Structural and chemical modifications of porous silicon for biomedical applications

The versatility in properties of porous silicon (PSi) has enabled a broad spectrum of applications, ranging from microelectronics and various types of sensors to its use as a biocompatible material in drug delivery. Structural properties of PSi were shown in this work to be adaptable post-fabrication using thermal annealing. Control over the average pore size of the material proved to be beneficial, when adjustments were necessary to accommodate larger biomolecules within the pores of the PSi. Furthermore, a facile method of fabricating PSi nanoparticles was introduced using a multilayer approach with a stepwise electrochemical etching process, where the comminution of the material was guided with formation of fragile, high porosity perforation layers at specific intervals. This method has been proven successful, being utilized in over 70 publications so far. For extended control over biocompatibility and biodistribution of PSi micro- and nanoparticles, two new surface modifications based on hydrolytically stabilized PSi were introduced. Amine-terminated thermally carbonized PSi, capable of carbodiimide crosslinking for further functionalization with biomolecules, and an alkyne-terminated hydrocarbonized PSi, enabling the use of click chemistry -based addition reaction for secondary functionalization. Solid-state properties of confined drug molecules adsorbed into PSi microparticles were also studied. As PSi is known to enhance aqueous dissolution and cellular permeability of poorly soluble drugs, more accurate information was sought on the effects of the mesoscale confinement. Small molecule drugs were observed to partially have a liquid-like behavior according to solid-state NMR analysis and participate in interactions with the pore walls, according the availability of specific functional groups. Slight disruption in short-range order of the adsorbed drugs was also found, as the confinement appeared to reduce the true density of the drug molecules below that of a bulk amorphous state. Study over the conditions for efficient drug adsorption into the pores showed the importance of solvent and drug solution concentration selection. Optimal choices enabled high drug payload within the PSi, without precipitation of crystalline drug on the external surface of the PSi microparticles.Huokoisen piin (porous silicon, PSi) monipuoliset ominaisuudet ovat mahdollistaneet runsaasti erilaisia sovelluksia, lähtien mikroelektroniikasta ja ilmaisimista aina tämän käyttöön bioyhteensopivana materiaalina lääkeannostelussa. Tässä työssä osoitettiin huokoisen piin rakenteen olevan jälkikäteen muokattavissa hallitusti lämpökäsittelyn avulla. Huokoskokoa kasvattamalla mahdollistettiin tarpeen vaatiessa suurempien biomolekyylien pääsy huokosiin. Tämän lisäksi esiteltiin menetelmä huokoisen piin nanopartikkelien valmistamiseksi syövyttämällä sähkökemiallisesti huokoinen monikerrosrakenne, missä tasaisin välimatkoin sijaitsevat hauraat korkean huokoisuuden kerrokset toimivat murtumista edistävinä kohtina. Menetelmää on sittemmin hyödynnetty tähän mennessä yli 70:ssä tieteellisessä julkaisussa. Huokoisen piin mikro- ja nanopartikkelien bioyhteensopivuuden ja kulkeutumisen hallintaan työssä kehitettiin kaksi uutta pintakemiallista muunnosta huokoiselle piille, mikä oli esikäsitelty heikosti veteen liukenevaksi. Muunnokset perustuivat vapaiden amiiniryhmien ja alkyynien saatavuuteen huokoisen piin pinnoilla. Näistä edellinen mahdollisti biologisen funktionalisoinnin karbodi-imidisilloituksen kautta, jälkimmäisen puolestaan mahdollistaen monipuolinen funktionalisointi kupariavusteisen sykloadditioreaktion kautta. Lääkemolekyylien fysikaalista olotilaa nanokokoluokan huokosissa tutkittiin huokoisen piin mikropartikkelien avulla. Huokosiin adsorboitujen niukkaliukoisten lääkeaineiden tiedetään liukenevan tehokkaasti veteen, mutta syitä tälle voi olla useita. Pienmolekyylilääkkeiden havaittiin olevan osittain nestemäisessä muodossa huokosten sisällä NMR-tutkimusten mukaan. Molekyylien lähijärjestys vaikutti myös osittain muuttuneen, huokosiin adsorboituneen lääkeaineen tiheyden ollessa tavallista amorfista tilaa alhaisempi. Lääkeaineen adsorptiota huokosiin pyrittiin myös tehostamaan seuraamalla liuottimen ja lääkeaineliuoksen konsentraation vaikutusta. Sopivin parametrein saavutettiin korkea lääkkeen hyötykuorma, ilman lääkemolekyylien kiteytymistä huokoisen piin mikropartikkelien ulkopinnoille

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. </p

Synaptic and fast switching memristance in porous silicon-based structures

Memristors are two terminal electronic components whose conductance depends on the amount of charge that has flown across them over time. This dependence can be gradual, such as in synaptic memristors, or abrupt, as in resistive switching memristors. Either of these memory effects are very promising for the development of a whole new generation of electronic devices. For the successful implementation of practical memristors, however, the development of low cost industry compatible memristive materials is required. Here the memristive properties of differently processed porous silicon structures are presented, which are suitable for different applications. Electrical characterization and SPICE simulations show that laser-carbonized porous silicon shows a strong synaptic memristive behavior influenced by defect diffusion, while wet-oxidized porous silicon has strong resistance switching properties, with switching ratios over 8000. Results show that practical memristors of either type can be achieved with porous silicon whose memristive properties can be adjusted by the proper material processing. Thus, porous silicon may play an important role for the successful realization of practical memristorics with cost-effective materials and processesThis work is part of ATTRACT that has received funding from the European Union’s Horizon 2020 Research and Innovation Programm

Effectiveness of porous silicon nanoparticle treatment at inhibiting the migration of a heterogeneous glioma cell population

BACKGROUND: Approximately 80% of brain tumours are gliomas. Despite treatment, patient mortality remains high due to local metastasis and relapse. It has been shown that transferrin-functionalised porous silicon nanoparticles (Tf@pSiNPs) can inhibit the migration of U87 glioma cells. However, the underlying mechanisms and the effect of glioma cell heterogeneity, which is a hallmark of the disease, on the efficacy of Tf@pSiNPs remains to be addressed. RESULTS: Here, we observed that Tf@pSiNPs inhibited heterogeneous patient-derived glioma cells’ (WK1) migration across small perforations (3 μm) by approximately 30%. A phenotypical characterisation of the migrated subpopulations revealed that the majority of them were nestin and fibroblast growth factor receptor 1 positive, an indication of their cancer stem cell origin. The treatment did not inhibit cell migration across large perforations (8 μm), nor cytoskeleton formation. This is in agreement with our previous observations that cellular-volume regulation is a mediator of Tf@pSiNPs’ cell migration inhibition. Since aquaporin 9 (AQP9) is closely linked to cellular-volume regulation, and is highly expressed in glioma, the effect of AQP9 expression on WK1 migration was investigated. We showed that WK1 migration is correlated to the differential expression patterns of AQP9. However, AQP9-silencing did not affect WK1 cell migration across perforations, nor the efficacy of cell migration inhibition mediated by Tf@pSiNPs, suggesting that AQP9 is not a mediator of the inhibition. CONCLUSION: This in vitro investigation highlights the unique therapeutic potentials of Tf@pSiNPs against glioma cell migration and indicates further optimisations that are required to maximise its therapeutic efficacies

Regenerative Electroless Etching of Silicon

Regenerative electroless etching (ReEtching), described herein for the first time, is a method of producing nanostructured semiconductors in which an oxidant (Ox1) is used as a catalytic agent to facilitate the reaction between a semiconductor and a second oxidant (Ox2) that would be unreactive in the primary reaction. Ox2 is used to regenerate Ox1, which is capable of initiating etching by injecting holes into the semiconductor valence band. Therefore, the extent of reaction is controlled by the amount of Ox2 added, and the rate of reaction is controlled by the injection rate of Ox2. This general strategy is demonstrated specifically for the production of highly luminescent, nanocrystalline porous Si from the reaction of V2O5 in HF(aq) as Ox1 and H2O2(aq) as Ox2 with Si powder and wafers

Ultralight and porous cellulose nanofibers/polyethyleneimine composite aerogels with exceptional performance for selective anionic dye adsorption

It is significant to develop new adsorbents with excellent adsorption performance and convenient operation ability for removing pollutants from wastewater owing to the growing environmental problems. In this paper, a novel ultralight aerogel-based adsorbent with highly porous structure and good mechanical integrity was fabricated based on the interaction of amine groups on polyethyleneimine (PEI) and hydroxyl groups on cellulose nanofibers (CNF), with epichlorohydrin (ECH) serving as a crosslinker. The obtained CNF/PEI aerogel showed excellent water stability in harsh conditions, fast water-activated shape recovery, and ultra-fast water transport. The adsorption capacity for methyl orange (MO) in batch can reach to1226 mg g−1 at pH 6. Furthermore, the membrane also exhibited excellent selective adsorption and filtration, and separation performance. Therefore, this paper presents a new strategy to prepare low-cost and highly efficient adsorbents to remove organic dyes from wastewater for potential practical applications.</p

Hierarchical Porous Silicon and Porous Silicon Nanowires Produced with Regenerative Electroless Etching (ReEtching) and Metal Assisted Catalytic Etching (MACE)

ReEtching produces nanostructured silicon when a catalytic agent, e.g. dissolved V2O5, is used to facilitate etching between Si and H2O2. H2O2 regenerates dissolved V in a 5+ oxidation state, which initiates etching by injecting holes into the Si valence band. Independent control over the extent of reaction (controlled by the amount of H2O2 added) and the rate of reaction (controlled by the rate at which H2O2 is pumped into the etchant solution) allows us to porosify Si substrates of arbitrary size, shape and doping, including wafers, single-crystal powders, polycrystalline powders, metallurgical grade powder, Si nanowires, Si pillars and Si powders that have been textured with metal-assisted catalytic etching (MACE). Similarly, improved control over the nucleation and etching in MACE is achieved by pumped delivery of reagents. Nanowires are not produced directly by MACE of powders, rather they form when a porosified layers is cleaved by capillary forces or sonication

Amine-modified hyaluronic acid-functionalized porous silicon nanoparticles for targeting breast cancer tumors

Peer reviewe

Size, Stability, and Porosity of Mesoporous Nanoparticles Characterized with Light Scattering

Silicon-based mesoporous nanoparticles have been extensively studied to meet the challenges in the drug delivery. Functionality of these nanoparticles depends on their properties which are often changing as a function of particle size and surrounding medium. Widely used characterization methods, dynamic light scattering (DLS), and transmission electron microscope (TEM) have both their weaknesses. We hypothesize that conventional light scattering (LS) methods can be used for a rigorous characterization of medium sensitive nanoparticles’ properties, like size, stability, and porosity. Two fundamentally different silicon-based nanoparticles were made: porous silicon (PSi) from crystalline silicon and silica nanoparticles (SN) through sol-gel process. We studied the properties of these mesoporous nanoparticles with two different multiangle LS techniques, DLS and static light scattering (SLS), and compared the results to dry-state techniques, TEM, and nitrogen sorption. Comparison of particle radius from TEM and DLS revealed significant overestimation of the DLS result. Regarding to silica nanoparticles, the overestimation was attributed to agglomeration by analyzing radius of gyration and hydrodynamic radius. In case of PSi nanoparticles, strong correlation between LS result and specific surface area was found. Our results suggest that the multiangle LS methods could be used for the size, stability, and structure characterization of mesoporous nanoparticles.Peer reviewe

Quantitative Analysis of Porous Silicon Nanoparticles Functionaliza-tion by 1H NMR

Porous silicon (PSi) nanoparticles have been applied in various fields, such as catalysis, imaging, and biomedical applications, because of their large specific surface area, easily modifiable surface chemistry, biocompatibility, and biodegradability. For biomedical applications, it is important to precisely control the surface modification of PSi-based materials and quantify the functionalization density, which determines the nanoparticle’s behavior in the biological system. Therefore, we propose here an optimized solution to quantify the functionalization groups on PSi, based on the nuclear magnetic resonance (NMR) method by combining the hydrolysis with standard 1H NMR experiments. We optimized the hydrolysis conditions to degrade the PSi, providing mobility to the molecules for NMR detection. The NMR parameters were also optimized by relaxation delay and the number of scans to provide reliable NMR spectra. With an internal standard, we quantitatively analyzed the surficial amine groups and their sequential modification of polyethylene glycol. Our investigation provides a reliable, fast, and straightforward method in quantitative analysis of the surficial modification characterization of PSi requiring a small amount of sample.Peer reviewe