Effect of Pore Size on Cell Behavior Using Melt Electrowritten Scaffolds

Advancements in hydrogel design for articular cartilage regeneration: A comprehensive review

This review paper explores the cutting-edge advancements in hydrogel design for articular cartilage regeneration (CR). Articular cartilage (AC) defects are a common occurrence worldwide that can lead to joint breakdown at a later stage of the disease, necessitating immediate intervention to prevent progressive degeneration of cartilage. Decades of research into the biomedical applications of hydrogels have revealed their tremendous potential, particularly in soft tissue engineering, including CR. Hydrogels are highly tunable and can be designed to meet the key criteria needed for a template in CR. This paper aims to identify those criteria, including the hydrogel components, mechanical properties, biodegradability, structural design, and integration capability with the adjacent native tissue and delves into the benefits that CR can obtain through appropriate design. Stratified-structural hydrogels that emulate the native cartilage structure, as well as the impact of environmental stimuli on the regeneration outcome, have also been discussed. By examining recent advances and emerging techniques, this paper offers valuable insights into developing effective hydrogel-based therapies for AC repair.

Cellular response in three-dimensional spheroids and tissues exposed to real and simulated microgravity: a narrative review

The rising aging population underscores the need for advances in tissue engineering and regenerative medicine. Alterations in cellular response in microgravity might be pivotal in unraveling the intricate cellular mechanisms governing tissue and organ regeneration. Microgravity could improve multicellular spheroid, tissue, and organ formation. This review summarizes microgravity-induced cellular alterations and highlights the potential of tissue engineering in microgravity for future breakthroughs in space travel, transplantation, drug testing, and personalized medicine.

Tuning porosity of macroporous hydrogels enables rapid rates of stress relaxation and promotes cell expansion and migration

Extracellular matrix (ECM) viscoelasticity broadly regulates cell behavior. While hydrogels can approximate the viscoelasticity of native ECM, it remains challenging to recapitulate the rapid stress relaxation observed in many tissues without limiting the mechanical stability of the hydrogel. Here, we develop macroporous alginate hydrogels that have an order of magnitude increase in the rate of stress relaxation as compared to bulk hydrogels. The increased rate of stress relaxation occurs across a wide range of polymer molecular weights (MWs), which enables the use of high MW polymer for improved mechanical stability of the hydrogel. The rate of stress relaxation in macroporous hydrogels depends on the volume fraction of pores and the concentration of bovine serum albumin, which is added to the hydrogels to stabilize the macroporous structure during gelation. Relative to cell spheroids encapsulated in bulk hydrogels, spheroids in macroporous hydrogels have a significantly larger area and smaller circularity because of increased cell migration. A computational model provides a framework for the relationship between the macroporous architecture and morphogenesis of encapsulated spheroids that is consistent with experimental observations. Taken together, these findings elucidate the relationship between macroporous hydrogel architecture and stress relaxation and help to inform the design of macroporous hydrogels for materials-based cell therapies.

Intervening to Preserve Function in Ischemic Cardiomyopathy with a Porous Hydrogel and Extracellular Matrix Composite in a Rat Myocardial Infarction Model

Multiple hydrogels are developed for injection therapy after myocardial infarction, with some incorporating substances promoting tissue regeneration and others emphasizing mechanical effects. In this study, porosity and extracellular matrix-derived digest (ECM) are incorporated, into a mechanically optimized, thermoresponsive, degradable hydrogel (poly(N-isopropylacrylamide-co-N-vinylpyrrolidone-co-MAPLA)) and evaluate whether this biomaterial injectate can abrogate adverse remodeling in rat ischemic cardiomyopathy. After myocardial infarction, rats are divided into four groups: NP (non-porous hydrogel) without either ECM or porosity, PM (porous hydrogel) from the same synthetic copolymer with mannitol beads as porogens, and PME with porosity and ECM digest added to the synthetic copolymer. PBS injection alone is a control group. Intramyocardial injections occurred 3 days after myocardial infarction followed by serial echocardiography and histological assessments 8 weeks after infarction. Echocardiographic function and neovascularization improved in the PME group compared to the other hydrogels and PBS injection. The PME group also demonstrated improved LV geometry and macrophage polarization (toward M2) compared to PBS, whereas differences are not observed in the NP or PM groups versus control. These results demonstrate further functional improvement may be achieved in hydrogel injection therapy for ischemic cardiomyopathy by incorporating porosity and ECM digest, representing combined mechanical and biological effects.

Utilization of Additive Manufacturing Techniques for the Development of a Novel Scaffolds with Magnetic Properties for Potential Application in Enhanced Bone Regeneration

This study focuses on designing and evaluating scaffolds with essential properties for bone regeneration, such as biocompatibility, macroporous geometry, mechanical strength, and magnetic responsiveness. The scaffolds are made using 3D printing with acrylic resin and iron oxides synthesized through solution combustion. Utilizing triply periodic minimal surfaces (TPMS) geometry and mask stereolithography (MSLA) printing, the scaffolds achieve precise geometrical features. The mechanical properties are enhanced through resin curing, and magnetite particles from synthesized nanoparticles and alluvial magnetite are added for magnetic properties. The scaffolds show a balance between stiffness, porosity, and magnetic responsiveness, with maximum compression strength between 4.8 and 9.2 MPa and Young's modulus between 58 and 174 MPa. Magnetic properties such as magnetic coercivity, remanence, and saturation are measured, with the best results from scaffolds containing synthetic iron oxides at 1% weight. The viscosity of the mixtures used for printing is between 350 and 380 mPas, and contact angles between 90° and 110° are achieved. Biocompatibility tests indicate the potential for clinical trials, though further research is needed to understand the impact of magnetic properties on cellular interactions and optimize scaffold design for specific applications. This integrated approach offers a promising avenue for the development of advanced materials capable of promoting enhanced bone regeneration.

Tissue Engineering Nasal Cartilage Grafts with Three-Dimensional Printing: A Comprehensive Review

Nasal cartilage serves a crucial structural function for the nose, where rebuilding the cartilaginous framework is an essential aspect of nasal reconstruction. Conventional methods of nasal reconstruction rely on autologous cartilage harvested from patients, which contributes to donor site pain and the potential for site-specific complications. Some patients are not ideal candidates for this procedure due to a lack of adequate substitute cartilage due to age-related calcification, differences in tissue quality, or due to prior surgeries. Tissue engineering, combined with three-dimensional printing technologies, has emerged as a promising method of generating biomimetic tissues to circumvent these issues to restore normal function and aesthetics. We conducted a comprehensive literature review to examine the applications of three-dimensional printing in conjunction with tissue engineering for the generation of nasal cartilage grafts. This review aims to compare various approaches and discuss critical considerations in the design of these grafts.

A 3D in vitro model of biphasic calcium phosphate (BCP) scaffold combined with human osteoblasts, osteoclasts, and endothelial cells as a platform to mimic the oral microenvironment for tissue regeneration

OBJECTIVES

This study aimed to develop an innovative 3D in vitro model based on the biphasic calcium phosphate (BCP) scaffold combined with human osteoblasts (hOBs), osteoclasts (hOCs), and endothelial cells to evaluate its effects on bone and vascular cells behavior.

METHODS

To this end, an optimized mixture of hydroxyapatite (HA) and β-tricalcium phosphate (TCP) with a weight ratio of 30/70 was employed to develop a BCP scaffold using the computer-aided design (CAD) approach. The BCP scaffold was combined with primary cultures of hOBs, hOCs and human umbilical vein endothelial cells (HUVECs).

RESULTS

Morphometric analyses using scanning electron microscopy (SEM) and X-ray micro-computed tomography, along with biomechanical testing, revealed that BCP scaffold exhibited a regular 3D structure with large interconnected internal pores (700 µm) and high mechanical strength. In terms of biological behavior, after 14 days of tri-culture with hOBs, hMCs and HUVECs, SEM, immunofluorescence, and histological analyses showed that all cell types were viable and adhered well to the entire surface of the scaffold. Interestingly, SEM and energy-dispersive X-ray spectroscopy analyses also revealed on the BCP scaffold the presence of mineralized matrix crystals of Ca, P, O and C within a tissue-like cell layer produced by the interaction of the three cell types.

CONCLUSIONS

Data confirmed the high performance of the BCP scaffold through biomechanical studies. Notably, for the first time, this study demonstrated the feasibility of combining BCP scaffold with hOBs, hOCs, and HUVEC, which remained viable and maintained their native phenotypes, creating also tissue-like cell layer.

CLINICAL SIGNIFICANCE

Although further investigation is needed, these results underscore the potential to develop a 3D in vitro model that mimics the oral microenvironment, which could be valuable for BTE approaches in vivo studies.

Biocomposite Scaffolds Based on Chitosan Extraction from Shrimp Shell Waste for Cartilage Tissue Engineering Application

Chitosan-based scaffolding possesses unique properties that make it highly suitable for tissue engineering applications. Chitosan is derived from deacetylating chitin, which is particularly abundant in the shells of crustaceans. This study aimed to extract chitosan from shrimp shell waste (Macrobrachium rosenbergii) and produce biocomposite scaffolds using the extracted chitosan for cartilage tissue engineering applications. Chitinous material from shrimp shell waste was deproteinized and deacetylated. The extracted chitosan was characterized and compared to commercial chitosan through various physicochemical analyses. The findings revealed that the extracted chitosan shares similar trends in the Fourier transform infrared spectroscopy spectrum, energy dispersive X-ray mapping, and X-ray diffraction pattern to commercial chitosan. Despite differences in the degree of deacetylation, these results underscore its comparable quality. The extracted chitosan was mixed with agarose, collagen, and gelatin to produce the blending biocomposite AG-CH-COL-GEL scaffold by freeze-drying method. Results showed AG-CH-COL-GEL scaffolds have a 3D interconnected porous structure with pore size 88-278 μm, high water uptake capacity (>90%), and degradation percentages in 21 days between 5.08% and 30.29%. Mechanical compression testing revealed that the elastic modulus of AG-CH-COL-GEL scaffolds ranged from 44.91 to 201.77 KPa. Moreover, AG-CH-COL-GEL scaffolds have shown significant potential in effectively inducing human chondrocyte proliferation and enhancing aggrecan gene expression. In conclusion, AG-CH-COL-GEL scaffolds emerge as promising candidates for cartilage tissue engineering with their optimal physical properties and excellent biocompatibility. This study highlights the potential of using waste-derived chitosan and opens new avenues for sustainable and effective tissue engineering solutions.

Revolutionizing Drug Discovery: The Impact of Distinct Designs and Biosensor Integration in Microfluidics-Based Organ-on-a-Chip Technology

Traditional drug development is a long and expensive process with high rates of failure. This has prompted the pharmaceutical industry to seek more efficient drug development frameworks, driving the emergence of organ-on-a-chip (OOC) based on microfluidic technologies. Unlike traditional animal experiments, OOC systems provide a more accurate simulation of human organ microenvironments and physiological responses, therefore offering a cost-effective and efficient platform for biomedical research, particularly in the development of new medicines. Additionally, OOC systems enable quick and real-time analysis, high-throughput experimentation, and automation. These advantages have shown significant promise in enhancing the drug development process. The success of an OOC system hinges on the integration of specific designs, manufacturing techniques, and biosensors to meet the need for integrated multiparameter datasets. This review focuses on the manufacturing, design, sensing systems, and applications of OOC systems, highlighting their design and sensing capabilities, as well as the technical challenges they currently face.

Decellularized extracellular matrix-decorated 3D nanofiber scaffolds enhance cellular responses and tissue regeneration

The use of decellularized extracellular matrix products in tissue regeneration is quite alluring yet practically challenging due to the limitations of its availability, harsh processing techniques, and host rejection. Scaffolds obtained by either incorporating extracellular matrix (ECM) material or coating the surface can resolve these challenges to some extent. However, these scaffolds lack the complex 3D network formed by proteins and growth factors observed in natural ECM. This study introduces an approach utilizing 3D nanofiber scaffolds decorated with dECM to enhance cellular responses and promote tissue regeneration. Notably, the dECM can be customized according to specific cellular requirements, offering a tailored environment for enhanced therapeutic outcomes. Two types of 3D expanded scaffolds, namely radially aligned scaffolds (RAS) and laterally expanded scaffolds (LES) fabricated by the gas-foaming expansion were utilized. To demonstrate the proof-of-concept, human dermal fibroblasts (HDFs) seeded on these scaffolds for up to 8 weeks, resulted in uniform and highly aligned cells which deposited ECM on the scaffolds. These cellular components were then removed from the scaffolds through decellularization (e.g., SDS treatment and freeze-thaw cycles). The dECM-decorated 3D expanded nanofiber scaffolds can direct and support cell alignment and proliferation along the underlying fibers upon recellularization. An in vitro inflammation assay indicates that dECM-decorated LES induces a lower immune response than dECM-decorated RAS. Further, subcutaneous implantation of dECM-decorated RAS and LES shows higher cell infiltration and angiogenesis within 7 and 14 days than RAS and LES without dECM decoration. Taken together, dECM-decorated 3D expanded nanofiber scaffolds hold great potential in tissue regeneration and tissue modeling. STATEMENT OF SIGNIFICANCE: Decellularized ECM scaffolds have attained widespread attention in biomedical applications due to their intricate 3D framework of proteins and growth factors. Mimicking such a complicated architecture is a clinical challenge. In this study, we developed natural ECM-decorated 3D electrospun nanofiber scaffolds with controlled alignments to mimic human tissue. Fibroblasts were cultured on these scaffolds for 8 weeks to deposit natural ECM and decellularized by either freeze-thawing or detergent to obtain decellularized ECM scaffolds. These scaffolds were tested in both in-vitro and in-vivo conditions. They displayed higher cellular attributes with lower immune response making them a good grafting tool in tissue regeneration.

Antibacterial and Osteogenic Dual-Functional Micronano Composite Scaffold Fabricated via Melt Electrowriting and Solution Electrospinning for Bone Tissue Engineering

The utilization of micronano composite scaffolds has been extensively demonstrated to confer the superior advantages in bone repair compared to single nano- or micron-sized scaffolds. Nevertheless, the enhancement of bioactivities within these composite scaffolds remains challenging. In this study, we propose a novel approach to combine melt electrowriting (MEW) and solution electrospinning (SES) techniques for the fabrication of a composite scaffold incorporating hydroxyapatite (HAP), an osteogenic component, and roxithromycin (ROX), an antibacterial active component. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) confirmed the hierarchical architecture of the nanofiber-microgrid within the scaffold, as well as the successful loading of HAP and ROX. The incorporation of HAP enhanced the water absorption capacity of the composite scaffold, thus promoting cell adhesion and proliferation, as well as osteogenic differentiation. Furthermore, ROX resulted in effective antibacterial capability without any observable cytotoxicity. Finally, the scaffolds were applied to a rat calvarial defect model, and the results demonstrated that the 20% HAP group exhibited superior new bone formation without causing adverse reactions. Therefore, our findings present a promising strategy for designing and fabricating bioactive scaffolds for bone regeneration.

A biocompatible pea protein isolate-derived bioink for 3D bioprinting and tissue engineering

Three-dimensional bioprinting is a potent biofabrication technique in tissue engineering but is limited by inadequate bioink availability. Plant-derived proteins are increasingly recognized as highly promising yet underutilized materials for biomedical product development and hold potential for use in bioink formulations. Herein, we report the development of a biocompatible plant protein bioink from pea protein isolate. Through pH shifting, ethanol precipitation, and lyophilization, the pea protein isolate (PPI) transformed from an insoluble to a soluble form. Next, it was modified with glycidyl methacrylate to obtain methacrylate-modified PPI (PPIGMA), which is photocurable and was used as the precursor of bioink. The mechanical and microstructural studies of the hydrogel containing 16% PPIGMA revealed a suitable compress modulus and a porous network with a pore size over 100 μm, which can facilitate nutrient and waste transportation. The PPIGMA bioink exhibited good 3D bioprinting performance in creating complex patterns and good biocompatibility as plenty of viable cells were observed in the printed samples after 3 days of incubation in the cell culture medium. No immunogenicity of the PPIGMA bioink was identified as no inflammation was observed for 4 weeks after implantation in Sprague Dawley rats. Compared with methacrylate-modified gelatin, the PPIGMA bioink significantly enhanced cartilage regeneration in vitro and in vivo, suggesting that it can be used in tissue engineering applications. In summary, the PPIGMA bioink can be potentially used for tissue engineering applications.

Meniscal repair with additive manufacture of bioresorbable polymer: From physicochemical characterization to implantation of 3D printed poly (L-co-D, L lactide-co-trimethylene carbonate) with autologous stem cells in rabbits

Three-dimensional (3D) structures are actually the state-of-the-art technique to create porous scaffolds for tissue engineering. Since regeneration in cartilage tissue is limited due to intrinsic cellular properties this study aims to develop and characterize three-dimensional porous scaffolds of poly (L-co-D, L lactide-co-trimethylene carbonate), PLDLA-TMC, obtained by 3D fiber deposition technique. The PLDLA-TMC terpolymer scaffolds (70:30), were obtained and characterized by scanning electron microscopy, gel permeation chromatography, differential scanning calorimetry, thermal gravimetric analysis, compression mechanical testing and study on in vitro degradation, which showed its amorphous characteristics, cylindrical geometry, and interconnected pores. The in vitro degradation study showed significant loss of mechanical properties compatible with a decrease in molar mass, accompanied by changes in morphology. The histocompatibility association of mesenchymal stem cells from rabbit's bone marrow, and PLDLA-TMC scaffolds, were evaluated in the meniscus regeneration, proving the potential of cell culture at in vivo tissue regeneration. Nine New Zealand rabbits underwent total medial meniscectomy, yielding three treatments: implantation of the seeded PLDLA-TMC scaffold, implantation of the unseeded PLDLA-TMC and negative control (defect without any implant). After 24 weeks, the results revealed the presence of fibrocartilage in the animals treated with polymer. However, the regeneration obtained with the seeded PLDLA-TMC scaffolds with mesenchymal stem cells had become intimal to mature fibrocartilaginous tissue of normal meniscus both macroscopically and histologically. This study demonstrated the effectiveness of the PLDLA-TMC scaffold in meniscus regeneration and the potential of mesenchymal stem cells in tissue engineering, without the use of growth factors. It is concluded that bioresorbable polymers represent a promising alternative for tissue regeneration.

Harnessing the potential of hydrogels for advanced therapeutic applications: current achievements and future directions

The applications of hydrogels have expanded significantly due to their versatile, highly tunable properties and breakthroughs in biomaterial technologies. In this review, we cover the major achievements and the potential of hydrogels in therapeutic applications, focusing primarily on two areas: emerging cell-based therapies and promising non-cell therapeutic modalities. Within the context of cell therapy, we discuss the capacity of hydrogels to overcome the existing translational challenges faced by mainstream cell therapy paradigms, provide a detailed discussion on the advantages and principal design considerations of hydrogels for boosting the efficacy of cell therapy, as well as list specific examples of their applications in different disease scenarios. We then explore the potential of hydrogels in drug delivery, physical intervention therapies, and other non-cell therapeutic areas (e.g., bioadhesives, artificial tissues, and biosensors), emphasizing their utility beyond mere delivery vehicles. Additionally, we complement our discussion on the latest progress and challenges in the clinical application of hydrogels and outline future research directions, particularly in terms of integration with advanced biomanufacturing technologies. This review aims to present a comprehensive view and critical insights into the design and selection of hydrogels for both cell therapy and non-cell therapies, tailored to meet the therapeutic requirements of diverse diseases and situations.

Effect of 3D-printed polycaprolactone/osteolectin scaffolds on the odontogenic differentiation of human dental pulp cells

Cell-based tissue engineering often requires the use of scaffolds to provide a three-dimensional (3D) framework for cell proliferation and tissue formation. Polycaprolactone (PCL), a type of polymer, has good printability, favorable surface modifiability, adaptability, and biodegradability. However, its large-scale applicability is hindered by its hydrophobic nature, which affects biological properties. Composite materials can be created by adding bioactive materials to the polymer to improve the properties of PCL scaffolds. Osteolectin is an odontogenic factor that promotes the maintenance of the adult skeleton by promoting the differentiation of LepR+ cells into osteoblasts. Therefore, the aim of this study was to evaluate whether 3D-printed PCL/osteolectin scaffolds supply a suitable microenvironment for the odontogenic differentiation of human dental pulp cells (hDPCs). The hDPCs were cultured on 3D-printed PCL scaffolds with or without pores. Cell attachment and cell proliferation were evaluated using EZ-Cytox. The odontogenic differentiation of hDPCs was evaluated by alizarin red S staining and alkaline phosphatase assays. Western blot was used to evaluate the expression of the proteins DSPP and DMP-Results: The attachment of hDPCs to PCL scaffolds with pores was significantly higher than to PCL scaffolds without pores. The odontogenic differentiation of hDPCs was induced more in PCL/osteolectin scaffolds than in PCL scaffolds, but there was no statistically significant difference. 3D-printed PCL scaffolds with pores are suitable for the growth of hDPCs, and the PCL/osteolectin scaffolds can provide a more favorable microenvironment for the odontogenic differentiation of hDPCs.

Quantitative Evaluation of the Pore and Window Sizes of Tissue Engineering Scaffolds on Scanning Electron Microscope Images Using Deep Learning

The morphological characteristics of tissue engineering scaffolds, such as pore and window diameters, are crucial, as they directly impact cell-material interactions, attachment, spreading, infiltration of the cells, degradation rate and the mechanical properties of the scaffolds. Scanning electron microscopy (SEM) is one of the most commonly used techniques for characterizing the microarchitecture of tissue engineering scaffolds due to its advantages, such as being easily accessible and having a short examination time. However, SEM images provide qualitative data that need to be manually measured using software such as ImageJ to quantify the morphological features of the scaffolds. As it is not practical to measure each pore/window in the SEM images as it requires extensive time and effort, only the number of pores/windows is measured and assumed to represent the whole sample, which may cause user bias. Additionally, depending on the number of samples and groups, a study may require measuring thousands of samples and the human error rate may increase. To overcome such problems, in this study, a deep learning model (Pore D2) was developed to quantify the morphological features (such as the pore size and window size) of the open-porous scaffolds automatically for the first time. The developed algorithm was tested on emulsion-templated scaffolds fabricated under different fabrication conditions, such as changing mixing speed, temperature, and surfactant concentration, which resulted in scaffolds with various morphologies. Along with the developed model, blind manual measurements were taken, and the results showed that the developed tool is capable of quantifying pore and window sizes with a high accuracy. Quantifying the morphological features of scaffolds fabricated under different circumstances and controlling these features enable us to engineer tissue engineering scaffolds precisely for specific applications. Pore D2, an open-source software, is available for everyone at the following link: https://github.com/ilaydakaraca/PoreD2.

Redifferentiation of genetically modified dedifferentiated chondrocytes in a microcavitary hydrogel

OBJECTIVES

We genetically modified dedifferentiated chondrocytes (DCs) using lentiviral vectors and adenoviral vectors encoding TGF-β3 (referred to as transgenic groups below) and encapsulated these DCs in the microcavitary hydrogel and investigated the combinational effect on redifferentiation of the genetically manipulated DCs.

RESULTS

The Cell Counting Kit-8 data indicated that both transgenic groups exhibited significantly higher cell viability in the first week but inferior cell viability in the subsequent timepoints compared with those of the control group. Real-time polymerase chain reaction and western blot analysis results demonstrated that both transgenic groups had a better effect on redifferentiation to some extent, as evidenced by higher expression levels of chondrogenic genes, suggesting the validity of combination with transgenic DCs and the microcavitary hydrogel on redifferentiation. Although transgenic DCs with adenoviral vectors presented a superior extent of redifferentiation, they also expressed greater levels of the hypertrophic gene type X collagen. It is still worth further exploring how to deliver TGF-β3 more efficiently and optimizing the appropriate parameters, including concentration and duration.

CONCLUSIONS

The results demonstrated the better redifferentiation effect of DCs with the combinational use of transgenic TGF-β3 and a microcavitary alginate hydrogel and implied that DCs would be alternative seed cells for cartilage tissue engineering due to their easily achieved sufficient cell amounts through multiple passages and great potential to redifferentiate to produce cartilaginous extracellular matrix.

Biomimetic gradient scaffolds for the tissue engineering and regeneration of rotator cuff enthesis

Rotator cuff tear is one of the most common musculoskeletal disorders, which often results in recurrent shoulder pain and limited movement. Enthesis is a structurally complex and functionally critical interface connecting tendon and bone that plays an essential role in maintaining integrity of the shoulder joint. Despite the availability of advanced surgical procedures for rotator cuff repair, there is a high rate of failure following surgery due to suboptimal enthesis healing and regeneration. Novel strategies based on tissue engineering are gaining popularity in improving tendon-bone interface (TBI) regeneration. Through incorporating physical and biochemical cues into scaffold design which mimics the structure and composition of native enthesis is advantageous to guide specific differentiation of seeding cells and facilitate the formation of functional tissues. In this review, we summarize the current state of research in enthesis tissue engineering highlighting the development and application of biomimetic scaffolds that replicate the gradient TBI. We also discuss the latest techniques for fabricating potential translatable scaffolds such as 3D bioprinting and microfluidic device. While preclinical studies have demonstrated encouraging results of biomimetic gradient scaffolds, the translation of these findings into clinical applications necessitates a comprehensive understanding of their safety and long-term efficacy.

Probiotic cultivated meat: bacterial-based scaffolds and products to improve cultivated meat

Cultivated meat is emerging to replace traditional livestock industries, which have ecological costs, including land and water overuse and considerable carbon emissions. During cultivated meat production, mammalian cells can increase their numbers dramatically through self-renewal/proliferation and transform into mature cells, such as muscle or fat cells, through maturation/differentiation. Here, we address opportunities for introducing probiotic bacteria into the cultivated meat industry, including using them to produce renewable antimicrobials and scaffolding materials. We also offer solutions to challenges, including the growth of bacteria and mammalian cells, the effect of probiotic bacteria on production costs, and the effect of bacteria and their products on texture and taste. Our summary provides a promising framework for applying microbial composites in the cultivated meat industry.

Reasoning on Pore Terminology in 3D Bioprinting

Terminology is pivotal for facilitating clear communication and minimizing ambiguity, especially in specialized fields such as chemistry. In materials science, a subset of chemistry, the term "pore" is traditionally linked to the International Union of Pure and Applied Chemistry (IUPAC) nomenclature, which categorizes pores into "micro", "meso", and "macro" based on size. However, applying this terminology in closely-related areas, such as 3D bioprinting, often leads to confusion owing to the lack of consensus on specific definitions and classifications tailored to each field. This review article critically examines the current use of pore terminology in the context of 3D bioprinting, highlighting the need for reassessment to avoid potential misunderstandings. We propose an alternative classification that aligns more closely with the specific requirements of bioprinting, suggesting a tentative size-based division of interconnected pores into 'parvo'-(d < 25 µm), 'medio'-(25 < d < 100 µm), and 'magno'-(d > 100 µm) pores, relying on the current understanding of the pore size role in tissue formation. The introduction of field-specific terminology for pore sizes in 3D bioprinting is essential to enhance the clarity and precision of research communication. This represents a step toward a more cohesive and specialized lexicon that aligns with the unique aspects of bioprinting and tissue engineering.

Microporous Annealed Particle (MAP) Scaffold Pore Size Influences Mesenchymal Stem Cell Metabolism and Proliferation Without Changing CD73, CD90, and CD105 Expression Over Two Weeks

Scaffold pore architecture is shown to influence stem cell fate through various avenues. It is demonstrated that microporous annealed particle (MAP) microgel diameter can be tuned to control scaffold pore size and, in turn, modulate mesenchymal stem cell (MSC) survivability, proliferation, metabolism, and migration, thereby enhancing bioactivity and guiding future applications of MAP for regenerative medicine.

Engineering periodontal tissue interfaces using multiphasic scaffolds and membranes for guided bone and tissue regeneration

Periodontal diseases are one of the greatest healthcare burdens worldwide. The periodontal tissue compartment is an anatomical tissue interface formed from the periodontal ligament, gingiva, cementum, and bone. This multifaceted composition makes tissue engineering strategies challenging to develop due to the interface of hard and soft tissues requiring multiphase scaffolds to recreate the native tissue architecture. Multilayer constructs can better mimic tissue interfaces due to the individually tuneable layers. They have different characteristics in each layer, with modulation of mechanical properties, material type, porosity, pore size, morphology, degradation properties, and drug-releasing profile all possible. The greatest challenge of multilayer constructs is to mechanically integrate consecutive layers to avoid delamination, especially when using multiple manufacturing processes. Here, we review the development of multilayer scaffolds that aim to recapitulate native periodontal tissue interfaces in terms of physical, chemical, and biological characteristics. Important properties of multiphasic biodegradable scaffolds are highlighted and summarised, with design requirements, biomaterials, and fabrication methods, as well as post-treatment and drug/growth factor incorporation discussed.

A ternary composite hydrogel based on sodium alginate, carboxymethyl cellulose and copper-doped 58S bioactive glass promotes cutaneous wound healing in vitro and in vivo

Hydrogels offer a novel approach to wound repair. In this study, we synthesized a ternary composite using sodium alginate (SA), carboxymethyl cellulose (CMC) and copper-doped 58S bioactive glass (BG). According to our mechanical testing results, the composite made of 7 wt% CMC and 7 wt% BG (SA-7CMC-7BG) showed optimal properties. In addition, our in vitro studies revealed the biocompatibility and bioactivity of SA-7CMC-7BG, with a negative zeta potential of -31.7 mV. Scanning electron microscope (SEM) images showed 273-μm-diameter pores, cell adhesion, and anchoring. The SA-7CMC-7BG closed 90.4 % of the mechanical scratch after 2 days. An in vivo wound model using Wistar rats showed that SA-7CMC-7BG promoted wound healing, with 85.57 % of the wounds healed after 14 days. Treatment with the SA-7CMC-7BG hydrogel caused a 1.6-, 65-, and 1.87-fold increase in transforming growth factor beta (TGF-β), Col I, and vascular endothelial growth factor (VEGF) expression, respectively that prevents fibrosis and promotes angiogenesis. Furthermore, interleukin 1β (IL-1β) expression was downregulated by 1.61-fold, indicating an anti-inflammatory effect of SA-7CMC-7BG. We also observed an increase in epidermal thickness, the number of fibroblast cells, and collagen deposition, which represent complementary pathology results confirming the effectiveness of the SA-7CMC-7BG hydrogel in cutaneous wound healing.

Optimization of 3D Synthetic Scaffolds for Neuronal Tissue Engineering Applications

The increasing prevalence of neurodegenerative diseases has spurred researchers to develop advanced 3D models that accurately mimic neural tissues. Hydrogels stand out as ideal candidates as their properties closely resemble those of the extracellular matrix. A critical challenge in this regard is to comprehend the influence of the scaffold's mechanical properties on cell growth and differentiation, thus enabling targeted modifications. In light of this, a synthesis and comprehensive analysis of acrylamide-based hydrogels incorporating a peptide has been conducted. Adequate cell adhesion and development is achieved due to their bioactive nature and specific interactions with cellular receptors. The integration of a precisely controlled physicochemical hydrogel matrix and inclusion of the arginine-glycine-aspartic acid peptide sequence has endowed this system with an optimal structure, thus providing a unique ability to interact effectively with biomolecules. The analysis fully examined essential properties governing cell behavior, including pore size, mechanical characteristics, and swelling ability. Cell-viability experiments were performed to assess the hydrogel's biocompatibility, while the incorporation of grow factors aimed to promote the differentiation of neuroblastoma cells. The results underscore the hydrogel's ability to stimulate cell viability and differentiation in the presence of the peptide within the matrix.

Injectable gelatin/glucosamine cryogel microbeads as scaffolds for chondrocyte delivery in cartilage tissue engineering

In this study, we fabricate squeezable cryogel microbeads as injectable scaffolds for minimum invasive delivery of chondrocytes for cartilage tissue engineering applications. The microbeads with different glucosamine concentrations were prepared by combining the water-in-oil emulsion and cryogelation through crosslinking of gelatin with glutaraldehyde in the presence of glucosamine. The physicochemical characterization results show the successful preparation of cryogel microbeads with uniform shape and size, high porosity, large pore size, high water uptake capacity, and good injectability. In vitro analysis indicates proliferation, migration, and differentiated phenotype of rabbit chondrocytes in the cryogel scaffolds. The seeded chondrocytes in the cryogel scaffold can be delivered by injecting through an 18G needle to fully retain the cell viability. Furthermore, the incorporation of glucosamine in the cryogel promoted the differentiated phenotype of chondrocytes in a dose-dependent manner, from cartilage-specific gene expression and protein production. The in vivo study by injecting the cryogel microbeads into the subcutaneous pockets of nude mice indicates good retention ability as well as good biocompatibility and suitable biodegradability of the cryogel scaffold. Furthermore, the injected chondrocyte/cryogel microbead constructs can form ectopic functional neocartilage tissues following subcutaneous implantation in 21 days, as evidenced by histological and immunohistochemical analysis.

Highly compliant biomimetic scaffolds for small diameter tissue-engineered vascular grafts (TEVGs) produced via melt electrowriting (MEW)

Biofabrication approaches toward the development of tissue-engineered vascular grafts (TEVGs) have been widely investigated. However, successful translation has been limited to large diameter applications, with small diameter grafts frequently failing due to poor mechanical performance, in particular mismatched radial compliance. Herein, melt electrowriting (MEW) of poly(ϵ-caprolactone) has enabled the manufacture of highly porous, biocompatible microfibre scaffolds with physiological anisotropic mechanical properties, as substrates for the biofabrication of small diameter TEVGs. Highly reproducible scaffolds with internal diameter of 4.0 mm were designed with 500 and 250µm pore sizes, demonstrating minimal deviation of less than 4% from the intended architecture, with consistent fibre diameter of 15 ± 2µm across groups. Scaffolds were designed with straight or sinusoidal circumferential microfibre architecture respectively, to investigate the influence of biomimetic fibre straightening on radial compliance. The results demonstrate that scaffolds with wave-like circumferential microfibre laydown patterns mimicking the architectural arrangement of collagen fibres in arteries, exhibit physiological compliance (12.9 ± 0.6% per 100 mmHg), while equivalent control geometries with straight fibres exhibit significantly reduced compliance (5.5 ± 0.1% per 100 mmHg). Further mechanical characterisation revealed the sinusoidal scaffolds designed with 250µm pores exhibited physiologically relevant burst pressures of 1078 ± 236 mmHg, compared to 631 ± 105 mmHg for corresponding 500µm controls. Similar trends were observed for strength and failure, indicating enhanced mechanical performance of scaffolds with reduced pore spacing. Preliminaryin vitroculture of human mesenchymal stem cells validated the MEW scaffolds as suitable substrates for cellular growth and proliferation, with high cell viability (>90%) and coverage (>85%), with subsequent seeding of vascular endothelial cells indicating successful attachment and preliminary endothelialisation of tissue-cultured constructs. These findings support further investigation into long-term tissue culture methodologies for enhanced production of vascular extracellular matrix components, toward the development of the next generation of small diameter TEVGs.

A leptin-loaded poly-ϵ-caprolactone 3D printing scaffold for odontoblastic differentiation in human dental pulp cells

This study investigated the effects on odontoblast differentiation of a 3D-printed poly-ϵ-caprolactone (PCL) scaffold that incorporated leptin. Material extrusion-type 3D printing with a 43 000-molecular weight PCL material was used to fabricate a PCL scaffold with a 6 mm diameter, 1 mm height, and 270-340 µm pore size. The experimental groups were PCL scaffolds (control group), PCL scaffolds with aminated surfaces (group A), and PCL scaffolds with leptin on the aminated surface (group L). The aminated surface was treated with 1,6-hexanediamine and verified by ninhydrin analysis. Leptin loading was performed using Traut's reagent and 4-(N-Maleimidomethyl)cyclohexane-1-carboxylic acid 3-sulfo-N-hydroxysuccinimide ester sodium salt (Sulfo-SMCC). Groups A and L showed significantly higher surface wettability, pulp cell adhesion, and proliferation than the control group. Group L exhibited increased alkaline phosphatase, calcification deposits, and mRNA and protein expression of dentin sialophosphoprotein and dentin matrix acidic phosphoprotein 1 compared with the control group. In this study, a 3D-printed PCL scaffold containing leptin was enhanced odontoblast differentiation and dental pulp cells adhesion and proliferation.

Physiologically engineered porous titanium/brushite scaffolds for critical-size bone defects: A design and manufacturing study

Repairing critical-size bone defects still represents a critical clinical challenge in the field of trauma surgery. This study focuses on a physiological design and manufacturing of porous composite scaffold (titanium Ti with 10 % mole iron doped brushite DCPD-Fe3+) which can mimic the biomechanical properties of natural cortical bone, specifically for the purpose of repairing critical-size defects. To achieve this, the principle of design of experiments (DOE) was applied for investigating the impact of sintering temperature, mineral ratio, and volume fraction of porosity on the mechanical properties of the fabricated scaffolds. The fabricated scaffolds had open porosity up to 60 %, with pore size approximately between 100 μm and 850 μm. The stiffness of the porous composite scaffolds varied between 3.30 GPa and 20.50 GPa, while the compressive strength ranged from approximately 130 MPa-165 MPa at sintering temperatures equal to or exceeding 1000 °C. Scaffolds with higher porosity and mineral content demonstrated lower stiffness values, resembling natural bone. Numerical simulation was employed by Ansys Workbench to investigate the stress and strain distribution of a critical size defect in mid-shaft femur which was designed to be replaced with the fabricated scaffold. The fabricated scaffolds showed flexible biomechanical behaviour at the bone/scaffold interface, generating lower stress levels and indicating a better match with the femoral shaft stiffness. The experimental and numerical findings demonstrated promising applications for manufacturing a patient-specific bone scaffold for critical and potentially large defects for reducing stress shielding and minimizing non-union risk.

3D-printed PCL scaffolds with anatomy-inspired bionic stratified structures for the treatment of growth plate injuries

The growth plate is a cartilaginous tissue with three distinct zones. Resident chondrocytes are highly organized in a columnar structure, which is critical for the longitudinal growth of immature long bones. Once injured, the growth plate may potentially be replaced by bony bar formation and, consequently, cause limb abnormalities in children. It is well-known that the essential step in growth plate repair is the remolding of the organized structure of chondrocytes. To achieve this, we prepared an anatomy-inspired bionic Poly(ε-caprolactone) (PCL) scaffold with a stratified structure using three-dimensional (3D) printing technology. The bionic scaffold is engineered by surface modification of NaOH and collagen Ⅰ (COL Ⅰ) to promote cell adhesion. Moreover, chondrocytes and bone marrow mesenchymal stem cells (BMSCs) are loaded in the most suitable ratio of 1:3 for growth plate reconstruction. Based on the anatomical structure of the growth plate, the bionic scaffold is designed to have three regions, which are the small-, medium-, and large-pore-size regions. These pore sizes are used to induce BMSCs to differentiate into similar structures such as the growth plate. Remarkably, the X-ray and histological results also demonstrate that the cell-loaded stratified scaffold can successfully rebuild the structure of the growth plate and reduce limb abnormalities, including limb length discrepancies and angular deformities in vivo. This study provides a potential method of preparing a bioinspired stratified scaffold for the treatment of growth plate injuries.

Three-Dimensional Printing of Polycaprolactone/Nano-Hydroxyapatite Composite Scaffolds with a Pore Size of 300/500 µm is Histocompatible and Promotes Osteogenesis Using Rabbit Cortical Bone Marrow Stem Cells

BACKGROUND Many patients have bone defects that exceed the healing size. This study aimed to construct polycaprolactone/nano-hydroxyapatite (PCL/nHA) composite scaffolds with different pore sizes and investigate the osteogenesis and histocompatibility of cortical bone mesenchymal stem cells (BMSCs-C) seeded on it after inoculation. MATERIAL AND METHODS After mixing PCL and nHA proportionally, three-dimensional (3D) printing was used to print scaffolds. Porosity, compressive strength, and elastic modulus of PCL/nHA scaffolds were tested. The proliferation of BMSCs-C cells was examined and osteogenesis, chondrogenesis, and adipogenesis were evaluated. BMSCs-C cells were inoculated into 3D printing scaffolds, and histocompatibility between BMSCs-C cells and scaffolds was observed by the cell count kit (CCK-8) assay and LIVE/DEAD staining. After inoculating BMSCs-C cells into scaffolds, alkaline phosphatase (ALP) activity and calcium content were measured. RESULTS There was no obvious difference in characteristics between the 3 PCL/nHA composite scaffolds. The porosity, compressive strength, and elastic modulus of the 300/500-μm scaffold were between those of the 300-μm and 500-μm scaffolds. With increasing pore size, the mechanical properties of the scaffold decrease. BMSCs-C cells demonstrated faster growth and better osteogenic, adipogenic, and chondrogenic differentiation; therefore, BMSCs-C cells were selected as seed cells. PCL/nHA composite scaffolds with different pore sizes had no obvious toxicity and demonstrated good biocompatibility. All scaffolds showed higher ALP activity and calcium content. CONCLUSIONS The 300/500 μm mixed pore size scaffold took into account the mechanical properties of the 300 μm scaffold and the cell culture area of the 500 μm scaffold, therefore, 300/500 μm scaffold is a better model for the construction of tissue engineering scaffolds.

Progress in microsphere-based scaffolds in bone/cartilage tissue engineering

Bone/cartilage repair and regeneration have been popular and difficult issues in medical research. Tissue engineering is rapidly evolving to provide new solutions to this problem, and the key point is to design the appropriate scaffold biomaterial. In recent years, microsphere-based scaffolds have been considered suitable scaffold materials for bone/cartilage injury repair because microporous structures can form more internal space for better cell proliferation and other cellular activities, and these composite scaffolds can provide physical/chemical signals for neotissue formation with higher efficiency. This paper reviews the research progress of microsphere-based scaffolds in bone/chondral tissue engineering, briefly introduces types of microspheres made from polymer, inorganic and composite materials, discusses the preparation methods of microspheres and the exploration of suitable microsphere pore size in bone and cartilage tissue engineering, and finally details the application of microsphere-based scaffolds in biomimetic scaffolds, cell proliferation and drug delivery systems.

Cell Guiding Multicomponent Nanoyarn Tendon Scaffolds with Tunable Morphology and Flexibility

Nanofibrous scaffolds are widely investigated for tendon tissue engineering due to their porous structure, high flexibility, and the ability to guide cells in a preferred direction. Previous research has shown that providing a microenvironment similar to in vivo settings improves tissue regeneration. Therefore, in this work, ingenious multicomponent nanoyarn scaffolds that mimic the fibrillar and tubular structures of tendons are developed for the first time through electrospinning and bundling nanoyarns followed by electrospinning of a nanofibrous shell around the bundle. Multicomponent nanoyarn scaffolds out of poly(ε-caprolactone) with varying porosity, density, and diameter were successfully produced by coelectrospinning with water-soluble poly(2-ethyl-2-oxazoline) as a sacrificial component. The diameter and fiber orientation of the nanoyarns were successfully tuned based on parameter-morphology models obtained by the design of experiments. Cyclic bending tests were performed, indicating that the flexibility of the multicomponent nanoyarn scaffolds depends on the morphology and can be tuned through controlling the number of nanoyarns in the bundle and the porosity. Indirect and direct cell culture tests using mouse and equine tendon cells revealed excellent cytocompatibility of the nanofibrous products and demonstrated the potential of the nanoyarns to guide the growing cells along the nanofiber direction, which is crucial for tendon tissue engineering.

Effect of In Vitro Culture Length on the Bone-Forming Capacity of Osteoblast-Derived Decellularized Extracellular Matrix Melt Electrowritten Scaffolds

Recent advancements in decellularization have seen the development of extracellular matrix (ECM)-decorated scaffolds for bone regeneration; however, little is understood of the impact of in vitro culture prior to decellularization on the performances of these constructs. Therefore, this study investigated the effect of in vitro culture on ECM-decorated melt electrowritten polycaprolactone scaffold bioactivity. The scaffolds were seeded with osteoblasts and cultured for 1, 2, or 4 weeks to facilitate bone-specific ECM deposition and subsequently decellularized to form an acellular ECM-decorated scaffold. The utilization of mild chemicals and DNase was highly efficient in removing DNA while preserving ECM structure and composition. ECM decoration of the melt electrowritten fibers was observed within the first week of culture, with increased ECM at 2 and 4 week culture periods. Infiltration of re-seeded cells as well as overall bone regeneration in a rodent calvarial model was impeded by a longer culture period. Thus, it was demonstrated that the length of culture has a key influence on the osteogenic properties of decellularized ECM-decorated scaffolds, with long-term culture (2+ weeks) causing pore obstruction and creating a physical barrier which interfered with bone formation. These findings have important implications for the development of effective ECM-decorated scaffolds for bone regeneration.

3D Co-Printing and Substrate Geometry Influence the Differentiation of C2C12 Skeletal Myoblasts

Cells are influenced by several biomechanical aspects of their microenvironment, such as substrate geometry. According to the literature, substrate geometry influences the behavior of muscle cells; in particular, the curvature feature improves cell proliferation. However, the effect of substrate geometry on the myogenic differentiation process is not clear and needs to be further investigated. Here, we show that the 3D co-printing technique allows the realization of substrates. To test the influence of the co-printing technique on cellular behavior, we realized linear polycaprolactone substrates with channels in which a fibrinogen-based hydrogel loaded with C2C12 cells was deposited. Cell viability and differentiation were investigated up to 21 days in culture. The results suggest that this technology significantly improves the differentiation at 14 days. Therefore, we investigate the substrate geometry influence by comparing three different co-printed geometries-linear, circular, and hybrid structures (linear and circular features combined). Based on our results, all structures exhibit optimal cell viability (>94%), but the linear pattern allows to increase the in vitro cell differentiation, in particular after 14 days of culture. This study proposes an endorsed approach for creating artificial muscles for future skeletal muscle tissue engineering applications.

Recent development in multizonal scaffolds for osteochondral regeneration

Osteochondral (OC) repair is an extremely challenging topic due to the complex biphasic structure and poor intrinsic regenerative capability of natural osteochondral tissue. In contrast to the current surgical approaches which yield only short-term relief of symptoms, tissue engineering strategy has been shown more promising outcomes in treating OC defects since its emergence in the 1990s. In particular, the use of multizonal scaffolds (MZSs) that mimic the gradient transitions, from cartilage surface to the subchondral bone with either continuous or discontinuous compositions, structures, and properties of natural OC tissue, has been gaining momentum in recent years. Scrutinizing the latest developments in the field, this review offers a comprehensive summary of recent advances, current hurdles, and future perspectives of OC repair, particularly the use of MZSs including bilayered, trilayered, multilayered, and gradient scaffolds, by bringing together onerous demands of architecture designs, material selections, manufacturing techniques as well as the choices of growth factors and cells, each of which possesses its unique challenges and opportunities.

The regulation of tendon stem cell distribution, morphology, and gene expression by the modulus of microfibers

The mechanical properties of a stem cell culture substrate significantly impact cell adhesion, survival, migration, proliferation, and differentiation in vitro. A major challenge in engineering artificial stem cell substrate is to properly identify the relevant physical features of native stem cell niches, which are likely different for each stem cell type. The behavior of tendon stem cells has potentially significant implications for tendon repair. Here, microfiber scaffolds with various modulus of elasticity are fabricated by near-field electrospinning, and their regulating effects on the in vitro behavior of tendon stem cells (TSCs) are discussed in this study. The number of pseudopodia shows a biphasic relationship with the modulus of scaffold. The proliferation, polarization ratio and alignment degree along the fibers of the TSCs increase with the increase of fiber modulus. TSCs cultured on the scaffold with moderate modulus (1429 MPa) show the upregulation of tendon-specific genes (Col-I, Tnmd, SCX and TNCF). These microfiber scaffolds provide great opportunities to modulate TSCs behavior at the micrometer scales. In conclusion, this study provides an instructive mechanical microenvironment for TSCs behaviors and may lead to the development of desirable engineered artificial stem cell substrate for tendon healing.

Synthesis, Characterization, Properties, and Biomedical Application of Chitosan-Based Hydrogels

The prospective applications of chitosan-based hydrogels (CBHs), a category of biocompatible and biodegradable materials, in biomedical disciplines such as tissue engineering, wound healing, drug delivery, and biosensing have garnered great interest. The synthesis and characterization processes used to create CBHs play a significant role in determining their characteristics and effectiveness. The qualities of CBHs might be greatly influenced by tailoring the manufacturing method to get certain traits, including porosity, swelling, mechanical strength, and bioactivity. Additionally, characterization methods aid in gaining access to the microstructures and properties of CBHs. Herein, this review provides a comprehensive assessment of the state-of-the-art with a focus on the affiliation between particular properties and domains in biomedicine. Moreover, this review highlights the beneficial properties and wide application of stimuli-responsive CBHs. The main obstacles and prospects for the future of CBH development for biomedical applications are also covered in this review.

A Novel Antimicrobial Hydrogel for the Management of Periodontal Diseases

OBJECTIVES

This study aimed to synthesise a drug-delivery system based on a porous polymer hydrogel, with antimicrobial properties against Porphyromonas gingivalis and potential to be used in tissue regeneration.

MATERIAL AND METHODS

2-Hydroxyethyl methacrylate monomers were polymerised using thermal and photoactivation in the presence of silver nitrate (AgNO₃) and/or chlorhexidine digluconate. Poly-2-hydroxyethyl methacrylate (pHEMA) hydrogels containing silver nanoparticles (AgNPs) and/or 0.12% chlorhexidine (CHX) were produced and characterised using cryo-SEM and confocal microscopy. Hydrogel degradation and leaching of AgNP were tested for 1.5 months. The antimicrobial properties were tested against P. gingivalis using broth culture system and disk diffusion tests.

RESULTS

Our methodology manufactured porous polymeric hydrogels doped with AgNPs and CHX. Hydrogels showed a successful delivery of CHX and sustainable release of AgNPs in a steady hydrogel degradation rate determined based on the weight loss of samples. Hydrogels with AgNPs or CHX had a significant antimicrobial effect against P. gingivalis, with CHX-hydrogels exhibiting a stronger effect than AgNP-hydrogels in the short-term assessment. AgNP-CHX hydrogels showed a compounded antimicrobial effect, whereas control hydrogels containing neither AgNPs nor CHX had no influence on bacterial growth (P < .05).

CONCLUSIONS

The dual-cured pHEMA hydrogel loaded with antimicrobial agents proved to be an efficient drug-delivery system against periodontopathogens, with the potential to be used as a scaffold for tissue regeneration.

Detection of Limbal Stem Cells Adhered to Melt Electrospun Silk Fibroin and Gelatin-Modified Polylactic Acid Scaffolds

Limbal stem cells (LSCs) are of paramount importance in corneal epithelial tissue repair. The cornea becomes opaque in case of limbal stem cell deficiency (LSCD), which may cause serious damage to the ocular visual function. There are many techniques to restore damaged epithelium, one of which is the transplantation of healthy cultured LSCs, usually onto a human amniotic membrane or onto bio-based engineered scaffolds in recent years. In this study, melt electrospun polylactic acid (PLA) was modified by silk fibroin or gelatin and further cultured with LSCs originating from three different donors. In terms of physicochemical properties, both modifications slightly increased PLA scaffold porosity (with a significantly larger pore area for the PLA/gelatin) and improved the scaffolds' swelling percentage, as well as their biodegradation rate. In terms of the scaffold application function, the aim was to detect/visualize whether LSCs adhered to the scaffolds and to further determine cell viability (total number), as well as to observe p63 and CK3 expressions in the LSCs. LSCs were attached to the surface of microfibers, showing flattened conformations or 3D spheres in the formation of colonies or agglomerations, respectively. All scaffolds showed the ability to bind the cells onto the surface of individual microfibers (PLA and PLA/gelatin), or in between the microfibers (PLA/silk fibroin), with the latter showing the most intense red fluorescence of the stained cells. All scaffolds proved to be biocompatible, while the PLA/silk fibroin scaffolds showed the highest 98% viability of 2.9 × 10⁶ LSCs, with more than 98% of p63 and less than 20% of CK3 expressions in the LSCs, thus confirming the support of their growth, proliferation and corneal epithelial differentiation. The results show the potential of these bio-engineered scaffolds to be used as an alternative clinical approach.

A review on design of scaffold for osteoinduction: Toward the unification of independent design variables

Biophysical stimulus quantifies the osteoinductivity of the scaffold concerning the mechanoregulatory mathematical models of scaffold-assisted cellular differentiation. Consider a set of independent structural variables ($) that comprises bulk porosity levels ([Formula: see text]) and a set of morphological features of the micro-structure ([Formula: see text]) associated with scaffolds, i.e., [Formula: see text]. The literature suggests that biophysical stimulus ([Formula: see text]) is a function of independent structural variables ($). Limited understanding of the functional correlation between biophysical stimulus and structural features results in the lack of the desired osteoinductivity in a scaffold. Consequently, it limits their broad applicability to assist bone tissue regeneration for treating critical-sized bone fractures. The literature indicates the existence of multi-dimensional independent design variable space as a probable reason for the general lack of osteoinductivity in scaffolds. For instance, known morphological features are the size, shape, orientation, continuity, and connectivity of the porous regions in the scaffold. It implies that the number of independent variables ([Formula: see text]) is more than two, i.e., [Formula: see text], which interact and influence the magnitude of [Formula: see text] in a unified manner. The efficiency of standard engineering design procedures to analyze the correlation between dependent variable ([Formula: see text]) and independent variables ($) in 3D mutually orthogonal Cartesian coordinate system diminishes proportionally with the increase in the number of independent variables ([Formula: see text]) (Deb in Optimization for engineering design-algorithms and examples, PHI Learning Private Limited, New Delhi, 2012). Therefore, there is an immediate need to devise a framework that has the potential to quantify the micro-structural's morphological features in a unified manner to increase the prospects of scaffold-assisted bone tissue regeneration.

Progress of Microfluidic Hydrogel-Based Scaffolds and Organ-on-Chips for the Cartilage Tissue Engineering

Cartilage degeneration is among the fundamental reasons behind disability and pain across the globe. Numerous approaches have been employed to treat cartilage diseases. Nevertheless, none have shown acceptable outcomes in the long run. In this regard, the convergence of tissue engineering and microfabrication principles can allow developing more advanced microfluidic technologies, thus offering attractive alternatives to current treatments and traditional constructs used in tissue engineering applications. Herein, the current developments involving microfluidic hydrogel-based scaffolds, promising structures for cartilage regeneration, ranging from hydrogels with microfluidic channels to hydrogels prepared by the microfluidic devices, that enable therapeutic delivery of cells, drugs, and growth factors, as well as cartilage-related organ-on-chips are reviewed. Thereafter, cartilage anatomy and types of damages, and present treatment options are briefly overviewed. Various hydrogels are introduced, and the advantages of microfluidic hydrogel-based scaffolds over traditional hydrogels are thoroughly discussed. Furthermore, available technologies for fabricating microfluidic hydrogel-based scaffolds and microfluidic chips are presented. The preclinical and clinical applications of microfluidic hydrogel-based scaffolds in cartilage regeneration and the development of cartilage-related microfluidic chips over time are further explained. The current developments, recent key challenges, and attractive prospects that should be considered so as to develop microfluidic systems in cartilage repair are highlighted.

Nano-Hydroxyapatite/PLGA Mixed Scaffolds as a Tool for Drug Development and to Study Metastatic Prostate Cancer in the Bone

(1) Background: Three-dimensional (3D) in vitro, biorelevant culture models that recapitulate cancer progression can help elucidate physio-pathological disease cues and enhance the screening of more effective therapies. Insufficient research has been conducted to generate in vitro 3D models to replicate the spread of prostate cancer to the bone, a key metastatic site of the disease, and to understand the interplay between the key cell players. In this study, we aim to investigate PLGA and nano-hydroxyapatite (nHA)/PLGA mixed scaffolds as a predictive preclinical tool to study metastatic prostate cancer (mPC) in the bone and reduce the gap that exists with traditional 2D cultures. (2) Methods: nHA/PLGA mixed scaffolds were produced by electrospraying, compacting, and foaming PLGA polymer microparticles, +/- nano-hydroxyapatite (nHA), and a salt porogen to produce 3D, porous scaffolds. Physicochemical scaffold characterisation together with an evaluation of osteoblastic (hFOB 1.19) and mPC (PC-3) cell behaviour (RT-qPCR, viability, and differentiation) in mono- and co-culture, was undertaken. (3) Results: The results show that the addition of nHA, particularly at the higher-level impacted scaffolds in terms of mechanical and degradation behaviour. The nHA 4 mg resulted in weaker scaffolds, but cell viability increased. Qualitatively, fluorescent imaging of cultures showed an increase in PC-3 cells compared to osteoblasts despite lower initial PC-3 seeding densities. Osteoblast monocultures, in general, caused an upregulation (or at least equivalent to controls) in gene production, which was highest in plain scaffolds and decreased with increases in nHA. Additionally, the genes were downregulated in PC3 and co-cultures. Further, drug toxicity tests demonstrated a significant effect in 2D and 3D co-cultures. (4) Conclusions: The results demonstrate that culture conditions and environment (2D versus 3D, monoculture versus co-culture) and scaffold composition all impact cell behaviour and model development.

Bone regeneration strategies based on organelle homeostasis of mesenchymal stem cells

The organelle modulation has emerged as a crucial contributor to the organismal homeostasis. The mesenchymal stem cells (MSCs), with their putative functions in maintaining the regeneration ability of adult tissues, have been identified as a major driver to underlie skeletal health. Bone is a structural and endocrine organ, in which the organelle regulation on mesenchymal stem cells (MSCs) function has most been discovered recently. Furthermore, potential treatments to control bone regeneration are developing using organelle-targeted techniques based on manipulating MSCs osteogenesis. In this review, we summarize the most current understanding of organelle regulation on MSCs in bone homeostasis, and to outline mechanistic insights as well as organelle-targeted approaches for accelerated bone regeneration.

Study of EGCG composite hydrogel for the treatment of radiation-induced skin injuries

With the rising incidence of cancer, radiotherapy has become an increasingly popular treatment modality. However, radiation-induced skin injuries (RSIs) have emerged as a commonly reported side effect of radiotherapy, thereby presenting a significant challenge in the field of radiotherapy. In this study, we report the successful synthesis of a photosensitive hydrogel via amide reaction for grafting the photosensitive group, methacrylate anhydride (MA), onto chitosan (CHI) and gelatin (GEL), with subsequent physical incorporation of epigallocatechin gallate (EGCG). The resulting composite photosensitive hydrogels exhibited favorable swelling properties, rheological properties, and biocompatibility, which promote angiogenesis and demonstrate notable therapeutic efficacy against RSIs. These findings provide valuable insights into the clinical utility of EGCG composite hydrogels for the effective management of RSIs.

Biofabrication of Poly(glycerol sebacate) Scaffolds Functionalized with a Decellularized Bone Extracellular Matrix for Bone Tissue Engineering

The microarchitecture of bone tissue engineering (BTE) scaffolds has been shown to have a direct effect on the osteogenesis of mesenchymal stem cells (MSCs) and bone tissue regeneration. Poly(glycerol sebacate) (PGS) is a promising polymer that can be tailored to have specific mechanical properties, as well as be used to create microenvironments that are relevant in the context of BTE applications. In this study, we utilized PGS elastomer for the fabrication of a biocompatible and bioactive scaffold for BTE, with tissue-specific cues and a suitable microstructure for the osteogenic lineage commitment of MSCs. In order to achieve this, the PGS was functionalized with a decellularized bone (deB) extracellular matrix (ECM) (14% and 28% by weight) to enhance its osteoinductive potential. Two different pore sizes were fabricated (small: 100-150 μm and large: 250-355 μm) to determine a preferred pore size for in vitro osteogenesis. The decellularized bone ECM functionalization of the PGS not only improved initial cell attachment and osteogenesis but also enhanced the mechanical strength of the scaffold by up to 165 kPa. Furthermore, the constructs were also successfully tailored with an enhanced degradation rate/pH change and wettability. The highest bone-inserted small-pore scaffold had a 12% endpoint weight loss, and the pH was measured at around 7.14. The in vitro osteogenic differentiation of the MSCs in the PGS-deB blends revealed a better lineage commitment of the small-pore-sized and 28% (w/w) bone-inserted scaffolds, as evidenced by calcium quantification, ALP expression, and alizarin red staining. This study demonstrates a suitable pore size and amount of decellularized bone ECM for osteoinduction via precisely tailored PGS elastomer BTE scaffolds.

About 3D Printability of Thermoplastic Collagen for Biomedical Applications

With more than 1.5 million total knee and hip implants placed each year, there is an urgent need for a drug delivery system that can effectively support the repair of bone infections. Scaffolds made of natural biopolymers are widely used for this purpose due to their biocompatibility, biodegradability, and suitable mechanical properties. However, the poor processability is a bottleneck, as highly customizable scaffolds are desired. The aim of the present research is to develop a scaffold made of thermoplastic collagen (TC) using 3D printing technology. The viscosity of the material was measured using a rheometer. A 3D bioplotter was used to fabricate the scaffolds out of TC. The mechanical properties of the TC scaffolds were performed using tension/compression testing on a Zwick/Roell universal testing machine. TC shows better compressibility with increasing temperature and a decrease in dynamic viscosity (η), storage modulus (G'), and loss modulus (G″). The compressive strength of the TC scaffolds was between 3-10 MPa, depending on the geometry (cylinder or cuboid, with different infills). We have demonstrated for the first time that TC can be used to fabricate porous scaffolds by 3D printing in various geometries.

Melt electrowriting of PLA, PCL, and composite PLA/PCL scaffolds for tissue engineering application

Fabrication of well-ordered and bio-mimetic scaffolds is one of the most important research lines in tissue engineering. Different techniques have been utilized to achieve this goal, however, each method has its own disadvantages. Recently, melt electrowriting (MEW) as a technique for fabrication of well-organized scaffolds has attracted the researchers' attention due to simultaneous use of principles of additive manufacturing and electrohydrodynamic phenomena. In previous research studies, polycaprolactone (PCL) has been mostly used in MEW process. PCL is a biocompatible polymer with characteristics that make it easy to fabricate well-arranged structures using MEW device. However, the mechanical properties of PCL are not favorable for applications like bone tissue engineering. Furthermore, it is of vital importance to demonstrate the capability of MEW technique for processing a broad range of polymers. To address aforementioned problems, in this study, three ten-layered box-structured well-ordered scaffolds, including neat PLA, neat PCL, and PLA/PCL composite are fabricated using an MEW device. Printing of the composite PLA/PCL scaffold using the MEW device is conducted in this study for the first time. The MEW device used in this study is a commercial fused deposition modeling (FDM) 3D printer which with some changes in its setup and configuration becomes prepared for being used as an MEW device. Since in most of previous studies, a setup has been designed and built for MEW process, the use of the FDM device can be considered as one of the novelties of this research. The printing parameters are adjusted in a way that scaffolds with nearly equal pore sizes in the range of 140 µm to 150 µm are fabricated. However, PCL fibers are mostly narrower (diameters in the range of 5 µm to 15 µm) than PLA fibers with diameters between 15 and 25 µm. Unlike the MEW process of PCL, accurate positioning of PLA fibers is difficult which can be due to higher viscosity of PLA melt compared to PCL melt. The printed composite PLA/PCL scaffold possesses a well-ordered box structure with improved mechanical properties and cell-scaffold interactions compared to both neat PLA and PCL scaffolds. Besides, the composite scaffold exhibits a higher swelling ratio than the neat PCL scaffold which can be related to the presence of less hydrophobic PLA fibers. This scaffold demonstrates an anisotropic behavior during uniaxial tensile test in which its Young's modulus, ultimate tensile stress, and strain to failure all depend on the direction of the applied tensile force. This anisotropy makes the composite PLA/PCL scaffold an exciting candidate for applications in heart tissue engineering. The results of in-vitro cell viability test using L929 mouse murine fibroblast and human umbilical vein endothelial (HUVEC) cells demonstrate that all of the printed scaffolds are biocompatible. In particular, the composite scaffold presents the highest cell viability value among the fabricated scaffolds. All in all, the composite PLA/PCL scaffold shows that it can be a promising substitution for neat PCL scaffold used in previous MEW studies.

Controlled formation of highly porous polylactic acid‑calcium phosphate granules with defined structure

Synthetic bone repair materials are becoming increasingly popular in tissue engineering as a replacement for autografts and human/animal-based bone grafts. The biomedical application requires precise control over the material composition and structure, as well as over the size of granulate used for filling the bone defects, as the pore size and interconnectivity affect the regeneration process. This paper proposes a process of alloplastic and biodegradable polylactic acid/β-tricalcium phosphate granulates preparation and its parameters described. Using solvent-induced phase separation technique, porous spheres have been obtained in various sizes and morphologies. The design of the experiment's approach generated an experimental plan for further statistical modeling using the resulting data. The statistical modeling approach to the data from conducting a designed set of experiments allowed analysis of the influence of process parameters on the properties of the resulting granules. We confirmed that the content of β-tricalcium phosphate plays the most significant role in the size distribution of prepared granulate. The shape of the particles becomes less spherical with higher phosphate concentration in the emulsion. The proposed technique allows preparing porous granulates in the 0.2-1.8 mm diameter range, where granules' mean diameter and sphericity are tunable with polymer and phosphate concentrations. The granulate created a potentially implantable scaffold for resected bone regeneration, as cytotoxicity tests assured the material is non-cytotoxic in vitro, and human mesenchymal stem cells have been cultured on the surface of granulates. Results from cell cultures seeded on the Resomer LR 706S granulates were the most promising.

Recent Advances in Macroporous Hydrogels for Cell Behavior and Tissue Engineering

Hydrogels have been extensively used as scaffolds in tissue engineering for cell adhesion, proliferation, migration, and differentiation because of their high-water content and biocompatibility similarity to the extracellular matrix. However, submicron or nanosized pore networks within hydrogels severely limit cell survival and tissue regeneration. In recent years, the application of macroporous hydrogels in tissue engineering has received considerable attention. The macroporous structure not only facilitates nutrient transportation and metabolite discharge but also provides more space for cell behavior and tissue formation. Several strategies for creating and functionalizing macroporous hydrogels have been reported. This review began with an overview of the advantages and challenges of macroporous hydrogels in the regulation of cellular behavior. In addition, advanced methods for the preparation of macroporous hydrogels to modulate cellular behavior were discussed. Finally, future research in related fields was discussed.

Discussing the final size and shape of the reconstructed tissues in tissue engineering

Tissue engineering (TE) has made a revolution in repairing, replacing, or regenerating tissues or organs, but it has still a long way ahead. The mechanical properties along with suitable physicochemical and biological characteristics are the initial criteria for scaffolds in TE that should be fulfilled. This research will provide another point of view toward TE challenges concerning the morphological and geometrical aspects of the reconstructed tissue and which parameters may affect it. Based on our survey, there is a high possibility that the final reconstructed tissue may be different in size and shape compared to the original design scaffold. Thereby, the 3D-printed scaffold might not guarantee an accurate tissue reconstruction. The main justification for this is the unpredicted behavior of cells, specifically in the outer layer of the scaffold. It can also be a concern when the scaffold is implanted while cell migration cannot be controlled through the in vivo signaling pathways, which might cause cancer challenges. To sum up, it is concluded that more studies are necessary to focus on the size and geometry of the final reconstructed tissue.