolated from porcine femoral condyle cartilage were subjected to two serial of size-based sorting into three subpopulations of different cell sizes, namely small (S1), medium (S2), and large (S3) chondrocytes. Zonal phenotype of the three subpopulations was characterised. To verify the benefit of stratified zonal chondrocyte implantation in the articular cartilage regeneration, a bilayer hydrogel construct composed of S1 chondrocytes overlaying a mixture of S2 and S3 (S2S3) chondrocytes was delivered to the rat osteochondral defect model. For chondrocyte expansion, two dynamic microcarrier cultures, sort-before-expansion and sort-after-expansion, which involved expansion after or before zonal cells sorting, were studied to identify the best sort-expansion strategy.

Size-sorted zonal chondrocytes showed zone-specific characteristics in qRT-PCR with a high level of PRG4 expression in S1 and high level of aggrecan, Type II and IX collagen expression in S2 and S3. Cartilage reformation capability of sorted zonal chondrocytes in three-dimensional fibrin hydrogel showed a similar trend in qRT-PCR, histology, extracellular matrix protein quantification and mechanical compression test, indicating the zonal characteristics of S1, S2 and S3 as superficial (SZ), middle (MZ) and deep (DZ) zone chondrocytes, respectively. Implantation of bilayered zonal chondrocytes resulted in better cartilage tissue regeneration in a rat osteochondral defect model than FT control group, with predominantly Type II hyaline cartilage tissue and significantly lower Type I collagen. Dynamic microcarrier expansion of sorted zonal chondrocytes was able to retain the zonal cell size difference that correlate to zonal phenotype, while maintaining the rounded chondrocyte morphology and F-actin distribution similar to that in mature articular cartilage. With the better retention of zonal cell size and zonal phenotype relation on microcarrier, zonal cells separation was achievable in the sort-after-expansion strategy with cells expanded on microcarrier, in comparison to cells expanded on TCP.

Inertial spiral microchannel device provides a label-free and high throughput method to separate zonal chondrocytes based on cell size. Stratified implantation of zonal chondrocytes has the potential to improve articular cartilage regeneration. Dynamic microcarrier culture allows for size-based zonal chondrocyte separation to be performed on expanded chondrocytes, thus overcoming the challenge of limited tissue availability from the patients. Our novel zonal chondrocyte isolation and expansion protocol provide a translatable strategy for stratified zonal chondrocyte implantation that could improve articular cartilage regeneration of critical size defects.

Adult articular cartilage mechanical functionality is dependent on the unique zonal organization of its tissue. Current mesenchymal stem cell (MSC)-based treatment has resulted in sub-optimal cartilage repair, with inferior quality of cartilage generated from MSCs in terms of the biochemical content, zonal architecture and mechanical strength when compared to normal cartilage. The phenotype of cartilage derived from MSCs has been reported to be influenced by the microenvironmental biophysical cues, such as the surface topography and substrate stiffness. In this study, the effect of nano-topographic surfaces to direct MSC chondrogenic differentiation to chondrocytes of different phenotypes was investigated, and the application of these pre-differentiated cells for cartilage repair was explored.

Specific nano-topographic patterns on the polymeric substrate were generated by nano-thermal imprinting on the PCL, PGA and PLA surfaces respectively. Human bone marrow MSCs seeded on these surfaces were subjected to chondrogenic differentiation and the phenotypic outcome of the differentiated cells was analyzed by real time PCR, matrix quantification and immunohistological staining. The influence of substrate stiffness of the nano-topographic patterns on MSC chondrogenesis was further evaluated. The ability of these pre-differentiated MSCs on different nano-topographic surfaces to form zonal cartilage was verified in in vitro 3D hydrogel culture. These pre-differentiated cells were then implanted as bilayered hydrogel constructs composed of superficial zone-like chondro-progenitors overlaying the middle/deep zone-like chondro-progenitors, was compared to undifferentiated MSCs and non-specifically pre-differentiated MSCs in a osteochondral defect rabbit model.

Nano-topographical patterns triggered MSC morphology and cytoskeletal structure changes, and cellular aggregation resulting in specific chondrogenic differentiation outcomes. MSC chondrogenesis on nano-pillar topography facilitated robust hyaline-like cartilage formation, while MSCs on nano-grill topography were induced to form fibro/superficial zone cartilage-like tissue. These phenotypic outcomes were further diversified and controlled by manipulation of the material stiffness. Hyaline cartilage with middle/deep zone cartilage characteristics was derived on softer nano-pillar surfaces, and superficial zone-like cartilage resulted on softer nano-grill surfaces. MSCs on stiffer nano-pillar and stiffer nano-grill resulted in mixed fibro/hyaline/hypertrophic cartilage and non-cartilage tissue, respectively. Further, the nano-topography pre-differentiated cells possessed phenotypic memory, forming phenotypically distinct cartilage in subsequent 3D hydrogel culture. Lastly, implantation of the bilayered hydrogel construct of superficial zone-like chondro-progenitors and middle/deep zone-like chondro-progenitors resulted in regeneration of phenotypically better cartilage tissue with higher mechanical function.

Our results demonstrate the potential of nano-topographic cues, coupled with substrate stiffness, in guiding the differentiation of MSCs to chondrocytes of a specific phenotype. Implantation of these chondrocytes in a bilayered hydrogel construct yielded cartilage with more normal architecture and mechanical function. Our approach provides a potential translatable strategy for improved articular cartilage regeneration using MSCs.

In orthopedic surgeries, it is critical to reduce the risks of drilling complications during bone fracture fixation, especially around critical organs such as in acetabula-pelvic procedures. Either over-drilling or x-ray overuse shall be avoided to reduce potential complications to the surrounding critical organs or tissues. Toward recognising perforation process during bong drilling, we employed drilling vibration signal analysis based on the measurements from miniature inertial sensors. Time-frequency analysis is used for features extractions, which show that information from drilling vibration measurements could reveal the drilling process, hence help doctors track the drilling process and avoid over-drilling.

We addressed the aforementioned challenges through inertial sensor development, vibration measurements, and time-frequency signal analysis. In the preliminary ex-vivo bone drilling experiment setup, an inertial sensor is mounted on a pig femur bone with two fixing nails and can capture 3-axes acceleration data during drilling procedures. A cordless drill is used with Kirschner wires (K-wires) and the diameter of the pin is 3.5 mm. The mounting locations of inertial sensors are close to actual drilling entries without affecting normal procedures. The recorded vibration signals indicate how the drill is interacting with surrounding bone tissues, which shall have different patterns along the deep drilling process. After normalisation, the power spectral density (PSD) is calculated to examine the frequency domain representation of the time series during drilling process. As the drilling vibration process along the bone is non-stationary, we further employ wavelet transform for more localised time-frequency analysis.

When the bone substance interacts with drill bits, compact substance and spongy substance have different bone densities and structures, thus inducing different vibration waveform patterns. In our preliminary experiments, we recorded acceleration data from the pig femur drilling process, where a surgical drill penetrates from compact substance, spongy substance and then to compact substance again. The article shows the feasibility study of estimating femur bone drilling process based on vibrations signals captured from low-cost miniature inertial sensors. Through a preliminary animal ex-vivo bone study, the proposed framework of time-frequency wavelet analysis indicates the drilling interface between compact substance and spongy substance. It shows potentials in perforation recognition along drilling process and more clinical studies will be performed for validating its capability in over-drilling avoidance.

To identify factors that predict poor patient-reported outcomes in patients with traumatic vertebral body fracture(s) of the thoracic and/or lumbar spine without neurological deficit.

There is a paucity of information on factors that predict poor patient-reported outcomes in patients with traumatic vertebral body fracture(s) of the thoracic and/or lumbar spine without neurological deficit.

Patients were identified from the Victorian Orthopaedic Trauma Outcomes Registry (VOTOR). VOTOR includes all patients with orthopaedic trauma admitted to the two adult Level 1 trauma centres in Victoria, Australia. Patient-reported outcomes and data on possible predictive factors, including demographic details, injury-related and treatment-based factors, were obtained from the VOTOR database.

Patient-reported outcomes were measured at 12 months post-injury using the 12-Item Short-Form Health Survey (SF-12), a Numerical Rating Scale (NRS) for pain, global outcome questions and data was collected on return to work or study. For the identification of predictive factors, univariate analyses of outcome vs. each predictor were carried out first, followed by logistic multiple regression.

344 patients were eligible for the study and data were obtained for 264 (76.7%) patients at 12 months follow-up. Patients reported ongoing pain at 12 months post-injury (moderate–severe: 33.5%), disability (70.1%) and inability to return to work or study (23.3%). A number of demographic, injury-related and treatment-based factors were identified as being predictive of poor patient-reported outcomes. Patients who had associated radius fracture(s) were more likely to have moderate to severe disability (odds ratio (OR) = 3.85, 95% confidence interval = 1.30–11.39), a poorer physical health status (OR = 3.73, 1.37–10.12) and moderate to severe pain (OR = 3.23, 1.22–8.56) at 12 months post-injury than patients without radius fracture. Patients who did not receive compensation for work-related or road traffic-related injuries were less likely to report moderate to severe pain (OR = 0.45, 0.23–0.90) or have a poorer mental health status (OR = 0.17, 0.04–0.70) at 12 months post-injury than those who received compensation.

The prognostic factors identified in this study may assist clinicians in the identification of patients requiring more intensive follow-up or additional rehabilitation to ultimately improve patient care.