Over the past few decades, gene therapy has gained immense importance in medical research as a promising treatment strategy for diseases such as cancer, AIDS, Alzheimer’s disease, and many genetic disorders. When a gene needs to be delivered to a target cell inside the human body, it has to pass a large number of barriers through the extracellular and intracellular environment. This is why the delivery of naked genes and nucleic acids is highly unfavorable, and gene delivery requires suitable vectors that can carry the gene cargo to the target site and protect it from biological degradation. To date, medical research has come up with two types of gene delivery vectors, which are viral and nonviral vectors. The ability of viruses to protect transgenes from biological degradation and their capability to efficiently cross cellular barriers have allowed gene therapy research to develop new approaches utilizing viruses and their different genomes as vectors for gene delivery. Although viral vectors are very efficient, science has also come up with numerous nonviral systems based on cationic lipids, cationic polymers, and inorganic particles that provide sustainable gene expression without triggering unwanted inflammatory and immune reactions, and that are considered nontoxic. In this review, we discuss in detail the latest data available on all viral and nonviral vectors used in gene delivery. The mechanisms of viral and nonviral vector-based gene delivery are presented, and the advantages and disadvantages of all types of vectors are also given.

Nowadays, the use of statistical approaches, i.e., Box–Bhenken designs, are becoming very effective for developing and optimizing pharmaceutical drug formulations. In the current work, a Box–Bhenken design was employed using Design Expert version 11 to develop, evaluate, and optimize a hydrogel-based formulation for sustained release of an antiviral drug, i.e., favipiravir. The hydrogels were prepared using the free radical polymerization technique. β-Cyclodextrin (β-CD), N,N′-methylenebisacrylamide (MBA), acrylic acid (AA), and potassium per sulfate (KPS) were used as oligomer, crosslinker, monomer, and initiator, respectively. Three variables, including β-CD (X₁), MBA (X₂), and AA (X₃) were used at various concentrations for the preparation of hydrogels, followed by evaluation of a sol–gel fraction, swelling, porosity, chemical compatibilities, in vitro drug release, and entrapment efficiency. The results of the studies revealed that the degree of swelling was pH dependent, the best swelling being at pH 7.2 (1976%). On the other hand, for the low sol fraction of 0.2%, the reasonable porosity made the hydrogel capable of loading 99% favipiravir, despite its hydrophobic nature. The maximum entrapment efficiency (99%) was observed in optimized hydrogel formulation (F15). Similarly, in vitro drug release studies showed that the prepared hydrogels exhibited a good, sustained release effect till the 24th hour. The kinetic modelling of drug release data revealed that the Korsmeyer–Peppas model was best fit model, describing a diffusion type of drug release from the prepared hydrogels. Conclusively, the outcomes predict that the hydrogel-based system could be a good choice for developing a sustained-release, once-daily dosage form of favipiravir for improved patient compliance.

In recent years, pH-sensitive hydrogels have been developed for the delivery of therapeutic agents to specific target sites that have a defined pH range. The use of pH-responsive polymers in hydrogels allows drug delivery to the desired pH range of the target organ. The primary aim is to increase the retention time of the drug in the small intestine by utilizing the swelling mechanism of the hydrogel at intestinal pH. In this study, polyethylene glycol (PEG) was used as a polymer to formulate a pH-sensitive hydrogel of Ezetimibe to deliver the drug to the small intestine where it inhibits the absorption of cholesterol. Design Expert software was applied to design and optimize the trial formulations in order to obtain an optimized formulation that has all the desired characteristics of the hydrogels. The PEG/Acrylic Acid hydrogels showed the maximum swelling at pH 6.8, which is consistent with the pH of the small intestine (pH 6–7.4). The maximum entrapment efficiency of the hydrogels was 99%. The hydrogel released 80–90% of the drug within 24 h and followed first-order release kinetics, which showed that the release from the drug was sustained. Hence, the results showed that the choice of a suitable polymer can lead to the development of an efficient drug-loaded hydrogel that can deliver the drug at the specific pH of the target organ.