Mechanical properties and cell cultural response of polycaprolactone scaffolds designed and fabricated via fused deposition modeling

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.

Enhanced Bone Healing in Critical-Sized Rabbit Femoral Defects: Impact of Helical and Alternate Scaffold Architectures

This study investigates the effect of scaffold architecture on bone regeneration, focusing on 3D-printed polylactic acid-bioceramic calcium phosphate (PLA-bioCaP) composite scaffolds in rabbit femoral condyle critical defects. We explored two distinct scaffold designs to assess their influence on bone healing and scaffold performance. Structures with alternate (0°/90°) and helical (0°/45°/90°/135°/180°) laydown patterns were manufactured with a 3D printer using a fused deposition modeling technique. The scaffolds were meticulously characterized for pore size, strut thickness, porosity, pore accessibility, and mechanical properties. The in vivo efficacy of these scaffolds was evaluated using a femoral condyle critical defect model in eight skeletally mature New Zealand White rabbits. Then, the results were analyzed micro-tomographically, histologically, and histomorphometrically. Our findings indicate that both scaffold architectures are biocompatible and support bone formation. The helical scaffolds, characterized by larger pore sizes and higher porosity, demonstrated significantly greater bone regeneration than the alternate structures. However, their lower mechanical strength presented limitations for use in load-bearing sites.

Faster Bone Gap Union in Medial Opening Wedge High Tibial Osteotomy With 3D-Printed Synthetic Bioresorbable Polycaprolactone and Tricalcium Phosphate Osteotomy Gap Fillers Compared to Allogeneic Osteotomy Gap Fillers: A Retrospective Matched-Pair Cohort Study

OBJECTIVE

The use of synthetic bone substitute material (BSM) as osteotomy gap fillers have been reported to improve outcomes in medial opening wedge high tibial osteotomy (MOWHTO). This study aims to evaluate the early radiological outcomes (bone union) and complication rates of the novel patient-specific 3D-printed honeycomb-structured polycaprolactone and tricalcium phosphate (PCL-TCP) synthetic graft compared to allogeneic bone grafts as an osteotomy gap filler in MOWHTO.

METHODS

A retrospective matched-pair analysis of patients who underwent MOWHTO with either PCL-TCP synthetic graft or allogenic femoral head allograft as osteotomy gap filler was performed. The osteotomy gap was split into equal zones (Zone 1-5), and bone union was evaluated on anteroposterior radiographs based on the van Hemert classification at 1, 3, 6, and 12 months postoperatively. Postoperative complications including infection, lateral hinge fractures, and persistent pain was measured. The study and control group were matched for age, smoking status, diabetes mellitus, and osteotomy gap size.

RESULTS

Significantly greater bone union progression was observed in the PCL-TCP group than in the allograft group at 1 month (Zones 1-3), 3 months (Zones 1-4), 6 months (Zones 1-2, 4), and 12 months (Zones 2-3, 5) postoperatively (P < 0.05). No significant difference in complications rates was noted between the two groups at 1 year.

CONCLUSIONS

Bone union rates observed in patients who underwent MOWHTO with the PCL-TCP synthetic graft osteotomy gap filler were superior to those in the allograft group at 1 year postoperatively, with no significant difference in complication rates (postoperative infection, lateral hinge fractures, and persistent pain).

Osteogenic Differentiation Capacity of Dental Pulp Stem Cells on 3D Printed Polyurethane/Boric Acid Scaffold

Additive manufacturing is growing in the area of dentistry and orthopedics due to the potential for the fabrication of individual implants. In this study, fused deposition modeling which is the most popular method was used to produce 3D scaffolds having a grid pattern from the polyurethane (PU) filament. Then, this scaffold was coated with boric acid (BA) with the thermionic vacuum arc technique. The microstructure analysis showed the macro-pores having a dimension of ~ 0.16 mm2. The BA coating increased the roughness in adverse decreased the wettability. The presence of BA on the scaffold before and after cell culture was confirmed by FESEM-EDS and ATR-FTIR. The Cell proliferation and osteogenic differentiation capacity of dental pulp stem cells (DPSCs) on uncoated and coated printed 3D PU scaffolds were also investigated. On the third day, cell viability was found to be higher (1.3-fold) in the groups containing BA. However, on the seventh day, the increase in cell proliferation in the PU+BA group was found to be less than in the other groups. According to Ca deposition analysis and Alizarin Red staining, PU+BA increased the calcium accumulation in the cells in both osteogenic induced and non-induced conditions at day 14. According to gene expression analysis, the Runx2 expression was not detected in PU+BA groups with and without differentiation medium (p ≤0.05). The expression of OCN was persistently increased up to 21-fold and 48-fold in cells on PU and PU+BA in osteogenic differentiation medium group after 14 days compared to control group (p ≤0.05). DSPP expression was observed only in PU+BA in osteogenic differentiation medium group. In line with the results that we have obtained, our 3D printed scaffolds have properties to trigger the differentiation of DPSCs cells in terms of osteogenicity.

3D-bioprinted alginate-based bioink scaffolds with β-tricalcium phosphate for bone regeneration applications

Background/purpose

3D-printed bone tissue engineering is becoming recognized as a key approach in dentistry for creating customized bone regeneration treatments fitting patients bone defects requirements. 3D bioprinting offers an innovative method to fabricate detailed 3D structures, closely emulating the native bone micro-environment and better bone regeneration. This study aimed to develop an 3D-bioprintable scaffold using a combination of alginate and β-tricalcium phosphate (β-TCP) with the Cellink® BioX printer, aiming to advance the field of tissue engineering.

Materials and methods

The physical and biological properties of the resulting 3D-printed scaffolds were evaluated at 10 %, 12 %, and 15 % alginate combined with 10 % β-TCP. The scaffolds were characterized through printability, swelling behavior, degradability, and element analysis. The biological assessment included cell viability, alkaline phosphatase (ALP) activity.

Results

10 % alginate/β-TCP 3D printed at 25 °C scaffold demonstrated the optimal condition for printability, swelling capability, and degradability of cell growth and nutrient diffusion. Addition of β-TCP particles significantly improved the 3D printed material viscosity over only alginate (P < 0.05). 10 % alginate/β-TCP enhanced MG-63 cell's proliferation (P < 0.05) and alkaline phosphatase activity (P < 0.001).

Conclusion

This study demonstrated in vitro that 10 % alginate/β-TCP bioink characteristic for fabricating 3D acellular bioprinted scaffolds was the best approach. 10 % alginate/β-TCP bioink 3D-printed scaffold exhibited superior physical properties and promoted enhanced cell viability and alkaline phosphatase activity, showing great potential for personalized bone regeneration treatments.

Bibliometric Analysis-Based Review of Fused Deposition Modeling 3D Printing Method (1994-2020)

This study aimed at the detailed bibliometric analysis (BA) of fused deposition modeling (FDM) to understand the trend and research area. Web of Science database was used for extracting data using keywords, and 2793 documents were analyzed. From the analysis, the most influential and productive authors, countries, sources, and so on were identified and corresponding interrelations were represented by a three-field plot. Lotka's law was derived for author productivity and its reliability was verified by the Kolmogorov-Smirnov (K-S) test. Bradford's law was used for identifying the core sources contributing to the field of FDM. From the trend topic analysis, it was found that initially the research was focused upon removing error related to deposition as well as part orientation, but with the course of time, it diversified to include topics such as optimization of printing parameters, materials, and applications. Based on the inferences from BA, the article also discusses on current research trend and highlights certain future areas for research work.

Optimization and evaluation of oxygen-plasma-modified, aligned, poly (Є-caprolactone) and silk fibroin nanofibrous scaffold for corneal stromal regeneration

The shortage of human donor corneas for transplantation necessitates the exploration of tissue engineering approaches to develop corneal substitutes. However, these substitutes must possess the necessary strength, transparency, and ability to regulate cell behaviour before they can be used in patients. In this study, we investigated the effectiveness of an oxygen plasma surface-modified poly-ε-caprolactone (PCL) combined with silk fibroin (SF) nanofibrous scaffold for corneal stromal regeneration. To fabricate the electrospun scaffolds, PCL and SF blends were used on a rotating mandrel. The optimization of the blend aimed to replicate the structural and functional properties of the human cornea, focusing on nanofibre alignment, mechanical characteristics, and in vitro cytocompatibility with human corneal stromal keratocytes. Surface modification of the scaffold resulted in improved transparency and enhanced cell interaction. Based on the evaluation, a composite nanofibrous scaffold with a 1:1 blend of PCL and SF was selected for a more comprehensive analysis. The biological response of keratocytes to the scaffold was assessed through cellular adhesion, proliferation, cytoskeletal organization, gene expression, and immunocytochemical staining. The scaffold facilitated the adhesion of corneal stromal cells, supporting cell proliferation, maintaining normal cytoskeletal organization, and promoting increased expression of genes associated with healthy corneal stromal keratocytes. These findings highlight the potential of a surface-modified PCL/SF blend (1:1) as a promising scaffolding material for corneal stromal regeneration. The developed scaffold not only demonstrated favourable biological interactions with corneal stromal cells but also exhibited characteristics aligned with the requirements for successful corneal tissue engineering. Further research and refinement of these constructs could lead to significant advancements in addressing the shortage of corneas for transplantation, ultimately improving the treatment outcomes for patients in need.

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.

3D printing for bone regeneration: challenges and opportunities for achieving predictability

3D printing offers attractive opportunities for large-volume bone regeneration in the oro-dental and craniofacial regions. This is enabled by the development of CAD-CAM technologies that support the design and manufacturing of anatomically accurate meshes and scaffolds. This review describes the main 3D-printing technologies utilized for the fabrication of these patient-matched devices, and reports on their pre-clinical and clinical performance including the occurrence of complications for vertical bone augmentation and craniofacial applications. Furthermore, the regulatory pathway for approval of these devices is discussed, highlighting the main hurdles and obstacles. Finally, the review elaborates on a variety of strategies for increasing bone regeneration capacity and explores the future of 4D bioprinting and biodegradable metal 3D printing.

Three-Dimensional Printed Hydroxyapatite Bone Substitutes Designed by a Novel Periodic Minimal Surface Algorithm Are Highly Osteoconductive

Autologous bone remains the gold standard bone substitute in clinical practice. Therefore, the microarchitecture of newly developed synthetic bone substitutes, which reflects the spatial distribution of materials in the scaffold, aims to recapitulate the natural bone microarchitecture. However, the natural bone microarchitecture is optimized to obtain a mechanically stable, lightweight structure adapted to the biomechanical loading situation. In the context of synthetic bone substitutes, the application of a Triply Periodic Minimum Surface (TPMS) algorithm can yield stable lightweight microarchitectures that, despite their demanding architectural complexity, can be produced by additive manufacturing. In this study, we applied the TPMS derivative Adaptive Density Minimal Surfaces (ADMS) algorithm to produce scaffolds from hydroxyapatite (HA) using a lithography-based layer-by-layer methodology and compared them with an established highly osteoconductive lattice microarchitecture. We characterized them for compression strength, osteoconductivity, and bone regeneration. The in vivo results, based on a rabbit calvaria defect model, showed that bony ingrowth into ADMS constructs as a measure of osteoconduction depended on minimal constriction as it limited the maximum apparent pore diameter in these scaffolds to 1.53 mm. Osteoconduction decreased significantly at a diameter of 1.76 mm. The most suitable ADMS microarchitecture was as osteoconductive as a highly osteoconductive orthogonal lattice microarchitecture in noncritical- and critical-size calvarial defects. However, the compression strength and microarchitectural integrity in vivo were significantly higher for scaffolds with their microarchitecture based on the ADMS algorithm when compared with high-connectivity lattice microarchitectures. Therefore, bone substitutes with high osteoconductivity can be designed with the advantages of the ADMS-based microarchitectures. As TPMS and ADMS microarchitectures are true lightweight structures optimized for high mechanical stability with a minimal amount of material, such microarchitectures appear most suitable for bone substitutes used in clinical settings to treat bone defects in weight-bearing and non-weight-bearing sites.

Polyhydroxyalkanoates: the natural biopolyester for future medical innovations

Polyhydroxyalkanoates (PHAs) are a family of natural microbial biopolyesters with the same basic chemical structure and diverse side chain groups. Based on their excellent biodegradability, biocompatibility, thermoplastic properties and diversity, PHAs are highly promising medical biomaterials and elements of medical devices for applications in tissue engineering and drug delivery. However, due to the high cost of biotechnological production, most PHAs have yet to be applied in the clinic and have only been studied at laboratory scale. This review focuses on the biosynthesis, diversity, physical properties, biodegradability and biosafety of PHAs. We also discuss optimization strategies for improved microbial production of commercial PHAs via novel synthetic biology tools. Moreover, we also systematically summarize various medical devices based on PHAs and related design approaches for medical applications, including tissue repair and drug delivery. The main degradation product of PHAs, 3-hydroxybutyrate (3HB), is recognized as a new functional molecule for cancer therapy and immune regulation. Although PHAs still account for only a small percentage of medical polymers, up-and-coming novel medical PHA devices will enter the clinical translation stage in the next few years.

Additive Manufacturing of Wet-Spun Polysulfone Medical Implants

Research on additive manufacturing (AM) of high-performance polymers provides novel materials and technologies for advanced applications in different sectors, such as aerospace and biomedical engineering. The present article is contextualized in this research trend by describing a novel AM protocol for processing a polysulfone (PSU)/N-methyl-2-pyrrolidone (NMP) solution into medical implant prototypes. In particular, an AM technique involving the patterned deposition of the PSU/NMP mixture in a coagulation bath was employed to fabricate PSU implants with different predefined shape, fiber diameter, and macropore size. Scanning electron microscopy (SEM) analysis highlighted a fiber transversal cross-section morphology characterized by a dense external skin layer and an inner macroporous/microporous structure, as a consequence of the nonsolvent-induced polymer solidification process. Physical-chemical and thermal characterization of the fabricated samples demonstrated that PSU processing did not affect its macromolecular structure and glass-transition temperature, as well as that after post-processing PSU implants did not contain residual solvent or nonsolvent. Mechanical characterization showed that the developed PSU scaffold tensile and compressive modulus could be changed by varying the macroporous architecture. In addition, PSU scaffolds supported the in vitro adhesion and proliferation of the BALB/3T3 clone A31 mouse embryo cell line. These findings encourage further research on the suitability of the developed processing method for the fabrication of customized PSU implants.

Stimuli-responsive biomaterials: smart avenue toward 4D bioprinting

3D bioprinting is an advanced technology combining cells and bioactive molecules within a single bioscaffold; however, this scaffold cannot change, modify or grow in response to a dynamic implemented environment. Lately, a new era of smart polymers and hydrogels has emerged, which can add another dimension, e.g., time to 3D bioprinting, to address some of the current approaches' limitations. This concept is indicated as 4D bioprinting. This approach may assist in fabricating tissue-like structures with a configuration and function that mimic the natural tissue. These scaffolds can change and reform as the tissue are transformed with the potential of specific drug or biomolecules released for various biomedical applications, such as biosensing, wound healing, soft robotics, drug delivery, and tissue engineering, though 4D bioprinting is still in its early stages and more works are required to advance it. In this review article, the critical challenge in the field of 4D bioprinting and transformations from 3D bioprinting to 4D phases is reviewed. Also, the mechanistic aspects from the chemistry and material science point of view are discussed too.

Highly piezoelectric, biodegradable, and flexible amino acid nanofibers for medical applications

Amino acid crystals are an attractive piezoelectric material as they have an ultrahigh piezoelectric coefficient and have an appealing safety profile for medical implant applications. Unfortunately, solvent-cast films made from glycine crystals are brittle, quickly dissolve in body fluid, and lack crystal orientation control, reducing the overall piezoelectric effect. Here, we present a material processing strategy to create biodegradable, flexible, and piezoelectric nanofibers of glycine crystals embedded inside polycaprolactone (PCL). The glycine-PCL nanofiber film exhibits stable piezoelectric performance with a high ultrasound output of 334 kPa [under 0.15 voltage root-mean-square (Vrms)], which outperforms the state-of-the-art biodegradable transducers. We use this material to fabricate a biodegradable ultrasound transducer for facilitating the delivery of chemotherapeutic drug to the brain. The device remarkably enhances the animal survival time (twofold) in mice-bearing orthotopic glioblastoma models. The piezoelectric glycine-PCL presented here could offer an excellent platform not only for glioblastoma therapy but also for developing medical implantation fields.

3D printed macroporous scaffolds of PCL and inulin-g-P(D,L)LA for bone tissue engineering applications

Bone repair and tissue-engineering (BTE) approaches require novel biomaterials to produce scaffolds with required structural and biological characteristics and enhanced performances with respect to those currently available. In this study, PCL/INU-PLA hybrid biomaterial was prepared by blending of the aliphatic polyester poly(ε-caprolactone) (PCL) with the amphiphilic graft copolymer Inulin-g-poly(D,L)lactide (INU-PLA) synthetized from biodegradable inulin (INU) and poly(lactic acid) (PLA). The hybrid material was suitable to be processed using fused filament fabrication 3D printing (FFF-3DP) technique rendering macroporous scaffolds. PCL and INU-PLA were firstly blended as thin films through solvent-casting method, and then extruded by hot melt extrusion (HME) in form of filaments processable by FFF-3DP. The physicochemical characterization of the hybrid new material showed high homogeneity, improved surface wettability/hydrophilicity as compared to PCL alone, and right thermal properties for FFF process. The 3D printed scaffolds exhibited dimensional and structural parameters very close to those of the digital model, and mechanical performances compatible with the human trabecular bone. In addition, in comparison to PCL, hybrid scaffolds showed an enhancement of surface properties, swelling ability, and in vitro biodegradation rate. In vitro biocompatibility screening through hemolysis assay, LDH cytotoxicity test on human fibroblasts, CCK-8 cell viability, and osteogenic activity (ALP evaluation) assays on human mesenchymal stem cells showed favorable results.

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).

Sinus augmentation with poly(ε)caprolactone-β tricalcium phosphate scaffolds, mesenchymal stem cells and platelet rich plasma for one-stage dental implantation in minipigs

PURPOSE

This study evaluated the efficacy of a tube-shaped poly(ε) caprolactone - β tricalcium phosphate (PCL-TCP) scaffold with the incorporation of human umbilical cord-derived mesenchymal stem cells (hUCMSCs) and platelet-rich plasma (PRP) for bone regeneration in the procedure of single-stage sinus augmentation and dental implantation in minipigs.

METHODS

Implants were placed in the bilateral sides of the maxillary sinuses of 5 minipigs and allocated to a PCL-TCP+hUCMSCs+PRP group (n=5), a PCL-TCP+PRP group (n=5), and a PCL-TCP-only group (n=6). After 12 weeks, bone regeneration was evaluated with soft X-rays, micro-computed tomography, fluorescence microscopy, and histomorphometric analysis.

RESULTS

Four implants failed (2 each in the PCL-TCP+hUCMSCs+PRP and PCL-TCP+hUCMSC groups). An analysis of the grayscale levels and bone-implant contact ratio showed significantly higher mean values in the PCL-TCP+hUCMSCs+PRP than in the PCL-TCP group (P=0.045 and P=0.016, respectively). In fluoromicroscopic images, new bone formation around the outer surfaces of the scaffolds was observed in the PCL-TCP+hUCMSCs+PRP group, suggesting a tenting effect of the specially designed scaffolds. Bone regeneration at the scaffold-implant interfaces was observed in all 3 groups.

CONCLUSIONS

Using a tube-shaped, honeycombed PCL-TCP scaffold with hUCMSCs and PRP may serve to enhance bone formation and dental implants' osseointegration in the procedure of simultaneous sinus lifting and dental implantation.

Microporous/Macroporous Polycaprolactone Scaffolds for Dental Applications

This study leverages the advantages of two fabrication techniques, namely, melt-extrusion-based 3D printing and porogen leaching, to develop multiphasic scaffolds with controllable properties essential for scaffold-guided dental tissue regeneration. Polycaprolactone-salt composites are 3D-printed and salt microparticles within the scaffold struts are leached out, revealing a network of microporosity. Extensive characterization confirms that multiscale scaffolds are highly tuneable in terms of their mechanical properties, degradation kinetics, and surface morphology. It can be seen that the surface roughness of the polycaprolactone scaffolds (9.41 ± 3.01 µm) increases with porogen leaching and the use of larger porogens lead to higher roughness values, reaching 28.75 ± 7.48 µm. Multiscale scaffolds exhibit improved attachment and proliferation of 3T3 fibroblast cells as well as extracellular matrix production, compared with their single-scale counterparts (an approximate 1.5- to 2-fold increase in cellular viability and metabolic activity), suggesting that these structures could potentially lead to improved tissue regeneration due to their favourable and reproducible surface morphology. Finally, various scaffolds designed as a drug delivery device were explored by loading them with the antibiotic drug cefazolin. These studies show that by using a multiphasic scaffold design, a sustained drug release profile can be achieved. The combined results strongly support the further development of these scaffolds for dental tissue regeneration applications.

Structural Mechanical Properties of 3D Printing Biomimetic Bone Replacement Materials

One of the primary challenges in developing bone substitutes is to create scaffolds with mechanical properties that closely mimic those of regenerated tissue. Scaffolds that mimic the structure of natural cancellous bone are believed to have better environmental adaptability. In this study, we used the porosity and thickness of pig cancellous bone as biomimetic design parameters, and porosity and structural shape as differential indicators, to design a biomimetic bone beam scaffold. The mechanical properties of the designed bone beam model were tested using the finite element method (FEM). PCL/β-TCP porous scaffolds were prepared using the FDM method, and their mechanical properties were tested. The FEM simulation results were compared and validated, and the effects of porosity and pore shape on the mechanical properties were analyzed. The results of this study indicate that the PCL/β-TCP scaffold, prepared using FDM 3D printing technology for cancellous bone tissue engineering, has excellent integrity and stability. Predicting the structural stability using FEM is effective. The triangle pore structure has the most stability in both simulations and tests, followed by the rectangle and honeycomb shapes, and the diamond structure has the worst stability. Therefore, adjusting the porosity and pore shape can change the mechanical properties of the composite scaffold to meet the mechanical requirements of customized tissue engineering.

Carbon nanoparticles-based hydrogel nanocomposite induces bone repair in vivo

The main objective of the current study is to fabricate a 3D scaffold using alginate hydrogel implemented with carbon nanoparticles (CNPs) as the filler. The SEM imaging revealed that the scaffold possesses a porous internal structure with interconnected pores. The swelling value of the scaffolds (more than 400%) provides a wet niche for bone cell proliferation and migration. The in vitro evaluations showed that the scaffolds were hemocompatible (with hemolysis induction lower than 5%) and cytocompatible (inducing significant proliferative effect (cell viability of 121 ± 4%, p < 0.05) for AlG/CNPs 10%). The in vivo studies showed that the implantation of the fabricated 3D nanocomposite scaffolds induced a bone-forming effect and mediated bone formation into the induced bone defect. In conclusion, these results implied that the fabricated NFC-integrated 3D scaffold exhibited promising characteristics beneficial for bone regeneration and can be applied as the bone tissue engineering scaffold.

Recent Biomedical Applications of Coupling Nanocomposite Polymeric Materials Reinforced with Variable Carbon Nanofillers

The hybridization between polymers and carbon materials is one of the most recent and crucial study areas which abstracted more concern from scientists in the past few years. Polymers could be classified into two classes according to the source materials synthetic and natural. Synthetic polymeric materials have been applied over a floppy zone of industrial fields including the field of biomedicine. Carbon nanomaterials including (fullerene, carbon nanotubes, and graphene) classified as one of the most significant sources of hybrid materials. Nanocarbons are improving significantly mechanical properties of polymers in nanocomposites in addition to physical and chemical properties of the new materials. In all varieties of proposed bio-nanocomposites, a considerable improvement in the microbiological performance of the materials has been explored. Various polymeric materials and carbon-course nanofillers were present, along with antibacterial, antifungal, and anticancer products. This review spots the light on the types of synthetic polymers-based carbon materials and presented state-of-art examples on their application in the area of biomedicine.

Designing of gradient scaffolds and their applications in tissue regeneration

Gradient scaffolds are isotropic/anisotropic three-dimensional structures with gradual transitions in geometry, density, porosity, stiffness, etc., that mimic the biological extracellular matrix. The gradient structures in biological tissues play a major role in various functional and metabolic activities in the body. The designing of gradients in the scaffold can overcome the current challenges in the clinic compared to conventional scaffolds by exhibiting excellent penetration capacity for nutrients & cells, increased cellular adhesion, cell viability & differentiation, improved mechanical stability, and biocompatibility. In this review, the recent advancements in designing gradient scaffolds with desired biomimetic properties, and their implication in tissue regeneration applications have been briefly explained. Furthermore, the gradients in native tissues such as bone, cartilage, neuron, cardiovascular, skin and their specific utility in tissue regeneration have been discussed in detail. The insights from such advances using gradient-based scaffolds can widen the horizon for using gradient biomaterials in tissue regeneration applications.

Biomimetic Growth of Hydroxyapatite in Hybrid Polycaprolactone/Graphene Oxide Ultra-Porous Scaffolds

This paper reports the preparation and characterization of hybrid scaffolds composed of polycaprolactone (PCL) and different graphene oxide (GO) amounts, intending to incorporate the intrinsic characteristics of their constituents, such as bioactivity and biocidal effect. These materials were fabricated by a solvent-casting/particulate leaching technique showing a bimodal porosity (macro and micro) that was around 90%. The highly interconnected scaffolds were immersed in a simulated body fluid, promoting the growth of a hydroxyapatite (HAp) layer, making them ideal candidates for bone tissue engineering. The growth kinetics of the HAp layer was influenced by the GO content, a remarkable result. Furthermore, as expected, the addition of GO neither significantly improves nor reduces the compressive modulus of PCL scaffolds. The thermal behavior of composites was investigated by differential scanning calorimetry, showing an increase in crystallinity as the addition of GO raised, which implies that GO nanosheets can act as seeds to induce the crystallization of PCL. The improved bioactivity was demonstrated by the deposition of an HAp layer on the surface of the scaffold with GO, especially with a 0.1% GO content.

Microbial Poly(hydroxybutyrate-co-hydroxyvalerate) Scaffold for Periodontal Tissue Engineering

In this study, we fabricated three dimensional (3D) porous scaffolds of poly(hydroxybutyrate-co-hydroxyvalerate) with 50% HV content. P(HB-50HV) was biosynthesized from bacteria Cupriavidus necator H16 and the in vitro proliferation of dental cells for tissue engineering application was evaluated. Comparisons were made with scaffolds prepared by poly(hydroxybutyrate) (PHB), poly(hydroxybutyrate-co-12%hydroxyvalerate) (P(HB-12HV)), and polycaprolactone (PCL). The water contact angle results indicated a hydrophobic character for all polymeric films. All fabricated scaffolds exhibited a high porosity of 90% with a sponge-like appearance. The P(HB-50HV) scaffolds were distinctively different in compressive modulus and was the material with the lowest stiffness among all scaffolds tested between the dry and wet conditions. The human gingival fibroblasts (HGFs) and periodontal ligament stem cells (PDLSCs) cultured onto the P(HB-50HV) scaffold adhered to the scaffold and exhibited the highest proliferation with a healthy morphology, demonstrating excellent cell compatibility with P(HB-50HV) scaffolds. These results indicate that the P(HB-50HV) scaffold could be applied as a biomaterial for periodontal tissue engineering and stem cell applications.

Preparation of 3D printed calcium sulfate filled PLA scaffolds with improved mechanical and degradation properties

Scaffold is one of the key components for tissue engineering application. Three-dimensional (3D) printing has given a new avenue to the scaffolds design to closely mimic the real tissue. However, material selection has always been a challenge in adopting 3D printing for scaffolds fabrication, especially for hard tissue. The fused filament fabrication technique is one of the economical 3D printing technology available today, which can efficiently fabricate scaffolds with its key features. In the present study, a hybrid polymer-ceramic scaffold has been prepared by combining the benefit of synthetic biodegradable poly (lactic acid) (PLA) and osteoconductive calcium sulphate (CaS), to harness the advantage of both materials. Composite PLA filament with maximum ceramic loading of 40 wt% was investigated for its printability and subsequently scaffolds were 3D printed. The composite filament was extruded at a temperature of 160 °C at a constant speed with an average diameter of 1.66 ± 0.34 mm. PLA-CaS scaffold with ceramic content of 10%, 20%, and 40% was 3D printed with square pore geometry. The developed scaffolds were characterized for their thermal stability, mechanical, morphological, and geometrical accuracy. The mechanical strength was improved by 29% at 20 wt% of CaS. The porosity was found to be 50-60% with an average pore size of 550 µm with well-interconnected pores. The effect of CaS particles on the degradation behaviour of scaffolds was also assessed over an incubation period of 28 days. The CaS particles acted as porogen and improved the surface chemistry for future cellular activity, while accelerating the degradation rate.

Personalized 3D printed bone scaffolds: A review

3D printed bone scaffolds have the potential to replace autografts and allografts because of advantages such as unlimited supply and the ability to tailor the scaffolds' biochemical, biological and biophysical properties. Significant progress has been made over the past decade in additive manufacturing techniques to 3D print bone grafts, but challenges remain in the lack of manufacturing techniques that can recapitulate both mechanical and biological functions of native bones. The purpose of this review is to outline the recent progress and challenges of engineering an ideal synthetic bone scaffold and to provide suggestions for overcoming these challenges through bioinspiration, high-resolution 3D printing, and advanced modeling techniques. The article provides a short overview of the progress in developing the 3D printed scaffolds for the repair and regeneration of critical size bone defects. STATEMENT OF SIGNIFICANCE: Treatment of critical size bone defects is still a tremendous clinical challenge. To address this challenge, diverse sets of advanced manufacturing approaches and materials have been developed for bone tissue scaffolds. 3D printing has sparked much interest because it provides a close control over the scaffold's internal architecture and in turn its mechanical and biological properties. This article provides a critical overview of the relationships between material compositions, printing techniques, and properties of the scaffolds and discusses the current technical challenges facing their successful translation to the clinic. Bioinspiration, high-resolution printing, and advanced modeling techniques are discussed as future directions to address the current challenges.

Unveiling the potential of melt electrowriting in regenerative dental medicine

For nearly three decades, tissue engineering strategies have been leveraged to devise effective therapeutics for dental, oral, and craniofacial (DOC) regenerative medicine and treat permanent deformities caused by many debilitating health conditions. In this regard, additive manufacturing (AM) allows the fabrication of personalized scaffolds that have the potential to recapitulate native tissue morphology and biomechanics through the utilization of several 3D printing techniques. Among these, melt electrowriting (MEW) is a versatile direct electrowriting process that permits the development of well-organized fibrous constructs with fiber resolutions ranging from micron to nanoscale. Indeed, MEW offers great prospects for the fabrication of scaffolds mimicking tissue specificity, healthy and pathophysiological microenvironments, personalized multi-scale transitions, and functional interfaces for tissue regeneration in medicine and dentistry. Excitingly, recent work has demonstrated the potential of converging MEW with other AM technologies and/or cell-laden scaffold fabrication (bioprinting) as a favorable route to overcome some of the limitations of MEW for DOC tissue regeneration. In particular, such convergency fabrication strategy has opened great promise in terms of supporting multi-tissue compartmentalization and predetermined cell commitment. In this review, we offer a critical appraisal on the latest advances in MEW and its convergence with other biofabrication technologies for DOC tissue regeneration. We first present the engineering principles of MEW and the most relevant design aspects for transition from flat to more anatomically relevant 3D structures while printing highly-ordered constructs. Secondly, we provide a thorough assessment of contemporary achievements using MEW scaffolds to study and guide soft and hard tissue regeneration, and draw a parallel on how to extrapolate proven concepts for applications in DOC tissue regeneration. Finally, we offer a combined engineering/clinical perspective on the fabrication of hierarchically organized MEW scaffold architectures and the future translational potential of site-specific, single-step scaffold fabrication to address tissue and tissue interfaces in dental, oral, and craniofacial regenerative medicine. STATEMENT OF SIGNIFICANCE: Melt electrowriting (MEW) techniques can further replicate the complexity of native tissues and could be the foundation for novel personalized (defect-specific) and tissue-specific clinical approaches in regenerative dental medicine. This work presents a unique perspective on how MEW has been translated towards the application of highly-ordered personalized multi-scale and functional interfaces for tissue regeneration, targeting the transition from flat to anatomically-relevant three-dimensional structures. Furthermore, we address the value of convergence of biofabrication technologies to overcome the traditional manufacturing limitations provided by multi-tissue complexity. Taken together, this work offers abundant engineering and clinical perspectives on the fabrication of hierarchically MEW architectures aiming towards site-specific implants to address complex tissue damage in regenerative dental medicine.

An explorative study on the antimicrobial effects and mechanical properties of 3D printed PLA and TPU surfaces loaded with Ag and Cu against nosocomial and foodborne pathogens

Antimicrobial 3D printed surfaces made of PLA and TPU polymers loaded with copper (Cu), and silver (Ag) nanoparticles (NPs) were developed via fused deposition modeling (FDM). The potential antimicrobial effect of the 3D printed surfaces against Escherichia coli, Listeria monocytogenes, Salmonella Typhimurium, and Staphylococcus aureus was evaluated. Furthermore, the mechanical characteristics, including surface topology and morphology, tensile test of specimens manufactured in three different orientations (XY, XZ, and ZX), water absorption capacity, and surface wettability were also assessed. The results showed that both Cu and Ag-loaded 3D printed surfaces displayed a higher inhibitory effect against S. aureus and L. monocytogenes biofilms compared to S. Typhimurium and E. coli biofilms. The results of SEM analysis revealed a low void fraction for the TPU and no voids for the PLA samples achieved through optimization and the small height (0.1 mm) of the printed layers. The best performing specimen in terms of its tensile was XY, followed by ZX and XZ orientation, while it indicated that Cu and Ag-loaded material had a slightly stiffer response than plain PLA. Additionally, Cu and Ag-loaded 3D printed surfaces revealed the highest hydrophobicity compared to the plain polymers making them excellent candidates for biomedical and food production settings to prevent initial bacterial colonization. The approach taken in the current study offers new insights for developing antimicrobial 3D printed surfaces and equipment to enable their application towards the inhibition of the most common nosocomial and foodborne pathogens and reduce the risk of cross-contamination and disease outbreaks.

Hybrid Manufacturing of Acrylonitrile Butadiene Styrene (ABS) via the Combination of Material Extrusion Additive Manufacturing and Injection Molding

Acrylonitrile Butadiene Styrene (ABS) is a common thermoplastic polymer that has been widely employed in the manufacturing industry due to its impact resistance, tensile strength, and rigidity. Additive manufacturing (AM) is a promising manufacturing technique being used to manufacture products with complex geometries, but it is a slow process producing mechanically inferior products when compared to traditional production processes like injection molding (IM). Thus, our hybrid manufacturing (HM) process combining materials extrusion AM and IM to create a single article was investigated in this study, in which eleven batches of specimens were made and extensively tested. These include the AM, IM, and hybrid manufactured (HYM) samples, in which the HYM samples were made by inserting AM substrates into the IM tool and were varied in infill density of AM preforms and geometries. The HYM samples outperformed AM parts in terms of mechanical performance while retaining customizability dependent on the HYM processing parameters, and the best mechanical performance for HYM samples was found to be comparable to that of IM samples, implying that the overmolding process in HM had primarily improved the mechanical performance of AM products. This work leads to a deeper knowledge of applications to confirm the optimal component fabrication in high design flexibility and mass production.

Calculation of stresses on 3D scaffolds fabricated using extrusion-based bioprinting using a semi-analytical approach

The scaffold is essential to tissue engineering. In particular, the mechanical property of scaffolds has a significant impact on the success rate of regeneration. While numerous techniques exist for measuring mechanical properties, Compression test, three-point bending test, and nano-indentation test are the most common. Nevertheless, the mechanical property of porous structures cannot be accurately measured by previous testing methods. Combining superposition principles with the Flamant solution, this study developed semi-analytical solutions. Through compression testing and FEM simulation, the semi-analytical solution was fully validated. The solution can calculate not only the maximum stress of layer-by-layer construction of complex 3D scaffolds, but also the maximum load-bearing capacity if the mechanical property of the material is known.

Direct 3D printing of decellularized matrix embedded composite polycaprolactone scaffolds for cartilage regeneration

Treatment options for large osteochondral injuries (OCIs) are limited by donor tissue scarcity, morbidity, and anatomic mismatch. 3D printing technology can produce patient-specific scaffolds to address these large defects. Thermoplastics like polycaprolactone (PCL) offer necessary mechanical properties, but lack bioactivity. We fabricated 3D printed PCL scaffolds embedded with polylactic acid microspheres containing decellularized cartilage matrix (DM). DM incorporation within polylactic acid microspheres prevented its thermal degradation during the 3D printing process. The scaffolds replicated the mechanical properties of native cartilage and demonstrated controlled release of DM proteins. Human mesenchymal stem cells (hMSCs) seeded on the composite scaffolds with DM and cultured in basal media self-assembled into aggregates mimicking mesenchymal condensates during embryonic development. The DM composite scaffolds also induced higher expression of biochemical markers of cartilage development than controls, providing evidence for their translational application in the treatment of OCIs. The present study demonstrates the potential of direct incorporation of DM with thermoplastics for 3D printing of patient-specific scaffolds for osteochondral regeneration.

Melt Electrowriting of Graded Porous Scaffolds to Mimic the Matrix Structure of the Human Trabecular Meshwork

The permeability of the human trabecular meshwork (HTM) regulates eye pressure via a porosity gradient across its thickness modulated by stacked layers of matrix fibrils and cells. Changes in HTM porosity are associated with increases in intraocular pressure and the progress of diseases such as glaucoma. Engineered HTMs could help to understand the structure–function relation in natural tissues and lead to new regenerative solutions. Here, melt electrowriting (MEW) is explored as a biofabrication technique to produce fibrillar, porous scaffolds that mimic the multilayer, gradient structure of native HTM. Poly(caprolactone) constructs with a height of 125–500 μm and fiber diameters of 10–12 μm are printed. Scaffolds with a tensile modulus between 5.6 and 13 MPa and a static compression modulus in the range of 6–360 kPa are obtained by varying the scaffold design, that is, the density and orientation of the fibers and number of stacked layers. Primary HTM cells attach to the scaffolds, proliferate, and form a confluent layer within 8–14 days, depending on the scaffold design. High cell viability and cell morphology close to that in the native tissue are observed. The present work demonstrates the utility of MEW for reconstructing complex morphological features of natural tissues.

A Roadmap to Fabricate Geometrically Accurate Three-Dimensional Scaffolds CO-Printed by Natural and Synthetic Polymers

Three-dimensional bioprinting is a promising field in regenerating patient-specific tissues and organs due to its inherent capability of releasing biocompatible materials encapsulating living cells in a predefined location. Due to the diverse characteristics of tissues and organs in terms of microstructures and cell types, a multinozzle extrusion-based 3D bioprinting system has gained popularity. The investigations on interactions between various biomaterials and cell-to-material can provide relevant information about the scaffold geometry, cell viability, and proliferation. Natural hydrogels are frequently used in bioprinting materials because of their high-water content and biocompatibility. However, the dominancy of liquid characteristics of only-hydrogel materials makes the printing process challenging. Polycaprolactone (PCL) is the most frequently used synthetic biopolymer. It can provide mechanical integrity to achieve dimensionally accurate fabricated scaffolds, especially for hard tissues such as bone and cartilage scaffolds. In this paper, we explored various multimaterial bioprinting strategies with our recently proposed bio-inks and PCL intending to achieve dimensional accuracy and mechanical aspects. Various strategies were followed to coprint natural and synthetic biopolymers and interactions were analyzed between them. Printability of pure PCL with various molecular weights was optimized with respect to different process parameters such as nozzle temperature, printing pressure, printing speed, porosity, and bed temperature to coprint with natural hydrogels. The relationship between the rheological properties and shape fidelity of natural polymers was investigated with a set of printing strategies during coprinting with PCL. The successful application of this research can help achieve dimensionally accurate scaffolds.

3D Fiber Reinforced Hydrogel Scaffolds by Melt Electrowriting and Gel Casting as a Hybrid Design for Wound Healing

Emerging biomanufacturing technologies have revolutionized the field of tissue engineering by offering unprecedented possibilities. Over the past few years, new opportunities arose by combining traditional and novel fabrication techniques, shaping the hybrid designs in biofabrication. One of the potential application fields is skin tissue engineering, in which a combination of traditional principles of wound dressing with advanced biofabrication methods could yield more efficient therapies. In this study, a hybrid design of fiber-reinforced scaffolds combined with gel casting is developed and the efficiency for in vivo wound healing applications is assessed. For this purpose, 3D fiber meshes produced by melt electrowriting are selectively filled with photocrosslinkable gelatin hydrogel matrices loaded with different growth factor carrier microspheres. Additionally, the influence of the inclusion of inorganic bioactive glass particles within the composite fibrous mesh is evaluated. Qualitative evaluation of secondary wound healing criteria and histological analysis shows that hybrid scaffolds containing growth factors and bioactive glass enhances the healing process significantly, compared to the designs merely providing a fiber-reinforced bioactive hydrogel matrix as the wound dressing. This study aims to explore a new application area for melt electrowriting as a powerful tool in fabricating hybrid therapeutic designs for skin tissue engineering.

Biomedical Applications of Polyhydroxyalkanoate in Tissue Engineering

Tissue engineering technology aids in the regeneration of new tissue to replace damaged or wounded tissue. Three-dimensional biodegradable and porous scaffolds are often utilized in this area to mimic the structure and function of the extracellular matrix. Scaffold material and design are significant areas of biomaterial research and the most favorable material for seeding of in vitro and in vivo cells. Polyhydroxyalkanoates (PHAs) are biopolyesters (thermoplastic) that are appropriate for this application due to their biodegradability, thermo-processability, enhanced biocompatibility, mechanical properties, non-toxicity, and environmental origin. Additionally, they offer enormous potential for modification through biological, chemical and physical alteration, including blending with various other materials. PHAs are produced by bacterial fermentation under nutrient-limiting circumstances and have been reported to offer new perspectives for devices in biological applications. The present review discusses PHAs in the applications of conventional medical devices, especially for soft tissue (sutures, wound dressings, cardiac patches and blood vessels) and hard tissue (bone and cartilage scaffolds) regeneration applications. The paper also addresses a recent advance highlighting the usage of PHAs in implantable devices, such as heart valves, stents, nerve guidance conduits and nanoparticles, including drug delivery. This review summarizes the in vivo and in vitro biodegradability of PHAs and conducts an overview of current scientific research and achievements in the development of PHAs in the biomedical sector. In the future, PHAs may replace synthetic plastics as the material of choice for medical researchers and practitioners.

A Comprehensive Review of Biopolymer Fabrication in Additive Manufacturing Processing for 3D-Tissue-Engineering Scaffolds

The selection of a scaffold-fabrication method becomes challenging due to the variety in manufacturing methods, biomaterials and technical requirements. The design and development of tissue engineering scaffolds depend upon the porosity, which provides interconnected pores, suitable mechanical strength, and the internal scaffold architecture. The technology of the additive manufacturing (AM) method via photo-polymerization 3D printing is reported to have the capability to fabricate high resolution and finely controlled dimensions of a scaffold. This technology is also easy to operate, low cost and enables fast printing, compared to traditional methods and other additive manufacturing techniques. This article aims to review the potential of the photo-polymerization 3D-printing technique in the fabrication of tissue engineering scaffolds. This review paper also highlights the comprehensive comparative study between photo-polymerization 3D printing with other scaffold fabrication techniques. Various parameter settings that influence mechanical properties, biocompatibility and porosity behavior are also discussed in detail.

Use of Polyesters in Fused Deposition Modeling for Biomedical Applications

In recent years, 3D printing techniques experienced a growing interest in several sectors, including the biomedical one. Their main advantage resides in the possibility to obtain complex and personalized structures in a cost-effective way impossible to achieve with traditional production methods. This is especially true for Fused Deposition Modeling (FDM), one of the most diffused 3D printing methods. The easy customization of the final products' geometry, composition and physico-chemical properties is particularly interesting for the increasingly personalized approach adopted in modern medicine. Thermoplastic polymers are the preferred choice for FDM applications, and a wide selection of biocompatible and biodegradable materials is available to this aim. Moreover, these polymers can also be easily modified before and after printing to better suit the body environment and the mechanical properties of biological tissues. This review focuses on the use of thermoplastic aliphatic polyesters for FDM applications in the biomedical field. In detail, the use of poly(ε-caprolactone), poly(lactic acid), poly(lactic-co-glycolic acid), poly(hydroxyalkanoate)s, thermo-plastic poly(ester urethane)s and their blends has been thoroughly surveyed, with particular attention to their main features, applicability and workability. The state-of-the-art is presented and current challenges in integrating the additive manufacturing technology in the medical practice are discussed. This article is protected by copyright. All rights reserved.

Bacterial cellulose as a potential biopolymer in biomedical applications: a state-of-the-art review

Throughout history, natural biomaterials have benefited society. Nevertheless, in recent years, tailoring natural materials for diverse biomedical applications accompanied with sustainability has become the focus. With the progress in the field of materials science, novel approaches for the production, processing, and functionalization of biomaterials to obtain specific architectures have become achievable. This review highlights an immensely adaptable natural biomaterial, bacterial cellulose (BC). BC is an emerging sustainable biopolymer with immense potential in the biomedical field due to its unique physical properties such as flexibility, high porosity, good water holding capacity, and small size; chemical properties such as high crystallinity, foldability, high purity, high polymerization degree, and easy modification; and biological characteristics such as biodegradability, biocompatibility, excellent biological affinity, and non-biotoxicity. The structure of BC consists of glucose monomer units polymerized via cellulose synthase in β-1-4 glucan chains, creating BC nano fibrillar bundles with a uniaxial orientation. BC-based composites have been extensively investigated for diverse biomedical applications due to their similarity to the extracellular matrix structure. The recent progress in nanotechnology allows the further modification of BC, producing novel BC-based biomaterials for various applications. In this review, we strengthen the existing knowledge on the production of BC and BC composites and their unique properties, and highlight the most recent advances, focusing mainly on the delivery of active pharmaceutical compounds, tissue engineering, and wound healing. Further, we endeavor to present the challenges and prospects for BC-associated composites for their application in the biomedical field.

Characterization of biocompatible scaffolds manufactured by fused filament fabrication of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

We characterize poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) scaffolds for tissue repair and regeneration, manufactured by three-dimensional fused filament fabrication (FFF). PHBH belongs to the class of polyhydroxyalkanoates with interesting biodegradable and biocompatible capabilities, especially attractive for tissue engineering. Equally, FFF stands as a promising manufacturing technology for the production of custom-designed scaffolds. We address thermal, rheological and cytotoxicity properties of PHBH, placing special emphasis on the mechanical response of the printed material in a wide deformation range. Indeed, effective mechanical properties are assessed in both the linear and nonlinear regime. To warrant uniqueness of the material parameters, these are measured directly through digital image correlation, both in tension and compression, while experimental data fitting of finite-element analyses is only adopted for the determination of the second invariant coefficient in the nonlinear regime. Mechanical data are clearly porosity dependent, and they are given for both the cubic and the honeycomb infill pattern. Local strain spikes due to the presence of defects are observed and measured: those falling in the range 70-100% lead to macro-crack development and, ultimately, to failure. Results suggest the significant potential attached to FFF printing of PHBH for customizable medical devices which are biocompatible and mechanically resilient.

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

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

Additive Manufacturing of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/Poly(D,L-lactide-co-glycolide) Biphasic Scaffolds for Bone Tissue Regeneration

Polyhydroxyalkanoates are biopolyesters whose biocompatibility, biodegradability, environmental sustainability, processing versatility, and mechanical properties make them unique scaffolding polymer candidates for tissue engineering. The development of innovative biomaterials suitable for advanced Additive Manufacturing (AM) offers new opportunities for the fabrication of customizable tissue engineering scaffolds. In particular, the blending of polymers represents a useful strategy to develop AM scaffolding materials tailored to bone tissue engineering. In this study, scaffolds from polymeric blends consisting of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(D,L-lactide-co-glycolide) (PLGA) were fabricated employing a solution-extrusion AM technique, referred to as Computer-Aided Wet-Spinning (CAWS). The scaffold fibers were constituted by a biphasic system composed of a continuous PHBV matrix and a dispersed PLGA phase which established a microfibrillar morphology. The influence of the blend composition on the scaffold morphological, physicochemical, and biological properties was demonstrated by means of different characterization techniques. In particular, increasing the content of PLGA in the starting solution resulted in an increase in the pore size, the wettability, and the thermal stability of the scaffolds. Overall, in vitro biological experiments indicated the suitability of the scaffolds to support murine preosteoblast cell colonization and differentiation towards an osteoblastic phenotype, highlighting higher proliferation for scaffolds richer in PLGA.

Clinical Application of Three-Dimensional Printing of Polycaprolactone/Beta-Tricalcium Phosphate Implants for Cranial Reconstruction

Polycaprolactone (PCL) implants are a biodegradable polymeric material with appropriate mechanical strength and durability for use in cranioplasty. They can be manufactured as patient- customized implants using a three-dimensional (3D) printer. Herein, the authors aimed to share our experience in cranioplasty of patients with deformed and asymmetric skulls using PCL/beta- tricalcium phosphate (ß-TCP) implants.

Seven patients underwent cranioplasty using patient-specific PCL/ß-TCP implants. Cranial computed tomography images were converted to a 3D model and mirrored to design a patient-specific implant. Based on the 3D simulation, an implant was 3D printed using PCL/ß-TCP. A 6-month follow-up was conducted with periodic visits and computed tomography scans. Symmetry after surgery and complications were evaluated.

Postoperatively, the soft tissue volumes increased to 15.8 ± 17.2 cm³ and 14.9 ± 15.7 cm³ at 2 weeks and 6 months of follow-up, respectively. The volume change from 2 weeks to 6 months was —4.4 ± 2.5%. Six patients achieved complete symmetry after cranioplasty, whereas 1 patient noticed partial symmetry. The symmetry remained unchanged at 6 months of follow-up. Upon palpation to assess smoothness, 6 patients exhibited a smooth edge interface, whereas 1 patient had a slightly irregular edge.

Based on these findings, 3D-printed PCL/ß-TCP implants are an excellent material for cranioplasty, and a favorable cosmetic outcome can be achieved. Specifically, these novel PCL/ß-TCP implants have good biocompatibility and mechanical strength without any postoperative foreign body reaction.

Computer vision-aided bioprinting for bone research

Bioprinting is an emerging additive manufacturing technology that has enormous potential in bone implantation and repair. The insufficient accuracy of the shape of bioprinted parts is a primary clinical barrier that prevents widespread utilization of bioprinting, especially for bone design with high-resolution requirements. During the last five years, the use of computer vision for process control has been widely practiced in the manufacturing field. Computer vision can improve the performance of bioprinting for bone research with respect to various aspects, including accuracy, resolution, and cell survival rate. Hence, computer vision plays a substantial role in addressing the current defect problem in bioprinting for bone research. In this review, recent advances in the application of computer vision in bioprinting for bone research are summarized and categorized into three groups based on different defect types: bone scaffold process control, deep learning, and cell viability models. The collection of printing parameters, data processing, and feedback of bioprinting information, which ultimately improves printing capabilities, are further discussed. We envision that computer vision may offer opportunities to accelerate bioprinting development and provide a new perception for bone research.