An integrative approach in developing scaffolds based on gellan gum and bioactive glass aimed for osteochondral tissue engineering

Abstract

Bilayer scaffolds based on gellan gum (GG) and nanoparticulate bioactive-glass (BAG) were developed by an integrative approach based on engineering principles and characterization in biomimetic bioreactors. The osteo-inductive GG-BAG layer containing 2 % w/w GG and 2 % w/w BAG (composition: 70 n/n % SiO2, 30 n/n % CaO) was produced by gelation followed by freeze-drying to obtain open porosity in axial and radial directions. The chondral layer was obtained by dispensing a warm 2 % w/w GG solution at 60˚C over the frozen macroporous GG-BAG layer at -25˚C. The temperatures were optimized by applying a one-dimensional unsteady-state heat transfer model so to obtain a thin integration zone, 0.5 – 1 mm thick. The scaffolds were evaluated regarding bioactivity in a biomimetic bioreactor with specially designed chambers to provide supply of two media relevant for chondral and bone tissues. In the present experiment, simulated body fluid (SBF) was supplied countercurrently continuously during 14 days of the experiment (1.1 ml min-1 flowrate), while dynamic compression (5 % deformation, 0.68 Hz frequency, 337.5 µm s-1 loading rate, 1 h / day) was applied on the chondral layer, from day 7 to day 14. SEM analyses have confirmed the retained integrity of the scaffolds, as well as formation of hydroxyapatite (HAp) uniformly throughout the osteo-layer of the scaffolds.Significantly higher bioactivity under biomimetic conditions compared to static controls resulted in slightly but significantly increased compression modulus. These results indicated a high potential of the applied integrative strategy for the development of biomimetic bilayer scaffolds.