Metal-organic frameworks (MOFs) are a fascinating class of crystalline porous materials composed of metal ions and organic ligands. Due to their attractive properties, MOFs can potentially offer biomedical field applications, such as drug delivery and imaging. This study aimed to systematically identify the affecting factors on the MOF characteristics and their effects on structural and biological characteristics. An electronic search was performed in four databases containing PubMed, Scopus, Web of Science, and Embase, using the relevant keywords. After analyzing the studies, 20 eligible studies were included in this review. As a result, various factors such as additives and organic ligand can influence the size and structure of MOFs. Additives are materials that can compete with ligand and may affect the nucleation and growth processes and, consequently, particle size. The nature and structure of ligand are influential in determining the size and structure of MOF. Moreover, synthesis parameters like the reaction time and initial reagents ratio are critical factors that should be optimized to regulate the size and structure. Of note is that the nature of the ligand and using a suitable additive can control the porosity of MOF. The more extended ligands aid in forming large pores. The choice of metallic nodes and organic ligand, and the MOF concentration are important factors since they can determine toxicity and biocompatibility of the final structure. The physicochemical properties of MOFs, such as hydrophobicity, affect the toxicity of nanoparticles. An increase in hydrophobicity causes increased toxicity of MOF. The biodegradability of MOF, as another property, depends on the organic ligand and metal ion and environmental conditions like pH. Photocleavable ligands can be served for controlled degradation of MOFs. Generally, by optimizing these affecting factors, MOFs with desirable properties will be obtained for biomedical applications.

Oral administration of medication is the first option when patient compliance is considered. However, many barriers face oral absorption of drugs that limit bioavailability in about 90% of therapeutic agents. Utilization of nanoparticulate drug delivery systems is a major strategy for increasing oral absorption. They can improve oral bioavailability through mechanisms such as protection of the drug in the GI tract, increasing cellular contact and residence time of the drug, protection of the drug from presystemic metabolism and efflux and increasing diffusion across the mucosal and epithelial layers. Liposomes are biocompatible carriers employed to improve oral bioavailability of drugs and in addition to the general advantages of nanocarriers for oral delivery, they offer benefits derived from their lipidic bilayer structure. They can better adhere to biomembranes, form mixed-micelle structures with bile salts to increase the solubility of poorly-soluble drugs and are suitable candidates for lymphatic uptake. They have been successful in improving oral bioavailability of a variety of compounds including peptide and proteins, hydrophilic and lipophilic drugs. Stability under GI conditions is the main concern for oral liposomes, however, promising approaches have been suggested to increase the stability of oral liposomes. These include: using appropriate lipid compositions, polymer coating, addition of stabilizing lipids to liposomal structures, preparation of double liposomes and proliposomes and some other innovative methods. The present review focuses on the role of liposomes in improving oral absorption of drugs, the problems encountered, and the types of liposomes designed to overcome these issues. Barriers to oral delivery will be discussed and examples of bioavailability enhancement upon encapsulation in various types of liposomes investigated.