## 1 Introduction  
Many drugs referred to as Class II and Class IV drugs have low solubility which limits their bioavailability and consequently their effectiveness as therapeutic agents [1]. The solubility and bioavailability are typically improved by particle size reduction, which is described by the Noyes Whitney equation [2]. Typically, micro and nano drug particles are formed via mechanical size reduction such as dry/wet milling and homogenization [3], and also via precipitation techniques [4]. Anti-solvent precipitation has been used to synthesize micro and nano particles of hydrophobic drugs [5; 6]. Here, an antisolvent is used to precipitate crystals from a solution whose properties can be controlled by altering process conditions and the use of additives [7; 8]. Dissolution rates of hydrophobic drugs have been enhanced by the addition of hydrophilic moieties to the formulation. For example, different cellulosic materials [9] have been used as co-precipitating agents and hydrophilic silica nanoparticles have been used to promote faster aqueous dissolution [10]. Various polymers have been employed as peptide carriers in diabetes, oncology, and cardiovascular drugs [11]. Solid dispersion is an increasingly popular method that uses hydroxypropyl methylcellulose (HPMC), polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and polymer micelles as carriers for insoluble drugs [12; 13]. Glucosamine hydrochloride has been used in solid dispersions [14] and hydrophobic molecules have been included in cyclodextrin [15] to enhance dissolution rates. A drug carrier can be directly incorporated into the drug crystal during anti-solvent precipitation, and the latter can play multiple roles. For example, it can serve as a nucleation site for crystal formation, provide colloidal stability during crystal formation, and be used as a drug delivery vehicle such as a targeting agent or one that alters bioavailability by changing the dissolution rate. It is well known that functionalization is an effective means with which to control aqueous behavior of nanotubes including colloidal stability as well as their solubilization capacity towards hydrophobic molecules [16; 17; 18]. Fiber-like carbon nanotubes (CNTs) can actually be incorporated into drug crystals, and if the functionalized CNTs) are hydrophilic, they can attract water molecules and bring them to drug crystals, leading up to faster dissolution. The hydrophilicity of functionalized CNTs can also be altered to change the dissolution rate, which is a phenomenon that can be used to control the release of the drug. One of the concerns for using CNTs in drug delivery and biomedical applications is the toxicity of oxidized CNTs. A number of in vitro and in vivo studies have been performed that show conflicting reports from both the type of CNTs and bioactivity of interest [19; 20; 21; 22; 23; 24; 25; 26; 27]. However, studies have shown that carboxylation is an effective way to reduce toxicity [28; 29]. The unique properties of carbon nanotubes have led to various applications in biological and environmental fields [30; 31]. There has been much interest regarding carbon nanotubes in nanomedicine and tissue engineering applications [32; 33; 34; 35; 36; 37; 38; 39]. The CNTs have been used to deliver a wide range of small and large molecules for controlled release. Small drug molecules as well as peptides, vaccines, antibodies, nucleic acids, proteins, and genes have been attached to CNTs [40; 41; 42; 43]. Targeted drug delivery using CNTs has been successful [44], and CNTs have shown permeability into tumor tissues via endocytosis [45]. The key to the applications of CNTs in drug delivery is their attachment to drug molecules. Different molecules/species can be attached to CNTs via covalent or non-covalent bonding. Covalent attachment to CNTs can provide secure loading of a molecule, and drugs such as paclitaxel, toxoid, doxorubicin, boron-bearing agents, methotrexate, and 10-hydroxycampotothecin have been linked to CNTs via non-biodegradable or degradable linkages [46; 47].