A novel method to fabricate bioabsorbable scaffolds

Chondroitin Sulfate and Hyaluronic Acid-Based PolyHIPE Scaffolds for Improved Osteogenesis and Chondrogenesis In Vitro

Osteochondral damage, affecting the articular cartilage and the underlying subchondral bone, presents significant challenges in clinical treatment. Such defects, commonly seen in knee and ankle joints, vary from small localized lesions to larger defects. Current medical therapies encounter several challenges, such as donor shortages, drug side effects, high costs, and rejection problems, often resulting in only temporary relief. Highly porous emulsion-templated polymers (polyHIPEs) offer numerous potential benefits in the fabrication of scaffolds for tissue engineering and regenerative medicine. Polymeric scaffolds synthesized using a high internal phase emulsion (HIPE) technique, called PolyHIPEs, involve polymerizing a continuous phase surrounding a dispersed internal phase to form a solid, foam-like structure. A dense, porous design encourages cell ingrowth, nutrient delivery, and waste disposal from the scaffold, mimicking the cells' natural microenvironment. This study used hydroxyethyl methacrylate (HEMA) and acrylamide (AAM) polyHIPE scaffolds combined with extracellular matrix (ECM) components of the tissue, such as methacrylated hyaluronic acid (MHA) and methacrylated chondroitin sulfate (MCS), to prepare polyHIPE scaffolds. The mouse preosteoblast MC3T3-E1 cells and primary rat chondrocytes (harvested from male Wistar rats) were seeded on the scaffolds and cultured for 21 days to assess the osteogenesis and chondrogenesis in vitro. When compared to the AAM-MHA and AAM-MCS groups at day 21, scaffold groups HEMA-MHA and HEMA-MCS showed a significant rise in alkaline phosphatase (ALP) and calcium content. Chondrogenic markers such as glycosaminoglycan (GAG) and hydroxyproline were also assessed over a 21-day time point. On day 21, it was found that GAG and hydroxyproline production were considerably higher in the HEMA-MHA and HEMA-MCS scaffolds than in the AAM-MHA and AAM-MCS scaffolds. The overall studies showed that polyHIPE monolith scaffolds could favor cell adherence, survival ability, proliferation, differentiation, and ECM formation over 21 days. Thus, incorporating ECM components enhanced osteogenesis and chondrogenesis in vitro and can be further used as tissue repair models.

Review on Engineering of Bone Scaffolds Using Conventional and Additive Manufacturing Technologies

Bone is a complex connective tissue that serves as mechanical and structural support for the human body. Bones' fractures are common, and the healing process is physiologically complex and involves both mechanical and biological aspects. Tissue engineering of bone scaffolds holds great promise for the future treatment of bone injuries. However, conventional technologies to prepare bone scaffolds cannot provide the required properties of human bones. Over the past decade, three-dimensional (3D) printing or additive manufacturing technologies have enabled control over the creation of bone scaffolds with personalized geometries, appropriate materials, and tailored pores. This article aims to review recent advances in the fabrication of bone scaffolds for bone repair and regeneration. A detailed review of bone fracture repair and an in-depth discussion on conventional manufacturing and 3D printing techniques are introduced with an emphasis on novel studies concepts, potentials, and limitations.

Biomimetic scaffold and 3D bioprinting in dental application: A review

Biomimetic scaffold and 3D bioprinting technologies have emerged as promising avenues in tissue engineering and regenerative medicine, offering innovative approaches to address the limitations of conventional tissue engineering methods. This review article provides a comprehensive overview of recent advancements, challenges, and future prospects in the field of biomimetic scaffold fabrication and 3D bioprinting techniques.

Preparation of fast-swelling porous superabsorbent hydrogels with high saline water absorbency under pressure by foaming and post surface crosslinking

Superabsorbent hydrogels have wide applications in many fields because of their unique water absorbing performance. In spite of decades of research about superabsorbent hydrogels, high water absorbency under pressure and fast-swelling are still challenging and highly desired for their applications in hygienic products and others. Here, we report preparation of fast-swelling porous starch-g-poly(acrylic acid)/poly(vinyl alcohol) superabsorbent hydrogels with high saline water absorbency under pressure by foaming and post surface crosslinking. 2,2'-Azobis(2-amidinopropane) dihydrochloride (AIBA) was used as a new porogen instead of conventional porogens like NaHCO3. Post surface crosslinking of the hydrogel was achieved using glycerol via the esterification reaction. AIBA is a better porogen than NaHCO3 regarding porosity and swelling performance of the hydrogels, and its content has great influences on structure and swelling performance of the hydrogels including water absorbency and swelling rate. Also, the surface crosslinking using glycerol can significantly enhance the saline water absorbency under pressure (2 kPa) but at the sacrifice of the swelling rate. Consequently, the hydrogels show high water absorbencies for deionized water (560 g/g), 0.9 wt% NaCl solution (58 g/g), 0.9 wt% NaCl solution under 2 kPa pressure (28 g/g) and fast-swelling (31 s to achieve a highly swelling state).

Freeze-Drying Process for the Fabrication of Collagen-Based Sponges as Medical Devices in Biomedical Engineering

This paper presents a systematic review of a key sector of the much promising and rapidly evolving field of biomedical engineering, specifically on the fabrication of three-dimensional open, porous collagen-based medical devices, using the prominent freeze-drying process. Collagen and its derivatives are the most popular biopolymers in this field, as they constitute the main components of the extracellular matrix, and therefore exhibit desirable properties, such as biocompatibility and biodegradability, for in vivo applications. For this reason, freeze-dried collagen-based sponges with a wide variety of attributes can be produced and have already led to a wide range of successful commercial medical devices, chiefly for dental, orthopedic, hemostatic, and neuronal applications. However, collagen sponges display some vulnerabilities in other key properties, such as low mechanical strength and poor control of their internal architecture, and therefore many studies focus on the settlement of these defects, either by tampering with the steps of the freeze-drying process or by combining collagen with other additives. Furthermore, freeze drying is still considered a high-cost and time-consuming process that is often used in a non-optimized manner. By applying an interdisciplinary approach and combining advances in other technological fields, such as in statistical analysis, implementing the Design of Experiments, and Artificial Intelligence, the opportunity arises to further evolve this process in a sustainable and strategic manner, and optimize the resulting products as well as create new opportunities in this field.

Gelatin/Na2Ti3O7 Nanocomposite Scaffolds: Mechanical Properties and Characterization for Tissue Engineering Applications

Materials and manufacturing technologies are necessary for tissue engineering and developing temporary artificial extracellular matrices. In this study, scaffolds were fabricated from freshly synthesized titanate (Na₂Ti₃O₇) and its precursor titanium dioxide and their properties were investigated. The scaffolds with improved properties were then mixed with gelatin to form a scaffold material using the freeze-drying technique. To determine the optimal composition for the compression test of the nanocomposite scaffold, a mixture design with three factors of gelatin, titanate, and deionized water was used. Then, the scaffold microstructures were examined by scanning electron microscopy (SEM) to determine the porosity of the nanocomposite scaffolds. The scaffolds were fabricated as a nanocomposite and determined their compressive modulus values. The results showed that the porosity of the gelatin/Na₂Ti₃O₇ nanocomposite scaffolds ranged from 67% to 85%. When the mixing ratio was 100:0, the degree of swelling was 22.98%. The highest swelling ratio of 85.43% was obtained when the freeze-drying technique was applied to the mixture of gelatin and Na₂Ti₃O₇ with a mixing ratio of 80:20. The specimens formed (gelatin:titanate = 80:20) exhibited a compressive modulus of 30.57 kPa. The sample with a composition of 15.10% gelatin, 2% Na₂Ti₃O₇, and 82.9% DI water, processed by the mixture design technique, showed the highest yield of 30.57 kPa in the compression test.

Scaffold Fabrication Techniques of Biomaterials for Bone Tissue Engineering: A Critical Review

Bone tissue engineering (BTE) is a promising alternative to repair bone defects using biomaterial scaffolds, cells, and growth factors to attain satisfactory outcomes. This review targets the fabrication of bone scaffolds, such as the conventional and electrohydrodynamic techniques, for the treatment of bone defects as an alternative to autograft, allograft, and xenograft sources. Additionally, the modern approaches to fabricating bone constructs by additive manufacturing, injection molding, microsphere-based sintering, and 4D printing techniques, providing a favorable environment for bone regeneration, function, and viability, are thoroughly discussed. The polymers used, fabrication methods, advantages, and limitations in bone tissue engineering application are also emphasized. This review also provides a future outlook regarding the potential of BTE as well as its possibilities in clinical trials.

Enhancing the Mechanical Properties of 3D-Printed Waterborne Polyurethane-Urea and Cellulose Nanocrystal Scaffolds through Crosslinking

In this work, shape-customized scaffolds based on waterborne polyurethane-urea (WBPUU) were prepared via the combination of direct ink writing 3D-printing and freeze-drying techniques. To improve the printing performance of the ink and guarantee a good shape fidelity of the scaffold, cellulose nanocrystals (CNC) were added during the synthesis of the WBPUU and some of the printed constructs were immersed in CaCl₂ prior to the freeze-drying process to promote ionic crosslinking between calcium ions and the polyurethane. The results showed that apart from allowing the ink to be successfully printed, obtaining scaffolds with good shape fidelity, the addition of the CNC resulted in a greater homogeneity of the porous structure as well as an increase of the swelling capacity of the scaffolds. Additionally, the CNC has a reinforcement effect in the printed systems, presenting a higher compression modulus as the CNC content increases. In the case of samples crosslinked by calcium ions, a rigid shell was observed by scanning electron microscopy, which resulted in stiffer scaffolds that presented a lower water absorption capacity as well as an enhancement of the thermal stability. These results showed the potential of this type of post-printing process to tune the mechanical properties of the scaffold, thus widening the potential of this type of material.

Chitosan-Based Scaffolds for Facilitated Endogenous Bone Re-Generation

Facilitated endogenous tissue engineering, as a facile and effective strategy, is emerging for use in bone tissue regeneration. However, the development of bioactive scaffolds with excellent osteo-inductivity to recruit endogenous stem cells homing and differentiation towards lesion areas remains an urgent problem. Chitosan (CS), with versatile qualities including good biocompatibility, biodegradability, and tunable physicochemical and biological properties is undergoing vigorously development in the field of bone repair. Based on this, the review focus on recent advances in chitosan-based scaffolds for facilitated endogenous bone regeneration. Initially, we introduced and compared the facilitated endogenous tissue engineering with traditional tissue engineering. Subsequently, the various CS-based bone repair scaffolds and their fabrication methods were briefly explored. Furthermore, the functional design of CS-based scaffolds in bone endogenous regeneration including biomolecular loading, inorganic nanomaterials hybridization, and physical stimulation was highlighted and discussed. Finally, the major challenges and further research directions of CS-based scaffolds were also elaborated. We hope that this review will provide valuable reference for further bone repair research in the future.

Study of a Hydrophilic Healing-Promoting Porcine Acellular Dermal Matrix

Sodium hyaluronate (SH) is recognized as the strongest natural humectant, since it contains a large number of hydroxyl and carboxyl groups in its structure, and can absorb 1000 times its own weight of water. The porcine acellular dermal matrix (pADM) has been widely used in biological materials for its biological activities, such as promoting cell proliferation and promoting wound healing. Enhancing the hydrophilic and moisturizing properties of the pADM is expected to further improve its ability to promote wound healing. However, there are no strong chemical bonds between SH and pADM. Therefore, SH was oxidized by sodium periodate in this study, and was further used to cross-link it with pADM. The microstructure, hydrophilicity, moisture retention, degradation and cytotoxicity of pADM cross-linked with different oxidation degrees of oxidized sodium hyaluronate (OSH) were studied. The results show that OSH-pADM maintained the secondary structure of natural collagen, as well as the good microporous structure of native pADM after cross-linking. With increasing oxidation degree, the surface hydrophilicity and moisture retention capacities of OSH-pADM increased; among them, OSH-pADM cross-linked with 40% oxidation degree of OSH was found to have the strongest moisture retention capacity. The hygroscopic kinetics at 93% RH were conformed to the second-order hygroscopic kinetics equation, indicating that the hygroscopic process was controlled by chemical factors. The degradation resistance of OSH-pADM also increased with increasing oxidation degree, and the cytotoxicity of OSH-pADM was acceptable. The in vivo full-thickness wound healing experiments showed that OSH-pADM had an obvious ability to promote wound healing. It can be speculated that OSH-pADM, with its good hydrophilic and moisturizing properties, physicochemical properties and biocompatibility, has great potential for facilitating wound repair.

(Bio)manufactured Solutions for Treatment of Bone Defects with Emphasis on US-FDA Regulatory Science Perspective

Bone defects, with second highest demand for surgeries around the globe, may lead to serious health issues and negatively influence patient lives. The advances in biomedical engineering and sciences have led to the development of several creative solutions for bone defect treatment. This review provides a brief summary of bone graft materials, an organized overview of top-down and bottom-up (bio)manufacturing approaches, plus a critical comparison between advantages and limitations of each method. We specifically discuss additive manufacturing techniques and their operation mechanisms in detail. Next, we review the hybrid methods and promising future directions for bone grafting, while giving a comprehensive US-FDA regulatory science perspective, biocompatibility concepts and assessments, and clinical considerations to translate a technology from a research laboratory to the market. The topics covered in this review could potentially fuel future research efforts in bone tissue engineering, and perhaps could also provide novel insights for other tissue engineering applications.

Recent update on electrospinning and electrospun nanofibers: current trends and their applications

Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made in techniques for creating electro-spun and non-electro-spun nanofibers. Nanofibers were the center of attention for industries and researchers due to their simplicity in manufacture and setup. The review discusses a thorough overview of both electrospinning and non-electrospinning processes, including their setup, fabrication process, components, and applications. The review starts with an overview of the field of nanotechnology, the background of electrospinning, the surge in demand for nanofiber production, the materials needed to make nanofibers, and the critical process variables that determine the characteristics of nanofibers. Additionally, the diverse applications of electrospun nanofibers, such as smart mats, catalytic supports, filtration membranes, energy storage/heritage components, electrical devices (batteries), and biomedical scaffolds, are then covered. Further, the review concentrates on the most recent and pertinent developments in nanofibers that are connected to the use of nanofibers, focusing on the most illustrative cases. Finally, challenges and their possible solutions, marketing, and the future prospects of nanofiber development are discussed.

Electrospinning is a versatile and viable technique for generating ultrathin fibers.

A Review of Biomaterials and Scaffold Fabrication for Organ-on-a-Chip (OOAC) Systems

Drug and chemical development along with safety tests rely on the use of numerous clinical models. This is a lengthy process where animal testing is used as a standard for pre-clinical trials. However, these models often fail to represent human physiopathology. This may lead to poor correlation with results from later human clinical trials. Organ-on-a-Chip (OOAC) systems are engineered microfluidic systems, which recapitulate the physiochemical environment of a specific organ by emulating the perfusion and shear stress cellular tissue undergoes in vivo and could replace current animal models. The success of culturing cells and cell-derived tissues within these systems is dependent on the scaffold chosen; hence, scaffolds are critical for the success of OOACs in research. A literature review was conducted looking at current OOAC systems to assess the advantages and disadvantages of different materials and manufacturing techniques used for scaffold production; and the alternatives that could be tailored from the macro tissue engineering research field.

Biocompatible Composite Materials Based on Porous Hydroxyapatite Ceramics and Copolymer of Lactide and Glycolide

The intensive development of reconstructive surgery and traumatology provides a stable demand for new materials for implants. Of particular interest are materials based on hydroxyapatite, which are chemically close to the elemental composition and structure of bone and have similar bioactive properties. The aim of this work was to obtain porous composite materials based on hydroxyapatite and a copolymer of lactide and glycolide with properties suitable for use as a material for bone implants. The phase and elemental composition of composites was investigated by infrared spectroscopy, X-ray diffraction, and X-ray photoelectronic spectroscopy methods, and it was established how the production process affects the composition of materials. Regularities of the formation of porosity by the methods of low-temperature adsorption of nitrogen, immersion in a liquid (determination of the pore space volume), measurement of the diffusion coefficient through the material (Franz cell), and surface properties of composite materials by the Hammett indicator method, by the lying drop method were revealed. Regularities were established between the surface properties and the composition of materials and their biocompatibility determined using monocytes isolated from human peripheral blood.

Recent Progress on Biodegradable Tissue Engineering Scaffolds Prepared by Thermally-Induced Phase Separation (TIPS)

Porous biodegradable scaffolds provide a physical substrate for cells allowing them to attach, proliferate and guide the formation of new tissues. A variety of techniques have been developed to fabricate tissue engineering (TE) scaffolds, among them the most relevant is the thermally-induced phase separation (TIPS). This technique has been widely used in recent years to fabricate three-dimensional (3D) TE scaffolds. Low production cost, simple experimental procedure and easy processability together with the capability to produce highly porous scaffolds with controllable architecture justify the popularity of TIPS. This paper provides a general overview of the TIPS methodology applied for the preparation of 3D porous TE scaffolds. The recent advances in the fabrication of porous scaffolds through this technique, in terms of technology and material selection, have been reviewed. In addition, how properties can be effectively modified to serve as ideal substrates for specific target cells has been specifically addressed. Additionally, examples are offered with respect to changes of TIPS procedure parameters, the combination of TIPS with other techniques and innovations in polymer or filler selection.

Hofmeister Effect-Assistant Fabrication of All-Natural Protein-based Porous Materials Templated from Pickering Emulsions

Porous materials derived from natural and biodegradable polymers have received growing interest. We demonstrate here an attractive method for the preparation of protein-based porous materials using emulsions stabilized by gliadin-chitosan hybrid particles (GCHPs) as the template, with the addition of gelatin and kosmotropic ions to improve the mechanical strength. The microstructure, mechanical properties, cytotoxicity, and fluid absorption behavior of porous materials were systematically investigated. This strategy facilitated the formation of porous materials with highly open and interconnected pore structure, which can be manipulated by altering the mass ratio of hexane or gelatin in the matrix. The Hofmeister effect resulted from kosmotropic ions greatly enhanced the Young's modulus and the compressive stress at 40% strain of porous materials from 0.56 to 6.84 MPa and 0.26 to 1.11 MPa, respectively. The developed all-natural porous materials were nontoxic to HaCaT cells; they also had excellent liquid (i.e., simulated body fluid and rabbit blood) absorption performance and advantages in resisting stress and maintaining geometry shape. The effects of different concentration amounts and type of salts in the Hofmeister series on the formation and performance of porous materials were also explored. Mechanical strength of porous materials was gradually enhanced when the (NH₄)₂SO₄ concentration increased from 0 to 35 wt %, and the other four kosmotropic salts, including Na₂S₂O₃, Na₂CO₃, NaH₂PO₄, and Na₂SO₄, also showed positive effects. This work opens a simple and feasible way to produce nontoxic and biodegradable porous materials with favorable mechanical strength and controllable pore structure. These materials have broad potential application in many fields involving biomedical and material science, such as cell culture, (bio)catalysis, and wound or bone defect healing.

Polymer-Based Scaffolds for Soft-Tissue Engineering

Biomaterials have been used since ancient times. However, it was not until the late 1960s when their development prospered, increasing the research on them. In recent years, the study of biomaterials has focused mainly on tissue regeneration, requiring a biomaterial that can support cells during their growth and fulfill the function of the replaced tissue until its regeneration. These materials, called scaffolds, have been developed with a wide variety of materials and processes, with the polymer ones being the most advanced. For this reason, the need arises for a review that compiles the techniques most used in the development of polymer-based scaffolds. This review has focused on three of the most used techniques: freeze-drying, electrospinning and 3D printing, focusing on current and future trends. In addition, the advantages and disadvantages of each of them have been compared.

Development of hybrid scaffold: Bioactive glass nanoparticles/chitosan for tissue engineering applications

Bone tissue engineering is gaining popularity as an alternative method for the treatment of osseous defects. A number of biodegradable polymers have been explored for tissue engineering purposes. A new family of biodegradable polymer/bioactive glass composite materials has been designed to be used in bone regeneration approaches. In this work, a hybrid scaffold of chitosan (CH) and bioactive glass nanoparticles (BGN) was prepared by the freeze-gelation method. This method has been studied by adjusting the concentration of acetic acid; this process can influence the structure properties of the scaffold. In this work, several BGN/CH composites have been prepared by varying the proportion of BGN in the hybrid scaffold (20, 40, 60, and 80%). Brunauer-Emmett-Teller results showed the increased surface area and porosity volume of our composite with decreasing BGN proportion. BGN/CH hybrid scaffold was characterized by using physicochemical techniques. Obtained results showed a macroporous morphology of the scaffold with a pore size of about 200 μm, and a homogeneous distribution of the BGN in the CH matrix. X-ray diffraction study confirmed the amorphous state of the BGN/CH hybrid scaffold. Interaction between CH and BGNs in the composite was confirmed. The in vitro assays showed adequate degradation properties, which is essential for the potential replacement by the new tissue. The in vitro bioactivity studies confirmed the formation of an apatite layer on the surface of the hybrid scaffold, which results in a direct bone bonding of the implant. These results indicate that BGN/CH hybrid scaffold developed is a potential candidate for bone tissue engineering.

Natural Polymeric Scaffolds in Bone Regeneration

Despite considerable advances in microsurgical techniques over the past decades, bone tissue remains a challenging arena to obtain a satisfying functional and structural restoration after damage. Through the production of substituting materials mimicking the physical and biological properties of the healthy tissue, tissue engineering strategies address an urgent clinical need for therapeutic alternatives to bone autografts. By virtue of their structural versatility, polymers have a predominant role in generating the biodegradable matrices that hold the cells in situ to sustain the growth of new tissue until integration into the transplantation area (i.e., scaffolds). As compared to synthetic ones, polymers of natural origin generally present superior biocompatibility and bioactivity. Their assembly and further engineering give rise to a wide plethora of advanced supporting materials, accounting for systems based on hydrogels or scaffolds with either fibrous or porous architecture. The present review offers an overview of the various types of natural polymers currently adopted in bone tissue engineering, describing their manufacturing techniques and procedures of functionalization with active biomolecules, and listing the advantages and disadvantages in their respective use in order to critically compare their actual applicability potential. Their combination to other classes of materials (such as micro and nanomaterials) and other innovative strategies to reproduce physiological bone microenvironments in a more faithful way are also illustrated. The regeneration outcomes achieved in vitro and in vivo when the scaffolds are enriched with different cell types, as well as the preliminary clinical applications are presented, before the prospects in this research field are finally discussed. The collection of studies herein considered confirms that advances in natural polymer research will be determinant in designing translatable materials for efficient tissue regeneration with forthcoming impact expected in the treatment of bone defects.

Bioactive polymeric scaffolds for osteogenic repair and bone regenerative medicine

The loss of bone tissue is a striking challenge in orthopedic surgery. Tissue engineering using various advanced biofunctional materials is considered a promising approach for the regeneration and substitution of impaired bone tissues. Recently, polymeric supportive scaffolds and biomaterials have been used to rationally promote the generation of new bone tissues. To restore the bone tissue in this context, biofunctional polymeric materials with significant mechanical robustness together with embedded materials can act as a supportive matrix for cellular proliferation, adhesion, and osteogenic differentiation. The osteogenic regeneration to replace defective tissues demands greater calcium deposits, high alkaline phosphatase activity, and profound upregulation of osteocalcin as a late osteogenic marker. Ideally, the bioactive polymeric scaffolds (BPSs) utilized for bone tissue engineering should impose no detrimental impacts and function as a carrier for the controlled delivery and release of the loaded molecules necessary for the bone tissue regeneration. In this review, we provide comprehensive insights into different synthetic and natural polymers used for the regeneration of bone tissue and discuss various technologies applied for the engineering of BPSs and their physicomechanical properties and biological effects.

Three-dimensional cell culture systems as an in vitro platform for cancer and stem cell modeling

Three-dimensional (3D) culture systems are becoming increasingly popular due to their ability to mimic tissue-like structures more effectively than the monolayer cultures. In cancer and stem cell research, the natural cell characteristics and architectures are closely mimicked by the 3D cell models. Thus, the 3D cell cultures are promising and suitable systems for various proposes, ranging from disease modeling to drug target identification as well as potential therapeutic substances that may transform our lives. This review provides a comprehensive compendium of recent advancements in culturing cells, in particular cancer and stem cells, using 3D culture techniques. The major approaches highlighted here include cell spheroids, hydrogel embedding, bioreactors, scaffolds, and bioprinting. In addition, the progress of employing 3D cell culture systems as a platform for cancer and stem cell research was addressed, and the prominent studies of 3D cell culture systems were discussed.

Polymeric scaffolds for dental pulp tissue engineering: A review

OBJECTIVES

The purpose of this review is to describe recent developments in pulp tissue engineering using scaffolds and/or stem cells. It is crucial to understand how this approach can revitalize damaged dentin-pulp tissue. Widespread scaffold materials, both natural and synthetic, and their fabrication methods, and stem-progenitor cells with the potential of pulp regeneration will be discussed.

DATA AND SOURCES

A review of literature was conducted through online databases, including MEDLINE by using the PubMed search engine, Scopus, and the Cochrane Library.

STUDY SELECTION

Studies were selected based on relevance, with a preference given to recent research, particularly from the past decade.

CONCLUSIONS

The use of biomaterial scaffolds and stem cells can be safe and potent for the regeneration of pulp tissue and re-establishment of tooth vitality. Natural and synthetic polymers have distinct advantages and limitations and in vitro and in vivo testing have produced positive results for cell attachment, proliferation, and angiogenesis. The type of biomaterial used for scaffold fabrication also facilitates stem cell differentiation into odontoblasts and the resulting biochemistry of tissue repair for each polymer and cell type was discussed. Multiple methods of scaffold design exist for pulp tissue engineering, which demonstrates the variability in tissue engineering applications in endodontics. This review explains the potential of evidence-based tissue engineering strategies and outcomes in pulp regeneration.

BMP-2-releasing gelatin microspheres/PLGA scaffolds for bone repairment of X-ray-radiated rabbit radius defects

The purpose of this research is to assess the feasibility of poly(lactic-co-glycolic) acid (PLGA) incorporating gelatin microspheres (PLGA/GMs scaffold) for enhancing osteogenesis in vitro and at a radius defect of rabbits after X-ray radiation in vivo. After incorporating gelatin microspheres, PLGA scaffold demonstrated improved mechanical properties. Moreover, a sustained release property of recombinant human bone morphogenetic protein-2 (BMP-2) was achieved in BMP-2-releasing PLGA/GMs scaffold. BMP-2-releasing PLGA/GMs scaffold also enhanced proliferation and osteogenesis of rabbit bone mesenchymal stem cells (BMSCs) in vitro, indicating the bioactivity of BMP-2. After finishing X-ray radiation of the radius bone, 20-mm radius bone defects were generated, followed by being implanted with BMP-2-releasing PLGA/GMs scaffolds with or without bone marrow. Both PLGA/GMs scaffolds containing bone marrow or BMP-2 showed more obvious enhancement for bone regeneration than the empty scaffolds (control) at the radius defect. In the X-ray radiated groups, however, the bone regeneration was inhibited either with bone marrow or BMP-2. When combined with bone marrow, the BMP-2 showed significantly high osteogenic effect, regardless of X-ray radiation. It is considered that it is a promising way to repair bone defects even after X-ray radiation by a combination of bone marrow with the BMP-2-releasing PLGA/GMs scaffold.

Polyhydroxyalkanoate (PHA): applications in drug delivery and tissue engineering

INTRODUCTION

The applications of naturally obtained polymers are tremendously increased due to them being biocompatible, biodegradable, environmentally friendly and renewable in nature. Among them, polyhydroxyalkanoates are widely studied and they can be utilized in many areas of human life research such as drug delivery, tissue engineering, and other medical applications.

AREAS COVERED

This review provides an overview of the polyhydroxyalkanoates biosynthesis and their possible applications in drug delivery in the range of micro- and nano-size. Moreover, the possible applications in tissue engineering are covered considering macro- and microporous scaffolds and extracellular matrix analogs.

EXPERT COMMENTARY

The majority of synthetic plastics are non-biodegradable so, in the last years, a renewed interest is growing to develop alternative processes to produce biologically derived polymers. Among them, PHAs present good properties such as high immunotolerance, low toxicity, biodegradability, so, they are promisingly using as biomaterials in biomedical applications.

Bioactive diatomite and POSS silica cage reinforced chitosan/Na-carboxymethyl cellulose polyelectrolyte scaffolds for hard tissue regeneration

Recently, natural polymers are reinforced with silica particles for hard tissue engineering applications to induce bone regeneration. In this study, as two novel bioactive agents, effects of diatomite and polyhedral oligomeric silsesquioxanes (POSS) on chitosan (CS)/Na-carboxymethylcellulose (Na-CMC) polymer blend scaffolds are examined. In addition, the effect of silica reinforcements was compared with Si-substituted nano-hydroxyapatite (Si-Hap) particles. The morphology, physical and chemical structures of the scaffolds were characterized with SEM, liquid displacement, FT-IR, mechanical analysis, swelling and degradation studies. The particle size and the crystal structure of diatomite, POSS and Si-Hap particles were determined with DLS and XRD analyses. In vitro studies were performed to figure out the cytotoxicity, proliferation, ALP activity, osteocalcin production and biomineralization to demonstrate the promising use of natural silica particles in bone regeneration. Freeze-dried scaffolds showed 190-307 μm pore size range and 61-70% porosity. Both inorganic reinforcements increased the mechanical strength, enhanced the water uptake capacity and fastened the degradation rate. The nanocomposite scaffolds did not show any cytotoxic effect and enhanced the surface mineralization in osteogenic medium. Thus, diatomite and POSS cage structures can be potential reinforcements for nanocomposite design in hard tissue engineering applications.

Injectable hydrogels from enzyme-catalyzed crosslinking as BMSCs-laden scaffold for bone repair and regeneration

Bone-marrow-derived mesenchymal stem cells possess great potential for tissue engineering and regenerative medicine. In the work, an injectable BMSCs-laden hydrogel system was formed by enzyme-catalyzed crosslinking of hyaluronic acid-tyramine and chondroitin sulfate-tyramine in the presence of hydrogen peroxide and horseradish peroxidase, which was used as a 3D scaffold to explore the behavior of the mesenchymal stem cells. Afterward, the gelation rate, mechanical properties, as well as the degradation process of the scaffold were well characterized and optimized. Furthermore, bone morphogenetic protein-2 was encapsulated in the scaffold, which was used to improve the osteogenic properties. The results illustrated that such a BMSCs-laden hydrogel not only offered a proper microenvironment for the adhesion, proliferation and differentiation of mesenchymal stem cells in vitro, but also promoted bone regeneration in vivo. Therefore, this injectable BMSCs-laden hydrogel may serve as an efficient 3D scaffold for bone repair and regeneration.

Hepatocyte culture on 3D porous scaffolds of PCL/PMCL

The development of three-dimensional (3D) porous scaffolds for soft tissue engineering mainly focused on manipulation of scaffold properties with cell behaviors. By emulsion freeze-drying method, four types of porous scaffolds were prepared from amorphous poly(4-methy-ε-caprolactone) (PMCL) and semi-crystalline poly(ε-caprolactone) (PCL) at different weight ratios, named as PMCL0, PMCL30, PMCL50 and PMCL70, respectively. Visual observation on cross-sectional images of the scaffolds appeared as sponge-like materials with three-dimensional and highly porous morphologies. However, the pore size, porosity and wettability of blends were not decreased linearly with increasing amorphous PMCL. Distinguished from PMCL30 or PMCL70, PMCL50 preserved intact PCL crystals distributed in amorphous matrix, resulting in the lowest Young's modulus (E) and relatively high wettability. From in vitro cell culture, it was observed that PMCL50 scaffold supported human induced hepatocytes (hiHeps) proliferation and function preservation best among all scaffolds. hiHeps on PMCL50 inclined to adopt fibroblastic morphology, whereas formed spheroidal morphology on PMCL0. It was suggested that our bare scaffolds with tailored properties have shown remarkable capability towards hiHep proliferation and function expression.

3D bioactive composite scaffolds for bone tissue engineering

Bone is the second most commonly transplanted tissue worldwide, with over four million operations using bone grafts or bone substitute materials annually to treat bone defects. However, significant limitations affect current treatment options and clinical demand for bone grafts continues to rise due to conditions such as trauma, cancer, infection and arthritis. Developing bioactive three-dimensional (3D) scaffolds to support bone regeneration has therefore become a key area of focus within bone tissue engineering (BTE). A variety of materials and manufacturing methods including 3D printing have been used to create novel alternatives to traditional bone grafts. However, individual groups of materials including polymers, ceramics and hydrogels have been unable to fully replicate the properties of bone when used alone. Favourable material properties can be combined and bioactivity improved when groups of materials are used together in composite 3D scaffolds. This review will therefore consider the ideal properties of bioactive composite 3D scaffolds and examine recent use of polymers, hydrogels, metals, ceramics and bio-glasses in BTE. Scaffold fabrication methodology, mechanical performance, biocompatibility, bioactivity, and potential clinical translations will be discussed.

A review on fabricating tissue scaffolds using vat photopolymerization

Vat Photopolymerization (stereolithography, SLA), an Additive Manufacturing (AM) or 3D printing technology, holds particular promise for the fabrication of tissue scaffolds for use in regenerative medicine. Unlike traditional tissue scaffold fabrication techniques, SLA is capable of fabricating designed scaffolds through the selective photopolymerization of a photopolymer resin on the micron scale. SLA offers unprecedented control over scaffold porosity and permeability, as well as pore size, shape, and interconnectivity. Perhaps even more significantly, SLA can be used to fabricate vascular networks that may encourage angio and vasculogenesis. Fulfilling this potential requires the development of new photopolymers, the incorporation of biochemical factors into printed scaffolds, and an understanding of the effects scaffold geometry have on cell viability, proliferation, and differentiation. This review compares SLA to other scaffold fabrication techniques, highlights significant advances in the field, and offers a perspective on the field's challenges and future directions.

STATEMENT OF SIGNIFICANCE

Engineering de novo tissues continues to be challenging due, in part, to our inability to fabricate complex tissue scaffolds that can support cell proliferation and encourage the formation of developed tissue. The goal of this review is to first introduce the reader to traditional and Additive Manufacturing scaffold fabrication techniques. The bulk of this review will then focus on apprising the reader of current research and provide a perspective on the promising use of vat photopolymerization (stereolithography, SLA) for the fabrication of complex tissue scaffolds.

Preparation of Poly(l-lactic acid) Scaffolds by Thermally Induced Phase Separation: Role of Thermal History

Poly-L-Lactic Acid (PLLA) scaffolds for tissue engineering were prepared via thermally induced phase separation of a ternary system PLLA/dioxane/tetrahydrofurane. An extension to solution of a previously developed method for solidification from the melt was adopted, the technique being based on a Continuous Cooling Transformation (CCT) approach, consisting in recording the thermal history of rapidly cooled samples and analysing the resulting morphology. Different foams were produced by changing the thermal history, the dioxane to THF ratio (50/50, 70/30, 90/10 v/v) and the polymer concentration (2, 2.5, 4 ° wt) in the starting ternary solution. Pore size, porosity, melting and crystallization behavior were studied, together with a morphological and kinetic analysis of the foams produced. A large variety of morphologies was achieved, the largest pore size (20 μm) was achieved at the highest polymer concentration (4 ° wt) and the lowest dioxane concentration (50/50 dioxane/THF v/v), whereas the largest porosity (90 °) was attained at the highest dioxane concentration (90/10). The average pore size is related to cooling rate, with a 1/3 power law exponent at low polymer concentrations and low dioxane content for thermal histories driven by low undercoolings. At high undercoolings, the growth of the demixed domains significantly departs from the diffusive-like regime.

Fabrication of an electroconductive, flexible, and soft poly(3,4-ethylenedioxythiophene)-thermoplastic polyurethane hybrid scaffold by in situ vapor phase polymerization

The inherent insolubility and brittleness of poly(3,4-ethylenedioxythiophene) (PEDOT) reduce its processability and practical applicability. Herein, we use in situ vapor phase polymerization (VPP) of 3,4-ethylenedioxythiophene (EDOT) on an oxidant-impregnated thermoplastic polyurethane (TPU) matrix comprising a three-dimensional silica particle assembly to produce a soft, flexible, and conductive TPU-PEDOT hybrid scaffold. The selective removal of silica yielded a highly porous (∼95%) skeletal structure, with the effective penetration, diffusion, and polymerization of EDOT resulting in uniform PEDOT formation both on the surface and the inner side of the TPU matrix. The mechanical and electrical properties of the obtained scaffold were investigated by bending, compression testing, and stress-strain and electrical measurements. The electrical resistance of the scaffold equaled 17 kΩ and did not change after ∼500-fold bending, whereas the observed elastic modulus was much lower (300 kPa) than that of TPU (3.3 MPa). In vitro biocompatibility was investigated by MC3T3-E1 cell culturing with cell viability evaluated using the WST assay and cell morphology examined by confocal microscopy. Thus, the soft and flexible TPU-PEDOT hybrid scaffold produced by VPP might be practically useful, implying that this preliminary investigation needs to be extended to study the behavior of muscle and nerve cells under electrical stimulation.

Biomedical Applications of Recombinant Silk-Based Materials

Silk is mostly known as a luxurious textile, which originates from silkworms first cultivated in China. A deeper look into the variety of silk reveals that it can be used for much more, in nature and by humanity. For medical purposes, natural silks were recognized early as a potential biomaterial for surgical threads or wound dressings; however, as biomedical engineering advances, the demand for high-performance, naturally derived biomaterials becomes more pressing and stringent. A common problem of natural materials is their large batch-to-batch variation, the quantity available, their potentially high immunogenicity, and their fast biodegradation. Some of these common problems also apply to silk; therefore, recombinant approaches for producing silk proteins have been developed. There are several research groups which study and utilize various recombinantly produced silk proteins, and many of these have also investigated their products for biomedical applications. This review gives a critical overview over of the results for applications of recombinant silk proteins in biomedical engineering.