Question

Aside from carbon nanotube, what else can we use for smart drug delivery? Give two examples and explain.

Answer 1

Biodegradable Polymerrs can be used for drug delivery.

Biocompatible polymers used in drug delivery are often biodegradable with the formation of non-harmful byproducts, such as non-toxic alcohols, acids and other easily eliminated low molecular weight products. They can indeed contribute to the drug release as a result of their erosion/degradation, in addition to drug diffusion through the polymeric material. Biodegradable polymer, in the development of drug delivery systems, must meet very specific requirements such as

a.Biocompatibility backbone of the polymer and its degradation products.

b.Mechanical strength sufficient to meet the needs of specific applications.

c.Degradability with degradation kinetics matching a biological process such as wound healing.

d.Processibility using available equipment.

e.Solubility in various solvents.

f.Chemical, structural and application versatility.

g.Economically acceptable shelf life.

h.European Medicine Evaluation Agency (EMEA) or Food and Drug Administration (FDA), USA. (Coulembiera et al., 2006).

Table 1.

Classification of biodegradable polymers used in drug delivery systems (Coulembiera et al., 2006).

Synthetic biodegradable polymers		Natural biodegradable polymers
Polyesters	Polyoxalates	Starch	Albumin
Polyorthoesters	Polyiminocarbonates	Hyaluronic acid	Dextran
Polyanhydrides	Polyurethanes	Heparin	Chitosan
Polydioxanones	Polyphosphazenes	Gelatin	–
Poly(a-cyanoacrylates)	–

Mesoporous silica systems

Mesoporous silica have highly ordered structures, larger pore size, and high surface area. Due to stable mesoporous structure and well-defined surface properties, mesoporous materials seem ideal for the encapsulation of pharmaceutical drugs, proteins and other biogenic molecules. Several mesoporous materials were used such as M41S, SBA, MSU, and HMS in drug delivery.

The surface area and pore size of the mesoporous silica is important for biotechnological and biomedical applications. For example, microsphere materials cannot serve as efficient agents for gene transfection or carriers for intracellular drug delivery because cells cannot efficiently engulf large particles via endocytosis. Also, mesoporous silica microspheres are within the size window of bacteria and could potentially trigger acute immune response in vivo.

MCM-41 as one of the importantly synthesized mesoporous materials has been firstly employed as a drug delivery matrix. Other groups of mesoporous materials with larger pore size such as SBA including SBA-15, SBA-16, SBA-1, SBA-3, HMS, and MSU were also used for drug delivery. For drug delivery based on mesoporous materials, several investigations using organic modified mesoporous silica have been reported. Zeng et al. (2005) carried out a study using MCM-41 materials modified by aminopropyl groups as drug-controlled delivery system of aspirin. The results showed that the releasing properties of this delivery system were affected by the amount of aminopropyl groups on the pore wall and the ordered structure of mesoporous materials.

SBA-15 is expected to have less restriction for the delivery of bulky molecules, because the pore size of SBA-15 is usually 6 nm in diameter, larger than the 3 nm pore of MCM-41.

Song et al. (2005) reported mesoporous SBA-15 materials functionalized with amine groups as drug matrixes. Ibuprofen (IBU) and bovine serum albumin (BSA) were selected as model drugs and loaded onto the unmodified and functionalized SBA-15. The release rate of ibuprofen from the SBA-15 functionalized was found to be effectively controlled as compared to that from pure SBA-15. Therefore, introduction of functional groups on the surface of SBA-15 to have specific host– guest interactions with drugs will also be important and good for controlled drug delivery.

Hollow mesoporous spheres (HMS) are another group of important mesostructured materials, which have been used for applications in drug delivery (Zhu et al., 2005). Zhu et al. reported a facile route for the preparation of HMS and employed for drug storage and delivery using ibuprofen. They compared the drug loading with MCM-41 and found that the HMS exhibited much more storage capacity than MCM-41 (Hartmann, 2005). Also, MSU mesoporous silica, has also been employed for drug delivery (Lehto et al., 2005). (Tourne-Peteilh et al. (2003) employed MSU as carriers for the drug pentapeptide. They found that the pentapeptide could be encapsulated in the mesoporous silica and would be released instantly upon solid washing with dimethylformamide.

For mesoporous silica materials based drug system, bioactivity is an important factor for its potential application. Bioactivity studies demonstrated that mesoporous silicas, MCM-48, MCM-41, and SBA-15, are bioactive materials for the drug delivery system. However, the biocompatibility is not so strong. Modification of silica with phosphorous material or active components such as hydroxyapatite will significantly improve its biocompatibility (Yousefpour and Taheran, 2013, Huang et al., 2012 and Vallet-Regi et al., 2005).