Porous Silicon Microparticles Research Articles

Nonfilling carbon coating of porous silicon micrometer-sized particles for high-performance lithium battery anodes.

Silicon is widely recognized as one of the most promising anode materials for lithium-ion batteries due to its 10 times higher specific capacity than graphite. Unfortunately, the large volume change of Si materials during their lithiation/delithiation process results in severe pulverization, loss of electrical contact, unstable solid-electrolyte interphase (SEI), and eventual capacity fading. Although there has been tremendous progress to overcome these issues through nanoscale materials design, improved volumetric capacity and reduced cost are still needed for practical application. To address these issues, we design a nonfilling carbon-coated porous silicon microparticle (nC-pSiMP). In this structure, porous silicon microparticles (pSiMPs) consist of many interconnected primary silicon nanoparticles; only the outer surface of the pSiMPs was coated with carbon, leaving the interior pore structures unfilled. Nonfilling carbon coating hinders electrolyte penetration into the nC-pSiMPs, minimizes the electrode-electrolyte contact area, and retains the internal pore space for Si expansion. SEI formation is mostly limited to the outside of the microparticles. As a result, the composite structure demonstrates excellent cycling stability with high reversible specific capacity (∼1500 mAh g(-1), 1000 cycles) at the rate of C/4. The nC-pSiMPs contain accurate void space to accommodate Si expansion while not losing packing density, which allows for a high volumetric capacity (∼1000 mAh cm(-3)). The areal capacity can reach over 3 mAh cm(-2) with the mass loading 2.01 mg cm(-2). Moreover, the production of nC-pSiMP is simple and scalable using a low-cost silicon monoxide microparticle starting material.

Surface engineering of porous silicon microparticles for intravitreal sustained delivery of rapamycin.

To understand the relationship between rapamycin loading/release and surface chemistries of porous silicon (pSi) to optimize pSi-based intravitreal delivery system. Three types of surface chemical modifications were studied: (1) pSi-COOH, containing 10-carbon aliphatic chains with terminal carboxyl groups grafted via hydrosilylation of undecylenic acid; (2) pSi-C12, containing 12-carbon aliphatic chains grafted via hydrosilylation of 1-dodecene; and (3) pSiO2-C8, prepared by mild oxidation of the pSi particles followed by grafting of 8-hydrocarbon chains to the resulting porous silica surface via a silanization. The efficiency of rapamycin loading follows the order (micrograms of drug/milligrams of carrier): pSiO2-C8 (105 ± 18) > pSi-COOH (68 ± 8) > pSi-C12 (36 ± 6). Powder X-ray diffraction data showed that loaded rapamycin was amorphous and dynamic drug-release study showed that the availability of the free drug was increased by 6-fold (compared with crystalline rapamycin) by using pSiO2-C8 formulation (P = 0.0039). Of the three formulations in this study, pSiO2-C8-RAP showed optimal performance in terms of simultaneous release of the active drug and carrier degradation, and drug-loading capacity. Released rapamycin was confirmed with the fingerprints of the mass spectrometry and biologically functional as the control of commercial crystalline rapamycin. Single intravitreal injections of 2.9 ± 0.37 mg pSiO2-C8-RAP into rabbit eyes resulted in more than 8 weeks of residence in the vitreous while maintaining clear optical media and normal histology of the retina in comparison to the controls. Porous silicon-based rapamycin delivery system using the pSiO2-C8 formulation demonstrated good ocular compatibility and may provide sustained drug release for retina.

Porous silicon microparticles for delivery of siRNA therapeutics.

Small interfering RNA (siRNA) can be used to suppress gene expression, thereby providing a new avenue for the treatment of various diseases. However, the successful implementation of siRNA therapy requires the use of delivery platforms that can overcome the major challenges of siRNA delivery, such as enzymatic degradation, low intracellular uptake and lysosomal entrapment. Here, a protocol for the preparation and use of a biocompatible and effective siRNA delivery system is presented. This platform consists of polyethylenimine (PEI) and arginine (Arg)-grafted porous silicon microparticles, which can be loaded with siRNA by performing a simple mixing step. The silicon particles are gradually degraded over time, thereby triggering the formation of Arg-PEI/siRNA nanoparticles. This delivery vehicle provides a means for protecting and internalizing siRNA, without causing cytotoxicity. The major steps of polycation functionalization, particle characterization, and siRNA loading are outlined in detail. In addition, the procedures for determining particle uptake, cytotoxicity, and transfection efficacy are also described.

Surface engineering of porous silicon to optimise therapeutic antibody loading and release.

The proinflammatory cytokine, tumor necrosis factor-α (TNF-α), is elevated in several diseases such as uveitis, rheumatoid arthritis and non-healing chronic wounds. Adding Infliximab, a chimeric IgG1 monoclonal antibody raised against TNF-α, to chronic wound fluid can neutralise human TNF-α, thereby providing a potential therapeutic option for chronic wound healing. However, to avoid the need for repeated application in a clinical setting, and to protect the therapeutic antibody from the hostile environment of the wound, suitable delivery vehicles are required. Porous silicon (pSi) is a biodegradable high surface area material commonly employed for drug delivery applications. In this study, the use of pSi microparticles (pSi MPs) for the controlled release of Infliximab to disease environments, such as chronic wounds, is demonstrated. Surface chemistry and pore parameters for Infliximab loading are first optimised in pSi films and loading conditions are transferred to pSi MPs. Loading regimens exceeding 60 μg of Infliximab per mg of pSi are achieved. Infliximab is released with zero-order release kinetics over the course of 8 days. Critically, the released antibody remains functional and is able to sequester TNF-α over a weeklong timeframe; suitable for a clinical application in chronic wound therapy.

Direct detection of illicit drugs from biological fluids by desorption/ionization mass spectrometry with nanoporous silicon microparticles.

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is a high throughput analytical technique capable of detecting low molecular weight analytes, including illicit drugs, and with potential applications in forensic toxicology as well as athlete and workplace testing, particularly for biological fluids (oral fluids, urine and blood). However, successful detection of illicit drugs using SALDI-MS often requires extraction steps to reduce the inherent complexity of biological fluids. Here, we demonstrate an all-in-one extraction and analytical system consisting of hydrophobically functionalized porous silicon microparticles (pSi-MPs) for affinity SALDI-MS of prescription and illicit drugs. This novel approach allows for the analysis of drugs from multiple biological fluids without sample preparation protocols. The effect of pSi-MP size, pore diameter, pore depth and functionalization on analytical performance is investigated. pSi-MPs were optimized for the rapid and high sensitivity detection of methadone, cocaine and 3,4-methylenedioxymethamphetamine (MDMA). This optimized system allowed extraction and detection of methadone from spiked saliva and clinical urine samples. Furthermore, by detecting oxycodone in additional clinical saliva and plasma samples, we were able to demonstrate the versatility of the pSi-MP SALDI-MS technique.

A new electrochemical sensor for the simultaneous determination of acetaminophen and codeine based on porous silicon/palladium nanostructure

A porous silicon/palladium nanostructure was prepared and used as a new electrode material for the simultaneous determination of acetaminophen (ACT) and codeine (COD). Palladium nanoparticles were assembled on porous silicon (PSi) microparticles by a simple redox reaction between the Pd precursor and PSi in an aqueous solution of hydrofluoric acid. This novel nanostructure was characterized by different spectroscopic and electrochemical techniques including scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, fourier transform infrared spectroscopy and cyclic voltammetry. The high electrochemical activity, fast electron transfer rate, high surface area and good antifouling properties of this nanostructure enhanced the oxidation peak currents and reduced the peak potentials of ACT and COD at the surface of the proposed sensor. Simultaneous determination of ACT and COD was explored using differential pulse voltammetry. A linear range of 1.0–700.0µmolL−1 was achieved for ACT and COD with detection limits of 0.4 and 0.3µmolL−1, respectively. Finally, the proposed method was used for the determination of ACT and COD in blood serum, urine and pharmaceutical compounds.

In vitro assessment of biopolymer-modified porous silicon microparticles for wound healing applications

The wound healing stands as very complex and dynamic process, aiming the re-establishment of the damaged tissue’s integrity and functionality. Thus, there is an emerging need for developing biopolymer-based composites capable of actively promoting cellular proliferation and reconstituting the extracellular matrix. The aims of the present work were to prepare and characterize biopolymer-functionalized porous silicon (PSi) microparticles, resulting in the development of drug delivery microsystems for future applications in wound healing. Thermally hydrocarbonized PSi (THCPSi) microparticles were coated with both chitosan and a mixture of chondroitin sulfate/hyaluronic acid, and subsequently loaded with two antibacterial model drugs, vancomycin and resveratrol. The biopolymer coating, drug loading degree and drug release behavior of the modified PSi microparticles were evaluated in vitro. The results showed that both the biopolymer coating and drug loading of the THCPSi microparticles were successfully achieved. In addition, a sustained release was observed for both the drugs tested. The viability and proliferation profiles of a fibroblast cell line exposed to the modified THCPSi microparticles and the subsequent reactive oxygen species (ROS) production were also evaluated. The cytotoxicity and proliferation results demonstrated less toxicity for the biopolymer-coated THCPSi microparticles at different concentrations and time points comparatively to the uncoated counterparts. The ROS production by the fibroblasts exposed to both uncoated and biopolymer-coated PSi microparticles showed that the modified PSi microparticles did not induce significant ROS production at the concentrations tested. Overall, the biopolymer-based PSi microparticles developed in this study are promising platforms for wound healing applications.

Enhanced gene delivery in porcine vasculature tissue following incorporation of adeno-associated virus nanoparticles into porous silicon microparticles.

There is an unmet clinical need to increase lung transplant successes, patient satisfaction and to improve mortality rates. We offer the development of a nanovector-based solution that will reduce the incidence of lung ischemic reperfusion injury (IRI) leading to graft organ failure through the successful ex vivo treatment of the lung prior to transplantation. The innovation is in the integrated application of our novel porous silicon (pSi) microparticles carrying adeno-associated virus (AAV) nanoparticles, and the use of our ex vivo lung perfusion/ventilation system for the modulation of pro-inflammatory cytokines initiated by ischemic pulmonary conditions prior to organ transplant that often lead to complications. Gene delivery of anti-inflammatory agents to combat the inflammatory cascade may be a promising approach to prevent IRI following lung transplantation. The rationale for the device is that the microparticle will deliver a large payload of virus to cells and serve to protect the AAV from immune recognition. The microparticle-nanoparticle hybrid device was tested both in vitro on cell monolayers and ex vivo using either porcine venous tissue or a pig lung transplantation model, which recapitulates pulmonary IRI that occurs clinically post-transplantation. Remarkably, loading AAV vectors into pSi microparticles increases gene delivery to otherwise non-permissive endothelial cells.

Cytotoxicity of mesoporous silicon microparticles with different surface modifications on ARPE‐19 cells

AbstractPurpose Retinal pigment epithelial (RPE) cells play a crucial role in the pathogenesis of age‐related macular degeneration (AMD). However, RPE is a challenging target in a therapeutical sense. In addition to its location, the possible hydrophobicity of drug molecules makes its medication even more challenging. Biodegradable porous silicon (PSi) microparticles could be a promising possibility for delivering hydrophobic drugs to RPE cells. In the present study, we aimed at testing the cytotoxicity of thermally oxidized (ToPSi) and thermally carbonized porous silicon (TCPSi) particles with and without additional surface modification with amino groups on human ARPE‐19 cells. Since the cytotoxicity of PSi particles cannot be tested by the commonly used MTT (3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5‐diphenyltetrazolium bromide) assay due to non‐specific redox reactions, our aim was also to search for alternative assays for working with mesoporous silicon materials.Methods ARPE‐19 cells were treated with microparticles at several concentrations for 24 h. Thereafter, cell viability was measured using a protease viability marker assay (CellTiter‐FluorTM) and a lactate dehydrogenase (LDH) release assay. Cells were also evaluated ocularly under an inverted microscope.Results All tested particles were well tolerated by ARPE‐19 cells. CellTiter‐Fluor assay seemed slightly more reliable than the LDH test.Conclusion Our results show that the tested porous silicon particles did not cause major cytotoxicity on ARPE‐19 cells, and CellTiter‐Fluor assay, especially together with ocular examination, could be suitable for testing cytotoxicity in association with mesoporous silicon particles.

A new electrochemical sensor based on porous silicon supported Pt–Pd nanoalloy for simultaneous determination of adenine and guanine

A new nanocomposite (porous silicon supported Pt–Pd nanoalloy) was prepared and used as an electrode material for simultaneous determination of adenine and guanine. For this purpose, Pt–Pd nanoparticles were supported on porous silicon microparticles by a simple galvanic reaction in a HF solution. The nanocomposite was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction spectroscopy and cyclic voltammetry. Incorporation of Pt–Pd/porous silicon (Pt–Pd/PSi) nanocomposite in the carbon nanotube paste electrode (CNTPE) increased the oxidation peak currents (about 3 folds) and reduced the overpotential of adenine and guanine. The effects of different parameters such as pH, accumulation time, accumulation potential, and potential scan rate on the sensitivity were investigated. The new developed sensor was then employed for simultaneous determination of purine bases with linear ranges of 0.10–10.0μmolL−1, using differential pulse voltammetry. Detection limits of 30 and 20nmolL−1 were achieved for adenine and guanine, respectively. Individual determination of purine bases were performed by amperometric technique with a linear range of 60.0nmolL−1–55.0μmolL−1 and detection limit of 30nmolL−1 for adenine, while the linear range of 40.0nmolL−1–53.4μmolL−1 with detection limit of 10nmolL−1 was achieved for guanine. Finally, the proposed electrochemical sensor was employed to determine adenine and guanine in single-strand deoxyribonucleic acid (ssDNA) samples.

Orange and blue luminescence emission to track functionalized porous silicon microparticles inside the cells of the human immune system.

Porous silicon micro-particles (micro-pSi) with size in the range of 1-10 μm are obtained by etching of silicon wafers followed by sonication. The derivatization of the micro-pSi surface by wet chemistry (silylation and coupling with a diamine) yields an interface, which exposes negative (carboxylic) or positive (amine) groups at pH 7.4. The surface modification, beyond the introduction of groups for the drug loading by covalent or electrostatic interactions, stabilizes the intense orange luminescence characteristic of the silicon nano-crystallites. Derivatization by amines introduces also a second emission in the blue region, which follows a different excitation pathway and can be attributed to the interface defects. The micro-pSi are efficiently internalized by human dendritic cells and do not show any toxic effect even at a concentration of 1 mg mL-1. The intrinsic luminescence of the differently functionalized micro-pSi is preserved inside the cells and permits the selective and efficient tracking of the microparticles without using molecular tags and thus leaving the organic coating available for the interaction with the drug. The results obtained suggest that the functionalized micro-pSi are an efficient platform for simultaneous imaging and delivery of therapeutic agents to the disease site.

In vivo biocompatibility of porous silicon biomaterials for drug delivery to the heart

Myocardial infarction (MI), commonly known as a heart attack, is the irreversible necrosis of heart muscle secondary to prolonged ischemia, which is an increasing problem in terms of morbidity, mortality and healthcare costs worldwide. Along with the idea to develop nanocarriers that efficiently deliver therapeutic agents to target the heart, in this study, we aimed to test the in vivo biocompatibility of different sizes of thermally hydrocarbonized porous silicon (THCPSi) microparticles and thermally oxidized porous silicon (TOPSi) micro and nanoparticles in the heart tissue. Despite the absence or low cytotoxicity, both particle types showed good in vivo biocompatibility, with no influence on hematological parameters and no considerable changes in cardiac function before and after MI. The local injection of THCPSi microparticles into the myocardium led to significant higher activation of inflammatory cytokine and fibrosis promoting genes compared to TOPSi micro and nanoparticles; however, both particles showed no significant effect on myocardial fibrosis at one week post-injection. Our results suggest that THCPSi and TOPSi micro and nanoparticles could be applied for cardiac delivery of therapeutic agents in the future, and the PSi biomaterials might serve as a promising platform for the specific treatment of heart diseases.

Antibody modified porous silicon microparticles for the selective capture of cells.

Herein, the ability of porous silicon (PSi) particles for selectively binding to specific cells is investigated. PSi microparticles with a high reflectance band in the reflectivity profile are fabricated, and subsequently passivated and modified with antibodies via the Cu(I)-catalyzed alkyne-azide cycloaddition reaction and succimidyl activation. To demonstrate the ability of the antibody-modified PSi particles to selectively bind to one cell type over others, HeLa cells were transfected with surface epitopes fused to fluorescent proteins. The antibody-functionalized PSi particles showed good selectivity for the corresponding surface protein on HeLa cells, with no significant cross-reactivity. The results are important for the application of PSi particles in cell sensing and drug delivery.

Chitosan-modified porous silicon microparticles for enhanced permeability of insulin across intestinal cell monolayers

Porous silicon (PSi) based particulate systems are emerging as an important drug delivery system due to its advantageous properties such as biocompatibility, biodegradability and ability to tailor the particles' physicochemical properties. Here, annealed thermally hydrocarbonized PSi (AnnTHCPSi) and undecylenic acid modified AnnTHCPSi (AnnUnTHCPSi) microparticles were developed as a PSi-based platform for oral delivery of insulin. Chitosan (CS) was used to modify the AnnUnTHCPSi microparticles to enhance the intestinal permeation of insulin. Surface modification with CS led to significant increase in the interaction of PSi microparticles with Caco-2/HT-29 cell co-culture monolayers. Compared to pure insulin, the CS-conjugated microparticles significantly improved the permeation of insulin across the Caco-2/HT-29 cell monolayers, with ca. 20-fold increase in the amount of insulin permeated and ca. 7-fold increase in the apparent permeability (Papp) value. Moreover, among all the investigated particles, the CS-conjugated microparticles also showed the highest amount of insulin associated with the mucus layer and the intestinal Caco-2 cells and mucus secreting HT-29 cells. Our results demonstrate that CS-conjugated AnnUnTHCPSi microparticles can efficiently enhance the insulin absorption across intestinal cells, and thus, they are promising microsystems for the oral delivery of proteins and peptides across the intestinal cell membrane.

Porous silicon oxide–PLGA composite microspheres for sustained ocular delivery of daunorubicin

A water-soluble anthracycline antibiotic drug (daunorubicin, DNR) was loaded into oxidized porous silicon (pSiO2) microparticles and then encapsulated with a layer of polymer (poly lactide-co-glycolide, PLGA) to investigate their synergistic effects in control of DNR release. Similarly fabricated PLGA–DNR microspheres without pSiO2, and pSiO2 microparticles without PLGA were used as control particles. The composite microparticles synthesized by a solid-in-oil-in-water emulsion method have mean diameters of 52.33±16.37μm for PLGA–pSiO2_21/40–DNR and the mean diameter of 49.31±8.87μm for PLGA–pSiO2_6/20–DNR. The mean size, 26.00±8μm, of PLGA–DNR was significantly smaller, compared with the other two (P<0.0001). Optical microscopy revealed that PLGA–pSiO2–DNR microspheres contained multiple pSiO2 particles. In vitro release experiments determined that control PLGA–DNR microspheres completely released DNR within 38days and control pSiO2–DNR microparticles (with no PLGA coating) released DNR within 14days, while the PLGA–pSiO2–DNR microspheres released DNR for 74days. Temporal release profiles of DNR from PLGA–pSiO2 composite particles indicated that both PLGA and pSiO2 contribute to the sustained release of the payload. The PLGA–pSiO2 composite displayed a more constant rate of DNR release than the pSiO2 control formulation, and displayed a significantly slower release of DNR than either the PLGA or pSiO2 formulations. We conclude that this system may be useful in managing unwanted ocular proliferation when formulated with antiproliferation compounds such as DNR.

Multivalent presentation of MPL by porous silicon microparticles favors T helper 1 polarization enhancing the anti-tumor efficacy of doxorubicin nanoliposomes.

Porous silicon (pSi) microparticles, in diverse sizes and shapes, can be functionalized to present pathogen-associated molecular patterns that activate dendritic cells. Intraperitoneal injection of MPL-adsorbed pSi microparticles, in contrast to free MPL, resulted in the induction of local inflammation, reflected in the recruitment of neutrophils, eosinophils and proinflammatory monocytes, and the depletion of resident macrophages and mast cells at the injection site. Injection of microparticle-bound MPL resulted in enhanced secretion of the T helper 1 associated cytokines IFN-γ and TNF-α by peritoneal exudate and lymph node cells in response to secondary stimuli while decreasing the anti-inflammatory cytokine IL-10. MPL-pSi microparticles independently exhibited anti-tumor effects and enhanced tumor suppression by low dose doxorubicin nanoliposomes. Intravascular injection of the MPL-bound microparticles increased serum IL-1β levels, which was blocked by the IL-1 receptor antagonist Anakinra. The microparticles also potentiated tumor infiltration by dendritic cells, cytotoxic T lymphocytes, and F4/80+ macrophages, however, a specific reduction was observed in CD204+ macrophages.

Oxidation-Induced Trapping of Drugs in Porous Silicon Microparticles.

An approach for the preparation of an oxidized porous silicon microparticle drug delivery system that can provide efficient trapping and sustained release of various drugs is reported. The method uses the contraction of porous silicon’s mesopores, which occurs during oxidation of the silicon matrix, to increase the loading and retention of drugs within the particles. First, a porous Si (pSi) film is prepared by electrochemical etching of p-type silicon with a resistivity of >0.65 Ω cm in a 1:1 (v/v) HF/ethanol electrolyte solution. Under these conditions, the pore walls are sufficiently thin to allow for complete oxidation of the silicon skeleton under mild conditions. The pSi film is then soaked in an aqueous solution containing the drug (cobinamide or rhodamine B test molecules were used in this study) and sodium nitrite. Oxidation of the porous host by nitrite results in a shrinking of the pore openings, which physically traps the drug in the porous matrix. The film is subsequently fractured by ultrasonication into microparticles. Upon comparison with commonly used oxidizing agents for pSi such as water, peroxide, and dimethyl sulfoxide, nitrite is kinetically and thermodynamically sufficient to oxidize the pore walls of the pSi matrix, precluding reductive (by Si) or oxidative (by nitrite) degradation of the drug payload. The drug loading efficiency is significantly increased (by up to 10-fold), and the release rate is significantly prolonged (by 20-fold) relative to control samples in which the drug is loaded by infiltration of pSi particles postoxidation. We find that it is important that the silicon skeleton be completely oxidized to ensure the drug is not reduced or degraded by contact with elemental silicon during the particle dissolution–drug release phase.

Optical tracking of drug release from porous silicon delivery vectors

The controlled and sustained delivery of drugs to a specific location within the body is vitally important for effective treatment of chronic diseases such as cancer. One route in achieving this is to develop drug carrying systems from which release of the drug molecules can be controlled. In this study, the authors present characterisation measurements on such a system – porous silicon microparticles. The kinetic of release of the anti-cancer agent, doxorubicin is tracked in live, endothelial cells over a period of 24 h. The results are consistent with a release process of molecular diffusion from a fixed supply reservoir, with a characteristic release lifetime of 2 h. Detailed stochastic modelling of the diffusion process, mimicking the random walk of drug molecules within a heterogeneous size distribution of pores, provides an excellent fit to the data and indicates a doxorubicin diffusion constant of 2 × 10−11 m2s−1.

Confinement Effects on Drugs in Thermally Hydrocarbonized Porous Silicon

Thermally hydrocarbonized porous silicon (THCPSi) microparticles were loaded with indomethacin (IMC) and griseofulvin (GSV) using three different payloads between 6.2-19.5 and 6.2-11.4 wt %, respectively. The drug loading parameters were selected to avoid crystallization of the drug molecules on the external surface of the particles that would block the pore entrances. The successfulness of the loadings was verified with TG, DSC, and XRPD measurements. The effects of the confinement of IMC and GSV into the small mesopores of THCPSi were analyzed with helium pycnometry, FTIR, and NMR spectroscopy. The results showed the density of the THCPSi loaded drugs to be ca. 10% lower than the bulk crystalline forms, while a melt quenched amorphous drugs showed a density reduction of 3-7.5%. DSC and FTIR results confirmed that the drugs reside in an amorphous form within the THCPSi pores. Similar results were obtained with NMR, which also indicated that IMC may reside as both amorphous clusters and individual molecules within the pores. The (1)H transverse relaxation times (T2) of amorphous and THCPSi loaded drugs showed IMC relaxation times of 0.28 ms for both the cases, whereas for GSV the values were 0.32 and 0.39 ms, respectively, indicating similar limited mobility in both cases. The results indicated that strong drug-carrier interactions were not necessary for stabilizing the amorphous state of the adsorbed drug. Dissolution tests using biorelevant media, fasted state simulated intestinal fluid (FaSSIF) and simulated gastric fluid (SGF), showed that THCPSi-loaded IMC and GSV were rapidly released in FaSSIF with comparable rates to the amorphous forms, whereas in SGF the THCPSi reduced the pH dependency in the dissolution of IMC.

Porous silicon confers bioactivity to polycaprolactone composites in vitro

Silicon is an essential element for healthy bone development and supplementation with its bioavailable form (silicic acid) leads to enhancement of osteogenesis both in vivo and in vitro. Porous silicon (pSi) is a novel material with emerging applications in opto-electronics and drug delivery which dissolves to yield silicic acid as the sole degradation product, allowing the specific importance of soluble silicates for biomaterials to be investigated in isolation without the elution of other ionic species. Using polycaprolactone as a bioresorbable carrier for porous silicon microparticles, we found that composites containing pSi yielded more than twice the amount of bioavailable silicic acid than composites containing the same mass of 45S5 Bioglass. When incubated in a simulated body fluid, the addition of pSi to polycaprolactone significantly increased the deposition of calcium phosphate. Interestingly, the apatites formed had a Ca:P ratio directly proportional to the silicic acid concentration, indicating that silicon-substituted hydroxyapatites were being spontaneously formed as a first order reaction. Primary human osteoblasts cultured on the surface of the composite exhibited peak alkaline phosphatase activity at day 14, with a proportional relationship between pSi content and both osteoblast proliferation and collagen production over 4 weeks. Culturing the composite with J744A.1 murine macrophages demonstrated that porous silicon does not elicit an immune response and may even inhibit it. Porous silicon may therefore be an important next generation biomaterial with unique properties for applications in orthopaedic tissue engineering.