Physical and biological properties of barium cross-linked alginate membranes

We describe the manufacture of highly stable and elastic alginate membranes with good cell adhesivity and adjustable permeability. Clinical grade, ultra-high viscosity alginate is gelled by diffusion of Ba2+ followed by use of the “crystal gun” [Zimmermann H. et al., Fabrication of homogeneously cross-linked, functional alginate microcapsules validated by NMR-, CLSM- and AFM-imaging. Biomaterials 2003;24:2083–96]. Burst pressure of well-hydrated membranes is between 34 and 325 kPa depending on manufacture and storage details. Water flows induced by sorbitol and raffinose (probably diffusional) are lower than those caused by PEG 6000, which may be related to a Hagen–Poiseuille flow. Hydraulic conductivity, Lp, from PEG-induced flows ranges between 2.4×10−12 and 6.5×10−12 m Pa−1 s−1. Hydraulic conductivity measured with hydrostatic pressure up to 6 kPa is 2–3 orders of magnitude higher and decreases with increasing pressure to about 3×10−10 m Pa−1 s−1 at 4 kPa. Mechanical introduction of 200 μm-diameter pores increases hydraulic conductivity dramatically without loss of mechanical stability or flexibility. NMR imaging with Cu2+ as contrast agent shows a layered structure in membranes cross-linked for 2 h. Phase contrast and atomic force microscopy in liquid environment reveals surface protrusions and cavities correlating with steps of the production process. Murine L929 cells adhere strongly to the rough surface of crystal-bombarded membranes. NaCl-mediated membrane swelling can be prevented by partial replacement of salt with sorbitol allowing cell culture on the membranes.