Fabrication and characterization of mechanically competent 3D printed polycaprolactone-reduced graphene oxide scaffolds

Reduced Graphene-Oxide-Doped Elastic Biodegradable Polyurethane Fibers for Cardiomyocyte Maturation

Conductive biomaterials offer promising solutions to enhance the maturity of cultured cardiomyocytes. While the conventional culture of cardiomyocytes on nonconductive materials leads to more immature characteristics, conductive microenvironments have the potential to support sarcomere development, gap junction formation, and beating of cardiomyocytes in vitro. In this study, we systematically investigated the behaviors of cardiomyocytes on aligned electrospun fibrous membranes composed of elastic and biodegradable polyurethane (PU) doped with varying concentrations of reduced graphene oxide (rGO). Compared to PU and PU-4%rGO membranes, the PU-10%rGO membrane exhibited the highest conductivity, approaching levels close to those of native heart tissue. The PU-rGO membranes retained anisotropic viscoelastic behavior similar to that of the porcine left ventricle and a superior tensile strength. Neonatal rat cardiomyocytes (NRCMs) and human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) on the PU-rGO membranes displayed enhanced maturation with cell alignment and enhanced sarcomere structure and gap junction formation with PU-10%rGO having the most improved sarcomere structure and CX-43 presence. hiPSC-CMs on the PU-rGO membranes exhibited a uniform and synchronous beating pattern compared with that on PU membranes. Overall, PU-10%rGO exhibited the best performance for cardiomyocyte maturation. The conductive PU-rGO membranes provide a promising matrix for in vitro cardiomyocyte culture with promoted cell maturation/functionality and the potential for cardiac disease treatment.

Bone-targeted lipoplex-loaded three-dimensional bioprinting bilayer scaffold enhanced bone regeneration

Clinical bone-morphogenetic protein 2 (BMP2) treatment for bone regeneration, often resulting in complications like soft tissue inflammation and ectopic ossification due to high dosages and non-specific delivery systems, necessitates research into improved biomaterials for better BMP2 stability and retention. To tackle this challenge, we introduced a groundbreaking bone-targeted, lipoplex-loaded, three-dimensional bioprinted bilayer scaffold, termed the polycaprolactone-bioink-nanoparticle (PBN) scaffold, aimed at boosting bone regeneration. We encapsulated BMP2 within the fibroin nanoparticle based lipoplex (Fibroplex) and functionalized it with DSS6 for bone tissue-specific targeting. 3D printing technology enables customized, porous PCL scaffolds for bone healing and soft tissue growth, with a two-step bioprinting process creating a cellular lattice structure and a bioink grid using gelatin-alginate hydrogel and DSS6-Fibroplex, shown to support effective nutrient exchange and cell growth at specific pore sizes. The PBN scaffold is predicted through in silico analysis to exhibit biased BMP2 release between bone and soft tissue, a finding validated by in vitro osteogenic differentiation assays. The PBN scaffold was evaluated for critical calvarial defects, focusing on sustained BMP2 delivery, prevention of soft tissue cell infiltration and controlled fiber membrane pore size in vivo. The PBN scaffold demonstrated a more than eight times longer BMP2 release time than that of the collagen sponge, promoting osteogenic differentiation and bone regeneration in a calvarial defect animal. Our findings suggest that the PBN scaffold enhanced the local concentration of BMP2 in bone defects through sustained release and improved the spatial arrangement of bone formation, thereby reducing the risk of heterotopic ossification.

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.

Clinical translation of polycaprolactone-based tissue engineering scaffolds, fabricated via additive manufacturing: A review of their craniofacial applications

The craniofacial region is characterized by its intricate bony anatomy and exposure to heightened functional forces presenting a unique challenge for reconstruction. Additive manufacturing has revolutionized the creation of customized scaffolds with interconnected pores and biomimetic microarchitecture, offering precise adaptation to various craniofacial defects. Within this domain, medical-grade poly(ε-caprolactone) (PCL) has been extensively used for the fabrication of 3D printed scaffolds, specifically tailored for bone regeneration. Its adoption for load-bearing applications was driven mainly by its mechanical properties, adjustable biodegradation rates, and high biocompatibility. The present review aims to consolidating current insights into the clinical translation of PCL-based constructs designed for bone regeneration. It encompasses recent advances in enhancing the mechanical properties and augmenting biodegradation rates of PCL and PCL-based composite scaffolds. Moreover, it delves into various strategies improving cell proliferation and the osteogenic potential of PCL-based materials. These strategies provide insight into the refinement of scaffold microarchitecture, composition, and surface treatments or coatings, that include certain bioactive molecules such as growth factors, proteins, and ceramic nanoparticles. The review critically examines published data on the clinical applications of PCL scaffolds in both extraoral and intraoral craniofacial reconstructions. These applications include cranioplasty, nasal and orbital floor reconstruction, maxillofacial reconstruction, and intraoral bone regeneration. Patient demographics, surgical procedures, follow-up periods, complications and failures are thoroughly discussed. Although results from extraoral applications in the craniofacial region are encouraging, intraoral applications present a high frequency of complications and related failures. Moving forward, future studies should prioritize refining the clinical performance, particularly in the domain of intraoral applications, and providing comprehensive data on the long-term outcomes of PCL-based scaffolds in bone regeneration. Future perspective and limitations regarding the transition of such constructs from bench to bedside are also discussed.

Development and Characterization of Heparin-Containing Hydrogel/3D-Printed Scaffold Composites for Craniofacial Reconstruction

Regeneration of cartilage and bone tissues remains challenging in tissue engineering due to their complex structures, and the need for both mechanical support and delivery of biological repair stimuli. Therefore, the goal of this study was to develop a composite scaffold platform for anatomic chondral and osteochondral repair using heparin-based hydrogels to deliver small molecules within 3D-printed porous scaffolds that provide structure, stiffness, and controlled biologic delivery. We designed a mold-injection system to combine hydrolytically degradable hydrogels and 3D-printed scaffolds that could be employed rapidly (< 30 min) in operating room settings (~23 °C). Micro-CT analysis demonstrated the effectiveness of our injection system through homogeneously distributed hydrogel within the pores of the scaffolds. Hydrogels and composite scaffolds exhibited efficient loading (~94%) of a small positively charged heparin-binding molecule (crystal violet) with sustained release over 14 days and showed high viability of encapsulated porcine chondrocytes over 7 days. Compression testing demonstrated nonlinear viscoelastic behavior where tangent stiffness decreased with scaffold porosity (porous scaffold tangent stiffness: 70%: 4.9 MPa, 80%: 1.5 MPa, and 90%: 0.20 MPa) but relaxation was not affected. Lower-porosity scaffolds (70%) showed stiffness similar to lower ranges of trabecular bone (4-8 MPa) while higher-porosity scaffolds (80% and 90%) showed stiffness similar to auricular cartilage (0.16-2 MPa). Ultimately, this rapid composite scaffold fabrication method may be employed in the operating room and utilized to control biologic delivery within load-bearing scaffolds.

Development of porcine skeletal muscle extracellular matrix-derived hydrogels with improved properties and low immunogenicity

Hydrogels derived from decellularized extracellular matrices (ECM) of animal origin show immense potential for regenerative applications due to their excellent cytocompatibility and biomimetic properties. Despite these benefits, the impact of decellularization protocols on the properties and immunogenicity of these hydrogels remains relatively unexplored. In this study, porcine skeletal muscle ECM (smECM) underwent decellularization using mechanical disruption (MD) and two commonly employed decellularization detergents, sodium deoxycholate (SDC) or Triton X-100. To mitigate immunogenicity associated with animal-derived ECM, all decellularized tissues were enzymatically treated with α-galactosidase to cleave the primary xenoantigen-the α-Gal antigen. Subsequently, the impact of the different decellularization protocols on the resultant hydrogels was thoroughly investigated. All methods significantly reduced total DNA content in hydrogels. Moreover, α-galactosidase treatment was crucial for cleaving α-Gal antigens, suggesting that conventional decellularization methods alone are insufficient. MD preserved total protein, collagen, sulfated glycosaminoglycan, laminin, fibronectin, and growth factors more efficiently than other protocols. The decellularization method impacted hydrogel gelation kinetics and ultrastructure, as confirmed by turbidimetric and scanning electron microscopy analyses. MD hydrogels demonstrated high cytocompatibility, supporting satellite stem cell recruitment, growth, and differentiation into multinucleated myofibers. In contrast, the SDC and Triton X-100 protocols exhibited cytotoxicity. Comprehensive in vivo immunogenicity assessments in a subcutaneous xenotransplantation model revealed MD hydrogels' biocompatibility and low immunogenicity. These findings highlight the significant influence of the decellularization protocol on hydrogel properties. Our results suggest that combining MD with α-galactosidase treatment is an efficient method for preparing low-immunogenic smECM-derived hydrogels with enhanced properties for skeletal muscle regenerative engineering and clinical applications.

Strontium/Silicon/Calcium-Releasing Hierarchically Structured 3D-Printed Scaffolds Accelerate Osteochondral Defect Repair

Articular cartilage defects are a global challenge, causing substantial disability. Repairing large defects is problematic, often exceeding cartilage's self-healing capacity and damaging bone structures. To tackle this problem, a scaffold-mediated therapeutic ion delivery system is developed. These scaffolds are constructed from poly(ε-caprolactone) and strontium (Sr)-doped bioactive nanoglasses (SrBGn), creating a unique hierarchical structure featuring macropores from 3D printing, micropores, and nanotopologies due to SrBGn integration. The SrBGn-embedded scaffolds (SrBGn-µCh) release Sr, silicon (Si), and calcium (Ca) ions, which improve chondrocyte activation, adhesion, proliferation, and maturation-related gene expression. This multiple ion delivery significantly affects metabolic activity and maturation of chondrocytes. Importantly, Sr ions may play a role in chondrocyte regulation through the Notch signaling pathway. Notably, the scaffold's structure and topological cues expedite the recruitment, adhesion, spreading, and proliferation of chondrocytes and bone marrow-derived mesenchymal stem cells. Si and Ca ions accelerate osteogenic differentiation and blood vessel formation, while Sr ions enhance the polarization of M2 macrophages. The findings show that SrBGn-µCh scaffolds accelerate osteochondral defect repair by delivering multiple ions and providing structural/topological cues, ultimately supporting host cell functions and defect healing. This scaffold holds great promise for osteochondral repair applications.

Advances in guided bone regeneration membranes: a comprehensive review of materials and techniques

Guided tissue/bone regeneration (GTR/GBR) is a widely used technique in dentistry to facilitate the regeneration of damaged bone and tissue, which involves guiding materials that eventually degrade, allowing newly created tissue to take its place. This comprehensive review the evolution of biomaterials for guided bone regeneration that showcases a progressive shift from non-resorbable to highly biocompatible and bioactive materials, allowing for more effective and predictable bone regeneration. The evolution of biomaterials for guided bone regeneration GTR/GBR has marked a significant progression in regenerative dentistry and maxillofacial surgery. Biomaterials used in GBR have evolved over time to enhance biocompatibility, bioactivity, and efficacy in promoting bone growth and integration. This review also probes into several promising fabrication techniques like electrospinning and latest 3D printing fabrication techniques, which have shown potential in enhancing tissue and bone regeneration processes. Further, the challenges and future direction of GTR/GBR are explored and discussed.

Graphene in 3D Bioprinting

Three-dimensional (3D) bioprinting is a fast prototyping fabrication approach that allows the development of new implants for tissue restoration. Although various materials have been utilized for this process, they lack mechanical, electrical, chemical, and biological properties. To overcome those limitations, graphene-based materials demonstrate unique mechanical and electrical properties, morphology, and impermeability, making them excellent candidates for 3D bioprinting. This review summarizes the latest developments in graphene-based materials in 3D printing and their application in tissue engineering and regenerative medicine. Over the years, different 3D printing approaches have utilized graphene-based materials, such as graphene, graphene oxide (GO), reduced GO (rGO), and functional GO (fGO). This process involves controlling multiple factors, such as graphene dispersion, viscosity, and post-curing, which impact the properties of the 3D-printed graphene-based constructs. To this end, those materials combined with 3D printing approaches have demonstrated prominent regeneration potential for bone, neural, cardiac, and skin tissues. Overall, graphene in 3D bioprinting may pave the way for new regenerative strategies with translational implications in orthopedics, neurology, and cardiovascular areas.

Multifunctional scaffolds for biomedical applications: Crafting versatile solutions with polycaprolactone enriched by graphene oxide

The pressing need for multifunctional materials in medical settings encompasses a wide array of scenarios, necessitating specific tissue functionalities. A critical challenge is the occurrence of biofouling, particularly by contamination in surgical environments, a common cause of scaffolds impairment. Beyond the imperative to avoid infections, it is also essential to integrate scaffolds with living cells to allow for tissue regeneration, mediated by cell attachment. Here, we focus on the development of a versatile material for medical applications, driven by the diverse time-definite events after scaffold implantation. We investigate the potential of incorporating graphene oxide (GO) into polycaprolactone (PCL) and create a composite for 3D printing a scaffold with time-controlled antibacterial and anti-adhesive growth properties. Indeed, the as-produced PCL-GO scaffold displays a local hydrophobic effect, which is translated into a limitation of biological entities-attachment, including a diminished adhesion of bacteriophages and a reduction of E. coli and S. aureus adhesion of ∼81% and ∼69%, respectively. Moreover, the ability to 3D print PCL-GO scaffolds with different heights enables control over cell distribution and attachment, a feature that can be also exploited for cellular confinement, i.e., for microfluidics or wound healing applications. With time, the surface wettability increases, and the scaffold can be populated by cells. Finally, the presence of GO allows for the use of infrared light for the sterilization of scaffolds and the disruption of any bacteria cell that might adhere to the more hydrophilic surface. Overall, our results showcase the potential of PCL-GO as a versatile material for medical applications.

The fabrication of the chitosan-based bioink for in vitro tissue repair and regeneration: A review

The repair and regeneration of the injured tissues or organs is a major challenge for biomedicine, and the emerging 3D bioprinting technology as a class of promising techniques in biomedical research for the development of tissue engineering and regenerative medicine. Chitosan-based bioinks, as the natural biomaterials, are considered as ideal materials for 3D bioprinting to design and fabricate the various scaffold due to their unique dynamic reversibility and fantastic biological properties. Our review aims to provide an overview of chitosan-based bioinks for in vitro tissue repair and regeneration, starting from modification of chitosan that affect these bioprinting processes. In addition, we summarize the advances in chitosan-based bioinks used in the various 3D printing strategies. Moreover, the biomedical applications of chitosan-based bioinks are discussed, primarily centered on regenerative medicine and tissue modeling engineering. Finally, current challenges and future opportunities in this field are discussed. The combination of chitosan-based bioinks and 3D bioprinting will hold promise for developing novel biomedical scaffolds for tissue or organ repair and regeneration.

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.

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.

Poly(3-hydroxybutyrate) (PHB) and Polycaprolactone (PCL) Based Blends for Tissue Engineering and Bone Medical Applications Processed by FDM 3D Printing

In the presented work, poly(3-hydroxybutyrate)-PHB-based composite blends for bone medical applications and tissue engineering are prepared and characterized. PHB used for the work was in two cases commercial and, in one case, was extracted by the chloroform-free route. PHB was then blended with poly(lactic acid) (PLA) or polycaprolactone (PCL) and plasticized by oligomeric adipate ester (Syncroflex, SN). Tricalcium phosphate (TCP) particles were used as a bioactive filler. Prepared polymer blends were processed into the form of 3D printing filaments. The samples for all the tests performed were prepared by FDM 3D printing or compression molding. Differential scanning calorimetry was conducted to evaluate the thermal properties, followed by optimization of printing temperature by temperature tower test and determination of warping coefficient. Tensile test, three-point flexural test, and compression test were performed to study the mechanical properties of materials. Optical contact angle measurement was conducted to determine the surface properties of these blends and their influence on cell adhesion. Cytotoxicity measurement of prepared blends was conducted to find out whether the prepared materials were non-cytotoxic. The best temperatures for 3D printing were 195/190, 195/175, and 195/165 °C for PHB-soap/PLA-SN, PHB/PCL-SN, and PHB/PCL-SN-TCP, respectively. Their mechanical properties (strengths ~40 MPa, moduli ~2.5 GPa) were comparable with human trabecular bone. The calculated surface energies of all blends were ~40 mN/m. Unfortunately, only two out of three materials were proven to be non-cytotoxic (both PHB/PCL blends).

Additive manufacturing of sustainable biomaterials for biomedical applications

Biopolymers are promising environmentally benign materials applicable in multifarious applications. They are especially favorable in implantable biomedical devices thanks to their excellent unique properties, including bioactivity, renewability, bioresorbability, biocompatibility, biodegradability and hydrophilicity. Additive manufacturing (AM) is a flexible and intricate manufacturing technology, which is widely used to fabricate biopolymer-based customized products and structures for advanced healthcare systems. Three-dimensional (3D) printing of these sustainable materials is applied in functional clinical settings including wound dressing, drug delivery systems, medical implants and tissue engineering. The present review highlights recent advancements in different types of biopolymers, such as proteins and polysaccharides, which are employed to develop different biomedical products by using extrusion, vat polymerization, laser and inkjet 3D printing techniques in addition to normal bioprinting and four-dimensional (4D) bioprinting techniques. This review also incorporates the influence of nanoparticles on the biological and mechanical performances of 3D-printed tissue scaffolds. This work also addresses current challenges as well as future developments of environmentally friendly polymeric materials manufactured through the AM techniques. Ideally, there is a need for more focused research on the adequate blending of these biodegradable biopolymers for achieving useful results in targeted biomedical areas. We envision that biopolymer-based 3D-printed composites have the potential to revolutionize the biomedical sector in the near future.

Graphene-Related Nanomaterials for Biomedical Applications

This paper builds on the context and recent progress on the control, reproducibility, and limitations of using graphene and graphene-related materials (GRMs) in biomedical applications. The review describes the human hazard assessment of GRMs in in vitro and in vivo studies, highlights the composition-structure-activity relationships that cause toxicity for these substances, and identifies the key parameters that determine the activation of their biological effects. GRMs are designed to offer the advantage of facilitating unique biomedical applications that impact different techniques in medicine, especially in neuroscience. Due to the increasing utilization of GRMs, there is a need to comprehensively assess the potential impact of these materials on human health. Various outcomes associated with GRMs, including biocompatibility, biodegradability, beneficial effects on cell proliferation, differentiation rates, apoptosis, necrosis, autophagy, oxidative stress, physical destruction, DNA damage, and inflammatory responses, have led to an increasing interest in these regenerative nanostructured materials. Considering the existence of graphene-related nanomaterials with different physicochemical properties, the materials are expected to exhibit unique modes of interactions with biomolecules, cells, and tissues depending on their size, chemical composition, and hydrophil-to-hydrophobe ratio. Understanding such interactions is crucial from two perspectives, namely, from the perspectives of their toxicity and biological uses. The main aim of this study is to assess and tune the diverse properties that must be considered when planning biomedical applications. These properties include flexibility, transparency, surface chemistry (hydrophil-hydrophobe ratio), thermoelectrical conductibility, loading and release capacity, and biocompatibility.

3D-printed PLA/Gel hybrid in liver tissue engineering: Effects of architecture on biological functions

The liver is one of the vital organs in the body, and the gold standard of treatment for liver function impairment is liver transplantation, which poses many challenges. The specific three-dimensional (3D) structure of liver, which significantly impacts the growth and function of its cells, has made biofabrication with the 3D printing of scaffolds suitable for this approach. In this study, to investigate the effect of scaffold geometry on the performance of HepG2 cells, poly-lactic acid (PLA) polymer was used as the input of the fused deposition modeling (FDM) 3D-printing machine. Samples with simple square and bioinspired hexagonal cross-sectional designs were printed. One percent and 2% of gelatin coating were applied to the 3D printed PLA to improve the wettability and surface properties of the scaffold. Scanning electron microscopy pictures were used to analyze the structural properties of PLA-Gel hybrid scaffolds, energy dispersive spectroscopy to investigate the presence of gelatin, water contact angle measurement for wettability, and weight loss for degradation. In vitro tests were performed by culturing HepG2 cells on the scaffold to evaluate the cell adhesion, viability, cytotoxicity, and specific liver functions. Then, high-precision scaffolds were printed and the presence of gelatin was detected. Also, the effect of geometry on cell function was confirmed in viability, adhesion, and functional tests. The albumin and urea production of the Hexagonal PLA scaffold was about 1.22 ± 0.02-fold higher than the square design in 3 days. This study will hopefully advance our understanding of liver tissue engineering toward a promising perspective for liver regeneration.

Effect of Pore Characteristics and Alkali Treatment on the Physicochemical and Biological Properties of a 3D-Printed Polycaprolactone Bone Scaffold

Polycaprolactone scaffolds were designed and 3D-printed with different pore shapes (cube and triangle) and sizes (500 and 700 μm) and modified with alkaline hydrolysis of different ratios (1, 3, and 5 M). In total, 16 designs were evaluated for their physical, mechanical, and biological properties. The present study mainly focused on the pore size, porosity, pore shapes, surface modification, biomineralization, mechanical properties, and biological characteristics that might influence bone ingrowth in 3D-printed biodegradable scaffolds. The results showed that the surface roughness in treated scaffolds increased compared to untreated polycaprolactone scaffolds (R _a = 2.3-10.5 nm and R _q = 17- 76 nm), but the structural integrity declined with an increase in the NaOH concentration especially in the scaffolds with small pores and a triangle shape. Overall, the treated polycaprolactone scaffolds particularly with the triangle shape and smaller pore size provided superior performance in mechanical strength similar to that of cancellous bone. Additionally, the in vitro study showed that cell viability increased in the polycaprolactone scaffolds with cubic pore shapes and small pore sizes, whereas mineralization was enhanced in the designs with larger pore sizes. Based on the results obtained, this study demonstrated that the 3D-printed modified polycaprolactone scaffolds exhibit a favorable mechanical property, biomineralization, and better biological properties; therefore, they can be applied in bone tissue engineering.

A Novel Zwitterionic Hydrogel Incorporated with Graphene Oxide for Bone Tissue Engineering: Synthesis, Characterization, and Promotion of Osteogenic Differentiation of Bone Mesenchymal Stem Cells

Zwitterionic materials are widely applied in the biomedical field due to their excellent antimicrobial, non-cytotoxicity, and antifouling properties but have never been applied in bone tissue engineering. In this study, we synthesized a novel zwitterionic hydrogel incorporated with graphene oxide (GO) using maleic anhydride (MA) as a cross-linking agent by grafted L-cysteine (L-Cys) as the zwitterionic material on maleilated chitosan via click chemistry. The composition and each reaction procedure of the novel zwitterionic hydrogel were characterized via X-ray diffraction (XRD) and Fourier transformed infrared spectroscopy (FT-IR), while the morphology was imaged by scanning electron microscope (SEM). In vitro cell studies, CCK-8 and live/dead assay, alkaline phosphatase activity, W-B, and qRT-CR tests showed zwitterionic hydrogel incorporated with GO remarkably enhanced the osteogenic differentiation of bone mesenchymal stem cells (BMSCs); it is dose-dependent, and 2 mg/mL GO is the optimum concentration. In vivo tests also indicated the same results. Hence, these results suggested the novel zwitterionic hydrogel exhibited porous characteristics similar to natural bone tissue. In conclusion, the zwitterionic scaffold has highly biocompatible and mechanical properties. When GO was incorporated in this zwitterionic scaffold, the zwitterionic scaffold slows down the release rate and reduces the cytotoxicity of GO. Zwitterions and GO synergistically promote the proliferation and osteogenic differentiation of rBMSCs in vivo and in vitro. The optimal concentration is 2 mg/mL GO.

Double crosslinked biomimetic composite hydrogels containing topographical cues and WAY-316606 induce neural tissue regeneration and functional recovery after spinal cord injury

Spinal cord injury (SCI) is an overwhelming and incurable disabling condition, for which increasing forms of multifunctional biomaterials are being tested, but with limited progression. The promising material should be able to fill SCI-induced cavities and direct the growth of new neurons, with effective drug loading to improve the local micro-organism environment and promote neural tissue regeneration. In this study, a double crosslinked biomimetic composite hydrogel comprised of acellularized spinal cord matrix (ASCM) and gelatin-acrylated-β-cyclodextrin-polyethene glycol diacrylate (designated G-CD-PEGDA) hydrogel, loaded with WAY-316606 to activate canonical Wnt/β-catenin signaling, and reinforced by a bundle of three-dimensionally printed aligned polycaprolactone (PCL) microfibers, was constructed. The G-CD-PEGDA component endowed the composite hydrogel with a dynamic structure with a self-healing capability which enabled cell migration, while the ASCM component promoted neural cell affinity and proliferation. The diffusion of WAY-316606 could recruit endogenous neural stem cells and improve neuronal differentiation. The aligned PCL microfibers guided neurite elongation in the longitudinal direction. Animal behavior studies further showed that the composite hydrogel could significantly recover the motor function of rats after SCI. This study provides a proficient approach to produce a multifunctional system with desirable physiological, chemical, and topographical cues for treating patients with SCI.

3D Fabrication and Characterisation of Electrically Receptive PCL-Graphene Scaffolds for Bioengineered In Vitro Tissue Models

Polycaprolactone (PCL) is a well-established biomaterial, offering extensive mechanical attributes along with low cost, biocompatibility, and biodegradability; however, it lacks hydrophilicity, bioactivity, and electrical conductivity. Advances in 3D fabrication technologies allow for these sought-after attributes to be incorporated into the scaffolds during fabrication. In this study, solvent-free Fused Deposition Modelling was employed to fabricate 3D scaffolds from PCL with increasing amounts of graphene (G), in the concentrations of 0.75, 1.5, 3, and 6% (w/w). The PCL+G scaffolds created were characterised physico-chemically, electrically, and biologically. Raman spectroscopy demonstrated that the scaffold outer surface contained both PCL and G, with the G component relatively uniformly distributed. Water contact angle measurement demonstrated that as the amount of G in the scaffold increases (0.75-6% w/w), hydrophobicity decreases; mean contact angle for pure PCL was recorded as 107.22 ± 9.39°, and that with 6% G (PCL+6G) as 77.56 ± 6.75°. Electrochemical Impedance Spectroscopy demonstrated a marked increase in electroactivity potential with increasing G concentration. Cell viability results indicated that even the smallest addition of G (0.75%) resulted in a significant improvement in electroactivity potential and bioactivity compared with that for pure PCL, with 1.5 and 3% exhibiting the highest statistically significant increases in cell proliferation.

Valorization of Kraft Lignin from Black Liquor in the Production of Composite Materials with Poly(caprolactone) and Natural Stone Groundwood Fibers

The development of new materials is currently focused on replacing fossil-based plastics with sustainable materials. Obtaining new bioplastics that are biodegradable and of the greenest possible origin could be a great alternative for the future. However, there are some limitations-such as price, physical properties, and mechanical properties-of these bioplastics. In this sense, the present work aims to explore the potential of lignin present in black liquor from paper pulp production as the main component of a new plastic matrix. For this purpose, we have studied the simple recovery of this lignin using acid precipitation, its thermoplastification with glycerin as a plasticizing agent, the production of blends with poly(caprolactone) (PCL), and finally the development of biocomposite materials reinforcing the blend of thermoplastic lignin and PCL with stone groundwood fibers (SGW). The results obtained show that thermoplastic lignin alone cannot be used as a bioplastic. However, its combination with PCL provided a tensile strength of, e.g., 5.24 MPa in the case of a 50 wt.% blend. In addition, when studying the properties of the composite materials, it was found that the tensile strength of a blend with 20 wt.% PCL increased from 1.7 to 11.2 MPa with 40 wt.% SGW. Finally, it was proven that through these biocomposites it is possible to obtain a correct fiber-blend interface.

Influence of rGO on the Crystallization Kinetics, Cytoxicity, and Electrical and Mechanical Properties of Poly (L-lactide-co-ε-caprolactone) Scaffolds

Biodegradable scaffolds of poly (L-lactide-co-ε-caprolactone) (PLCL) and reduced graphene oxide (rGO) were prepared by TIPS (thermally induced phase separation). The nonisothermal cold crystallization kinetics were investigated by differential scanning calorimetry (DSC) with various cooling rates. The experimental values indicate that nonisothermal crystallization improves with cooling rate, but the increasing rGO concentration delays crystallization at higher temperatures. The activation energies were calculated by the Kissinger equation; the values were very similar for PLCL and for its compounds with rGO. The electrical conductivity measurements show that the addition of rGO leads to a rapid transition from insulating to conductive scaffolds with a percolation value of ≈0.4 w/w. Mechanical compression tests show that the addition of rGO improves the mechanical properties of porous substrates. In addition, it is an anisotropic material, especially at compositions of 1% w/w of rGO. All of the samples with different rGO content up to 1% are cytotoxic for C2C12 myoblast cells.

Graphene Family Nanomaterials for Stem Cell Neurogenic Differentiation and Peripheral Nerve Regeneration

Stem cells play a critical role in peripheral nerve regeneration. Nerve scaffolds fabricated by specific materials can help induce the neurogenic differentiation of stem cells. Therefore, it is a potential strategy to enhance therapeutic efficiency. Graphene family nanomaterials are widely applied in repairing peripheral nerves. However, the mechanism underlying the pro-regeneration effects remains elusive. In this review, we first discuss the properties of graphene family nanomaterials, including monolayer and multilayer graphene, few-layer graphene, graphene oxide, reduced graphene oxide, and graphene quantum dots. We also introduce their applications in regulating stem cell differentiation. Then, we review the potential mechanisms of the neurogenic differentiation of stem cells facilitated by the materials. Finally, we discuss the existing challenges in this field to advance the development of nerve biomaterials.

Three-Dimensional Printing of Customized Scaffolds with Polycaprolactone-Silk Fibroin Composites and Integration of Gingival Tissue-Derived Stem Cells for Personalized Bone Therapy

Regenerative biomaterials play a crucial role in the success of maxillofacial reconstructive procedures. Yet today, limited options are available when choosing polymeric biomaterials to treat critical size bony defects. Further, there is a requirement for 3D printable regenerative biomaterials to fabricate customized structures confined to the defect site. We present here a 3D printable composite formulation consisting of polycaprolactone (PCL) and silk fibroin microfibers and have established a robust protocol for fabricating customized 3D structures of complex geometry with the composite. The 3D printed composite scaffolds demonstrated higher compressive modulus than 3D printed scaffolds of PCL alone. Furthermore, the compressive modulus of PCL-Antheraea mylitta (AM) silk scaffolds is higher than that of the PCL-Bombyx mori (BM) silk scaffolds at their respective ratios. Compressive modulus of PCL-25AM silk scaffolds (73.4 MPa) is higher than that of PCL-25BM silk scaffolds (65.1 MPa). Compressive modulus of PCL-40AM silk scaffolds (106.1 MPa) is higher than that of PCL-40BM silk scaffolds (77.7 MPa). Moreover, we have isolated, characterized, and integrated human gingival mesenchymal stem cells (hGMSCs), an effective autologous cell source, onto the 3D printed scaffolds to evaluate their bone regeneration potential. The results demonstrated that PCL-silk microfiber composite scaffolds of Antheraea mylitta origin showed much higher bioactivity than the Bombyx mori ones because of arginine-glycine-aspartic acid (RGD) sequences present in the Antheraea mylitta silk fibroin protein favoring cell attachment and proliferation. By day 14, the metabolic activity of hGMSCs was highest in PCL-40AM (4.5 times higher than that at day 1). In addition, to show the translational potential of this work, we have fabricated a patient defect-specific model (mandible) using the CT scan obtained by the micro-CT imaging to understand the printability of the composite for fabricating complex structures to restore maxillofacial bony defects with precision when applied in a clinical scenario.

3D-Printing Graphene Scaffolds for Bone Tissue Engineering

Graphene-based materials have recently gained attention for regenerating various tissue defects including bone, nerve, cartilage, and muscle. Even though the potential of graphene-based biomaterials has been realized in tissue engineering, there are significantly many more studies reporting in vitro and in vivo data in bone tissue engineering. Graphene constructs have mainly been studied as two-dimensional (2D) substrates when biological organs are within a three-dimensional (3D) environment. Therefore, developing 3D graphene scaffolds is the next clinical standard, yet most have been fabricated as foams which limit control of consistent morphology and porosity. To overcome this issue, 3D-printing technology is revolutionizing tissue engineering, due to its speed, accuracy, reproducibility, and overall ability to personalize treatment whereby scaffolds are printed to the exact dimensions of a tissue defect. Even though various 3D-printing techniques are available, practical applications of 3D-printed graphene scaffolds are still limited. This can be attributed to variations associated with fabrication of graphene derivatives, leading to variations in cell response. This review summarizes selected works describing the different fabrication techniques for 3D scaffolds, the novelty of graphene materials, and the use of 3D-printed scaffolds of graphene-based nanoparticles for bone tissue engineering.

Preparation and Characterization of an Electrospun Whey Protein/Polycaprolactone Nanofiber Membrane for Chromium Removal from Water

Chromium pollution represents a worldwide concern due to its high toxicity and bioaccumulation in organisms and ecosystems. An interesting material to remove metal ions from water is a whey-protein-based material elaborated by electrospinning, which is an emerging method to produce adsorbent membranes with diverse applications. The aim of this study was to prepare an adsorbent membrane of whey protein isolate (WPI) and polycaprolactone (PCL) by electrospinning to remove chromium ions from water. The adsorbent membrane was synthesized by a central composed design denaturing WPI using 2-Mercaptoethanol and mixing it with PCL to produce electrospun nanofibers. The adsorbent membrane was characterized by denaturation, Scanning Electron Microscope, Fourier-Transform Infrared Spectroscopy, Contact Angle, Thermogravimetric Analysis, and X-ray Photoelectron Spectrometry. The adsorption properties of this membrane were assessed in the removal of chromium. The removal performance of the membrane was enhanced by an increase in temperature showing an endothermic adsorption process. The adsorption process of chromium ions onto the nanofiber membrane followed the Sips adsorption isotherm, while the adsorption kinetics followed a pseudo-second kinetics where the maximum adsorption capacity was 31.0 mg/g at 30 °C and pH 2. This work provides a novel method to fabricate a hybrid membrane with amyloid-type fibrils of WPI and PCL, which is a promising adsorbent to remove heavy metal ions from water.

Ultra-low binder content 3D printed calcium phosphate graphene scaffolds as resorbable, osteoinductive matrices that support bone formation in vivo

Bone regenerative engineering could replace autografts; however, no synthetic material fulfills all design criteria. Nanocarbons incorporated into three-dimensional printed (3DP) matrices can improve properties, but incorporation is constrained to low wt%. Further, unmodified nanocarbons have limited osteogenic potential. Functionalization to calcium phosphate graphene (CaPG) imparts osteoinductivity and osteoconductivity, but loading into matrices remained limited. This work presents ultra-high content (90%), 3DP-CaPG matrices. 3DP-CaPG matrices are highly porous (95%), moderately stiff (3 MPa), and mechanically robust. In vitro, they are cytocompatible and induce osteogenic differentiation of human mesenchymal stem cells (hMSCs), indicated by alkaline phosphatase, mineralization, and COL1α1 expression. In vivo, bone regeneration was studied using a transgenic fluorescent-reporter mouse non-union calvarial defect model. 3DP-CaPG stimulates cellular ingrowth, retains donor cells, and induces osteogenic differentiation. Histology shows TRAP staining around struts, suggesting potential osteoclast activity. Apparent resorption of 3DP-CaPG was observed and presented no toxicity. 3DP-CaPG represents an advancement towards a synthetic bone regeneration matrix.

Additive Manufactured Poly(ε-caprolactone)-graphene Scaffolds: Lamellar Crystal Orientation, Mechanical Properties and Biological Performance

Understanding the mechano-biological coupling mechanisms of biomaterials for tissue engineering is of major importance to assure proper scaffold performance in situ. Therefore, it is of paramount importance to establish correlations between biomaterials, their processing conditions, and their mechanical behaviour, as well as their biological performance. With this work, it was possible to infer a correlation between the addition of graphene nanoparticles (GPN) in a concentration of 0.25, 0.5, and 0.75% (w/w) (GPN0.25, GPN0.5, and GPN0.75, respectively) in three-dimensional poly(ε-caprolactone) (PCL)-based scaffolds, the extrusion-based processing parameters, and the lamellar crystal orientation through small-angle X-ray scattering experiments of extruded samples of PCL and PCL/GPN. Results revealed a significant impact on the scaffold's mechanical properties to a maximum of 0.5% of GPN content, with a significant improvement in the compressive modulus of 59 MPa to 93 MPa. In vitro cell culture experiments showed the scaffold's ability to support the adhesion and proliferation of L929 fibroblasts (fold increase of 28, 22, 23, and 13 at day 13 (in relation to day 1) for PCL, GPN0.25, GPN0.5, and GPN0.75, respectively) and bone marrow mesenchymal stem/stromal cells (seven-fold increase for all sample groups at day 21 in relation to day 1). Moreover, the cells maintained high viability, regular morphology, and migration capacity in all the different experimental groups, assuring the potential of PCL/GPN scaffolds for tissue engineering (TE) applications.

Fabrication of Polymer/Graphene Biocomposites for Tissue Engineering

Graphene-based materials (GBM) are considered one of the 21st century’s most promising materials, as they are incredibly light, strong, thin and have remarkable electrical and thermal properties. As a result, over the past decade, their combination with a diverse range of synthetic polymers has been explored in tissue engineering (TE) and regenerative medicine (RM). In addition, a wide range of methods for fabricating polymer/GBM scaffolds have been reported. This review provides an overview of the most recent advances in polymer/GBM composite development and fabrication, focusing on methods such as electrospinning and additive manufacturing (AM). As a future outlook, this work stresses the need for more in vivo studies to validate polymer/GBM composite scaffolds for TE applications, and gives insight on their fabrication by state-of-the-art processing technologies.

Comprehensive Review on Design and Manufacturing of Bio-scaffolds for Bone Reconstruction

Bio-scaffolds are synthetic entities widely employed in bone and soft-tissue regeneration applications. These bio-scaffolds are applied to the defect site to provide support and favor cell attachment and growth, thereby enhancing the regeneration of the defective site. The progressive research in bio-scaffold fabrication has led to identification of biocompatible and mechanically stable materials. The difficulties in obtaining grafts and expenditure incurred in the transplantation procedures have also been overcome by the implantation of bio-scaffolds. Drugs, cells, growth factors, and biomolecules can be embedded with bio-scaffolds to provide localized treatments. The right choice of materials and fabrication approaches can help in developing bio-scaffolds with required properties. This review mostly focuses on the available materials and bio-scaffold techniques for bone and soft-tissue regeneration application. The first part of this review gives insight into the various classes of biomaterials involved in bio-scaffold fabrication followed by design and simulation techniques. The latter discusses the various additive, subtractive, hybrid, and other improved techniques involved in the development of bio-scaffolds for bone regeneration applications. Techniques involving multimaterial printing and multidimensional printing have also been briefly discussed.

3D Bioprinting of Polycaprolactone-Based Scaffolds for Pulp-Dentin Regeneration: Investigation of Physicochemical and Biological Behavior

In this study, two structurally different scaffolds, a polycaprolactone (PCL)/45S5 Bioglass (BG) composite and PCL/hyaluronic acid (HyA) were fabricated by 3D printing technology and were evaluated for the regeneration of dentin and pulp tissues, respectively. Their physicochemical characterization was performed by field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), atomic force microscopy (AFM), contact angle, and compressive strength tests. The results indicated that the presence of BG in the PCL/BG scaffolds promoted the mechanical properties, surface roughness, and bioactivity. Besides, a surface treatment of the PCL scaffold with HyA considerably increased the hydrophilicity of the scaffolds which led to an enhancement in cell adhesion. Furthermore, the gene expression results showed a significant increase in expression of odontogenic markers, e.g., dentin sialophosphoprotein (DSPP), osteocalcin (OCN), and dentin matrix protein 1 (DMP-1) in the presence of both PCL/BG and PCL/HyA scaffolds. Moreover, to examine the feasibility of the idea for pulp-dentin complex regeneration, a bilayer PCL/BG-PCL/HyA scaffold was successfully fabricated and characterized by FESEM. Based on these results, it can be concluded that PCL/BG and PCL/HyA scaffolds have great potential for promoting hDPSC adhesion and odontogenic differentiation.

Etched 3D-Printed Polycaprolactone Constructs Functionalized with Reduced Graphene Oxide for Enhanced Attachment of Dental Pulp-Derived Stem Cells

A core challenge in the field of tissue engineering is the ability to establish pipeline workflows for the design and characterization of scaffold technologies with clinically translatable attributes. The parallel development of biomaterials and stem cell populations represents a self-sufficient and streamlined approach for establishing such a pipeline. In the current study, rat dental pulp stem cell (rDPSC) populations were established to assess functionalized polycaprolactone (PCL) constructs. Initial optimization and characterization of rDPSC extraction and culture conditions confirmed that cell populations were readily expandable and demonstrated surface markers associated with multi-potency. Subset populations were transduced to express DsRed fluorescent protein as a mechanism of tracking both cells and cell-derived extracellular matrix content on complex scaffold architecture. Thermoplastic constructs included reduced graphene oxide (rGO) as an additive to promote cellular attachment and were further modified by surface etching a weak acetic acid solution to roughen surface topographical features, which was observed to dramatically improve cell surface coverage in vitro. Based on these data, the modified rGO-functionalized PCL constructs represent a versatile platform for bone tissue engineering, capable of being applied as a standalone matrix or in conjunction with bio-active payloads such as DPSCs or other bio-inks.

Cryogenic 3D printing of modified polylactic acid scaffolds with biomimetic nanofibrous architecture for bone tissue engineering

The individualized polylactic acid (PLA) scaffolds fabricated by 3D printing technique have a good application prospect in the bone tissue engineering field. However, 3D printed PLA scaffold mainly manufactured by using a Fused Deposition Modelling fabrication technique (FDM) has some disadvantages, such as having smooth surface, strong hydrophobicity, poor cell adhesion, undesirable bioactivity, the degradation and deterioration at a high temperature triggering an inflammatory response. In this work, the aminated modified polylactic acid nanofibrous scaffold prepared by cryogenic 3D printing technology is designed to provide a feasible countermeasure to solve the key problems existing at present. The prepared scaffolds were fully characterized in terms of physico-chemical and morphological analyses, and the collected results revealed that the using of the cryogenic 3D printing technology can effectively avoid the degradation and deterioration of PLA at a high temperature required by FDM technique and promote the formation of nanofibrous structures. The in vitro tests with MC3T3-E1 cells confirmed that the cell-responsive biomimetic fibrous architecture and improved hydrophilicity due to the introduction of hydrophilic active amino groups provided a bioactive interface for cell adhesion and growth. Meanwhile, the active amino groups introduced by ammonolysis reaction can act as active sites for biomineralization. Thus, the as-prepared scaffolds may hold great potential for bone tissue engineering applications.

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.