Enhanced 3 µm luminescence properties based on effective energy transfer Yb3+ : 2F5/2→Dy3+ : 6H5/2 in fluoaluminate glass modified by TeO2.

Enhanced 3 µm luminescence of Dy3+ based on the effective process of Yb3+:F5/22→Dy3+:H5/26 with a higher energy transfer coefficient of 7.36×10-39 cm6/s in fluoaluminate glass modified by TeO2 was obtained. The energy transfer efficiency from Yb3+ to Dy3+ in Dy3+/Yb3+ codoped glass was as high as 80%, indicating the effective energy transfer of Yb3+. The higher temperature of the glass transition (Tg) and larger characteristic temperatures (ΔT,Kgl) revealed better thermal properties of the prepared glasses compared with the traditional fluoaluminate glasses, which is of great benefit to fiber drawing. The lower hydroxyl content (15.7 ppm) indicated better fluorescence properties of the glass. It was noted that the longer lifetime of 572 µs and higher emission cross section of 5.22×10-21 cm2 along with the bandwidth of 245 nm around 3 µm proved potential applications in mid-IR laser materials of the present glass.

Oxygen vacancy healing boosts the piezoelectricity of bone scaffolds.

Although barium titanate (BaTiO3) presented tremendous potential in achieving self-powered stimulation to accelerate bone repair, pervasive oxygen vacancies restricted the full play of its piezoelectric performance. Herein, BaTiO3-GO nanoparticles were synthesized by the in situ growth of BaTiO3 on graphene oxide (GO), and subsequently introduced into poly-L-lactic acid (PLLA) powders to prepare PLLA/BaTiO3-GO scaffolds by laser additive manufacturing. During the synthesis process, CO and C-OH in GO would respectively undergo cleavage and dehydrogenation at high temperature to form negatively charged oxygen groups, which were expected to occupy positively charged oxygen vacancies in BaTiO3 and thereby inhibit the formation of oxygen vacancies. Moreover, GO could be partially reduced to reduced graphene oxide, which could act as a conductive phase to facilitate polarization charge transfer, thus further improving the piezoelectric performance. The results showed that the oxygen peak at the specific electron binding energy in O 1s declined from 54.4% to 14.6% and the Ti3+ peak that was positively correlated with oxygen vacancies apparently weakened for BaTiO3-GO, illustrating that the introduced GO significantly decreased the oxygen vacancy. As a consequence, the piezoelectric current of PLLA/BaTiO3-GO increased from 80 to 147.3 nA compared with that of PLLA/BaTiO3. The enhanced piezoelectric current effectively accelerated cell differentiation by upregulating alkaline phosphatase expression, calcium salt deposition and calcium influx. This work provides a novel insight for the design of self-powered stimulation scaffolds for bone regeneration.

A CuS@g-C3N4 heterojunction endows scaffold with synergetic antibacterial effect.

Graphitic carbon nitride (g-C3N4) had aroused tremendous attention in photodynamic antibacterial therapy due to its excellent energy band structure and appealing optical performance. Nevertheless, the superfast electron-hole recombination and dense biofilm formation abated its photodynamic antibacterial effect. To this end, a nanoheterojunction was synthesized via in-situ growing copper sulfide (CuS) on g-C3N4 (CuS@g-C3N4). On the one hand, CuS could form Fermi level difference with g-C3N4 to accelerate carrier transfer and thus facilitate electron-hole separation. On the other hand, CuS could respond near-infrared light to generate localized thermal to disrupt biofilm. Then the CuS@g-C3N4 nanoparticle was introduced into the poly-l-lactide (PLLA) scaffold. The photoelectrochemistry results demonstrated that the electron-hole separation efficiency was apparently enhanced and thereby brought an approximate sevenfold increase in reactive oxygen species (ROS) production. The thermal imaging indicated that the scaffold possesses a superior photothermal effect, which effectively eradicated the biofilm by disrupting its extracellular DNA and thereby facilitated to the entry of ROS. The entered ROS could effectively kill the bacteria by causing protein, K+, and nucleic acid leakage and glutathione consumption. As a consequence, the scaffold displayed an antibacterial rate of 97.2% and 98.5% against E. coli and S. aureus, respectively.

Photoexcited wireless electrical stimulation elevates nerve cell growth.

Electrical stimulation was restrained by an external power supply and wires, despite its ability to promote nerve cell growth. Bismuth sulfide (Bi2S3) offered a novel prospect for achieving wireless electrical stimulation due to its photoelectric effect. Herein, silver nanoparticles (Ag NPs) were in-situ grown on Bi2S3 surface (Ag/Bi2S3) and then mixed with poly-L-lactic acid (PLLA) powders to fabricate PLLA-Ag/Bi2S3 conduits. On the one hand, Bi2S3 would generate photocurrent under light excitation, forming a wireless electrical stimulation. On the other hand, Ag NPs would form localized electrical fields under light excitation to inhibit rapid electron-hole recombination of Bi2S3. Moreover, Ag NPs would act as electron mediators to accelerate electron transfer, further elevating photocurrent. Electrochemical tests and FDTD simulations revealed the localized electrical fields generated by Ag NPs acted on Bi2S3, resulting in a boosted electron-hole separation evidenced by a reduction in photoluminescence intensity. EIS measurements demonstrated a faster electron transfer occurred on Ag/Bi2S3. As a result, the photocurrent of PLLA-Ag/Bi2S3 increased from 0.26 to 1.03 µA as compared with PLLA-Bi2S3. The enhanced photocurrent effectively promoted cell differentiation by up-regulating Ca2+ influx and nerve growth-related protein SYN1 expression. This work suggested a promising countermeasure in the design of photocurrent stimulation conduits for nerve repair.

Constructing core-shell structured BaTiO3@carbon boosts piezoelectric activity and cell response of polymer scaffolds.

Piezoelectric composites have shown great potential in constructing electrical microenvironment for bone healing since their integration of polymer flexibility and ceramic piezoelectric coefficient. Herein, core-shell structured BaTiO3@carbon (BT@C) hybrid nanoparticles were prepared by in situ oxidative self-polymerization and template carbonization. Then the BT@C was introduced into polyvinylidene fluoride (PVDF) scaffolds manufactured by selective laser sintering. On one hand, the carbon shell could strengthen the local electric field loaded on BT in poling process owing to it served as a diffusion layer to provide space for charge transfer and accumulation. In this case, more electric domain within BT would be aligned along the polarization field direction and thus promoted the paly of BT's piezoelectric activity. On the other hand, the carbon shell could induce the formation of ß phase due to the sp2 hybrid-bonded carbon atoms in carbon shell forming electrostatic interaction with hydrogen atoms in PVDF chains, which further enhanced the piezoelectric response of the scaffolds. Results showed that the scaffold presented augmented piezoelectric performance with output voltage of 5.7 V and current of 79.8 nA. The improved electrical signals effectively accelerated cell proliferation and differentiation. Furthermore, the scaffold displayed improved mechanical performance due to rigid particle strengthen effect.

Microstructure evolution and texture tailoring of reduced graphene oxide reinforced Zn scaffold.

Zinc (Zn) possesses desirable degradability and favorable biocompatibility, thus being recognized as a promising bone implant material. Nevertheless, the insufficient mechanical performance limits its further clinical application. In this study, reduced graphene oxide (RGO) was used as reinforcement in Zn scaffold fabricated via laser additive manufacturing. Results showed that the homogeneously dispersed RGO simultaneously enhanced the strength and ductility of Zn scaffold. On one hand, the enhanced strength was ascribed to (i) the grain refinement caused by the pinning effect of RGO, (ii) the efficient load shift due to the huge specific surface area of RGO and the favorable interface bonding between RGO and Zn matrix, and (iii) the Orowan strengthening by the homogeneously distributed RGO. On the other hand, the improved ductility was owing to the RGO-induced random orientation of grain with texture index reducing from 20.5 to 7.3, which activated more slip systems and provided more space to accommodate dislocation. Furthermore, the cell test confirmed that RGO promoted cell growth and differentiation. This study demonstrated the great potential of RGO in tailoring the mechanical performance and cell behavior of Zn scaffold for bone repair.

Graphene-assisted barium titanate improves piezoelectric performance of biopolymer scaffold.

Biopolymer scaffold is expected to generate electrical stimulation, aiming to mimic an electrical microenvironment to promote cell growth. In this work, graphene and barium titanate (BT) was introduced into selective laser sintered poly-l-lactic acid (PLLA) scaffold. BT as one piezoelectric ceramic was used as the piezoelectric source, whereas graphene served as superior conductive filler. Significantly, the incorporated graphene enhanced the electrical conductivity and thereby increased the electric field strength applied on BT nanoparticles during poling. In this case, more electric domain within BT rearranged along the poling field direction, thus promoting the piezoelectric response of the composites. Results showed that the PLLA/BT/graphene scaffold exhibited relatively high output voltage of 1.4 V and current of 10 nA. Cells tests proved that these electrical signals considerably promoted cell proliferation and differentiation. Moreover, the scaffold exhibited improved mechanical properties due to the rigid particle enhancement effect and increased crystallinity.

Electrostatic self-assembly of pFe3O4 nanoparticles on graphene oxide: A co-dispersed nanosystem reinforces PLLA scaffolds.

Cell responses and mechanical properties are vital for scaffold in bone regeneration. Fe3O4 nanoparticles with excellent magnetism can provide magnetic stimulation for cell growth, while graphene oxide (GO) nanosheets are commonly used as reinforcement phases due to their high strength. However, Fe3O4 or GO is tended to agglomerate in matrix. In present study, a novel co-dispersed Fe3O4-GO nanosystem was constructed through electrostatic self-assembly of positively charged Fe3O4 (pFe3O4) on negatively charged GO nanosheets. In the nanosystem, pFe3O4 nanoparticles and GO nanosheets support each other, which effectively alleviates the π-π stacking between GO nanosheets and magnetic attraction between pFe3O4 nanoparticles. Subsequently, the nanosystem was incorporated into poly L-lactic acid (PLLA) scaffolds fabricated using selective laser sintering. The results confirmed that the pFe3O4-GO nanosystem exhibited a synergistic enhancement effect on stimulating cell responses by integrating the capturing effect of GO and the magnetic simulation effect of pFe3O4. The activity, proliferation and differentiation of cells grown on scaffolds were significantly enhanced. Moreover, the nanosystem also exhibited a synergistic enhancement effect on mechanical properties of scaffolds, since the pFe3O4 loaded on GO improved the efficiency of stress transfer in matrix. The tensile stress and compressive strength of scaffolds were increased by 67.1% and 132%, respectively. In addition, the nanosystem improved the degradation capability and hydrophilicity of scaffolds.

Functionalized BaTiO3 enhances piezoelectric effect towards cell response of bone scaffold.

Piezoelectric effect of polyvinylidene fluoride (PVDF) plays a crucial role in restoring the endogenous electrical microenvironment of bone tissue, whereas more ß phase in PVDF leads to higher piezoelectric performance. Nanoparticles can induce the nucleation of the ß phase. However, they are prone to aggregate in PVDF matrix, resulting in weakened nucleation ability of ß phase. In this work, the hydroxylated BaTiO3 nanoparticles were functionalized with polydopamine to promote their dispersion in PVDF scaffolds fabricated via selective laser sintering. On one hand, the catechol groups of polydopamine could form hydrogen bonding with the hydroxyl groups of the BaTiO3. On the other hand, the amino groups of polydopamine were able to bond with CF group of PVDF. As a result, the functionalized BaTiO3 nanoparticles homogeneously distributed in PVDF matrix, which significantly increased the ß phase fraction from 46% to 59% with an enhanced output voltage by 356%. Cell testing confirmed the enhanced surface electric cues significantly promoted cell adhesion, proliferation and differentiation. Furthermore, the scaffolds exhibited enhanced tensile strength and modulus, which was ascribed to the rigid particle strengthening effect and the improved interfacial adhesion. This study suggested that the piezoelectric scaffolds shown a potential application in bone repair.

Surface modification enhances interfacial bonding in PLLA/MgO bone scaffold.

The poor interfacial bonding and resultant agglomeration of nanoparticles in polymer-based composite severely deteriorated their reinforcement effect. In this work, MgO nanoparticles (MgO-NPs) were surface modified with Poly (L-lactic acid-co-malic acid) (PLMA) to improve the interfacial compatibility in Poly-l-lactic acid (PLLA) scaffold manufactured by selective laser sintering. PLMA possess a hydrophilic end with carboxyl group (comes from the malic acid) and an l-lactic acid chain. On one hand, the carboxyl group was able to form hydrogen bonding with the hydroxyl groups of MgO-NPs. On the other hand, the l-lactic acid chain containing the hydroxyl groups could react with the carboxyl group of PLLA. Results revealed that the scaffold exhibited significantly enhanced compressive strength and modulus by 47.1% and 237.7%, respectively, which could be ascribed to the enhanced interfacial bonding between PLLA and MgO-NPs, as well as the rigid particle reinforcement. In addition, the scaffold was favorable for cell adhesion, proliferation and differentiation, owing to the improved hydrophilic and suitable pH environment. It was suggested the scaffold was a promising material for bone repair application.