We present a new approach which aims to translate freeform biofabrication into the surgical field, while staying true to the practical constraints of the operating theatre. Herein we describe the development of a handheld biofabrication tool, dubbed the ‘biopen’, which enables the deposition of living cells and biomaterials in a manual, direct-write fashion. A gelatin–methacrylamide/hyaluronic acid–methacrylate (GelMa/HAMa) hydrogel was printed and UV crosslinked during the deposition process to generate surgically sculpted 3D structures. Custom titanium nozzles were fabricated to allow printing of multiple ink formulations in a collinear (side-by-side) geometry. Independently applied extrusion pressure for both chambers allows for geometric control of the printed structure and for the creation of compositional gradients. In vitro experiments demonstrated that human adipose stem cells maintain high viability (>97%) one week after biopen printing in GelMa/HAMa hydrogels. The biopen described in this study paves the way for the use of 3D bioprinting during the surgical process. The ability to directly control the deposition of regenerative scaffolds with or without the presence of live cells during the surgical process presents an exciting advance not only in the fields of cartilage and bone regeneration but also in other fields where tissue regeneration and replacement are critical.

Three-dimensional (3D) bioprinting is driving major innovations in the area of cartilage tissue engineering. Extrusion-based 3D bioprinting necessitates a phase change from a liquid bioink to a semi-solid crosslinked network achieved by a photo-initiated free radical polymerization reaction that is known to be cytotoxic. Therefore, the choice of the photocuring conditions has to be carefully addressed to generate a structure stiff enough to withstand the forces phisiologically applied on articular cartilage, while ensuring adequate cell survival for functional chondral repair. We recently developed a handheld 3D printer called “Biopen”. To progress towards translating this freeform biofabrication tool into clinical practice, we aimed to define the ideal bioprinting conditions that would deliver a scaffold with high cell viability and structural stiffness relevant for chondral repair. To fulfill those criteria, free radical cytotoxicity was confined by a co-axial Core/Shell separation. This system allowed the generation of Core/Shell GelMa/HAMa bioscaffolds with stiffness of 200KPa, achieved after only 10 seconds of exposure to 700 mW/cm² of 365 nm UV-A, containing >90% viable stem cells that retained proliferative capacity. Overall, the Core/Shell handheld 3D bioprinting strategy enabled rapid generation of high modulus bioscaffolds with high cell viability, with potential for in situ surgical cartilage engineering.

Photo-crosslinkable hydrogels, in particular gelatin methacryloyl (GelMa), are gaining increasing importance in biofabrication and tissue engineering. While GelMa is often described as mechanically ‘tunable’, clear relationships linking the photocrosslinking conditions to reaction rates, and the resulting mechanical properties, have not been described. Meanwhile the conditions employed in the literature are disparate, and difficult to compare. In this work, in situ rheological measurements were used to quantify the relative rate of reaction of GelMa hydrogels with respect to light intensity, exposure time and photo-initiator concentration. In addition the UV degradation of the photo-initiator Irgacure 2959 was measured by UV-vis spectroscopy, and used to estimate the rate of free radical production as a function of light exposure. Using these data an expression was derived which predicts the mechanical properties of GelMa hydrogels produced across a wide range of crosslinking conditions. The model was validated through fabrication of a GelMa gradient which matched predicted properties. Human mesenchymal stem cells encapsulated in crosslinked GelMa exhibited high (>90%) viability post encapsulation, however metabolic activity over one week was influenced by the intensity of light used during crosslinking. The expressions described may be used to aid rational choices of GelMa photocrosslinking conditions, especially in cell encapsulation experiments where minimising the cytotoxic elements in the reaction is a priority.

We reviewed 124 patients with a conventional pelvic chondrosarcoma who had been treated over a period of 20 years. We recorded the type of tumour (central or peripheral), type of operation (limb salvage surgery or hemipelvectomy), the grade of tumour, local recurrence and/or metastases, in order to identify the factors which might influence survival. More satisfactory surgical margins were achieved for central tumours or in those patients treated by hemipelvectomy. However, grade 1 tumours, whatever the course, did not develope metastases or cause death, while grade 3 tumours had the worst outcome and prognosis. Central, high-grade tumours require aggressive surgical treatment in order to achieve adequate surgical margins, particularly in those lesions located close to the sacroiliac joint. By contrast, grade 1 peripheral chondrosarcomas may be treated with contaminated margins in order to reduce operative morbidity, but without reducing survival.

Early vascular invasion is a key factor in bone allograft incorporation. It may reduce the complications related to slow and incomplete bone integration. Bone-marrow-derived stromal stem cells associated with platelet-rich plasma are potent angiogenic inducers proven to release vascular endothelial growth factor. Our goal was to test whether the combination of stromal stem cells and platelet-rich plasma is able to increase massive allograft integration in a large animal model with sacrifice at 4 months. A critical defect was made in the mid-diaphysis of the metatarsal bone of 10 sheep; the study group received an allograft plus stromal stem cells, platelet-rich plasma, and collagen (six animals) and the control group received only the allograft (four animals). Investigation was done with radiographs, mechanical tests and histomorphometric analysis, including new vascularization. Results showed substantial new bone formation in the allograft of the study group. Bone formation is correlated with better vascular invasion and remodeling of the graft in the study group. These results confirm the key role played by stromal stem cells and platelet-rich plasma in bone repair. Further studies are needed to better define the role stromal stem cells play when implanted alone.