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• 1.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Quantifying apatite formation and cation leaching from mesoporous bioactive glasses in vitro: a SEM, solid-state NMR and powder XRD study2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 15, p. 7214-7223Article in journal (Refereed)

By employing solid-state nuclear magnetic resonance (NMR) spectroscopy, powder X-ray diffraction (PXRD), and scanning electron microscopy coupled with energy-dispersive X-ray (EDX) spectroscopy, we compare the biomimetic growth of calcium hydroxyapatite (HA) from an ordered mesoporous bioactive glass (MBG) in simulated body fluid (SBF) and buffered water solutions. For the latter medium, we also examine the effects of using two different MBG concentrations. We evaluate the predicting powers of PXRD and P-31 NMR for directly quantifying the relative amounts of biomimetic amorphous calcium phosphate (ACP) and HA: we observe a very good agreement between the two analytical techniques. Thanks to their mesoporous channel system, fluids readily penetrate throughout sub-mm sized MBG grains, as evidenced by EDX. The latter revealed distinct element-mappings across the material after its exposure to SBF compared to water. Under our in vitro conditions involving relatively high MBG-loadings in the solutions, the HA formation reduces in SBF relative to buffered water, particularly for increasing MBG concentration. These features stem from a high [Ca2+]/[PO43-] ratio resulting in the fluid medium, which retards the HA crystallization by inducing a rapid ACP precipitation and an accompanying depletion of phosphate ions in the solution. This has bearings on the design of bioactivity comparisons of bioglasses exhibiting significantly different cation compositions.

• 2.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Local structures of mesoporous bioactive glasses and their surface alterations in vitro: inferences from solid-state nuclear magnetic resonance2012In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 370, no 1963, p. 1376-1399Article in journal (Refereed)

We review the benefits of using Si-29 and H-1 magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy for probing the local structures of both bulk and surface portions of mesoporous bioactive glasses (MBGs) of the CaO-SiO2-(P2O5) system. These mesoporous materials exhibit an ordered pore arrangement, and are promising candidates for improved bone and tooth implants. We discuss experimental MAS NMR results from three MBGs displaying different Ca, Si and P contents: the Si-29 NMR spectra were recorded either directly by employing radio-frequency pulses to Si-29, or by magnetization transfers from neighbouring protons using cross polarization, thereby providing quantitative information about the silicate speciation present in the pore wall and at the MBG surface, respectively. The surface modifications were monitored for the three MBGs during their immersion in a simulated body fluid (SBF) for intervals between 30 min and one week. The results were formulated as a reaction sequence describing the interconversions between the distinct silicate species. We generally observed a depletion of Ca2+ ions at the MBG surface, and a minor condensation of the silicate-surface network over one week of SBF soaking.

• 3.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Composition-Structure Correlations of Bioactive Glasses Explored by Multinuclear Solid-state NMR Spectroscopy2015Doctoral thesis, comprehensive summary (Other academic)

This PhD thesis presents a study of structure-composition correlations of bioactive glasses (BGs) by employing solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.

Silicate-based Na2O−CaO−SiO2−P2O5 BGs are utilized clinically and are extensively investigated for bone regeneration purposes. Once implanted in the human body, they facilitate bone regeneration by partially dissolving in the body fluids, followed by the formation of a biomimetic surface-layer of calcium hydroxy-carbonate apatite (HCA). Eventually, the implanted BG totally integrates with the bone. The bioactivity of melt-prepared BGs depends on their composition and structure, primarily on the phosphorus content and the average silicate-network connectivity (NC). We explored these composition-structure relationships for a set of BGs for which the NC and phosphorus contents were varied independently.

The short-range structural features of the glasses were explored using 29Si and 31P magic-angle-spinning (MAS) NMR spectroscopy. 31P MAS NMR revealed that the orthophosphate content is directly proportional to the total P content of the glass, with a linear correlation observed between the orthophosphate content and the silicate network connectivity. The bearings of the results for future BG design are discussed.

By using multiple-quantum coherence-based 31P NMR experiments, the spatial distribution of orthophosphate groups was probed in the melt prepared BGs, as well as in two mesoporous bioactive glasses prepared by an evaporation-induced self-assembly technique. The results evidence randomly distributed orthophosphate groups in the melt-prepared BGs, whereas the pore-walls of the mesoporous bioactive glasses constitute nanometer-sized clusters of calcium phosphate. The distribution of Na+ ions among the phosphate/silicate groups were studied by heteronuclear dipolar-based 23Na−31P NMR experiments, verifying that sodium is dispersed nearly randomly in the glasses.

The phosphorus and proton environments in biomimetically grown HCA were investigated by using 1H and 31P MAS NMR experiments. Our studies revealed that the biomimetic HCA shared many local structural features with synthetic and well-ordered hydroxy-apatite.

• 4.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Solid-State (31)P and (1)H NMR Investigations of Amorphous and Crystalline Calcium Phosphates Grown Biomimetically From a Mesoporous Bioactive Glass2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 42, p. 20572-20582Article in journal (Refereed)

By exploiting (1)H and (31)P magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, we explore the proton and orthophosphate environments in biomimetic amorphous calcium phosphate (ACP) and hydroxyapatite (HA), as grown in vitro at the surface of a 10CaO-85SiO(2)-5P(2)O(5) mesoporous bioactive glass (MBG) in either a simulated body fluid or buffered water. Transmission electron microscopy confirmed the presence of a calcium phosphate layer comprising nanocrystalline HA Two-dimensional (1)H-(31)P heteronudear correlation NMR established predominantly (1)H(2)O <->(31)PO(4)(3-) and O(1)H <->(31)PO(4)(3-) contacts in the amorphous and crystalline component, respectively, of the MBG surface-layer; these two pairs exhibit distinctly different (1)H <->(31)P cross-polarization dynamics, revealing a twice as large squared effective (1)H-(31)P dipolar coupling constant in ACP compared with HA. These respective observations are mirrored in synthetic (well-crystalline) HA, and the amorphous calcium orthophosphate (CaP) clusters that are present in the pristine MBG pore walls: besides highlighting very similar local (1)H and (31)P environments in synthetic and biomimetic HA, our findings evidence closely related NMR characteristics, and thereby similar local structures, of the CaP clusters in the pristine MBG relative to biomimetic ACP.

• 5.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Na/Ca Intermixing around Silicate and Phosphate Groups in Bioactive Phosphosilicate Glasses Revealed by Heteronuclear Solid-State NMR and Molecular Dynamics Simulations2015In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 119, no 17, p. 5701-5715Article in journal (Refereed)

We characterize the intermixing of network-modifying Na+/Ca2+ ions around the silicate (QSin) and phosphate (QPn) tetrahedra in a series of 16 Na2O–CaO–SiO2–P2O5 glasses, whose P content and silicate network connectivity were varied independently. The set includes both bioactive and bioinactive compositions and also encompasses two soda-lime-silicate members devoid of P, as well as two CaO–SiO2 glasses and one Na2O–SiO2–P2O5 glass. The various Si/P↔Na/Ca contacts were probed by molecular dynamics (MD) simulations together with heteronuclear magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) experimentation utilizing 23Na{31P} and 23Na{29Si} REDOR, as well as 31P{ 23Na} and 29Si{23Na} REAPDOR. We introduce an approach for quantifying the extent of Na+/Ca2+ ordering around a given QPn or QSin group, encoded by the preference factor 0⩽ PM ⩽ 1 conveying the relative weights of a random cation intermixing (PM = 0) and complete preference/ordering (PM = 1) for one of the species M, which represents either Na+ or Ca2+. The MD-derived preference factors reveal phosphate and silicate species surrounded by Na+/Ca2+ ions intermixed nearly randomly (PM ≲ 0.15), except for the QSi4 and QSi1 groups, which manifest more significant cation ordering with preference for Na+ and Ca2+, respectively. The overall weak preferences are essentially independent of the Si and P contents of the glass, whereas PM primarily correlates with the total amount of network modifiers: as the latter is increased, the Na/Ca distribution around the {QP0, QSi1, QSi2} groups with preference for Ca2+ tend to randomize (i.e., PCa decreases), while the PNa-values grow slightly for the {QP1, QSi3, QSi4} species already preferring coordination of Na. The set of experimental preference factors {PCa} for the orthophosphate (QP0) groups extracted from 31P{23Na} REAPDOR NMR-derived M2(P–Na) dipolar second moments agrees well with the MD-generated counterparts. Our results on the Na/Ca intermixing in soda-lime-silicate glasses are discussed in relation to previous reports, highlighting the dependence of the conclusion on the approach to data evaluation.

• 6.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Toward a Rational Design of Bioactive Glasses with Optimal Structural Features: Composition-Structure Correlations Unveiled by Solid-State NMR and MD Simulations2014In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 3, p. 833-844Article in journal (Refereed)

The physiological responses of silicate-based bioactive glasses (BGs) are known to depend critically on both the P content (np) of the glass and its silicate network connectivity ((N) over bar (SI)(BO)). However, while the bioactivity generally displays a nonmonotonic dependence on np itself, recent work suggest that it is merely the net orthophosphate content that directly links to the bioactivity. We exploit molecular dynamics (MD) simulations combined with P-31 and Si-29 solid-state nuclear magnetic resonance (NMR) spectroscopy to explore the quantitative relationships between (N) over bar (SI)(BO), npand the silicate and phosphate speciations in a series of Na2O-CaO-SiO2-P2O5 glasses spanning 2.1 <=(N) over bar (SI)(BO) <= 2.9 and variable P2O5 contents up to 6.0 mol %. The fractional population of the orthophosphate groups remains independent of np at a fixed (N) over bar (SI)(BO)-value, but is reduced slightly as (N) over bar (SI)(BO) increases. Nevertheless, P remains predominantly as readily released orthophosphate ions, whose content may be altered essentially independently of the network connectivity, thereby offering a route to optimize the glass bioactivity. We discuss the observed composition-structure links in relation to known composition-bioactivity correlations, and define how Na2O-CaO-SiO2-P2O5 compositions exhibiting an optimal bioactivity can be designed by simultaneously altering three key parameters: the silicate network connectivity, the (ortho)phosphate content, and the n(Na)/n(ca) molar ratio.

• 7.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Direct Probing of the Phosphate-Ion Distribution in Bioactive Silicate Glasses by Solid-State NMR: Evidence for Transitions between Random/Clustered Scenarios2013In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 25, no 9, p. 1877-1885Article in journal (Refereed)

By employing P-31 multiple-quantum coherence-based solid-state nuclear magnetic resonance spectroscopy, we present the first comprehensive experimental assessment of the nature of the orthophosphate ion distributions in silicate based bioactive glasses (BGs). Results are provided both from melt prepared BG and evaporation-induced self-assembly-derived mesoporous bioactive glass (MEBG) structures of distinct compositions. The phosphate species are randomly dispersed in melt-derived BGs (comprising 44-55 mol % SiO2) of the Na2O-CaO-SiO2-P2O5 system, whereas a Si-rich (86 mol % SiO2) and Ca-poor ordered MBG structure exhibits nanometer-sized amorphous calcium phosphate clusters, conservatively estimated to comprise at least nine orthophosphate groups. A Ca-richer MBG (58 mol % SiO2) reveals a less pronounced phosphate clustering. We rationalize the variable structural role of P in these amorphous biomatetials.

• 8.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Multicolor Fluorescent Labeling of Cellulose Nanofibrils by Click Chemistry2015In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 4, p. 1293-1300Article in journal (Refereed)

We have chemically modified cellulose nanofibrils (CNF) with furan and maleimide groups, and selectively labeled the modified CNF with fluorescent probes; 7-mercapto-4-methylcoumarin and fluorescein diacetate 5-maleimide, through two specific click chemistry reactions: Diels-Alder cycloaddition and the thiol-Michael reaction. Characterization by solid-state C-13 NMR and infrared spectroscopy was used to follow the surface modification and estimate the substitution degrees. We demonstrate that the two luminescent dyes could be selectively labeled onto CNF, yielding a multicolor CNF that was characterized by UV/visible and fluorescence spectroscopies. It was demonstrated that the multicolor CNF could be imaged using a confocal laser scanning microscope.

• 9.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Investigation of chloromethane complexes of cryptophane-A analogue with butoxy groups using C-13 NMR in the solid state and solution along with single crystal X-ray diffraction2015In: Magnetic Resonance in Chemistry, ISSN 0749-1581, E-ISSN 1097-458X, Vol. 53, no 8, p. 596-602Article in journal (Refereed)

Host-guest complexes between cryptophane-A analogue with butoxy groups (cryptophane-But) and chloromethanes (chloroform, dichloromethane) were investigated in the solid state by means of magic-angle spinning C-13 NMR spectroscopy. The separated local fields method with C-13-H-1 dipolar recoupling was used to determine the residual dipolar coupling for the guest molecules encaged in the host cavity. In the case of chloroform guest, the residual dipolar interaction was estimated to be about 19kHz, consistent with a strongly restricted mobility of the guest in the cavity, while no residual interaction was observed for encaged dichloromethane. In order to rationalize this unexpected result, we performed single crystal X-ray diffraction studies, which confirmed that both guest molecules indeed were present inside the cryptophane cavity, with a certain level of disorder. To improve the insight in the dynamics, we performed a C-13 NMR spin-lattice relaxation study for the dichloromethane guest in solution. The system was characterized by chemical exchange, which was slow on the chemical shift time scale but fast with respect to the relaxation rates. Despite these disadvantageous conditions, we demonstrated that the data could be analyzed and that the results were consistent with an isotropic reorientation of dichloromethane within the cryptophane cavity.

• 10.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry. Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
Assessing the Phosphate Distribution in Bioactive Phosphosilicate Glasses by P-31 Solid-State NMR and Molecular Dynamics Simulations2014In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 29, p. 8863-8876Article in journal (Refereed)

Melt-derived bioactive phosphosilicate glasses are widely utilized as bone-grafting materials for various surgical applications. However, the insight into their structural features over a medium-range scale up to similar to 1 nm remains limited. We present a comprehensive assessment of the spatial distribution of phosphate groups across the structures of 11 Na2O-CaO-SiO2-P2O5 glasses that encompass both bioactive and nonbioactive compositions, with the P contents and silicate network connectivities varied independently. Both parameters are known to strongly influence the bioactivity of the glass in vitro. The phosphate distribution was investigated by double-quantum 3113 nuclear magnetic resonance (NMR) experiments under magic-angle spinning (MAS) conditions and by molecular dynamics (MD) simulations. The details of the phosphate-ion dispersion were probed by evaluating the MD-derived glass models against various scenarios of randomly distributed, as well as clustered, phosphate groups. From comparisons of the P-P interatomic-distance spreads and the statistics of small phosphate clusters assessed for variable cutoff radii, we conclude that the spatial arrangement of the P atoms in phosphosilicate glasses is well-approximated by a statistical distribution, particularly across a short-range scale of <= 450 pm. The primary distinction is reflected in slightly closer P-P interatomic contacts in the MD-derived structures over the distance span of 450-600 pm relative to that of randomly distributed phosphate groups. The nature of the phosphate-ion dispersion remains independent of the silicate network polymerization and nearly independent of the P content of the glass throughout our explored parameter space of 1-6 mol % P2O5 and silicate network connectivities up to 2.9.

• 11.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Two heteronuclear dipolar results at the price of one: Quantifying Na/P contacts in phosphosilicate glasses and biomimetic hydroxy-apatite2015In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 251, p. 52-56Article in journal (Refereed)

The analysis of S{I} recoupling experiments applied to amorphous solids yields a heteronuclear second moment M-2(S-I) that represents the effective through-space dipolar interaction between the detected S spins and the neighboring I-spin species. We show that both M-2(S-I) and M-2(I-S) values are readily accessible from a sole S{I} or I{S} experiment, which may involve either S or I detection, and is naturally selected as the most favorable option under the given experimental conditions. For the common case where I has half-integer spin, an I{S} REDOR implementation is preferred to the S{I} REAPDOR counterpart. We verify the procedure by Na-23{P-31} REDOR and P-31{Na-23} REAPDOR NMR applied to Na2O-CaO-SiO2-P2O5 glasses and biomimetic hydroxyapatite, where the M-2(P-Na) values directly determined by REAPDOR agree very well with those derived from the corresponding M-2(Na-P) results measured by REDOR. Moreover, we show that dipolar second moments are readily extracted from the REAPDOR NMR protocol by a straightforward numerical fitting of the initial dephasing data, in direct analogy with the well-established procedure to determine M-2(S-I) values from REDOR NMR experiments applied to amorphous materials; this avoids the problems with time-consuming numerically exact simulations whose accuracy is limited for describing the dynamics of a priori unknown multi-spin systems in disordered structures.

• 12.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Quantitative composition–bioactivity relationships of phosphosilicate glasses: Bearings from the phosphorus content and network polymerization2018In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 502, p. 106-117Article in journal (Refereed)

Bioactive phosphosilicate glasses integrate with bone/tooth tissues by forming a bone-mineral mimicking surface layer of calcium hydroxyapatite (HA). The HA formation (“in vitrobioactivity”) in a simulated body fluid (SBF) solution is known to depend both on the P content (nP) and silicate network connectivity ($\bar{N}_{\text{BO}}^{\text{Si}}$) of the glass, but the precise bioactivity–composition relationships remain poorly understood. We present a comprehensive study that clarifies the dependence of the in vitro bioactivity on the {nP, $\bar{N}_{\text{BO}}^{\text{Si}}$} parameters for Na2O–CaO–SiO2–P2O5 glass powders (2.6–6.0 mol% P2O5) exposed to SBF for 24 h, using infrared (IR) and solid-state 31P nuclear magnetic resonance (NMR) spectroscopy in conjunction with measured Ca and P concentrations in the solution. IR-derived relative apatite amounts reveal that an increase in the P content of the pristine glass promotes apatite formation by gradually reducing its dependence on the silicate network polymerization: increasing nP widens the $\bar{N}_{\text{BO}}^{\text{Si}}$ range that provides a high and nearly constant amount of HA, which scales roughly linearly with nP; these properties assist future design of P-rich bioactive glasses. All glasses provide significant HA formation for increasing $\bar{N}_{\text{BO}}^{\text{Si}}$ values up to ≈2.6, above which the in vitro bioactivity is lost due to insufficient glass dissolution. We also discuss the complex dependence of the SBF-testing outcome on the mass concentration and composition of the glass powder, as well as on its particle sizes, highlighting critical concerns that may guide developments of improved in vitro bioactivity-testing protocols. A strong dependence of the HA formation on the particle sizes is observed for glass powders with low P2O5 content (2.6 mol%), as opposed to their P-richer counterparts that reveal no pronounced particle-size effects.

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