Three-dimensional printed PCL-hydroxyapatite scaffolds filled with CNTs for bone cell growth stimulation

3D-Printed PCL/SrHA@DFO Bone Tissue Engineering Scaffold with Bone Regeneration and Vascularization Function

The application of a three-dimensional (3D)-printed biological functional scaffold in the repair of bone defects is a promising strategy. In this study, strontium-containing hydroxyapatite (SrHA) powder was synthesized by the hydrothermal method, and then poly(ε-caprolactone) (PCL)/HA and PCL/SrHA composite scaffolds were prepared by the high-temperature melt extrusion 3D printing technology. The basic physical and chemical properties, in vitro biological properties, osteogenesis, and angiogenesis abilities of the scaffold were studied. The results showed that HA and SrHA were uniformly embedded in the composite scaffold, and the scaffold exhibited a 3D interconnected porous structure and rough microsurface. The in vitro release curve showed that Sr2+ and Ca2+ were continuously released from the PCL/SrHA scaffold. In order to verify the performance of the composite scaffold in bone regeneration, the proliferation and osteogenic differentiation of mouse embryonic osteoblasts (MC3T3E1) grown on the scaffold were evaluated. The experimental results showed that the incorporation of SrHA significantly promoted cell proliferation. Compared with the PCL/HA scaffold, the PCL/SrHA scaffold could better promote cell osteogenic differentiation. Deferoxamine (DFO) was loaded on the surface of the PCL/SrHA scaffold. By studying the proliferation, angiogenesis, and expression of osteogenesis and angiogenesis-related genes of human umbilical vein endothelial cells (HUVECs) on PCL/SrHA@DFO scaffold, it was verified that DFO had the ability to promote angiogenesis. It could induce angiogenesis in vitro in combination with Sr2+. Therefore, we believe that the composite scaffold has potential application prospects in the field of bone tissue engineering.

Bioactive polymers: A comprehensive review on bone grafting biomaterials

The application of bone grafting materials in bone tissue engineering is paramount for treating severe bone defects. In this comprehensive review, we explore the significance and novelty of utilizing bioactive polymers as grafts for successful bone repair. Unlike metals and ceramics, polymers offer inherent biodegradability and biocompatibility, mimicking the native extracellular matrix of bone. While these polymeric micro-nano materials may face challenges such as mechanical strength, various fabrication techniques are available to overcome these shortcomings. Our study not only investigates diverse biopolymeric materials but also illuminates innovative fabrication methods, highlighting their importance in advancing bone tissue engineering.

Nanomaterials-Based Hybrid Bioink Platforms in Advancing 3D Bioprinting Technologies for Regenerative Medicine

3D bioprinting is recognized as the ultimate additive biomanufacturing technology in tissue engineering and regeneration, augmented with intelligent bioinks and bioprinters to construct tissues or organs, thereby eliminating the stipulation for artificial organs. For 3D bioprinting of soft tissues, such as kidneys, hearts, and other human body parts, formulations of bioink with enhanced bioinspired rheological and mechanical properties were essential. Nanomaterials-based hybrid bioinks have the potential to overcome the above-mentioned problem and require much attention among researchers. Natural and synthetic nanomaterials such as carbon nanotubes, graphene oxides, titanium oxides, nanosilicates, nanoclay, nanocellulose, etc. and their blended have been used in various 3D bioprinters as bioinks and benefitted enhanced bioprintability, biocompatibility, and biodegradability. A limited number of articles were published, and the above-mentioned requirement pushed us to write this review. We reviewed, explored, and discussed the nanomaterials and nanocomposite-based hybrid bioinks for the 3D bioprinting technology, 3D bioprinters properties, natural, synthetic, and nanomaterial-based hybrid bioinks, including applications with challenges, limitations, ethical considerations, potential solution for future perspective, and technological advancement of efficient and cost-effective 3D bioprinting methods in tissue regeneration and healthcare.

Biofabrication Strategies for Oral Soft Tissue Regeneration

Gingival recession, a prevalent condition affecting the gum tissues, is characterized by the exposure of tooth root surfaces due to the displacement of the gingival margin. This review explores conventional treatments, highlighting their limitations and the quest for innovative alternatives. Importantly, it emphasizes the critical considerations in gingival tissue engineering leveraging on cells, biomaterials, and signaling factors. Successful tissue-engineered gingival constructs hinge on strategic choices such as cell sources, scaffold design, mechanical properties, and growth factor delivery. Unveiling advancements in recent biofabrication technologies like 3D bioprinting, electrospinning, and microfluidic organ-on-chip systems, this review elucidates their precise control over cell arrangement, biomaterials, and signaling cues. These technologies empower the recapitulation of microphysiological features, enabling the development of gingival constructs that closely emulate the anatomical, physiological, and functional characteristics of native gingival tissues. The review explores diverse engineering strategies aiming at the biofabrication of realistic tissue-engineered gingival grafts. Further, the parallels between the skin and gingival tissues are highlighted, exploring the potential transfer of biofabrication approaches from skin tissue regeneration to gingival tissue engineering. To conclude, the exploration of innovative biofabrication technologies for gingival tissues and inspiration drawn from skin tissue engineering look forward to a transformative era in regenerative dentistry with improved clinical outcomes.

Advances in Material-Assisted Electromagnetic Neural Stimulation

Bioelectricity plays a crucial role in organisms, being closely connected to neural activity and physiological processes. Disruptions in the nervous system can lead to chaotic ionic currents at the injured site, causing disturbances in the local cellular microenvironment, impairing biological pathways, and resulting in a loss of neural functions. Electromagnetic stimulation has the ability to generate internal currents, which can be utilized to counter tissue damage and aid in the restoration of movement in paralyzed limbs. By incorporating implanted materials, electromagnetic stimulation can be targeted more accurately, thereby significantly improving the effectiveness and safety of such interventions. Currently, there have been significant advancements in the development of numerous promising electromagnetic stimulation strategies with diverse materials. This review provides a comprehensive summary of the fundamental theories, neural stimulation modulating materials, material application strategies, and pre-clinical therapeutic effects associated with electromagnetic stimulation for neural repair. It offers a thorough analysis of current techniques that employ materials to enhance electromagnetic stimulation, as well as potential therapeutic strategies for future applications.

Three-Dimensional-Printed Composite Scaffolds Containing Poly-ε-Caprolactone and Strontium-Doped Hydroxyapatite for Osteoporotic Bone Restoration

A challenge in tissue engineering and the pharmaceutical sector is the development of controlled local release of drugs that raise issues when systemic administration is applied. Strontium is an example of an effective anti-osteoporotic agent, used in treating osteoporosis due to both anti-resorptive and anabolic mechanisms of action. Designing bone scaffolds with a higher capability of promoting bone regeneration is a topical research subject. In this study, we developed composite multi-layer three-dimensional (3D) scaffolds for bone tissue engineering based on nano-hydroxyapatite (HA), Sr-containing nano-hydroxyapatite (SrHA), and poly-ε-caprolactone (PCL) through the material extrusion fabrication technique. Previously obtained HA and SrHA with various Sr content were used for the composite material. The chemical, morphological, and biocompatibility properties of the 3D-printed scaffolds obtained using HA/SrHA and PCL were investigated. The 3D composite scaffolds showed good cytocompatibility and osteogenic potential, which is specifically recommended in applications when faster mineralization is needed, such as osteoporosis treatment.

Magnesium-oxide-enhanced bone regeneration: 3D-printing of gelatin-coated composite scaffolds with sustained Rosuvastatin release

Critical-size bone defects are one of the main challenges in bone tissue regeneration that determines the need to use angiogenic and osteogenic agents. Rosuvastatin (RSV) is a class of cholesterol-lowering drugs with osteogenic potential. Magnesium oxide (MgO) is an angiogenesis component affecting apatite formation. This study aims to evaluate 3D-printed Polycaprolactone/β-tricalcium phosphate/nano-hydroxyapatite/ MgO (PCL/β-TCP/nHA/MgO) scaffolds as a carrier for MgO and RSV in bone regeneration. For this purpose, PCL/β-TCP/nHA/MgO scaffolds were fabricated with a 3D-printing method and coated with gelatin and RSV. The biocompatibility and osteogenicity of scaffolds were examined with MTT, ALP, and Alizarin red staining. Finally, the scaffolds were implanted in a bone defect of rat's calvaria, and tissue regeneration was investigated after 3 months. Our results showed that the simultaneous presence of RSV and MgO improved biocompatibility, wettability, degradation rate, and ALP activity but decreased mechanical strength. PCL/β-TCP/nHA/MgO/gelatin-RSV scaffolds produced sustained release of MgO and RSV within 30 days. CT images showed that PCL/β-TCP/nHA/MgO/gelatin-RSV scaffolds filled approximately 86.83 + 4.9 % of the defects within 3 months and improved angiogenesis, woven bone, and osteogenic genes expression. These results indicate the potential of PCL/β-TCP/nHA/MgO/gelatin-RSV scaffolds as a promising tool for bone regeneration and clinical trials.

In Vitro and In Vivo Evaluation of 3D Printed Poly(Ethylene Glycol) Dimethacrylate-Based Photocurable Hydrogel Platform for Bone Tissue Engineering

This study focuses to develop a unique hybrid hydrogel bioink formulation that incorporates poly(ethylene glycol) dimethacrylate (PEGDMA), gelatin (Gel), and methylcellulose (MC). This formulation achieves the necessary viscosity for extrusion-based three-dimensional (3D) printing of scaffolds intended for bone regeneration. After thorough optimization of the hybrid bioink system with Gel, three distinct scaffold groups are investigated in vitro: 0%, 3%, and 6% (w/v) Gel. These scaffold groups are examined for their morphology, mechanical strength, biodegradation, in vitro cell proliferation and differentiation, and in vivo bone formation using a rat cranial defect model. Among these scaffold compositions, the 3% Gel scaffold exhibits the most favorable characteristics, prompting further evaluation as a rat mesenchymal stem cell (rMSC) carrier in a critical-size cranial defect within a Lewis rat model. The compressive strength of all three scaffold groups range between 1 and 2 MPa. Notably, the inclusion of Gel in the scaffolds leads to enhanced bioactivity and cell adhesion. The Gel-containing scaffolds notably amplify osteogenic differentiation, as evidenced by alkaline phosphatase (ALP) and Western blot analyses. The in vivo results, as depicted by microcomputed tomography, showcase augmented osteogenesis within cell-seeded scaffolds, thus validating this innovative PEGDMA-based scaffold system as a promising candidate for cranial bone defect healing.

Towards Polycaprolactone-Based Scaffolds for Alveolar Bone Tissue Engineering: A Biomimetic Approach in a 3D Printing Technique

The alveolar bone is a unique type of bone, and the goal of bone tissue engineering (BTE) is to develop methods to facilitate its regeneration. Currently, an emerging trend involves the fabrication of polycaprolactone (PCL)-based scaffolds using a three-dimensional (3D) printing technique to enhance an osteoconductive architecture. These scaffolds are further modified with hydroxyapatite (HA), type I collagen (CGI), or chitosan (CS) to impart high osteoinductive potential. In conjunction with cell therapy, these scaffolds may serve as an appealing alternative to bone autografts. This review discusses research gaps in the designing of 3D-printed PCL-based scaffolds from a biomimetic perspective. The article begins with a systematic analysis of biological mineralisation (biomineralisation) and ossification to optimise the scaffold's structural, mechanical, degradation, and surface properties. This scaffold-designing strategy lays the groundwork for developing a research pathway that spans fundamental principles such as molecular dynamics (MD) simulations and fabrication techniques. Ultimately, this paves the way for systematic in vitro and in vivo studies, leading to potential clinical applications.

Micro-porous PLGA/β-TCP/TPU scaffolds prepared by solvent-based 3D printing for bone tissue engineering purposes

The 3D printing process of fused deposition modelling is an attractive fabrication approach to create tissue-engineered bone substitutes to regenerate large mandibular bone defects, but often lacks desired surface porosity for enhanced protein adsorption and cell adhesion. Solvent-based printing leads to the spontaneous formation of micropores on the scaffold's surface upon solvent removal, without the need for further post processing. Our aim is to create and characterize porous scaffolds using a new formulation composed of mechanically stable poly(lactic-co-glycol acid) and osteoconductive β-tricalcium phosphate with and without the addition of elastic thermoplastic polyurethane prepared by solvent-based 3D-printing technique. Large-scale regenerative scaffolds can be 3D-printed with adequate fidelity and show porosity at multiple levels analysed via micro-computer tomography, scanning electron microscopy and N2 sorption. Superior mechanical properties compared to a commercially available calcium phosphate ink are demonstrated in compression and screw pull out tests. Biological assessments including cell activity assay and live-dead staining prove the scaffold's cytocompatibility. Osteoconductive properties are demonstrated by performing an osteogenic differentiation assay with primary human bone marrow mesenchymal stromal cells. We propose a versatile fabrication process to create porous 3D-printed scaffolds with adequate mechanical stability and osteoconductivity, both important characteristics for segmental mandibular bone reconstruction.

Biocompatible 3D-Printed Tendon/Ligament Scaffolds Based on Polylactic Acid/Graphite Nanoplatelet Composites

Three-dimensional (3D) printing technology has become a popular tool to produce complex structures. It has great potential in the regenerative medicine field to produce customizable and reproducible scaffolds with high control of dimensions and porosity. This study was focused on the investigation of new biocompatible and biodegradable 3D-printed scaffolds with suitable mechanical properties to assist tendon and ligament regeneration. Polylactic acid (PLA) scaffolds were reinforced with 0.5 wt.% of functionalized graphite nanoplatelets decorated with silver nanoparticles ((f-EG)+Ag). The functionalization of graphene was carried out to strengthen the interface with the polymer. (f-EG)+Ag exhibited antibacterial properties against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), an important feature for the healing process and prevention of bacterial infections. The scaffolds' structure, biodegradation, and mechanical properties were assessed to confirm their suitability for tendon and ligamentregeneration. All scaffolds exhibited surface nanoroughness created during printing, which was increased by the filler presence. The wet state dynamic mechanical analysis proved that the incorporation of reinforcement led to an increase in the storage modulus, compared with neat PLA. The cytotoxicity assays using L929 fibroblasts showed that the scaffolds were biocompatible. The PLA+[(f-EG)+Ag] scaffolds were also loaded with human tendon-derived cells and showed their capability to maintain the tenogenic commitment with an increase in the gene expression of specific tendon/ligament-related markers. The results demonstrate the potential application of these new 3D-printed nanocomposite scaffolds for tendon and ligament regeneration.

Engineering 3D-Printed Advanced Healthcare Materials for Periprosthetic Joint Infections

The use of additive manufacturing or 3D printing in biomedicine has experienced fast growth in the last few years, becoming a promising tool in pharmaceutical development and manufacturing, especially in parenteral formulations and implantable drug delivery systems (IDDSs). Periprosthetic joint infections (PJIs) are a common complication in arthroplasties, with a prevalence of over 4%. There is still no treatment that fully covers the need for preventing and treating biofilm formation. However, 3D printing plays a major role in the development of novel therapies for PJIs. This review will provide a deep understanding of the different approaches based on 3D-printing techniques for the current management and prophylaxis of PJIs. The two main strategies are focused on IDDSs that are loaded or coated with antimicrobials, commonly in combination with bone regeneration agents and 3D-printed orthopedic implants with modified surfaces and antimicrobial properties. The wide variety of printing methods and materials have allowed for the manufacture of IDDSs that are perfectly adjusted to patients' physiognomy, with different drug release profiles, geometries, and inner and outer architectures, and are fully individualized, targeting specific pathogens. Although these novel treatments are demonstrating promising results, in vivo studies and clinical trials are required for their translation from the bench to the market.

Early In Vivo Osteogenic and Inflammatory Response of 3D Printed Polycaprolactone/Carbon Nanotube/Hydroxyapatite/Tricalcium Phosphate Composite Scaffolds

The development of advanced biomaterials and manufacturing processes to fabricate biologically and mechanically appropriate scaffolds for bone tissue is a significant challenge. Polycaprolactone (PCL) is a biocompatible and degradable polymer used in bone tissue engineering, but it lacks biofunctionalization. Bioceramics, such as hydroxyapatite (HA) and β tricalcium phosphate (β-TCP), which are similar chemically to native bone, can facilitate both osteointegration and osteoinduction whilst improving the biomechanics of a scaffold. Carbon nanotubes (CNTs) display exceptional electrical conductivity and mechanical properties. A major limitation is the understanding of how PCL-based scaffolds containing HA, TCP, and CNTs behave in vivo in a bone regeneration model. The objective of this study was to evaluate the use of three-dimensional (3D) printed PCL-based composite scaffolds containing CNTs, HA, and β-TCP during the initial osteogenic and inflammatory response phase in a critical bone defect rat model. Gene expression related to early osteogenesis, the inflammatory phase, and tissue formation was evaluated using quantitative real-time PCR (RT-qPCR). Tissue formation and mineralization were assessed by histomorphometry. The CNT+HA/TCP group presented higher expression of osteogenic genes after seven days. The CNT+HA and CNT+TCP groups stimulated higher gene expression for tissue formation and mineralization, and pro- and anti-inflammatory genes after 14 and 30 days. Moreover, the CNT+TCP and CNT+HA/TCP groups showed higher gene expressions related to M1 macrophages. The association of CNTs with ceramics at 10wt% (CNT+HA/TCP) showed lower expressions of inflammatory genes and higher osteogenic, presenting a positive impact and balanced cell signaling for early bone formation. The association of CNTs with both ceramics promoted a minor inflammatory response and faster bone tissue formation.

Recent advances on 3D-printed PCL-based composite scaffolds for bone tissue engineering

Population ageing and various diseases have increased the demand for bone grafts in recent decades. Bone tissue engineering (BTE) using a three-dimensional (3D) scaffold helps to create a suitable microenvironment for cell proliferation and regeneration of damaged tissues or organs. The 3D printing technique is a beneficial tool in BTE scaffold fabrication with appropriate features such as spatial control of microarchitecture and scaffold composition, high efficiency, and high precision. Various biomaterials could be used in BTE applications. PCL, as a thermoplastic and linear aliphatic polyester, is one of the most widely used polymers in bone scaffold fabrication. High biocompatibility, low cost, easy processing, non-carcinogenicity, low immunogenicity, and a slow degradation rate make this semi-crystalline polymer suitable for use in load-bearing bones. Combining PCL with other biomaterials, drugs, growth factors, and cells has improved its properties and helped heal bone lesions. The integration of PCL composites with the new 3D printing method has made it a promising approach for the effective treatment of bone injuries. The purpose of this review is give a comprehensive overview of the role of printed PCL composite scaffolds in bone repair and the path ahead to enter the clinic. This study will investigate the types of 3D printing methods for making PCL composites and the optimal compounds for making PCL composites to accelerate bone healing.

Recent Developments in 3D Bio-Printing and Its Biomedical Applications

The fast-developing field of 3D bio-printing has been extensively used to improve the usability and performance of scaffolds filled with cells. Over the last few decades, a variety of tissues and organs including skin, blood vessels, and hearts, etc., have all been produced in large quantities via 3D bio-printing. These tissues and organs are not only able to serve as building blocks for the ultimate goal of repair and regeneration, but they can also be utilized as in vitro models for pharmacokinetics, drug screening, and other purposes. To further 3D-printing uses in tissue engineering, research on novel, suitable biomaterials with quick cross-linking capabilities is a prerequisite. A wider variety of acceptable 3D-printed materials are still needed, as well as better printing resolution (particularly at the nanoscale range), speed, and biomaterial compatibility. The aim of this study is to provide expertise in the most prevalent and new biomaterials used in 3D bio-printing as well as an introduction to the associated approaches that are frequently considered by researchers. Furthermore, an effort has been made to convey the most pertinent implementations of 3D bio-printing processes, such as tissue regeneration, etc., by providing the most significant research together with a comprehensive list of material selection guidelines, constraints, and future prospects.

Biomedical applications of three-dimensional bioprinted craniofacial tissue engineering

Anatomical complications of the craniofacial regions often present considerable challenges to the surgical repair or replacement of the damaged tissues. Surgical repair has its own set of limitations, including scarcity of the donor tissues, immune rejection, use of immune suppressors followed by the surgery, and restriction in restoring the natural aesthetic appeal. Rapid advancement in the field of biomaterials, cell biology, and engineering has helped scientists to create cellularized skeletal muscle-like structures. However, the existing method still has limitations in building large, highly vascular tissue with clinical application. With the advance in the three-dimensional (3D) bioprinting technique, scientists and clinicians now can produce the functional implants of skeletal muscles and bones that are more patient-specific with the perfect match to the architecture of their craniofacial defects. Craniofacial tissue regeneration using 3D bioprinting can manage and eliminate the restrictions of the surgical transplant from the donor site. The concept of creating the new functional tissue, exactly mimicking the anatomical and physiological function of the damaged tissue, looks highly attractive. This is crucial to reduce the donor site morbidity and retain the esthetics. 3D bioprinting can integrate all three essential components of tissue engineering, that is, rehabilitation, reconstruction, and regeneration of the lost craniofacial tissues. Such integration essentially helps to develop the patient-specific treatment plans and damage site-driven creation of the functional implants for the craniofacial defects. This article is the bird's eye view on the latest development and application of 3D bioprinting in the regeneration of the skeletal muscle tissues and their application in restoring the functional abilities of the damaged craniofacial tissue. We also discussed current challenges in craniofacial bone vascularization and gave our view on the future direction, including establishing the interactions between tissue-engineered skeletal muscle and the peripheral nervous system.

3D printed-electrospun PCL/hydroxyapatite/MWCNTs scaffolds for the repair of subchondral bone

Osteochondral defect caused by trauma or osteoarthritis exhibits a major challenge in clinical treatment with limited symptomatic effects at present. The regeneration and remodeling of subchondral bone play a positive effect on cartilage regeneration and further promotes the repair of osteochondral defects. Making use of the strengths of each preparation method, the combination of 3D printing and electrospinning is a promising method for designing and constructing multi-scale scaffolds that mimic the complexity and hierarchical structure of subchondral bone at the microscale and nanoscale, respectively. In this study, the 3D printed-electrospun poly(ɛ-caprolactone)/nano-hydroxyapatites/multi-walled carbon nanotubes (PCL/nHA/MWCNTs) scaffolds were successfully constructed by the combination of electrospinning and layer-by-layer 3D printing. The resulting dual-scale scaffold consisted of a dense layer of disordered nanospun fibers and a porous microscale 3D scaffold layer to support and promote the ingrowth of subchondral bone. Herein, the biomimetic PCL/nHA/MWCNTs scaffolds enhanced cell seeding efficiency and allowed for higher cell-cell interactions that supported the adhesion, proliferation, activity, morphology and subsequently improved the osteogenic differentiation of bone marrow mesenchymal stem cells in vitro. Together, this study elucidates that the construction of 3D printed-electrospun PCL/nHA/MWCNTs scaffolds provides an alternative strategy for the regeneration of subchondral bone and lays a foundation for subsequent in vivo studies.

Carbon nanomaterials for drug delivery and tissue engineering

Carbon nanomaterials are some of the state-of-the-art materials used in drug-delivery and tissue-engineering research. Compared with traditional materials, carbon nanomaterials have the advantages of large specific surface areas and unique properties and are more suitable for use in drug delivery and tissue engineering after modification. Their characteristics, such as high drug loading and tissue loading, good biocompatibility, good targeting and long duration of action, indicate their great development potential for biomedical applications. In this paper, the synthesis and application of carbon dots (CDs), carbon nanotubes (CNTs) and graphene in drug delivery and tissue engineering are reviewed in detail. In this review, we discuss the current research focus and existing problems of carbon nanomaterials in order to provide a reference for the safe and effective application of carbon nanomaterials in drug delivery and tissue engineering.

Recent advances in 3D-printed polylactide and polycaprolactone-based biomaterials for tissue engineering applications

The three-dimensional printing (3DP) also known as the additive manufacturing (AM), a novel and futuristic technology that facilitates the printing of multiscale, biomimetic, intricate cytoarchitecture, function-structure hierarchy, multi-cellular tissues in the complicated micro-environment, patient-specific scaffolds, and medical devices. There is an increasing demand for developing 3D-printed products that can be utilized for organ transplantations due to the organ shortage. Nowadays, the 3DP has gained considerable interest in the tissue engineering (TE) field. Polylactide (PLA) and polycaprolactone (PCL) are exemplary biomaterials with excellent physicochemical properties and biocompatibility, which have drawn notable attraction in tissue regeneration. Herein, the recent advancements in the PLA and PCL biodegradable polymer-based composites as well as their reinforcement with hydrogels and bio-ceramics scaffolds manufactured through 3DP are systematically summarized and the applications of bone, cardiac, neural, vascularized and skin tissue regeneration are thoroughly elucidated. The interaction between implanted biodegradable polymers, in-vivo and in-vitro testing models for possible evaluation of degradation and biological properties are also illustrated. The final section of this review incorporates the current challenges and future opportunities in the 3DP of PCL- and PLA-based composites that will prove helpful for biomedical engineers to fulfill the demands of the clinical field.

Enhanced osteogenic differentiation of stem cells by 3D printed PCL scaffolds coated with collagen and hydroxyapatite

Bone tissue engineering uses various methods and materials to find suitable scaffolds that regenerate lost bone due to disease or injury. Poly(ε-caprolactone) (PCL) can be used in 3D printing for producing biodegradable scaffolds by fused deposition modeling (FDM). However, the hydrophobic surfaces of PCL and its non-osteogenic nature reduces adhesion and cell bioactivity at the time of implantation. This work aims to enhance bone formation, osteogenic differentiation, and in vitro biocompatibility via PCL scaffolds modification with Hydroxyapatite (HA) and Collagen type I (COL). This study evaluated the osteosupportive capacity, biological behavior, and physicochemical properties of 3D-printed PCL, PCL/HA, PCL/COL, and PCL/HA/COL scaffolds. Biocompatibility and cells proliferation were investigated by seeding human adipose tissue-derived mesenchymal stem cells (hADSCs) onto the scaffolds, which were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, and 6-diamidino-2-phenylindole (DAPI) staining. In addition, the bone differentiation potential of the hADSCs was assessed using calcium deposition, alkaline phosphatase (ALP) activity, and bone-related protein and genes. Although all constructed scaffolds support hADSCs proliferation and differentiation, the results showed that scaffold coating with HA and COL can boost these capacities in a synergistic manner. According to the findings, the tricomponent 3D-printed scaffold can be considered as a promising choice for bone tissue regeneration and rebuilding.

Direct Ink Writing: A 3D Printing Technology for Diverse Materials

Additive manufacturing (AM) has gained significant attention due to its ability to drive technological development as a sustainable, flexible, and customizable manufacturing scheme. Among the various AM techniques, direct ink writing (DIW) has emerged as the most versatile 3D printing technique for the broadest range of materials. DIW allows printing of practically any material, as long as the precursor ink can be engineered to demonstrate appropriate rheological behavior. This technique acts as a unique pathway to introduce design freedom, multifunctionality, and stability simultaneously into its printed structures. Here, a comprehensive review of DIW of complex 3D structures from various materials, including polymers, ceramics, glass, cement, graphene, metals, and their combinations through multimaterial printing is presented. The review begins with an overview of the fundamentals of ink rheology, followed by an in-depth discussion of the various methods to tailor the ink for DIW of different classes of materials. Then, the diverse applications of DIW ranging from electronics to food to biomedical industries are discussed. Finally, the current challenges and limitations of this technique are highlighted, followed by its prospects as a guideline toward possible futuristic innovations.

Polymers in Technologies of Additive and Inkjet Printing of Dosage Formulations

Technologies for obtaining dosage formulations (DF) for personalized therapy are currently being developed in the field of inkjet (2D) and 3D printing, which allows for the creation of DF using various methods, depending on the properties of pharmaceutical substances and the desired therapeutic effect. By combining these types of printing with smart polymers and special technological approaches, so-called 4D printed dosage formulations are obtained. This article discusses the main technological aspects and used excipients of a polymeric nature for obtaining 2D, 3D, 4D printed dosage formulations. Based on the literature data, the most widely used polymers, their properties, and application features are determined, and the technological characteristics of inkjet and additive 3D printing are shown. Conclusions are drawn about the key areas of development and the difficulties that arise in the search and implementation in the production of new materials and technologies for obtaining those dosage formulations.

Fabrication and Characterization of PCL/HA Filament as a 3D Printing Material Using Thermal Extrusion Technology for Bone Tissue Engineering

The most common three-dimensional (3D) printing method is material extrusion, where a pre-made filament is deposited layer-by-layer. In recent years, low-cost polycaprolactone (PCL) material has increasingly been used in 3D printing, exhibiting a sufficiently high quality for consideration in cranio-maxillofacial reconstructions. To increase osteoconductivity, prefabricated filaments for bone repair based on PCL can be supplemented with hydroxyapatite (HA). However, few reports on PCL/HA composite filaments for material extrusion applications have been documented. In this study, solvent-free fabrication for PCL/HA composite filaments (HA 0%, 5%, 10%, 15%, 20%, and 25% weight/weight PCL) was addressed, and parameters for scaffold fabrication in a desktop 3D printer were confirmed. Filaments and scaffold fabrication temperatures rose with increased HA content. The pore size and porosity of the six groups’ scaffolds were similar to each other, and all had highly interconnected structures. Six groups’ scaffolds were evaluated by measuring the compressive strength, elastic modulus, water contact angle, and morphology. A higher amount of HA increased surface roughness and hydrophilicity compared to PCL scaffolds. The increase in HA content improved the compressive strength and elastic modulus. The obtained data provide the basis for the biological evaluation and future clinical applications of PCL/HA material.

Emerging zero-dimensional to four-dimensional biomaterials for bone regeneration

Bone is one of the most sophisticated and dynamic tissues in the human body, and is characterized by its remarkable potential for regeneration. In most cases, bone has the capacity to be restored to its original form with homeostatic functionality after injury without any remaining scarring. Throughout the fascinating processes of bone regeneration, a plethora of cell lineages and signaling molecules, together with the extracellular matrix, are precisely regulated at multiple length and time scales. However, conditions, such as delayed unions (or nonunion) and critical-sized bone defects, represent thorny challenges for orthopedic surgeons. During recent decades, a variety of novel biomaterials have been designed to mimic the organic and inorganic structure of the bone microenvironment, which have tremendously promoted and accelerated bone healing throughout different stages of bone regeneration. Advances in tissue engineering endowed bone scaffolds with phenomenal osteoconductivity, osteoinductivity, vascularization and neurotization effects as well as alluring properties, such as antibacterial effects. According to the dimensional structure and functional mechanism, these biomaterials are categorized as zero-dimensional, one-dimensional, two-dimensional, three-dimensional, and four-dimensional biomaterials. In this review, we comprehensively summarized the astounding advances in emerging biomaterials for bone regeneration by categorizing them as zero-dimensional to four-dimensional biomaterials, which were further elucidated by typical examples. Hopefully, this review will provide some inspiration for the future design of biomaterials for bone tissue engineering.

Machine Learning-Driven Biomaterials Evolution

Biomaterials is an exciting and dynamic field, which uses a collection of diverse materials to achieve desired biological responses. While there is constant evolution and innovation in materials with time, biomaterials research has been hampered by the relatively long development period required. In recent years, driven by the need to accelerate materials development, the applications of machine learning in materials science has progressed in leaps and bounds. The combination of machine learning with high-throughput theoretical predictions and high-throughput experiments (HTE) has shifted the traditional Edisonian (trial and error) paradigm to a data-driven paradigm. In this review, each type of biomaterial and their key properties and use cases are systematically discussed, followed by how machine learning can be applied in the development and design process. The discussions are classified according to various types of materials used including polymers, metals, ceramics, and nanomaterials, and implants using additive manufacturing. Last, the current gaps and potential of machine learning to further aid biomaterials discovery and application are also discussed.

Polycaprolactone usage in additive manufacturing strategies for tissue engineering applications: A review

Polycaprolactone (PCL) has been extensively applied on tissue engineering because of its low-melting temperature, good processability, biodegradability, biocompatibility, mechanical resistance, and relatively low cost. The advance of additive manufacturing (AM) technologies in the past decade have boosted the fabrication of customized PCL products, with shorter processing time and absence of material waste. In this context, this review focuses on the use of AM techniques to produce PCL scaffolds for various tissue engineering applications, including bone, muscle, cartilage, skin, and cardiovascular tissue regeneration. The search for optimized geometry, porosity, interconnectivity, controlled degradation rate, and tailored mechanical properties are explored as a tool for enhancing PCL biocompatibility and bioactivity. In addition, rheological and thermal behavior is discussed in terms of filament and scaffold production. Finally, a roadmap for future research is outlined, including the combination of PCL struts with cell-laden hydrogels and 4D printing.

Bone Scaffolds: An Incorporation of Biomaterials, Cells, and Biofactors

Large injuries to bones are still one of the most challenging musculoskeletal problems. Tissue engineering can combine stem cells, scaffold biomaterials, and biofactors to aid in resolving this complication. Therefore, this review aims to provide information on the recent advances made to utilize the potential of biomaterials for making bone scaffolds and the assisted stem cell therapy and use of biofactors for bone tissue engineering. The requirements and different types of biomaterials used for making scaffolds are reviewed. Furthermore, the importance of stem cells and biofactors (growth factors and extracellular vesicles) in bone regeneration and their use in bone scaffolds and the key findings are discussed. Lastly, some of the main obstacles in bone tissue engineering and future trends are highlighted.

Mesenchymal stem cell-based nanoparticles and scaffolds in regenerative medicine

Mesenchymal stem cells (MSCs) are adult stem cells owing to their regenerative potential and multilineage potency. MSCs have wide-scale applications either in their native cellular form or in conjugation with specific biomaterials as nanocomposites. Majorly, these natural or synthetic biomaterials are being used in the form of metallic and non-metallic nanoparticles (NPs) to encapsulate MSCs within hydrogels like alginate or chitosan or drug cargo loading into MSCs. In contrast, nanofibers of polymer scaffolds such as polycaprolactone (PCL), poly-lactic-co-glycolic acid (PLGA), poly-L-lactic acid (PLLA), silk fibroin, collagen, chitosan, alginate, hyaluronic acid (HA), and cellulose are used to support or grow MSCs directly on it. These MSCs based nanotherapies have application in multiple domains of biomedicine including wound healing, bone and cartilage engineering, cardiac disorders, and neurological disorders. This study focused on current approaches of MSCs-based therapies and has been divided into two major sections. The first section elaborates on MSC-based nano-therapies and their plausible applications including exosome engineering and NPs encapsulation. The following section focuses on the various MSC-based scaffold approaches in tissue engineering. Conclusively, this review mainly focused on MSC-based nanocomposite's current approaches and compared their advantages and limitations for building effective regenerative medicines.

Carbon nanotube-reinforced cell-derived matrix-silk fibroin hierarchical scaffolds for bone tissue engineering applications

In bone tissue engineering, the development of advanced biomimetic scaffolds has led to the quest for biomotifs in scaffold design that better recreate the bone matrix structure and composition and hierarchy at different length scales. In this study, an advanced hierarchical scaffold consisting of silk fibroin combined with a decellularized cell-derived extracellular matrix and reinforced with carbon nanotubes was developed. The goal of the carbon nanotube-reinforced cell-derived matrix-silk fibroin hierarchical scaffolds is to harvest the individual properties of their constituents to introduce hierarchical capacity in order to improve standard silk fibroin scaffolds. The scaffolds were fabricated using enzymatic cross-linking, freeze modeling, and decellularization methods. The developed scaffolds were assessed for the pore structure and mechanical properties showing satisfying results to be used in bone regeneration. The developed carbon nanotube-reinforced cell-derived matrix-silk fibroin hierarchical scaffolds were shown to be bioactive in vitro and expressed no hemolytic effect. Furthermore, cellular in vitro studies on human adipose-derived stem cells (hASCs) showed that scaffolds supported cell proliferation. The hASCs seeded onto these scaffolds evidenced similar metabolic activity to standard silk fibroin scaffolds but increased ALP activity. The histological staining showed cell infiltration into the scaffolds and visible collagen production. The expression of several osteogenic markers was investigated, further supporting the osteogenic potential of the developed carbon nanotube-reinforced cell-derived matrix-silk fibroin hierarchical scaffolds. The hemolytic assay demonstrated the hemocompatibility of the hierarchical scaffolds. Overall, the carbon nanotube-reinforced cell-derived matrix-silk fibroin hierarchical scaffolds presented the required architecture for bone tissue engineering applications.

Design of 3D Scaffolds for Hard Tissue Engineering: From Apatites to Silicon Mesoporous Materials

Advanced bioceramics for bone regeneration constitutes one of the pivotal interests in the multidisciplinary and far-sighted scientific trajectory of Prof. Vallet Regí. The different pathologies that affect osseous tissue substitution are considered to be one of the most important challenges from the health, social and economic point of view. 3D scaffolds based on bioceramics that mimic the composition, environment, microstructure and pore architecture of hard tissues is a consolidated response to such concerns. This review describes not only the different types of materials utilized: from apatite-type to silicon mesoporous materials, but also the fabrication techniques employed to design and adequate microstructure, a hierarchical porosity (from nano to macro scale), a cell-friendly surface; the inclusion of different type of biomolecules, drugs or cells within these scaffolds and the influence on their successful performance is thoughtfully reviewed.

Poly(Lactic Acid)/Graphite Nanoplatelet Nanocomposite Filaments for Ligament Scaffolds

The anterior cruciate ligament (ACL) is one of the most prone to injury in the human body. Due to its insufficient vascularization and low regenerative capacity, surgery is often required when it is ruptured. Most of the current tissue engineering (TE) strategies are based on scaffolds produced with fibers due to the natural ligament's fibrous structure. In the present work, composite filaments based on poly(L-lactic acid) (PLA) reinforced with graphite nanoplatelets (PLA+EG) as received, chemically functionalized (PLA+f-EG), or functionalized and decorated with silver nanoparticles [PLA+((f-EG)+Ag)] were produced by melt mixing, ensuring good filler dispersion. These filaments were produced with diameters of 0.25 mm and 1.75 mm for textile-engineered and 3D-printed ligament scaffolds, respectively. The resulting composite filaments are thermally stable, and the incorporation of graphite increases the stiffness of the composites and decreases the electrical resistivity, as compared to PLA. None of the filaments suffered significant degradation after 27 days. The composite filaments were processed into 3D scaffolds with finely controlled dimensions and porosity by textile-engineered and additive fabrication techniques, demonstrating their potential for ligament TE applications.

Bioactive Calcium Phosphate-Based Composites for Bone Regeneration

Calcium phosphates (CaPs) are widely accepted biomaterials able to promote the regeneration of bone tissue. However, the regeneration of critical-sized bone defects has been considered challenging, and the development of bioceramics exhibiting enhanced bioactivity, bioresorbability and mechanical performance is highly demanded. In this respect, the tuning of their chemical composition, crystal size and morphology have been the matter of intense research in the last decades, including the preparation of composites. The development of effective bioceramic composite scaffolds relies on effective manufacturing techniques able to control the final multi-scale porosity of the devices, relevant to ensure osteointegration and bio-competent mechanical performance. In this context, the present work provides an overview about the reported strategies to develop and optimize bioceramics, while also highlighting future perspectives in the development of bioactive ceramic composites for bone tissue regeneration.

The Application of Polycaprolactone in Three-Dimensional Printing Scaffolds for Bone Tissue Engineering

Bone tissue engineering commonly encompasses the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the propagation of cells to regenerate damaged tissues or organs. 3D printing technology has been extensively applied to allow direct 3D scaffolds manufacturing. Polycaprolactone (PCL) has been widely used in the fabrication of 3D scaffolds in the field of bone tissue engineering due to its advantages such as good biocompatibility, slow degradation rate, the less acidic breakdown products in comparison to other polyesters, and the potential for loadbearing applications. PCL can be blended with a variety of polymers and hydrogels to improve its properties or to introduce new PCL-based composites. This paper describes the PCL used in developing state of the art of scaffolds for bone tissue engineering. In this review, we provide an overview of the 3D printing techniques for the fabrication of PCL-based composite scaffolds and recent studies on applications in different clinical situations. For instance, PCL-based composite scaffolds were used as an implant surgical guide in dental treatment. Furthermore, future trend and potential clinical translations will be discussed.

Fabrication of Biocompatible Polycaprolactone–Hydroxyapatite Composite Filaments for the FDM 3D Printing of Bone Scaffolds

Recently, three-dimensional printing (3DP) technology has been widely adopted in biology and biomedical applications, thanks to its capacity to readily construct complex 3D features. Using hot-melt extrusion 3DP, scaffolds for bone tissue engineering were fabricated using a composite of biodegradable polycaprolactone (PCL) and hydroxyapatite (HA). However, there are hardly any published reports on the application of the fused deposition modeling (FDM) method using feed filaments, which is the most common 3D printing method. In this study, we report on the fabrication and characterization of biocompatible filaments made of polycaprolactone (PCL)/hydroxyapatite (HA), a raw material mainly used for bone scaffolds, using FDM 3D printing. A series of filaments with varying HA content, from 5 to 25 wt.%, were fabricated. The mechanical and electrical properties of the various structures, printed using a commercially available 3D printer, were examined. Specifically, mechanical tensile tests were performed on the 3D-printed filaments and specimens. In addition, the electrical dielectric properties of the 3D-printed structures were investigated. Our method facilitates the fabrication of biocompatible structures using FDM-type 3DP, creating not only bone scaffolds but also testbeds for mimicking bone structure that may be useful in various fields of study.

Nanomaterials for bioprinting: functionalization of tissue-specific bioinks

Three-dimensional (3D) bioprinting is rapidly evolving, offering great potential for manufacturing functional tissue analogs for use in diverse biomedical applications, including regenerative medicine, drug delivery, and disease modeling. Biomaterials used as bioinks in printing processes must meet strict physiochemical and biomechanical requirements to ensure adequate printing fidelity, while closely mimicking the characteristics of the native tissue. To achieve this goal, nanomaterials are increasingly being investigated as a robust tool to functionalize bioink materials. In this review, we discuss the growing role of different nano-biomaterials in engineering functional bioinks for a variety of tissue engineering applications. The development and commercialization of these nanomaterial solutions for 3D bioprinting would be a significant step towards clinical translation of biofabrication.

Innovations in Craniofacial Bone and Periodontal Tissue Engineering - From Electrospinning to Converged Biofabrication

From a materials perspective, the pillars for the development of clinically translatable scaffold-based strategies for craniomaxillofacial (CMF) bone and periodontal regeneration have included electrospinning and 3D printing (biofabrication) technologies. Here, we offer a detailed analysis of the latest innovations in 3D (bio)printing strategies for CMF bone and periodontal regeneration and provide future directions envisioning the development of advanced 3D architectures for successful clinical translation. First, the principles of electrospinning applied to the generation of biodegradable scaffolds are discussed. Next, we present on extrusion-based 3D printing technologies with a focus on creating scaffolds with improved regenerative capacity. In addition, we offer a critical appraisal on 3D (bio)printing and multitechnology convergence to enable the reconstruction of CMF bones and periodontal tissues. As a future outlook, we highlight future directions associated with the utilization of complementary biomaterials and (bio)fabrication technologies for effective translation of personalized and functional scaffolds into the clinics.

Nitrogen-Doped Multiwalled Carbon Nanotubes Enhance Bone Remodeling through Immunomodulatory Functions

It has been reported that multiwalled carbon nanotubes (MWCNTs) can reportedly positively affect growth and differentiation of bone-related cells and therefore offer great potential in biomedical applications. To overcome negative immune responses that limit their application, specific doping and functionalization can improve their biocompatibility. Here, we demonstrated that nitrogen-doped carboxylate-functionalized MWCNTs (N-MWCNTs) enhance bone remodeling both in vitro and in vivo with excellent biocompatibility, via stimulation of both bone resorption and formation. We revealed that 0.2 μg/mL N-MWCNTs not only increase the transcription of osteoblastogenic and osteoclastogenic genes but also up-regulate the activities of both TRAP and AKP in the differentiation of bone marrow stromal cells (BMSCs). Additionally, intramuscular administration of N-MWCNTs at a dosage of 1.0 mg/kg body weight enhances bone mineral density and bone mass content in mice, as well as induces potentiated degree of TRAP- and ARS-positive staining in the femur. The positive regulation of N-MWCNTs on bone remodeling is initiated by macrophage phagocytosis, which induces altered production of inflammatory cytokines by immune response pathways, and consequently up-regulates IL1α, IL10, and IL16. These cytokines collectively regulate the central osteoclastogenic transcription factor NFATc1 and osteoblastogenic BMP signaling, the suppression of which confirmed that these factors respectively participate in N-MWCNT-mediated regulation of osteoclastic and osteoblastic bone marrow stem cell activities. These results suggest that N-MWCNTs can be readily generalized for use as biomaterials in bone tissue engineering for metabolic bone disorders.

Additively manufactured BaTiO3 composite scaffolds: A novel strategy for load bearing bone tissue engineering applications

Piezoelectric ceramics, such as BaTiO₃, have gained considerable attention in bone tissue engineering applications thanks to their biocompatibility, ability to sustain a charged surface as well as improve bone cells' adhesion and proliferation. However, the poor processability and brittleness of these materials hinder the fabrication of three-dimensional scaffolds for load bearing tissue engineering applications. For the first time, this study focused on the fabrication and characterisation of BaTiO₃ composite scaffolds by using a multi-material 3D printing technology. Polycaprolactone (PCL) was selected and used as dispersion phase for its low melting point, easy processability and wide adoption in bone tissue engineering. The proposed single-step extrusion-based strategy enabled a faster and solvent-free process, where raw materials in powder forms were mechanically mixed and subsequently fed into the 3D printing system for further processing. PCL, PCL/hydroxyapatite and PCL/BaTiO₃ composite scaffolds were successfully produced with high level of consistency and an inner architecture made of seamlessly integrated layers. The inclusion of BaTiO₃ ceramic particles (10% wt.) significantly improved the mechanical performance of the scaffolds (54 ± 0.5 MPa) compared to PCL/hydroxyapatite scaffolds (40.4 ± 0.1 MPa); moreover, the presence of BaTiO₃ increased the dielectric permittivity over the entire frequency spectrum and tested temperatures. Human osteoblasts Saos-2 were seeded on scaffolds and cellular adhesion, proliferation, differentiation and deposition of bone-like extracellular matrix were evaluated. All tested scaffolds (PCL, PCL/hydroxyapatite and PCL/BaTiO₃) supported cell growth and viability, preserving the characteristic cellular osteoblastic phenotype morphology, with PCL/BaTiO₃ composite scaffolds exhibiting higher mineralisation (ALP activity) and deposited bone-like extracellular matrix (osteocalcin and collagen I). The single-step multi-material additive manufacturing technology used for the fabrication of electroactive PCL/BaTiO₃ composite scaffolds holds great promise for sustainability (reduced material waste and manufacturing costs) and it importantly suggests PCL/BaTiO₃ scaffolds as promising candidates for load bearing bone tissue engineering applications to solve unmet clinical needs.

Reinforced 3D Composite Structures of γ-, α-Al2O3 with Carbon Nanotubes and Reduced GO Ribbons Printed from Boehmite Gels

The ability of boehmite to form printable inks has sparked interest in the manufacturing of 3D alumina (Al₂O₃) and composite structures by enabling direct ink writing methods while avoiding the use of printing additives. These materials may exhibit high porosity due to the printing and sintering procedures, depending on the intended application. The 3D-printed porous composite structures of γ-Al₂O₃ and α-Al₂O₃ containing 2 wt.% of carbon nanotubes or reduced graphene oxide ribbons were fabricated from boehmite gels, followed by different heat treatments. The reinforcing effect of these carbon nanostructures was evidenced by compression tests carried out on the different alumina structures. A maximum relative increase of 50% in compressive strength was achieved for the γ-Al₂O₃ composite structure reinforced with reduced graphene oxide ribbons, which was also accompanied by an increase in the specific surface area.

3D printing PCL/nHA bone scaffolds: exploring the influence of material synthesis techniques

Background

It is known that a number of parameters can influence the post-printing properties of bone tissue scaffolds. Previous research has primarily focused on the effect of parameters associated with scaffold design (e.g., scaffold porosity) and specific scaffold printing processes (e.g., printing pressure). To our knowledge, no studies have investigated variations in post-printing properties attributed to the techniques used to synthesize the materials for printing (e.g., melt-blending, powder blending, liquid solvent, and solid solvent).

Methods

Four material preparation techniques were investigated to determine their influence on scaffold properties. Polycaprolactone/nano-hydroxyapatite 30% (wt.) materials were synthesized through melt-blending, powder blending, liquid solvent, and solid solvent techniques. The material printability and the properties of printed scaffolds, in terms of swelling/degradation, mechanical strength, morphology, and thermal properties, were examined and compared to one another using Kruskal-Wallis nonparametric statistical analysis.

Results

Material prepared through the liquid solvent technique was found to have limited printability, while melt-blended material demonstrated the highest degree of uniformity and lowest extent of swelling and degradation. Scaffolds prepared with powder-blended material demonstrated the highest Young’s modulus, yield strength, and modulus of resilience; however, they also demonstrated the highest degree of variability. The higher degree of inhomogeneity in the material was further supported by thermal gravimetric analysis. While scaffolds printed from melt-blended, powder-blended, and solid solvent materials demonstrated a high degree of micro-porosity, the liquid solvent material preparation technique resulted in minimal micro-porosity.

Conclusions

Study results indicate that specific techniques used to prepare materials influence the printing process and post-printing scaffold properties. Among the four techniques examined, melt-blended materials were found to be the most favorable, specifically when considering the combination of printability, consistent mechanical properties, and efficient preparation. Techniques determined to be favourable based on the properties investigated should undergo further studies related to biological properties and time-dependent properties beyond 21-days.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40824-021-00204-y.

Multifunctional Biopolymers‐Based Composite Materials for Biomedical Applications: A Systematic Review

Biopolymers are considered as a favorable group of substances with a broad array of applications, of which biomedical field stands out. The interesting features of biopolymers such as low‐cost, non‐cytotoxicity, hydrophilicity, biodegradation and biocompatibility make them promising and excellent feedstock to be used in implantable devices. The bounteous reactive functional groups in the backbone structure of polysaccharides and its derivatives could be utilized to develop hydrogels, nano‐composite and 3D scaffolds with appealing structures and desired features, leading to promising research attention towards biomedical fields. The present review describes the foremost properties as well as potential of different biopolymers, and their composites for application in implantable biomedical systems. This work may introduce readers about the comprehension of state‐of‐the‐art advances, real present challenges along with the future anticipation of eco‐friendly and biomimetic techniques for the modification of biopolymeric materials to improve their biomedical applications.

Leveraging advances in chemistry to design biodegradable polymeric implants using chitosan and other biomaterials

The metamorphosis of biodegradable polymers in biomedical applications is an auspicious myriad of indagation. The utmost challenge in clinical conditions includes trauma, organs failure, soft and hard tissues, infection, cancer and inflammation, congenital disorders which are still not medicated efficiently. To overcome this bone of contention, proliferation in the concatenation of biodegradable materials for clinical applications has emerged as a silver bullet owing to eco-friendly, nontoxicity, exorbitant mechanical properties, cost efficiency, and degradability. Several bioimplants are designed and fabricated in a way to reabsorb or degrade inside the body after performing the specific function rather than eliminating the bioimplants. The objective of this comprehensive is to unfurl the anecdote of emerging biological polymers derived implants including silk, lignin, soy, collagen, gelatin, chitosan, alginate, starch, etc. by explicating the selection, fabrication, properties, and applications. Into the bargain, emphasis on the significant characteristics of current discernment and purview of nanotechnology integrated biopolymeric implants has also been expounded. This robust contrivance shed light on recent inclinations and evolution in tissue regeneration and targeting organs followed by precedency and fly in the ointment concerning biodegradable implants evolved by employing fringe benefits provided by 3D printing technology for building tissues or organs construct for implantation.

Carbon Nanomaterials for Electro-Active Structures: A Review

The use of electrically conductive materials to impart electrical properties to substrates for cell attachment proliferation and differentiation represents an important strategy in the field of tissue engineering. This paper discusses the concept of electro-active structures and their roles in tissue engineering, accelerating cell proliferation and differentiation, consequently leading to tissue regeneration. The most relevant carbon-based materials used to produce electro-active structures are presented, and their main advantages and limitations are discussed in detail. Particular emphasis is put on the electrically conductive property, material synthesis and their applications on tissue engineering. Different technologies, allowing the fabrication of two-dimensional and three-dimensional structures in a controlled way, are also presented. Finally, challenges for future research are highlighted. This review shows that electrical stimulation plays an important role in modulating the growth of different types of cells. As highlighted, carbon nanomaterials, especially graphene and carbon nanotubes, have great potential for fabricating electro-active structures due to their exceptional electrical and surface properties, opening new routes for more efficient tissue engineering approaches.

Advances in Biodegradable 3D Printed Scaffolds with Carbon-Based Nanomaterials for Bone Regeneration

Bone possesses an inherent capacity to fix itself. However, when a defect larger than a critical size appears, external solutions must be applied. Traditionally, an autograft has been the most used solution in these situations. However, it presents some issues such as donor-site morbidity. In this context, porous biodegradable scaffolds have emerged as an interesting solution. They act as external support for cell growth and degrade when the defect is repaired. For an adequate performance, these scaffolds must meet specific requirements: biocompatibility, interconnected porosity, mechanical properties and biodegradability. To obtain the required porosity, many methods have conventionally been used (e.g., electrospinning, freeze-drying and salt-leaching). However, from the development of additive manufacturing methods a promising solution for this application has been proposed since such methods allow the complete customisation and control of scaffold geometry and porosity. Furthermore, carbon-based nanomaterials present the potential to impart osteoconductivity and antimicrobial properties and reinforce the matrix from a mechanical perspective. These properties make them ideal for use as nanomaterials to improve the properties and performance of scaffolds for bone tissue engineering. This work explores the potential research opportunities and challenges of 3D printed biodegradable composite-based scaffolds containing carbon-based nanomaterials for bone tissue engineering applications.