Effect of screw position on bone tissue differentiation within a fixed femoral fracture

Plate and screw constructs are routinely used in the treatment of long bone fractures. Despite considerable advancements in technology and techniques, there can still be complications in the healing of long bone fractures. Non-unions, delayed unions, and hardware failures are common complications observed in clinical practice following open reduction and internal fixation of fractures [1]. Potential causes of these adverse clinical effects may be disruptive to the periosteal and endosteal blood supply, stress shielding effects, and inadequate mechanical stability. The goal of the present study was to explore the effect of screw position on the fracture healing and formation of new bone tissue with mechanoregulatory algorithms in a computational model. An idealized poroelastic 3D finite element (FE) model of a femur with a 5 mm fracture gap, including a plate-screw construct was developed. Nineteen different plate-screw combinations, created by varying the number and position of screws within the plate, were created to identify a construct with the most favourable attributes for fracture healing. The first phase of the study evaluated constructs through mechanical stress analyses to identify those constructs with high loadsupport capability. The second phase of the study evaluated healing and bone formation with a biphasic mechanoregulatory algorithm to simulate tissue differentiation for fixation within selected constructs. The results of our analysis demonstrated a 4-screw symmetrical construct with the largest distance between screws to provide the most favourable balance of stability and optimized conditions to promote fracture healing.

Serum-free media for articular chondrocytes in vitro expansion

Background In vitro chondrocyte expansion is a major challenge in cell-based therapy for human articular cartilage repair. Classical culture conditions usually use animal serum as a medium supplement, which raises a number of undesirable questions. In the present study, two kinds of defined, serum-free media were developed to expand chondrocytes in monolayer culture for the purpose of cartilage tissue engineering. Methods Bovine chondrocytes were expanded in serum-free media supplemented with fibroblast growth factor-2 and platelet-derived growth factor or fibroblast growth factor-2 and insulin-like growth factor. Expansion culture in a conventional 10% fetal bovine serum （FBS） medium served as control. Fibronectin coating was used to help cell adhesion in serum-free medium. Next, in vitro three-dimensional pellet culture was used to evaluate the chondrocyte capacity. Cell pellets were expanded in different media to re-express the differentiated phenotype （re-differentiation） and to form cartilaginous tissue. The pellets were assessed by glycosaminoglycans contents, collagen II, collagen I and collagen X immunohistological staining. Results Chondrocytes cultured in serum-free media showed no proliferation difference than cells grown with 10% FBS medium. In addition, chondrocytes expanded in both serum-free media expressed more differentiated phenotypes at the end of monolayer culture, as indicated by higher gene expression ratios of collagen type II to collagen type I. Pellets derived from chondrocytes cultured in both serum-free media displayed comparable chondrogenic capacities to pellets from cells expanded in 10% FBS medium. Conclusion These findings provide alternative culture approaches for chondrocytes in vitro expansion, which may benefit the clinical use of autologous chondrocytes implantation.