However cellulose based materials are highly modifiable (Klemm et al., 2011), with which it is possible to improve the properties of NFC in drug release and retaining. Furthermore, this study did not focus on physical nor 3-deazaneplanocin A cell line chemical properties of the molecules; however the native NFC is known to have a slight negative surface charge (Kolakovic et al., 2012 and Wang et al., 2011), thus it can be expected to have some repelling forces between the negatively charged 123I-NaI and 99mTc-HSA. Indeed, the results indicated that in the dual-radionuclide imaging study, the release of 123I-NaI was more rapid from the hydrogels than

from the control saline injections. The chemical properties are more important in smaller scale, thus the repulsion forces by the negative charges are greater than the hindrance of the nanofibrous matrix of the hydrogel itself, which relates to molecular size, ABT-888 manufacturer a physical factor. 99mTc-HSA also has a negative charge; however

the size of the molecule is considerably larger than 123I-NaI, therefore the physical effect of the NFC matrix in the controlled release is more dominant. Positively charged molecules were not investigated in this study, however considering the effects of the negatively charged molecules (123I-NaI and 99mTc-HSA); it is likely that a more noticeable sustained release effect would be observed with positively charged molecules. In addition, during the study on 99mTc-HSA and hydrogel preparations, it is unlikely but possible that a small amount of the free/unbound pertechnetate from the HSA radiotracer would label the NFC matrix while mixing the 99mTc-HSA solutions with the biomaterial prior to injection. The labeling for both 99mTc-HSA and 99mTc-NFC utilized spontaneous stannous chloride reduction methods; therefore we believed the else labeling mechanism could be the same. In the case of erroneous

biomaterial labeling during the study, results would show as a false positive data of slower 99mTc-HSA release from the biomaterial, as some of the NFC would be labeled to 99mTc-NFC instead of the 99mTc-HSA. However, during the radiochemical purity test of the 99mTc-HSA, the amount of free pertechnetate was observed very low (impurities were found below the allowed 5% indicated by the manufacturer). Therefore, only the free portion of the radiolabel amongst the impurities of the total activity is theoretically able to form bonds with the NFC biomaterial, which would still amount to much less than 5% of the whole activity. This suggests that the 99mTc-HSA related data obtained in this study is still reliable, as the amount of possible erroneous activity detected from the biomaterial during the image acquisition is considerably lower. Most injectable biomaterials are prepared in solution, while the gelation is triggered by an external signal, for example phototriggering (Zhang et al.