Research Program
Biomolecular Devices and Analysis

Objectives

• Surface functionalize porous alumina microfiltration membranes
• Fabricate thin film collagen membranes of varying physical characteristics on modified alumina
• Complete evaluation/confirmation of surface functionalization and thin film composite (TFC) membrane fabrication.
• Determine surface characteristics such as contact angle, zeta potential, thickness, surface roughness, porosity etc., of the thin film composite membranes.
• Evaluate permeate flux and permeability under microfiltration conditions with membranes of varying physical functionality.

Methods
A commercially available porous alumina substrate was surface activated (functionalized) using concentrated sulfuric acid. Collagen monomers and fibrils of varying fibril density and length were coated onto the surface by spinning varying number of collagen layers on the surface activated alumina. Both activated membrane and the collagen thin film membranes were characterized by EKA (Electrokinetic Analysis), SEM, pressure-driven flux, water contact angle and ATR-FTIR (surface chemistry).

Summary
It is important to purify DNA before PCR to improve the sensitivity and efficiency of the amplification. For blood the major interferant is heme, and in our earlier investigation we demonstrated that by combining CA membranes (cast on polypropylene support) with electrophoresis, DNA is completely separated from heme. We also demonstrated that the purified DNA is undamaged.  However, the membranes suffer from low flux, which means low productivity. It is important to understand the physico-chemical characteristics of the membranes by which the separation occurs, in order to enhance the bio-separation performance and flux of the membranes, and to fully understand the separation mechanisms.  Membrane properties such as surface charge, hydrophilicity, roughness and pore size can affect separation efficiencies for biomolecules. Hence, tailoring the membrane characteristics and studying these characteristics are critical to designing a successful separation tool. 

With this background, a more uniform pore size, chemically and thermally inert alumina membrane was identified as the porous support and the biocompatible collagen was identified as the film material. The alumina was activated by surface functionalization to improve the stability of the collagen thin films on the support. Collagen films were spin cast using a dilute commercial sample from calf skin with 1 to 9 layers with varying thickness using a spin casting machine. This year we developed a more robust thin film material that combines a higher flux with separation compared to the previously reported CA membranes.

We have succeeded in fabricating, characterizing and testing performance variables (flux, rejection) for the collagen membranes. The permeability (pore size) is reported to be of the order 10^-6 to 10^-7 m/S.kPa, pure water flux values of the order 10^-4 to 10^-5 m/S at 30 psi which are at least an order of magnitude higher than the CA membranes we developed earlier. As the water contact angle changed, the zeta potential (surface charge) was unchanged upon increasing the number of layers.  However the positive zeta potential of the uncoated alumina membranes was reduced by 50%.  The SEM morphology reveals the transition from monomer to fibril upon increasing the number of layers. With these results we foresee a greater potential in the application of these membranes to biomolecule separations.

Accomplishments

• Fabricated collagen membranes on activated alumina substrates, forming bilayer membranes with tailorable surface properties
• Linked surface morphology, surface charge and pore size of collagen membranes to performance variables (flux and permeability)
• Developed collagen-alumina thin film composite NF membranes with permeability and flux at least an order of magnitude higher than CA membranes spin cast on polypropylene supports.