The fast release of stem cells from alginate-fibrin microbeads in injectable scaffolds for bone tissue engineering

Genipin stabilized fibrin microbeads: Carrying cytokines to form niches for stem cell differentiation

Niches, which are combinations of extracellular matrix and cytokines, play essential roles in the stem cell biology. In this study, genipin stabilized fibrin microbeads (gFMBs) were prepared through oil emulsion method. Then, sonic hedgehog (SHH) was crosslinked to the surface of gFMBs by using genipin. These gFMBs were designated as gFMB@SHH since SHH was attached to their surface. Moreover, ectomesenchymal stem cells (EMSCs) were cultured, characterized, and used to test gFMB@SHH. Genipin not only changed the color of fibrin microbeads (FMBs) to deep blue, but also stabilized FMBs by delaying their degradation in vitro. In addition to the nontoxic and proliferation promoting effects of gFMB@SHH on EMSCs, gFMBs@SHH could induce neural differentiation of EMSCs by stimulating the SHH/Gli pathway. Therefore, genipin stabilized fibrin microbeads might be a promising structure to construct niches for in vitro stem cell researches.

Oxidized ionic polysaccharide hydrogels: Review on derived scaffolds characteristics and tissue engineering applications

Polysaccharide-based hydrogels have gained prominence due to their non-toxicity, biocompatibility, and structural adaptability for constructing tissue engineering scaffolds. Polysaccharide crosslinking is necessary for hydrogel stability in vivo. The periodate oxidation enables the modification of native polysaccharide characteristics for wound healing and tissue engineering applications. It produces dialdehydes, which are used to crosslink biocompatible amine-containing macromolecules such as chitosan, gelatin, adipic acid dihydrazide, silk fibroin, and peptides via imine/hydrazone linkages. Crosslinked oxidized ionic polysaccharide hydrogels have been studied for wound healing, cardiac and liver tissue engineering, bone, cartilage, corneal tissue regeneration, abdominal wall repair, nucleus pulposus regeneration, and osteoarthritis. Several modified hydrogel systems have been synthesized using antibiotics and inorganic substances to improve porosity, mechanical and viscoelastic properties, desired swelling propensity, and antibacterial efficacy. Thus, the injectable hydrogels provide a host-tissue-mimetic environment with high cell adhesion and viability, making them appropriate for scarless wound healing and tissue engineering applications. This review describes the oxidation procedure for alginate, hyaluronic acid, gellan gum, pectin, xanthan gum and chitosan, as well as the characteristics of the resulting materials. Furthermore, a critical review of scientific advances in wound healing and tissue engineering applications has been provided.

Injectable periodontal ligament stem cell-metformin-calcium phosphate scaffold for bone regeneration and vascularization in rats

OBJECTIVES

Injectable and self-setting calcium phosphate cement scaffold (CPC) capable of encapsulating and delivering stem cells and bioactive agents would be highly beneficial for dental and craniofacial repairs. The objectives of this study were to: (1) develop a novel injectable CPC scaffold encapsulating human periodontal ligament stem cells (hPDLSCs) and metformin (Met) for bone engineering; (2) test bone regeneration efficacy in vitro and in vivo.

METHODS

hPDLSCs were encapsulated in degradable alginate fibers, which were then mixed into CPC paste. Five groups were tested: (1) CPC control; (2) CPC + hPDLSC-fibers + 0% Met (CPC + hPDLSCs + 0%Met); (3) CPC + hPDLSC-fibers + 0.1% Met (CPC + hPDLSCs + 0.1%Met); (4) CPC + hPDLSC-fibers + 0.2% Met (CPC + hPDLSCs + 0.2%Met); (5) CPC + hPDLSC-fibers + 0.4% Met (CPC + hPDLSCs + 0.4%Met). The injectability, mechanical properties, metformin release, and hPDLSC osteogenic differentiation and bone mineral were determined in vitro. A rat cranial defect model was used to evaluate new bone formation.

RESULTS

The novel construct had good injectability and physical properties. Alginate fibers degraded in 7 days and released hPDLSCs, with 5-fold increase of proliferation (p＜0.05). The ALP activity and mineral synthesis of hPDLSCs were increased by Met delivery (p＜0.05). Among all groups, CPC+hPDLSCs+ 0.1%Met showed the greatest cell mineralization and osteogenesis, which were 1.5-10 folds those without Met (p＜0.05). Compared to CPC control, CPC+hPDLSCs+ 0.1%Met enhanced bone regeneration in rats by 9 folds, and increased vascularization by 3 folds (p＜0.05).

CONCLUSIONS

The novel injectable construct with hPDLSC and Met encapsulation demonstrated excellent efficacy for bone regeneration and vascularization in vivo in an animal model. CPC+hPDLSCs+ 0.1%Met is highly promising for dental and craniofacial applications.

Degradable hydrogel fibers encapsulate and deliver metformin and periodontal ligament stem cells for dental and periodontal regeneration

Human periodontal ligament stem cells (hPDLSCs) are promising cells for dental and periodontal regeneration. This study aimed to develop novel alginate-fibrin fibers that encapsulates hPDLSCs and metformin, to investigate the effect of metformin on the osteogenic differentiation of hPDLSCs, and to determine the regulatory role of the Shh/Gli1 signaling pathway in the metformin-induced osteogenic differentiation of hPDLSCs for the first time. CCK8 assay was used to evaluate hPDLSCs. Alkaline phosphatase (ALP) staining, alizarin red S staining, and the expression of osteogenic genes were evaluated. Metformin and hPDLSCs were encapsulated in alginate-fibrinogen solutions, which were injected to form alginate-fibrin fibers. The activation of Shh/Gli1 signaling pathway was examined using qRT-PCR and western blot. A mechanistic study was conducted by inhibiting the Shh/Gli1 pathway using GANT61. The administration of 50 μM metformin resulted in a significant upregulation of osteogenic gene expression in hPDLSCs by 1.4-fold compared to the osteogenic induction group (P < 0.01), including ALP and runt-related transcription factor-2 (RUNX2). Furthermore, metformin increased ALP activity by 1.7-fold and bone mineral nodule formation by 2.6-fold (P<0.001). We observed that hPDLSCs proliferated with the degradation of alginate-fibrin fibers, and metformin induced their differentiation into the osteogenic lineage. Metformin also promoted the osteogenic differentiation of hPDLSCs by upregulating the Shh/Gli1 signaling pathway by 3- to 6- fold compared to the osteogenic induction group (P<0.001). The osteogenic differentiation ability of hPDLSCs were decreased 1.3- to 1.6-fold when the Shh/Gli1 pathway was inhibited, according to ALP staining and alizarin red S staining (P<0.01). Metformin enhanced the osteogenic differentiation of hPDLSCs via the Shh/Gli1 signaling pathway. Degradable alginate-fibrin hydrogel fibers encapsulating hPDLSCs and metformin have significant potential for use in dental and periodontal tissue engineering applications. Alginate-fibrin fibers encapsulating hPDLSCs and metformin have a great potential for use in the treatment of maxillofacial bone defects caused by trauma, tumors, and tooth extraction. Additionally, they may facilitate the regeneration of periodontal tissue in patients with periodontitis.

Technological advances in fibrin for tissue engineering

Fibrin is a promising natural polymer that is widely used for diverse applications, such as hemostatic glue, carrier for drug and cell delivery, and matrix for tissue engineering. Despite the significant advances in the use of fibrin for bioengineering and biomedical applications, some of its characteristics must be improved for suitability for general use. For example, fibrin hydrogels tend to shrink and degrade quickly after polymerization, particularly when they contain embedded cells. In addition, their poor mechanical properties and batch-to-batch variability affect their handling, long-term stability, standardization, and reliability. One of the most widely used approaches to improve their properties has been modification of the structure and composition of fibrin hydrogels. In this review, recent advances in composite fibrin scaffolds, chemically modified fibrin hydrogels, interpenetrated polymer network (IPN) hydrogels composed of fibrin and other synthetic or natural polymers are critically reviewed, focusing on their use for tissue engineering.

Novel injectable calcium phosphate scaffold with human periodontal ligament stem cell encapsulation in microbeads for bone regeneration

Objectives: 1) Develop a novel construct of human periodontal ligament stem cells (hPDLSCs) encapsulated in degradable alginate microbeads (DAMB) with human platelet lysate (hPL) and injectable calcium phosphate cement (ICPC); 2) Investigate the proliferation and osteogenic differentiation of hPDLSCs in ICPC with hPL as a xeno-free supplement and animal serum replacement for bone tissue engineering applications.

Methods: hPDLSCs were encapsulated in alginate-fibrin microbeads (DAMB + fibrin), alginate-hPL degradable microbeads (DAMB + hPL), or alginate-fibrin-hPL microbeads (DAMB + fibrin + hPL). The proliferation and osteogenic differentiation of hPDLSCs were investigated in culturing with the ICPC scaffold.

Results: Flexural strength of ICPC was 8.4 ± 0.91 MPa, and elastic modulus was 1.56 ± 0.1 GPa, exceeding those of cancellous bone. hPDLSCs had higher viability in DAMB + fibrin + hPL group than in DAMB + fibrin. ALP was 69.97 ± 16.96 mU/mg for ICPC + DAMB + fibrin + hPL group, higher than 30.68 ± 2.86 mU/mg of ICPC + DAMB + fibrin (p &lt; 0.05) and 4.12 ± 1.65 mU/mg of control (p &lt; 0.01). At 7 days, osteogenic gene expressions (ALP, RUNX2, COL1, and OPN) in ICPC + DAMB + fibrin + hPL and ICPC + DAMB + fibrin were 4–11 folds that of control. At 21 days, the hPDLSC-synthesized bone mineral amounts in ICPC + DAMB + fibrin + hPL and ICPC + DAMB + fibrin were 13.2 folds and 11.1 folds that of control group, respectively.

Conclusion: The novel injectable CPC scaffold encapsulating hPDLSCs and hPL is promising to protect and deliver hPDLSCs. The hPL-based medium significantly enhanced the osteogenic differentiation of hPDLSCs in ICPC + DAMB + fibrin + hPL construct, suggesting a promising xeno-free approach for bone tissue regeneration applications.

Human periodontal ligament stem cell encapsulation in alginate-fibrin-platelet lysate microbeads for dental and craniofacial regeneration

OBJECTIVE

Tissue engineering is promising for dental and craniofacial regeneration. The objectives of this study were to develop a novel xeno-free alginate-fibrin-platelet lysate hydrogel with human periodontal ligament stem cells (hPDLSCs) for dental regeneration, and to investigate the proliferation and osteogenic differentiation of hPDLSCs using hPL as a cell culture nutrient supplement.

METHODS

hPDLSCs were cultured with Dulbecco's modified eagle medium (DMEM), DMEM + 10% fetal bovine serum (FBS), and DMEM + hPL (1%, 2.5%, and 5%). hPDLSCs were encapsulated in alginate-fibrin microbeads (Alg+Fib), alginate-hPL microbeads (Alg+hPL), or alginate-fibrin-hPL microbeads (Alg+Fib+hPL). hPDLSCs encapsulated in alginate microbeads were induced with an osteogenic medium containing hPL or FBS. Quantitative real-time polymerase chain reaction (qRT-PCR), alkaline phosphatase (ALP) activity, ALP staining, and alizarin red (ARS) staining was investigated.

RESULTS

hPDLSCs were released faster from Alg+Fib+hPL than from Alg+hPL. At 14 days, ALP activity was 44.1 ± 7.61 mU/mg for Alg+Fib+hPL group, higher than 28.07 ± 5.15 mU/mg of Alg+Fib (p<0.05) and 0.95 ± 0.2 mU/mg of control (p<0.01). At 7 days, osteogenic genes (ALP, RUNX2, COL1, and OPN) in Alg+Fib+hPL and Alg+Fib were 3-10 folds those of control. At 21 days, the hPDLSC-synthesized bone mineral amount in Alg+Fib+hPL and Alg+Fib was 7.5 folds and 4.3 folds that of control group, respectively.

CONCLUSIONS

The 2.5% hPL was determined to be optimal for hPDLSCs. Adding hPL into alginate hydrogel improved the viability of the hPDLSCs encapsulated in the microbeads. The hPL-based medium enhanced the osteogenic differentiation of hPDLSCs in Alg+Fib+hPL construct, showing a promising xeno-free approach for delivering hPDLSCs to enhance dental, craniofacial and orthopedic regenerations.

Genipin-crosslinked fibrin seeded with oxidized alginate microbeads as a novel composite biomaterial strategy for intervertebral disc cell therapy

Discectomy procedures alleviate disability caused by intervertebral disc (IVD) herniation, but do not repair herniation-induced annulus fibrosus (AF) defects. Cell therapy shows promise for IVD repair, yet cell delivery biomaterials capable of sealing AF defects and restoring biomechanical function have poor biological performance. To balance the biomechanical and biological demands of IVD cell delivery biomaterials, we engineered an injectable composite biomaterial using cell-laden, degradable oxidized alginate (OxAlg) microbeads (MBs) to deliver AF cells within high-modulus genipin-crosslinked fibrin (FibGen) hydrogels (FibGen + MB composites). Conceptually, the high-modulus FibGen would immediately stabilize injured IVDs, while OxAlg MBs would protect and release cells required for long-term healing. We first showed that AF cells microencapsulated in OxAlg MBs maintained high viability and, upon release, displayed phenotypic AF cell morphology and gene expression. Next, we created cell-laden FibGen + MB composites and demonstrated that OxAlg MBs functionalized with RGD peptides (MB-RGD) minimized AF cell apoptosis and retained phenotypic gene expression. Further, we showed that cell-laden FibGen + MB composites are biomechanically stable and promote extracellular matrix (ECM) synthesis in long-term in vitro culture. Lastly, we evaluated cell-laden FibGen + MB-RGD composites in a long-term bovine caudal IVD organ culture bioreactor and found that composites had low herniation risk, provided superior biomechanical and biological repair to discectomy controls, and retained anabolic cells within the IVD injury space. This novel injectable composite hydrogel strategy shows promise as an IVD cell delivery sealant with potentially broad applications for its capacity to balance biomechanical and biological performance.

3D Bioprinted Alginate-Silk-Based Smart Cell-Instructive Scaffolds for Dual Differentiation of Human Mesenchymal Stem Cells

Designing smart bioinks, which can provide multifunctionality and instructive cues to cells, is a current need of the tissue engineering field. Addressing these parameters, this work aims at developing a smart dual 3D bioprinted scaffold that is capable of differentiating human mesenchymal stem cells into two different lineages within the same construct without providing any exogenous cues. Here, biocompatible alginate- and silk-based bioinks were developed to print self-standing structures with the ability of spatially controlled differentiation of the encapsulated hMSCs. We present this proof of concept and have demonstrated a smart design where the incorporation of phosphate groups enhanced the osteogenic differentiation, whereas the addition of silk promoted the chondrogenic differentiation. Altogether, the present work suggests the potential of the developed bioinks for use in creating clinically viable osteochondral grafts.

Preparation and Characterization of Plasma-Derived Fibrin Hydrogels Modified by Alginate di-Aldehyde

Fibrin hydrogels are one of the most popular scaffolds used in tissue engineering due to their excellent biological properties. Special attention should be paid to the use of human plasma-derived fibrin hydrogels as a 3D scaffold in the production of autologous skin grafts, skeletal muscle regeneration and bone tissue repair. However, mechanical weakness and rapid degradation, which causes plasma-derived fibrin matrices to shrink significantly, prompted us to improve their stability. In our study, plasma-derived fibrin was chemically bonded to oxidized alginate (alginate di-aldehyde, ADA) at 10%, 20%, 50% and 80% oxidation, by Schiff base formation, to produce natural hydrogels for tissue engineering applications. First, gelling time studies showed that the degree of ADA oxidation inhibits fibrin polymerization, which we associate with fiber increment and decreased fiber density; moreover, the storage modulus increased when increasing the final volume of CaCl₂ (1% w/v) from 80 µL to 200 µL per milliliter of hydrogel. The contraction was similar in matrices with and without human primary fibroblasts (hFBs). In addition, proliferation studies with encapsulated hFBs showed an increment in cell viability in hydrogels with ADA at 10% oxidation at days 1 and 3 with 80 µL of CaCl₂; by increasing this compound (CaCl₂), the proliferation does not significantly increase until day 7. In the presence of 10% alginate oxidation, the proliferation results are similar to the control, in contrast to the sample with 20% oxidation whose proliferation decreases. Finally, the viability studies showed that the hFB morphology was maintained regardless of the degree of oxidation used; however, the quantity of CaCl₂ influences the spread of the hFBs.

Current advances in cell therapeutics: A biomacromolecules application perspective

INTRODUCTION

Many chronic diseases have evolved and to circumvent the limitations of using conventional drug therapies, smart cell encapsulating delivery systems have been explored to customize the treatment with alignment to disease longevity. Cell therapeutics has advanced in tandem with improvements in biomaterials that can suitably deliver therapeutic cells to achieve targeted therapy. Among the promising biomacromolecules for cell delivery are those that share bio-relevant architecture with the extracellular matrix and display extraordinary compatibility in the presence of therapeutic cells. Interestingly, many biomacromolecules that fulfil these tenets occur naturally and can form hydrogels.

AREAS COVERED

This review provides a concise incursion into the paradigm shift to cell therapeutics using biomacromolecules. Advances in the design and use of biomacromolecules to assemble smart therapeutic cell carriers is discussed in light of their pivotal role in enhancing cell encapsulation and delivery. In addition, the principles that govern the application of cell therapeutics in diabetes, neuronal disorders, cancers and cardiovascular disease are outlined.

EXPERT OPINION

Cell therapeutics promises to revolutionize the treatment of various secretory cell dysfunctions. Current and future advances in designing functional biomacromolecules will be critical to ensure that optimal delivery of therapeutic cells is achieved with desired biosafety and potency.

Synthesis of Fibrin-Type I Collagen Biomaterials via an Acidic Gel

Fibrin-Type I collagen composite gels have been widely studied as biomaterials, in which both networks are usually formed simultaneously at a neutral pH. Here, we describe a new protocol in which mixed concentrated solutions of collagen and fibrinogen were first incubated at acidic pH to induce fibrinogen gel formation, followed by a pH change to neutral inducing collagen fiber formation. Thrombin was then added to form fibrin-collagen networks. Using this protocol, mixed gels containing 20 mg.mL⁻¹ fibrin and up to 10 mg.mL⁻¹ collagen could be prepared. Macroscopic observations evidenced that increasing the content of collagen increases the turbidity of the gels and decreases their shrinkage during the fibrinogen-to-fibrin conversion. The presence of collagen had a minor influence on the rheological properties of the gels. Electron microscopy allowed for observation of collagen fibers within the fibrin network. 2D cultures of C2C12 myoblasts on mixed gels revealed that the presence of collagen favors proliferation and local alignment of the cells. However, it interferes with cell differentiation and myotube formation, suggesting that further control of in-gel collagen self-assembly is required to elaborate fully functional biomaterials.

Investigation and Comparison of the Effect of TGF-β3, kartogenin and Avocado/Soybean Unsaponifiables on the In-vitro and In-vivo Chondrogenesis of Human Adipose-Derived Stem Cells on Fibrin Scaffold

Due to the lack of suitable therapeutic approaches to cartilage defect, the objective of this study was to determine the effect of Transforming growth factor-β3 (TGF-β3), avocado/soybean (ASU) and Kartogenin (KGN) on chondrogenic differentiation in human adipose-derived stem cells (hADSCs) on fibrin scaffold. hADSCs seeded in fibrin scaffold and cultured in chondrogenic media. These cells were divided into 4 groups (control, TGF-β3, ASU and KGN). Cell viability was estimated by MTT assay. Differentiated cells were evaluated by histological and immunohistochemical (IHC) techniques. Expression genes [sex determining region Y-box 9 (SOX9), Aggrecan (AGG), type II collagen (Coll II) and type X collagen (Coll X)] were assessed by real-time PCR. For a study on an animal model, differentiated cells in fibrin scaffolds were subcutaneously transplanted in rats. Histological and immunohistochemistry were done in the animal model. The results of the real-time PCR indicated that SOX9, AGG and Col II genes expression in TGF-β3, KGN and ASU groups were significantly higher (p < 0.01) compared to the control group, Col X gene expression only in the TGF-β3 group was significantly higher (p< 0.01) compared to the control group. The glycosaminoglycan (GAG) deposition was higher in TGF-β3, KGN and ASU groups compared to the control group. The immunohistological analysis showed the distribution of collagen type X in the extracellular matrix in the fibrin scaffold TGF-β3 group was significantly higher in control, KGN and ASU groups, and (p < 0.001). ASU, particularly KGN, was suitable for successful chondrogenic differentiation of hADSCs and a suppressor of the consequent hypertrophy.

Modulation of Conductivity of Alginate Hydrogels Containing Reduced Graphene Oxide through the Addition of Proteins

Modifying hydrogels in order to enhance their conductivity is an exciting field with applications in cardio and neuro-regenerative medicine. Therefore, we have designed hybrid alginate hydrogels containing uncoated and protein-coated reduced graphene oxide (rGO). We specifically studied the adsorption of three different proteins, BSA, elastin, and collagen, and the outcomes when these protein-coated rGO nanocomposites are embedded within the hydrogels. Our results demonstrate that BSA, elastin, and collagen are adsorbed onto the rGO surface, through a non-spontaneous phenomenon that fits Langmuir and pseudo-second-order adsorption models. Protein-coated rGOs are able to preclude further adsorption of erythropoietin, but not insulin. Collagen showed better adsorption capacity than BSA and elastin due to its hydrophobic nature, although requiring more energy. Moreover, collagen-coated rGO hybrid alginate hydrogels showed an enhancement in conductivity, showing that it could be a promising conductive scaffold for regenerative medicine.

Novel calcium phosphate cement with biofilm-inhibition and platelet lysate delivery to enhance osteogenesis of encapsulated human periodontal ligament stem cells

Osteomyelitis is caused by Staphylococcus aureus (S. aureus), with associated progressive bone loss. This study developed for the first time a calcium phosphate cement (CPC) for delivery of doxycycline (DOX) and human platelet lysate (hPL) to fight against S. aureus infection and enhance the osteogenesis of human periodontal ligament stem cells (hPDLSCs). Chitosan-containing CPC scaffolds were fabricated in the absence (CPCC) or presence of DOX (CPCC+DOX). In addition, hPL was encapsulated in alginate microbeads and incorporated into CPCC+DOX (CPCC+DOX+ hPL). Flexural strength of CPCC+DOX + hPL was (5.56 ± 0.55) MPa, lower than (8.26 ± 1.6) MPa of CPCC+DOX (p < 0.05), but exceeding the reported strength of cancellous bone. CPCC+DOX and CPCC+DOX + hPL exhibited strong antibacterial activity against S. aureus, reducing biofilm CFU by 4 orders of magnitude. The hPDLSCs encapsulated in microbeads were co-cultured with the CPCs. The hPDLSCs were able to be released from the microbeads and showed a high proliferation rate, increasing by about 8 folds at 14 days for all groups. The hPL was released from the scaffold and promoted the osteogenic differentiation of hPDLSCs. ALP activity was 28.07 ± 5.15 mU/mg for CPCC+DOX + hPL, higher than 17.36 ± 2.37 mU/mg and 1.34 ± 0.37 mU/mg of CPCC+DOX and CPCC, respectively (p < 0.05). At 7 days, osteogenic genes (ALP, RUNX2, COL-1, and OPN) in CPCC+DOX + hPL were 3-10 folds those of control. The amount of hPDLSC-synthesized bone mineral with CPCC+DOX + hPL was 3.8 folds that of CPCC (p < 0.05). In summary, the novel CPC + DOX + hPL-hPDLSCs scaffold exhibited strong antibacterial activity, excellent cytocompatibility and hPDLSC osteogenic differentiation, showing a promising approach for treatment and prevention of bone infection and enhancement of bone regeneration.

Osteoclast-Mediated Cell Therapy as an Attempt to Treat Elastin Specific Vascular Calcification

Inflammation and stiffness in the arteries is referred to as vascular calcification. This process is a prevalent yet poorly understood consequence of cardiovascular disease and diabetes mellitus, comorbidities with few treatments clinically available. Because this is an active process similar to bone formation, it is hypothesized that osteoclasts (OCs), bone-resorbing cells in the body, could potentially work to reverse existing calcification by resorbing bone material. The receptor activator of nuclear kappa B-ligand (RANKL) is a molecule responsible for triggering a response in monocytes and macrophages that allows them to differentiate into functional OCs. In this study, OC and RANKL delivery were employed to determine whether calcification could be attenuated. OCs were either delivered via direct injection, collagen/alginate microbeads, or collagen gel application, while RANKL was delivered via injection, through either a porcine subdermal model or aortic injury model. While in vitro results yielded a decrease in calcification using OC therapy, in vivo delivery mechanisms did not provide control or regulation to keep cells localized long enough to induce calcification reduction. However, these results do provide context and direction for the future of OC therapy, revealing necessary steps for this treatment to effectively reduce calcification in vivo. The discrepancy between in vivo and in vitro success for OC therapy points to the need for a more stable and time-controlled delivery mechanism that will allow OCs not only to remain at the site of calcification, but also to be regulated so that they are healthy and functioning normally when introduced to diseased tissue.

Cellulose Nanocrystal-Fibrin Nanocomposite Hydrogels Promoting Myotube Formation

Cellulose nanocrystals (CNCs) have been widely studied as fillers to form reinforced nanocomposites with a wide range of applications, including the biomedical field. Here, we evaluated the possibility to combine them with fibrinogen and obtain fibrin hydrogels with improved mechanical stability as potential cellular scaffolds. In diluted conditions at a neutral pH, it was evidenced that fibrinogen could adsorb on CNCs in a two-step process, favoring their alignment under flow. Composite hydrogels could be prepared from concentrated fibrinogen solutions and nanocrystals in amounts up to 0.3 wt %. CNCs induced a significant modification of the initial fibrin fibrillogenesis and final fibrin network structure, and storage moduli of all nanocomposites were larger than those of pure fibrin hydrogels. Moreover, optimal conditions were found that promoted muscle cell differentiation and formation of long myotubes. These results provide original insights into the interactions of CNCs with proteins with key physiological functions and offer new perspectives for the design of injectable fibrin-based formulations.

Cobalt doped nano-hydroxyapatite incorporated gum tragacanth-alginate beads as angiogenic-osteogenic cell encapsulation system for mesenchymal stem cell based bone tissue engineering

Angiogenic-osteogenic cell encapsulation system is a technical need for human mesenchymal stem cell (hMSC)-based bone tissue engineering (BTE). Here, we have developed a highly efficient hMSC encapsulation system by incorporating bivalent cobalt doped nano-hydroxyapatite (HAN) and gum tragacanth (GT) as angiogenic-osteogenic components into the calcium alginate (CA) beads. Physico-chemical characterizations revealed that the swelling and degradation of HAN incorporated CA-GT beads (GT-HAN) were 1.34 folds and 2 folds higher than calcium alginate (CA) beads. Furthermore, the diffusion coefficient of solute molecule was found 2.5-fold higher in GT-HAN with respect to CA bead. It is observed that GT-HAN supports the long-term viability of encapsulated hMSC and causes 50% less production of reactive oxygen species (ROS) in comparison to CA beads. The expression of osteogenic differentiation markers was found 1.5-2.5 folds higher in the case of GT-HAN in comparison to CA. A similar trend was observed for hypoxia inducible factor 1 alpha (HIF-1α) and vascular endothelial growth factor (VEGF). The soluble secretome from hMSC encapsulated in the GT-HAN induced proliferation of endothelial cells and supported tube formation (2.5-fold higher than CA beads). These results corroborated that GT-HAN could be used as an angiogenic-osteogenic cell encapsulation matrix for hMSC encapsulation and BTE application.

Alginate microgels as delivery vehicles for cell-based therapies in tissue engineering and regenerative medicine

Conventional stem cell delivery typically utilize administration of directly injection of allogenic cells or domesticated autogenic cells. It may lead to immune clearance of these cells by the host immune systems. Alginate microgels have been demonstrated to improve the survival of encapsulated cells and overcome rapid immune clearance after transplantation. Moreover, alginate microgels can serve as three-dimensional extracellular matrix to support cell growth and protect allogenic cells from rapid immune clearance, with functions as delivery vehicles to achieve sustained release of therapeutic proteins and growth factors from the encapsulated cells. Besides, cell-loaded alginate microgels can potentially be applied in regenerative medicine by serving as injectable engineered scaffolds to support tissue regrowth. In this review, the properties of alginate and different methods to produce alginate microgels are introduced firstly. Then, we focus on diverse applications of alginate microgels for cell delivery in tissue engineering and regenerative medicine.

Applications of oxidized alginate in regenerative medicine

Because of its ideal degradation rate and features, oxidized alginate (OA) is selected as an appropriate substitute and has been introduced into hydrogels, microspheres, 3D-printed/composite scaffolds, membranes, and electrospinning and coating materials. By taking advantage of OA, the OA-based materials can be easily functionalized and deliver drugs or growth factors to promote tissue regeneration. In 1928, it was first found that alginate could be oxidized using periodate, yielding OA. Since then, considerable progress has been made in the research on the modification and application of alginate after oxidation. In this article, we summarize the key properties and existing applications of OA and various OA-based materials and discuss their prospects in regenerative medicine.

3D bioprinting of hepatocytes: core-shell structured co-cultures with fibroblasts for enhanced functionality

With the aim of understanding and recapitulating cellular interactions of hepatocytes in their physiological microenvironment and to generate an artificial 3D in vitro model, a co-culture system using 3D extrusion bioprinting was developed. A bioink based on alginate and methylcellulose (algMC) was first shown to be suitable for bioprinting of hepatocytes; the addition of Matrigel to algMC enhanced proliferation and morphology of them in monophasic scaffolds. Towards a more complex system that allows studying cellular interactions, we applied core-shell bioprinting to establish tailored 3D co-culture models for hepatocytes. The bioinks were specifically functionalized with natural matrix components (based on human plasma, fibrin or Matrigel) and used to co-print fibroblasts and hepatocytes in a spatially defined, coaxial manner. Fibroblasts acted as supportive cells for co-cultured hepatocytes, stimulating the expression of certain biomarkers of hepatocytes like albumin. Furthermore, matrix functionalization positively influenced both cell types in their respective compartments by enhancing their adhesion, viability, proliferation and function. In conclusion, we established a functional co-culture model with independently tunable compartments for different cell types via core-shell bioprinting. This provides the basis for more complex in vitro models allowing co-cultivation of hepatocytes with other liver-specific cell types to closely resemble the liver microenvironment.

Biologization of Pcl-Mesh Using Platelet Rich Fibrin (Prf) Enhances Its Regenerative Potential In Vitro

INTRODUCTION

Resorbable synthetic scaffolds are promising for different indications, especially in the context of bone regeneration. However, they require additional biological components to enhance their osteogenic potential. In addition to different cell types, autologous blood-derived matrices offer many advantages to enhance the regenerative capacity of biomaterials. The present study aimed to analyze whether biologization of a PCL-mesh coated using differently centrifuged Platelet rich fibrin (PRF) matrices will have a positive influence on primary human osteoblasts activity in vitro. A polymeric resorbable scaffold (Osteomesh, OsteoporeTM (OP), Singapore) was combined with differently centrifuged PRF matrices to evaluate the additional influence of this biologization concept on bone regeneration in vitro. Peripheral blood of three healthy donors was used to gain PRF matrices centrifuged either at High (710× g, 8 min) or Low (44× g, 8 min) relative centrifugal force (RCF) according to the low speed centrifugation concept (LSCC). OP-PRF constructs were cultured with pOBs. POBs cultured on the uncoated OP served as a control. After three and seven days of cultivation, cell culture supernatants were collected to analyze the pOBs activity by determining the concentrations of VEGF, TGF-β1, PDGF, OPG, IL-8, and ALP- activity. Immunofluorescence staining was used to evaluate the Osteopontin expression of pOBs. After three days, the group of OP+PRFLow+pOBs showed significantly higher expression of IL-8, TGF-ß1, PDGF, and VEGF compared to the group of OP+PRFHigh+pOBs and OP+pOBs. Similar results were observed on day 7. Moreover, OP+PRFLow+pOBs exhibited significantly higher activity of ALP compared to OP+PRFHigh+pOBs and OP+pOBs. Immunofluorescence staining showed a higher number of pOBs adherent to OP+PRFLow+pOBs compared to the groups OP+PRFHigh+pOBs and OP+pOBs. To the best of our knowledge, this study is the first to investigate the osteoblasts activity when cultured on a PRF-coated PCL-mesh in vitro. The presented results suggest that PRFLow centrifuged according to LSCC exhibits autologous blood cells and growth factors, seem to have a significant effect on osteogenesis. Thereby, the combination of OP with PRFLow showed promising results to support bone regeneration. Further in vivo studies are required to verify the results and carry out potential results for clinical translation.

Enhanced proliferation and angiogenic phenotype of endothelial cells via negatively-charged alginate and chondroitin sulfate microsphere hydrogels

Sodium alginate-based hydrogel was the one of the most used polymers for cell delivery. However, the adsorption of extracellular matrix and proteins was inhibited due to the formation of a hydrated surface layer of these hydrogels. In this study, a novel cell delivery system, negatively-charged alginate and chondroitin sulfate microsphere hydrogel (nCACSMH), was fabricated with excellent permeability and biocompatibility in the action of a high voltage direct-current electric field. Negative charge was introduced to the surface of nCACSMH to obtain the expanded network and enhanced permeability. Additionally, the increasing content of chondroitin sulfate in nCACSMH could give rise to the charge density and its asymmetric structure, thus the uneven, plicate and expanded surface of nCACSMH which was favorable to cell proliferation was developed. Moreover, chondroitin sulfate was released with the degradation of nCACSMH, which played a crucial role in maintaining the normal physiological functions of cells. Thus the proliferation of human umbilical vein endothelial cells (HUVECs) was further accelerated and the angiogenesis related genes expression in endothelial cells was continuously and dramatically up-regulated. After 4 d, the proliferation and viability of HUVECs were significantly improved, the cells were distributed evenly in nCACSMH. The novel nCACSMH has the potential to be used as cell delivery, three-dimensional (3D) cell cultures for cell therapy, 3D bioprinting, high-throughput screening for drugs, and disease model for regeneration and constructing of tissue engineering.

Antibacterial calcium phosphate cement with human periodontal ligament stem cell-microbeads to enhance bone regeneration and combat infection

Infectious bone defects remain a significant challenge in orthopedics and dentistry. Calcium phosphate cement (CPC) have attracted significant interest in use as local drug delivery system, which with great potential to control release of antibiotics for the treatment of infectious bone defects. Within the current study, a novel antibacterial scaffold of chitosan-reinforced calcium phosphate cement delivering doxycycline hyclate (CPCC + DOX) was developed. Furthermore, the capacity of CPCC + DOX scaffolds for bone regeneration was enhanced by the human periodontal ligament stem cells (hPDLSCs) encapsulated in alginate beads. CPCC + DOX scaffolds were fabricated to contain different concentrations of DOX. Flexural strength of CPCC + DOX ranged from 5.56 ± 0.70 to 6.2 ± 0.72 MPa, which exceeded the reported strength of cancellous bone. Scaffolds exhibited continual DOX release, reaching 80% at 21 days. Scaffold with 5 mg/ml DOX (CPCC + DOX5mg) had a strong antibacterial effect, with a 4-log colony forming unit reduction against S. aureus and P. gingivalis. The proliferation and osteogenic differentiation of hPDLSCs encapsulated in alginate hydrogel microbeads were investigated in culture with CPCC + DOX scaffolds. CPCC + DOX5mg had no negative effect on proliferation of hPDLSCs. Alkaline phosphatase activity, mineral synthesis, and osteogenic gene expressions for CPCC + DOX5mg group were much higher than control group. DOX did not compromise the osteogenic induction. In summary, the novel CPCC + DOX scaffold exhibited excellent mechanical properties and strong antibacterial activity, while supporting the proliferation and osteogenic differentiation of hPDLSCs. The CPCC + DOX + hPDLSCs construct is promising to enhance bone regeneration and combat bone infections in dental, craniofacial, and orthopedic applications.

The osteogenic differentiation of human dental pulp stem cells in alginate-gelatin/Nano-hydroxyapatite microcapsules

Background

Microcapsule is considered as a promising 3D microenvironment for Bone Tissue Engineering (BTE) applications. Microencapsulation of cells in an appropriate scaffold not only protected the cells against excess stress but also promoted cell proliferation and differentiation. Through the current study, we aimed to microcapsulate the human Dental Pulp Stem Cells (hDPSCs) and evaluated the proliferation and osteogenic differentiation of those cells by using MTT assay, qRT-PCR, Alkaline phosphatase, and Alizarine Red S.

Results

The SEM results revealed that Alg/Gel microcapsules containing nHA showed a rough and more compact surface morphology in comparison with the Alg/Gel microcapsules. Moreover, the microencapsulation by Alg/Gel/nHA could improve cell proliferation and induce osteogenic differentiation. The cells cultured in the Alg/Gel and Alg/Gel/nHA microcapsules showed 1.4-fold and 1.7-fold activity of BMP-2 gene expression more in comparison with the control group after 21 days. The mentioned amounts for the BMP-2 gene were 2.5-fold and 4-fold more expression for the Alg/Gel and Alg/Gel/nHA microcapsules after 28 days. The nHA, addition to hDPSCs-laden Alg/Gel microcapsule, could up-regulate the bone-related gene expressions of osteocalcin, osteonectin, and RUNX-2 during the 21 and 28 days through the culturing period, too. Calcium deposition and ALP activities of the cells were observed in accordance with the proliferation results as well as the gene expression analysis.

Conclusion

The present study demonstrated that microencapsulation of the hDPSCs inside the Alg/Gel/nHA hydrogel could be a potential approach for regenerative dentistry in the near future.

Graphical abstract

How is Biodegradable Scaffold Effective in Gap Non-union? Insights from an Experiment

OBJECTIVE

To evaluate the role of composite (Chitosan/Chondroitin sulphate/gelatin/nano-bioglass) scaffold in the union of critical size bone defect created in the rabbit's ulna.

METHODS

The composite (Chitosan/Chondroitin sulphate/gelatin/nano-bioglass) scaffold was fabricated using the freeze-drying technique under standard laboratory conditions. The scaffold was cut into the appropriate size and transferred into the defect created (critical bone size defect 1 cm) over the right ulna in the rabbit. The scaffold was not implanted on the left side thus the left side ulna served as control. Results were assessed on serial radiological examination. Rabbits were sacrificed at 20 weeks for histopathological examination (Haematoxylin-Eosin staining and Mason's trichrome staining) and scanning electron microscope observation. Radiological scoring was done by Lane and Sandhu's scoring.

RESULTS

Among 12 rabbits, 10 could complete the follow-up. Among those 10 rabbits, 8 among the test group showed good evidence of bone formation at the gap non-union scaffold implanted site. Histological evidence of new bone formation, collagen synthesis, scaffold resorption, minimal chondrogenesis was evident by 20 weeks in the test group. Two rabbits had poor bone formation.

CONCLUSION

The chitosan-chondroitin sulphate-gelatin-nano-bioglass composite scaffold is efficient in osteoconduction and osteoinduction in the gap non-union model as it is biocompatible, bioactive, and non-immunogenic as well.

An injectable and antibacterial calcium phosphate scaffold inhibiting Staphylococcus aureus and supporting stem cells for bone regeneration

Staphylococcus aureus (S. aureus) is the major pathogen for osteomyelitis, which can lead to bone necrosis and destruction. There has been no report on antibacterial calcium phosphate cement (CPC) against S. aureus. The aims of this study were to: (1) develop novel antibacterial CPC-chitosan-alginate microbead scaffold; (2) investigate mechanical and antibacterial properties of CPC-chitosan-penicillin-alginate scaffold; (3) evaluate the encapsulation and delivery of human umbilical cord mesenchymal stem cells (hUCMSCs). Flexural strength, elastic modulus and work-of-fracture of the CPC-chitosan-penicillin-alginate microbeads scaffold and CPC-chitosan scaffold were evaluated. Penicillin release profile and antibacterial effects on S. aureus were determined. The hUCMSC delivery and release from penicillin-alginate microbeads were investigated. Injectable CPC-chitosan-penicillin-alginate microbeads scaffold was developed for the first time. CPC-chitosan-penicillin-alginate microbeads scaffold had a flexural strength of 3.16 ± 0.55 MPa, matching that of cancellous bone. With sustained penicillin release, the new scaffold had strong antibacterial effects on S. aureus, with an inhibition zone diameter of 32.2 ± 2.5 mm, greater than that of penicillin disk control (15.1 ± 2.0 mm) (p < 0.05). Furthermore, this injectable and antibacterial scaffold had no toxic effects, yielding excellent hUCMSC viability, which was similar to that of CPC control without antibacterial activity (p > 0.05). CPC-chitosan-penicillin-microbeads scaffold had injectability, good strength, strong antibacterial effects, and good biocompatibility to support stem cell viability for osteogenesis. CPC-chitosan-penicillin-microbeads scaffold is promising for dental, craniofacial and orthopedic applications to combat infections and promote bone regeneration.

An antibacterial and injectable calcium phosphate scaffold delivering human periodontal ligament stem cells for bone tissue engineering

Osteomyelitis and post-operative infections are major problems in orthopedic, dental and craniofacial surgeries. It is highly desirable for a tissue engineering construct to kill bacteria, while simultaneously delivering stem cells and enhancing cell function and tissue regeneration. The objectives of this study were to: (1) develop a novel injectable calcium phosphate cement (CPC) scaffold containing antibiotic ornidazole (ORZ) while encapsulating human periodontal ligament stem cells (hPDLSCs), and (2) investigate the inhibition efficacy against Staphylococcus aureus (S. aureus) and the promotion of hPDLSC function for osteogenesis for the first time. ORZ was incorporated into a CPC-chitosan scaffold. hPDLSCs were encapsulated in alginate microbeads (denoted hPDLSCbeads). The ORZ-loaded CPCC+hPDLSCbeads scaffold was fully injectable, and had a flexural strength of 3.50 ± 0.92 MPa and an elastic modulus of 1.30 ± 0.45 GPa, matching those of natural cancellous bone. With 6 days of sustained ORZ release, the CPCC+10ORZ (10% ORZ) scaffold had strong antibacterial effects on S. aureus, with an inhibition zone of 12.47 ± 1.01 mm. No colonies were observed in the CPCC+10ORZ group from 3 to 7 days. ORZ-containing scaffolds were biocompatible with hPDLSCs. CPCC+10ORZ+hPDLSCbeads scaffold with osteogenic medium had 2.4-fold increase in alkaline phosphatase (ALP) activity and bone mineral synthesis by hPDLSCs, as compared to the control group (p < 0.05). In conclusion, the novel antibacterial construct with stem cell delivery had injectability, good strength, strong antibacterial effects and biocompatibility, supporting osteogenic differentiation and bone mineral synthesis of hPDLSCs. The injectable and mechanically-strong CPCC+10ORZ+hPDLSCbeads construct has great potential for treating bone infections and promoting bone regeneration.

Polymer microcapsules and microbeads as cell carriers for in vivo biomedical applications

Polymer microcarriers are being extensively explored as cell delivery vehicles in cell-based therapies and hybrid tissue and organ engineering. Spherical microcarriers are of particular interest due to easy fabrication and injectability. They include microbeads, composed of a porous matrix, and microcapsules, where matrix core is additionally covered with a semipermeable membrane. Microcarriers provide cell containment at implantation site and protect the cells from host immunoresponse, degradation and shear stress. Immobilized cells may be genetically altered to release a specific therapeutic product directly at the target site, eliminating side effects of systemic therapies. Cell microcarriers need to fulfil a number of extremely high standards regarding their biocompatibility, cytocompatibility, immunoisolating capacity, transport, mechanical and chemical properties. To obtain cell microcarriers of specified parameters, a wide variety of polymers, both natural and synthetic, and immobilization methods can be applied. Yet so far, only a few approaches based on cell-laden microcarriers have reached clinical trials. The main issue that still impedes progress of these systems towards clinical application is limited cell survival in vivo. Herein, we review polymer biomaterials and methods used for fabrication of cell microcarriers for in vivo biomedical applications. We describe their key limitations and modifications aiming at improvement of microcarrier in vivo performance. We also present the main applications of polymer cell microcarriers in regenerative medicine, pancreatic islet and hepatocyte transplantation and in the treatment of cancer. Lastly, we outline the main challenges in cell microimmobilization for biomedical purposes, the strategies to overcome these issues and potential future improvements in this area.

Recent Trends in Three-Dimensional Bioinks Based on Alginate for Biomedical Applications

Three-dimensional (3D) bioprinting is an appealing and revolutionary manufacturing approach for the accurate placement of biologics, such as living cells and extracellular matrix (ECM) components, in the form of a 3D hierarchical structure to fabricate synthetic multicellular tissues. Many synthetic and natural polymers are applied as cell printing bioinks. One of them, alginate (Alg), is an inexpensive biomaterial that is among the most examined hydrogel materials intended for vascular, cartilage, and bone tissue printing. It has also been studied pertaining to the liver, kidney, and skin, due to its excellent cell response and flexible gelation preparation through divalent ions including calcium. Nevertheless, Alg hydrogels possess certain negative aspects, including weak mechanical characteristics, poor printability, poor structural stability, and poor cell attachment, which may restrict its usage along with the 3D printing approach to prepare artificial tissue. In this review paper, we prepare the accessible materials to be able to encourage and boost new Alg-based bioink formulations with superior characteristics for upcoming purposes in drug delivery systems. Moreover, the major outcomes are discussed, and the outstanding concerns regarding this area and the scope for upcoming examination are outlined.

Alginate/laponite hydrogel microspheres co-encapsulating dental pulp stem cells and VEGF for endodontic regeneration

Considering the complicated and irregular anatomical structure of root canal systems, injectable microspheres have received considerable attention as cell carriers in endodontic regeneration. Herein, we developed injectable hybrid RGD-alginate/laponite (RGD-Alg/Lap) hydrogel microspheres, co-encapsulating human dental pulp stem cells (hDPSCs) and vascular endothelial growth factor (VEGF). These microspheres were prepared by the electrostatic microdroplet method with an average size of 350~450 μm. By adjusting the content of laponite, the rheological properties and the degradation rate of the microspheres in vitro could be conditioned. The release of VEGF from the RGD-Alg/0.5%Lap microspheres was in a sustained manner for 28 days while the bioactivity of VEGF was preserved. In addition, the encapsulated hDPSCs were evenly distributed in microspheres with a cell viability exceeding 85%. The deposition of abundant extracellular matrix such as fibronectin (FN) and collagen type I (Col-I) was shown in microspheres after 7 days. The laponite in the system significantly up-regulated the expression of odontogenic-related genes of hDPSCs at day 7. Furthermore, after subcutaneous implantation with tooth slices in a nude mouse model for 1 month, the hDPSCs-laden RGD-Alg/0.5%Lap+VEGF microspheres significantly promoted the regeneration of pulp-like tissues as well as the formation of new micro-vessels. These results demonstrated the great potential of laponite-enhanced hydrogel microspheres in vascularized dental pulp regeneration. STATEMENT OF SIGNIFICANCE: Injectable cell-laden microspheres have recently gained great attention in endodontic regeneration. Here we first developed hybrid alginate/laponite hydrogel microspheres (size about 350~450 μm) by electrostatic microdroplet method, which exhibited tunability in mechanical property and sustained release ability. The incorporation of laponite and the sustained release of VEGF supported not only dental pulp stem cells differentiation in vitro but neotissue regeneration in vivo. These features combined with the simplicity in preparation, made the microspheres ideally suited to simultaneous cells and growth factors delivery in dental pulp regeneration and even other tissue regeneration application.

Exquisite design of injectable Hydrogels in Cartilage Repair

Cartilage damage is still a threat to human beings, yet there is currently no treatment available to fully restore the function of cartilage. Recently, due to their unique structures and properties, injectable hydrogels have been widely studied and have exhibited high potential for applications in therapeutic areas, especially in cartilage repair. In this review, we briefly introduce the properties of cartilage, some articular cartilage injuries, and now available treatment strategies. Afterwards, we propose the functional and fundamental requirements of injectable hydrogels in cartilage tissue engineering, as well as the main advantages of injectable hydrogels as a therapy for cartilage damage, including strong plasticity and excellent biocompatibility. Moreover, we comprehensively summarize the polymers, cells, and bioactive molecules regularly used in the fabrication of injectable hydrogels, with two kinds of gelation, i.e., physical and chemical crosslinking, which ensure the excellent design of injectable hydrogels for cartilage repair. We also include novel hybrid injectable hydrogels combined with nanoparticles. Finally, we conclude with the advances of this clinical application and the challenges of injectable hydrogels used in cartilage repair.

Soft Actuated Hybrid Hydrogel with Bioinspired Complexity to Control Mechanical Flexure Behavior for Tissue Engineering

Hydrogels exhibit excellent properties that enable them as nanostructured scaffolds for soft tissue engineering. However, single-component hydrogels have significant limitations due to the low versatility of the single component. To achieve this goal, we have designed and characterized different multi-component hydrogels composed of gelatin, alginate, hydroxyapatite, and a protein (BSA and fibrinogen). First, we describe the surface morphology of the samples and the main characteristics of the physiological interplay by using fourier transform infrared (FT-IR), and confocal Raman microscopy. Then, their degradation and swelling were studied and mechanical properties were determined by rheology measurements. Experimental data were carefully collected and quantitatively analyzed by developing specific approaches and different theoretical models to determining the most important parameters. Finally, we determine how the nanoscale of the system influences its macroscopic properties and characterize the extent to which degree each component maintains its own functionality, demonstrating that with the optimal components, in the right proportion, multifunctional hydrogels can be developed.

Injectable Functional Biomaterials for Minimally Invasive Surgery

Injectable materials represent very attractive ready-to-use biomaterials for application in minimally invasive surgical procedures. It is shown that this approach to treat, for example, vertebral fracture, craniofacial defects, or tumor resection has significant clinical potential in the biomedical field. In the last four decades, calcium phosphate cements have been widely used as injectable materials for orthopedic surgery due to their excellent properties in terms of biocompatibility and osteoconductivity. However, few clinical studies have demonstrated certain weaknesses of these cements, which include high viscosity, long degradation time, and difficulties being manipulated. To overcome these limitations, the use of sol-gel technology has been investigated, which has shown good results for synthesis of injectable calcium phosphate-based materials. In the last few decades, injectable hydrogels have gained increasing attention owing to their structural similarities with the extracellular matrix, easy process conditions, and potential applications in minimally invasive surgery. However, the need to protect cells during injection leads to the development of double network injectable hydrogels that are capable of being cross-linked in situ. This review will provide the current state of the art and recent advances in the field of injectable biomaterials for minimally invasive surgery.

BSA- and Elastin-Coated GO, but Not Collagen-Coated GO, Enhance the Biological Performance of Alginate Hydrogels

The use of embedded cells within alginate matrices is a developing technique with great clinical applications in cell-based therapies. However, one feature that needs additional investigation is the improvement of alginate-cells viability, which could be achieved by integrating other materials with alginate to improve its surface properties. In recent years, the field of nanotechnology has shown the many properties of a huge number of materials. Graphene oxide (GO), for instance, seems to be a good choice for improving alginate cell viability and functionality. We previously observed that GO, coated with fetal bovine serum (FBS) within alginate hydrogels, improves the viability of embedded myoblasts. In the current research, we aim to study several proteins, specifically bovine serum albumin (BSA), type I collagen and elastin, to discern their impact on the previously observed improvement on embedded myoblasts within alginate hydrogels containing GO coated with FBS. Thus, we describe the mechanisms of the formation of BSA, collagen and elastin protein layers on the GO surface, showing a high adsorption by BSA and elastin, and a decreasing GO impedance and capacitance. Moreover, we described a better cell viability and protein release from embedded cells within hydrogels containing protein-coated GO. We conclude that these hybrid hydrogels could provide a step forward in regenerative medicine.

The Construction and Application of Three-Dimensional Biomaterials

Biomaterials have been widely explored and applied in many areas, especially in the field of tissue engineering. The interface of biomaterials and cells has been deeply investigated. However, it has been demonstrated that conventional 2D biomaterials fail to maintain the 3D structures and phenotypes of cells, which is the result of their limited ability to mimic the latter's complex extracellular matrix. To overcome this challenge, cell cultivation dependent on 3D biomaterials has emerged as an alternative strategy to make the recovery of 3D structures and functions of cells possible. Thus, with the thriving development of 3D cell culture in tissue engineering, a holistic review of the construction and application of 3D biomaterials is desired. Here, recent developments in 3D biomaterials for tissue engineering are reviewed. An overview of various approaches to construct 3D biomaterials, such as electro-jetting/-spinning, micro-molding, microfluidics, and 3D bio-printing, is first presented. Their typical applications in constructing cell sheets, vascular structures, cell spheroids, and macroscopic cellular constructs are described as well. Following these two sections, the current status and challenges are analyzed, as well as the future outlook of 3D biomaterials for tissue engineering.

Microcarriers for Upscaling Cultured Meat Production

Due to the considerable environmental impact and the controversial animal welfare associated with industrial meat production, combined with the ever-increasing global population and demand for meat products, sustainable production alternatives are indispensable. In 2013, the world's first laboratory grown hamburger made from cultured muscle cells was developed. However, coming at a price of $300.000, and being produced manually, substantial effort is still required to reach sustainable large-scale production. One of the main challenges is scalability. Microcarriers (MCs), offering a large surface/volume ratio, are the most promising candidates for upscaling muscle cell culture. However, although many MCs have been developed for cell lines and stem cells typically used in the medical field, none have been specifically developed for muscle stem cells and meat production. This paper aims to discuss the MCs' design criteria for skeletal muscle cell proliferation and subsequently for meat production based on three scenarios: (1) MCs are serving only as a temporary substrate for cell attachment and proliferation and therefore they need to be separated from the cells at some stage of the bioprocess, (2) MCs serve as a temporary substrate for cell proliferation but are degraded or dissolved during the bioprocess, and (3) MCs are embedded in the final product and therefore need to be edible. The particularities of each of these three bioprocesses will be discussed from the perspective of MCs as well as the feasibility of a one-step bioprocess. Each scenario presents advantages and drawbacks, which are discussed in detail, nevertheless the third scenario appears to be the most promising one for a production process. Indeed, using an edible material can limit or completely eliminate dissociation/degradation/separation steps and even promote organoleptic qualities when embedded in the final product. Edible microcarriers could also be used as a temporary substrate similarly to scenarios 1 and 2, which would limit the risk of non-edible residues.

3D printing of layered mesoporous bioactive glass/sodium alginate-sodium alginate scaffolds with controllable dual-drug release behaviors

Scaffolds with controlled drug release are valuable for bone tissue engineering, but constructing the scaffolds with controllable dual-drug release behaviors is still a challenge. In this study, layered mesoporous bioactive glass/sodium alginate-sodium alginate (MBG/SA-SA) scaffolds with controllable dual-drug release behaviors were fabricated by 3D printing. The porosity and compressive strength of three-dimensional (3D) printed MBG/SA-SA scaffolds by cross-linking are about 78% and 4.2 MPa, respectively. As two model drugs, bovine serum albumin (BSA) and ibuprofen (IBU) were separately loaded in SA layer and MBG/SA layer, resulting in a relatively fast release of BSA and a sustained release of IBU. Furthermore, layered MBG/SA-SA scaffolds were able to stimulate human bone mesenchymal stem cells (hBMSCs) adhesion, proliferation and osteogenic differentiation than SA scaffolds. Hence, the 3D printed MBG/SA-SA scaffolds would be prospective for the treatment of bone defects.

Therapeutic compression materials and wound dressings for chronic venous insufficiency: A comprehensive review

Chronic venous insufficiency (CVI) is a common disorder worldwide. Related pathophysiological mechanisms reportedly involve venous pooling and reduced venous return, leading to heaviness, aching, itchiness, tiredness, varicosities, pigmentation, and even lower limb ulceration. Approaches adopted to manage CVI at various stages of clinical-etiology-anatomy-pathophysiology include compression therapy, pharmacological treatment, ultrasound treatment, surgery, electrical or wireless microcurrent stimulation, and pulsed electromagnetic treatment. Among these, polymer-based therapeutic compression materials and wound dressings play increasingly key roles in treating all stages of CVI because of their unique physical, mechanical, chemical, and biological functions. However, the characteristics, working mechanisms, and effectiveness of these CVI treatment materials are not comprehensively understood. The present systematic review examines the structures, properties, types, and applications of various polymer-based compression materials and wound dressings used in prophylaxis and treatment of CVI. Existing problems, limitations, and future trends of CVI treatment materials are also discussed. This review could contribute to the design and application of new functional polymer materials and dressings to enhance the efficiency of CVI treatments, thereby facilitating patients' self-care ability and long-term health improvement.

Iron oxide nanoparticle-calcium phosphate cement enhanced the osteogenic activities of stem cells through WNT/β-catenin signaling

Calcium phosphate cement (CPC), functionalized with iron oxide nanoparticles (IONP), is of great promise to promote osteoinduction and new bone formation. In this work, the IONP powder was added into the CPC powder to fabricate CPC + IONP scaffolds and the effects of the novel composite on bone matrix formation and osteogenesis of human dental pulp stem cells (hDPSCs) were explored. A series of CPC + IONP magnetic scaffolds with different IONP contents (1%, 3% and 6%) were fabricated using 5% chitosan solution as the cement liquid. Western blotting and RT-PCR were used to analyze the signaling pathway. The IONP incorporation substantially enhanced the performance of CPC + IONP, with increases in both mechanical strength and cellular activities. The IONP addition greatly promoted the osteogenesis of hDPSCs, elevating the ALP activity, the expression of osteogenic marker genes and bone matrix formation with 1.5-2-fold increases. The 3% IONP incorporation showed the most enhancement among all groups. Activation of the extracellular signal-related kinases WNT/β-catenin in DPSCs was observed, and this activation was attenuated by the WNT inhibitor DKK1. The results indicated that the osteogenic behavior of hDPSCs was likely driven by CPC + IONP via the WNT signaling pathway. In conclusion, incorporate IONP into CPC scaffold remarkably enhanced the spreading, osteogenic differentiation and bone mineral synthesis of stem cell. Therefore, this method had great potential for bone tissue engineering. The novel CPC + IONP composite scaffolds with stem cells are promising to provide an innovative strategy to enhance bone regenerative therapies.

Effects of concentration variation on the physical properties of alginate-based substrates and cell behavior in culture

Nowadays alginate capsules exhibit good biocompatibility and high permeability for nutrients and metabolic wastes making them appealing biomaterial for therapeutic cell encapsulation. Further study of the characteristics of alginate beads which are highly dependent on various environmental conditions to create an optimum microenvironment for cells is also critical. Thus, in this study, the effect of concentration variation on the physical properties of alginate-based beads and entrapped-cells behavior was analyzed. Results showed that the increase of Ca ions concentration brought about the decrease of the average diameter, prolongation of dissolution time, reduction of permeability and swelling, and a rise of crosslinking extent and shrinkage of capsules; while raising sodium alginate concentration had an opposite effect on the diameter and shrinkage. Moreover, the addition of gelatin enhanced the penetration and swelling and slowed down the shrinkage of capsules. And MC3T3-E1 cells enclosed in the particles in which the concentration of calcium chloride, sodium alginate and gelatin was 2.5%, 2.0% and 0.5% (w/v %) had preferable abilities of proliferation and higher expression of alkaline phosphatase. Overall, the ability to tailor this system to support in vitro growth of MC3T3-E1 cells might have significance for the future use of other cell types in regenerative medicine.

Animal Models for Stem Cell-Based Pulp Regeneration: Foundation for Human Clinical Applications

IMPACT STATEMENT

Animal models are essential for tissue regeneration studies. This review summarizes and discusses the small and large animal models, including mouse, ferret, dog, and miniswine that have been utilized to experiment and to demonstrate stem cell-mediated dental pulp tissue regeneration. We describe the models based on the location where the tissue regeneration is tested-either ectopic, semiorthotopic, or orthotopic. Developing and utilizing optimal animal models for both mechanistic and translational studies of pulp regeneration are of critical importance to advance this field.

High mannoronic acid containing alginate affects the differentiation of Wharton's jelly-derived stem cells to hepatocyte-like cell

For transplantation of cell into injured tissues, cells should be transferred to the damaged site through an adequate carrier. Nevertheless, the nutrient-limited and hypoxic condition in the carrier can bring about broad cell death. This study set to assess the impact of alginate concentrations on the differentiation and the proliferation of cells encapsulated in alginate hydrogels. Human Wharton's Jelly-derived Mesenchymal Stem Cells (HWJ-MSCs) were encapsulated in two concentrations of alginate hydrogel. Then, the proliferation and the hepatic differentiation were evaluated with an MTT assay and the enzyme-linked immunosorbent assay software and urea production. The results demonstrated that the proliferation of cell and urea production in 1.5% alginate concentration was higher than in 2.5% alginate concentration in the hydrogels of alginate. We deduce that the optimized alginate hydrogel concentration is necessary for achieving comparable cell activities in three-dimensional culture.

Spine Intervention—An Update on Injectable Biomaterials

Back pain is the second most common reason for primary-care physician visits after the common cold. New understanding of the spine pathophysiology and biomechanics led to the development of novel injectable biomaterials to treat those pain generators. Although not all biomaterials are currently ready for common use, there is significant interest by the medical community to invest time, resources, and energy to optimize these injectables. This review introduces basic concepts and advancements in the field of bioinjectables tailored for the vertebral body. Also, we highlight advances in injectable biomaterials which were presented at the Groupe de Recherche Interdisciplinaire sur les Biomatériaux Ostéoarticulaires Injectables (GRIBOI) (Interdisciplinary Research Society for Injectable Osteoarticular Biomaterials) meeting in March 2018 in Los Angeles, CA. Indeed, multidisciplinary translational research and international meetings such as GRIBOI bring together scientists and clinicians with different backgrounds/expertise to discuss injectable biomaterials innovations tailored for the interventional pain management field.

Cell encapsulation: Overcoming barriers in cell transplantation in diabetes and beyond

Cell-based therapy is emerging as a promising strategy for treating a wide range of human diseases, such as diabetes, blood disorders, acute liver failure, spinal cord injury, and several types of cancer. Pancreatic islets, blood cells, hepatocytes, and stem cells are among the many cell types currently used for this strategy. The encapsulation of these "therapeutic" cells is under intense investigation to not only prevent immune rejection but also provide a controlled and supportive environment so they can function effectively. Some of the advanced encapsulation systems provide active agents to the cells and enable a complete retrieval of the graft in the case of an adverse body reaction. Here, we review various encapsulation strategies developed in academic and industrial settings, including the state-of-the-art technologies in advanced preclinical phases as well as those undergoing clinical trials, and assess their advantages and challenges. We also emphasize the importance of stimulus-responsive encapsulated cell systems that provide a "smart and live" therapeutic delivery to overcome barriers in cell transplantation as well as their use in patients.