Interior Pore Surfaces Research Articles

Analysis of polydisperse polymer adsorption on porous cellulose fibers.

The adsorption of cationic water-soluble polymers onto negatively charged porous wood pulp fibers is an essential aspect of papermaking. Adsorption data can be displayed as a direct plot of the amount adsorbed, Γ, versus the amount of polymer added or as an isotherm plot showing the amount adsorbed versus the residual unadsorbed polymer. In either data presentation, the analysis is more transparent if the units of each axis are the same (e.g., mg/g or meq/g), giving dimensionless slopes. Values for Γmax, ΓI, f I , and Γme can be extracted from many isotherms where: Γmax is the maximum capacity of the fibers to adsorb polymer; ΓI is the y-axis isotherm intercept and gives the maximum dose that can be fully adsorbed; f I is the slope of the direct plot at ΓI, and f I is the mass fraction of the added polymer that can access interior (pore) surfaces; and, Γme is the saturated amount of polymer adsorbed on exterior surfaces. Additionally, the molecular weight distribution of theadsorbing polymer in conjunction with the adsorption isotherm can be used to estimate the molecular weight distributions of adsorbed polymer on interior and exterior fiber surfaces as functions of the polymer dose.

Foldamer-based ultrapermeable and highly selective artificial water channels that exclude protons.

The outstanding capacity of aquaporins (AQPs) for mediating highly selective superfast water transport1-7 has inspired recent development of supramolecular monovalent ion-excluding artificial water channels (AWCs). AWC-based bioinspired membranes are proposed for desalination, water purification and other separation applications8-18. While some recent progress has been made in synthesizing AWCs that approach the water permeability and ion selectivity of AQPs, a hallmark feature of AQPs-high water transport while excluding protons-has not been reproduced. We report a class of biomimetic, helically folded pore-forming polymeric foldamers that can serve as long-sought-after highly selective ultrafast water-conducting channels with performance exceeding those of AQPs (1.1 × 1010 water molecules per second for AQP1), with high water-over-monovalent-ion transport selectivity (~108 water molecules over Cl- ion) conferred by the modularly tunable hydrophobicity of the interior pore surface. The best-performing AWC reported here delivers water transport at an exceptionally high rate, namely, 2.5 times that of AQP1, while concurrently rejecting salts (NaCl and KCl) and even protons.

PoreMS: a software tool for generating silica pore models with user-defined surface functionalisation and pore dimensions

ABSTRACT Mass transport under confinement is at the heart of all processes employing functionalised mesoporous silica materials, such as liquid chromatography, heterogeneous catalysis, and gas adsorption. Molecular simulation studies of mass transport in such settings require pore models that replicate the geometry, dimensions, and chemical structure of a surface-functionalised silica mesopore. We present a software tool that facilitates rapid model building of functionalised silica pores for systematic studies of confinement effects in various applications of relevant materials. The tool allows to choose the chemical structure and density of the ligands and to control the residual hydroxylation of the silica surface. Individual ligands can be placed at a user-defined position on the surface. Moreover, the tool supports an independent functionalisation of the interior and exterior pore surface. We explain each step of the pore generation, discuss the underlying assumptions and limitations, and introduce examples of generated cylindrical pore models for chromatography and catalysis.

Surface Chemical Functionalization to Achieve Extreme Levels of Molecular Confinement in Hybrid Nanocomposites

AbstractPolymer confinement is realized in hybrid nanocomposites where individual polymer molecules are confined by a nanoporous matrix to dimensions less than the molecular size of the polymer. Here it is shown that by functionalizing the interior pore surfaces of a nanoporous organosilicate matrix, the pores can be filled with polystyrene molecules to achieve extreme levels of molecular confinement not previously possible. This provides opportunities for unique thermal and mechanical properties. It is shown that pore surface functionalization markedly impacts the polymer mobility during polymer infiltration by affecting the polymer–pore surface interaction, addressing the challenge of filling high‐molecular‐weight polymer molecules into nanoscale‐confined spaces. This allows for achieving extreme levels of molecular confinement with the loss of interchain entanglement and extensive polymer elongation along the pore axis. The glass transition temperature of the polymer is suppressed compared to bulk polymer melt, and is significantly affected by the polymer–surface interaction, which changes the polymer segmental mobility. The polymer–surface interaction also affects the interfacial polymer–pore sliding shear stress during polymer pullout from the nanopores, markedly affecting the fracture resistance of the nanocomposite.

Selective external surface functionalization of large-pore silica materials capable of protein loading

Differentiating the chemical properties of the external and pore surfaces of sol-gel derived mesoporous materials by selective functionalization is important to advancing their application as platforms for biological catalysis, sensing and drug delivery. Prior selective functionalization approaches to concentrating functional groups at the external surface of particles have been limited to small pores (≤5.5 nm diameter) incapable of loading large biological molecules. This work investigates the selective exterior surface functionalization by amines of larger-pored (>7 nm diameter) mesoporous silica particles, which are synthesized by dual surfactant templating and hydrothermal aging. Previously developed selective functionalization techniques rely on choice of functionalization precursor, functionalization reaction time, or pore blocking (by leaving pore templates in as-synthesized materials). The effectiveness of these strategies are compared for larger-pored materials using the precursors (3-aminopropyl)tris(methoxyethoxyethoxy)silane (APTMEES) and (3-aminopropyl)triethoxysilane (APTES). The extent of amine functionalization is determined as a function of precursor reaction time (10 or 20 min) in both as-synthesized and template-extracted materials by confocal laser scanning microscopy of the ∼10 μm diameter particles tagged with fluorescein isothiocyanate. Reaction time, regardless of pore template presence, is demonstrated to be the controlling variable for achieving selective exterior functionalization in these larger pored mesoporous materials. Under the conditions used, 10 min of functionalization with APTMEES localizes amine groups at the exterior of the particles, while 20 min functionalizes both the exterior and the interior pore surfaces. Protein accessibility within pores, before and after selective and full functionalization, is visually confirmed by confocal fluorescence imaging of Rhodamine B tagged lysozyme loaded particles.

Microstructural evolution of sintered silver at elevated temperatures

Reduction in the sintering temperature of metal powders by lowering particle size into the nanoparticle range has resulted in a new class of porous sintered joining materials. Especially promising are sintered silver based materials which can be used to form bonds between wide-bandgap semiconductor die and circuit boards for use in high temperature applications. This work shows that for these materials the exterior sintered silver surface oxidizes preventing surface morphology changes, while the interior pore surfaces of the porous silver remain largely oxide-free. These pore surfaces facilitate fast atomic movement resulting in grain growth and changes in the internal microstructure. Morphology changes in the temperature range 200–400°C are presented both as statistical averages of grain size and, uniquely in this type of study, by tracking individual pores and grains. It is shown that the internal structure will undergo changes during high temperature storage in contrast to the stable outer surface. A new technique, utilizing the electromigration effect to check the relative surface mobility of atoms in the interior pores and exterior surfaces was used to support the conclusions deduced from thermal ageing experiments. Finally, we speculate that the stability of the exterior surface could be reproduced in the interior if the chemistry of the paste was altered to allow formation of a passivating layer on the interior pores during the final stages of the sintering process, resulting in formation of a stable die attach material for applications of up to 400°C, for which there is an urgent need.

Efficient gold(III) detection, separation and recovery from urban mining waste using a facial conjugate adsorbent

This study developed an efficient fine-tuning conjugate adsorbent for simultaneous gold (Au(III)) detection and recovery from urban mining waste. The adsorbent was prepared by indirect and dense immobilization of 6-((2-(2-hydroxy-1-naphthoyl)hydrazono)methyl) benzoic acid (HMBA) onto fine-tuned surface patterning of nanostructure inorganic silica. This adsorbent has the large surface area-to-volume ratios and uniformly shaped pores in nanostructures in its cage cavities. Therefore, the conjugate adsorbent permitted to fast and specific Au(III) ions capturing via a colorimetric naked-eye visualization based on the stable complexation [Au(III)–HMBA]n+ mechanism. The small energy gap for the complex compared with the HMBA suggested the easily excitation of electrons according to the electron transfer or energy transferred mechanism, which results in the intense color of the stable complexation mechanism. The influence of several variables such as solution acidity, initial concentrations and the addition of diverse ions for Au(III) detection and recovery has also been considered and evaluated. The detection limit of the conjugate adsorbent at optimum conditions was 0.11μg/L. The Au(III) sorption forms a monolayer on the interior pore surfaces of the conjugate adsorbent and showed high sorption capacity (203.42mg/g). In addition, the sorption uptake on the adsorbent reaching equilibrium was rapid and adsorbent was also exhibited high Au(III) ion selectivity in ionic competition. Acidified thiourea was used in the elution of the Au(III) and conjugate adsorbent exhibited in terms of reproducibility and versatility over a number of analysis/regeneration cycles. Therefore, the present conjugate adsorbent offered a low-cost material for potential application of ultra-trace Au(III) detection and recovery from urban mining waste scraps.

Multi-functionalization of nanoporous catalytic materials to enhance reaction yield: Statistical mechanical modeling for conversion reactions with restricted diffusive transport

ABSTRACTMulti-functionalization of catalytically-active nanomaterials provides a valuable tool for enhancing reaction yield by shifting reaction equilibrium, and potentially also by adjusting reaction-diffusion kinetics. For example, multi-functionalization of mesoporous silica to make the interior pore surface hydrophobic can enhance yield in dehydration reactions. Detailed molecular-level modeling to describe the pore environment, as well as the reaction and diffusion kinetics is challenging, although we briefly discuss current strategies. Our focus, however, is on coarse-grained stochastic modeling of the overall catalytic process for highly restricted transport within narrow pores (with single-file diffusion), while accounting for a tunable interaction of the pore interior with reaction products. We show that making the pore interior unfavorable to products can significantly enhance yield due to both thermodynamic and kinetics factors.

PH Dictates the Release of Hydrophobic Drug Cocktail from Mesoporous Nanoarchitecture

Combination therapy has been a norm in clinical practice to effectively treat cancer. Besides polytherapy, nowadays, smart and nanobased drug carriers are extensively being explored to deliver drugs according to pathophysiological environment of diseases. In this regard, herein we designed intelligent mesoporous architecture, incorporating both combinational therapy with smart nanotechnology, to simultaneously deliver two highly hydrophobic chemotherapeutic drugs in response to extracellular and/or intracellular acidic environ of tumor. Novelty of the system lies in the employment of acid responsive ZnO QDs to clog not only the nanochannels of mesoporous silica, encapsulating one hydrophobic drug, but also exploitation of chelate forming propensity of another hydrophobic drug (curcumin) to load a significant quantity onto the surface of ZnO nanolids. Cell viability results revealed an extraordinarily high cytotoxic efficiency of that lethal drug cocktail even at a concentration as low as 3 μg/mL nanocarrier. We envision that this sophisticated nanocarrier, which utilizes both interior pore and exterior surface of nanolids for loading different hydrophobic guest molecules and their subsequent acid responsive release, will undoubtedly, illustrates its remarkable potential in targeted chemotherapy.

Efficient detection and extraction of cobalt(II) from lithium ion batteries and wastewater by novel composite adsorbent

This study developed a novel composite adsorbent for highly selective and sensitive detection and extraction of cobalt (Co(II)) from lithium-ion batteries (LIBs) and wastewater. The composite adsorbent was prepared by indirect immobilization of 6-((2-(2-hydroxy-1-naphthoyl)hydrazono)methyl)benzoic acid (HMBA) onto mesoporous silica monoliths. The composite adsorbent enhanced the color formation by stable complexation as [Co(II)–HMBA]n+ complexes during detection and sorption operations. The data evident the one-step detection of wide range Co(II) concentrations into interior pore surface coverage of the composite adsorbent from solutions without using high tech instruments, which was unique feature of this adsorbent. The influence of different sorption parameters, such as: initial Co(II) concentration, equilibration time, solution pH and the presence of competing ions and reuses were studied and discussed systematically. The effective pH range for Co(II) ions detection and sorption was neutral pH region and the maximum sorption capacity of the adsorbent was as high as 189.37mg/g. The adsorbed Co(II) was eluted with stripping agent (0.3M HCl) and simultaneously regenerated into initial form for the next capturing operations after rinsing with water. The data also clarified that the composite adsorbent was selectively extracted Co(II) from LIBs even in the presence of high concentration diverse ions. Importantly, the composite adsorbent was retaining functionality in spite of many chemical treatments during sorption–elution-recovery/regeneration cycles. Therefore, the present study revealed that such a low-cost material could be used as potential adsorbent for the selective detection and recovery of Co(II) ions from LIBs and wastewater streams.

Visual monitoring and removal of divalent copper, cadmium, and mercury ions from water by using mesoporous cubic Ia3d aluminosilica sensors

The design of a simple, pH-dependent, micro-object optical sensor based on mesoporous Ia3d aluminosilica pellets functionalized by a porphyrinic chelating ligand for the monitoring and removal of ultra-trace levels of toxic metals, such as Hg(II), Cu(II), and Cd(II), from aqueous media, such as drinking water and biological fluids, is described in this study. This micro-object optical sensor has large surface area-to-volume ratios and uniformly shaped pores in three-dimensional (3D) nanoscale gyroidal structures, and its active sites consist of heteroatoms arranged around uniformly shaped pores in 3D nanoscale gyroidal mesostructures. These mesostructures are densely coated with chelating ligand to permit ultra-fast, specific, pH-dependent visualization and the removal of toxic metals at sub-picomolar concentrations (∼10−11moldm−3) from aqueous media, including drinking water and a suspension of red blood cells, via a colorimetric signal visible to the naked eye, as well as via UV–Vis reflectance spectroscopy. The adsorption of metal ions forms a monolayer on the interior pore surfaces of the pellets in this sensor system. Given that the pellets exhibit long-term stability, reproducibility, and versatility over a number of analysis/regeneration cycles, they can be useful for the fabrication of inexpensive sensor devices for naked-eye detection of toxic pollutants. Furthermore, the usage of the pellets to remove metal ions from a physiological fluid (i.e., blood cells) was evaluated.

Optical mesosensor for capturing of Fe(III) and Hg(II) ions from water and physiological fluids

This study developed a pH-dependent mesosensor for the optical and selective removal of Hg2+ ions from drinking water and physiological fluids. The fine-tuned surface patterning of the mesoscopic solid aluminosilica scaffolding architectures, which was achieved using a dispersible active agent such as a cationic surfactant, resulted in the dense immobilization of addressable diphenylcarbazide chelating agent. These mesosensor responses can be triggered by the target species and can transduce measurable optical signals under synergistic pH conditions, thus enabling the binding of Fe3+ and Hg2+ metals into a hydrophobic chelating pocket to be simulated. Results verified the one-step removal and optical adsorption efficiency of ultra-trace, wide-range (0.001mg dm−3 to 2.0mg dm−3) concentrations of Fe3+ and Hg2+ ions into the interior pore surface coverage of the DPC-modified mesosensor from drinking water. Importantly, the mesosensor can be repeatedly recycled without damaging the unique mesostructures. Furthermore, the hemolysis test of Hg2+ ion toxicity in red blood cells (RBCs) and the counteraction effect of the phosphatidylserine (Ptd-L-Ser) receptor exposure of RBCs were also investigated in a physiological system such as human blood. Results indicated that the strong binding site-metal interaction enabled the remarkably selective removal of Hg2+ ions from physiological fluids.

Enhancing the bioactivity of Poly(lactic-co-glycolic acid) scaffold with a nano-hydroxyapatite coating for the treatment of segmental bone defect in a rabbit model

PurposePoly(lactic-co-glycolic acid) (PLGA) is excellent as a scaffolding matrix due to feasibility of processing and tunable biodegradability, yet the virgin scaffolds lack osteoconduction and osteoinduction. In this study, nano-hydroxyapatite (nHA) was coated on the interior surfaces of PLGA scaffolds in order to facilitate in vivo bone defect restoration using biomimetic ceramics while keeping the polyester skeleton of the scaffolds.MethodsPLGA porous scaffolds were prepared and surface modification was carried out by incubation in modified simulated body fluids. The nHA coated PLGA scaffolds were compared to the virgin PLGA scaffolds both in vitro and in vivo. Viability and proliferation rate of bone marrow stromal cells of rabbits were examined. The constructs of scaffolds and autogenous bone marrow stromal cells were implanted into the segmental bone defect in the rabbit model, and the bone regeneration effects were observed.ResultsIn contrast to the relative smooth pore surface of the virgin PLGA scaffold, a biomimetic hierarchical nanostructure was found on the surface of the interior pores of the nHA coated PLGA scaffolds by scanning electron microscopy. Both the viability and proliferation rate of the cells seeded in nHA coated PLGA scaffolds were higher than those in PLGA scaffolds. For bone defect repairing, the radius defects had, after 12 weeks implantation of nHA coated PLGA scaffolds, completely recuperated with significantly better bone formation than in the group of virgin PLGA scaffolds, as shown by X-ray, Micro-computerized tomography and histological examinations.ConclusionnHA coating on the interior pore surfaces can significantly improve the bioactivity of PLGA porous scaffolds.

Influence of the alkyl chain length of cyanine dyes on their adsorption by Na+-montmorillonite from aqueous solutions

Adsorption of cyanine dyes from aqueous solution onto the surface of Na+-montmorillonite (Na+-MMT) was investigated spectrophotometrically. A set of four linear alkyl chain cyanine dyes (D-C5, D-C7, D-C10, and D-C18), were used in this work to evaluate the effect of carbon chain length on the efficiency of dye adsorption. The loading of the dye onto Na+-MMT surface was increased with increasing the length of alkyl chain. The effect of the contact time, initial concentration of the dye, pH of solution and temperature on the adsorption process were studied. Adsorption isotherms were established and found to correlate well with the Freundlich, Langmuir, and Dubinin–Radushkevich adsorption models. Values of the constants Kf and 1/n determined from the Freundlich isotherm decreased with the increase in the tail length of the dye (D-C5→D-C18). The same trend was observed for the Langmuir adsorption constant, KL. The E values calculated from Dubinin–Radushkevich isotherm increased with increasing the alkyl chain length of the cyanine dyes but still less than 16kJmol−1, suggesting physical adsorption process. Further, the thermodynamic parameters (the enthalpy, ΔH, Gibb’s free energy, ΔG, and entropy, ΔS) characteristics of Na+-MMT/dye interaction were evaluated. The adsorption of cyanine dyes onto Na+-MMT was not spontaneous and endothermic. The magnitudes of ΔH and ΔS have dropped on going from D-C5 to D-C18. In contrast, as the size of the alkyl tail on the dye increased, Gibb’s free energy ΔG was decreased. As far as the adsorption kinetics is concerned, the present adsorption regime followed pseudo-second-order kinetic model rather than pseudo-first-order model. The intraparticle diffusion model resulted in the existence of both the bulk and intraparticle diffusions of the dye molecules into the interior pore surface of Na+-MMT particles.

Dynamics of 1,3-Diphenylpropane Tethered to the Interior Pore Surfaces of MCM-41

The diffusive motions of covalently tethered 1,3-diphenylpropane (DPP) via a silyl-aryl-ether linkage in the mesopores of MCM-41 were studied by quasielastic neutron scattering. The geometric effect of pore radius was investigated with samples having pores that ranged from 1.6 to 3.0 nm in diameter and highest achievable DPP grafting density. The effect of molecular crowding was investigated in 3.0 nm diameter pores for surface coverage ranging from 0.60 to 1.61 DPP/nm2. Temperature dependence was determined for large pore diameter samples from 240 to 370 K. As the DPP molecules remain attached over this entire temperature range, data were analyzed in terms of a model of localized diffusion inside a sphere. Only the motions of the DPP hydrogen atoms were considered because of the high sensitivity of neutron scattering to the presence of hydrogen. As atoms far from the attachment point have a greater range of motion than those nearer the tether, the radius of the sphere limiting the motion of individual hydrogen atoms was allowed to increase based on the atom’s distance from the tether point. Both smaller pore diameters and higher DPP grafting density resulted in larger amplitude motion while the diffusion coefficient was greatest in the largest pores at highest DPP density. These observations support a model where the DPP molecules prefer an orientation allowing close proximity to the MCM-41 pore surface and are forced into the pore interior by either the steric effect of small pore diameter or by increased competition for surface area at high molecule surface coverage.

Different Functionalization of the Internal and External Surfaces in Mesoporous Materials for Biosensing Applications Using “Click” Chemistry

We report the use of copper(I)-catalyzed alkyne-azide cycloaddition reaction (CuAAC) to selectively functionalize the internal and external surfaces of mesoporous materials. Porous silicon rugate filters with narrow line width reflectivity peaks were employed to demonstrate this selective surface functionalization approach. Hydrosilylation of a dialkyne species, 1,8-nonadiyne, was performed to stabilize the freshly fabricated porous silicon rugate filters against oxidation and to allow for further chemical derivatization via "click" CuAAC reactions. The external surface was modified through CuAAC reactions performed in the absence of nitrogen-based Cu(I)-stabilizing species (i.e., ligand-free reactions). To subsequently modify the interior pore surface, stabilization of the Cu(I) catalyst was required. Optical reflectivity measurements, water contact angle measurements, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to demonstrate the ability of the derivatization approach to selectively modify mesoporous materials with different surface chemistry on the exterior and interior surfaces. Furthermore, porous silicon rugate filters modified externally with the cell-adhesive peptide Gly-Arg-Gly-Asp-Ser (GRGDS) allowed for cell adhesion via formation of focal adhesion points. Results presented here demonstrate a general approach to selectively modify mesoporous silicon samples with potential applications for cell-based biosensing.

Spontaneous Waveguide Raman Spectroscopy of Self-Assembled Monolayers in Silica Micropores

Advances in nanoscience are critically dependent on the ability to control and probe chemical and physical phenomena in confined geometries. A key challenge is to identify confinement structures with high surface area to volume ratios and controlled surface boundaries that can be probed quantitatively at the molecular level. Herein we report an approach for probing molecular structures within nano- to microscale pores by the application of spontaneous Raman spectroscopy. We demonstrate the method by characterization of the structural features of picomole quantities of well-organized octadecyltrichlorosilane (OTS) monolayers self-assembled on the interior pore surfaces of high aspect ratio (1 μm diameter × 1-10 cm length), near-atomically smooth silica microstructured optical fibers (MOFs). The simple Raman backscattering collection geometry employed is well suited for a wide variety of diagnostic applications as demonstrated by tracking the combustion of the hydrocarbon chains of the OTS self-assembled monolayer (SAM) and spectral confirmation of the formation of an adsorbed monolayer of human serum albumin (HSA) protein. Using this MOF Raman approach, molecular processes in precisely defined, highly confined geometries can be probed at high pressures and temperatures, with a wide range of excitation wavelengths from the visible to the near-IR, and under other external perturbations such as electric and magnetic fields.

Tuning the cellular uptake and cytotoxicity properties of oligonucleotide intercalator-functionalized mesoporous silica nanoparticles with human cervical cancer cells HeLa

A series of organically functionalized, MCM-41 type mesoporous silica nanoparticle materials (PAP-LP-MSN and AP-PAP-MSN) with different pore sizes (5.7 nm and 2.5 nm, respectively) were synthesized and characterized. We selectively decorated the exterior particle surface of PAP-LP-MSN and the interior pore surface of AP-PAP-MSN with an oligonucleotide intercalating phenanthridinium functionality. While phenanthridinium itself is a cell membrane impermeable molecule, we demonstrated that both phenanthridinium-immobilized PAP-LP-MSN and AP-PAP-MSN materials could indeed be internalized by live human cervical cancer cells (HeLa). We discovered that the PAP-LP-MSN nanoparticles with the phenanthridium groups located on the exterior surface were able to bind to cytoplasmic oligonucleotides, such as messenger RNAs, of HeLa cells resulting in severe cell growth inhibition. In contrast, the cytotoxicity of AP-PAP-MSN, where the same oligonucleotide intercalating molecules were anchored inside the pores, was significantly lowered upon the endocytosis by HeLa cells. We envision that this approach of combining the selective functionalization of the two different surfaces (exterior particle and interior pore surfaces) with morphology control of mesoporous silica nanoparticles would lead to a new generation of nanodevices with tunable biocompatibility and cell membrane trafficking properties for many biomedical applications.

Biocatalysis as a discovery tool: from nanoscale to high-throughput and beyond

Differentiating the chemical properties of the external and pore surfaces of sol-gel derived mesoporous materials by selective functionalization is important to advancing their application as platforms for biological catalysis, sensing and drug delivery. Prior selective functionalization approaches to concentrating functional groups at the external surface of particles have been limited to small pores (≤5.5 nm diameter) incapable of loading large biological molecules. This work investigates the selective exterior surface functionalization by amines of larger-pored (>7 nm diameter) mesoporous silica particles, which are synthesized by dual surfactant templating and hydrothermal aging. Previously developed selective functionalization techniques rely on choice of functionalization precursor, functionalization reaction time, or pore blocking (by leaving pore templates in as-synthesized materials). The effectiveness of these strategies are compared for larger-pored materials using the precursors (3-aminopropyl)tris(methoxyethoxyethoxy)silane (APTMEES) and (3-aminopropyl)triethoxysilane (APTES). The extent of amine functionalization is determined as a function of precursor reaction time (10 or 20 min) in both as-synthesized and template-extracted materials by confocal laser scanning microscopy of the ∼10 μm diameter particles tagged with fluorescein isothiocyanate. Reaction time, regardless of pore template presence, is demonstrated to be the controlling variable for achieving selective exterior functionalization in these larger pored mesoporous materials. Under the conditions used, 10 min of functionalization with APTMEES localizes amine groups at the exterior of the particles, while 20 min functionalizes both the exterior and the interior pore surfaces. Protein accessibility within pores, before and after selective and full functionalization, is visually confirmed by confocal fluorescence imaging of Rhodamine B tagged lysozyme loaded particles.

Transfer of apatite coating from porogens to scaffolds: Uniform apatite coating within porous poly(DL‐lactic‐co‐glycolic acid) scaffold in vitro

Strategies to bone tissue engineering have focused on the use of synthetic or natural degradable materials as scaffolds for cell transplantation to guide bone regeneration. Biocompatibility, biodegradability, biomechanical integrity, and osteoconductivity are important requirements for the scaffold materials. This study explored a new approach of apatite coating to enhance the osteoconductivity of a synthetic degradable poly(DL-lactic-co-glycolic acid) (PLGA) scaffold. The new approach was developed to ensure a relatively uniform apatite coating on the interior pore surfaces deep inside a scaffold, even for a relatively thick scaffold with small pores. Apatite was first coated on the surface of paraffin spheres of the desirable sizes. The paraffin spheres were then molded to form a foam. PLGA/pyridine solution was cast into the interspaces among the paraffin spheres. After the paraffin spheres were dissolved and removed by cyclohexane, PLGA scaffold with controlled pore size, good interconnectivity and high porosity was obtained with apatite left on the pore surface uniformly throughout the whole scaffold. The scaffold and apatite coating were characterized using thermogravimetry analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffractometry.