Polymer-Bioactive Glass Composite Filaments for 3D Scaffold Manufacturing by Fused Deposition Modeling: Fabrication and Characterization

Promoting neurovascularized bone regeneration with a novel 3D printed inorganic-organic magnesium silicate/PLA composite scaffold

Critical-size bone defect repair presents multiple challenges, such as osteogenesis, vascularization, and neurogenesis. Current biomaterials for bone repair need more consideration for the above functions. Organic-inorganic composites combined with bioactive ions offer significant advantages in bone regeneration. In our work, we prepared an organic-inorganic composite material by blending polylactic acid (PLA) with 3-aminopropyltriethoxysilane (APTES)-modified magnesium silicate (A-M2S) and fabricated it by 3D printing. With the increase of A-M2S proportion, the hydrophilicity and mineralization ability showed an enhanced trend, and the compressive strength and elastic modulus were increased from 15.29 MPa and 94.61 MPa to 44.30 MPa and 435.77 MPa, respectively. Furthermore, A-M2S/PLA scaffolds not only exhibited good cytocompatibility of bone marrow mesenchymal stem cells (BMSCs), human umbilical vein endothelial cells (HUVECs), and Schwann cells (SCs), but also effectively promoted osteogenesis, angiogenesis, and neurogenesis in vitro. After implanting 10% A-M2S/PLA scaffolds in vivo, the scaffolds showed the most effective repair of cranium defects compared to the blank and control group (PLA). Additionally, they promoted the secretion of proteins related to bone regeneration and neurovascular formation. These results provided the basis for expanding the application of A-M2S and PLA in bone tissue engineering and presented a novel concept for neurovascularized bone repair.

Engineering of Bioresorbable Polymers for Tissue Engineering and Drug Delivery Applications

Herein, the recent advances in the development of resorbable polymeric-based biomaterials, their geometrical forms, resorption mechanisms, and their capabilities in various biomedical applications are critically reviewed. A comprehensive discussion of the engineering approaches for the fabrication of polymeric resorbable scaffolds for tissue engineering, drug delivery, surgical, cardiological, aesthetical, dental and cardiovascular applications, are also explained. Furthermore, to understand the internal structures of resorbable scaffolds, representative studies of their evaluation by medical imaging techniques, e.g., cardiac computer tomography, are succinctly highlighted. This approach provides crucial clinical insights which help to improve the materials' suitable and viable characteristics for them to meet the highly restrictive medical requirements. Finally, the aspects of the legal regulations and the associated challenges in translating research into desirable clinical and marketable materials of polymeric-based formulations, are presented.

Effect of the Addition of Inorganic Fillers on the Properties of Degradable Polymeric Blends for Bone Tissue Engineering

Bone tissue exhibits self-healing properties; however, not all defects can be repaired without surgical intervention. Bone tissue engineering offers artificial scaffolds, which can act as a temporary matrix for bone regeneration. The aim of this study was to manufacture scaffolds made of poly(lactic acid), poly(ε-caprolactone), poly(propylene fumarate), and poly(ethylene glycol) modified with bioglass, beta tricalcium phosphate (TCP), and/or wollastonite (W) particles. The scaffolds were fabricated using a gel-casting method and observed with optical and scanning electron microscopes. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR), differential scanning calorimetry (DSC), thermogravimetry (TG), wettability, and degradation tests were conducted. The highest content of TCP without W in the composition caused the highest hydrophilicity (water contact angle of 61.9 ± 6.3°), the fastest degradation rate (7% mass loss within 28 days), moderate ability to precipitate CaP after incubation in PBS, and no cytotoxicity for L929 cells. The highest content of W without TCP caused the highest hydrophobicity (water contact angle of 83.4 ± 1.7°), the lowest thermal stability, slower degradation (3% mass loss within 28 days), and did not evoke CaP precipitation. Moreover, some signs of cytotoxicity on day 1 were observed. The samples with both TCP and W showed moderate properties and the best cytocompatibility on day 4. Interestingly, they were covered with typical cauliflower-like hydroxyapatite deposits after incubation in phosphate-buffered saline (PBS), which might be a sign of their excellent bioactivity.

Trends in bioactivity: inducing and detecting mineralization of regenerative polymeric scaffolds

Due to limitations of biological and alloplastic grafts, regenerative engineering has emerged as a promising alternative to treat bone defects. Bioactive polymeric scaffolds are an integral part of such an approach. Bioactivity importantly induces hydroxyapatite mineralization that promotes osteoinductivity and osseointegration with surrounding bone tissue. Strategies to confer bioactivity to polymeric scaffolds utilize bioceramic fillers, coatings and surface treatments, and additives. These approaches can also favorably impact mechanical and degradation properties. A variety of fabrication methods are utilized to prepare scaffolds with requisite morphological features. The bioactivity of scaffolds may be evaluated with a broad set of techniques, including in vitro (acellular and cellular) and in vivo methods. Herein, we highlight contemporary and emerging approaches to prepare and assess scaffold bioactivity, as well as existing challenges.

3D-printed PCL framework assembling ECM-inspired multi-layer mineralized GO-Col-HAp microscaffold for in situ mandibular bone regeneration

BACKGROUND

In recent years, natural bone extracellular matrix (ECM)-inspired materials have found widespread application as scaffolds for bone tissue engineering. However, the challenge of creating scaffolds that mimic natural bone ECM's mechanical strength and hierarchical nano-micro-macro structures remains. The purposes of this study were to introduce an innovative bone ECM-inspired scaffold that integrates a 3D-printed framework with hydroxyapatite (HAp) mineralized graphene oxide-collagen (GO-Col) microscaffolds and find its application in the repair of mandibular bone defects.

METHODS

Initially, a 3D-printed polycaprolactone (PCL) scaffold was designed with cubic disks and square pores to mimic the macrostructure of bone ECM. Subsequently, we developed multi-layer mineralized GO-Col-HAp microscaffolds (MLM GCH) to simulate natural bone ECM's nano- and microstructural features. Systematic in vitro and in vivo experiments were introduced to evaluate the ECM-inspired structure of the scaffold and to explore its effect on cell proliferation and its ability to repair rat bone defects.

RESULTS

The resultant MLM GCH/PCL composite scaffolds exhibited robust mechanical strength and ample assembly space. Moreover, the ECM-inspired MLM GCH microscaffolds displayed favorable attributes such as water absorption and retention and demonstrated promising cell adsorption, proliferation, and osteogenic differentiation in vitro. The MLM GCH/PCL composite scaffolds exhibited successful bone regeneration within mandibular bone defects in vivo.

CONCLUSIONS

This study presents a well-conceived strategy for fabricating ECM-inspired scaffolds by integrating 3D-printed PCL frameworks with multilayer mineralized porous microscaffolds, enhancing cell proliferation, osteogenic differentiation, and bone regeneration. This construction approach holds the potential for extension to various other biomaterial types.

Biodegradable Polymers in Biomedical Applications: A Review-Developments, Perspectives and Future Challenges

Biodegradable polymers are materials that, thanks to their remarkable properties, are widely understood to be suitable for use in scientific fields such as tissue engineering and materials engineering. Due to the alarming increase in the number of diagnosed diseases and conditions, polymers are of great interest in biomedical applications especially. The use of biodegradable polymers in biomedicine is constantly expanding. The application of new techniques or the improvement of existing ones makes it possible to produce materials with desired properties, such as mechanical strength, controlled degradation time and rate and antibacterial and antimicrobial properties. In addition, these materials can take virtually unlimited shapes as a result of appropriate design. This is additionally desirable when it is necessary to develop new structures that support or restore the proper functioning of systems in the body.

Development, Physiochemical characterization, Mechanical and Finite element analysis of 3D printed Polylactide-β-TCP/α-Al2O3 composite

Herein, material extrusion (MEX) technique is utilized to develop 3D printed models based on reinforcing β-Ca3(PO4)2/α-Al2O3 composite in polylactide (PLA) matrix. β-Ca3(PO4)2/α-Al2O3 composite has been synthesized through co-precipitation method and the phase content of β-Ca3(PO4)2 and α-Al2O3 components are respectively determined as 64 and 36 wt%. The resultant β-Ca3(PO4)2/α-Al2O3 composite mixed with PLA at various weight ratios were extruded as filaments and subsequently 3D printed into definite shapes for the physiochemical, morphological and mechanical evaluation. 3D printed bodies that comprise 5 wt % β-Ca3(PO4)2/α-Al2O3 composite yielded an increasing tensile, compressive and flexural strength in the corresponding order of ∼15, ∼15 and 22% than 3D printed pure PLA. Further, the Representative volume element (RVE) unit cells developed based on the various investigated compositions of PLA-β-Ca3(PO4)2/α-Al2O3 were subjected to mechanical evaluation through Finite element analysis (FEA) under both static and dynamic loading conditions on ASTM standard specimens. The results from experimental and FEA analysis demonstrated good uniformity that confirmed the reinforcement of 5 wt % β-Ca3(PO4)2/α-Al2O3 in PLA matrix as an optimum combination to yield better mechanical strength.

Gymnemic acid-conjugated gelatin scaffold for enhanced bone regeneration: A novel insight to tissue engineering

Bone tissue engineering deals with the design of bone scaffolds. The selection of porous scaffold for osteoblast attachment and suppression of microbial infections are the major challenges that were addressed by designing gelatin scaffolds conjugated with gymnemic acid. Gelatin scaffold was prepared by loading gymnemic acid and morphological characterization, porosity, water absorption behavior, and biocompatibility of the scaffold were studied. The scaffold was introduced to the rat calvarial bone defect (BD) and analyzed the serum C reactive protein, alkaline phosphatase activity, and histology for 1 month to study the reconstruction. Adult Sprague-Dawley rats were used as sham operated control, animal with BD, and animal with BD which was implanted with scaffold (BDMB). The scanning electron micrograph revealed porous nature of scaffold. There was no significant difference in water absorption ability of scaffold. The C reactive protein was not observed in the serum collected on the 5th day postsurgery, supported the biocompatibility. The alkaline phosphatase activity in BDMB was increased when compared with BD on 15th and 20th day and then decreased. New bone tissue formation was detected with hematoxylin-eosin staining. The scaffold is effective in enhancing bone regeneration, which will have therapeutic significance in orthopedics and dentistry.

Use of 3D-printed polylactic acid/bioceramic composite scaffolds for bone tissue engineering in preclinical in vivo studies: A systematic review

3D-printed composite scaffolds have emerged as an alternative to deal with existing limitations when facing bone reconstruction. The aim of the study was to systematically review the feasibility of using PLA/bioceramic composite scaffolds manufactured by 3D-printing technologies as bone grafting materials in preclinical in vivo studies. Electronic databases were searched using specific search terms, and thirteen manuscripts were selected after screening. The synthesis of the scaffolds was carried out using mainly extrusion-based techniques. Likewise, hydroxyapatite was the most used bioceramic for synthesizing composites with a PLA matrix. Among the selected studies, seven were conducted in rats and six in rabbits, but the high variability that exists regarding the experimental process made it difficult to compare them. Regarding the results, PLA/Bioceramic composite scaffolds have shown to be biocompatible and mechanically resistant. Preclinical studies elucidated the ability of the scaffolds to be used as bone grafts, allowing bone growing without adverse reactions. In conclusion, PLA/Bioceramics scaffolds have been demonstrated to be a promising alternative for treating bone defects. Nevertheless, more care should be taken when designing and performing in vivo trials, since the lack of standardization of the processes, which prevents the comparison of the results and reduces the quality of the information. STATEMENT OF SIGNIFICANCE: 3D-printed polylactic acid/bioceramic composite scaffolds have emerged as an alternative to deal with existing limitations when facing bone reconstruction. Since preclinical in vivo studies with animal models represent a mandatory step for clinical translation, the present manuscript analyzed and discussed not only those aspects related to the selection of the bioceramic material, the synthesis of the implants and their characterization. But provides a new approach to understand how the design and perform of clinical trials, as well as the selection of the analysis methods, may affect the obtained results, by covering authors' knowledgebase from veterinary medicine to biomaterial science. Thus, this study aims to systematically review the feasibility of using polylactic acid/bioceramic scaffolds as grafting materials in preclinical trials.

Biomaterials combined with ADSCs for bone tissue engineering: current advances and applications

In recent decades, bone tissue engineering, which is supported by scaffold, seed cells and bioactive molecules (BMs), has provided new hope and direction for treating bone defects. In terms of seed cells, compared to bone marrow mesenchymal stem cells, which were widely utilized in previous years, adipose-derived stem cells (ADSCs) are becoming increasingly favored by researchers due to their abundant sources, easy availability and multi-differentiation potentials. However, there is no systematic theoretical basis for selecting appropriate biomaterials loaded with ADSCs. In this review, the regulatory effects of various biomaterials on the behavior of ADSCs are summarized from four perspectives, including biocompatibility, inflammation regulation, angiogenesis and osteogenesis, to illustrate the potential of combining various materials with ADSCs for the treatment of bone defects. In addition, we conclude the influence of additional application of various BMs on the bone repair effect of ADSCs, in order to provide more evidences and support for the selection or preparation of suitable biomaterials and BMs to work with ADSCs. More importantly, the associated clinical case reports and experiments are generalized to provide additional ideas for the clinical transformation and application of bone tissue engineering loaded with ADSCs.

Advanced Bioactive Glasses: The Newest Achievements and Breakthroughs in the Area

Bioactive glasses (BGs) are especially useful materials in soft and bone tissue engineering and even in dentistry. They can be the solution to many medical problems, and they have a huge role in the healing processes of bone fractures. Interestingly, they can also promote skin regeneration and wound healing. Bioactive glasses are able to attach to the bone tissues and form an apatite layer which further initiates the biomineralization process. The formed intermediate apatite layer makes a connection between the hard tissue and the bioactive glass material which results in faster healing without any complications or side effects. This review paper summarizes the most recent advancement in the preparation of diverse types of BGs, such as silicate-, borate- and phosphate-based bioactive glasses. We discuss their physical, chemical, and mechanical properties detailing how they affect their biological performances. In order to get a deeper insight into the state-of-the-art in this area, we also consider their medical applications, such as bone regeneration, wound care, and dental/bone implant coatings.

3D printing of piezoelectric and bioactive barium titanate-bioactive glass scaffolds for bone tissue engineering

Bone healing is a complex process orchestrated by various factors, such as mechanical, chemical and electrical cues. Creating synthetic biomaterials that combine several of these factors leading to tailored and controlled tissue regeneration, is the goal of scientists worldwide. Among those factors is piezoelectricity which creates a physiological electrical microenvironment that plays an important role in stimulating bone cells and fostering bone regeneration. However, only a limited number of studies have addressed the potential of combining piezoelectric biomaterials with state-of-the-art fabrication methods to fabricate tailored scaffolds for bone tissue engineering. Here, we present an approach that takes advantage of modern additive manufacturing techniques to create macroporous biomaterial scaffolds based on a piezoelectric and bioactive ceramic-crystallised glass composite. Using binder jetting, scaffolds made of barium titanate and 45S5 bioactive glass are fabricated and extensively characterised with respect to their physical and functional properties. The 3D-printed ceramic-crystallised glass composite scaffolds show both suitable mechanical strength and bioactive behaviour, as represented by the accumulation of bone-like calcium phosphate on the surface. Piezoelectric scaffolds that mimic or even surpass bone with piezoelectric constants ranging from 1 to 21 pC/N are achieved, depending on the composition of the composite. Using MC3T3-E1 osteoblast precursor cells, the scaffolds show high cytocompatibility coupled with cell attachment and proliferation, rendering the barium titanate/45S5 ceramic-crystallised glass composites promising candidates for bone tissue engineering.

Three-Dimensional Scaffolds for Bone Tissue Engineering

Immobilization using external or internal splints is a standard and effective procedure to treat minor skeletal fractures. In the case of major skeletal defects caused by extreme trauma, infectious diseases or tumors, the surgical implantation of a bone graft from external sources is required for a complete cure. Practical disadvantages, such as the risk of immune rejection and infection at the implant site, are high in xenografts and allografts. Currently, an autograft from the iliac crest of a patient is considered the "gold standard" method for treating large-scale skeletal defects. However, this method is not an ideal solution due to its limited availability and significant reports of morbidity in the harvest site (30%) as well as the implanted site (5-35%). Tissue-engineered bone grafts aim to create a mechanically strong, biologically viable and degradable bone graft by combining a three-dimensional porous scaffold with osteoblast or progenitor cells. The materials used for such tissue-engineered bone grafts can be broadly divided into ceramic materials (calcium phosphates) and biocompatible/bioactive synthetic polymers. This review summarizes the types of materials used to make scaffolds for cryo-preservable tissue-engineered bone grafts as well as the distinct methods adopted to create the scaffolds, including traditional scaffold fabrication methods (solvent-casting, gas-foaming, electrospinning, thermally induced phase separation) and more recent fabrication methods (fused deposition molding, stereolithography, selective laser sintering, Inkjet 3D printing, laser-assisted bioprinting and 3D bioprinting). This is followed by a short summation of the current osteochondrogenic models along with the required scaffold mechanical properties for in vivo applications. We then present a few results of the effects of freezing and thawing on the structural and mechanical integrity of PLLA scaffolds prepared by the thermally induced phase separation method and conclude this review article by summarizing the current regulatory requirements for tissue-engineered products.

Additive Manufacturing of Bioactive Glass and Its Polymer Composites as Bone Tissue Engineering Scaffolds: A Review

Bioactive glass (BG) and its polymer composites have demonstrated great potential as scaffolds for bone defect healing. Nonetheless, processing these materials into complex geometry to achieve either anatomy-fitting designs or the desired degradation behavior remains challenging. Additive manufacturing (AM) enables the fabrication of BG and BG/polymer objects with well-defined shapes and intricate porous structures. This work reviewed the recent advancements made in the AM of BG and BG/polymer composite scaffolds intended for bone tissue engineering. A literature search was performed using the Scopus database to include publications relevant to this topic. The properties of BG based on different inorganic glass formers, as well as BG/polymer composites, are first introduced. Melt extrusion, direct ink writing, powder bed fusion, and vat photopolymerization are AM technologies that are compatible with BG or BG/polymer processing and were reviewed in terms of their recent advances. The value of AM in the fabrication of BG or BG/polymer composites lies in its ability to produce scaffolds with patient-specific designs and the on-demand spatial distribution of biomaterials, both contributing to effective bone defect healing, as demonstrated by in vivo studies. Based on the relationships among structure, physiochemical properties, and biological function, AM-fabricated BG or BG/polymer composite scaffolds are valuable for achieving safer and more efficient bone defect healing in the future.

Additive Manufacturing of Polymer/Bioactive Glass Scaffolds for Regenerative Medicine: A Review

Tissue engineering (TE) is a branch of regenerative medicine with enormous potential to regenerate damaged tissues using synthetic grafts such as scaffolds. Polymers and bioactive glasses (BGs) are popular materials for scaffold production because of their tunable properties and ability to interact with the body for effective tissue regeneration. Due to their composition and amorphous structure, BGs possess a significant affinity with the recipient's tissue. Additive manufacturing (AM), a method that allows the creation of complex shapes and internal structures, is a promising approach for scaffold production. However, despite the promising results obtained so far, several challenges remain in the field of TE. One critical area for improvement is tailoring the mechanical properties of scaffolds to meet specific tissue requirements. In addition, achieving improved cell viability and controlled degradation of scaffolds is necessary to ensure successful tissue regeneration. This review provides a critical summary of the potential and limitations of polymer/BG scaffold production via AM covering extrusion-, lithography-, and laser-based 3D-printing techniques. The review highlights the importance of addressing the current challenges in TE to develop effective and reliable strategies for tissue regeneration.

Medical-Grade Poly(Lactic Acid)/Hydroxyapatite Composite Films: Thermal and In Vitro Degradation Properties

Production of biocompatible composite scaffolds shifts towards additive manufacturing where thermoplastic biodegradable polymers such as poly(lactic acid) (PLA) are used as matrices. Differences between industrial- and medical-grade polymers are often overlooked although they may affect properties and degradation behaviour as significantly as the filler addition. In the present research, composite films based on medical-grade PLA and biogenic hydroxyapatite (HAp) with 0, 10, and 20 wt.% of HAp were prepared by solvent casting technique. The degradation of composites incubated in phosphate-buffered saline solution (PBS) at 37 °C after 10 weeks showed that the higher HAp content slowed down the hydrolytic PLA degradation and improved its thermal stability. Morphological nonuniformity after degradation was indicated by the different glass transition temperatures (T_g) throughout the film. The T_g of the inner part of the sample decreased significantly faster compared with the outer part. The decrease was observed prior to the weight loss of composite samples.

A simple and fast method for screening production of polymer-ceramic filaments for bone implant printing using commercial fused deposition modelling 3D printers

3D printing is a promising technique for obtaining bone implants. However, 3D printed bone implants, especially those printed using fused deposition modelling, are still in the experimental phase despite decades of work. Research on new materials faces numerous limitations, such as reagents' cost and machines' high prices to produce filaments for 3D printing polymer-ceramic composites for fused deposition modelling. This paper presents a simple, low-cost, and fast method of obtaining polymer-ceramic filaments using apparatus consisting of parts available in a hardware store. The method's versatility for producing the filaments was demonstrated on two different biodegradable polymers - polylactic acid and polycaprolactone - and different concentrations of calcium phosphate - β-tricalcium phosphate - in the composite, up to 50 % by weight. For screening purposes, numerous scaffolds were 3D printed from the obtained filaments on a commercial 3D printer. Structural, mechanical, and biological tests show that the 3D printed scaffolds are suitable for bone implants, as their structure, mechanical, and non-cytotoxic properties are evident. Moreover, the proposed method of composite forming is a simplification of the processes of manufacturing and researching 3D printed materials with potential applications in the regeneration of bone tissue.

Bioceramic scaffolds with triply periodic minimal surface architectures guide early-stage bone regeneration

The pore architecture of porous scaffolds is a critical factor in osteogenesis, but it is a challenge to precisely configure strut-based scaffolds because of the inevitable filament corner and pore geometry deformation. This study provides a pore architecture tailoring strategy in which a series of Mg-doped wollastonite scaffolds with fully interconnected pore networks and curved pore architectures called triply periodic minimal surfaces (TPMS), which are similar to cancellous bone, are fabricated by a digital light processing technique. The sheet-TPMS pore geometries (s-Diamond, s-Gyroid) contribute to a 3‒4-fold higher initial compressive strength and 20%-40% faster Mg-ion-release rate compared to the other-TPMS scaffolds, including Diamond, Gyroid, and the Schoen's I-graph-Wrapped Package (IWP) in vitro. However, we found that Gyroid and Diamond pore scaffolds can significantly induce osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Analyses of rabbit experiments in vivo show that the regeneration of bone tissue in the sheet-TPMS pore geometry is delayed; on the other hand, Diamond and Gyroid pore scaffolds show notable neo-bone tissue in the center pore regions during the early stages (3-5 weeks) and the bone tissue uniformly fills the whole porous network after 7 weeks. Collectively, the design methods in this study provide an important perspective for optimizing the pore architecture design of bioceramic scaffolds to accelerate the rate of osteogenesis and promote the clinical translation of bioceramic scaffolds in the repair of bone defects.

A Review on Manufacturing Processes of Biocomposites Based on Poly(α-Esters) and Bioactive Glass Fillers for Bone Regeneration

The incorporation of bioactive and biocompatible fillers improve the bone cell adhesion, proliferation and differentiation, thus facilitating new bone tissue formation upon implantation. During these last 20 years, those biocomposites have been explored for making complex geometry devices likes screws or 3D porous scaffolds for the repair of bone defects. This review provides an overview of the current development of manufacturing process with synthetic biodegradable poly(α-ester)s reinforced with bioactive fillers for bone tissue engineering applications. Firstly, the properties of poly(α-ester), bioactive fillers, as well as their composites will be defined. Then, the different works based on these biocomposites will be classified according to their manufacturing process. New processing techniques, particularly additive manufacturing processes, open up a new range of possibilities. These techniques have shown the possibility to customize bone implants for each patient and even create scaffolds with a complex structure similar to bone. At the end of this manuscript, a contextualization exercise will be performed to identify the main issues of process/resorbable biocomposites combination identified in the literature and especially for resorbable load-bearing applications.

The Mechanical, Thermal, and Chemical Properties of PLA-Mg Filaments Produced via a Colloidal Route for Fused-Filament Fabrication

The effect of Mg particles on the thermal, chemical, physical, and primarily mechanical properties of 3D-printed PLA/Mg composites is studied in this paper. Recently, new colloidal processing has been proposed to introduce Mg particles into the PLA matrix, which ensures good dispersion of the particles and better thermal properties, allowing for thermal processing routes such as extrusion or 3D printing via fused-filament fabrication. The thermal and physical properties are here studied in 1D single-filament-printed PLA/Mg composites with 0 to 10 wt.% of Mg particles by Differential Scanning Calorimetry (DSC); we analyse the PLA chain modifications produced, the crystallinity fraction, and the different crystalline forms of the PLA after thermal processing. Fourier Transform Infrared Spectroscopy (FTIR) is used to confirm the influence of the PLA/Mg colloidal processing after printing. The mechanical properties are measured with a universal tensile test machine on the 1D single-printed filaments via fused-filament fabrication (FFF); the filaments were naturally aged to stable conditions. Filaments with and without a notch are studied to obtain the materials' tensile strength, elastic modulus, and fracture toughness. Different analytical models to explain the results of the PLA-Mg were studied, in which the minimum values for the interface strength of the PLA-Mg composites were calculated.

Surface Modification of 3D-Printed PCL/BG Composite Scaffolds via Mussel-Inspired Polydopamine and Effective Antibacterial Coatings for Biomedical Applications

A wide variety of composite scaffolds with unique geometry, porosity and pore size can be fabricated with versatile 3D printing techniques. In this work, we fabricated 3D-printed composite scaffolds of polycaprolactone (PCL) incorporating bioactive glass (BG) particles (13-93 and 13-93B3 compositions) by using fused deposition modeling (FDM). The scaffolds were modified with a "mussel-inspired surface coating" to regulate biological properties. The chemical and surface properties of scaffolds were analyzed by Fourier transform infrared spectroscopy (FTIR), contact angle and scanning electron microscopy (SEM). Polydopamine (PDA) surface-modified composite scaffolds exhibited attractive properties. Firstly, after the surface modification, the adhesion of a composite coating based on gelatin incorporated with strontium-doped mesoporous bioactive glass (Sr-MBGNs/gelatin) was significantly improved. In addition, cell attachment and differentiation were promoted, and the antibacterial properties of the scaffolds were increased. Moreover, the bioactivity of these scaffolds was also significantly influenced: a hydroxyapatite layer formed on the scaffold surface after 3 days of immersion in SBF. Our results suggest that the promoting effect of PDA coating on PCL-BG scaffolds leads to improved scaffolds for bone tissue engineering.

3D-Printing for Critical Sized Bone Defects: Current Concepts and Future Directions

The management and definitive treatment of segmental bone defects in the setting of acute trauma, fracture non-union, revision joint arthroplasty, and tumor surgery are challenging clinical problems with no consistently satisfactory solution. Orthopaedic surgeons are developing novel strategies to treat these problems, including three-dimensional (3D) printing combined with growth factors and/or cells. This article reviews the current strategies for management of segmental bone loss in orthopaedic surgery, including graft selection, bone graft substitutes, and operative techniques. Furthermore, we highlight 3D printing as a technology that may serve a major role in the management of segmental defects. The optimization of a 3D-printed scaffold design through printing technique, material selection, and scaffold geometry, as well as biologic additives to enhance bone regeneration and incorporation could change the treatment paradigm for these difficult bone repair problems.

Recent Advances in Multi-Material 3D Printing of Functional Ceramic Devices

In recent years, functional ceramic devices have become smaller, thinner, more refined, and highly integrated, which makes it difficult to realize their rapid prototyping and low-cost manufacturing using traditional processing. As an emerging technology, multi-material 3D printing offers increased complexity and greater freedom in the design of functional ceramic devices because of its unique ability to directly construct arbitrary 3D parts that incorporate multiple material constituents without an intricate process or expensive tools. Here, the latest advances in multi-material 3D printing methods are reviewed, providing a comprehensive study on 3D-printable functional ceramic materials and processes for various functional ceramic devices, including capacitors, multilayer substrates, and microstrip antennas. Furthermore, the key challenges and prospects of multi-material 3D-printed functional ceramic devices are identified, and future directions are discussed.

3D printing of inorganic-biopolymer composites for bone regeneration

In most cases, bone injuries heal without complications, however, there is an increasing number of instances where bone healing needs major clinical intervention. Available treatment options have severe drawbacks, such as donor site morbidity and limited availability for autografting. Bone graft substitutes containing growth factors would be a viable alternative, however they have been associated with dose-related safety concerns and lack control over spatial architecture to anatomically match bone defect sites. 3D printing offers a solution to produce patient specific bone graft substitutes that are customized to the patient bone defect with temporal control over the incorporated therapeutics to maximize their efficacy. Inspired by the natural constitution of bone tissue, composites made of inorganic phases, such as nanosilicate particles, calcium phosphate, and bioactive glasses, combined with biopolymer matrices have been investigated as building blocks for the biofabrication of bone constructs. Besides capturing elements of the bone physiological structure, these inorganic/organic composites can be designed for specific cohesivity, rheological and mechanical properties, while both inorganic and organic constituents contribute to the composite bioactivity. This review provides an overview of 3D printed composite biomaterial-inks for bone tissue engineering. Furthermore, key aspects in biomaterial-ink design, 3D printing techniques, and the building blocks for composite biomaterial-inks are summarized.

3D printing polylactic acid polymer-bioactive glass loaded with bone cement for bone defect in weight-bearing area

The treatment of bone defects in weight-bearing areas is mainly to transplant filling materials into the defect area, to provide immediate and strong support for weight-bearing. At present, the commonly used filling material is bone cement, which can only provide physical support without bone regeneration effect. The long-term stress at the interface may cause the loosening of bone cement. The ideal filling material should provide not only strong mechanical support but also promote bone regeneration. We introduce a 3D printing frame-filling structure in this study. The structure was printed with polylactic acid/bioactive glass as the frame, and bone cement as the filler. In this system, bone cement was used to provide immediate fixation, and the frame provided long-term fixation by promoting osteogenic induction and conduction between the interface. The results showed that the degradation of bioactive glass in the frame promoted osteogenic metabolism, induced M2 polarization of macrophages, and inhibited local inflammatory response. The in vivo study revealed that implantation of the frame-filling structure significantly promoted bone regeneration in the femoral bone defect area of New Zealand white rabbits. For a bone defect in a weight-bearing area, long-term stability could be obtained by bone integration through this frame-filling structure.

3D-Printed PLA-Bioglass Scaffolds with Controllable Calcium Release and MSC Adhesion for Bone Tissue Engineering

Large bone defects are commonly treated by replacement with auto- and allografts, which have substantial drawbacks including limited supply, donor site morbidity, and possible tissue rejection. This study aimed to improve bone defect treatment using a custom-made filament for tissue engineering scaffolds. The filament consists of biodegradable polylactide acid (PLA) and a varying amount (up to 20%) of osteoconductive S53P4 bioglass. By employing an innovative, additive manufacturing technique, scaffolds with optimized physico-mechanical and biological properties were produced. The scaffolds feature adjustable macro- and microporosity (200–2000 µm) with adaptable mechanical properties (83–135 MPa). Additionally, controllable calcium release kinetics (0–0.25 nMol/µL after 24 h), tunable mesenchymal stem cell (MSC) adhesion potential (after 24 h by a factor of 14), and proliferation (after 168 h by a factor of 18) were attained. Microgrooves resulting from the 3D-printing process on the surface act as a nucleus for cell aggregation, thus being a potential cell niche for spheroid formation or possible cell guidance. The scaffold design with its adjustable biomechanics and the bioglass with its antimicrobial properties are of particular importance for the preclinical translation of the results. This study comprehensibly demonstrates the potential of a 3D-printed bioglass composite scaffold for the treatment of critical-sized bone defects.

3D printed gelatin/decellularized bone composite scaffolds for bone tissue engineering: Fabrication, characterization and cytocompatibility study

Three-dimensional (3D) printing technology enables the design of personalized scaffolds with tunable pore size and composition. Combining decellularization and 3D printing techniques provides the opportunity to fabricate scaffolds with high potential to mimic native tissue. The aim of this study is to produce novel decellularized bone extracellular matrix (dbECM)-reinforced composite-scaffold that can be used as a biomaterial for bone tissue engineering. Decellularized bone particles (dbPTs, ∼100 ​μm diameter) were obtained from rabbit femur and used as a reinforcement agent by mixing with gelatin (GEL) in different concentrations. 3D scaffolds were fabricated by using an extrusion-based bioprinter and crosslinking with microbial transglutaminase (mTG) enzyme, followed by freeze-drying to obtain porous structures. Fabricated 3D scaffolds were characterized morphologically, mechanically, and chemically. Furthermore, MC3T3-E1 mouse pre-osteoblast cells were seeded on the dbPTs reinforced GEL scaffolds (GEL/dbPTs) and cultured for 21 days to assess cytocompatibility and cell attachment. We demonstrate the 3D-printability of dbPTs-reinforced GEL hydrogels and the achievement of homogenous distribution of the dbPTs in the whole scaffold structure, as well as bioactivity and cytocompatibility of GEL/dbPTs scaffolds. It was shown that Young's modulus and degradation rate of scaffolds were enhanced with increasing dbPTs content. Multiphoton microscopy imaging displayed the interaction of cells with dbPTs, indicating attachment and proliferation of cells around the particles as well as into the GEL-particle hydrogels. Our results demonstrate that GEL/dbPTs hydrogel formulations have potential for bone tissue engineering.

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.

Can 3D-Printed Bioactive Glasses Be the Future of Bone Tissue Engineering?

According to the Global Burden of Diseases, Injuries, and Risk Factors Study, cases of bone fracture or injury have increased to 33.4% in the past two decades. Bone-related injuries affect both physical and mental health and increase the morbidity rate. Biopolymers, metals, ceramics, and various biomaterials have been used to synthesize bone implants. Among these, bioactive glasses are one of the most biomimetic materials for human bones. They provide good mechanical properties, biocompatibility, and osteointegrative properties. Owing to these properties, various composites of bioactive glasses have been FDA-approved for diverse bone-related and other applications. However, bone defects and bone injuries require customized designs and replacements. Thus, the three-dimensional (3D) printing of bioactive glass composites has the potential to provide customized bone implants. This review highlights the bottlenecks in 3D printing bioactive glass and provides an overview of different types of 3D printing methods for bioactive glass. Furthermore, this review discusses synthetic and natural bioactive glass composites. This review aims to provide information on bioactive glass biomaterials and their potential in bone tissue engineering.

In vitro biomineralization potential in simulated wound fluid and antibacterial efficacy of biologically-active glass nanoparticles containing B2O3/ZnO

In the present study, SiO₂-CaO-B₂O₃-ZnO (SCBZ), SiO₂-CaO-B₂O₃ (SCB), SiO₂-CaO-ZnO (SCZ) and SiO₂-CaO (SC) silicate-based glasses were synthesized by the sol-gel method to elucidate the influence of B₂O₃ and ZnO substitution on glass characteristics aiming to further use in wound healing applications. The amorphous nature, spherical-shaped morphology and nano-sized primary particles of glasses were revealed by XRD and SEM analysis. Moreover, investigating the antibacterial activity of glasses against E.coli and S.aureus bacteria indicated the improved antibacterial properties of SCBZ glass against both bacterial strains compared with SCB and SCZ glasses. Assessment of ion release revealed that the incorporation of zinc induces a more stable glass network with a lower tendency to dissolution contrary to the incorporation of boron, which facilitated the dissolution of glass by the formation of more reactive SiOB and BO bonds. Glasses were immersed in Simulated Wound Fluid (SWF) to predict their mineralization susceptibility. Morphological studies and FTIR analysis showed the formation of cauliflower-like hydroxy-carbonated apatite on the surface of SCB and SC glasses after 14 days. In contrast, the presence of Zn in SCBZ and SCZ glasses inhibited the formation of crystalline apatite and induced the deposition of spherical-shaped amorphous apatite. Our study suggests that the co-incorporation of B and Zn in SCBZ glass make this material a potential multifunctional candidate for accelerating the healing of skin wounds.

3D Printing for Bone-Cartilage Interface Regeneration

Due to the vasculature defects and/or the avascular nature of cartilage, as well as the complex gradients for bone-cartilage interface regeneration and the layered zonal architecture, self-repair of cartilage and subchondral bone is challenging. Currently, the primary osteochondral defect treatment strategies, including artificial joint replacement and autologous and allogeneic bone graft, are limited by their ability to simply repair, rather than induce regeneration of tissues. Meanwhile, over the past two decades, three-dimension (3D) printing technology has achieved admirable advancements in bone and cartilage reconstruction, providing a new strategy for restoring joint function. The advantages of 3D printing hybrid materials include rapid and accurate molding, as well as personalized therapy. However, certain challenges also exist. For instance, 3D printing technology for osteochondral reconstruction must simulate the histological structure of cartilage and subchondral bone, thus, it is necessary to determine the optimal bioink concentrations to maintain mechanical strength and cell viability, while also identifying biomaterials with dual bioactivities capable of simultaneously regenerating cartilage. The study showed that the regeneration of bone-cartilage interface is crucial for the repair of osteochondral defect. In this review, we focus on the significant progress and application of 3D printing technology for bone-cartilage interface regeneration, while also expounding the potential prospects for 3D printing technology and highlighting some of the most significant challenges currently facing this field.

Bioactive Inks Development for Osteochondral Tissue Engineering: A Mini-Review

Nowadays, a prevalent joint disease affecting both cartilage and subchondral bone is osteoarthritis. Osteochondral tissue, a complex tissue unit, exhibited limited self-renewal potential. Furthermore, its gradient properties, including mechanical property, bio-compositions, and cellular behaviors, present a challenge in repairing and regenerating damaged osteochondral tissues. Here, tissue engineering and translational medicine development using bioprinting technology provided a promising strategy for osteochondral tissue repair. In this regard, personalized stratified scaffolds, which play an influential role in osteochondral regeneration, can provide potential treatment options in early-stage osteoarthritis to delay or avoid the use of joint replacements. Accordingly, bioactive scaffolds with possible integration with surrounding tissue and controlling inflammatory responses have promising future tissue engineering perspectives. This minireview focuses on introducing biologically active inks for bioprinting the hierarchical scaffolds, containing growth factors and bioactive materials for 3D printing of regenerative osteochondral substitutes.

Chitosan-coated pore wall polycaprolactone three-dimensional porous scaffolds fabricated by porogen leaching method for bone tissue engineering: a comparative study on blending technique to fabricate scaffolds

One of the significant challenges in the fabrication of scaffolds for tissue engineering lies in the direct interaction of bioactive agents with cells in the scaffolds matrix, which curbs the effectiveness of bioactive agents resulting in diminished cell recognition and attachment ability of the scaffolds. Here, three-dimensional porous scaffolds were fabricated using polycaprolactone (PCL) and chitosan, by two approaches, i.e., blending and surface coating to compare their overall effectiveness. Blended scaffolds (Chi-PCL) were compared with the scaffolds fabricated using surface coating technique, where chitosan was coated on the pore wall of PCL scaffolds (C-PCL). The C-PCL exhibited a collective improvement in bioactivities of the stem cell on the scaffold, because of the cell compatible environment provided by the presence of chitosan over the scaffolds interface. The C-PCL showed the enhanced cell attachment and proliferation behavior of the scaffolds along with two-fold increase in hemolysis compatibility compared to Chi-PCL. Furthermore, the compression strength in C-PCL increased by 24.52% and 8.62% increase in total percentage porosity compared to Chi-PCL was attained. Along with this, all the bone markers showed significant upregulation in C-PCL scaffolds, which supported the surface coating technique over the conventional methods, even though the pore size of C-PCL was compromised by 19.98% compared with Chi-PCL.

Biological and bioactivity assessment of dextran nanocomposite hydrogel for bone regeneration

Insufficient biological and bioactive properties of dextran hydrogels limit their applications as promising scaffolds for tissue engineering. We developed nanocomposite dextran hydrogels comprised of bioactive glass (nBGC: 64% SiO2, 31% CaO, 5% P₂O₅) nanoparticles with an average particle size of 77 nm using a chemical crosslinking of dextran chains to form 3D hydrogel networks. In the current study; bioactivity of the obtained nanocomposite hydrogels was evaluated through the formation of apatite crystal structures after the incubation in simulated body fluid (SBF) at various submersion periods and nBGC content. The scanning electron microscopy (SEM) micrographs represented an enhanced hydroxyapatite formation on the cross section of nanocomposite comprising of nBGC content from 2 to 8 (% by wt). Biomineralization results of Dex-8 (% by wt) composite during 7, 14 and 28 days immersion indicated the apatite layer formation and the growth of apatite crystal size on the surface and cross section of the nanocomposite. Moreover, MTT assessments indicated that human osteosarcoma cells (SaOS-2) were able to adhere and spread within the dextran hydrogels reinforced with the bioactive glass nanoparticles. With regard to enhanced bioactivity and biocompatibility, the developed dextran-nBGC hydrogel could be considered as a suitable candidate for bone tissue engineering application.

The Challenge of 3D Bioprinting of Composite Natural Polymers PLA/Bioglass: Trends and Benefits in Cleft Palate Surgery

Cleft lip and palate is the fourth most common congenital malformation. Its prevalence is about 1 in 750 to 1 in 2000 live births. The consequences of this malformation are major: maxillary growth deficit, unaesthetic appearance, phonation disorders, difficulty in eating, and psycho-social disorders. Cleft palate repair establishes the division between the oral and nasal cavities. The alveolar bone graft is a key step. Different sites of autogenous bone harvesting are used, the most common being the iliac crest. Nevertheless, the large number of complications associated with harvesting has led to the use of substitute biomaterials. Bioactive glasses, discovered in 1969, are a group of synthetic silica-based materials with bone-bonding properties. Although 45S5 granular composition is commonly used in bone surgery to repair critical defects, it is only rarely used in the repair of cleft palates because this galenic form is only moderately adapted. However, advances in bone tissue engineering allow the shaping of three-dimensional scaffolds, which support colonization by host cells. Recent advances in computer-aided design/computer-aided manufacturing (CAD/CAM) have even led to the 3D printing of scaffolds combining 45S5 bioglass with a natural and biocompatible poly-lactic acid matrix. The shape of the parts is customized and adapted to the particular shape of the critical bone defects. The objective of this literature review is to highlight the particularities of alveolar defects subsequent to facial clefts, then to detail the characteristics of the materials and technologies used to elaborate 3D matrices by bioprinting. Finally, we will explore research directions regarding their use in reconstructive surgery of cleft palates.

Biomaterials and nanomedicine for bone regeneration: Progress and future prospects

Bone defects pose a heavy burden on patients, orthopedic surgeons, and public health resources. Various pathological conditions cause bone defects including trauma, tumors, inflammation, osteoporosis, and so forth. Auto- and allograft transplantation have been developed as the most commonly used clinic treatment methods, among which autologous bone grafts are the golden standard. Yet the repair of bone defects, especially large-volume defects in the geriatric population or those complicated with systemic disease, is still a challenge for regenerative medicine from the clinical perspective. The fast development of biomaterials and nanomedicine favors the emergence and promotion of efficient bone regeneration therapies. In this review, we briefly summarize the progress of novel biomaterial and nanomedical approaches to bone regeneration and then discuss the current challenges that still hinder their clinical applications in treating bone defects.

3D Printed Composite Scaffolds in Bone Tissue Engineering: A systematic review

OBJECTIVE

This study aimed to analyze the effect of fabrication factors on both biological and physico-chemical features of 3-dimensional (3D) printed composite scaffolds.

METHOD

Electronic search was done according to the PRISMA guideline in PubMed and Scopus databases limited to English articles published until May 2021.Studies in which composite scaffolds were fabricated through computer-aided design and computer-aided manufacturing (CAD-CAM)-based methods were included.Articles regarding the features of the scaffolds fabricated through indirect techniques were excluded.

RESULTS

Full text of 121 studies were reviewed, and 69 met the inclusion criteria. According to analyzed studies, PCL and HA were the most commonly used polymer and ceramic,respectively. Besides,the Solvent-based technique was the most commonly used composition technique, which enabled preparing blends with high concentrations of ceramic materials. The most common fabrication method used in the included studies was Fused deposition modeling (FDM).The addition of bio-ceramics enhanced the mechanical features and the biological behaviors of the printed scaffolds in a ratio-dependent manner. However,studies that analyzed the effect of ceramic weight ratio showed that scaffolds with the highest ceramic content did not necessarily possess the optimal biological and non-biological features.

CONCLUSION

The biological and physico-chemical behaviors of the scaffold can be affected by pre-printing factors, including utilized materials, composition techniques, and fabrication methods. Fabricating scaffolds with high mineral content as of the natural bone may not provide the optimal condition for bone formation. Therefore, it is recommended that future studies compare the efficiency of different kinds of biomaterials rather than different weight ratios of one type.

A Composite Lactide-Mineral 3D-Printed Scaffold for Bone Repair and Regeneration

Orthopedic tumor resection, trauma, or degenerative disease surgeries can result in large bone defects and often require bone grafting. However, standard autologous bone grafting has been associated with donor site morbidity and/or limited quantity. As an alternate, allografts with or without metallic or polyether-etherketone have been used as grafting substitutes. However, these may have drawbacks as well, including stress shielding, pseudarthrosis, disease-transmission, and infection. There is therefore a need for alternative bone substitutes, such as the use of mechanically compliant three-dimensional (3D)-printed scaffolds. Several off-the-shelf materials are available for low-cost fused deposition 3D printing such as polylactic acid (PLA) and polycaprolactone (PCL). We have previously described the feasibility of 3D-printed PLA scaffolds to support cell activity and extracellular matrix deposition. In this study, we investigate two medical-grade filaments consistent with specifications found in American Society for Testing and Materials (ASTM) standard for semi-crystalline polylactide polymers for surgical implants, a pure polymer (100M) and a copolymeric material (7415) for their cytocompatibility and suitability in bone tissue engineering. Moreover, we assessed the impact on osteo-inductive properties with the addition of beta-tricalcium phosphate (β-TCP) minerals and assessed their mechanical properties. 100M and 7415 scaffolds with the additive β-TCP demonstrated superior mesenchymal stem cells (MSCs) differentiation detected via increased alkaline phosphatase activity (6-fold and 1.5-fold, respectively) and mineralized matrix deposition (14-fold and 5-fold, respectively) in vitro. Furthermore, we evaluated in vivo compatibility, biosafety and bone repair potential in a rat femur window defect model. 100M+β -TCP implants displayed a positive biosafety profile and showed significantly enhanced new bone formation compared to 100M implants evidenced by μCT (39 versus 25% bone volume/tissue volume ratio) and histological analysis 6 weeks post-implantation. These scaffolds are encouraging composite biomaterials for repairing bone applications with a great potential for clinical translation. Further analyses are required with appropriate evaluation in a larger critical-sized defect animal model with long-term follow-up.

Composite Scaffolds for Bone Tissue Regeneration Based on PCL and Mg-Containing Bioactive Glasses

Simple Summary

Polycaprolactone (PCL) is a bioresorbable and biocompatible polymer that has been widely used in long-term implants. However, when it comes to regenerative medicine, PCL suffers from some shortcomings such as a slow degradation rate, poor mechanical properties, and low cell adhesion. The incorporation of ceramics such as bioactive glasses into the PCL matrix has yielded a class of hybrid biomaterials with remarkably improved mechanical properties, controllable degradation rates, and enhanced bioactivity, which are suitable for bone tissue engineering. The use of conventional approaches (such as solvent casting and particulate leaching, phase separation, electrospinning, freeze drying, etc.) in realizing these composite scaffolds strongly affects the control of both the internal and the external architecture of scaffolds, including pore size, pore morphology, and overall structure porosity. Accordingly, 3D printing was used in this study because of the benefits offered over conventional methods, such as high flexibility in shape and size, high reproducibility, capabilities of precise control over internal architecture down to the microscale level, and a customized design that can be tailored to specific patient needs. The optimization of the scaffold structure was previously investigated in terms of architecture through the combination of the Taguchi method and CAD drawing, and, in this study, it was investigated by varying the composition of the composite material.

Abstract

Polycaprolactone (PCL) is widely used in additive manufacturing for the construction of scaffolds for tissue engineering because of its good bioresorbability, biocompatibility, and processability. Nevertheless, its use is limited by its inadequate mechanical support, slow degradation rate and the lack of bioactivity and ability to induce cell adhesion and, thus, bone tissue regeneration. In this study, we fabricated 3D PCL scaffolds reinforced with a novel Mg-doped bioactive glass (Mg-BG) characterized by good mechanical properties and biological reactivity. An optimization of the printing parameters and scaffold fabrication was performed; furthermore, an extensive microtopography characterization by scanning electron microscopy and atomic force microscopy was carried out. Nano-indentation tests accounted for the mechanical properties of the scaffolds, whereas SBF tests and cytotoxicity tests using human bone-marrow-derived mesenchymal stem cells (BM-MSCs) were performed to evaluate the bioactivity and in vitro viability. Our results showed that a 50/50 wt% of the polymer-to-glass ratio provides scaffolds with a dense and homogeneous distribution of Mg-BG particles at the surface and roughness twice that of pure PCL scaffolds. Compared to pure PCL (hardness H = 35 ± 2 MPa and Young’s elastic modulus E = 0.80 ± 0.05 GPa), the 50/50 wt% formulation showed H = 52 ± 11 MPa and E = 2.0 ± 0.2 GPa, hence, it was close to those of trabecular bone. The high level of biocompatibility, bioactivity, and cell adhesion encourages the use of the composite PCL/Mg-BG scaffolds in promoting cell viability and supporting mechanical loading in the host trabecular bone.

Boron nitride nanotube scaffolds: emergence of a new era in regenerative medicine

Tissue engineering scaffolds have transformed from passive geometrical supports for cell adhesion, extension and proliferation to active, dynamic systems that can in addition, trigger functional maturation of the cells in response to external stimuli. Such 'smart' scaffolds require the incorporation of active response elements that can respond to internal or external stimuli. One of the key elements that direct the cell fate processes is mechanical stress. Different cells respond to various types and magnitudes of mechanical stresses. The incorporation of a pressure-sensitive element in the tissue engineering scaffold therefore, will aid in tuning the cell response to the desired levels. Boron nitride nanotubes (BNNTs) are analogous to carbon nanotubes and have attracted considerable attention due to their unique amalgamation of chemical inertness, piezoelectric property, biocompatibility and, thermal and mechanical stability. Incorporation of BNNTs in scaffolds confers them with piezoelectric property that can be used to stimulate the cells seeded on them. Biorecognition and solubilization of BNNTs can be engineered through surface functionalization with different biomolecules. Over the years, the importance of BNNT has grown in the realm of healthcare nanotechnology. This review discusses the salient properties of BNNTs, the influence of functionalization on theirin vitroandin vivobiocompatibility, and the uniqueness of BNNT-incorporated tissue engineering scaffolds.

Hexagonal pore geometry and the presence of hydroxyapatite enhance deposition of mineralized bone matrix on additively manufactured polylactic acid scaffolds

Additive manufacturing (AM) has revolutionized the design of regenerative scaffolds for orthopaedic applications, enabling customizable geometric designs and material compositions that mimic bone. However, the available evidence is contradictory with respect to which geometric designs and material compositions are optimal. There is a lack of studies that systematically compare different pore sizes and geometries in conjunction with the presence or absence of calcium phosphates. We therefore evaluated the physicochemical and biological properties of additively manufactured scaffolds based on polylactic acid (PLA) in combination with hydroxyapatite (HA). HA was either incorporated in the polymeric matrix or introduced as a coating, yielding 15 and 2% wt., respectively. Pore sizes of the scaffolds varied between 200 and 450 μm and were shaped either triangularly or hexagonally. All scaffolds supported the adhesion, proliferation and differentiation of both primary mouse osteoblasts and osteosarcoma cells up to four weeks, with only small differences in the production of alkaline phosphatase (ALP) between cells grown on different pore geometries and material compositions. However, mineralization of the PLA scaffolds was substantially enhanced in the presence of HA, either embedded in the PLA matrix or as a coating at the surface level, and by larger hexagonal pores. In conclusion, customized HA/PLA composite porous scaffolds intended for the repair of critical size bone defects were obtained by a cost-effective AM method. Our findings indicate that the analysis of osteoblast adhesion and differentiation on experimental scaffolds alone is inconclusive without the assessment of mineralization, and the effects of geometry and composition on bone matrix deposition must be carefully considered in order to understand the regenerative potential of experimental scaffolds.

Materials and Manufacturing Techniques for Polymeric and Ceramic Scaffolds Used in Implant Dentistry

Preventive and regenerative techniques have been suggested to minimize the aesthetic and functional effects caused by intraoral bone defects, enabling the installation of dental implants. Among them, porous three-dimensional structures (scaffolds) composed mainly of bioabsorbable ceramics, such as hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) stand out for reducing the use of autogenous, homogeneous, and xenogenous bone grafts and their unwanted effects. In order to stimulate bone formation, biodegradable polymers such as cellulose, collagen, glycosaminoglycans, polylactic acid (PLA), polyvinyl alcohol (PVA), poly-ε-caprolactone (PCL), polyglycolic acid (PGA), polyhydroxylbutyrate (PHB), polypropylenofumarate (PPF), polylactic-co-glycolic acid (PLGA), and poly L-co-D, L lactic acid (PLDLA) have also been studied. More recently, hybrid scaffolds can combine the tunable macro/microporosity and osteoinductive properties of ceramic materials with the chemical/physical properties of biodegradable polymers. Various methods are suggested for the manufacture of scaffolds with adequate porosity, such as conventional and additive manufacturing techniques and, more recently, 3D and 4D printing. The purpose of this manuscript is to review features concerning biomaterials, scaffolds macro and microstructure, fabrication techniques, as well as the potential interaction of the scaffolds with the human body.

Applications of 3D printed bone tissue engineering scaffolds in the stem cell field

Due to traffic accidents, injuries, burns, congenital malformations and other reasons, a large number of patients with tissue or organ defects need urgent treatment every year. The shortage of donors, graft rejection and other problems cause a deficient supply for organ and tissue replacement, repair and regeneration of patients, so regenerative medicine came into being. Stem cell therapy plays an important role in the field of regenerative medicine, but it is difficult to fill large tissue defects by injection alone. The scientists combine three-dimensional (3D) printed bone tissue engineering scaffolds with stem cells to achieve the desired effect. These scaffolds can mimic the extracellular matrix (ECM), bone and cartilage, and eventually form functional tissues or organs by providing structural support and promoting attachment, proliferation and differentiation. This paper mainly discussed the applications of 3D printed bone tissue engineering scaffolds in stem cell regenerative medicine. The application examples of different 3D printing technologies and different raw materials are introduced and compared. Then we discuss the superiority of 3D printing technology over traditional methods, put forward some problems and limitations, and look forward to the future.

A Polymer for Application as a Matrix Phase in a Concept of In Situ Curable Bioresorbable Bioactive Load-Bearing Continuous Fiber Reinforced Composite Fracture Fixation Plates

The use of bioresorbable fracture fixation plates made of aliphatic polyesters have good potential due to good biocompatibility, reduced risk of stress-shielding, and eliminated need for plate removal. However, polyesters are ductile, and their handling properties are limited. We suggested an alternative, PLAMA (PolyLActide functionalized with diMethAcrylate), for the use as the matrix phase for the novel concept of the in situ curable bioresorbable load-bearing composite plate to reduce the limitations of conventional polyesters. The purpose was to obtain a preliminary understanding of the chemical and physical properties and the biological safety of PLAMA from the prospective of the novel concept. Modifications with different molecular masses (PLAMA-500 and PLAMA-1000) were synthesized. The efficiency of curing was assessed by the degree of convergence (DC). The mechanical properties were obtained by tensile test and thermomechanical analysis. The bioresorbability was investigated by immersion in simulated body fluid. The biocompatibility was studied in cell morphology and viability tests. PLAMA-500 showed better DC and mechanical properties, and slower bioresorbability than PLAMA-1000. Both did not prevent proliferation and normal morphological development of cells. We concluded that PLAMA-500 has potential for the use as the matrix material for bioresorbable load-bearing composite fracture fixation plates.

Porous bioactive glass micro- and nanospheres with controlled morphology: developments, properties and emerging biomedical applications

In recent years, porous bioactive glass micro/nanospheres (PBGSs) have emerged as attractive biomaterials in various biomedical applications where such engineered particles provide suitable functions, from tissue engineering to drug delivery. The design and synthesis of PBGSs with controllable particle size and pore structure are critical for such applications. PBGSs have been successfully synthesized using melt-quenching and sol-gel based methods. The morphology of PBGSs is controllable by tuning the processing parameters and precursor characteristics during the synthesis. In this comprehensive review on PBGSs, we first overview the synthesis approaches for PBGSs, including both melt-quenching and sol-gel based strategies. Sol-gel processing is the primary technology used to produce PBGSs, allowing for control over the chemical compositions and pore structure of particles. Particularly, the influence of pore-forming templates on the morphology of PBGSs is highlighted. Recent progress in the sol-gel synthesis of PBGSs with sophisticated pore structures (e.g., hollow mesoporous, dendritic fibrous mesoporous) is also covered. The challenges regarding the control of particle morphology, including the influence of metal ion precursors and pore expansion, are discussed in detail. We also highlight the recent achievements of PBGSs in a number of biomedical applications, including bone tissue regeneration, wound healing, therapeutic agent delivery, bioimaging, and cancer therapy. Finally, we conclude with our perspectives on the directions of future research based on identified challenges and potential new developments and applications of PBGSs.