Influence of Drug-Silica Electrostatic Interactions on Drug Release from Mesoporous Silica-Based Oral Delivery Systems

Hollow mesoporous silica nanoparticles for drug formulation and delivery: Opportunities for cancer therapy

The advantages of large surface area, high volume ratio, good biocompatibility, and controllable surface functionalization make hollow mesoporous silica nanoparticles (HMSNs) an ideal drug carrier. HMSNs can achieve high efficiency, targeting, and controlled release by adjusting the microstructure and surface modification of its particles, which makes it broad application prospects in the field of medical therapy, especially in cancer therapy. Numerous studies have shown that preparation method, shape, particle size, hollow inner diameter, aperture and wall thickness of the HMSNs, the characteristics of the drugs, the interaction between the drugs and the carriers, and the external environment all closely affect the drug delivery, release, and efficacy. The external environment includes temperature, pH value, light intensity, magnetic field intensity, enzyme type and concentration, etc. This review summarizes the research progress of HMSNs as carrier materials in the past five years, analyzes the existing problems in the application process and presents the development prospects of HMSNs.

Controlled Release of Hydrophilic Drug from Hollow Nanodots

Here the challenge of limited encapsulation efficiency of ionizable hydrophilic molecules in silica materials is addressed. Two effective strategies are showcased that allow high encapsulation efficiency of salicylic acid, while simultaneously maintaining the morphology and particle size of silica nanocapsules. These promising approaches involve the formation and encapsulation of a prodrug or the complexation of the hydrophilic payload with a hydrophobic moiety to form a complex that is dissociated in acidic conditions. Well-defined core-shell silica nanocapsules with a diameter of 6 nm are obtained and exhibited an encapsulation efficiency of over 90%. High amounts of salicylic acid are released in acidic conditions from silica nanocapsules entrapping the prodrug or the complex, leading to pH-responsive characteristics. This work demonstrates promising strategies for the encapsulation and the controlled release of hydrophilic fertilizers, pesticides or drugs.

Molecular-properties based formulation guidance tree for amorphous and supersaturable mesoporous silica preparations of poorly soluble compounds

A huge majority of new chemical entities (NCEs) advancing through the drug discovery pipeline often have poor aqueous solubility. This requires formulation scientists to search for solubility enhancement strategies, within the constraints of time and material. To address these challenges, a strategic platform formulation is often required for a rapid compound screening to enable early exploratory PK and toxicology studies. Through this work, we present an option of a material-sparing, high yielding and solubility-enabling amorphous API and HPMCAS-L co-loaded mesoporous silica-based formulation. The usability of this platform formation strategy was assessed for a physico-chemically diverse set of eleven compounds. The formulation approach was successful in stabilizing the model compounds mesoporous silica. Additionally, through the presence of HPMCAS-L, the precipitation risk in supersaturable aqueous environment was significantly reduced. Finally, this manuscript provides fundamental, computational and experimental molecular-properties based formulation guidance tree to a priori gauge the (1) possibility of generating solid-state stable amorphous formulations and (2) sustaining in vitro supersaturation in extreme non-sink dissolution conditions. This unique and conceptual formulation guidance tree is believed to be extremely beneficial to drug discovery formulators to triage NCEs and streamline solubility-enabling formulation efforts.

Candesartan Cilexetil Formulations in Mesoporous Silica: Preparation, Enhanced Dissolution In Vitro, and Oral Bioavailability In Vivo

Candesartan cilexetil (CC) is one of well-tolerated antihypertensive drugs, while its poor solubility and low bioavailability limit its use. Herein, two mesoporous silica (Syloid XDP 3150 and Syloid AL-1 FP) and the corresponding amino-modified products (N-XDP 3150 and N-AL-1 FP) have been selected as the carriers of Candesartan cilexetil to prepare solid dispersion through solvent immersion, and characterized through using powder X-ray diffraction analysis, infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy, and solid-state nuclear magnetic resonance spectroscopy, etc. The state of CC changed from crystalline to amorphous after loading onto the silica carriers, in which no interactions between CC and silica existed. Then, the dissolution behaviors in vitro were studied through using flow-through cell dissolution method. CC-XDP 3150 sample exhibited the most extensive dissolution, and the cumulative release of CC from it was 1.88-fold larger than that of CC. Moreover, the pharmacokinetic results in rats revealed that the relative bioavailability of CC-XDP 3150 and CC-N-XDP 3150 solid dispersions were estimated to be 326 % % and 238 % % in comparison with CC, respectively. Clearly, pore size, pore volume, and surface properties of silica carrier have remarkable effect on loading, dissolution and bioavailability of CC. In brief, this work will provide valuable information in construction of mesoporous silica-based delivery system toward poorly water-soluble drugs.

A Descriptive Review on the Potential Use of Diatom Biosilica as a Powerful Functional Biomaterial: A Natural Drug Delivery System

Although various chemically synthesized materials are essential in medicine, food, and agriculture, they can exert unexpected side effects on the environment and human health by releasing certain toxic chemicals. Therefore, eco-friendly and biocompatible biomaterials based on natural resources are being actively explored. Recently, biosilica derived from diatoms has attracted attention in various biomedical fields, including drug delivery systems (DDS), due to its uniform porous nano-pattern, hierarchical structure, and abundant silanol functional groups. Importantly, the structural characteristics of diatom biosilica improve the solubility of poorly soluble substances and enable sustained release of loaded drugs. Additionally, diatom biosilica predominantly comprises SiO2, has high biocompatibility, and can easily hybridize with other DDS platforms, including hydrogels and cationic DDS, owing to its strong negative charge and abundant silanol groups. This review explores the potential applications of various diatom biosilica-based DDS in various biomedical fields, with a particular focus on hybrid DDS utilizing them.

Effect of Organic Solvent on the Mass Transfer Mechanism of Coumarin 102 in a Single Octadecylsilyl Silica Gel/Organic Solvent-Water System by Laser Trapping and Fluorescence Microspectroscopy

Understanding mass transfer kinetics within individual porous particles is crucial for theoretically explaining the retention and elution behaviors in chromatography and drug delivery. Using laser trapping and fluorescence microspectroscopy, we investigated the diffusion mechanism of coumarin 102 (C102) into single octadecylsilyl particle in acetonitrile (ACN)/water, N,N-dimethylformamide (DMF)/water, and 1-butanol (BuOH)/water solutions. The intraparticle diffusion behavior of C102 was evaluated using the spherical diffusion equation, allowing us to determine the intraparticle diffusion coefficients (Dintra): (8-10) × 10-9 cm2 s-1 for ACN, (10-16) × 10-9 cm2 s-1 for DMF, and (4-6) × 10-9 cm2 s-1 for BuOH. The obtained Dintra values were further analyzed using a pore and surface diffusion model. Thus, we revealed that the diffusion mechanism of C102 differed depending on the organic solvent: surface diffusion for ACN and DMF and pore and surface diffusions for BuOH were observed. This difference is attributed to the formation of a concentrated liquid phase of ACN and DMF at the interface of the alkyl chain and the bulk solution in the pore.

Phosphatidylserine and/or Sialic Acid Modified Liposomes Increase Uptake by Tumor-associated Macrophages and Enhance the Anti-tumor Effect

DOX liposomes have better therapeutic effects and lower toxic side effects. The targeting ability of liposomes is one of the key factors affecting the therapeutic effect of DOX liposomes. This study developed two types of targeted liposomes. Sialic acid (SA)-modified liposomes were designed to target the highly expressed Siglec-1 receptor on tumor-associated macrophages surface. Phosphatidylserine (PS)-modified liposomes were designed to promote phagocytosis by monocyte-derived macrophages through PS apoptotic signaling. In order to assess and compare the therapeutic potential of different targeted pathways in the context of anti-tumor treatment, we compared four phosphatidylserine membrane materials (DOPS, DSPS, DPPS and DMPS) and found that liposomes prepared using DOPS as material could significantly improve the uptake ability of RAW264.7 cells for DOX liposomes. On this basis, normal DOX liposomes (CL-DOX) and SA-modified DOX liposomes (SAL-DOX), PS-modified DOX liposomes (PS-CL-DOX), SA and PS co-modified DOX liposomes (PS-SAL-DOX) were prepared. The anti-tumor cells function of each liposome on S180 and RAW264.7 in vitro was investigated, and it was found that SA on the surface of liposomes can increase the inhibitory effect. In vivo efficacy results exhibited that SAL-DOX and PS-CL-DOX were superior to other groups in terms of ability to inhibit tumor growth and tumor inhibition index, among which SAL-DOX had the best anti-tumor effect. Moreover, SAL-DOX group mice had high expression of IFN-γ as well as IL-12 factors, which could significantly inhibit mice tumor growth, improve the immune microenvironment of the tumor site, and have excellent targeted delivery potential.

Functionalized Periodic Mesoporous Silica Nanoparticles for Inhibiting the Progression of Atherosclerosis by Targeting Low-Density Lipoprotein Cholesterol

Atherosclerotic disease is a substantial global burden, and existing treatments, such as statins, are recommended to lower low-density lipoprotein cholesterol (LDL-C) levels and inhibit the progression of atherosclerosis. However, side effects, including gastrointestinal unease, potential harm to the liver, and discomfort in the muscles, might be observed. In this study, we propose a novel method using periodic mesoporous silica nanoparticles (PMS) to create heparin-modified PMS (PMS-HP) with excellent biocompatibility, enabling selective removal of LDL-C from the blood. In vitro, through the introduction of PMS-HP into the plasma of mice, we observed that, compared to PMS alone, PMS-HP could selectively adsorb LDL-C while avoiding interference with valuable components such as plasma proteins and high-density lipoprotein cholesterol (HDL-C). Notably, further investigations revealed that the adsorption of LDL-C by PMS-HP could be well-fitted to quasi-first-order (R2 = 0.993) and quasi-second-order adsorption models (R2 = 0.998). Likewise, in vivo, intravenous injection of PMS-HP enabled targeted LDL-C adsorption (6.5 ± 0.73 vs. 8.6 ± 0.76 mM, p < 0.001) without affecting other plasma constituents, contributing to reducing intravascular plaque formation (3.66% ± 1.06% vs. 1.87% ± 0.79%, p < 0.05) on the aortic wall and inhibiting vascular remodeling (27.2% ± 6.55% vs. 38.3% ± 1.99%, p < 0.05). Compared to existing lipid adsorption techniques, PMS-HP exhibited superior biocompatibility and recyclability, rendering it valuable for both in vivo and in vitro applications.

Bioinspired synthesis of bioactive glass nanocomposites for hyaluronic acid delivery to bone and skin

In this study, we present nanocomposites of bioactive glass (BG) and hyaluronic acid (HA) (nano-BGHA) for effective delivery of HA to skin and bone. The synthesis of the nanocomposites has been carried out through the bio-inspired method, which is a modification of the traditional Stober's synthesis as it avoids using ethanol, ammonia, synthetic surfactants, or high-temperature calcination. This environmentally friendly, bio-inspired route allowed the synthesis of mesoporous nanocomposites with an average hydrodynamic radius of ∼190 nm and an average net surface charge of ∼-21 mV. Most nanocomposites are amorphous and bioactive in nature with over 70 % cellular viability for skin and bone cell lines even at high concentrations, along with high cellular uptake (90-100 %). Furthermore, the nanocomposites could penetrate skin cells in a transwell set-up and artificial human skin membrane (StratM®), thus depicting an attractive strategy for the delivery of HA to the skin. The purpose of the study is to develop nanocomposites of HA and BG that can have potential applications in non-invasive treatments that require the delivery of high molecular weight HA such as in the case of osteoarthritis, sports injury treatments, eye drops, wound healing, and some anticancer treatments, if further investigated. The presence of BG further enhances the range to bone-related applications. Additionally, the nanocomposites can have potential cosmeceutical applications where HA is abundantly used, for instance in moisturizers, dermal fillers, shampoos, anti-wrinkle creams, etc.

Study of Disordered Mesoporous Silica Regarding Intrinsic Compound Affinity to the Carrier and Drug-Accessible Surface Area

There is increasing research interest in using mesoporous silica for the delivery of poorly water-soluble drugs that are stabilized in a noncrystalline form. Most research has been done on ordered silica, whereas far fewer studies have been published on using nonordered mesoporous silica, and little is known about intrinsic drug affinity to the silica surface. The present mechanistic study uses inverse gas chromatography (IGC) to analyze the surface energies of three different commercially available disordered mesoporous silica grades in the gas phase. Using the more drug-like probe molecule octane instead of nitrogen, the concept of a "drug-accessible surface area" is hereby introduced, and the effect on drug monolayer capacity is addressed. In addition, enthalpic interactions of molecules with the silica surface were calculated based on molecular mechanics, and entropic energy contributions of volatiles were estimated considering molecular flexibility. These free energy contributions were used in a regression model, giving a successful comparison with experimental desorption energies from IGC. It is proposed that a simplified model for drugs based only on the enthalpic interactions can provide an affinity ranking to the silica surface. Following this preformulation research on mesoporous silica, future studies may harness the presented concepts to guide formulation scientists.

Silica nanoparticles: A review of their safety and current strategies to overcome biological barriers

Silica nanoparticles (SNP) have gained tremendous attention in the recent decades. They have been used in many different biomedical fields including diagnosis, biosensing and drug delivery. Medical uses of SNP for anti-cancer, anti-microbial and theranostic applications are especially prominent due to their exceptional performance to deliver many different small molecules and recently biologics (mRNA, siRNA, antigens, antibodies, proteins, and peptides) at targeted sites. The physical and chemical properties of SNP such as large specific surface area, tuneable particle size and porosity, excellent biodegradability and biocompatibility make them an ideal drug delivery and diagnostic platform. Based on the available data and the pre-clinical performance of SNP, recent interest has driven these innovative materials towards clinical application with many of the formulations already in Phase I and Phase II trials. Herein, the progress of SNP in biomedical field is reviewed, and their safety aspects are analysed. Importantly, we critically evaluate the key structural characteristics of SNP to overcome different biological barriers including the blood-brain barrier (BBB), skin, tumour barrier and mucosal barrier. Future directions, potential pathways, and target areas towards rapid clinical translation of SNP are also recommended.

Non-ionic surfactant-assisted controlled release of oxyresveratrol on dendritic fibrous silica for topical applications

We present a simple and eco-friendly method for controlled drug release using a surfactant-assisted method. Oxyresveratrol (ORES) was co-loaded with a non-ionic surfactant onto KCC-1, a dendritic fibrous silica, using an ethanol evaporation technique. The carriers were characterized using FE-SEM, TEM, XRD, N₂ adsorption-desorption, FTIR, and Raman spectroscopy, and the loading and encapsulation efficiencies were assessed using TGA and DSC techniques. Contact angle and zeta potential were used to determine the surfactant arrangement and the particle charges. To investigate the effects of different surfactants (Tween 20, Tween 40, Tween 80, Tween 85, and Span 80) on ORES release, we conducted experiments under different pH and temperature conditions. Results showed that the types of surfactants, drug loading content, pH, and temperature significantly affected the drug release profile. The percentage of drug loading efficiency of the carriers was in the range of 80 %-100 %, and the release of ORES was in the order of M/KCC-1 > M/K/S80 > M/K/T40 > M/K/T20 > MK/T80 > M/K/T85 at 24 h. Furthermore, the carriers provided excellent protection for ORES against UVA and maintained its antioxidant activity. KCC-1 and Span 80 enhanced the cytotoxicity to HaCaT cells, while Tween 80 suppressed the cytotoxicity.

Mesoporous Drug Delivery System: From Physical Properties of Drug in Solid State to Controlled Release

Mesoporous materials, which exhibit great potential in the control of polymorphs and delivery of poorly water-soluble drugs, have obtained considerable attention in the field of pharmaceutical science. The physical properties and release behaviors of amorphous or crystalline drugs may be affected by formulating them into mesoporous drug delivery systems. In the past few decades, an increasing amount of papers have been written about mesoporous drug delivery systems, which play a crucial role in improving the properties of drugs. Herein, mesoporous drug delivery systems are comprehensively reviewed in terms of their physicochemical characteristics, control of polymorphic forms, physical stability, in vitro performance, and in vivo performance. Moreover, the challenges and strategies of developing robust mesoporous drug delivery systems are also discussed.

Application of Amyloid-Based Hybrid Membranes in Drug Delivery

The properties of amyloid fibrils, e.g., unique structural characteristics and superior biocompatibility, make them a promising vehicle for drug delivery. Here, carboxymethyl cellulose (CMC) and whey protein isolate amyloid fibril (WPI-AF) were used to synthesize amyloid-based hybrid membranes as vehicles for the delivery of cationic and hydrophobic drugs (e.g., methylene blue (MB) and riboflavin (RF)). The CMC/WPI-AF membranes were synthesized via chemical crosslinking coupled with phase inversion. The zeta potential and scanning electron microscopy results revealed a negative charge and a pleated surface microstructure with a high content of WPI-AF. FTIR analysis showed that the CMC and WPI-AF were cross-linked via glutaraldehyde and the interacting forces between membrane and MB or RF was found to be electrostatic interaction and hydrogen bonding, respectively. Next, the in vitro drug release from membranes was monitored using UV-vis spectrophotometry. Additionally, two empirical models were used to analyze the drug release data and relevant rate constant and parameters were determined accordingly. Moreover, our results indicated that in vitro drug release rates depended on the drug–matrix interactions and transport mechanism, which could be controlled by altering the WPI-AF content in membrane. This research provides an excellent example of utilizing two-dimensional amyloid-based materials for drug delivery.

Synthesis and characterization of silica nanoparticles from rice ashes coated with chitosan/cancer cell membrane for hepatocellular cancer treatment

Dual pH-sensitive smart nanocarriers based on silica nanoparticles (SNPs) extracted from rice husk ashes (RHAs) to effectively inhibit liver cancer cell proliferation were investigated. The SNPs were coated with chitosan (CH) and loaded with doxorubicin (DOX), then functionalized with cell membrane (CM) for homologous targeting ability. The FTIR spectra showed an absorption wave number at 1083 cm^-1 which confirmed the existence of the SiOSi group, ratifying that the nanocarriers belong to silica species. The Korsmeyer-Peppas kinetic model reported R² values of 0.996 and 0.931 for pH = 5.4 and pH = 7.4, respectively, demonstrating pH-responsive behavior of the nanocarriers. The cytotoxicity test confirmed that the HepG2 cell line treated with different SNP-CH-CM concentrations had no detectable significant cell toxicity, however, SNP-CH-DOX-CM induced greater cell death. In vivo tests revealed that SNP-CH-DOX-CM suppressed liver cancer growth in nude mice, demonstrating high pharmaceutical capability. Histological examination of vital organs showed that the targeted drug delivery system (DDS) had minor in vivo toxicity. In the light of its high treatment efficacy and minimal side effects, the investigated DDS is promising for the therapy of liver cancer.

Impact of Properties of Hydrated Silicon Dioxide as Core Material on the Characteristics of Drug-containing Particles Prepared by the 2-step Process Melt Granulation Technology, MALCORE®

Drug-containing particles (DCPs) are frequently used as cores in the development of solid oral dosage forms. The wet layering technique, which is a typical approach for preparing DCPs, requires the use of solvents and a long manufacturing time. In our previous study, we developed a novel manufacturing technology, MALCORE^®, which can solve these problems through melt granulation. However, particle size control methods for DCPs in MALCORE^® and the effect of the physical properties of the hydrated silicon dioxide (HSD) used for the core have not been clarified. The aim of this study was to examine the effects of the particle and pore sizes of HSD on the properties of the prepared DCPs. The results showed that the DCPs prepared using MALCORE^® could be controlled by the particle size of HSD. The drug-loading efficiency tended to decrease as HSD particle size increased. Additionally, the amount of drug layering in DCPs increased as the pore size of HSD increased, but HSDs with a pore size much larger than the particle size were not able to properly layer the drug. These findings are helpful for applying MALCORE^® to a variety of oral drug formulations.

Physical stability and dissolution behaviors of amorphous pharmaceutical solids: Role of surface and interface effects

Amorphous pharmaceutical solids (APS) are single- or multi-component systems in which drugs exist in high-energy states with long-range disordered molecular packing. APSs have become one of the most effective and widely used pharmaceutical delivery approaches for poorly water-soluble drugs in the last several decades. Considerable efforts have been made to investigate the physical stability and dissolution behaviors of APSs, however, the underlying mechanisms remain imperfectly understood. Recent studies reveal that surface and interface properties of APSs could strongly affect the physical stability and dissolution behaviors. This paper provides a comprehensive overview of recent studies focusing on the physical stability and dissolution behaviors of APSs from both surface and interface perspectives. We highlight the role of surface or interface properties in nucleation, crystal growth, phase separation, dissolution, and supersaturation. Meanwhile, the challenges and scope of research on surface and interface properties in the future are also briefly discussed. This review contributes to a better understanding of the surface- and interface-facilitated processes, which will provide more efficient and rational guidance for the design of APSs.

Efficient delivery of the Bcl-2 antisense oligonucleotide G3139 via nucleus-targeted aCD33-NKSN nanoparticles

G3139 is an antisense oligodeoxyribonucleotide (ODN) developed as a Bcl-2 down-regulating agent for the treatment of acute myelogenous leukemia (AML). However, the clinical efficacy of G3139 has been shown to be limited due to its rapid plasma clearance and low permeability. To enhance the effective delivery of G3139, this work prepared a novel nano gene delivery vector (aCD33-NKSN) consisting of a CD33 antigbody (aCD33), a nuclear localization signal (NLS), gene fusion peptides (KALA), and stearic acid (SA) for CD33 antigen targeting and nuclear localization. The aCD33-NKSN/G3139 nanoparticles were spherical and uniformly sized with a positive charge and sustained release. They had an excellent G3139 loading capacity and colloidal stability. The aCD33-NKSN/G3139 delivered G3139 into the nucleus of Kasumi-1 cells and aCD33-NKSN/G3139 could more effectively inhibited Bcl-2 expression and induced apoptosis in Kasumi-1 cells versus free G3139. The aCD33-NKSN/G3139 administration was more effective at inhibiting tumor growth, and significantly prolonged the survival time of mice in contrast to free G3139. The results illustrate that aCD33-NKSN/G3139 nanoparticles could improve the antitumor activity of encapsulated G3139 due to aCD33 targeting and the ability to perform nuclear localization, The results offer a promising clinical application potential for the treatment of acute myeloid leukemia.

Influence of API physico-chemical properties on amorphization capacity of several mesoporous silica loading methods

The objective of this work was to evaluate the impact of physico-chemical properties of pharmaceutical drugs on the optimal mesoporous silica loading methods. Indeed, a good combination between drug and loading process has to be studied to promote the deepest penetration of the drug inside the mesopores, allowing high drug amorphization. Six molecules, namely lidocaine and its hydrochloride, ibuprofen, ketoprofen, artemether and miconazole, with different physico-chemical properties (the ionized character, the acid-base character, the HBDA number, the solubility in sc-CO₂ and the behavior under subcritical CO₂) were used to produce drug-silica formulations. Different impregnation processes (physical mixing, melting, wetting, sc-CO₂ and subcritical CO₂ impregnations) have been compared for each drug, in terms of drug recovery and crystallinity. Formulations showed drug percentage close to 100% except for supercritical soluble drug formulations impregnated by using sc-CO₂. However, the basic drug character provided less or no drug loss during impregnation. Processing insoluble sc-CO₂ molecule under supercritical conditions led to less crystallinity than the correspondent physical mixture suggesting an interesting repulsive effect that forces the drug penetration within the mesopores. Besides, it has been also highlighted that the HBDA number is not sufficient to predict the final drug loading. Melting methods have high interest considering the drugs tested and subcritical CO₂ could increase the loading, especially for drugs with high molten viscosity. This study showed that a plethora of loading methods can be used to provide high drug loaded MS formulations with a wide choice of equipment.

Recent Advances in Enhancement of Dissolution and Supersaturation of Poorly Water-Soluble Drug in Amorphous Pharmaceutical Solids: A Review

Amorphization is one of the most effective pharmaceutical approaches to enhance the dissolution and oral bioavailability of poorly water-soluble drugs. In recent years, amorphous formulations have been experiencing rapid development both in theoretical and practical application. Based on using different types of stabilizing agents, amorphous formulations can be mainly classified as polymer-based amorphous solid dispersion, coamorphous formulation, mesoporous silica-based amorphous formulation, etc. This paper summarizes recent advances in the dissolution and supersaturation of these amorphous formulations. Moreover, we also highlight the roles of stabilizing agents such as polymers, low molecular weight co-formers, and mesoporous silica. Maintaining supersaturation in solution is a key factor for the enhancement of dissolution profile and oral bioavailability, and thus, the strategies and challenges for maintaining supersaturation are also discussed. With an in-depth understanding of the inherent mechanisms of dissolution behaviors, the design of amorphous pharmaceutical formulations will become more scientific and reasonable, leading to vigorous development of commercial amorphous drug products.

Hydrogels as Drug Delivery Systems: A Review of Current Characterization and Evaluation Techniques

Owing to their tunable properties, controllable degradation, and ability to protect labile drugs, hydrogels are increasingly investigated as local drug delivery systems. However, a lack of standardized methodologies used to characterize and evaluate drug release poses significant difficulties when comparing findings from different investigations, preventing an accurate assessment of systems. Here, we review the commonly used analytical techniques for drug detection and quantification from hydrogel delivery systems. The experimental conditions of drug release in saline solutions and their impact are discussed, along with the main mathematical and statistical approaches to characterize drug release profiles. We also review methods to determine drug diffusion coefficients and in vitro and in vivo models used to assess drug release and efficacy with the goal to provide guidelines and harmonized practices when investigating novel hydrogel drug delivery systems.