Kellomäki M, Kulmala T, Ellä V, Länsman S (1), Ashammakhi N (1), Waris T, Törmälä P.

1. Department of Surgery, Oulu University Hospital, Oulu, FIN
2. Institute of Biomaterials, Tampere University of Technology, Tampere, FIN

Introduction
Knitted P(L/D)LA 96/4 scaffolds have been developed for MCP and MTP joints of RA patients. Current studies show in vitro and in vivo behavior of one size.

Materials and methods
P(L/DL)LA 96/4 was melt-spun to 4-ply multifilament with individual filament f appr. 80 mm. The multifilament was knitted to tubular single jersey. The knitted tube was rolled to the cylindrical scaffolds of f 15 mm, h 3-3.5 mm and heat-treated for the desired shape. Packed scaffolds were g-sterilized. Porosity and pore size of the scaffolds was measured. The in vitro (PBS, 37°C) and in vivo (rat subcutis) scaffolds were subjected to static compression testing. Tissue ingrowth was followed.

Results
Porosity of the scaffolds was around 80% Scaffolds had open porosity throughout the structure, because the porosity is formed by mesh loops and by layers of the mesh. Pores consisted of small pores (between the individual filaments inside a fibre bundle) and large pores (size of the mesh loops). Large pores were 400-700 mm and small pores were generally less than 50 mm. When compressed, in vitro scaffolds lasted almost unchanged 42 weeks (comparable to the retention time of the corresponding fibres). From in vivo scaffolds the reinforcing effect of ingrown tissue was easily seen compared to in vitro. Cells and tissues filled gradually in the scaffolds and at 6 weeks in vivo the cells and tissues had organized and were mainly fibrous tissue.

Conclusions
As joints are immobilized postoperatively, the properties of the scaffolds were found to be suitable.

Keywords
bioreconstructive, scaffold, polylactides