Osteogenic potentials in canine mesenchymal stem cells: unraveling the efficacy of polycaprolactone/hydroxyapatite scaffolds in veterinary bone regeneration

BACKGROUND

The integration of stem cells, signaling molecules, and biomaterial scaffolds is fundamental for the successful engineering of functional bone tissue. Currently, the development of composite scaffolds has emerged as an attractive approach to meet the criteria of ideal scaffolds utilized in bone tissue engineering (BTE) for facilitating bone regeneration in bone defects. Recently, the incorporation of polycaprolactone (PCL) with hydroxyapatite (HA) has been developed as one of the suitable substitutes for BTE applications owing to their promising osteogenic properties. In this study, a three-dimensional (3D) scaffold composed of PCL integrated with HA (PCL/HA) was prepared and assessed for its ability to support osteogenesis in vitro. Furthermore, this scaffold was evaluated explicitly for its efficacy in promoting the proliferation and osteogenic differentiation of canine bone marrow-derived mesenchymal stem cells (cBM-MSCs) to fill the knowledge gap regarding the use of composite scaffolds for BTE in the veterinary orthopedics field.

RESULTS

Our findings indicate that the PCL/HA scaffolds substantially supported the proliferation of cBM-MSCs. Notably, the group subjected to osteogenic induction exhibited a markedly upregulated expression of the osteogenic gene osterix (OSX) compared to the control group. Additionally, the construction of 3D scaffold constructs with differentiated cells and an extracellular matrix (ECM) was successfully imaged using scanning electron microscopy. Elemental analysis using a scanning electron microscope coupled with energy-dispersive X-ray spectroscopy confirmed that these constructs possessed the mineral content of bone-like compositions, particularly the presence of calcium and phosphorus.

CONCLUSIONS

This research highlights the synergistic potential of PCL/HA scaffolds in concert with cBM-MSCs, presenting a multidisciplinary approach to scaffold fabrication that effectively regulates cell proliferation and osteogenic differentiation. Future in vivo studies focusing on the repair and regeneration of bone defects are warranted to further explore the regenerative capacity of these constructs, with the ultimate goal of assessing their potential in veterinary clinical applications.

A comprehensive bench-to-bed look into the application of gamma-sterilized 3D-printed polycaprolactone/hydroxyapatite implants for craniomaxillofacial defects, an in vitro, in vivo, and clinical study

This study investigates the safety and efficacy of 3D-printed polycaprolactone/hydroxyapatite (PCL/HA) scaffolds for patient-specific cranioplasty surgeries, employing liquid deposition modeling (LDM) technology. This research is pioneering as it explores the impact of gamma radiation on PCL/HA scaffolds and utilizes printing ink with the highest content of HA known in the composite. The mechanical, morphological, and macromolecular stability of the gamma-sterilized scaffolds were verified before implantation. Subsequent research involving animal subjects was conducted to explore the effects of sterilized implants. Eventually, three clinical cases were selected for the implantation studies as part of a phase 1 non-randomized open-label clinical trial. It was shown that a 25 kGy gamma-ray dose for sterilizing the printed implants did not alter the required geometrical precision of the printed implants. The implants exhibited well-distributed HA and strength comparable to cancellous bone. Gamma radiation reduced hydrophobicity and water uptake capacity without inducing pyrogenic or inflammatory responses. Personalized PCL/HA substitutes successfully treated various craniomaxillofacial defects, including trauma-induced facial asymmetry and congenital deformities. HA nanoparticles in the ink stimulated significant osteoconductive responses within three months of implantation. Moreover, the results revealed that while larger implants may exhibit a slower bone formation response in comparison to smaller implants, they generally had an acceptable rate and volume of bone formation. This clinical trial suggests the application of a sterilized PCL/HA composite for craniomaxillofacial surgery is safe and could be considered as a substitute for autologous bone.

Evaluation of the Morphological Effects of Hydroxyapatite Nanoparticles on the Rheological Properties and Printability of Hydroxyapatite/Polycaprolactone Nanocomposite Inks and Final Scaffold Features

This study is focused on the importance of nanohydroxyapatite (nHA) particle morphology with the same particle size range on the rheological behavior of polycaprolactone (PCL) composite ink with nHA as a promising candidate for additive manufacturing technologies. Two different physiologic-like nHA morphologies, that is, plate and rod shape, with particles size less than 100 nm were used. nHA powders were well characterized and the printing inks were prepared by adding the different ratios of nHA powders to 50% w/v of PCL solution (nHA/PCL: 35/65, 45/55, 55/45, and 65/35 w/w%). Subsequently, the influence of nHA particle morphology and concentration on the printability and rheological properties of composite inks was investigated. HA nanopowder analysis revealed significant differences in their microstructural properties, which affected remarkably the composite ink printability in several ways. For instance, adding up to 65% w/w of plate-like nHA to the PCL solution was possible, while nanorod HA could not be added above 45% w/w. The printed constructs were successfully fabricated using the extrusion-based printing method and had a porous structure with interconnected pores. Total porosity and surface area increased with nHA content due to the improved fiber stability following deposition of material ink. Consequently, degradation rate and bioactivity increased, while compressive properties decreased. While nanorod HA particles had a more significant impact on the mechanical strength than plate-like morphology, the latter showed less crystalline order, which makes them more bioactive than nanorod HA. It is therefore important to note that the nHA microstructure broadly affects the printability of printing ink and should be considered according to the intended biomedical applications.

Review on Bioinspired Design of ECM-Mimicking Scaffolds by Computer-Aided Assembly of Cell-Free and Cell Laden Micro-Modules

Tissue engineering needs bioactive drug delivery scaffolds capable of guiding cell biosynthesis and tissue morphogenesis in three dimensions. Several strategies have been developed to design and fabricate ECM-mimicking scaffolds suitable for directing in vitro cell/scaffold interaction, and controlling tissue morphogenesis in vivo. Among these strategies, emerging computer aided design and manufacturing processes, such as modular tissue unit patterning, promise to provide unprecedented control over the generation of biologically and biomechanically competent tissue analogues. This review discusses recent studies and highlights the role of scaffold microstructural properties and their drug release capability in cell fate control and tissue morphogenesis. Furthermore, the work highlights recent advances in the bottom-up fabrication of porous scaffolds and hybrid constructs through the computer-aided assembly of cell-free and/or cell-laden micro-modules. The advantages, current limitations, and future challenges of these strategies are described and discussed.

Fabrication and Testing of Multi-Hierarchical Porous Scaffolds Designed for Bone Regeneration via Additive Manufacturing Processes

Bone implants or replacements are very scarce due to the low donor availability and the high rate of body rejection. For this reason, tissue engineering strategies have been developed as alternative solutions to this problem. This research sought to create a cellular scaffold with an intricate and complex network of interconnected pores and microchannels using salt leaching and additive manufacturing (3D printing) methods that mimic the hierarchical internal structure of the bone. A biocompatible hydrogel film (based on poly-ethylene glycol) was used to cover the surface of different polymeric scaffolds. This thin film was then exposed to various stimuli to spontaneously form wrinkled micropatterns, with the aim of increasing the contact area and the material’s biocompatibility. The main innovation of this study was to include these wrinkled micropatterns on the surface of the scaffold by taking advantage of thin polymer film surface instabilities. On the other hand, salt and nano-hydroxyapatite (nHA) particles were included in the polymeric matrix to create a modified filament for 3D printing. The printed part was leached to eliminate porogen particles, leaving homogenously distributed pores on the structure. The pores have a mean size of 26.4 ± 9.9 μm, resulting in a global scaffold porosity of ~42% (including pores and microchannels). The presence of nHA particles, which display a homogeneous distribution according to the FE-SEM and EDX results, have a slight influence on the mechanical resistance of the material, but incredibly, despite being a bioactive compound for bone cells, did not show a significant increase in cell viability on the scaffold surface. However, the synergistic effect between the presence of the hydrogel and the pores on the material does produce an increase in cell viability compared to the control sample and the bare PCL material.

Engineer a pre-metastatic niched microenvironment to attract breast cancer cells by utilizing a 3D printed polycaprolactone/nano-hydroxyapatite osteogenic scaffold - An in vitro model system for proof of concept

Breast cancer bone metastasis is not a random process. It is affected by the local microenvironment which determines the propensity of cancer cells to invade and colonize into the secondary sites. This microenvironment is termed a pre-metastatic niche. With the flexibility to incorporate different biofactors, tissue-engineering scaffolds provide an advantageous environment to promote "designed" osteogenesis that may mimic the bony pre-metastatic niche. In the current study, designed polycaprolactone (PCL) scaffolds enriched with nano-hydroxyapatite (nHA) were fabricated through three-dimensional (3D) printing. Subsequently, human mesenchymal stem cells (hMSCs) were seeded onto PCL-nHA scaffolds for osteogenic differentiation to establish the pre-metastatic niched microenvironment. Furthermore, transwell migration assay was used to investigate recruitment of MDA-MB-231, MCF-7, and MDA-MB-453 breast cancer cells to the osseous PCL-nHA scaffolds. Our results showed that the mRNA levels of alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2), and osteocalcin (OCN) of hMSCs on the PCL-nHA scaffolds were dramatically increased compared those with the PCL scaffolds (control) at day 7, 14, and 28. Meanwhile, the migration analysis showed that the higher maturation of osteogenesis and bone metabolism collectively contributed to the creation of a more favorable niched site for the cancerous invasion. Moreover, one of the hypothesized key mediators for the promoted migration, CXCL12, was confirmed using an assay of antagonist LIT-927. This early study demonstrated that a designed tissue engineering scaffold can be utilized to create a bone-mimicking environment that serves as a novel platform to recapitulate the pre-metastatic niche and help interrogate the scheme of bone metastasis by breast cancer.

Functional tissue-engineered microtissue formed by self-aggregation of cells for peripheral nerve regeneration

Background

Peripheral nerve injury (PNI) is one of the essential causes of physical disability with a high incidence rate. The traditional tissue engineering strategy, Top-Down strategy, has some limitations. A new tissue-engineered strategy, Bottom-Up strategy (tissue-engineered microtissue strategy), has emerged and made significant research progress in recent years. However, to the best of our knowledge, microtissues are rarely used in neural tissue engineering; thus, we intended to use microtissues to repair PNI.

Methods

We used a low-adhesion cell culture plate to construct adipose-derived mesenchymal stem cells (ASCs) into microtissues in vitro, explored the physicochemical properties and microtissues components, compared the expression of cytokines related to nerve regeneration between microtissues and the same amount of two-dimension (2D)-cultured cells, co-cultured directly microtissues with dorsal root ganglion (DRG) or Schwann cells (SCs) to observe the interaction between them using immunocytochemistry, quantitative reverse transcription polymerase chain reaction (qRT-PCR), enzyme-linked immunosorbent assay (ELISA). We used grafts constructed by microtissues and polycaprolactone (PCL) nerve conduit to repair sciatic nerve defects in rats.

Results

The present study results indicated that compared with the same number of 2D-cultured cells, microtissue could secrete more nerve regeneration related cytokines to promote SCs proliferation and axons growth. Moreover, in the direct co-culture system of microtissue and DRG or SCs, axons of DRG grown in the direction of microtissue, and there seems to be a cytoplasmic exchange between SCs and ASCs around microtissue. Furthermore, microtissues could repair sciatic nerve defects in rat models more effectively than traditional 2D-cultured ASCs.

Conclusion

Tissue-engineered microtissue is an effective strategy for stem cell culture and therapy in nerve tissue engineering.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02676-0.

Breast Cancer Cells Metastasize to the Tissue-Engineered Premetastatic Niche by Using an Osteoid-Formed Polycaprolactone/Nanohydroxyapatite Scaffold

It has been deemed that the premetastatic niche (PMN) plays a critical role in facilitating bone metastasis of breast cancer cells. Tissue engineering scaffolds provide an advantageous environment to promote osteogenesis that may mimic the bony premetastatic niches (BPMNs). In this study, human mesenchymal stem cells (hMSCs) were seeded onto designed polycaprolactone/nanohydroxyapatite (PCL-nHA) scaffolds for osteogenic differentiation. Subsequently, a coculture system was used to establish the tissue-engineered BPMNs by culturing breast cancer cells, hMSCs, and osteoid-formed PCL-nHA scaffolds. Afterwards, a migration assay was used to investigate the recruitment of MDA-MB-231, MCF-7, and MDA-MB-453 cells to the BPMNs' supernatants. The cancer stem cell (CSC) properties of these migrated cells were investigated by flow cytometry. Our results showed that the mRNA expression levels of alkaline phosphatase (ALP), Osterix, runt-related transcription factor 2 (Runx2), and collagen type I alpha 1 (COL1A1) on the PCL-nHA scaffolds were dramatically increased compared to the PCL scaffolds on days 11, 18, and 32. The expression of CXCL12 in these BPMNs was increased gradually over coculturing time, and it may be a feasible marker for BPMNs. Furthermore, migration analysis results showed that the higher maturation of BPMNs collectively contributed to the creation of a more favorable niched site for the cancerous invasion. The subpopulation of breast cancer stem cells (BCSCs) was more likely to migrate to fertile BPMNs. The proportion of BCSCs in metastatic MDA-MB-231, MCF-7, and MDA-MB-453 cells were increased by approximately 63.47%, 149.48%, and 127.60%. The current study demonstrated that a designed tissue engineering scaffold can provide a novel method to create a bone-mimicking environment that serves as a useable platform to recapitulate the BPMNs and help interrogate the scheme of bone metastasis by breast cancer.

Additive Manufacturing: The Next Generation of Scapholunate Ligament Reconstruction

Background  Ligament reconstruction, as a surgical method used to stabilize joints, requires significant strength and tissue anchoring to restore function. Historically, reconstructive materials have been fraught with problems from an inability to withstand normal physiological loads to difficulties in fabricating the complex organization structure of native tissue at the ligament-to-bone interface. In combination, these factors have prevented the successful realization of nonautograft reconstruction. Methods  A review of recent improvements in additive manufacturing techniques and biomaterials highlight possible options for ligament replacement. Description of Technique  In combination, three dimensional-printing and electrospinning have begun to provide for nonautograft options that can meet the physiological load and architectures of native tissues; however, a combination of manufacturing methods is needed to allow for bone-ligament enthesis. Hybrid biofabrication of bone-ligament tissue scaffolds, through the simultaneous deposition of disparate materials, offer significant advantages over fused manufacturing methods which lack efficient integration between bone and ligament materials. Results  In this review, we discuss the important chemical and biological properties of ligament enthesis and describe recent advancements in additive manufacturing to meet mechanical and biological requirements for a successful bone-ligament-bone interface. Conclusions  With continued advancement of additive manufacturing technologies and improved biomaterial properties, tissue engineered bone-ligament scaffolds may soon enter the clinical realm.

Bioactivity and Bone Cell Formation with Poly-ε-Caprolactone/Bioceramic 3D Porous Scaffolds

This study applied poly-ε-caprolactone (PCL), a biomedical ceramic powder as an additive (nano-hydroxyapatite (nHA) or β-tricalcium diphosphate (β-TCP)), and sodium chloride (NaCl) and ammonium bicarbonate ((NH4)HCO3) as porogens; these stuffs were used as scaffold materials. An improved solvent-casting/particulate-leaching method was utilized to fabricate 3D porous scaffolds. In this study we examined the physical properties (elastic modulus, porosity, and contact angle) and degradation properties (weight loss and pH value) of the 3D porous scaffolds. Both nHA and β-TCP improved the mechanical properties (elastic modulus) of the 3D porous scaffolds. The elastic modulus (0.15~1.865 GPa) of the various composite scaffolds matched that of human cancellous bone (0.1~4.5 GPa). Osteoblast-like (MG63) cells were cultured, a microculture tetrazolium test (MTT) was conducted and alkaline phosphatase (ALP) activity of the 3D porous scaffolds was determined. Experimental results indicated that both nHA and β-TCP powder improved the hydrophilic properties of the scaffolds. The degradation rate of the scaffolds was accelerated by adding nHA or β-TCP. The MTT and ALP activity tests indicated that the scaffolds with a high ratio of nHA or β-TCP had excellent properties of in vitro biocompatibility (cell attachment and proliferation).

The efficiency of PCL/HAp electrospun nanofibers in bone regeneration: a review

Electrospinning is a method which produces various nanofiber scaffolds for different tissues was attractive for researchers. Nanofiber scaffolds could be made from several biomaterials and polymers. Quality and virtues of final scaffolds depend on used biomaterials (even about single substance, the origin is effective), additives (such as some molecules, ions, drugs, and inorganic materials), electrospinning parameter (voltage, injection speed, temperature, …), etc. In addition to its benefits, which makes it more attractive is the possibility of modifications. Common biomaterials in bone tissue engineering such as poly-caprolactone (PCL), hydroxyapatite (HAp), and their important features, electrospinning nanofibers were widely studied. Related investigations indicate the critical role of even small parameters (like the concentration of PCL or HAp) in final product properties. These changes also, cause deference in cell proliferation, adhesion, differentiation, and in vivo repair process. In this review was focussed on PCL/HAp based nanofibers and additives that researchers used for scaffold improvement. Then, reviewing properties of gained nanofibers, their effect on cell behaviour, and finally, their valency in bone tissue engineering studies (in vitro and in vivo).

Fabrication of Biocompatible Polycaprolactone–Hydroxyapatite Composite Filaments for the FDM 3D Printing of Bone Scaffolds

Recently, three-dimensional printing (3DP) technology has been widely adopted in biology and biomedical applications, thanks to its capacity to readily construct complex 3D features. Using hot-melt extrusion 3DP, scaffolds for bone tissue engineering were fabricated using a composite of biodegradable polycaprolactone (PCL) and hydroxyapatite (HA). However, there are hardly any published reports on the application of the fused deposition modeling (FDM) method using feed filaments, which is the most common 3D printing method. In this study, we report on the fabrication and characterization of biocompatible filaments made of polycaprolactone (PCL)/hydroxyapatite (HA), a raw material mainly used for bone scaffolds, using FDM 3D printing. A series of filaments with varying HA content, from 5 to 25 wt.%, were fabricated. The mechanical and electrical properties of the various structures, printed using a commercially available 3D printer, were examined. Specifically, mechanical tensile tests were performed on the 3D-printed filaments and specimens. In addition, the electrical dielectric properties of the 3D-printed structures were investigated. Our method facilitates the fabrication of biocompatible structures using FDM-type 3DP, creating not only bone scaffolds but also testbeds for mimicking bone structure that may be useful in various fields of study.

Tissue Engineering Microtissue: Construction, Optimization, and Application

Until now, there is no clear definition of microtissue; it usually refers to the microtissue formed by the aggregation of seed cells under the action of cell-cell or cell-extracellular matrix (ECM). Compared with traditional cell monolayer culture, cells are cultivated into a three-dimensional microstructure in a specific way. The microstructure characteristics of microtissue are similar to natural tissues and can promote cell proliferation and differentiation. Therefore, it has a broader range of biomedical applications in tissue engineering. The traditional tissue engineering strategy is to add high-density seed cells and biomolecules on a preformed scaffold to construct a tissue engineering graft. However, due to the destruction of the ECM of the cells cultured in a monolayer during the digestion process with trypsin, the uneven distribution of the cells in the scaffold, and the damage of various adverse factors after the cells are implanted in the scaffold, this strategy is often ineffective, and the subsequent applications still face challenges. This article reviews the latest researches of a new strategy-tissue engineering microtissue strategy; discuss several traditional construction methods, structure, and function optimization; and practical application of microtissue. The review aims to provide a reference for future research on tissue engineering microtissue. Impact statement The traditional tissue engineering strategies have several disadvantages, researchers have conducted extensive research on tissue engineering microtissues in recent years, and they make significant progress. Microtissue is a kind of microtissue with three-dimensional structure, its microstructure is similar to that of natural tissue. In addition, microtissue implantation can protect cells from mechanical interference, inflammation, and other adverse factors. Furthermore, it improves the survival rate of cells and the therapeutic effect of tissue-engineered grafts. However, the practical conditions, advantages, and disadvantages of tissue engineering microtissue have not been fully elucidated. The purpose of this review is to discuss the latest research progress of microtissue and provide a reference for future research.

Bioinspired Design of Novel Microscaffolds for Fibroblast Guidance toward In Vitro Tissue Building

Porous microscaffolds (μ-scaffs) play a crucial role in modular tissue engineering as they control cell functions and guide hierarchical tissue formation toward building new functional tissue analogues. In the present study, we developed a new route to prepare porous polycaprolactone (PCL) μ-scaffs with a bioinspired trabecular structure that supported in vitro adhesion, growth, and biosynthesis of human dermal fibroblasts (HDFs). The method involved the use of poly(ethylene oxide) (PEO) as a biocompatible porogen and a fluidic emulsion/porogen leaching/particle coagulation process to obtain spherical μ-scaffs with controllable diameter and full pore interconnectivity. To achieve this objective, we investigated the effect of PEO concentration and the temperature of the coagulation bath on the μ-scaff architecture, while we modulated the μ-scaff diameter distribution by varying the PCL-PEO amount in the starting solution and changing the flow rate of the continuous phase (Q_CP). μ-Scaff morphology, pore architecture, and diameter distribution were assessed using scanning electron microscopy (SEM) analysis, microcomputed tomography (microCT), and Image analysis. We reported that the selection of 60 wt % PEO concentration, together with a 4 °C coagulation bath temperature and ultrasound postprocessing, allowed for the design and fabrication of μ-scaff with porosity up to 80% and fully interconnected pores on both the μ-scaff surface and the core. Furthermore, μ-scaff diameter distributions were finely tuned in the 100-600 μm range with the coefficient of variation lower than 5% by selecting the PCL-PEO concentration in the 1-10% w/v range and Q_CP of either 8 or 18 mL/min. Finally, we investigated the capability of the HDF-seeded PCL μ-scaff to form hybrid (biological/synthetic) tissue in vitro. Cell culture tests demonstrated that PCL μ-scaff enabled HDF adhesion, proliferation, colonization, and collagen biosynthesis within inter- and intraparticle spaces and guided the formation of a large (centimeter-sized) viable tissue construct.

Biofunctional Extracellular Matrix-Polycaprolactone-Hydroxyapatite Scaffold and Synovium Mesenchymal Stem Cells/Chondrocytes for Repairing Cartilage Defects

Articular cartilage defects and degeneration can be caused by multiple factors, and the current clinical treatment schemes for pathological changes are relatively limited. Engineered cartilage tissue represents an alternative therapy for repairing cartilage defects in regenerative medicine. The scaffold material is considered the framework of tissue engineering; thus, scaffold material selection plays a crucial role in the therapy outcome. Polycaprolactone (PCL)-hydroxyapatite (HA) has been applied as a scaffold material for bone and cartilage tissue engineering with nontoxic, harmless metabolites and proper physical properties. The extracellular matrix (ECM) is mainly composed of collagen and proteoglycan, as well as a large number of growth factors and cytokines, which provide a tissue-specific microenvironment for host cells. Adipose-derived stem cells are pluripotent stem cells, and transforming growth factor-β3 (TGF-β3) enables mesenchymal stem cells to promote ECM production. This study, via in vitro and in vivo experiments, elucidated that the synovium mesenchymal stem cells (SMSCs) + chondrocytes + ECM-PCL-HA repair system, which is constructed upon the ECM-PCL-HA scaffold material, exhibits an adequate chondrogenic ability and reparatory effect. Overall, ECM-PCL-HA can be defined as a biofunctional scaffold material. The SMSCs + chondrocytes + ECM-PCL-HA repair system showed good confluency between the new cartilage and the surface, as well as the interface of the adjacent host cartilage. Furthermore, the structure of new cartilage tissue is consistent with adjacency. Thus, it can be used as a preferred plan for articular cartilage defect repair.

3D printing PCL/nHA bone scaffolds: exploring the influence of material synthesis techniques

Background

It is known that a number of parameters can influence the post-printing properties of bone tissue scaffolds. Previous research has primarily focused on the effect of parameters associated with scaffold design (e.g., scaffold porosity) and specific scaffold printing processes (e.g., printing pressure). To our knowledge, no studies have investigated variations in post-printing properties attributed to the techniques used to synthesize the materials for printing (e.g., melt-blending, powder blending, liquid solvent, and solid solvent).

Methods

Four material preparation techniques were investigated to determine their influence on scaffold properties. Polycaprolactone/nano-hydroxyapatite 30% (wt.) materials were synthesized through melt-blending, powder blending, liquid solvent, and solid solvent techniques. The material printability and the properties of printed scaffolds, in terms of swelling/degradation, mechanical strength, morphology, and thermal properties, were examined and compared to one another using Kruskal-Wallis nonparametric statistical analysis.

Results

Material prepared through the liquid solvent technique was found to have limited printability, while melt-blended material demonstrated the highest degree of uniformity and lowest extent of swelling and degradation. Scaffolds prepared with powder-blended material demonstrated the highest Young’s modulus, yield strength, and modulus of resilience; however, they also demonstrated the highest degree of variability. The higher degree of inhomogeneity in the material was further supported by thermal gravimetric analysis. While scaffolds printed from melt-blended, powder-blended, and solid solvent materials demonstrated a high degree of micro-porosity, the liquid solvent material preparation technique resulted in minimal micro-porosity.

Conclusions

Study results indicate that specific techniques used to prepare materials influence the printing process and post-printing scaffold properties. Among the four techniques examined, melt-blended materials were found to be the most favorable, specifically when considering the combination of printability, consistent mechanical properties, and efficient preparation. Techniques determined to be favourable based on the properties investigated should undergo further studies related to biological properties and time-dependent properties beyond 21-days.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40824-021-00204-y.

Fabrication of nanoparticles for bone regeneration: new insight into applications of nanoemulsion technology

Introducing synthetic bone substitutes into the clinic was a major breakthrough in the regenerative medicine of bone. Despite many advantages of currently available bone implant materials such as biocompatiblity and osteoconductivity, they still suffer from relatively poor bioactivity, osteoinductivity and osteointegration. These properties can be effectively enhanced by functionalization of implant materials with nanoparticles such as osteoinductive hydroxyapatite nanocrystals, resembling inorganic part of the bone, or bioactive polymer nanoparticles providing sustained delivery of pro-osteogenic agents directly at implantation site. One of the most widespread techniques for fabrication of nanoparticles for bone regeneration applications is nanoemulsification. It allows manufacturing of nanoscale particles (<100 nm) that are injectable, 3D-printable, offer high surface-area-to-volume-ratio and minimal mass transport limitations. Nanoparticles obtained by this technique are of particular interest for biomedical engineering due to fabrication procedures requiring low surfactant concentrations, which translates into reduced risk of surfactant-related in vivo adverse effects and improved biocompatibility of the product. This review discusses nanoemulsion technology and its current uses in manufacturing of nanoparticles for bone regeneration applications. In the first section, we introduce basic concepts of nanoemulsification including nanoemulsion formation, properties and preparation methods. In the next sections, we focus on applications of nanoemulsions in fabrication of nanoparticles used for delivery of drugs/biomolecules facilitating osteogenesis and functionalization of bone implants with special emphasis on biomimetic hydroxyapatite nanoparticles, synthetic polymer nanoparticles loaded with bioactive compounds and bone-targeting nanoparticles. We also highlight key challenges in formulation of nanoparticles via nanoemulsification and outline potential further improvements in this field.

Modular Strategies to Build Cell-Free and Cell-Laden Scaffolds towards Bioengineered Tissues and Organs

Engineering three-dimensional (3D) scaffolds for functional tissue and organ regeneration is a major challenge of the tissue engineering (TE) community. Great progress has been made in developing scaffolds to support cells in 3D, and to date, several implantable scaffolds are available for treating damaged and dysfunctional tissues, such as bone, osteochondral, cardiac and nerve. However, recapitulating the complex extracellular matrix (ECM) functions of native tissues is far from being achieved in synthetic scaffolds. Modular TE is an intriguing approach that aims to design and fabricate ECM-mimicking scaffolds by the bottom-up assembly of building blocks with specific composition, morphology and structural properties. This review provides an overview of the main strategies to build synthetic TE scaffolds through bioactive modules assembly and classifies them into two distinct schemes based on microparticles (µPs) or patterned layers. The µPs-based processes section starts describing novel techniques for creating polymeric µPs with desired composition, morphology, size and shape. Later, the discussion focuses on µPs-based scaffolds design principles and processes. In particular, starting from random µPs assembly, we will move to advanced µPs structuring processes, focusing our attention on technological and engineering aspects related to cell-free and cell-laden strategies. The second part of this review article illustrates layer-by-layer modular scaffolds fabrication based on discontinuous, where layers' fabrication and assembly are split, and continuous processes.

Biomimetic open porous structured core-shell microtissue with enhanced mechanical properties for bottom-up bone tissue engineering

Background: Microtissues constructed with hydrogels promote cell expansion and specific differentiation by mimicking the microarchitecture of native tissues. However, the suboptimal mechanical property and osteogenic activity of microtissues fabricated by natural polymers need further improvement for bone reconstruction application. Core-shell designed structures are composed of an inner core part and an outer part shell, combining the characteristics of different materials, which improve the mechanical property of microtissues. Methods: A micro-stencil array chip was used to fabricate an open porous core-shell micro-scaffold consisting of gelatin as shell and demineralized bone matrix particles modified with bone morphogenetic protein-2 (BMP-2) as core. Single gelatin micro-scaffold was fabricated as a control. Rat bone marrow mesenchymal stem cells (BMSCs) were seeded on the micro-scaffolds, after which they were dynamic cultured and osteo-induced in mini-capsule bioreactors to fabricate microtissues. The physical characteristics, biocompatibility, osteo-inducing and controlled release ability of the core-shell microtissue were evaluated in vitro respectively. Then microtissues were tested in vivo via ectopic implantation and orthotopic bone implantation in rat model. Results: The Young's modulus of core-shell micro-scaffold was nearly triple that of gelatin micro-scaffold, which means the core-shell micro-scaffolds have better mechanical property. BMSCs rapidly proliferated and retained the highest viability on core-shell microtissues. The improved osteogenic potential of core-shell microtissues was evidenced by the increased calcification based on von kossa staining and osteo-relative gene expression. At 3months after transplantation, core-shell microtissue group formed the highest number of mineralized tissues in rat ectopic subcutaneous model, and displayed the largest amount of new bony tissue deposition in rat orthotopic cranial defect. Conclusion: The novel core-shell microtissue construction strategy developed may become a promising cell delivery platform for bone regeneration.

Anti-GPC3 antibody-modified sorafenib-loaded nanoparticles significantly inhibited HepG2 hepatocellular carcinoma

Sorafenib (SFB) has improved the treatment of hepatocellular carcinoma (HCC) and has fewer severe side effects than other agents used for that purpose. However, due to a lack of tumor-specific targeting, the concentration of the drug in tumor tissue cannot be permanently maintained at a level that inhibits tumor growth. To overcome this problem, we developed a novel SFB-loaded polymer nanoparticle (NP). The NP (a TPGS-b-PCL copolymer that was synthesized from ε-caprolactone and d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) via ring-opening polymerization) contains Pluronic P123 and SFB, and its surface is modified with anti-GPC3 antibody to produce the polymer nanoparticle (NP-SFB-Ab). The Ab-conjugated NPs had higher cellular uptake by HepG2 cells than did non-antibody-conjugated SPD-containing nanoparticles (NP-SFB). The NP-SFB-Ab also displayed better stability characteristics, released higher levels of SFB into cell culture medium, and was more cytotoxic to tumor cells than was non-targeted NP-SFB and free SFB. The NP-SFB-Ab downregulated expression of the anti-apoptosis molecule MCL-1, which led to polymerization of Bax and Bak in mitochondrial cytosol. The NP-SFB-AB also promoted the mitochondrial release of cytochrome C, resulting in cellular apoptosis. Moreover, the NP-SFB-Ab significantly inhibited the growth of HepG2 xenograft tumors in nude mice without producing obvious side effects. These findings suggest that NP-SFB-Ab is a promising new method for achieving targeted therapy of HCC.