Structural design and properties of hydrogel biomaterials

Doctoral thesis, 2011

Today a range of materials are used in medical applications; such materials are collectively denoted as biomaterials. A special class of biomaterials currently given much scientific interest is hydrogels. In particular a contemporary research topic is to create multicomponent materials in which synergetic effects are achieved. The works this thesis is based on aimed to create new potential multicomponent hydrogel biomaterials, where the presented materials can be divided into three groups: superabsorbents (SAPs), films with tuneable permeability and systems with inducible gelation. The materials were characterized with regard to macroscopically observed properties of importance for material performance. Based on observed properties, components in the materials and material structures conclusions were drawn about important structural design characteristics. Polyacrylic acid (PAA) based SAPs, in which microfibrillated cellulose (MFC) was used as a filler material, were synthesized. For the investigated SAPs some MFC was found to be equivalent to the same mass of traditional crosslinker with regard to modifying equilibrium swelling and shear modulus. Furthermore, the resistance to fracture upon compression was improved for MFC containing gels. Films composed of MFC and the water soluble polymer hydroxypropyl methylcellulose (HPMC) were prepared. The water permeability of the films displayed a dependence on HPMC content opposite of what is commonly expected. The films exhibited large, close to one-dimensional, swelling. Also, films composed of crosslinked polydimethylsiloxanes (PDMS) and carbomer micro particles (PAA based) or sucrose were synthesized. The permeability of water vapour through those films was tuneable by the addition of carbomer, but not by addition of sucrose. This was explained by that the swollen carbomer retained open channels with high diffusion in the films. In contrast, the highly elastic and hydrophobic PDMS probably sealed the pores left by dissolved sucrose. Gels based on nanocapsules of carboxymethyl-hexanoyl chitosan (CHC) with in situ gelling capability were found to have properties making them highly promising for biomedical, and in particular drug delivery applications. Hopefully the presented materials will act as inspiration for structural design, contribute to the understanding of structure-properties correlations and perhaps even contribute to improvement of people’s quality of life through new products reaching the market.