Surface chemistry and pore size affect carrier properties of mesoporous silicon microparticles

Self-Nanoemulsion Intrigues the Gold Phytopharmaceutical Chrysin: In Vitro Assessment and Intrinsic Analgesic Effect

Chrysin is a natural flavonoid with a wide range of bioactivities. Only a few investigations have assessed the analgesic activity of chrysin. The lipophilicity of chrysin reduces its aqueous solubility and bioavailability. Hence, self-nanoemulsifying drug delivery systems (SNEDDS) were designed to overcome this problem. Kollisolv GTA, Tween 80, and Transcutol HP were selected as oil, surfactant, and cosurfactant, respectively. SNEDDS A, B, and C were prepared, loaded with chrysin (0.1%w/w), and extensively evaluated. The optimized formula (B) encompasses 25% Kollisolv GTA, 18.75% Tween 80, and 56.25% Transcutol HP was further assessed. TEM, in vitro release, and biocompatibility towards the normal oral epithelial cell line (OEC) were estimated. Brain targeting and acetic acid-induced writhing in a mouse model were studied. After testing several adsorbents, powdered SNEDDS B was formulated and evaluated. The surfactant/cosurfactant (S/CoS) ratio of 1:3 w/w was appropriate for the preparation of SNEDDS. Formula B exhibited instant self-emulsification, spherical nanoscaled droplets of 155.4 ± 32.02 nm, and a zeta potential of - 12.5 ± 3.40 mV. The in vitro release proved the superiority of formula B over chrysin suspension (56.16 ± 10.23 and 9.26 ± 1.67%, respectively). The biocompatibility of formula B towards OEC was duplicated (5.69 ± 0.03 µg/mL). The nociceptive pain was mitigated by formula B more efficiently than chrysin suspension as the writhing numbers reduced from 8.33 ± 0.96 to 0 after 60 min of oral administration. Aerosil R972 was selected as an adsorbent, and its chemical compatibility was confirmed. In conclusion, our findings prove the therapeutic efficacy of chrysin self-nanoemulsion as a potential targeting platform to combat pain.

Enhanced dissolution of anticancer drug letrozole from mesoporous zeolite clinoptilolite

High dissolution of anticancer drugs directly adsorbed onto porous carriers is indispensable for the development of drug delivery systems with high bioavailability. We report direct adsorption/loading of the anticancer drug letrozole (LTZ) onto the clinoptilolite (CLI) zeolite after the surface activation.In vitroLTZ dissolution from the CLI zeolites reached 95 % after 23 h in an acidic medium, being faster than the dissolution of the pure LTZ molecules. Fast dissolution occurs due to uniform exposure of the LTZ onto the external surface of the CLI zeolites, being accessible to the solvent for dissolution. On the other hand, the LTZ molecules were hidden in the bulk phase, giving a slow dissolution rate. Small positive value of the CLI/LTZ adsorption energy of 0.06 eV suggests that the release process is favourable in aqueous media. The main merit of the CLI/LTZ system is its quick onset of action and high bioavailability. This work demonstrates a possibility of enhancement of the dissolution of poorly soluble LTZ from the CLI zeolite, being promising for the further development of drug delivery systems.

Understanding Fenofibrate Release from Bare and Modified Mesoporous Silica Nanoparticles

To investigate the impact of the surface functionalization of mesoporous silica nanoparticle (MSN) carriers in the physical state, molecular mobility and the release of Fenofibrate (FNB) MSNs with ordered cylindrical pores were prepared. The surface of the MSNs was modified with either (3-aminopropyl) triethoxysilane (APTES) or trimethoxy(phenyl)silane (TMPS), and the density of the grafted functional groups was quantified via ¹H-NMR. The incorporation in the ~3 nm pores of the MSNs promoted FNB amorphization, as evidenced via FTIR, DSC and dielectric analysis, showing no tendency to undergo recrystallization in opposition to the neat drug. Moreover, the onset of the glass transition was slightly shifted to lower temperatures when the drug was loaded in unmodified MSNs, and MSNs modified with APTES composite, while it increased in the case of TMPS-modified MSNs. Dielectric studies have confirmed these changes and allowed researchers to disclose the broad glass transition in multiple relaxations associated with different FNB populations. Moreover, DRS showed relaxation processes in dehydrated composites associated with surface-anchored FNB molecules whose mobility showed a correlation with the observed drug release profiles.

Characterization of Drugs with Good Glass Formers in Loaded-Mesoporous Silica and Its Theoretical Value Relevance with Mesopores Surface and Pore-Filling Capacity

The incorporation of a drug into mesoporous silica (MPS) is a promising strategy to stabilize its amorphous form. However, the drug within MPS has shown incomplete release, despite a supersaturated solution being generated. This indicates the determination of maximum drug loading in MPS below what is experimentally necessary to maximize the drug doses in the system. Therefore, this study aimed to characterize the drugs with good glass former loaded-mesoporous silica, determine the maximum drug loading, and compare its theoretical value relevance to monolayer covering the mesoporous (MCM) surface, as well as pore-filling capacity (PFC). Solvent evaporation and melt methods were used to load each drug into MPS. In addition, the glass transition of ritonavir (RTV) and cyclosporine A (CYP), as well as the melting peak of indomethacin (IDM) and saccharin (SAC) in mesoporous silica, were not discovered in the modulated differential scanning calorimetry (MDSC) curve, demonstrating that each drug was successfully incorporated into the mesopores. The amorphization of RTV-loaded MPS (RTV/MPS), CYP-loaded MPS (CYP/MPS), and IDM-loaded MPS (IDM/MPS) were confirmed as a halo pattern in powder X-ray diffraction measurements and a single glass transition event in the MDSC curve. Additionally, the good glass formers, nanoconfinement effect of MPS and silica surface interaction contributed to the amorphization of RTV, CYP and IDM within MPS. Meanwhile, the crystallization of SAC was observed in SAC-loaded MPS (SAC/MPS) due to its weak silica surface interaction and high recrystallization tendency. The maximum loading amount of RTV/MPS was experimentally close to the theoretical amount of MCM, showing monomolecular adsorption of RTV on the silica surface. On the other hand, the maximum loading amount of CYP/MPS and IDM/MPS was experimentally lower than the theoretical amount of MCM due to the lack of surface interaction. However, neither CYP or IDM occupied the entire silica surface, even though some drugs were adsorbed on the MPS surface. Moreover, the maximum loading amount of SAC/MPS was experimentally close to the theoretical amount of PFC, suggesting the multilayers of SAC within the MPS. Therefore, this study demonstrates that the characterization of drugs within MPS, such as molecular size and interaction of drug-silica surface, affects the loading efficiency of drugs within MPS that influence its relevance with the theoretical value of drugs.

Colonic Delivery of α-Linolenic Acid by an Advanced Nutrient Delivery System Prolongs Glucagon-Like Peptide-1 Secretion and Inhibits Food Intake in Mice

Scope

Nutrients stimulate the secretion of glucagon‐like peptide‐1 (GLP‐1), an incretin hormone, secreted from enteroendocrine L‐cells which decreases food intake. Thus, GLP‐1 analogs are approved for the treatment of obesity, yet cost and side effects limit their use. L‐cells are mainly localized in the distal ileum and colon, which hinders the utilization of nutrients targeting GLP‐1 secretion. This study proposes a controlled delivery system for nutrients, inducing a prolonged endogenous GLP‐1 release which results in a decrease food intake.

Methods and Results

α‐Linolenic acid (αLA) was loaded into thermally hydrocarbonized porous silicon (THCPSi) particles. In vitro characterization and in vivo effects of αLA loaded particles on GLP‐1 secretion and food intake were studied in mice. A total of 40.4 ± 3.2% of loaded αLA is released from particles into biorelevant buffer over 24 h, and αLA loaded THCPSi significantly increased in vitro GLP‐1 secretion. Single‐dose orally given αLA loaded mesoporous particles increased plasma active GLP‐1 levels at 3 and 4 h and significantly reduced the area under the curve of 24 h food intake in mice.

Conclusions

αLA loaded THCPSi particles could be used to endogenously stimulate sustain gastrointestinal hormone release and reduce food intake.

Ultrahigh nanostructured drug payloads from degradable mesoporous silicon aerocrystals

Porous silicon has found increased attention as a drug delivery system due to its unique features such as high drug payloads, surface area and biodegradation. In this study supercritical fluid (SCF) assisted drying of ultrahigh porosity (>90%) silicon particles and flakes was shown to result in much higher mesopore volumes (~4.66 cm³/g) and surface areas (~680 m²/g) than with air-drying. The loading and physical state of the model drug (S)-(+)-Ibuprofen in SCF dried matrices was quantified and assessed using thermogravimetric analysis, differential scanning calorimetry, UV-Vis spectrophotometry, gravimetric analysis, gas adsorption and electron microscopy. Internal drug payloads of up to 72% were achieved which was substantially higher than values published for both conventionally dried porous silicon (17-51%) and other mesoporous materials (7-45%). In-vitro degradability kinetics of SCF-dried matrices in simulated media was also found to be faster than air-dried controls. The in-vitro release studies provided improved but sustained drug dissolution at both pH 2.0 and pH 7.4.

Investigation of silicon nanoparticles produced by centrifuge chemical vapor deposition for applications in therapy and diagnostics

Porous silicon (PSi) is a biocompatible and biodegradable material, which can be utilized in biomedical applications. It has several favorable properties, which makes it an excellent material for building engineered nanosystems for drug delivery and diagnostic purposes. One significant hurdle for commercial applications of PSi is the lack of industrial scale production of nanosized PSi particles. Here, we report a novel two-step production method for PSi nanoparticles. The method is based on centrifuge chemical vapor deposition (cCVD) of elemental silicon in an industrial scale reactor followed by electrochemical post-processing to porous particles. Physical properties, biocompatibility and in vivo biodistribution of the cCVD produced nanoparticles were investigated and compared to PSi nanoparticles conventionally produced from silicon wafers by pulse electrochemical etching. Our results demonstrate that the cCVD production provides PSi nanoparticles with comparable physical and biological quality to the conventional method. This method may circumvent several limitations of the conventional method such as the requirements for high purity monocrystalline silicon substrates as starting material and the material losses during the top-down milling process of the pulse-etched films to porous nanoparticles. However, the electroless etching required for the porosification of cCVD-produced nanoparticles limited control over the pore size, but is amenable for scaling of the production to industrial requirements.

Bone Morphogenic Protein 2-Loaded Porous Silicon Carriers for Osteoinductive Implants

Bone morphogenetic proteins (BMPs) are probably the most important growth factors in bone formation and healing. However, the utilization of BMPs in clinical applications is mainly limited due to the protein poor solubility at physiological pH, rapid clearance and relatively short biological half-life. Herein, we develop degradable porous silicon (PSi)-based carriers for sustained delivery of BMP-2. Two different loading approaches are examined, physical adsorption and covalent conjugation, and their effect on the protein loading and release rate is thoroughly studied. The entrapment of the protein within the PSi nanostructures preserved its bioactivity for inducing osteogenic differentiation of rabbit bone marrow mesenchymal stems cells (BM-MSCs). BM-MSCs cultured with the BMP-2 loaded PSi carriers exhibit a relatively high alkaline phosphatase (ALP) activity. We also demonstrate that exposure of MSCs to empty PSi (no protein) carriers generates some extent of differentiation due to the ability of the carrier's degradation products to induce osteoblast differentiation. Finally, we demonstrate the integration of these promising BMP-2 carriers within a 3D-printed patient-specific implant, constructed of poly(caprolactone) (PCL), as a potential bone graft for critical size bone defects.

Mesoporous Silicon Particles Favor the Induction of Long-Lived Humoral Responses in Mice to a Peptide-Based Vaccine

Vaccinology faces the challenge of developing improved immunization approaches that are able to induce long-term immunity with the desired Th profile according to the pathology. In this context, new vehicles for efficient antigen delivery that exert adjuvant effects play a critical role in addressing this goal. Herein, mesoporous silicon particles (PSiP) were assessed as carriers for a peptide-based vaccine targeting the receptor for advanced glycation end products (RAGE), which is a relevant receptor in Alzheimer´s disease and other diseases. A RAGE peptide was adsorbed onto PSiP (PSiP vaccine) and administered to BALB/c mice, leading to immune responses that were similar in magnitude to those induced by the soluble peptide. However, the response induced by PSiP lasted for a significantly longer period when compared with the behavior of the group immunized with the peptide alone. Therefore, PSiP are proposed as carriers to enhance immune memory, which is critical in vaccination. This study opens interesting perspectives related to the application of PSiP in vaccinology.

Impact of Pore Size and Surface Chemistry of Porous Silicon Particles and Structure of Phospholipids on Their Interactions

By exploiting its porous structure and high loading capacity, porous silicon (PSi) is a promising biomaterial to fabricate protocells and biomimetic reactors. Here, we have evaluated the impact of physicochemical properties of PSi particles [thermally oxidized PSi, TOPSi; annealed TOPSi, AnnTOPSi; (3-aminopropyl) triethoxysilane functionalized thermally carbonized PSi, APTES-TCPSi; and thermally hydrocarbonized PSi, THCPSi] on their surface interactions with different phospholipids. All of the four phospholipids were similarly adsorbed by the surface of PSi particles, except for TOPSi. Among four PSi particles, TOPSi with hydrophilic surface and smaller pore size showed the weakest adsorption toward phosphatidylcholines. By increasing the pore size from roughly 12.5 to 18.0 nm (TOPSi vs AnnTOPSi), the quantity of phosphatidylcholines adsorbed by TOPSi was enhanced to the same level of hydrophilic APTES-TCPSi and hydrophobic THCPSi. The 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) exhibited the highest release ratio of phospholipids from all four PSi particles, and phosphatidylserine (DPPS) showed the lowest release ratio of phospholipids from PSi particles, except for TOPSi, which adsorbed less phospholipids due to the small pore size. There is consistency in the release extent of phospholipids from PSi particles and the isosteric heat of adsorption. Overall, our study demonstrates the importance of pore size and surface chemistry of PSi particles as well as the structure of phospholipids on their interactions. The obtained information can be employed to guide the selection of PSi particles and phospholipids to fabricate highly ordered structures, for example, protocells, or biomimetic reactors.

Thermally Carbonized Porous Silicon and Its Recent Applications

Recent progress in research on thermally carbonized porous silicon (TCPSi) and its applications is reported. Despite a slow start, thermal carbonization has now started to gain interest mainly due to new emerging areas for applications. These new areas, such as optical sensing, drug delivery, and energy storage, require stable surface chemistry and physical properties. TCPSi is known to have all of these desired properties. Herein, the above-listed properties of TCPSi are summarized, and the carbonization processes, functionalization, and characterization of TCPSi are reviewed. Moreover, some of the emerging fields of TCPSi applications are discussed and recent advances in the fields are introduced.

Biogenic Nanostructured Porous Silicon as a Carrier for Stabilization and Delivery of Natural Therapeutic Species

Nanostructured mesoporous silicon (pSi) derived from the silicon-accumulator plant Tabasheer (Bambuseae) is demonstrated to serve as a potential carrier matrix for carrying and stabilizing naturally active, but otherwise metastable, therapeutic agents. Particularly, in this study, garlic oil containing phytochemicals (namely, allicin) that are capable of inhibiting Staphylococcus aureus (S. aureus) bacterial growth were incorporated into Tabasheer-derived porous silicon. Thermogravimetric analysis (TGA) indicated that relatively high amounts of the extract (53.1 ± 2.2 wt %) loaded into pSi are possible by simple infiltration. Furthermore, by assessing the antibacterial activity of the samples using a combination technique of agar disk diffusion and turbidity assays against S. aureus, we report that biogenic porous silicon can be utilized to stabilize and enhance the therapeutic effects of garlic oil for up to 4 weeks when the samples were stored under refrigerated conditions (4 °C) and 1 week at room temperature (25 °C). Critically, under ultraviolet (UV) light (365 nm) irradiation for 24 h intervals, plant-derived pSi is shown to have superior performance in protecting garlic extracts over porous silica (pSiO₂) derived from the same plant feedstock or extract-only controls. The mechanism for this effect has also been investigated.

Investigating the Effects of Loading Factors on the In Vitro Pharmaceutical Performance of Mesoporous Materials as Drug Carriers for Ibuprofen

The aim of the study was to investigate the effects of the loading factors, i.e., the initial drug loading concentration and the ratio of the drug to carriers, on the in vitro pharmaceutical performance of drug-loaded mesoporous systems. Ibuprofen (IBU) was used as a model drug, and two non-ordered mesoporous materials of commercial silica Syloid^® 244FP (S244FP) and Neusilin^® US2 (NS2) were selected in the study. The IBU-loaded mesoporous samples were prepared by a solvent immersion method with a rotary evaporation drying technique and characterized by polarized light microscopy (PLM), Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC). Dissolution experiments were performed in simulated gastric media at 37 °C under non-sink conditions. The concentration of IBU in solution was determined by HPLC. The study showed that the dissolution rate of IBU can be improved significantly using the mesoporous S224FP carriers due to the conversion of crystalline IBU into the amorphous form. Both of the loading factors affected the IBU dissolution kinetics. Due to the molecular interaction between the IBU and NS2 carriers, the loading factors had little effects on the drug release kinetics with incomplete drug desorption recovery and insignificant dissolution enhancement. Care and extensive evaluation must therefore be taken when mesoporous materials are chosen as carrier delivery systems.

Controlled Delivery of Levothyroxine Using Porous Silicon as a Drug Nanocontainer

Porous silicon (pSi) materials are regarded as promising drug delivery vehicles due to their biocompatibility, in vivo degradation, and resorption. We examine pSi films as a platform for the controlled delivery of levothyroxine, as a means to overcome problems with consistent dosage of this drug by oral administration. Oxidized pSi films were modified with 3-(aminopropyl)triethoxysilane (APTES), creating a surface chemistry that increased levothyroxine drug loading capacity by 50 % and sustained drug release under physiological conditions for 14 days. Release kinetics from APTES-functionalized films initially followed a zero-order release profile, which is highly desirable for drug delivery. The loading and release profiles of levothyroxine suggest that the film size required to deliver a therapeutic dose is feasible for further consideration as an implantable delivery system.

Novel delivery systems for improving the clinical use of peptides

Peptides have long been recognized as a promising group of therapeutic substances to treat various diseases. Delivery systems for peptides have been under development since the discovery of insulin for the treatment of diabetes. The challenge of using peptides as drugs arises from their poor bioavailability resulting from the low permeability of biological membranes and their instability. Currently, subcutaneous injection is clinically the most common administration route for peptides. This route is cost-effective and suitable for self-administration, and the development of appropriate dosing equipment has made performing the repeated injections relatively easy; however, only few clinical subcutaneous peptide delivery systems provide sustained peptide release. As a result, frequent injections are needed, which may cause discomfort and additional risks resulting from a poor administration technique. Controlled peptide delivery systems, able to provide required therapeutic plasma concentrations over an extended period, are needed to increase peptide safety and patient compliancy. In this review, we summarize the current peptidergic drugs, future developments, and parenteral peptide delivery systems. Special emphasis is given to porous silicon, a novel material in peptide delivery. Biodegradable and biocompatible porous silicon possesses some unique properties, such as the ability to carry exceptional high peptide payloads and to modify peptide release extensively. We have successfully developed porous silicon as a carrier material for improved parenteral peptide delivery. Nanotechnology, with its different delivery systems, will enable better use of peptides in several therapeutic applications in the near future.

Influence of Surface Chemistry on the Release of an Antibacterial Drug from Nanostructured Porous Silicon

Nanostructured mesoporous silicon possesses important properties advantageous to drug loading and delivery. For controlled release of the antibacterial drug triclosan, and its associated activity versus Staphylococcus aureus, previous studies investigated the influence of porosity of the silicon matrix. In this work, we focus on the complementary issue of the influence of surface chemistry on such properties, with particular regard to drug loading and release kinetics that can be ideally adjusted by surface modification. Comparison between drug release from as-anodized, hydride-terminated hydrophobic porous silicon and the oxidized hydrophilic counterpart is complicated due to the rapid bioresorption of the former; hence, a hydrophobic interface with long-term biostability is desired, such as can be provided by a relatively long chain octyl moiety. To minimize possible thermal degradation of the surfaces or drug activity during loading of molten drug species, a solution loading method has been investigated. Such studies demonstrate that the ability of porous silicon to act as an effective carrier for sustained delivery of antibacterial agents can be sensitively altered by surface functionalization.

Promoting the "water-wire" mechanism of double proton transfer in [2,2'-bipyridyl]-3,3'-diol by porous gold nanoparticles

The effect of nanopores in porous gold nanoparticles (Au NPs) on excited-state double proton transfer (DPT) in [2,2'-bipyridyl]-3,3'-diol (BP(OH)2) in an aqueous environment is the main focus of the present work. DPT in BP(OH)2 is known to take place through two mechanisms. In a bulk environment, an open solvated molecule facilitates the process and emits at 460 nm whereas, in a confined situation, formation of a "water wire" between the prototropic centers leads to the transfer of protons. It has been shown spectroscopically in the present study that in the nanovessels provided by nanoporous Au NPs, the unconventional mechanism of DPT through the formation of a "water wire" is promoted due to the presence of a limited number of water molecules around the probe. Experiments in the presence of solid pure Au, Ag and Au/Ag NPs were performed to support our proposition. Time-resolved fluorescence spectral changes confirm our findings.

Improved stability and biocompatibility of nanostructured silicon drug carrier for intravenous administration

Nanotechnology has attracted considerable interest in the field of biomedicine, where various nanoparticles (NPs) have been introduced as efficient drug carrier systems. Mesoporous silicon (PSi) is one of the most promising materials in this field due to its low toxicity, good biodegradability, high surface area, tunable pore size and controllable surface functionality. However, recognition by the reticuloendothelial system and particle agglomeration hinder the use of PSi for intravenous applications. The present paper describes a dual-PEGylation method, where two PEG molecules with different sizes (0.5 and 2 kDa) were grafted simultaneously in a single process onto thermally oxidized PSi NPs to form a high-density PEG coating with both brush-like and mushroom-like conformation. The material was characterized in detail and the effects of the dual-PEGylation on cell viability, protein adsorption and macrophage uptakes were evaluated. The results show that dual-PEGylation improves the colloidal stability of the NPs in salt solutions, prolongs their half-lives, and minimizes both protein adsorption and macrophage uptake. Therefore, these new dual-PEGylated PSi NPs are potential candidates for intravenous applications.

High drug load, stable, manufacturable and bioavailable fenofibrate formulations in mesoporous silica: a comparison of spray drying versus solvent impregnation methods

Encapsulation of drugs in mesoporous silica using co-spray drying process has been recently explored as potential industrial method. However, the impact of spray drying on manufacturability, physiochemical stability and bioavailability in relation to conventional drug load processes are yet to be fully investigated. Using a 2(3) factorial design, this study aims to investigate the effect of drug-loading process (co-spray drying and solvent impregnation), mesoporous silica pore size (SBA-15, 6.5 nm and MCM-41, 2.5 nm) and percentage drug load (30% w/w and 50% w/w) on material properties, crystallinity, physicochemical stability, release profiles and bioavailability of fenofibrate (FEN) loaded into mesoporous silica. From the scanning electronic microscopy (SEM) images, powder X-ray diffraction and Differential scanning calorimetry measurements, it is indicated that the co-spray drying process was able to load up to 50% (w/w) FEN in amorphous form onto the mesoporous silica as compared to the 30% (w/w) for solvent impregnation. The in vitro dissolution rate of the co-spray dried formulations was also significantly (p = 0.044) better than solvent impregnated formulations at the same drug loading. Six-month accelerated stability test at 40 °C/75 RH in open dish indicated excellent physical and chemical stability of formulations prepared by both methods. The amorphous state of FEN and the enhanced dissolution profiles were well preserved, and very low levels of degradation were detected after storage. The dog data for the three selected co-spray-dried formulations revealed multiple fold increment in FEN bioavailability compared to the reference crystalline FEN. These results validate the viability of co-spray-dried mesoporous silica formulations with high amorphous drug load as potential drug delivery systems for poorly water soluble drugs.

Cefazolin-loaded mesoporous silicon microparticles show sustained bactericidal effect against Staphylococcus aureus

Cefazolin is an antibiotic frequently used in preoperative prophylaxis of orthopedic surgery and to fight secondary infections post-operatively. Although its systemic delivery in a bulk or bolus dose is usually effective, the local and controlled release can increase its effectiveness by lowering dosages, minimizing total drug exposure, abating the development of antibiotic resistance and avoiding the cytotoxic effect. A delivery system based on mesoporous silicon microparticles was developed that is capable of efficiently loading and continuously releasing cefazolin over several days. The in vitro release kinetics from mesoporous silicon microparticles with three different nanopore sizes was evaluated, and minimal inhibitory concentration of cefazolin necessary to eliminate a culture of Staphylococcus aureus was identified to be 250 µg/mL. A milder toxicity toward mesenchymal stem cells was observed from mesoporous silicon microparticles over a 7-day period. Medium pore size-loaded mesoporous silicon microparticles exhibited long-lasting bactericidal properties in a zone inhibition assay while they were able to kill all the bacteria growing in suspension cultures within 24 h. This study demonstrates that the sustained release of cefazolin from mesoporous silicon microparticles provides immediate and long-term control over bacterial growth both in suspension and adhesion while causing minimal toxicity to a population of mesenchymal stem cell. Mesoporous silicon microparticles offer significant advantageous properties for drug delivery applications in tissue engineering as it favorably extends drug bioavailability and stability, while reducing concomitant cytotoxicity to the surrounding tissues.

Porous silicon nanoparticles for nanomedicine: preparation and biomedical applications

The research on porous silicon (PSi) materials for biomedical applications has expanded greatly since the early studies of Leigh Canham more than 25 years ago. Currently, PSi nanoparticles are receiving growing attention from the scientific biomedical community. These nanostructured materials have emerged as promising multifunctional and versatile platforms for nanomedicine in drug delivery, diagnostics and therapy. The outstanding properties of PSi, including excellent in vivo biocompatibility and biodegradability, have led to many applications of PSi for delivery of therapeutic agents. In this review, we highlight current advances and recent efforts on PSi nanoparticles regarding the production properties, efficient drug delivery, multidrug delivery, permeation across biological barriers, biosafety and in vivo tracking for biomedical applications. The constant boost on successful preclinical in vivo data reported so far makes this the ‘golden age’ for PSi, which is expected to finally be translated into the clinic in the near future.

Synthesis and surface modification of mesoporous silica nanoparticles and its application as carriers for sustained drug delivery

High drug loading is one of the important issues in the drug delivery research, especially the drug delivery system by oral administration. If high drug loading carriers are utilized the times of drug intake could be significantly reduced. Accordingly in this study, ordered mesoporous SBA-15 modified with (3-aminopropyl) triethoxysilane (APTES) was used as a carrier for nonsteroidal anti-inflammatory drug and optimization of the loading process was done. SBA-15 silica material with rope-like morphology was synthesized and modified by post-synthesis method with APTES. The synthesized SBA-15 and modified SBA-15 were characterized by XRD, SEM, thermal analysis and FT-IR spectroscopy. Loading optimization experiments were performed by changing the factors affecting the drug loading, such as temperature, time, stirring rate, Ibuprofen/SBA-15 ratio. The results of drug delivery experiments showed that the surface modification of SBA-15 with amino groups significantly increases the drug loading and decreases the drug delivery rate.

Tumour homing peptide-functionalized porous silicon nanovectors for cancer therapy

Tumour targeting nanoparticles (NPs) have demonstrated great potential for enhancing anticancer drug delivery to tumour sites and for reducing the side effects of chemotherapy. However, many nanoparticulate delivery systems still lack efficient tumour accumulation. In this work, we present a porous silicon (PSi) nanovector functionalized with a tumour-homing peptide, which targets the mammary-derived growth inhibitor (MDGI) expressing cancer cells both in vitro and in vivo, thereby enhancing the accumulation of the NPs in the tumours. We demonstrated that the tumour homing peptide (herein designated as CooP) functionalized thermally hydrocarbonized PSi (THCPSi) NPs homed specifically to the subcutaneous MDGI-expressing xenograft tumours. The THCPSi-CooP NPs were stable in human plasma and their uptake by MDGI-expressing cancer cells measured by confocal microscopy and flow cytometry was significantly increased compared to the non-functionalized THCPSi NPs. After intravenous injections into nude mice bearing MDGI-expressing tumours, effective targeting was detected and THCPSi-CooP NPs showed ~9-fold higher accumulation in the tumour site compared to the control THCPSi NPs. Accumulation of both NPs in the vital organs was negligible.

Recent advances in porous silicon technology for drug delivery

Porous silicon (pSi) is a nanostructured carrier system that has received considerable attention over the past 10 years, for use in a wide variety of biomedical applications, including biosensing, biomedical imaging, tissue scaffolds and drug delivery. This interest is due to several key features of pSi, including excellent in vivo biocompatibility, the ease of surface chemistry modification and the control over its 3D porous network structure. With control of these physical parameters pSi has successfully been used for the delivery of a variety of therapeutics, ranging from small-molecule drugs to larger peptide/protein-type therapeutics. In this review, the authors provide a brief overview of pSi fabrication methods, particularly with regard to the need to passivate the highly reactive Si-Hx surface species of native pSi, typically via thermal oxidation, hydrocarbonization or hydrosilylation. This surface modification, in turn, controls both the loading and release of therapeutics. The authors will then report on specific case studies of leading examples on the use of pSi as a therapeutic-delivery system. Specifically, the first reported in vivo study that demonstrated the use of pSi to improve the delivery of a Biopharmaceutical Classification System Class 2 poorly soluble drug (indomethacin), by using thermally oxidized pSi, is discussed, as well as highlighting a study that determined the biodistribution of 18F-radiolabeled thermally hydrocarbonized pSi after oral dosing. The authors also report on the development of composite pSi–poly(D,L-lactide-co-glycolide) microparticles for the controlled delivery of protein therapeutics. Finally, the use of pSi in the delivery of bioactives, such as the successful use of thermally carbonized pSi to deliver Melanotan II, an unspecific agonist for the melanocortin receptors that are involved in controlling fluid uptake is discussed. With a growing body of literature reporting the successful use of pSi to deliver a range of therapeutics, we are entering what may be a golden age for this drug-delivery system, which may finally see the long-held promises finally achieved.

Engineering porous silicon nanostructures as tunable carriers for mitoxantrone dihydrochloride

Nanostructured porous silicon (PSi) thin films, fabricated by the electrochemical anodization of single crystalline Si wafers, are studied as delivery systems for the anticancer drug mitoxantrone dihydrochloride (MTX). The surface chemistry of the PSi carriers was tailored by surface alkylation using thermal hydrosilylation of 1-dodecene and undecylenic acid, followed by physical adsorption or covalent attachment of MTX to the Si scaffold. The nanostructure and the physiochemical properties of the different carriers were characterized by attenuated total reflectance Fourier transform infrared spectroscopy, nitrogen adsorption-desorption and contact angle measurements, demonstrating that surface alkylation results in a pronounced effect on the hydrophobicity/hydrophilicity of the scaffolds and a volumetric gain in pore wall, which in turn results in a decrease in pore diameter (>23%) and available porous volume (>40%). The effect of these key parameters on MTX loading efficacy, release profile, Si scaffold erosion kinetics and in vitro cytotoxicity on human breast carcinoma (MDA-MB-231) cells was studied and compared to the behavior of neat PSi carriers. We show that the chemically modified PSi carriers exhibit sustained release for several days to weeks with minimal to no burst effect, while for the native PSi MTX release was completed within 5h with a substantial burst release of ~40%. Moreover, our in vitro cytotoxicity experiments have clearly demonstrated that the MTX released from all PSi carriers maintained its cytotoxic effect towards MDA-MB-231 cells, in comparison to the low toxicity of the PSi carriers.

Mesoporous systems for poorly soluble drugs

Utilization of inorganic mesoporous materials in formulations of poorly water-soluble drugs to enhance their dissolution and permeation behavior is a rapidly growing area in pharmaceutical materials research. The benefits of mesoporous materials in drug delivery applications stem from their large surface area and pore volume. These properties enable the materials to accommodate large amounts of payload molecules, protect them from premature degradation, and promote controlled and fast release. As carriers with various morphologies and chemical surface properties can be produced, these materials may even promote adsorption from the gastrointestinal tract to the systemic circulation. The main concern regarding their clinical applications is still the safety aspect even though most of them have been reported to be safely excreted, and a rather extensive toxicity screening has already been conducted with the most frequently studied mesoporous materials. In addition, the production of the materials on a large scale and at a reasonable cost may be a challenge when considering the utilization of the materials in industrial processes. However, if mesoporous materials could be employed in the industrial crystallization processes to produce hybrid materials with poorly soluble compounds, and hence to enhance their oral bioavailability, this might open new avenues for the pharmaceutical industry to employ nanotechnology in their processes.

Surface chemistry of porous silicon and implications for drug encapsulation and delivery applications

Porous silicon (pSi) has a number of unique properties that appoint it as a potential drug delivery vehicle; high loading capacity, controllable surface chemistry and structure, and controlled release properties. The native Si(y)SiH(x) terminated pSi surface is highly reactive and prone to spontaneous oxidation. Surface modification is used to stabilize the pSi surface but also to produce surfaces with desired drug delivery behavior, typically via oxidation, hydrosilylation or thermal carbonization. A number of advanced characterization techniques have been used to analyze pSi surface chemistry, including X-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry. Surface modification not only stabilizes the pSi surface but determines its charge, wettability and dissolution properties. Manipulation of these parameters can impact drug encapsulation by altering drug-pSi interactions. pSi has shown to be a successful vehicle for the delivery of poorly soluble drugs and protein therapeutics. Surface modification influences drug pore penetration, crystallinity, loading level and dissolution rate. Surface modification of pSi shows great potential for drug delivery applications by controlling pSi-drug interactions. Controlling these interactions allows specific drug release behaviors to be engineered to aid in the delivery of previously challenging therapeutics. Within this review, different pSi modification techniques will be outlined followed by a summary of how pSi surface modification has been used to improve drug encapsulation and delivery.

Effect of size on the cellular endocytosis and controlled release of mesoporous silica nanoparticles for intracellular delivery

Due to the unique physicochemical properties and membrane-permeable capacity, mesoporous silica nanoparticles (MSNs) are considered as an ideal carrier for intracellular delivery. Herein, we endeavored to address the size effect of MSNs on the cellular uptake, endosomal escape and controlled release, the key steps for the intracellular delivery. The well-ordered MSNs in the range from 55-nm to 440-nm with similar pore texture were prepared by modified base-catalyzed sol-gel method. With MC3T3-E1 model cell line, the in vitro results indicated that after 12 h cultivation, MSNs within 55 ~ 440 nm could all be internalized into the cells, and further escaped out of the endosomal compartment. The efficiency of the cellular uptake and endosomal escape strongly depended on the particle size, with the best efficiencies from 100-nm MSNs. Furthermore, the MTT results indicated that these MSNs materials were all biocompatible. The controlled release experiments with hydrophobic dexamethasone and hydrophilic vitamin C as models showed that for these small-molecular drugs, the loading amount all mainly determined by the surface area of the MSNs, and the subsequent release of the drug dramatically decreased with the increasing of the particle size. By contrast, the release rate of vitamin C was much quicker than that of the dexamethasone. These findings presented here could provide new means to tailor the size of MSNs and thus to guide the design of MSNs-based intracellular delivery system. Due to the good cell biocompatibility, high cellular uptake and endosomal escape, we conjectured that the 100-nm MSNs are more favorable for the intracellular delivery of drugs in live cells.

Native and Complexed IGF-1: Biodistribution and Pharmacokinetics in Infantile Neuronal Ceroid Lipofuscinosis

Infantile neuronal ceroid lipofuscinosis (INCL) is a severe neurodegenerative disorder of childhood characterized by selective death of cortical neurons. Insulin-like growth factor 1 (IGF-1) is important in embryonic development and is considered as a potential therapeutic agent for several disorders of peripheral and central nervous systems. In circulation IGF-1 is mainly bound to its carrier protein IGFBP-3. As a therapeutic agent IGF-1 has shown to be more active as free than complexed form. However, this may cause side effects during the prolonged treatment. In addition to IGFBP-3 the bioavailability of IGF-1 can be modulated by using mesoporous silicon nanoparticles (NPs) which are optimal carriers for sustained release of unstable peptide hormones like IGF-1. In this study we compared biodistribution, pharmacokinetics, and bioavailability of radiolabeled free IGF-1, IGF-1/IGFBP-3, and IGF-1/NP complexes in a Cln1-/- knockout mouse model. IGF-1/NP was mainly accumulated in liver and spleen in all studied time points, whereas minor and more constant amounts were measured in other organs compared to free IGF-1 or IGF-1/IGFBP-3. Also concentration of IGF-1/NP in blood was relatively high and stable during studied time points suggesting continuous release of IGF-1 from the particles.

In vitro dissolution methods for hydrophilic and hydrophobic porous silicon microparticles

Porous silicon (PSi) is an innovative inorganic material that has been recently developed for various drug delivery systems. For example, hydrophilic and hydrophobic PSi microparticles have been utilized to improve the dissolution rate of poorly soluble drugs and to sustain peptide delivery. Previously, the well-plate method has been demonstrated to be a suitable in vitro dissolution method for hydrophilic PSi particles but it was not applicable to poorly wetting hydrophobic thermally hydrocarbonized PSi (THCPSi) particles. In this work, three different in vitro dissolution techniques, namely centrifuge, USP Apparatus 1 (basket) and well-plate methods were compared by using hydrophilic thermally carbonized PSi (TCPSi) microparticles loaded with poorly soluble ibuprofen or freely soluble antipyrine. All the methods showed a fast and complete or nearly complete release of both model compounds from the TCPSi microparticles indicating that all methods described in vitro dissolution equally. Based on these results, the centrifuge method was chosen to study the release of a peptide (ghrelin antagonist) from the THCPSi microparticles since it requires small sample amounts and achieves good particle suspendability. Sustained peptide release from the THCPSi microparticles was observed, which is in agreement with an earlier in vivo study. In conclusion, the centrifuge method was demonstrated to be a suitable tool for the evaluation of drug release from hydrophobic THCPSi particles, and the sustained peptide release from THCPSi microparticles was detected.

Comparison of mesoporous silicon and non-ordered mesoporous silica materials as drug carriers for itraconazole

Mesoporous materials have an ability to enhance dissolution properties of poorly soluble drugs. In this study, different mesoporous silicon (thermally oxidized and thermally carbonized) and non-ordered mesoporous silica (Syloid AL-1 and 244) microparticles were compared as drug carriers for a hydrophobic drug, itraconazole (ITZ). Different surface chemistries pore volumes, surface areas, and particle sizes were selected to evaluate the structural effect of the particles on the drug loading degree and on the dissolution behavior of the drug at pH 1.2. The results showed that the loaded ITZ was apparently in amorphous form, and that the loading process did not change the chemical structure/morphology of the particles' surface. Incorporation of ITZ in both microparticles enhanced the solubility and dissolution rate of the drug, compared to the pure crystalline drug. Importantly, the physicochemical properties of the particles and the loading procedure were shown to have an effect on the drug loading efficiency and drug release kinetics. After storage under stressed conditions (3 months at 40 °C and 70% RH), the loaded silica gel particles showed practically similar dissolution profiles as before the storage. This was not the case with the loaded mesoporous silicon particles due to the almost complete chemical degradation of ITZ after storage.