Porous alginate hydrogels or scaffolds have applications in cartilage regeneration and the treatment of cartilage lesions or diseases, like osteoarthritis1,2 . Successful growth of cells within a scaffold is dependent on a variety of different factors, including pore size and orientation, and behaviour of the gel under mechanical loading3 . These two factors are interconnected; pore size and orientation have been shown to affect mechanical loading in hydrogels3, but, in turn, compression causes deformation of the gel which may affect both pore size and orientation.
The hydrogels considered in this study have the potential for use in treating osteo-chondral defects. The cylindrical scaffolds (diameter ~ 8 mm, height ~ 4 mm) investigated were produced through ionotropic gelation of alginate sol with Ca2+ ions4 . Running parallel to the cylindrical axis of the scaffolds are channels, or pores (diameter ~ 100 μm). We used μ-MRI (with a 7 T static magnetic field) to image the gels. Both high resolution images (in-plane resolution of 50 x 50 μm) and longitudinal relaxation rates were used to investigate pore volume fraction in the scaffolds. The gels are imaged uncompressed and under compression. Consolidation curves (monitoring gel thickness with time) were obtained throughout the compression with MRI. The results are discussed in the context of 1) changes to the compressive behaviour (e.g. final strain, apparent viscosity) of the gels as a result of pore volume fraction and 2) changes to pore volume fraction (in terms of pore size and orientation) as a result of the compression.