Biomimetic microtopography to enhance osteogenesis in vitro.

Biomimicry is being used in the next generation of biomaterials. Tuning material surface features such as chemistry, stiffness and topography allow the control of cell adhesion, proliferation, growth and differentiation. Here, microtopographical features with nanoscale depths, similar in scale to osteoclast resorption pits, were used to promote in vitro bone formation in basal medium. Primary human osteoblasts were used to represent an orthopaedically relevant cell type and analysis of adhesions, cytoskeleton, osteospecific proteins (phospho-Runx2 and osteopontin) and mineralisation (alizarin red) was performed. The results further demonstrate the potential for biomimicry in material design and show that the osteoblast response can be tuned from changes in feature size.

Osteoprogenitor response to semi-ordered and random nanotopographies.

In bone tissue engineering, it is desirable to use materials to control the differentiation of mesenchymal stem cell populations in order to gain direct bone apposition to implant materials. It has been known for a number of years that microtopography can alter cell adhesion, proliferation and gene expression. More recently, the literature reveals that nanotopography is also of importance. Here, the reaction of primary human osteoprogenitor cell populations to nanotopographies down to 10 nm in size is considered. The topographies were originally produced by colloidal lithography and polymer demixing on silicon and then embossed (through an intermediate nickel shim) into polymethylmethacrylate. The biological testing considered cell morphology (image analysis of cell spreading and scanning electron microscopy), cell cytoskleton and adhesion formation (fluorescent staining of actin, tubulin, vimentin and vinculin) and then subsequent cell growth and differentiation (fluorescent staining of osteocalcin and osteopontin). The results demonstrated that the nanotopographies stimulated the osteoprogenitor cell differentiation towards an osteoblastic phenotype.

Osteoprogenitor response to defined topographies with nanoscale depths.

In the development of the next generation of orthopaedic implants for load-bearing applications, an ability to influence osteoprogenitor population activity and function will be highly desirable. This will allow the formation of hard-tissue directly onto the implant, i.e. osseointegration, rather than the formation of fibrous capsules which form around many of the current, non-bioactive, prosthesis. The formation of capsules leads to micromotion due to modulus mismatch and ultimately to fracture and the need for revision surgery. Microtopography and latterly nanotopography have been shown to elicit influence over adhesion, proliferation and gene expression of a wide number of cell types. This study has examined the possibility of modulating cell adhesion using a range of nanometric scale shallow pits and grooves. The topographies were manufactured using photolithography followed by the production of nickel shims and finally embossing into polymethylmethacrylate. Cell testing with human osteoprogenitor populations showed that the nanotopographies allowed control of cell adhesion, cytoskeleton, growth and production of the osteoblastic markers osteocalcin and osteopontin. It is concluded that the human bone marrow stromal cells are highly responsive to nanoscale features.

The fibroblast response to tubes exhibiting internal nanotopography.

The use of three-dimensional scaffolds in cell and tissue engineering is widespread; however, the use of such scaffolds, which bear additional cellular cues such as nanotopography, is as yet in its infancy. This paper details the novel fabrication of nylon tubes bearing nanotopography via polymer demixing, and reports that the topography greatly influenced fibroblast adhesion, spreading, morphology and cytoskeletal organisation. The use of such frameworks that convey both the correct mechanical support for tissue formation and stimulate cells through topographical cues may pave the way for future production of intelligent materials and scaffolds.