Surfactant as a Critical Factor When Tuning the Hydrophilicity in Three-Dimensional Polyester-Based Scaffolds: Impact of Hydrophilicity on Their Mechanical Properties and the Cellular Response of Human Osteoblast-Like Cells

Aspirin/PLGA coated 3D-printed Ti-6Al-4V alloy modulate macrophage polarization to enhance osteoblast differentiation and osseointegration

Although titanium (Ti) and Ti-based alloy have been widely used as dental and orthopedic implant materials, its bioinertness hindered the rapid osseointegration. Therefore, it is recommended to acquire ideal topographic and chemical characteristics through surface modification methods. 3D printing is a delicate manufacture technique which possesses superior controllability and reproducibility. While aspirin serve as a well-established non-steroidal anti-inflammatory agent. Recently, the importance of immune system in regulating bone dynamics has attracted increasing attention. We herein superimposed the aspirin/poly (lactic-co-glycolic acid) (ASP/PLGA) coating on the 3D-printed Ti-6Al-4V surface with uniform micro-structure to establish the Ti64-M-ASP/PLGA substrate. Scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and contact angle test confirmed the successful fabrication of the Ti64-M-ASP/PLGA substrate, with increased wettability and sustained release pattern of ASP. Compared with the Ti64 base material, the Ti64-M-ASP/PLGA substrate showed enhanced M2 and depressed M1 genes and proteins expressions in macrophages. The novel Ti64-M-ASP/PLGA substrate also displayed enhanced osteoblast proliferation, adhesion, extracellular mineralization ability and osteogenic gene expressions when cultured with macrophage conditioned medium in vitro. Furthermore, rat femora implantation model was used for in vivo evaluation. After 4 weeks of implantation, push out test, micro-computed tomography (micro-CT) and histological analyses all confirmed the superior osseointegration capabilities of the Ti64-M-ASP/PLGA implant than the other groups. Our study revealed the synergistic role played by 3D-printed micro topography and immunoregulatory drug aspirin in promoting osteogenesis in vitro and accelerating osseointegration in vivo, thus providing a promising method for better modifying the implant surface. Graphical abstract.

3D Printed Gelatin/Sodium Alginate Hydrogel Scaffolds Doped with Nano-Attapulgite for Bone Tissue Repair

INTRODUCTION

Bone tissue engineering (BTE) is a new strategy for bone defect repair, but the difficulties in the fabrication of scaffolds with personalized structures still limited their clinical applications. The rapid development in three-dimensional (3D) printing endows it capable of controlling the porous structures of scaffolds with high structural complexity and provides flexibility to meet specific needs of bone repair.

METHODS

In this study, sodium alginate (SA)/gelatin (Gel) hydrogel scaffolds doped with different contents of nano-attapulgite were fabricated via 3D printing. The surface microstructure, hydrophilicity and mechanical properties were fully evaluated. Furthermore, mouse bone marrow-derived mesenchymal stem cells (BMSCs) were cultured with the composite hydrogels in vitro, and proliferation and osteoblastic differentiation were assessed. A rabbit tibia plateau defect model was used to evaluate the osteogenic potential of the composite hydrogel in vivo.

RESULTS

When increasing nano-ATP content, the Gel/SA/nano-ATP composite hydrogels showed better mechanical property and printability. Moreover, Gel/SA/nano-ATP composite hydrogels showed excellent bioactivity, and a significant mineralization effect was observed on the surface after being incubated in simulated body fluid (SBF) for 14 days. The Gel/SA/nano-ATP composite hydrogel also showed good biocompatibility and promoted the osteogenesis of BMSCs. Finally, histological analysis demonstrates that the Gel/SA/nano-ATP composite hydrogels could effectively enhance bone regeneration in vivo.

CONCLUSION

These properties render the Gel/SA/nano-ATP composite hydrogel scaffolds an ideal bone tissue engineering material for the repair of bone defects.

Arginine induces protein self-assembly into nanofibers for triggering osteogenic differentiation of stem cells

Although silk proteins are considered promising in building a scaffold for tissue engineering, one of the silk proteins, Bombyx mori silk sericin (BS), has limited processability in producing nanofibrous scaffolds because its surface charge anisotropy promotes gelation instead. To overcome this daunting challenge, we developed a mild and simple procedure for assembling BS into nanofibers and nanofibrous scaffolds. Briefly, arginine was added to the aqueous BS solution to reduce the negative charge of BS, thereby inducing BS to self-assemble into nanofibers in the solution. Circular dichroism (CD) and Fourier transform infrared (FT-IR) spectra showed that arginine promoted the formation of β-sheet conformation in BS and increased its thermal stability. Furthermore, the arginine-induced BS nanofiber solution could be casted into scaffolds made of abundant network-like nanofibrous structures. The BS scaffolds promoted cell adhesion and growth and stimulated osteogenic differentiation of the bone marrow mesenchymal stem cells (BMSCs) in the absence of differentiation inducers in culture media. Our study presents a new strategy for assembling proteins into osteogenic nanofibrous scaffolds for inducing stem cell differentiation in regenerative medicine.

Effects of the bonding intensity between hyaluronan and gelatin on chondrogenic phenotypic maintenance

Although there have been many reports on the use of crosslinked hyaluronic acid and gelatin derivatives as injectable hydrogels in cartilage tissue engineering, however, almost no reports have analyzed the kinds of bonding intensity that were most conducive for the maintenance of cartilage phenotypes. Herein, the biomimetic composite hydrogels based on thiolated hyaluronic acid and modified gelatin derivatives with physical mixed, weak, and strong bonding intensity were fabricated, wherein the thiolated hyaluronic acid ensured the basic network structure of composite hydrogels, and gelatin derivatives endowed the bioactivity to hydrogels. These physicochemical properties of composite hydrogels implied that strong bonding intensity (HA-GSH) contributed to the maintenance of a more uniform pore structure, and increased the ability of water retention and resistance to degradation. Further immunohistochemical and RT-PCR analyses demonstrated that the HA-GSH hydrogel greatly improved the expression level of the associated cartilage matrix and the possibility of hyaline cartilage formation in comparison to the physically blended HA-Gel gel and weak bonding crosslinked HA-GMA gel. Overall, all results proved that strong bonding intensity of the disulfide bonds in the HA-GSH hydrogel was more beneficial for the proliferation of chondrocytes and the maintenance of the hyaline cartilage phenotype, which might provide valuable inspiration for designing cartilage repair scaffolds.

Altered Surface Hydrophilicity on Copolymer Scaffolds Stimulate the Osteogenic Differentiation of Human Mesenchymal Stem Cells

BACKGROUND

Recent studies have suggested that both poly(l-lactide-co-1,5-dioxepan-2-one) (or poly(LLA-co-DXO)) and poly(l-lactide-co-ε-caprolactone) (or poly(LLA-co-CL)) porous scaffolds are good candidates for use as biodegradable scaffold materials in the field of tissue engineering; meanwhile, their surface properties, such as hydrophilicity, need to be further improved.

METHODS

We applied several different concentrations of the surfactant Tween 80 to tune the hydrophilicity of both materials. Moreover, the modification was applied not only in the form of solid scaffold as a film but also a porous scaffold. To investigate the potential application for tissue engineering, human bone marrow mesenchymal stem cells (hMSCs) were chosen to test the effect of hydrophilicity on cell attachment, proliferation, and differentiation. First, the cellular cytotoxicity of the extracted medium from modified scaffolds was investigated on HaCaT cells. Then, hMSCs were seeded on the scaffolds or films to evaluate cell attachment, proliferation, and osteogenic differentiation. The results indicated a significant increasing of wettability with the addition of Tween 80, and the hMSCs showed delayed attachment and spreading. PCR results indicated that the differentiation of hMSCs was stimulated, and several osteogenesis related genes were up-regulated in the 3% Tween 80 group. Poly(LLA-co-CL) with 3% Tween 80 showed an increased messenger Ribonucleic acid (mRNA) level of late-stage markers such as osteocalcin (OC) and key transcription factor as runt related gene 2 (Runx2).

CONCLUSION

A high hydrophilic scaffold may speed up the osteogenic differentiation for bone tissue engineering.

Rapid construction of polyetheretherketone (PEEK) biological implants incorporated with brushite (CaHPO4·2H2O) and antibiotics for anti-infection and enhanced osseointegration

Polyetheretherketone (PEEK) is an ideal implant material for orthopedic and dental application due to its high biocompatibility and mechanical property. However, biological inertness of PEEK hinders the effective clinical applications in treating bone defect, especially in the situation accompanied by bacterial infection. In this study, a layer-by-layer (LBL) deposition method with controlled cycles was developed to rapidly construct brushite (CaHPO₄·2H₂O) (CaP) layers containing gentamicin sulfate (GS) on PEEK to obtain CaP-and-GS modified PEEK, named as PEEK/CaP-GS. Different PEEK/CaP-GS, like PEEK/CaP-GS*3, PEEK/CaP-GS*6 and PEEK/CaP-GS*9 were conveniently prepared by repeating the LBL cycles to 3, 6 and 9 times, respectively. The morphology, structure and surface property of the fabricated PEEK/CaP-GS were carefully characterized. In vitro antibacterial experiments illustrated that all of the PEEK/CaP-GS samples had excellent and sustained antibacterial property. Cell proliferation experiments revealed the acceptable biocompatibility and cell osteogenic differentiation of PEEK/CaP-GS, especially in PEEK/CaP-GS*6. X-ray, μ-CT, and histological analysis showed that PEEK/CaP-GS exhibited in vivo antibacterial activity and osseointegration ability in the treatment of bone defect with infection. In both the in vitro and the in vivo experiments, PEEK/CaP-GS*6 prepared from the 6 LBL cycles exhibited the best antibacterial and osseointegration ability for bone healing. This work opens new avenue of the facile and effective modification of PEEK with special biological functions for clinical application, especially for the implants requiring excellent antibacterial and osseointegration ability.

Polymer Microparticles with Defined Surface Chemistry and Topography Mediate the Formation of Stem Cell Aggregates and Cardiomyocyte Function

Surface-functionalized microparticles are relevant to fields spanning engineering and biomedicine, with uses ranging from cell culture to advanced cell delivery. Varying topographies of biomaterial surfaces are also being investigated as mediators of cell-material interactions and subsequent cell fate. To investigate competing or synergistic effects of chemistry and topography in three-dimensional cell cultures, methods are required to introduce these onto microparticles without modification of their underlying morphology or bulk properties. In this study, a new approach for surface functionalization of poly(lactic acid) (PLA) microparticles is reported that allows decoration of the outer shell of the polyesters with additional polymers via aqueous atom transfer radical polymerization routes. PLA microparticles with smooth or dimpled surfaces were functionalized with poly(poly(ethylene glycol) methacrylate) and poly[N-(3-aminopropyl)methacrylamide] brushes, chosen for their potential abilities to mediate cell adhesion. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analysis indicated homogeneous coverage of the microparticles with polymer brushes while maintaining the original topographies. These materials were used to investigate the relative importance of surface chemistry and topography both on the formation of human immortalized mesenchymal stem cell (hiMSCs) particle-cell aggregates and on the enhanced contractility of cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CMs). The influence of surface chemistry was found to be more important on the size of particle-cell aggregates than topographies. In addition, surface chemistries that best promoted hiMSC attachment also improved hiPSC-CM attachment and contractility. These studies demonstrated a new route to obtain topo-chemical combinations on polyester-based biomaterials and provided clear evidence for the predominant effect of surface functionality over micron-scale dimpled topography in cell-microparticle interactions. These findings, thus, provide new guiding principles for the design of biomaterial interfaces to direct cell function.

Three-Dimensional Polydopamine Functionalized Coiled Microfibrous Scaffolds Enhance Human Mesenchymal Stem Cells Colonization and Mild Myofibroblastic Differentiation

Electrospinning has been widely applied for tissue engineering due to its versatility of fabricating extracellular matrix (ECM) mimicking fibrillar scaffolds. Yet there are still challenges such as that these two-dimensional (2D) tightly packed, hydrophobic fibers often hinder cell infiltration and cell-scaffold integration. In this study, polycaprolactone (PCL) was electrospun into a grounded coagulation bath collector, resulting in 3D coiled microfibers with in situ surface functionalization with hydrophilic, catecholic polydopamine (pDA). The 3D scaffolds showed biocompatibility and were well-integrated with human bone marrow derived human mesenchymal stem cells (hMSCs), with significantly higher cell penetration depth compared to that of the 2D PCL microfibers from traditional electrospinning. Further differentiation of human mesenchymal stem cells (hMSCs) into fibroblast phenotype in vitro indicates that, compared to the stiff, tightly packed, 2D scaffolds which aggravated myofibroblasts related activities, such as upregulated gene and protein expression of α-smooth muscle actin (α-SMA), 3D scaffolds induced milder myofibroblastic differentiation. The flexible 3D fibers further allowed contraction with the well-integrated, mechanically active myofibroblasts, monitored under live-cell imaging, whereas the stiff 2D scaffolds restricted that.

In Vivo Host Response and Degradation of Copolymer Scaffolds Functionalized with Nanodiamonds and Bone Morphogenetic Protein 2

The aim is to evaluate the effect of modifying poly[(l-lactide)-co-(ε-caprolactone)] scaffolds (PLCL) with nanodiamonds (nDP) or with nDP+physisorbed BMP-2 (nDP+BMP-2) on in vivo host tissue response and degradation. The scaffolds are implanted subcutaneously in Balb/c mice and retrieved after 1, 8, and 27 weeks. Molecular weight analysis shows that modified scaffolds degrade faster than the unmodified. Gene analysis at week 1 shows highest expression of proinflammatory markers around nDP scaffolds; although the presence of inflammatory cells and foreign body giant cells is more prominent around the PLCL. Tissue regeneration markers are highly expressed in the nDP+BMP-2 scaffolds at week 8. A fibrous capsule is detectable by week 8, thinnest around nDP scaffolds and at week 27 thickest around PLCL scaffolds. mRNA levels of ALP, COL1α2, and ANGPT1 are significantly upregulating in the nDP+BMP-2 scaffolds at week 1 with ectopic bone seen at week 8. Even when almost 90% of the scaffold is degraded at week 27, nDP are observable at implantation areas without adverse effects. In conclusion, modifying PLCL scaffolds with nDP does not aggravate the host response and physisorbed BMP-2 delivery attenuates inflammation while lowering the dose of BMP-2 to a relatively safe and economical level.

A perfusion bioreactor system efficiently generates cell-loaded bone substitute materials for addressing critical size bone defects

Critical size bone defects and non‐union fractions are still challenging to treat. Cell‐loaded bone substitutes have shown improved bone ingrowth and bone formation. However, a lack of methods for homogenously colonizing scaffolds limits the maximum volume of bone grafts. Additionally, therapy robustness is impaired by heterogeneous cell populations after graft generation. Our aim was to establish a technology for generating grafts with a size of 10.5 mm in diameter and 25 mm of height, and thus for grafts suited for treatment of critical size bone defects. Therefore, a novel tailor‐made bioreactor system was developed, allowing standardized flow conditions in a porous poly(L‐lactide‐co‐caprolactone) material. Scaffolds were seeded with primary human mesenchymal stem cells derived from four different donors. In contrast to static experimental conditions, homogenous cell distributions were accomplished under dynamic culture. Additionally, culture in the bioreactor system allowed the induction of osteogenic lineage commitment after one week of culture without addition of soluble factors. This was demonstrated by quantitative analysis of calcification and gene expression markers related to osteogenic lineage. In conclusion, the novel bioreactor technology allows efficient and standardized conditions for generating bone substitutes that are suitable for the treatment of critical size defects in humans.

Degradable Polymer with Protein Resistance in a Marine Environment

Protein resistance is the central issue in marine antibiofouling. We have prepared poly(ε-caprolactone) (PCL)-based polyurethane with 2-(dimethylamino) ethyl methacrylate (DEM) as pendant groups by a combination of the thiol-ene click reaction and the condensation reaction. By the use of quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance (SPR), we have investigated the adsorption of fibrinogen, bovine serum albumin (BSA), and lysozyme on the polymer surface. The polymer exhibits protein resistance in seawater but not in fresh water because DEM pendant groups carry net neutral charges in the former. The evaluation of antibacterial adhesion of the polymer by using Micrococcus luteus demonstrates that the polymer can effectively inhibit the settlement of marine bacteria. Our studies also show that the polymer is degradable in marine environments.