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Black phosphorous (BP) is recognized as an effective reinforcement for polymer scaffold because of its excellent mechanical property and biocompatibility. Nevertheless, its poor stability in physiological environment limits its application in bone repair. In this work, BP was modified with dopamine by self-polymerization approach (donated as BP@PDA) to improve its stability, and then was introduced into poly-L-lactic acid (PLLA) scaffold fabricated by selective laser sintering technology. Results showed the compressive and tensile strength of PLLA/BP@PDA scaffold were improved by 105% and 50%, respectively. The enhanced strength was ascribed to the increased stability of BP and the improved compatibility of BP@PDA with PLLA matrix after modifying with polydopamine. Simultaneously, the bioactivity of PLLA scaffold was significantly improved. It was attributed to that BP@PDA provided the sustained source of PO43- ions which could capture Ca2+ ions from physiological medium to facilitate in situ biomineralization, thereby promoting cell adhesion, proliferation and differentiation. This study demonstrated the great potential of BP@PDA in bone repair.

Poly-L-lactic acid (PLLA) lacks osteogenic activity, which limits its application in bone repair. Zinc (Zn) is widely applied to strengthen the biological properties of polymers due to its excellent osteogenic activity. In the present study, Zn-doped mesoporous silica (Zn-MS) particles were synthesized by one-pot hydrothermal method. Then, the particles were induced into PLLA scaffolds prepared by selective laser sintering technique, aiming to improve their osteogenic activity. Our results showed that the synthesized particles possessed rosette-like morphology and uniform mesoporous structure, and the composite scaffold displayed the sustained release of Zn ion in a low concentration range, which was attributed to the shield effect of the PLLA matrix and the strong bonding interaction of Si-O-Zn. The scaffold could evidently promote osteogenesisdifferentiation of mouse bone marrow mesenchymal stem cells by upregulating their osteogenesis-related gene expression. Besides, Zn-MS particles could significantly increase the compressive strength of the PLLA scaffold because of their rosettelike morphology and mesoporous structure, which can form micromechanical interlocking with the PLLA matrix. The Zn-MS particles possess great potential to improve various polymer scaffold properties due to their advantageous morphology andphysicochemical properties.

Polyvinylidene fluoride (PVDF), as a typical piezoelectric polymer, has a great potential in reconstructing the electrical microenvironment of bone tissue. In present study, graphene oxide (GO) was introduced into PVDF scaffold manufactured via selective laser sintering, aiming to enhance piezoelectric effect of PVDF by increasing β phase content. In detail, the oxygen-containing functional groups of GO could form strong hydrogen bonding with fluorine groups of PVDF. The interaction would force the fluorine groups to be arranged in parallel and perpendicular to the polymer chain, thereby inducing the transformation from α phase to β phase. Results demonstrated that the PVDF/0.3GO scaffold with improved β phase exhibited the maximal output voltage (~8.2 V) and current (~101.6 nA), which were improved by 82.2% and 68.2%, respectively, in comparison with pure PVDF. In vitro cell culture confirmed that enhanced electrical charges could significantly improve cell behavior. Moreover, the scaffold presented a 97.9% increase in compressive strength and 24.5% increase in tensile strength, which was attributed to GO reinforcements forming strong interaction with PVDF chains. These positive results suggested that the scaffold might have possible application in bone tissue engineering. Keywords: Bone regeneration, Piezoelectric, Polyvinylidene fluoride, Graphene oxide, Selective laser sintering

Reduced graphene oxide (RGO) shows great advantages as nano reinforcement for zinc (Zn) based implants owing to its excellent fracture strength, large specific surface area and good biocompatibility. Nevertheless, the poor interfacial bonding between Zn matrix and RGO impairs the strengthening efficiency. In this work, titanium carbide (TiC) was used as an interface bridging between Zn matrix and RGO to improve the interface adhesion. On one hand, TiC was in-situ generated on RGO plane through chemical vapor deposition, and tightly integrated together via chemical bond. On the other hand, a semi-coherent bonding was formed between TiC and Zn matrix, owing to the small lattice misfit and similar atomic arrangement between the (200)Zn plane and (002)TiC plane. Results showed that TiC@RGO offered an improved strengthening efficiency with tensile strength of scaffolds increasing from 30.6 to 59.9 MPa, as the TiC nanoparticles considerably enhanced the load transfer strengthening of RGO and contributed an Orowan strengthening. Significantly, it also improved the plasticity of Zn scaffolds, since the semi-coherent structure inhibited the premature stress concentration and dislocation accumulation. Moreover, TiC@RGO promoted the cell differentiation behavior of Zn scaffolds.

Implant-related bacterial infection is a serious complication, which even causes implant failure. Silver (Ag) nanoparticles are broadly used antibacterial agents due to their excellent antibacterial ability and broad-spectrum bactericidal property. However, the significance of burst release cannot be entirely ignored. In this study, Ag doped mesoporous bioactive glasses (Ag-MBG) nanospheres were synthesized using modified Stober method, then incorporated into poly L-lactic acid (PLLA) matrix to prepare the composite scaffolds via selective laser sintering (SLS) technology. Herein, Mesoporous bioactive glasses (MBG) sol had many negatively-charged silicon hydroxyl groups, which could adsorb positively-charged Ag ions by electrostatic interaction and eventually form Si-O-Ag bonds into MBG. Moreover, MBG promoted osteoblast colonization due to its continuous release of Si ions. The results showed the Ag-MBG/PLLA scaffold could sustainedly release Ag ions for 28 days, and exhibited significantly antibacterial ability against Escherichia coli, its bacterial inhibition rate was over 80%. In addition, the composite scaffold also showed good cytocompatibility. It may be concluded that the prepared Ag-MBG/PLLA scaffold has great potential to repair implant-associated bone infection.

Ceramic-metal composite materials, namely cermets, are provided with characteristics of both ceramic and metal. Herein, for the first time bio-cermets based on β-tricalcium phosphate (β-TCP) bioceramic with biodegradable iron being reinforcement phase, were fabricated using the powder metallurgic method. The phase composition, microstructure, mechanical properties and in vitro cell behaviors of bio-cermets were investigated. The results revealed that atomic diffusion occurred between the iron and β-TCP matrix during the sintering process. The bio-cermets attained remarkable increase in fracture toughness (1.16–1.55 MPa m1/2) compared to the β-TCP bioceramic (0.54 MPa m1/2). The bio-cermets with 10 vol% iron showed the highest compressive strength (640 MPa), significantly higher than that of plain β-TCP bioceramic (285 MPa). The in vitro cell behaviors test indicated that the bio-cermets did not showed any sign of toxicity; the iron ions released from bio-cermets up-regulated bone-related gene expression of bone mesenchymal stem cells. The bio-cermets developed in this study represent potential bone substitutes for application in the load-bearing bone defects.

Graphene oxide (GO) usually serves as a reinforce phase in polymer because of its superior mechanical strength and high specific surface area. In this work, GO was grafted with L-lactic acid monomer (denoted as GO@PLLA) to overcome the aggregation in matrix and then incorporated into the poly-L-lactic acid (PLLA) scaffold fabricated by selective laser sintering. In hybrid scaffold, GO@PLLA exhibited uniform dispersion in the matrix. Furthermore, mechanical interlock between GO@PLLA and PLLA matrix formed and reinforced the interface bonding. On the other hand, the heterogeneous distributed GO acted as effective nucleating agent and resultantly enhanced the crystallization. Results showed that the tensile and compressive strength of scaffolds increased by 143.3% and 127.6%, respectively. Meanwhile, the scaffold exhibited an increased degradation rate of 37.9%, which could be attributed to the abundant hydrophilic functional groups on GO. Moreover, the scaffold exhibited favorable bioactivity and biocompatibility. Herein, the developed hybrid scaffold showed potential capacity for bone tissue engineering.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has a great potential in bone repair, but unfortunately, the poor mechanical properties limit its further application. In this work, zinc oxide (ZnO) nanoparticles were incorporated into PHBV porous scaffold fabricated by selective laser sintering technique. It was because ZnO nanoparticles could provide nucleating sites for the orderly stacking of polymer chains, thereby enhancing the crystallinity of PHBV. It was well known that the mechanical properties of PHBV scaffold could be enhanced with the increase of crystallinity. More significantly, the released Zn2+ would combine negatively charged cell membranes of bacterial through electrostatic interaction and consequently destructed the protein structure and resulted in the death of bacterial, which was highly desired in reducing the risk of implant infection. Results indicated that the relative crystallinity of scaffold with 3 wt.% ZnO increased remarkably from 38% to 64% compared to pure PHBV scaffold, which effectively enhanced the compression strength and modulus by 56% and 51.5%, respectively. Moreover, the scaffold had a favorable antibacterial activity. Cell culture experiments proved that the scaffold could promote the cell behaviors. The positive results demonstrated the scaffold may serve as a potential replacement in bone repair.

Fe has attracted great attention as biodegradable bone implant. Unfortunately, its degradation rate is too slow for bone repair. It is well known that the lower the electrode potential is, the faster the metals degrade. In the case of dissolving low electrode potential species (Mg for instance) into Fe lattice, the corrosion potential of the matrix can be negatively shifted and the overall degradation rate can be accelerated. However, Fe and Mg are immiscible in equilibrium due to their large differences in melting and boiling temperature. In this study, a supersaturated Fe–Mg solid solution was developed in solid-state by mechanical alloying (MA). In detail, Fe particles experienced cycled mechanical impact and friction during MA, which produced a large number of dislocations and defects. In this condition, Mg atoms were forcibly diffused into Fe lattice along with the motion of dislocations and defects. The results showed that about 8.5 at.% Mg was dissolved in Fe (0.02 at.% in equilibrium). Subsequently, the MA powders were fabricated into bone implants by selective laser melting (SLM), in which the fast laser scanning speed resulted in a rapid cooling rate. The molten liquid passed the immiscible zone quickly, thereby avoiding the separation of Mg solute. SLMed implants exhibited a lowered electrode potential (−0.93 V) comparing with Fe. Additionally, the implants also had good cytocompatibility and promoted cell proliferation.

Poly l-lactic acid (PLLA) was limited in the further orthopaedic application due to its insufficient mechanical property and poor bioactivity. Graphene oxide (GO) is an effective reinforcement, whereas silicon-doped hydroxyapatite (Si-HA) possesses excellent bioactivity, but either GO or Si-HA tends to aggregate in PLLA matrix. In this study, a GO@Si-HA nanosystem was achieved by in-situ growth of Si-HA on GO, and then incorporated into PLLA scaffold fabricated by laser sintering technology. On one hand, Si-HA on the surface of GO effectively prevented the aggregation of GO by acting as a barrier between GO nanosheets. On the other hand, GO hindered the aggregation of Si-HA by means of anchoring Si-HA. Results displayed that the compressive strength and modulus of the PLLA/GO@Si-HA composite scaffold were enhanced by 85% and 120%, respectively. Meanwhile, the scaffold exhibited significantly improved bioactivity, and consequently promoted cell adhesion, proliferation and differentiation. The developed PLLA/GO@Si-HA composite scaffold with excellent mechanical properties and superior bioactivity could serve as a promising substitute for bone repairing.

Polyvinylidene fluoride (PVDF)/barium titanate (BaTiO3) composites are becoming increasingly attractive in bone repair since it combines the advantage of polymer flexibility and ceramic piezoelectric constant. Herein, silver (Ag) nanoparticles were decorated on polydopamine functioned BaTiO3 (Ag-pBT) by in situ growth. Then the strawberry-like structured Ag-pBT nanoparticles were introduced into PVDF scaffold fabricated by selective laser sintering. On one hand, Ag nanoparticles would act as a conductive phase to enhance the strength of the polarized electric field on BaTiO3, thereby forcing more domains to be aligned in the direction of the electric field and make piezoelectric effect of BaTiO3 fully play in composite scaffold. On the other hand, Ag nanoparticles would attack multiple targets in bacteria by release of Ag+ and production of reactive oxygen species. In fact, the antibacterial activity is highly desirable for bone repair. Results demonstrated that the PVDF/4Ag-pBT scaffold exhibited enhanced piezoelectric properties with output current and voltage increased by 50% and 40% than that of PVDF/pBT, respectively. In vitro cell culture confirmed that the enhanced electric output further promoted cell proliferation and differentiation. Meanwhile, the scaffold presented robust antibacterial activity against E.coli.

Polymer sphere-based scaffolds, which are prepared by bonding the adjacent spheres via sintering the randomly packed spheres, feature uniform pore structure, full three-dimensional (3D) interconnection, and considerable mechanical strength. However, bioceramic sphere-based scaffolds fabricated by this method have never been reported. Due to high melting temperature of bioceramic, only limited diffusion rate can be achieved when sintering the bioceramic spheres, which is far from enough to form robust bonding between spheres. In the present study, for the first time we fabricated 3D interconnected β-tricalcium phosphate ceramic sphere-based (PG/TCP) scaffolds by introducing phosphate-based glass (PG) as sintering additive and placing uniaxial pressure during the sintering process. The sintering mechanism of PG/TCP scaffolds was unveiled. The PG/TCP scaffolds had hierarchical pore structure, which was composed by interconnected macropores (>200 μm) among spheres, pores (20–120 μm) in the interior of spheres, and micropores (1–3 μm) among the grains. During the sintering process, partial PG reacted with β-TCP, forming β-Ca2P2O7; metal ions from PG substituted to Ca2+ sites of β-TCP. The mechanical properties (compressive strength 2.8–10.6 MPa; compressive modulus 190–620 MPa) and porosity (30%–50%) of scaffolds could be tailored by manipulating the sintering temperatures. The introduction of PG accelerated in vitro degradation of scaffolds, and the PG/TCP scaffolds showed good cytocompatibility. This work may offer a new strategy to prepare bioceramic scaffolds with satisfactory physicochemical properties for application in bone regeneration.