This suggests that NFC as an injectable drug releasing biomaterial is indeed more suitable for larger compounds, such

as macromolecular protein and peptide drugs. Additionally, protein drugs suffer from delivery problems, which need to be overcome for effective treatment (Jain et al., 2013). As an injectable hydrogel, NFC could solve some of the challenges related to the delivery of biopharmaceuticals. The pharmacokinetic models that we constructed could be used to further evaluate the release properties of NFC or other biomaterials in conjunction with SPECT/CT imaging. In our study the deconvolution and Loo–Riegelman models described the amount ready to be absorbed, which relates to the release rate of the compound. This could be useful in further analyzing poorly absorbing compounds (such as the HSA in our case), and can be used to complement drug-biomaterial studies when small-animal imaging is in use. This is especially true in situations where poor absorption BAY 73-4506 is the reason for an apparent slow rate of release, which might be an erroneous indication by the SPECT/CT. Therefore, the detected activity at the injection site might not be because of slow rate of release from the biomaterial, but actually

due to very poor absorption. As we proposed earlier, the high biodurability of NFC suggests that as for a non-biodegrading material, it could have a potential use as a long-term drug releasing biomaterial; ideal as an extended release product for chronic diseases. In addition, NFC hydrogels imbedded with therapeutic compounds could find a potential application as a local

delivery biomedical device. Topical and Vorinostat nmr subcutaneous conditions could be treated with easily injectable NFC hydrogels that can be later enzymatically removed. The steady and continuous release of drug from the hydrogels could be further improved through formulation processes, in addition, nanofibrillar cellulose has not shown cytotoxic properties in previous CYTH4 studies (Vartiainen et al., 2011, Alexandrescu et al., 2013 and Pitkänen et al., 2010), which supports the idea of NFC as a potential biomaterial. However, it should be noted that studies considering the safety of plant-derived NFC in humans have not been done and especially with possible long-term exposure, this should be investigated thoroughly. The possible chemical interactions between proteins and NFC should be investigated individually. NFC contains many hydroxyl groups as well as some carboxyl groups which might interact with the drug compounds imbedded within the matrix; therefore making the predictions of release profiles difficult for different compounds. However, considering the current increase of interest in pharmaceutical research towards the possibilities of macromolecular protein and peptide drugs, NFC might offer an additional method for parenteral delivery, as the effective delivery of protein drugs has been one of the main challenges in pharmaceutical sciences (Kumar et al., 2006).