Accelerating bone formation for the treatment of defects and fractures

Rapid, effective repair of large bone defects or fractures is still a challenging issue in orthopaedic surgery. If the defect or fracture is too large, natural bone repair often cannot occur and therefore, medical treatment is required. Cell therapy using either stem cells or bone cells is a promising new therapy for such cases. Clinical trials, however, have so far generated mixed results in terms of speed and quality of repair. Thus, improving bone formation is one of the hurdles in the translation of regenerative medicine for bone repair.

Bone has a unique ability to repair itself with the process of bone repair following the same pathway as healthy bone development. Direct or ‘intramembranous’ bone development within the body is characterised by a complex series of reactions which ultimately result in the growth of bone.

Inspired by natural bone formation, the Biomaterials Group at the Institute for Science & Technology in Medicine (ISTM), together with orthopaedic surgeon, Mr Konduru of the University Hospital of North Midlands (UHNM), have developed a simple and convenient technique to improve bone growth. This technique uses surface modification to change the environment the cells are grown in to force them to form clusters or aggregates of particular sizes. An osteoblast cell line and human bone marrow-derived stem cells have both been used to test this new bone growth method and have provided clear evidence that the aggregates produced from this technique can enhance bone formation by following the same pathway as natural bone growth or repair (Figure 1). 

Figure 1: SEM elemental analysis showing calcium production in bone aggregates and monolayer samples after 3 day osteogenic stimulation. A: big aggregate; B: small aggregate; C: monolayer 

Cell aggregation is an essential step in natural ‘intramembranous’ bone formation because the way in which the cells are in contact with one another induces several events to take place to form an osteoid which will then become the centre for new bone formation. Our data has shown that growing osteoblast cells in aggregate form can generate far more mineralised matrix (the building blocks of bone) than culturing them in a standard monolayer fashion. Furthermore, the size of the aggregate has a significant influence on the mineral content and composition within that bone aggregate. Four important molecules required for the formation of bone, COL1, ALP, OPN and OCN, displayed different expression patterns depending on the aggregate size (Figure 2).

Figure 2: Prediction and matching of the gene expression of different osteoblast culture environments (monolayer, small and big aggregate) in the bone development stages.

It is therefore proposed that growing bone cells in an aggregate form will encourage them towards developing bone, while the size of the aggregate will determine how quickly they will develop bone. This aggregation study offers a simple but effective model that can be used to quickly create high quality bone for use in fundamental investigations or even clinical applications.