Osteon-mimetic 3D nanofibrous scaffold enhances stem cell proliferation and osteogenic differentiation for bone regeneration

Polyhydroxybutyrate-based osteoinductive mineralized electrospun structures that mimic components and tissue interfaces of the osteon for bone tissue engineering

Scaffolds for bone tissue engineering should enable regeneration of bone tissues with its native hierarchically organized extracellular matrix (ECM) and multiple tissue interfaces. To achieve this, inspired by the structure and properties of bone osteon, we fabricated polyhydroxybutyrate (PHB)-based mineralized electrospun fibrous scaffolds. After studying multiple PHB-based fibers, we chose 7%PHB/1%Gelatin fibers (PG) to fabricate mineralized fibers that mimic mineralized collagen fibers in bone. The mineralized PG (mPG) surface had a rough, hydrophilic layer of low crystalline calcium phosphate which was biocompatible to bone marrow stromal cells (BMSCs), induced their proliferation and was osteoinductive. Subsequently, by modulating the electrospinning process, we fabricated mPG-based novel higher order fibrous scaffolds that mimic the macroscale geometries of osteons of bone ECM. Inspired by the aligned collagen fibers in bone lamellae, we fabricated mPG scaffolds with aligned fibers that could direct anisotropic elongation of mouse BMSC (mBMSCs). Further, we fabricated electrospun mPG-based osteoinductive tubular constructs which can mimic cylindrical bone components like osteons or lamellae or be used as long bone analogues based on their dimensions. Finally, to regenerate tissue interfaces in bone, we introduced a novel bi-layered scaffold-based approach. An electrospun bi-layered tubular construct that had PG in the outer layer and 7%PHB/0.5%Polypyrrole fibers (PPy) in the inner layer was fabricated. The bi-layered tubular construct underwent preferential surface mineralization only on its outer layer. This outer mineralized layer supported osteogenesis while the inner PPy layer could support neural cell growth. Thus, the bi-layered tubular construct may be used to regenerate haversian canal in the osteons which hosts nerve fibers. Overall, the study introduced novel techniques to fabricate biomimetic structures that can regenerate components of bone osteon and its multiple tissue interfaces. The study lays foundation for the fabrication of a modular scaffold that can regenerate bone with its hierarchical structure and complex tissue interfaces.

Pulmonary decellularized extracellular matrix (dECM) modified polyethylene terephthalate three-dimensional cell carriers regulate the proliferation and paracrine activity of mesenchymal stem cells

Introduction: Mesenchymal stem cells (MSCs) possess a high degree of self-renewal capacity and in vitro multi-lineage differentiation potential. Decellularized materials have garnered considerable attention due to their elevated biocompatibility, reduced immunogenicity, excellent biodegradability, and the ability to partially mimic the in vivo microenvironment conducive to cell growth. To address the issue of mesenchymal stem cells losing their stem cell characteristics during two-dimensional (2D) cultivation, this study established three-dimensional cell carriers modified with lung decellularized extracellular matrix and assessed its impact on the life activities of mesenchymal stem cells. Methods: This study employed PET as a substrate material, grafting with polydopamine (PDA), and constructing a decellularized extracellular matrix (dECM) coating on its surface, thus creating the PET/PDA/dECM three-dimensional (3D) composite carrier. Subsequently, material characterization of the cellular carriers was conducted, followed by co-culturing with human umbilical cord mesenchymal stem cells in vitro, aiming to investigate the material's impact on the proliferation and paracrine activity of mesenchymal stem cells. Results and Discussion: Material characterization demonstrated successful grafting of PDA and dECM materials, and it had complete hydrophilicity, high porosity, and excellent mechanical properties. The material was rich in various ECM proteins (collagen I, collagen IV , laminin, fibronectin, elastin), indicating good biocompatibility. In long-term in vitro cultivation (14 days) experiments, the PET/PDA/dECM three-dimensional composite carrier significantly enhanced adhesion and proliferation of human umbilical cord-derived mesenchymal stem cells (HUCMSCs), with a proliferation rate 1.9 times higher than that of cells cultured on tissue culture polystyrene (TCPS) at day 14. Furthermore, it effectively maintained the stem cell characteristics, expressing specific antigens for HUCMSCs. Through qPCR, Western blot, and ELISA experiments, the composite carrier markedly promoted the expression and secretion of key cell factors in HUCMSCs. These results demonstrate that the PET/PDA/dECM composite carrier holds great potential for scaling up MSCs' long-term in vitro cultivation and the production of paracrine factors.

Engineering antibacterial shrinkage‐free trinary PLGA‐based GBR membrane for bone regeneration

The purpose of this study was preparation of a multilayer electrospun poly (lactic‐co‐glycolic acid) (PLGA)‐based guided bone regeneration (GBR) membrane with controlled shrinkage behavior and alveolar bone regeneration property. First, PLGA copolymer, and zinc‐doped hydroxyapatite (Zn‐HAp) particles were prepared and characterized using fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), proton nuclear magnetic resonance, and X‐ray diffraction analysis. Since the electrospun PLGA scaffolds showed about 80% shrinkage at physiological conditions (phosphate‐buffered saline, 37°C), the effect of factors such as fiber‐alignment, and additives including natural polymers such as gelatin and chitosan, and Zn‐HAp particles; as well as solution preparation method was investigated on the shrinkage ratio. The results showed that it is possible to eliminate the shrinkage of the scaffold in the physiological environment through appropriate design of a tri‐layer PLGA‐CHI/PLGA‐Gel/PLGA‐Gel‐ZnHAp membrane. The designed tri‐layer membrane demonstrated a bubble point smaller than 7 μm, and improved mechanical properties compared with the individual sub‐layer scaffolds. Additionally, it exhibited enhanced antibacterial activity when compared with a similar three‐layer membrane in which HAp was used instead of Zn‐HAp. This observation suggests a synergistic antibacterial effect resulting from the presence of both zinc ions in Zn‐HAp and chitosan . Osteogenic differentiation of adipose‐derived mesenchymal stem cells cultured on the optimal multilayer composite scaffold, was investigated using alkaline phosphatase and Alizarin red staining assays, and the results suggested that the scaffold could support  osteogenic differentiation of the stem cells. The designed membrane was implanted in critical size (1 cm) mandibular defects in dogs, and bone regeneration was monitored by computed tomography. Defects treated with the GBR membrane, and the control group showed 69.31% and 44.63%, newly mineralized tissue, respectively, after 8 weeks post implantation. Based on our results, the engineered 3‐layer scaffold is a promising candidate as a GBR membrane for periodontal applications.

3D interconnected porous PMMA scaffold integrating with advanced nanostructured CaP-based biomaterials for rapid bone repair and regeneration

Bioactive scaffolds with polymer and nanostructured bioactive glass-based composites are promising materials for regenerative applications in consequence of close mimics of natural bone composition. Poly methyl methacrylate (PMMA) is a highly preferred thermoplastic polymer for orthopedic applications as it has good biocompatibility. Different kinds of bioactive, biodegradable as well as biocompatible biomaterial composites such as Bioglass (BG), Hydroxyapatite (Hap), and Tricalcium phosphate (TCP) can be integrated with PMMA, so as to augment the bioactivity, porosity as well as regeneration of hard tissues in human body. Among the bioactive glass, 60S BG (Bioactive glass with 60 percentage of Silica without Sodium ions) is better materials among aforementioned systems owning to mechanical stability as well as controlled bioactive material. In this work, the fabrication of PMMA-CaP (calcium phosphate)-based scaffolds were carried out by Thermal Induced Phase Separation method (TIPS). X-ray diffractogram analysis (XRD) is used to examine the physiochemical properties of the scaffolds that evidently reveal the presence of calcium phosphate besides calcium phosphate silicate phases. The Field Emission Scanning Electron Microscopy (FESEM) studies obviously exhibited the microstructure of the scaffolds as well as their interconnected porous morphology. The PMMA/60S BG/TCP (C50) scaffold has the maximum pore size, measuring 77 ± 23 μm, while the average pore size ranges from 50 ± 20 to 80 ± 23 μm. By performing a liquid displacement method, the C50 scaffold is found to have the largest porosity of 50%, high hydrophilicity of 118.16°, and a compression test reveals the scaffolds to have a maximum compressive strength of 0.16 MPa. The emergence of bone-like apatite on the scaffold surface after 1st and 21st days of SBF immersion is further supported by in vitro bioactivity studies. Cytocompatibility and hemocompatibility analyses undoubtedly confirmed the biocompatibility behavior of PMMA-based bioactive scaffolds. Nano-CT investigation demonstrates that PMMA-CaP scaffolds provide more or less alike morphologies of composites that resemble the natural bone. Therefore, this combination of scaffolds could be considered as potential biomaterials for bone regeneration application. This detailed study promisingly demonstrates the eminence of the unique scaffolds in the direction of regenerative medicines.

Bilayer scaffolds/membranes for bone tissue engineering applications: A systematic review

OBJECTIVE

This systematic review evaluates the purpose, materials, physio-mechanical, and biological effects of bilayer scaffolds/membranes used for bone tissue engineering applications.

METHODS

A comprehensive electronic search of English-language literature from 2012 to October 2022 was conducted in PubMed, Scopus, ScienceDirect, and Google Scholar online databases according to the PRISMA 2020 guidelines. The quality of animal studies was evaluated through the SYRCLE's risk of bias tool.

RESULTS

A total of 77 studies were sought for retrieval, and 39 studies met the inclusion criteria. According to the synthesis results, most bilayers had a dense barrier layer that prevented connective tissue penetration and a loose osteogenic layer that supported cell migration and osteogenesis. PLGA, PCL, and chitosan were the most common polymers in the barrier layers, while the most utilized polymers in osteogenic layers were PLGA and gelatin. Electrospinning and solvent casting were the most common fabrication methods to design the bilayer structures. Many studies reported higher biological results for bilayers compared to their single layers. Also, fabricated bilayers' in vitro osteogenesis and in vivo new bone formation were significantly superior or at least comparable to the frequently used commercial membranes.

CONCLUSION

1) Bilayers with two distinct layers and different materials, porosities, mechanical properties, and biological behavior can significantly improve heterogeneous bone regeneration; 2) the addition of ceramics and/or drugs to the osteogenic layer enhances the osteogenic properties of the bilayers; 3) fabrication method and pore size of the layers play an important role in determining the mechanical and biological behavior of them.

An Update on Adipose-Derived Stem Cells for Regenerative Medicine: Where Challenge Meets Opportunity

Over the last decade, adipose-derived stem cells (ADSCs) have attracted increasing attention in the field of regenerative medicine. ADSCs appear to be the most advantageous cell type for regenerative therapies owing to their easy accessibility, multipotency, and active paracrine activity. This review highlights current challenges in translating ADSC-based therapies into clinical settings and discusses novel strategies to overcome the limitations of ADSCs. To further establish ADSC-based therapies as an emerging platform for regenerative medicine, this review also provides an update on the advancements in this field, including fat grafting, wound healing, bone regeneration, skeletal muscle repair, tendon reconstruction, cartilage regeneration, cardiac repair, and nerve regeneration. ADSC-based therapies are expected to be more tissue-specific and increasingly important in regenerative medicine.

Tough Porous Silk Nanofiber-Derived Cryogels with Osteogenic and Angiogenic Capacity for Bone Repair

Tough porous cryogels with angiogenesis and osteogenesis features remain a design challenge for utility in bone regeneration. Here, building off of the recent efforts to generate tough silk nanofiber-derived cryogels with osteogenic activity, deferoxamine (DFO) is loaded in silk nanofiber-derived cryogels to introduce angiogenic capacity. Both the mechanical cues (stiffness) and the sustained release of DFO from the gels are controlled by tuning the concentration of silk nanofibers in the system, achieving a modulus above 400 kPa and slow release of the DFO over 60 days. The modulus of the cryogels and the released DFO induce osteogenic and angiogenic activity, which facilitates bone regeneration in vivo in femur defects in rat, resulting in faster regeneration of vascularized bone tissue. The tunable physical and chemical cues derived from these nanofibrous-microporous structures support the potential for silk cryogels in bone tissue regeneration.

Fiber diameters and parallel patterns: proliferation and osteogenesis of stem cells

Due to the innate extracellular matrix mimicking features, fibrous materials exhibited great application potential in biomedicine. In developing excellent fibrous biomaterial, it is essential to reveal the corresponding inherent fiber features' effects on cell behaviors. Due to the inevitable 'interference' cell adhesions to the background or between adjacent fibers, it is difficult to precisely reveal the inherent fiber diameter effect on cell behaviors by using a traditional fiber mat. A single-layer and parallel-arranged polycaprolactone fiber pattern platform with an excellent non-fouling background is designed and constructed herein. In this unique material platform, the 'interference' cell adhesions through interspace between fibers to the environment could be effectively ruled out by the non-fouling background. The 'interference' cell adhesions between adjacent fibers could also be excluded from the sparsely arranged (SA) fiber patterns. The influence of fiber diameter on stem cell behaviors is precisely and comprehensively investigated based on eliminating the undesired 'interference' cell adhesions in a controllable way. On the SA fiber patterns, small diameter fiber (SA-D1, D1 means 1 μm in diameter) may seriously restrict cell proliferation and osteogenesis when compared to the middle (SA-D8) and large (SA-D56) ones and SA-D8 shows the optimal osteogenesis enhancement effect. At the same time, the cells present similar proliferation ability and even the highest osteogenic ability on the densely arranged (DA) fiber patterns with small diameter fiber (DA-D1) when compared to the middle (DA-D8) and large (DA-D56) ones. The 'interference' cell adhesion between adjacent fibers under dense fiber arrangement may be the main reason for inducing these different cell behavior trends along with fiber diameters. Related results and comparisons have illustrated the effects of fiber diameter on stem cell behaviors more precisely and objectively, thus providing valuable reference and guidance for developing effective fibrous biomaterials.

A silk fibroin/chitosan/nanohydroxyapatite biomimetic bone scaffold combined with autologous concentrated growth factor promotes the proliferation and osteogenic differentiation of BMSCs and repair of critical bone defects

Purpose

With the goal of increasing the translational efficiency of bone tissue engineering for practical clinical applications, biomimetic composite scaffolds combined with autologous endogenous growth factors for repairing bone defects have become a current research hotspot. In this study, we prepared a silk fibroin/chitosan/nanohydroxyapatite (SF/CS/nHA) composite biomimetic scaffold and then combined it with autologous concentrated growth factor (CGF) to explore the effect of this combination on the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and the efficiency of repairing critical radial defects.

Methods

Three kinds of SF/CS/nHA composite biomimetic scaffolds with mass fractions of 3%, 4%, and 5% were prepared by vacuum freeze-drying and chemical cross-linking methods, and the characteristics of the scaffolds were evaluated. In vitro, BMSCs were seeded on SF/CS/nHA scaffolds, and then CGF was added. The morphology and proliferation of BMSCs were evaluated by live-dead staining, phalloidin staining, and CCK-8 assays. ALP staining, alizarin red staining, cellular immunofluorescence, RT-PCR, and Western blotting were used to detect the osteogenic differentiation of BMSCs. In vivo, a rabbit radius critical bone defect model was constructed, and the SF/CS/nHA-BMSC scaffold cell complex combined with CGF was implanted. The effect on bone defect repair was evaluated by 3D CT scanning, HE staining, Masson staining, and immunohistochemistry.

Results

The characteristics of 4% SF/CS/nHA were the most suitable for repairing bone defects. In vitro, the SF/CS/nHA combined CGF group showed better adhesion, cell morphology, proliferation, and osteogenic differentiation of BMSCs than the other groups (P < 0.05 for all). In vivo imaging examination and histological analysis demonstrated that the SF/CS/nHA scaffold combined with CGF had better efficiency in bone defect repair than the other scaffolds (P < 0.05 for all).

Conclusions

A SF/CS/nHA composite biomimetic bone scaffold combined with autologous CGF promoted the proliferation and osteogenic differentiation of BMSCs in vitro and improved the repair efficiency of critical bone defects in vivo. This combination may have the potential for clinical translation due to its excellent biocompatibility.