Three-dimensional biomaterial degradation — Material choice, design and extrinsic factor considerations

Collagen/polyester-polyurethane porous scaffolds for use in meniscal repair

Focusing on the regeneration of damaged knee meniscus, we propose a hybrid scaffold made of poly(ester-urethane) (PEU) and collagen that combines suitable mechanical properties with enhanced biological integration. To ensure biocompatibility and degradability, the degradable PEU was prepared from a poly(ε-caprolactone), L-lysine diisocyanate prepolymer (PCL di-NCO) and poly(lactic-co-glycolic acid) diol (PLGA). The resulting PEU (Mn = 52 000 g mol-1) was used to prepare porous scaffolds using the solvent casting (SC)/particle leaching (PL) method at an optimized salt/PEU weight ratio of 5 : 1. The morphology, pore size and porosity of the scaffolds were evaluated by SEM showing interconnected pores with a uniform size of around 170 μm. Mechanical properties were found to be close to those of the human meniscus (Ey ∼ 0.6 MPa at 37 °C). To enhance the biological properties, incorporation of collagen type 1 (Col) was then performed via soaking, injection or forced infiltration. The latter yielded the best results as shown by SEM-EDX and X-ray tomography analyses that confirmed the morphology and highlighted the efficient pore Col-coating with an average of 0.3 wt% Col in the scaffolds. Finally, in vitro L929 cell assays confirmed higher cell proliferation and an improved cellular affinity towards the proposed scaffolds compared to culture plates and a gold standard commercial meniscal implant.

Biomaterial-based mechanical regulation facilitates scarless wound healing with functional skin appendage regeneration

Scar formation resulting from burns or severe trauma can significantly compromise the structural integrity of skin and lead to permanent loss of skin appendages, ultimately impairing its normal physiological function. Accumulating evidence underscores the potential of targeted modulation of mechanical cues to enhance skin regeneration, promoting scarless repair by influencing the extracellular microenvironment and driving the phenotypic transitions. The field of skin repair and skin appendage regeneration has witnessed remarkable advancements in the utilization of biomaterials with distinct physical properties. However, a comprehensive understanding of the underlying mechanisms remains somewhat elusive, limiting the broader application of these innovations. In this review, we present two promising biomaterial-based mechanical approaches aimed at bolstering the regenerative capacity of compromised skin. The first approach involves leveraging biomaterials with specific biophysical properties to create an optimal scarless environment that supports cellular activities essential for regeneration. The second approach centers on harnessing mechanical forces exerted by biomaterials to enhance cellular plasticity, facilitating efficient cellular reprogramming and, consequently, promoting the regeneration of skin appendages. In summary, the manipulation of mechanical cues using biomaterial-based strategies holds significant promise as a supplementary approach for achieving scarless wound healing, coupled with the restoration of multiple skin appendage functions.

Development of novel polymer haemoglobin based particles as an antioxidant, antibacterial and an oxygen carrier agents

This innovative work aims to develop highly biocompatible and degradable nanoparticles by encapsulating haemoglobin (Hb) within poly-ε-caprolactone for novel biomedical applications. We used a modified double emulsion solvent evaporation method to fabricate the particles. A Scanning electron microscope (SEM) characterized them for surface morphology. Fourier Transform Infrared Spectroscopy (FTIR) and Ultraviolet-visible spectroscopies (UV-visible) elucidated preserved chemical and biological structure of encapsulated haemoglobin. The airproof equilibrium apparatus obtained the oxygen-carrying capacity and P50 values. The DPPH assay assessed free radical scavenging potential. The antibacterial properties were observed using four different bacterial strains by disk diffusion method. The MTT assay investigates the cytotoxic effects on mouse fibroblast cultured cell lines (L-929). The MTT assay showed that nanoparticles have no toxicity over large concentrations. The well-preserved structure of Hb within particles, no toxicity, high oxygen affinity, P50 value, and IC50 values open the area of new research, which may be used as artificial oxygen carriers, antioxidant, and antibacterial agents, potential therapeutic agents as well as drug carrier particles to treat the cancerous cells. The novelty of this work is the antioxidant and antibacterial properties of developed nanoparticles are not been reported yet. Results showed that the prepared particles have strong antioxidant and antibacterial potential.

Recent Advances in Bioelectronics for Localized Drug Delivery

The last decade has witnessed remarkable advancements in bioelectronics, ushering in a new era of wearable and implantable devices for drug delivery. By utilizing miniaturized system design and/or flexible materials, bioelectronics illustrates ideal integration with target organs and tissues, making them ideal platforms for localized drug delivery. Furthermore, the development of electrically assisted drug delivery systems has enhanced the efficiency and safety of therapeutic administration, particularly for the macromolecules that encounter additional challenges in penetrating biological barriers. In this review, a concise overview of recent progress in bioelectronic devices for in vivo localized drug delivery, with highlights on the latest trends in device design, working principles, and their corresponding functionalities, is provided. The reported systems based on their targeted delivery locations as wearable systems, ingestible systems, and implantable systems are categorized. Each category is introduced in detail by highlighting the special requirements for devices and the corresponding solutions. The remaining challenges in this field and future directions are also discussed.

Exploring the potential of polysaccharide-based hybrid hydrogel systems for their biomedical and therapeutic applications: A review

Hydrogels are a versatile category of biomaterials that have been widely applied in the fields of biomedicine for the last several decades. The three-dimensional polymeric crosslinked hydrophilic structures of the hydrogel can proficiently hold drugs, nanoparticles, and cells, making them a potential delivery system. However, disadvantages like low mechanical strength, poor biocompatibility, and unusual in-vivo biodegradation are associated with conventional hydrogels. To overcome these hurdles, hybrid hydrogels are designed using two or more structurally different polymeric units. Polysaccharides, characterized by their innate biocompatibility, biodegradability, and abundance, establish an ideal foundation for the development of these hybrid hydrogels. This review aims to discuss the studies that have utilized naturally occurring polysaccharides to prepare hybrid systems, which were aimed for various biomedical applications such as tissue engineering, bone and cartilage regeneration, wound healing, skin cancer treatment, antimicrobial therapy, osteoarthritis treatment, and drug delivery. Furthermore, this review extensively examines the properties of the employed polysaccharides within hydrogel matrices, emphasizing the advantageous characteristics that make them a preferred choice. Furthermore, the challenges associated with the commercial implementation of these systems are explored alongside an assessment of the current patent landscape.

Harnessing biomaterial architecture to drive anticancer innate immunity

Immunomodulation is a powerful therapeutic approach that harnesses the body's own immune system and reprograms it to treat diseases, such as cancer. Innate immunity is key in mobilizing the rest of the immune system to respond to disease and is thus an attractive target for immunomodulation. Biomaterials have widely been employed as vehicles to deliver immunomodulatory therapeutic cargo to immune cells and raise robust antitumor immunity. However, it is key to consider the design of biomaterial chemical and physical structure, as it has direct impacts on innate immune activation and antigen presentation to stimulate downstream adaptive immunity. Herein, we highlight the widespread importance of structure-driven biomaterial design for the delivery of immunomodulatory cargo to innate immune cells. The incorporation of precise structural elements can be harnessed to improve delivery kinetics, uptake, and the targeting of biomaterials into innate immune cells, and enhance immune activation against cancer through temporal and spatial processing of cargo to overcome the immunosuppressive tumor microenvironment. Structural design of immunomodulatory biomaterials will profoundly improve the efficacy of current cancer immunotherapies by maximizing the impact of the innate immune system and thus has far-reaching translational potential against other diseases.

Effects of ceramic additives and bioactive coatings on the degradation of polylactic acid-based bone scaffolds under hydrolytic conditions

Polylactic acid (PLA) has been extensively used for the manufacturing of scaffolds in bone tissue engineering applications. Due to the low hydrophilicity and the acidic degradation process of this biomaterial, different strategies have been proposed to increase the biofunctionality of the support structure. The use of ceramic particles is a generally preferred option to increase the osteoconductivity of the base material, while acting as buffers to maintain the pH level of the surroundings tissues. Surface modification is another approach to overcome the limitations of PLA for tissue engineering applications. In this work, the degradation profile of 3D-printed PLA scaffolds containing beta-tricalcium phosphate (β-TCP) and calcium carbonate (CaCO3 ) particles has been studied under hydrolytic conditions. Composite samples treated with plasma and coated with Aloe vera extracts were also studied to evaluate the effect of this surface modification method. The characterization of the 3D structures included its morphological, calorimetric and mechanical evaluation. According to the results obtained, the proposed composite scaffolds allowed an adequate maintenance of the pH level of the surrounding medium, with no effects observed on the morphology and mechanical properties of these structures. Hence, these samples showed potential to be further investigated as candidates for bone tissue regeneration.

A Compilation of Study Models for Dental Pulp Regeneration

Efforts to heal damaged pulp tissue through tissue engineering have produced positive results in pilot trials. However, the differentiation between real regeneration and mere repair is not possible through clinical measures. Therefore, preclinical study models are still of great importance, both to gain insights into treatment outcomes on tissue and cell levels and to develop further concepts for dental pulp regeneration. This review aims at compiling information about different in vitro and in vivo ectopic, semiorthotopic, and orthotopic models. In this context, the differences between monolayer and three-dimensional cell cultures are discussed, a semiorthotopic transplantation model is introduced as an in vivo model for dental pulp regeneration, and finally, different animal models used for in vivo orthotopic investigations are presented.

Nonmulberry silk fibroin-based biomaterials: Impact on cell behavior regulation and tissue regeneration

Silk fibroin (SF) is a promising biomaterial due to its good biocompatibility, easy availability, and high mechanical properties. Compared with mulberry silk fibroin (MSF), nonmulberry silk fibroin (NSF) isolated from typical nonmulberry silkworm silk exhibits unique arginine-glycine-aspartic acid (RGD) sequences with favorable cell adhesion enhancing effect. This inherent property probably makes the NSF more suitable for cell culture and tissue regeneration-related applications. Accordingly, various types of NSF-based biomaterials, such as particles, films, fiber mats, and 3D scaffolds, are constructed and their application potential in different biomedical fields is extensively investigated. Based on these promising NSF biomaterials, this review firstly makes a systematical comparison between the molecular structure and properties of MSF and typical NSF and highlights the unique properties of NSF. In addition, we summarize the effective fabrication strategies from degummed nonmulberry silk fibers to regenerated NSF-based biomaterials with controllable formats and their recent application progresses in cell behavior regulation and tissue regeneration. Finally, current challenges and future perspectives for the fabrication and application of NSF-based biomaterials are discussed. Related research and perspectives may provide valuable references for designing and modifying effective NSF-based and other natural biomaterials. STATEMENT OF SIGNIFICANCE: There exist many reviews about mulberry silk fibroin (MSF) biomaterials and their biomedical applications, while that about nonmulberry silk fibroin (NSF) biomaterials is scarce. Compared with MSF, NSF exhibits unique arginine-glycine-aspartic acid sequences with promising cell adhesion enhancing effect, which makes NSF more suitable for cell culture and tissue regeneration related applications. Focusing on these advanced NSF biomaterials, this review has systematically compared the structure and properties of MSF and NSF, and emphasized the unique properties of NSF. Following that, the effective construction strategies for NSF-based biomaterials are summarized, and their recent applications in cell behavior regulations and tissue regenerations are highlighted. Furthermore, current challenges and future perspectives for the fabrication and application of NSF-based biomaterials were discussed.

Polyelectrolyte Complex Hydrogels with Controlled Mechanics Affect Mesenchymal Stem Cell Differentiation Relevant to Growth Plate Injuries

The growth plate is a complex cartilage structure in long bones that mediates growth in children. When injured, the formation of a "bony bar" can occur which impedes normal growth and can cause angular deformities or growth arrest. Current treatments for growth plate injuries are limited and result in poor patient outcomes, necessitating research toward novel treatments that can prevent bony bar formation and stimulate cartilage regeneration. This study investigates alginate-chitosan polyelectrolyte complex (PEC) hydrogels as an injectable biomaterial system to prevent bony bar formation. Biomaterial properties including stiffness and degradation are quantified, and the effect that material properties have on mesenchymal stem cell (MSC) fate is quantified in vitro. Specifically, this study aims to elucidate the effectiveness of biomaterial-based control over the differentiation behavior of MSCs toward osteogenic or chondrogenic lineages using biochemical metabolite assays and quantitative real time PCR. Further, the PEC hydrogels are employed in a rat growth plate injury model to determine their effectiveness in preventing bony bar formation in vivo. Results indicate that hydrogel composition and material properties affect the differentiation tendency of MSCs in vitro, and the PEC hydrogels show promise as an injectable biomaterial for growth plate injuries.

Tuning the affinity of amphiphilic guest molecules in a supramolecular polymer transient network

Dynamicity plays a central role in biological systems such as in the cellular microenvironment. Here, the affinity and dynamics of different guest molecules in a transient supramolecular polymer hydrogel system, i.e. the host network, are investigated. The hydrogel system consists of bifunctional ureido-pyrimidinone (UPy) poly(ethylene glycol) polymers. A monofunctional complementary UPy guest is introduced, designed to interact with the host network based on UPy–UPy interactions. Furthermore, two other guest molecules are synthesized, being cholesterol and dodecyl (c12) guests; both designed to interact with the host network via hydrophobic interactions. At the nanoscale in solution, differences in morphology of the guest molecules were observed. The UPy–guest molecule formed fibers, and the cholesterol and c12 guests formed aggregates. Furthermore, cellular internalization of fluorescent guest molecules was studied. No cellular uptake of the UPy–cy5 guest was observed, whereas the cholesterol–cy5 guest showed membrane binding and cellular uptake. Also the c12–cy5 guest showed cellular uptake. Formulation of the guest molecules into the UPy hydrogel system was done to study the guest–host affinity. No changes in mechanical properties as measured with rheology were found upon guest–hydrogel formulation. Fluorescence recovery after photobleaching showed the diffusive properties of the cy5-functionalized guests throughout the host network. The c12 guest displayed a relatively fast mobility, the UPy guest displayed a decrease in mobility, and the cholesterol–guest remained relatively stable in the host network with little mobility. This demonstrates the tunable dynamic differences of affinity-based interaction between guest molecules and the host network. Interestingly, the cholesterol guest is internalized in cells and is robustly incorporated in the hydrogel network, while the UPy guest is not taken up by cells but shows an affinity to the hydrogel network. These results show the importance of guest–hydrogel affinity for future drug release. However, if modified with cholesterol these guests, or future drugs, will be taken up by cells; if modified with a UPy unit this does not occur. In this way both the drug–hydrogel interaction and the cell internalization behavior can be tuned. Regulating the host–guest dynamics in transient hydrogels opens the door to various drug delivery purposes and tissue engineering.

Dynamicity plays a central role in biological systems, which can be mimicked by tuning dynamicity in hydrogel networks.

A brief review of mRNA therapeutics and delivery for bone tissue engineering

The therapeutics for bone tissue regeneration requires constant advancements owing to the steady increase in the number of patients suffering from bone-related disorders, and also to find efficient and cost-effective treatment modalities. One of the major advancements in the field of therapeutics is the development of mRNAs. mRNAs, which have been extensively tested for the vaccines, could be very well utilized as a potential inducer for bone regeneration. The ability of mRNAs to enter the cells and instruct the cellular machinery to produce the required native proteins such as BMP or VEGF is a great way to avoid the issues faced with growth factor deliveries such as the production cost, loss of biological function etc. However, there have been a few hurdles for using mRNAs as an effective therapeutic agent, such as proper dosing, tolerating the degradation by RNases, improving the half-life, controlling the spatio-temporal release and reducing the off-target effects. This brief review discusses the various developments in the field of mRNA therapeutics especially for bone tissue engineering, how nano-formulations are being developed to effectively deliver the mRNAs into the cells by evading the immune responses, how researchers have developed certain strategies to increase the half-life, to successfully deliver the mRNAs to specific bone defect area and bring about effective bone regeneration.

GOx/Hb Cascade Oxidized Crosslinking of Silk Fibroin for Tissue-Responsive Wound Repair

Promising wound dressings can achieve rapid soft-tissue filling while refactoring the biochemical and biophysical microenvironment to recruit endogenous cells, facilitating tissue healing, integration, and regeneration. In this study, a tissue biomolecule-responsive hydrogel matrix, employing natural silk fibroin (SF) as a functional biopolymer and haemoglobin (Hb) as a peroxidase-like biocatalyst, was fabricated through cascade enzymatic crosslinking. The hydrogels possessed mechanical tunability and displayed adjustable gelation times. A tyrosine unit on SF stabilised the structure of Hb during the cascade oxidation process; thus, the immobilized Hb in SF hydrogels exhibited higher biocatalytic efficiency than the free enzyme system, which provided a continuously antioxidative system. The regulation of the dual enzyme ratio endowed the hydrogels with favourable biocompatibility, biodegradability, and adhesion strength. These multifunctional hydrogels provided a three-dimensional porous extracellular matrix-like microenvironment for promoting cell adhesion and proliferation. A rat model with a full-thickness skin defect revealed accelerated wound regeneration via collagen deposition, re-epithelialisation and revascularisation. Enzyme-loaded hydrogels are an attractive and high-safety biofilling material with the potential for wound healing, tissue regeneration, and haemostasis.

Human Induced Pluripotent Stem Cell-Derived Neural Progenitor Cells Produce Distinct Neural 3D In Vitro Models Depending on Alginate/Gellan Gum/Laminin Hydrogel Blend Properties

Stable and predictive neural cell culture models are a necessary premise for many research fields. However, conventional 2D models lack 3D cell-material/-cell interactions and hence do not reflect the complexity of the in vivo situation properly. Here two alginate/gellan gum/laminin (ALG/GG/LAM) hydrogel blends are presented for the fabrication of human induced pluripotent stem cell (hiPSC)-based 3D neural models. For hydrogel embedding, hiPSC-derived neural progenitor cells (hiNPCs) are used either directly or after 3D neural pre-differentiation. It is shown that stiffness and stress relaxation of the gel blends, as well as the cell differentiation strategy influence 3D model development. The embedded hiNPCs differentiate into neurons and astrocytes within the gel blends and display spontaneous intracellular calcium signals. Two fit-for-purpose models valuable for i) applications requiring a high degree of complexity, but less throughput, such as disease modeling and long-term exposure studies and ii) higher throughput applications, such as acute exposures or substance screenings are proposed. Due to their wide range of applications, adjustability, and printing capabilities, the ALG/GG/LAM based 3D neural models are of great potential for 3D neural modeling in the future.

The design criteria and therapeutic strategy of functional scaffolds for spinal cord injury repair

Spinal cord injury (SCI) remains a therapeutic challenge in clinic. Current drug and cell therapeutics have obtained significant efficacy but are still in the early stages for complete neural and functional recovery. In the past few decades, functional scaffolds (FSs) have been rapidly developed to bridge the lesion and provide a framework for tissue regeneration in SCI repair. Moreover, a FS can act as an adjuvant for locally delivering drugs in the lesion with a designed drug release profile, and supplying a biomimetic environment for implanted cells. In this review, the design criteria of FSs for SCI treatment are summarized according to their biocompatibility, mechanical properties, morphology, architecture, and biodegradability. Subsequently, FSs designed for SCI repair in the scope of drug delivery, cell implantation and combination therapy are introduced, respectively. And how a FS promotes their therapeutic efficacy is analyzed. Finally, the challenges, perspectives, and potential of FSs for SCI treatment are discussed. Hopefully, this review may inspire the future development of potent FSs to facilitate SCI repair in clinic.

Fabrication of Vascularized DPSC Constructs for Efficient Pulp Regeneration

Dental pulp regeneration is a promising approach to restore the vitality of necrotic teeth. We have previously reported the fabrication of scaffold-free cell constructs containing only dental pulp stem cells (DPSCs) and their ability to form pulp-like tissue in the pulpless tooth. However, the DPSC construct could not build pulp-like tissue with a full root length because it is difficult to induce blood vessels from a small root canal foramen. Therefore, we hypothesized that vascular structure could be preformed in the DPSC construct by employing endothelial differentiation capability of DPSCs, and vascularized constructs might facilitate dental pulp regeneration in the pulpless tooth. In this study, vascularized DPSC constructs were fabricated by inducing endothelial differentiation, and then we investigated the behavior of differentiated DPSCs, the internal structure of cell constructs, and their pulp regenerative ability in vivo. We observed that DPSCs positive for CD31 and von Willebrand factor were localized at the outer layer of constructs and formed a reticulated lumen structure. The cells constituting the outer layer of the construct expressed endothelial differentiation markers at higher levels than cells in the inner part. These results indicated that DPSCs in the outer layer differentiated into endothelial cells and formed vascular-like structures in the cell construct. Next, a vascularized DPSC construct was transplanted into the human pulpless tooth that was implanted into immunodeficient mice in the subcutaneous space. After 6 wk of implantation, the vascularized construct formed pulp-like tissues with higher density of human CD31-positive blood vessels when compared with specimens implanted with a DPSC construct without prevascularization. These results suggest that the vascular structure formed in the DPSC construct facilitated the blood supply and enhanced pulp regeneration. This study demonstrates that a vascularized DPSC construct is a prospective biomaterial as an implant for novel dental pulp regeneration.

Designing biomaterials for the delivery of RNA therapeutics to stimulate bone healing

Ribonucleic acids (small interfering RNA, microRNA, and messenger RNA) have been emerging as a promising new class of therapeutics for bone regeneration. So far, however, research has mostly focused on stability and complexation of these oligonucleotides for systemic delivery. By comparison, delivery of RNA nanocomplexes from biomaterial carriers can facilitate a spatiotemporally controlled local delivery of osteogenic oligonucleotides. This review provides an overview of the state-of-the-art in the design of biomaterials which allow for temporal and spatial control over RNA delivery. We correlate this concept of spatiotemporally controlled RNA delivery to the most relevant events that govern bone regeneration to evaluate to which extent tuning of release kinetics is required. In addition, inspired by the physiological principles of bone regeneration, potential new RNA targets are presented. Finally, considerations for clinical translation and upscaled production are summarized to stimulate the design of clinically relevant RNA-releasing biomaterials.

Highly Porous and Superabsorbent Biomaterial Made of Marine-Derived Polysaccharides and Ascorbic Acid as an Optimal Dressing for Exuding Wound Management

There are many modern wound dressings that have promising properties for repairing skin damage. However, due to various types of wounds and the problems they cause, there is still a great demand for new, effective healing strategies. The aim of this study was to create superabsorbent wound dressing made of marine-derived polysaccharides (agarose and chitosan) using the freeze-drying method. The secondary goal was its comprehensive evaluation for potential use as an external superabsorbent bandage for wounds with high exudation. Due to the well-known positive effect of ascorbic acid (vitamin C) on the healing process, biomaterial enriched with vitamin C was prepared and compared to the variant without the addition of ascorbic acid. It was shown that the produced foam-like wound dressing had a very porous structure, which was characterized by hydrophilicity, allowing a large amount of human fluids to be absorbed. According to in vitro tests on human fibroblasts, biomaterial was nontoxic and supportive to cell proliferation. Vitamin C-enriched dressing also had the ability to significantly reduce matrix metalloproteinase-2 production and to promote platelet-derived growth factor-BB synthesis by fibroblasts, which is desired during chronic wound treatment. The material has features of the eco-friendly wound care product since it was made of naturally-derived polysaccharides and was proved to be biodegradable. Importantly, despite degradable character, it was stable in the chronic and infected wound microenvironment, maintaining high integrity after 8-week incubation in the enzymatic solutions containing lysozyme and collagenases. The obtained results clearly showed that developed biomaterial possesses all necessary features of the external dressing for the management of exudate from both acute and chronic non-healing wounds.

Role of Hyaluronic Acids and Potential as Regenerative Biomaterials in Wound Healing

The skin can protect the body from external harm, sense environmental changes, and maintain physiological homeostasis. Cutaneous repair and regeneration associated with surgical wounds, acute traumas, and chronic diseases are a central concern of healthcare. Patients may experience the failure of current treatments due to the complexity of the healing process; therefore, emerging strategies are needed. Hyaluronic acids (HAs, also known as hyaluronan), a glycosaminoglycan (GAG) of the extracellular matrix (ECM), play key roles in cell differentiation, proliferation, and migration throughout tissue development and regeneration. Recently, HA derivatives have been developed as regenerative biomaterials for treating skin damage and injury. In this review, the healing process, namely, hemostasis, inflammation, proliferation, and maturation, is described and the role of HAs in the healing process is discussed. This review also provides recent examples in the development of HA derivatives for wound healing.

Topographical and Biomechanical Guidance of Electrospun Fibers for Biomedical Applications

Electrospinning is gaining increasing interest in the biomedical field as an eco-friendly and economic technique for production of random and oriented polymeric fibers. The aim of this review was to give an overview of electrospinning potentialities in the production of fibers for biomedical applications with a focus on the possibility to combine biomechanical and topographical stimuli. In fact, selection of the polymer and the eventual surface modification of the fibers allow selection of the proper chemical/biological signal to be administered to the cells. Moreover, a proper design of fiber orientation, dimension, and topography can give the opportunity to drive cell growth also from a spatial standpoint. At this purpose, the review contains a first introduction on potentialities of electrospinning for the obtainment of random and oriented fibers both with synthetic and natural polymers. The biological phenomena which can be guided and promoted by fibers composition and topography are in depth investigated and discussed in the second section of the paper. Finally, the recent strategies developed in the scientific community for the realization of electrospun fibers and for their surface modification for biomedical application are presented and discussed in the last section.

A dual-phase scaffold produced by rotary jet spinning and electrospinning for tendon tissue engineering

Tendon is a highly hierarchical and oriented tissue that provides high mechanical strength. Tendon injuries lead to loss of function, disability, and a decrease in quality of life. The limited healing capacity of tendon tissue leads to scar tissue formation, which can affect mechanical strength and cause a re-tear. Tissue engineering can be the solution to achieving complete and proper healing of tendon. The developed constructs should be mechanically strong while maintaining a suitable environment for cell proliferation. In this study, a dual-phase fibrous scaffold was produced by combining fibrous mats produced by rotary jet spinning (RJS) and wet electrospinning (WES), with the intent of improving the healing capacity of the construct. Dual-phase scaffolds were formed from aligned poly(ϵ-caprolactone) (PCL) fibers (Shell) produced by RJS and randomly oriented PCL or PCL/gelatin fibers (Core) produced by WES systems. The scaffolds mimicked i) the repair phase of tendon healing, in which randomly-oriented collagen type III is deposited by randomly-oriented WES fibers and ii) the remodeling stage, in which aligned collagen type I fibers are deposited by aligned RJS fibers. In vitro studies showed that the presence of randomly-oriented core fibers inside the aligned PCL fiber shell of the dual-phase scaffold increased the initial attachment and viability of cells. Scanning electron microscopy and confocal microscopy analysis showed that the presence of aligned RJS fibers supported the elongation of cells through aligned fibers which improves tendon tissue healing by guiding oriented cell proliferation and extracellular matrix deposition. Tenogenic differentiation of human adipose-derived mesenchymal stem cells on scaffolds was studied when supplemented with growth differentiation factor 5 (GDF-5). GDF-5 treatment improved the viability, collagen type III deposition and scaffold penetration of human adipose derived stem cells. The developed FSPCL/ESPCL-Gel 3:1 scaffold (FS = centrifugal force spinning/RJS, ES = wet electrospinning, Gel = gelatin) sustained high mechanical strength, and improved cell viability and orientation while supporting tenogenic differentiation.

Bioprintability: Physiomechanical and Biological Requirements of Materials for 3D Bioprinting Processes

Three-dimensional (3D) bioprinting is an additive manufacturing process that utilizes various biomaterials that either contain or interact with living cells and biological systems with the goal of fabricating functional tissue or organ mimics, which will be referred to as bioinks. These bioinks are typically hydrogel-based hybrid systems with many specific features and requirements. The characterizing and fine tuning of bioink properties before, during, and after printing are therefore essential in developing reproducible and stable bioprinted constructs. To date, myriad computational methods, mechanical testing, and rheological evaluations have been used to predict, measure, and optimize bioinks properties and their printability, but none are properly standardized. There is a lack of robust universal guidelines in the field for the evaluation and quantification of bioprintability. In this review, we introduced the concept of bioprintability and discussed the significant roles of various physiomechanical and biological processes in bioprinting fidelity. Furthermore, different quantitative and qualitative methodologies used to assess bioprintability will be reviewed, with a focus on the processes related to pre, during, and post printing. Establishing fully characterized, functional bioink solutions would be a big step towards the effective clinical applications of bioprinted products.

Proteins and Peptides as Important Modifiers of the Polymer Scaffolds for Tissue Engineering Applications-A Review

Polymer scaffolds constitute a very interesting strategy for tissue engineering. Even though they are generally non-toxic, in some cases, they may not provide suitable support for cell adhesion, proliferation, and differentiation, which decelerates tissue regeneration. To improve biological properties, scaffolds are frequently enriched with bioactive molecules, inter alia extracellular matrix proteins, adhesive peptides, growth factors, hormones, and cytokines. Although there are many papers describing synthesis and properties of polymer scaffolds enriched with proteins or peptides, few reviews comprehensively summarize these bioactive molecules. Thus, this review presents the current knowledge about the most important proteins and peptides used for modification of polymer scaffolds for tissue engineering. This paper also describes the influence of addition of proteins and peptides on physicochemical, mechanical, and biological properties of polymer scaffolds. Moreover, this article sums up the major applications of some biodegradable natural and synthetic polymer scaffolds modified with proteins and peptides, which have been developed within the past five years.

A Synergistic Relationship between Polycaprolactone and Natural Polymers Enhances the Physical Properties and Biological Activity of Scaffolds

Biomaterials for tissue engineering include natural and synthetic polymers, but their clinical application is still limited due to various disadvantages associated with the use of these polymers. This uncertainty of the polymeric approach in tissue engineering launches an opportunity to address a key question: can we eliminate the disadvantages of both natural and synthetic polymers by combining them to form a synergistic relationship? To answer this question, we fabricated scaffolds from elastin, collagen, fibrin, and electrospun polycaprolactone (PCL) with different ratios. The material characterization of these scaffolds investigated degradation, water contact angle, angiogenesis by an ex ovo chorion allantoic membrane (CAM) assay, and mechanical and structural properties. Biological activity and specific differentiation pathways (MSC, adipogenic, osteogenic, myogenic, and chondrogenic) were studied by using human adipose-derived stem cells. Results indicated that all composite polymers degraded at a different rate, thus affecting their mechanical integrity. Cell-based assays demonstrated continual proliferative and viable properties of the cells on all seeded scaffolds with the particular initiation of a differentiation pathway among which the PCL/collagen/fibrin composite was the most angiogenic material with maximum vasculature. We were able to tailor the physical and biological properties of PCL-based composites to form a synergistic relationship for various tissue regeneration applications.

Enzymatically crosslinked silk and silk-gelatin hydrogels with tunable gelation kinetics, mechanical properties and bioactivity for cell culture and encapsulation

Silk fibroin (SF) was enzymatically crosslinked with tyramine-substituted silk fibroin (SF-TA) or gelatin (G-TA) to fabricate hybrid hydrogels with tunable gelation kinetics, mechanical properties and bioactivity. Horseradish peroxidase (HRP)/hydrogen peroxide (H2O2) mediated crosslinking of SF in physiological buffers results in slow gelation and limited mechanical properties. Moreover, SF lacks cell attachment sequences, leading to poor cell-material interactions. These shortcomings can limit the uses of enzymatically crosslinked silk hydrogels in injectable tissue fillings, 3D bioprinting or cell microencapsulation, where rapid gelation and high bioactivity are desired. Here SF/SF-TA and SF/G-TA composite hydrogels were characterized for hydrogel properties and the influence of conjugated cyclic arginine-glycine-aspartic acid (RGD) peptide or G-TA content on bioactivity was explored. Both SF-TA and G-TA significantly increased gelation kinetics, improved mechanical properties and delayed enzymatic degradation in a concentration-dependent manner. β-Sheet formation and hydrogel stiffening were accelerated by SF-TA content but delayed by G-TA. Both cyclic RGD and G-TA significantly improved morphology and metabolic activity of human mesenchymal stem cells (hMSCs) cultured on or encapsulated in composite hydrogels. The hydrogel formulations introduced in this study provide improved control of gel formation and properties, along with biocompatible systems that can be utilized in tissue engineering and cell delivery applications.

Dextran-based tube-guides for the regeneration of the rat sciatic nerve after neurotmesis injury

In this work, dextran-based nerve tube-guides were prepared, characterized and used in a standardized animal model of neurotmesis injury. Non-porous and porous transparent tube-guides were obtained by photocrosslinking of two co-macromonomers based on dextran and poly(ε-caprolactone) (PCL). Swelling capacity of the tube-guides ranged from 40-60% with no visible constriction of their inner diameter. In vitro hydrolytic degradation tests showed that the tube-guides maintained their structural integrity up to 6 months. The in vivo performance of the tube-guides was evaluated by entubulation of the rat sciatic nerve after a neurotmesis injury, with a 10 mm-gap between the nerve stumps. The results showed that the tube-guides were able to promote the regeneration of the nerve in a similar manner to what was observed with conventional techniques (nerve graft and end-to-end suture). Stereological analysis proved that nerve regeneration occurred, and both tube-guides presented fibre diameter and g-ratio closer to healthy sciatic nerves. The histomorphometric analysis of Tibialis anterior (TA) skeletal muscle showed decreased neurogenic atrophy in the porous tube-guides treated group, presenting measurements that are similar to the uninjured control.

Influence of the mechanical properties of biomaterials on degradability, cell behaviors and signaling pathways: current progress and challenges

We have clarified the influence of the mechanical properties of biomaterials on degradability and cell response, and also mechanical design targets and approaches.

Injectable Citrate-Based Hydrogel as an Angiogenic Biomaterial Improves Cardiac Repair after Myocardial Infarction

Implanted medical biomaterials are closely in contact with host biological systems via biomaterial-cell/tissue interactions, and these interactions play pivotal roles in regulating cell functions and tissue regeneration. However, many biomaterials degrade over time, and these degradation products also have been shown to interact with host cells/tissue. Therefore, it may prove useful to specifically design implanted biomaterials with degradation products which greatly improve the performance of the implant. Herein, we report an injectable, citrate-containing polyester hydrogel which can release citrate as a cell regulator via hydrogel degradation and simultaneously show sustained release of an encapsulated growth factor Mydgf. By coupling the therapeutic effect of the hydrogel degradation product (citrate) with encapsulated Mydgf, we observed improved postmyocardial infarction (MI) heart repair in a rat MI model. Intramyocardial injection of our Mydgf-loaded citrate-containing hydrogel was shown to significantly reduce scar formation and infarct size, increase wall thickness and neovascularization, and improve heart function. This bioactive injectable hydrogel-mediated combinatorial approach offers myriad advantages including potential adjustment of delivery rate and duration, improved therapeutic effect, and minimally invasive administration. Our rational design combining beneficial degradation product and controlled release of therapeutics provides inspiration toward the next generation of biomaterials aiming to revolutionize regenerative medicine.

Performance of Polyester-Based Electrospun Scaffolds under In Vitro Hydrolytic Conditions: From Short-Term to Long-Term Applications

The evaluation of the performance of polyesters under in vitro physiologic conditions is essential to design scaffolds with an adequate lifespan for a given application. In this line, the degradation-durability patterns of poly(lactide-co-glycolide) (PLGA), polydioxanone (PDO), polycaprolactone (PCL) and polyhydroxybutyrate (PHB) scaffolds were monitored and compared giving, as a result, a basis for the specific design of scaffolds from short-term to long-term applications. For this purpose, they were immersed in ultra-pure water and phosphate buffer solution (PBS) at 37 °C. The scaffolds for short-time applications were PLGA and PDO, in which the molar mass diminished down to 20% in a 20-30 days lifespan. While PDO developed crystallinity that prevented the geometry of the fibres, those of PLGA coalesced and collapsed. The scaffolds for long-term applications were PCL and PHB, in which the molar mass followed a progressive decrease, reaching values of 10% for PCL and almost 50% for PHB after 650 days of immersion. This resistant pattern was mainly ascribed to the stability of the crystalline domains of the fibres, in which the diameters remained almost unaffected. From the perspective of an adequate balance between the durability and degradation, this study may serve technologists as a reference point to design polyester-based scaffolds for biomedical applications.

Pulp Regeneration by 3-dimensional Dental Pulp Stem Cell Constructs

Dental pulp regeneration therapy for the pulpless tooth has attracted recent attention, and clinical trial studies are underway with the tissue engineering approach. However, there remain many concerns, including the extended period for regenerating the dental pulp. In addition, the use of scaffolds increases the risk of inflammation and infection. To establish a basic technology for novel dental pulp regenerative therapy that allows transplant of pulp-like tissue, we attempted to fabricate scaffold-free 3-dimensional (3D) cell constructs composed of dental pulp stem cells (DPSCs). Furthermore, we assessed viability of these 3D DPSC constructs for dental pulp regeneration through in vitro and in vivo studies. For the in vitro study, we obtained 3D DPSC constructs by shaping sheet-like aggregates of DPSCs with a thermoresponsive hydrogel. DPSCs within constructs remained viable even after prolonged culture; furthermore, 3D DPSC constructs possessed a self-organization ability necessary to serve as a transplant tissue. For the in vivo study, we filled the human tooth root canal with DPSC constructs and implanted it subcutaneously into immunodeficient mice. We found that pulp-like tissues with rich blood vessels were formed within the human root canal 6 wk after implantation. Histologic analyses revealed that transplanted DPSCs differentiated into odontoblast-like mineralizing cells at sites in contact with dentin; furthermore, human CD31-positive endothelial cells were found at the center of regenerated tissue. Thus, the self-organizing ability of 3D DPSC constructs was active within the pulpless root canal in vivo. In addition, blood vessel-rich pulp-like tissues can be formed with DPSCs without requiring scaffolds or growth factors. The technology established in this study allows us to prepare DPSC constructs with variable sizes and shapes; therefore, transplantation of DPSC constructs shows promise for regeneration of pulpal tissue in the pulpless tooth.

PCL and PCL-based materials in biomedical applications

Biodegradable polymers have met with an increasing demand in medical usage over the last decades. One of such polymers is poly(ε-caprolactone) (PCL), which is a polyester that has been widely used in tissue engineering field for its availability, relatively inexpensive price and suitability for modification. Its chemical and biological properties, physicochemical state, degradability and mechanical strength can be adjusted, and therefore, it can be used under harsh mechanical, physical and chemical conditions without significant loss of its properties. Degradation time of PCL is quite long, thus it is used mainly in the replacement of hard tissues in the body where healing also takes an extended period of time. It is also used at load-bearing tissues of the body by enhancing its stiffness. However, due to its tailorability, use of PCL is not restricted to one type of tissue and it can be extended to engineering of soft tissues by decreasing its molecular weight and degradation time. This review outlines the basic properties of PCL, its composites, blends and copolymers. We report on various techniques for the production of different forms, and provide examples of medical applications such as tissue engineering and drug delivery systems covering the studies performed in the last decades.

Fast-degrading PLA/ORMOGLASS fibrous composite scaffold leads to a calcium-rich angiogenic environment

The success of scaffold implantation in acellular tissue engineering approaches relies on the ability of the material to interact properly with the biological environment. This behavior mainly depends on the design of the graft surface and, more precisely, on its capacity to biodegrade in a well-defined manner (nature of ions released, surface-to-volume ratio, dissolution profile of this release, rate of material resorption, and preservation of mechanical properties). The assessment of the biological behavior of temporary templates is therefore very important in tissue engineering, especially for composites, which usually exhibit complicated degradation behavior. Here, blended polylactic acid (PLA) calcium phosphate ORMOGLASS (organically modified glass) nanofibrous mats have been incubated up to 4 weeks in physiological simulated conditions, and their morphological, topographical, and chemical changes have been investigated. The results showed that a significant loss of inorganic phase occurred at the beginning of the immersion and the ORMOGLASS maintained a stable composition afterward throughout the degradation period. As a whole, the nanostructured scaffolds underwent fast and heterogeneous degradation. This study reveals that an angiogenic calcium-rich environment can be achieved through fast-degrading ORMOGLASS/PLA blended fibers, which seems to be an excellent alternative for guided bone regeneration.

Injectable Pore-Forming Hydrogel Scaffolds for Complex Wound Tissue Engineering: Designing and Controlling Their Porosity and Mechanical Properties

Traumatic soft tissue wounds present a significant reconstructive challenge. The adoption of closed-circuit negative pressure wound therapy (NPWT) has enabled surgeons to temporize these wounds before reconstruction. Such systems use porous synthetic foam scaffolds as wound fillers at the interface between the negative pressure system and the wound bed. The idea of using a bespoke porous biomaterial that enhances wound healing, as filler for an NPWT system, is attractive as it circumvents concerns regarding reconstructive delay and the need for dressing changes that are features of the current systems. Porous foam biomaterials are mechanically robust and able to synthesize in situ. Hence, they exhibit potential to fulfill the niche for such a functionalized injectable material. Injectable scaffolds are currently in use for minimally invasive surgery, but the design parameters for large-volume expansive foams remain unclear. Potential platforms include hydrogel systems, (particularly superabsorbent, superporous, and nanocomposite systems), polyurethane-based moisture-cured foams, and high internal phase emulsion polymer systems. The aim of this review is to discuss the design parameters for such future biomaterials and review potential candidate materials for further research into this up and coming field.

Local biological effects of adipose stromal vascular fraction delivery systems after subcutaneous implantation in a murine model

The aim of this study was to test alginate beads and silk fibroin non-woven mats as stromal vascular fraction delivery systems to support cell implantation for tissue repair and regeneration, through trophic and immunomodulant paracrine signaling. Furthermore, in vivo scaffold biocompatibility was histologically analyzed in a murine model at different time endpoints, with particular focus on construct-induced vascularization and neoangiogenesis. The fibroin mat induced a typical foreign body reaction, recruiting macrophages and giant cells and concurrently promoted neovascularization of the implanted construct. Conversely, alginate beads triggered a more circumscribed, chronic inflammatory reaction, which decreased over time. The combined in vivo implantation of alginate beads and fibroin mat with stromal vascular fraction promoted vascularization and integration of scaffolds into the surrounding subcutaneous environment. The new blood vessel ingrowth should, hopefully, support engineered cell viability and functionality, as well as the transport of soluble bioactive molecules. Due to their neovascularization properties, stromal vascular fraction administration, using alginate or fibroin scaffolds, is a new, promising, cost-effective tissue engineering approach.

3D-Printed Scaffolds and Biomaterials: Review of Alveolar Bone Augmentation and Periodontal Regeneration Applications

To ensure a successful dental implant therapy, the presence of adequate vertical and horizontal alveolar bone is fundamental. However, an insufficient amount of alveolar ridge in both dimensions is often encountered in dental practice due to the consequences of oral diseases and tooth loss. Although postextraction socket preservation has been adopted to lessen the need for such invasive approaches, it utilizes bone grafting materials, which have limitations that could negatively affect the quality of bone formation. To overcome the drawbacks of routinely employed grafting materials, bone graft substitutes such as 3D scaffolds have been recently investigated in the dental field. In this review, we highlight different biomaterials suitable for 3D scaffold fabrication, with a focus on “3D-printed” ones as bone graft substitutes that might be convenient for various applications related to implant therapy. We also briefly discuss their possible adoption for periodontal regeneration.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

Adult Stem Cell Therapies for Wound Healing: Biomaterials and Computational Models

The increased incidence of diabetes and tumors, associated with global demographic issues (aging and life styles), has pointed out the importance to develop new strategies for the effective management of skin wounds. Individuals affected by these diseases are in fact highly exposed to the risk of delayed healing of the injured tissue that typically leads to a pathological inflammatory state and consequently to chronic wounds. Therapies based on stem cells (SCs) have been proposed for the treatment of these wounds, thanks to the ability of SCs to self-renew and specifically differentiate in response to the target bimolecular environment. Here, we discuss how advanced biomedical devices can be developed by combining SCs with properly engineered biomaterials and computational models. Examples include composite skin substitutes and bioactive dressings with controlled porosity and surface topography for controlling the infiltration and differentiation of the cells. In this scenario, mathematical frameworks for the simulation of cell population growth can provide support for the design of bioconstructs, reducing the need of expensive, time-consuming, and ethically controversial animal experimentation.

Improved properties of composite collagen hydrogels: protected oligourethanes and silica particles as modulators

This paper reports the structure–property relationship of novel biomedical hydrogels derived from collagen, water-soluble oligourethanes, and silica.

Myocardial infarction: stem cell transplantation for cardiac regeneration

It is estimated that by 2030, almost 23.6 million people will perish from cardiovascular disease, according to the WHO. The review discusses advances in stem cell therapy for myocardial infarction, including cell sources, methods of differentiation, expansion selection and their route of delivery. Skeletal muscle cells, hematopoietic cells and mesenchymal stem cells (MSCs) and embryonic stem cells (ESCs)-derived cardiomyocytes have advanced to the clinical stage, while induced pluripotent cells (iPSCs) are yet to be considered clinically. Delivery of cells to the sites of injury and their subsequent retention is a major issue. The development of supportive scaffold matrices to facilitate stem cell retention and differentiation are analyzed. The review outlines clinical translation of conjugate stem cell-based cellular therapeutics post-myocardial infarction.

Biodegradable poly(lactide-co-glycolide-co-ε-caprolactone) block copolymers - evaluation as drug carriers for a localized and sustained delivery system

To develop an appropriate drug carrier for drug delivery systems, we prepared random poly(lactide-co-glycolide-co-ε-caprolactone) (PLGC) copolymers in comparison to commercial poly(lactic acid-co-glycolic acid) (PLGA) grades. The molecular weights of PLGC copolymers varied from 20k to 90k g mol^-1 in the total polyester segments, when poly-l-lactic acid (PLLA), polyglycolic acid (PGA), and polycaprolactone (PCL) compositions were kept constant. The lengths of PLGC copolymers varied from 10 : 10 : 80 to 40 : 40 : 20 in the PLLA : PGA : PCL segments, when the molecular weights of the total polyester segments were kept constant. The crystalline properties of the PLGA copolymers can be changed to amorphous by the incorporation of PCL segments. In vitro and in vivo degradation behavior can be easily tuned from a few days to a few weeks by changing the chemical composition of the PLGC copolymers. The in vivo inflammation associated with the PLGC implants was less pronounced than that associated with PLGA. In this study, as drug delivery carriers for locally implantable paclitaxel (Ptx) dosages, Ptx-loaded PLGC and PLGA films showed in vitro and in vivo Ptx release for 35 days. The orders of Ptx release showed profiles similar to those of in vitro and in vivo degradation of PLGC. Using near-infrared (NIR) fluorescence imaging, we confirmed the sustained release of NIR over an extended period from IR-780-loaded PLGC and PLGA implanted in live animals. In conclusion, we confirmed that compared to PLGA, PLGC effectively acts as a drug carrier for drug delivery systems.

Fabrication of Biomimetic Bone Tissue Using Mesenchymal Stem Cell-Derived Three-Dimensional Constructs Incorporating Endothelial Cells

The development of technologies to promote vascularization of engineered tissue would drive major developments in tissue engineering and regenerative medicine. Recently, we succeeded in fabricating three-dimensional (3D) cell constructs composed of mesenchymal stem cells (MSCs). However, the majority of cells within the constructs underwent necrosis due to a lack of nutrients and oxygen. We hypothesized that incorporation of vascular endothelial cells would improve the cell survival rate and aid in the fabrication of biomimetic bone tissues in vitro. The purpose of this study was to assess the impact of endothelial cells combined with the MSC constructs (MSC/HUVEC constructs) during short- and long-term culture. When human umbilical vein endothelial cells (HUVECs) were incorporated into the cell constructs, cell viability and growth factor production were increased after 7 days. Furthermore, HUVECs were observed to proliferate and self-organize into reticulate porous structures by interacting with the MSCs. After long-term culture, MSC/HUVEC constructs formed abundant mineralized matrices compared with those composed of MSCs alone. Transmission electron microscopy and qualitative analysis revealed that the mineralized matrices comprised porous cancellous bone-like tissues. These results demonstrate that highly biomimetic bone tissue can be fabricated in vitro by 3D MSC constructs incorporated with HUVECs.