Functional cell phenotype induction with TGF-ß1 and collagen-polyurethane scaffold for annulus fibrosus rupture repair.

Appropriate cell sources, bioactive factors and biomaterials for generation of functional and integrated annulus fibrosus (AF) tissue analogues are still an unmet need. In the present study, the AF cell markers, collagen type I, cluster of differentiation 146 (CD146), mohawk (MKX) and smooth muscle protein 22α (SM22α) were found to be suitable indicators of functional AF cell induction. In vitro 2D culture of human AF cells showed that transforming growth factor ß1 (TGF-ß1) upregulated the expression of the functional AF markers and increased cell contractility, indicating that TGF-ß1-pre-treated AF cells were an appropriate cell source for AF tissue regeneration. Furthermore, a tissue engineered construct, composed of polyurethane (PU) scaffold with a TGF-ß1-supplemented collagen type I hydrogel and human AF cells, was evaluated with in vitro 3D culture and ex vivo preclinical bioreactor-loaded organ culture models. The collagen type I hydrogel helped maintaining the AF functional phenotype. TGF-ß1 supplement within the collagen I hydrogel further promoted cell proliferation and matrix production of AF cells within in vitro 3D culture. In the ex vivo IVD organ culture model with physiologically relevant mechanical loading, TGF-ß1 supplement in the transplanted constructs induced the functional AF cell phenotype and enhanced collagen matrix synthesis. In conclusion, TGF-ß1-containing collagen-PU constructs can induce the functional cell phenotype of human AF cells in vitro and in situ. This combined cellular, biomaterial and bioactive agent therapy has a great potential for AF tissue regeneration and rupture repair.

Anterior column reconstruction of the thoracolumbar spine with a new modular PEEK vertebral body replacement device: retrospective clinical and radiologic cohort analysis of 48 cases with 1.7-years follow-up.

PURPOSE: To evaluate whether a new PEEK vertebral body replacement can maintain the sagittal alignment as an anterior column reconstruction device in thoracic and lumbar spinal defects due to trauma or tumor. METHODS: Retrospective review of 48 patients who underwent a corpectomy between T5 and L5 due to trauma or tumor and were stabilized with the new PEEK vertebral body replacement, between 2013 and 2017. We excluded patients who underwent a corpectomy for infection or degenerative disease and patients without complete follow-up in our institution. The primary outcome was the bi-segmental kyphotic angle (BKA). Secondary outcomes were the assessment of pedicle screw loosening, cage height, and subsidence or tilting of the cage. The clinical outcomes were assessed through the COMI-Score, EuroQol-5D, and Karnofsky indexes. Bony fusion and complications were registered. RESULTS: After the surgery BKA decreased by 12.1° (p < 0.001). At the end of the follow-up, we observed a mean loss of reduction of 1.6° (p = 0.002). This was accompanied by an increase in subsidence of 2.1 mm (p < 0.001) and mean tilting of the cage of 1.4° (p = 0.003). The height of the cage and other parameters did not experience any changes. Clinically, the COMI-Score (p = 0.02) and the EuroQol-5D Index (p = 0.012) showed significant improvement, same as Karnofsky-Index (p = 0.015) at final follow-up. The fusion rate according to Bridwell was 92.1%. The 2% late complications were related to implant malpositioning. CONCLUSION: The new PEEK expandable vertebral body replacement is effective and safe in thoracic and lumbar anterior column reconstruction in tumor and trauma diseases.

A review of the application of reinforced hydrogels and silk as biomaterials for intervertebral disc repair.

The degeneration of the intervertebral disc (IVD) within the spinal column represents a major pain source for many patients. Biological restoration or repair of the IVD using "compressive-force-resistant" and at the same time "cytocompatible" materials would be desirable over current purely mechanical solutions, such as spinal fusion or IVD implants. This review provides an overview of recent research on the repair of the inner (nucleus pulposus = NP) and the outer (annulus fibrous = AF) parts of the IVD tissue. Many studies have addressed NP repair using hydrogel-like materials. However, only a few studies have so far focused on AF repair. As the AF possesses an extremely low self-healing capacity and special attention to shear-force resistance is essential, special repair designs are required. In our review, we stated the challenges in IVD repair and highlighted the use of composite materials such as silk biomaterials and fibrin cross-linked reinforced hydrogels. We elaborated on the origin of silk and its many in tissue engineering. Furthermore, techniques such as electrospinning and 3D printing technologies allow the fabrication of versatile and functionalised 3D scaffolds. We summarised the research that has been conducted in the field of regenerative medicine over the recent years, with a special focus on the potential application and the potential of combining silk and reinforced - and thus mechanically tailored - hydrogels for IVD repair.

3D scaffolds co-seeded with human endothelial progenitor and mesenchymal stem cells: evidence of prevascularisation within 7 days.

Blood supply is a critical issue in most tissue engineering approaches for large defect healing. As vessel ingrowth from surrounding tissues is proven to be insufficient, current strategies are focusing on the neo-vascularisation process. In the present study, we developed an in vitro pre-vascularised construct using 3D polyurethane (PU) scaffolds, based on the association of human Endothelial Progenitor Cells (EPC, CD34+ and CD133+) with human Mesenchymal Stem Cells (MSC). We showed the formation of luminal tubular structures in the co-seeded scaffolds as early as day 7 in culture. These tubular structures were proven positive for endothelial markers von Willebrand Factor and PECAM-1. Of special significance in our constructs is the presence of CD146-positive cells, as a part of the neovasculature scaffolding. These cells, coming from the mesenchymal stem cells population (MSC or EPC-depleted MSC), also expressed other markers of pericyte cells (NG2 and αSMA) that are known to play a pivotal function in the stabilisation of newly formed pre-vascular networks. In parallel, in co-cultures, osteogenic differentiation of MSCs occurred earlier when compared to MSCs monocultures, suggesting the close cooperation between the two cell populations. The presence of angiogenic factors (from autologous platelet lysates) in association with osteogenic factors seems to be crucial for both cell populations' cooperation. These results are promising for future clinical applications, as all components (cells, growth factors) can be prepared in an autologous way.

Percutaneous cement augmentation for the treatment of depression fractures of the tibial plateau.

The management of insufficiency fractures of the tibial plateau in osteoporotic patients can be very challenging, since it is difficult to achieve a stable fixation, an essential condition for the patients' early mobilization. We present a minimally invasive technique for the treatment of proximal tibial plateau fractures, "tibiaplasty", using percutaneous polymethylmethacrylate augmentation. Five osteoporotic patients (7 fractures) with a non-traumatic insufficiency tibial plateau fracture were treated with this technique at the authors' institution from 2006 to 2008. The patients' median age was 79 (range 62-88) years. The intervention was performed percutaneously under general or spinal anesthesia; after the intervention, immediate full weight bearing was allowed. The technique was feasible in all patients and no complications related to the intervention were observed. All patients reported a relevant reduction in pain, were able to mobilize with full weight bearing and would undergo the operation again. No secondary loss of reduction or progression of arthrosis was observed in radiological controls; no revision surgery was required. Our initial results indicate that tibiaplasty is a good treatment option for the management of insufficiency in tibial plateau fractures in osteoporotic patients. The technique is minimally invasive, safe and allows immediate mobilization without restrictions. In our group of patients, we found excellent early to mid-term results.

A papain-induced disc degeneration model for the assessment of thermo-reversible hydrogel-cells therapeutic approach.

Nucleus pulposus (NP) regeneration by the application of injectable cell-embedded hydrogels is an appealing approach for tissue engineering. We investigated a thermo-reversible hydrogel (TR-HG), based on a modified polysaccharide with a thermo-reversible polyamide [poly(N-isopropylacrylamide), pNIPAM], which is made to behave as a liquid at room temperature and hardens at > 32 °C. In order to test the hydrogel, a papain-induced bovine caudal disc degeneration model (PDDM), creating a cavity in the NP, was employed. Human mesenchymal stem cells (hMSCs) or autologous bovine NP cells (bNPCs) were seeded in TR-HG; hMSCs were additionally preconditioned with rhGDF-5 for 7 days. Then, TR-HG was reversed to a fluid and the cell suspension injected into the PDDM and kept under static loading for 7 days. Experimental design was: (D1) fresh disc control + PBS injection; (D2) PDDM + PBS injection; (D3) PDDM + TR-HG (material control); (D4) PDDM + TR-HG + bNPCs; (D5) PDDM + TR-HG + hMSCs. Magnetic resonance imaging performed before and after loading, on days 9 and 16, allowed imaging of the hydrogel-filled PDDM and assessment of disc height and volume changes. In gel-injected discs the NP region showed a major drop in volume and disc height during culture under static load. The RT-PCR results of injected hMSCs showed significant upregulation of ACAN, COL2A1, VCAN and SOX9 during culture in the disc cavity, whereas the gene expression profile of NP cells remained unchanged. The cell viability of injected cells (NPCs or hMSCs) was maintained at over 86% in 3D culture and dropped to ~72% after organ culture. Our results underline the need for load-bearing hydrogels that are also cyto-compatible.