# Cellulose Nanofibers and Other Biopolymers for Biomedical Applications. A Review
## 4 Outline of Biomedical Applications
### Delivery of Bioactive Molecules  
Drug delivery systems (DDS) are used to achieve a higher therapeutic effect of a pharmaceutical drug or natural compound in a specific diseased site. Uses of biopolymers in nanotechnology DDS have better biocompatibility, biodegradability and lower immunogenicity than synthetic counterparts. Biopolymers, such as silk, collagen, gelatin, starch, cellulose and chitosan can be easily made into suspensions that serve as delivery vehicles for drug molecules [29]. CNFs have been used as a matrix former for sustained drug delivery and as a film for the immediate release of poorly soluble drugs [161]. In addition to the work carried out on the controlled release of drugs to obtain wound healing dressings produced from nanocellulose others work investigated the potential for drug delivery have been reported. [PERSON] et al. studied the possibility of using BNC-acrylic acid (AA) hydrogels for drug delivery [162]. AA was grafted onto the surface of BNC by electron-beam irradiation obtaining hydrogels with thermo and pH-responsive properties [162]. BNC was also evaluated as a matrix for controlled drug release for other drugs, such as famotidine and tizanidine [163]. CNC was also utilisedas a vehicle for drug-delivery systems. CNC was used to stabiliser the alginate matrix to produce higher encapsulation and control the release rate of theophylline in the treatment of respiratory-related illness, as well as to control the release rate of bovine serum albumin (BSA) [164; 165]. [PERSON] et al. [166] extensively studied the use of CNC as a drug carrier element. In this work, the negatively charged surface of CNC, due to the sulphate groups of the acid hydrolysis using sulfuric acids interact with the positive charge of doxorubicin hydrochloride (DOX) and tetracycline hydrochloride (TET). Approximately 80% of DOX and TET was released within the first 4 h. CNC was also functionalised with cetyl trimethylammonium bromide (CTAB) to change the hydrophilic nature of the surface into hydrophobic. The functionalised CNC was used to encapsulate hydrophobic anticancer compounds, such as etoposide (ETOP), docetaxel (DTX) and paclitaxel (PTX) showing a slower and controlled release of the drugs. Oxidised CNC by TEMPO-mediated oxidation was also tested in this study presenting a loading efficacy of 14% w/w for procaine hydrochloride showing 80% of drug released in an hour. Cellulose nanofibers (CNF) was also reported to be used for drug delivery by several authors [166; 167; 168; 169]. CNF was used as a pharmaceutical excipient of indomethacin, metoprolol tartrate, verapamil hydrochloride, nadolol, ibuprofen and atenol. Except for the indomethacin, all the drugs were embodied prevalently in the CNF network, showing a quick discharge rate in the period of 10-14 days and a much slower discharge rate over time up to 60 days [168; 169]. CNF films were used for controlled drug delivery containing water-insoluble drugs, such as indomethacin, itraconazole or beclomethasone dipropionate. The results showed that indomethacin was released in a period of 15-30 days; however, beclomethasone dipropionate and itraconazole were released more gradually over a period of 90 days [169]. [PERSON] et al. [170] developed a thermoresponsive framework by the addition of multilayers of CNF and N-isopropyl acrylamide. This structure presents a controlled porosity and release by temperature adjustment. CNF was also used to placed chitosan-benzalkonium chloride (BAC) complex showing antimicrobial action against _S. aureus and E. coli_, being able to be used as new drug-delivery frameworks [171]. Chitosan nanoparticles have also been used to deliver medications, such as methotrexate and 5-fluorouracil over a sustained period of time in the treatment of cancer [172]. Designer biopolymers (DBPs) are genetically engineered biomacromolecules designed to condense plasmid DNA and overcome intra- and extra-cellular barriers for successful gene delivery [173].