A biomaterial is defined as a material, either man-made or natural, intended to interact with

biological systems. It does not have a chemical effect in the organism, nor thus it need to be

metabolised to be active like for example drugs 1. When inserted into the body, a local

tissue inflammatory reaction called foreign body reaction is induced 2. This reaction may

either favour or adversely affect the tissue repair process.

Cellulose and its derivatives are well tolerated by most tissues and cells 3-5. These nontoxic

materials have good biocompability, therefore, they offer several possibilities in

medical applications. Regenerated cellulose sponges have also been used in experimental

surgery for decades as it does not affect the healing process, but acts as a chemoattractant

inducing cells involved in the repair process to migrate towards it 6-8.

We have studied different biomaterials including cellulose in search for an optimal bone

substitute. In bone defects, regenerated cellulose supported with cotton fibres was shown to

allow new bone in-growth to some degree 9-11. Oxidation with periodate and hydrogen

peroxide, or carbamination further improved its biocompability but not enough to be used

as bone substitutes. We also expected to increase the osteostimulating property of

regenerated cellulose by coating it with a silica-rich hydroxyapatite (HA) as it resembles the

mineral composition of bone. To our disappointment, the HA-coated cellulose did not

promote bone formation but favoured instead inflammation and fibroplasia. Since the bone

implant study revealed unexpectedly an enormous ability of the HA-implants to induce

granulation tissue, the coated cellulose was tested subcutaneously as well. These studies

showed that the HA-coated cellulose not only attracted inflammatory cells but also bone

marrow-derived progenitor cells of both haematopoietic and mesenchymal origin (see box

1). In this chapter, we will discuss cellulose as implant material with emphasis on the cell

guiding properties of regenerated cellulose coated with silica-rich HA.