Tuning mechanical reinforcement and bioactivity of 3D printed ternary nanocomposites by interfacial peptide-polymer conjugates

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

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

Rapid Prototyping Technologies: 3D Printing Applied in Medicine

Three-dimensional printing technology has been used for more than three decades in many industries, including the automotive and aerospace industries. So far, the use of this technology in medicine has been limited only to 3D printing of anatomical models for educational and training purposes, which is due to the insufficient functional properties of the materials used in the process. Only recent advances in the development of innovative materials have resulted in the flourishing of the use of 3D printing in medicine and pharmacy. Currently, additive manufacturing technology is widely used in clinical fields. Rapid development can be observed in the design of implants and prostheses, the creation of biomedical models tailored to the needs of the patient and the bioprinting of tissues and living scaffolds for regenerative medicine. The purpose of this review is to characterize the most popular 3D printing techniques.

Polysaccharide-based biomaterials in a journey from 3D to 4D printing

3D printing is a state-of-the-art technology for the fabrication of biomaterials with myriad applications in translational medicine. After stimuli-responsive properties were introduced to 3D printing (known as 4D printing), intelligent biomaterials with shape configuration time-dependent character have been developed. Polysaccharides are biodegradable polymers sensitive to several physical, chemical, and biological stimuli, suited for 3D and 4D printing. On the other hand, engineering of mechanical strength and printability of polysaccharide-based scaffolds along with their aneural, avascular, and poor metabolic characteristics need to be optimized varying printing parameters. Multiple disciplines such as biomedicine, chemistry, materials, and computer sciences should be integrated to achieve multipurpose printable biomaterials. In this work, 3D and 4D printing technologies are briefly compared, summarizing the literature on biomaterials engineering though printing techniques, and highlighting different challenges associated with 3D/4D printing, as well as the role of polysaccharides in the technological shift from 3D to 4D printing for translational medicine.

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.

Hybrid biofabrication of 3D osteoconductive constructs comprising Mg-based nanocomposites and cell-laden bioinks for bone repair

Tissue engineering approaches for bone repair have rapidly evolved due to the development of novel biofabrication technologies, providing an opportunity to fabricate anatomically-accurate living implants with precise placement of specific cell types. However, limited availability of biomaterial inks, that can be 3D-printed with high resolution, while providing high structural support and the potential to direct cell differentiation and maturation towards the osteogenic phenotype, remains an ongoing challenge. Aiming towards a multifunctional biomaterial ink with high physical stability and biological functionality, this work describes the development of a nanocomposite biomaterial ink (Mg-PCL) comprising of magnesium hydroxide nanoparticles (Mg) and polycaprolactone (PCL) thermoplastic for 3D printing of strong and bioactive bone regenerative scaffolds. We characterised the Mg nanoparticle system and systematically investigated the cytotoxic and osteogenic effects of Mg supplementation to human mesenchymal stromal cells (hMSCs) 2D-cultures. Next, we prepared Mg-PCL biomaterial ink using a solvent casting method, and studied the effect of Mg over mechanical properties, printability and scaffold degradation. Furthermore, we delivered MSCs within Mg-PCL scaffolds using a gelatin-methacryloyl (GelMA) matrix, and evaluated the effect of Mg over cell viability and osteogenic differentiation. Nanocomposite Mg-PCL could be printed with high fidelity at 20 wt% of Mg content, and generated a mechanical reinforcement between 30%-400% depending on the construct internal geometry. We show that Mg-PCL degrades faster than standard PCL in an accelerated-degradation assay, which has positive implications towards in vivo implant degradation and bone regeneration. Mg-PCL did not affect MSCs viability, but enhanced osteogenic differentiation and bone-specific matrix deposition, as demonstrated by higher ALP/DNA levels and Alizarin Red calcium staining. Finally, we present proof of concept of Mg-PCL being utilised in combination with a bone-specific bioink (Sr-GelMA) in a coordinated-extrusion bioprinting strategy for fabrication of hybrid constructs with high stability and synergistic biological functionality. Mg-PCL further enhanced the osteogenic differentiation of encapsulated MSCs and supported bone ECM deposition within the bioink component of the hybrid construct, evidenced by mineralised nodule formation, osteocalcin (OCN) and collagen type-I (Col I) expression within the bioink filaments. This study demonstrated that magnesium-based nanocomposite bioink material optimised for extrusion-based 3D printing of bone regenerative scaffolds provide enhanced mechanical stability and bone-related bioactivity with promising potential for skeletal tissue regeneration.

Converging functionality: Strategies for 3D hybrid-construct biofabrication and the role of composite biomaterials for skeletal regeneration

The evolution of additive manufacturing (AM) technologies, biomaterial development and our increasing understanding of cell biology has created enormous potential for the development of personalized regenerative therapies. In the context of skeletal tissue engineering, physical and biological demands play key roles towards successful construct implantation and the achievement of bone, cartilage and blood vessel tissue formation. Nevertheless, meeting such physical and biological demands to mimic the complexity of human tissues and their functionality is still a significant ongoing challenge. Recent studies have demonstrated that combination of AM technologies and advanced biomaterials has great potential towards skeletal tissue engineering. This review aims to analyze how the most prominent technologies and discoveries in the field converge towards the development of advanced constructs for skeletal regeneration. Particular attention is placed on hybrid biofabrication strategies, combining bioinks for cell delivery with biomaterial inks providing physical support. Hybrid biofabrication has been the focus of recent emerging strategies, however there has been limited review and analysis of these techniques and the challenges involved. Furthermore, we have identified that there are multiple hybrid fabrication strategies, here we present a category system where each strategy is reviewed highlighting their distinct advantages, challenges and potential applications. In addition, bioinks and biomaterial inks are the main components of the hybrid biofabrication strategies, where it is recognized that such platforms still lack optimal physical and biological functionality. Thus, this review also explores the development of composite materials specifically targeting the enhancement of physical and biological functionality towards improved skeletal tissue engineering. STATEMENT OF SIGNIFICANCE: Biofabrication strategies capable of recreating the complexity of native tissues could open new clinical possibilities towards patient-specific regenerative therapies and disease models. Several reviews target the existing additive manufacturing (AM) technologies that may be utilised for biomedical purposes. However, this work presents a unique perspective, describing how such AM technologies have been recently translated towards hybrid fabrication strategies, targeting the fabrication of constructs with converging physical and biological properties. Furthermore, we address composite bioinks and biomaterial inks that have been engineered to overcome traditional limitations, and might be applied to the hybrid fabrication strategies outlined. This work offers ample perspectives and insights into the current and future challenges for the fabrication of skeletal tissues aiming towards clinical and biomedical applications.

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

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

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.

Bioinspired multifunctional adhesive system for next generation bio-additively designed dental restorations

Resin-based composite has overtaken dental amalgam as the most popular material for the repair of lost or damaged tooth structure. In spite of the popularity, the average composite lifetime is about half that of amalgam restorations. The leading cause of composite-restoration failure is decay at the margin where the adhesive is applied. The adhesive is intended to seal the composite/tooth interface, but the adhesive seal to dentin is fragile and readily degraded by acids, enzymes and other oral fluids. The inherent weakness of this material system is attributable to several factors including the lack of antimicrobial properties, remineralization capabilities and durable mechanical performance - elements that are central to the integrity of the adhesive/dentin (a/d) interfacial seal. Our approach to this problem offers a transition from a hybrid to a biohybrid structure. Discrete peptides are tethered to polymers to provide multi-bio-functional adhesive formulations that simultaneously achieve antimicrobial and remineralization properties. The bio-additive materials design combines several functional properties with the goal of providing an adhesive that will serve as a durable barrier to recurrent decay at the composite/tooth interface. This article provides an overview of our multi-faceted approach which uses peptides tethered to polymers and new polymer chemistries to achieve the next generation adhesive system - an adhesive that provides antimicrobial properties, repair of defective dentin and enhanced mechanical performance.

3D-printed cryomilled poly(ε-caprolactone)/graphene composite scaffolds for bone tissue regeneration

In this study, composite scaffolds based on poly(caprolactone) (PCL) and non-covalently functionalized few-layer graphene (FLG) were manufactured by an extrusion-based system for the first time. For that, functionalized FLG powder was obtained through the evaporation of a functionalized FLG aqueous suspension prepared from a graphite precursor. Cryomilling was shown to be an efficient mixing method, producing a homogeneous dispersion of FLG particles onto the PCL polymeric matrix. Thereafter, fused deposition modeling (FDM) was used to print 3D scaffolds and their morphology, thermal, biodegradability, mechanical, and cytotoxicity properties were analysed. The presence of functionalized FLG demonstrated to induce slight changes in the microstructure of the scaffold, did not affect the thermal stability and enhanced significantly the compressive modulus. The composite scaffolds presented a porosity of around 40% and a mean pore size in the range of 300 μm. The cell viability and proliferation of SaOs-2 cells were assessed and the results showed good cell viability and long-term proliferation onto produced composite scaffolds. Therefore, these new FLG/PCL scaffolds comprised adequate morphological, thermal, mechanical, and biological properties to be used in bone tissue regeneration.