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Inorganic nanosols enable the embedding of bioactive agents, biomolecules or even whole living cells into metal oxide matrices. In simplest case the metal oxide matrix consists of pure silica. The bioactive nanocomposites can be used as bulk product or as thin biocatalytic coating.

Bioactive nanocomposites contain significant properties:

  • the embedding of various types of biomolecules into the sol-gel matrix is possible, even microorganisms and living cells (e.g. yeast, islets of Langerhans) stay alive in the inorganic matrix
  • the biomolecules embedded keep their conformation and their chemical and physical properties
  • external reagents are able to be transported to the biomolecules embedded, so chemical reactions and interactions are possible bioactive nanocomposites can be prepared and used as coatings, bulk-material or fibres.

Depending on the composition of the bioactive nanocomposites (biocers) the degree of immobilisation of embedded bioactive agents can be controlled.

The permanent encapsulation of natural components (e.g. biopolymers like collagen, gelatine, chitosan orhyaluronacid) can lead to an improvement of the compatibility of implant surfaces.

Even pure SiO2-nanosol coatings contain an improved cell adhesion and cell proliferation to marrow or connective tissue cells compared to the common used uncoated titanium implants. The increased incorporation of gelatine or collagen and inorganic bone components (like calcium or phosphate ions) into the SiO2 coating improves drastically the cell adhesion. Furthermore the mechanical properties of bioactive nanocomposite coatings are quite similar to the once of natural bone material.

The immobilisation of sterical big biocomponents (e.g. enzymes, other proteins or cells and spores) enable applications in biotechnology (immobilised biocatalysators), in biosensoric (immobilised enzymes and antibodies) and medical diagnostics (e.g. immobilised proteins), because of the controllable porosity of the inorganic matrix a mainly unhindered diffusion of smaller components into or out of the matrix is possible. For this reason inside the nanocomposites quite similar enzyme activities are obtained, so inside a sol-gel layer biocatalytic reactions are performed with high efficiency.

The applications of such biocomposites (e.g. immobilised yeast as biocatalyst for fermentation) are intensively investigated.

Nanosol-immobilised vegetative cells Applications
Saccharomyces cerevisiae
(dry yeast)
Biocatalysts (e.g. alkoholic fermentation)
Bacillus sphaericus
An isolate from uranium mining deposits (bacteria, spores, s-layer proteins)
High efficient, regenerable biofilters for uran- and copper salts, owing a specific bonding profil
Rhodococcus spec.
An isolate from river water Halotolerant fungus Leup2
Biocatalysts for degradation of phenol and glycol substances in industrial waste water

Table 1: Applications of biocers for biofiltration and biocatalysis

 

The delayed or controlled release of embedded bioactive agents (e.g. antimicrobials, pharmaceuticals, repellent or aromatic agents) out of the sol-gel matrix enables multiple applications. An advantage of those nanosol coatings is their controllable porosity, so the release of the bioactive agents can be controlled in a wide range. Furthermore the embedding of different types of substances in the same coating enables bio effects in an increased range.

Sol-gel immobilised bioactive agent Application
Silver, organic biocides Antimicrobial coatings for medical application
Heparin, hirudin Anticoagulation coatings for medical application
Natural or synthetic agents Transdermal and therapeutic systems

Table 2: Examples for nanosol coatings with controlled release of active agents

 

For example investigations on nanosol coatings on catheter show that the antimicrobial effects against both gram-positive and gram-negative bacteria can be enhanced by combination of different immobilised biocides.