I know that a good portion of this issue is having an inert material like glass or metal. But I would have assumed more plastics could be used like ultra high density polyethelyyen. does it have something to do with the material having pores so that the cells can adhere to it and intagrate it.

Also so could implanting titanium mesh in high stress bones help people with osteoporosis through acting as aditional scaffolding.

Titanium and other metals (or alloys thereof) have been used for bone replacement (e.g., in hip joints), a key issue being the extent of metallic debris fragments generated if it is a metal on metal implant - small fragments are also generated with plastic polymers. Titanium has been used because of its strength (e.g., ability to support weight), resistance to corrosion/degradation and biocompatibility, such as ability to maintain normal cell and regenerative functions. So a certain degree of porosity is required and this will also affect cell seeding/migration, matrix deposition, vascularization and movement of nutrients.

David Wynick may be able to comment, but I think metal on polyethylene implants are still very popular because of cost (lower than titanium)-performance ratios over the lifetime of the materials in situ. I would imagine that plastics can be engineered to have a similar porosity and other properties charactersitic of metal implants. I guess surgeon preference may also come into it (e.g., expertise/familiarity in one procedure over others)?

Titanium has also been used as a mesh for metallic scaffolding in bone regeneration. Porous scaffolds provide a 3D-framework for reparative cells and/or regenerative factors, and they may have to be load-bearing as well. For a scaffold that has been introduced with cells in situ (e.g., stem cells) it may also have the capacity to restrict movement of these cells away from the implant site. Bone scaffolds can be modified to make them more biocompatible, e.g., with the introduction of biological or synthetic polymers and/or cells. Here is a quite comprehensive article that covers the properties of various metal bone scaffolds - https://www.mdpi.com/1996-1944/2/3/790/pdf. Costs are a consideration - from that article I see that tantalum (don’t remember this from the Periodic Table!!) has been used in bone implants, has excellent biocompatibility but has high manufacturing costs (see - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2883027/).

For an example of a type of titanium mesh cage for fractured lumbar vertebra used in patients with osteoporosis see - http://www.hindawi.com/journals/bmri/2014/853897/.

Last edited by Steve Lolait (25th Oct 2015 12:00:26)