Fabrication and properties of PLA/nano-HA composite scaffolds with balanced mechanical properties and biological functions for bone tissue engineering application

A Bioactive Degradable Composite Bone Cement Based on Calcium Sulfate and Magnesium Polyphosphate

Calcium sulfate bone cement (CSC) is extensively used as a bone repair material due to its ability to self-solidify, degradability, and osteogenic ability. However, the fast degradation, low mechanical strength, and insufficient biological activity limit its application. This study used magnesium polyphosphate (MPP) and constructed a composite bone cement composed of calcium sulfate (CS), MPP, tricalcium silicate (C3S), and plasticizer hydroxypropyl methylcellulose (HPMC). The optimized CS/MPP/C3S composite bone cement has a suitable setting time of approximately 15.0 min, a compressive strength of 26.6 MPa, and an injectability of about 93%. The CS/MPP/C3S composite bone cement has excellent biocompatibility and osteogenic capabilities; our results showed that cell proliferation is up to 114% compared with the control after 5 days. After 14 days, the expression levels of osteogenic-related genes, including Runx2, BMP2, OCN, OPN, and COL-1, are about 1.8, 2.8, 2.5, 2.2, and 2.2 times higher than those of the control, respectively, while the alkaline phosphatase activity is about 1.7 times higher. Therefore, the CS/MPP/C3S composite bone cement overcomes the limitations of CSC and has more effective potential in bone repair.

Engineering innovations in medicine and biology: Revolutionizing patient care through mechanical solutions

The overlap between mechanical engineering and medicine is expanding more and more over the years. Engineers are now using their expertise to design and create functional biomaterials and are continually collaborating with physicians to improve patient health. In this review, we explore the state of scientific knowledge in the areas of biomaterials, biomechanics, nanomechanics, and computational fluid dynamics (CFD) in relation to the pharmaceutical and medical industry. Focusing on current research and breakthroughs, we provide an overview of how these fields are being used to create new technologies for medical treatments of human patients. Barriers and constraints in these fields, as well as ways to overcome them, are also described in this review. Finally, the potential for future advances in biomaterials to fundamentally change the current approach to medicine and biology is also discussed.

Achieving the ideal balance between biological and mechanical requirements in composite bone scaffolds through a voxel-based approach

Achieving successful bone regeneration necessitates the design of scaffolds that meet diverse biological and mechanical requirements, often leading to conflicts in the design parameters. A key conflict arises between scaffold porosity and stiffness. Increasing porosity facilitates cell infiltration and nutrient exchange, promoting bone regeneration. However, higher porosity compromises scaffold stiffness, which is crucial for providing structural support in the defective region. Furthermore, appropriate scaffold stiffness is crucial for preventing stress shielding. Conventional geometry-based design methods utilizing single-phase materials have limited flexibility in resolving such conflicts. To address this challenge, we propose a voxel-based method for designing composite scaffolds composed of hydroxyapatite (HA) and polylactic acid (PLA). Our strategy involves first satisfying primary biological requirements by selecting appropriate porosity, pore shape, and size. Subsequently, scaffold stiffness requirements are met by selecting suitable phase materials and tuning their contents. The study demonstrates that the voxel-based approach effectively balances both biological and mechanical requirements in scaffold design. This method addresses the limitations of traditional designs by achieving an optimal balance between porosity and stiffness, which is crucial for scaffold performance in biomedical applications. Moreover, the scaffolds designed using this method can be manufactured using voxel-based 3D printing technology, which is emerging in the field. Future advancements in voxel-based 3D printing technology will further enhance the feasibility and practicality of this approach for bone tissue engineering applications.

Osseointegration enhancement by controlling dispersion state of carbonate apatite in polylactic acid implant

Osteoconductive ceramics (OCs) are often used to endow polylactic acid (PLA) with osseointegration ability. Conventionally, OC powder is dispersed in PLA. However, considering cell attachment to the implant, OCs may be more favorable when they exist in the form of aggregations, such as granules, and are larger than the cells rather than being dispersed like a powder. In this study, to clarify the effects of the dispersion state of OCs on the osseointegration ability, carbonate apatite (CAp), a bone mineral analog that is osteoconductive and bioresorbable, powder-PLA (P-PLA), and CAp granule-PLA (G-PLA) composite implants were fabricated via thermal pressing. The powder and granule sizes of CAp were approximately 1 and 300-600 µm, respectively. G-PLA exhibited a higher water wettability and released calcium and phosphate ions faster than P-PLA. When cylindrical G-PLA, P-PLA, and PLA were implanted in rabbit tibial bone defects, G-PLA promoted bone maturation compared to P-PLA and pure PLA. Furthermore, G-PLA bonded directly to the host bone, whereas P-PLA bonded across the osteoid layers. Consequently, the bone-to-implant contact of G-PLA was 1.8- and 5.6-fold higher than those of P-PLA and PLA, respectively. Furthermore, the adhesive shear strength of G-PLA was 1.9- and 3.0-fold higher than those of P-PLA and PLA, respectively. Thus, G-PLA achieved earlier and stronger osseointegration than P-PLA or PLA. The findings of this study highlight the significance of the state of dispersion of OCs in implants as a novel strategy for material development.

Contribution to Knowledge on Bioapatites: Does Mg Level Reflect the Organic Matter and Water Contents of Enamel?

The matter constituting the enamels of four types of organisms was studied. The variability of the ions was presented in molar units. It was proven that the changes in water contents of the enamel are significantly positively related to changes in Mg; inversely, there is also a strong connection with changes in Ca and P, the main components of bioapatite. The variability in the organic matter has the same strong and positive characteristics and is also coupled with changes in Mg contents. Amelogenins in organic matter, which synthesize enamel rods, likely have a role in adjusting the amount of Mg, thus establishing the amount of organic matter and water in the whole enamel; this adjustment occurs through an unknown mechanism. Ca, P, Mg, and Cl ions, as well as organic matter and water, participate in the main circulation cycle of bioapatites. The selection of variations in the composition of bioapatite occurs only along particular trajectories, where the energy of transformation linearly depends on the following factors: changes in the crystallographic d parameter; the increase in the volume, V, of the crystallographic cell; the momentum transfer, which is indirectly expressed by ΔsinΘ value. To our knowledge, these findings are novel in the literature. The obtained results indicate the different chemical and crystallographic affinities of the enamels of selected animals to the human ones. This is essential when animal bioapatites are transformed into dentistic or medical substitutes for the hard tissues. Moreover, the role of Mg is shown to control the amount of water in the apatite and in detecting organic matter in the enamels.

Tetracalcium phosphate/polycaprolactone composite scaffold: Mechanical reinforcement, biodegradability regulation and bioactivity induction

Polycaprolactone (PCL) is considered a potential biomaterial due to its good biocompatibility, but its slow degradability and insufficient mechanical properties limit its wide application in bone tissue engineering. Tetracalcium phosphate's (TTCP) good degradability and inherent high stiffness are expected to compensate for the aforementioned defects of PCL and endow it with good biological activity. This goal of this study was to obtain bioactive PCL composite scaffolds with tuneable degradation properties and good mechanical strength via selective laser sintering technology (SLS). Composite porous scaffolds with TTCP contents of 0%, 5%, 10%, 15%, 20%, and 25% were prepared, and the experimental results showed that the addition of TTCP significantly improved the mechanical properties of the scaffold. Notably, the tensile strength of the composite scaffold with 20% TTCP content reached 15.2 MPa, which was 2.9 times that of pure PCL, and the best flexural strength was found in the scaffold with 15% TTCP content (4.7 MPa). More importantly, the introduced TTCP not only achieved the effective pH regulation of the soaking solution and the promotion of biodegradation, but also provided the scaffold with good bioactivity and biocompatibility.

Biocomposites containing poly(lactic acid) and chitosan for 3D printing - Assessment of mechanical, antibacterial and in vitro biodegradability properties

New bone repair materials are needed for treatment of trauma- and disease-related skeletal defects as they still represent a major challenge in clinical practice. Additionally, new strategies are required to combat orthopedic device-related infections (ODRI), given the rising incidence of total joint replacement and fracture fixation surgeries in increasingly elderly populations. Recently, the convergence of additive manufacturing (AM) and bone tissue engineering (BTE) has facilitated the development of bone healthcare to achieve personalized three-dimensional (3D) scaffolds. This study focused on the development of a 3D printable bone repair material, based on the biopolymers poly(lactic acid) (PLA) and chitosan. Two different types of PLA and chitosan differing in their molecular weight (MW) were explored. The novel feature of this research was the successful 3D printing using biocomposite filaments composed of PLA and 10 wt% chitosan, with clear chitosan entrapment within the PLA matrix confirmed by Scanning Electron Microscopy (SEM) images. Tensile testing of injection molded samples indicated an increase in stiffness, compared to pure PLA scaffolds, suggesting potential for improved load-bearing characteristics in bone scaffolds. However, the potential benefit of chitosan on the biocomposite stiffness could not be reproduced in compression testing of 3D printed cylinders. The antibacterial assays confirmed antibacterial activity of chitosan when dissolved in acetic acid. The study also verified the biodegradability of the scaffolds, with a process producing an acidic environment that could potentially be neutralized by chitosan. In conclusion, the study indicated the feasibility of the proposed PLA/chitosan biocomposite for 3D printing, demonstrating adequate mechanical strength, antibacterial properties and biodegradability, which could serve as a new material for bone repair.

Mechanism and application of 3D-printed degradable bioceramic scaffolds for bone repair

Bioceramics have attracted considerable attention in the field of bone repair because of their excellent osteogenic properties, degradability, and biocompatibility. To resolve issues regarding limited formability, recent studies have introduced 3D printing technology for the fabrication of bioceramic bone repair scaffolds. Nevertheless, the mechanisms by which bioceramics promote bone repair and clinical applications of 3D-printed bioceramic scaffolds remain elusive. This review provides an account of the fabrication methods of 3D-printed degradable bioceramic scaffolds. In addition, the types and characteristics of degradable bioceramics used in clinical and preclinical applications are summarized. We have also highlighted the osteogenic molecular mechanisms in biomaterials with the aim of providing a basis and support for future research on the clinical applications of degradable bioceramic scaffolds. Finally, new developments and potential applications of 3D-printed degradable bioceramic scaffolds are discussed with reference to experimental and theoretical studies.

Fused Deposition Modeling Printed PLA/Nano β-TCP Composite Bone Tissue Engineering Scaffolds for Promoting Osteogenic Induction Function

Purpose

Large bone defects caused by congenital defects, infections, degenerative diseases, trauma, and tumors often require personalized shapes and rapid reconstruction of the bone tissue. Three-dimensional (3D)-printed bone tissue engineering scaffolds exhibit promising application potential. Fused deposition modeling (FDM) technology can flexibly select and prepare printed biomaterials and design and fabricate bionic microstructures to promote personalized large bone defect repair. FDM-3D printing technology was used to prepare polylactic acid (PLA)/nano β-tricalcium phosphate (TCP) composite bone tissue engineering scaffolds in this study. The ability of the bone-tissue-engineered scaffold to repair bone defects was evaluated in vivo and in vitro.

Methods

PLA/nano-TCP composite bone tissue engineering scaffolds were prepared using FDM-3D printing technology. The characterization data of the scaffolds were obtained using relevant detection methods. The physical and chemical properties, biocompatibility, and in vitro osteogenic capacity of the scaffolds were investigated, and their bone repair capacity was evaluated using an in vivo animal model of rabbit femur bone defects.

Results

The FDM-printed PLA/nano β-TCP composite scaffolds exhibited good personalized porosity and shape, and their osteogenic ability, biocompatibility, and bone repair ability in vivo were superior to those of pure PLA. The merits of biodegradable PLA and bioactive nano β-TCP ceramics were combined to improve the overall biological performance of the composites.

Conclusion

The FDM-printed PLA/nano-β-TCP composite scaffold with a ratio of 7:3 exhibited good personalized porosity and shape, as well as good osteogenic ability, biocompatibility, and bone repair ability. This study provides a promising strategy for treating large bone defects.

Polycarboxy/Sulfo Betaine-Calcium Phosphate Hybrid Materials with a Remineralization Potential

Biomacromolecules control mineral formation during the biomineralization process, but the effects of the organic components' functionality on the type of mineral phase is still unclear. The biomimetic precipitation of calcium phosphates in a physiological medium containing either polycarboxybetaine (PCB) or polysulfobetaine (PSB) was investigated in this study. Amorphous calcium phosphate (ACP) or a mixture of octacalcium phosphate (OCP) and dicalcium phosphate dihydrate (DCPD) in different ratios were identified depending on the sequence of initial solution mixing and on the type of the negative functional group of the polymer used. The more acidic character of the sulfo group in PSB than the carboxy one in PCB determines the dominance of the acidic solid phases, namely, an acidic amorphous phase or DCPD. In the presence of PCB, the formation of ACP with acicular particles arranged in bundles with the same orientation was observed. A preliminary study on the remineralization potential of the hybrid material with the participation of PSB and a mixture of OCP and DCPD did not show an increase in enamel density, contrary to the materials based on PCB and ACP. Moreover, the latter showed the creation of a newly formed crystal layer similar to that of the underlying enamel. This defines PCB/ACP as a promising material for enamel remineralization.

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.

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

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

A Review of the Application of Natural and Synthetic Scaffolds in Bone Regeneration

The management of bone defects is complicated by the presence of clinical conditions, such as critical-sized defects created by high-energy trauma, tumour resection, infection, and skeletal abnormalities, whereby the bone regeneration capacity is compromised. A bone scaffold is a three-dimensional structure matrix serving as a template to be implanted into the defects to promote vascularisation, growth factor recruitment, osteogenesis, osteoconduction, and mechanical support. This review aims to summarise the types and applications of natural and synthetic scaffolds currently adopted in bone tissue engineering. The merits and caveats of natural and synthetic scaffolds will be discussed. A naturally derived bone scaffold offers a microenvironment closer to in vivo conditions after decellularisation and demineralisation, exhibiting excellent bioactivity, biocompatibility, and osteogenic properties. Meanwhile, an artificially produced bone scaffold allows for scalability and consistency with minimal risk of disease transmission. The combination of different materials to form scaffolds, along with bone cell seeding, biochemical cue incorporation, and bioactive molecule functionalisation, can provide additional or improved scaffold properties, allowing for a faster bone repair rate in bone injuries. This is the direction for future research in the field of bone growth and repair.

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.

Nano-Hydroxyapatite Composite Scaffolds Loaded with Bioactive Factors and Drugs for Bone Tissue Engineering

Nano-hydroxyapatite (n-HAp) is similar to human bone mineral in structure and biochemistry and is, therefore, widely used as bone biomaterial and a drug carrier. Further, n-HAp composite scaffolds have a great potential role in bone regeneration. Loading bioactive factors and drugs onto n-HAp composites has emerged as a promising strategy for bone defect repair in bone tissue engineering. With local delivery of bioactive agents and drugs, biological materials may be provided with the biological activity they lack to improve bone regeneration. This review summarizes classification of n-HAp composites, application of n-HAp composite scaffolds loaded with bioactive factors and drugs in bone tissue engineering and the drug loading methods of n-HAp composite scaffolds, and the research direction of n-HAp composite scaffolds in the future is prospected.

Design Strategies and Biomimetic Approaches for Calcium Phosphate Scaffolds in Bone Tissue Regeneration

Bone is a complex biologic tissue, which is extremely relevant for various physiological functions, in addition to movement, organ protection, and weight bearing. The repair of critical size bone defects is a still unmet clinical need, and over the past decades, material scientists have been expending efforts to find effective technological solutions, based on the use of scaffolds. In this context, biomimetics which is intended as the ability of a scaffold to reproduce compositional and structural features of the host tissues, is increasingly considered as a guide for this purpose. However, the achievement of implants that mimic the very complex bone composition, multi-scale structure, and mechanics is still an open challenge. Indeed, despite the fact that calcium phosphates are widely recognized as elective biomaterials to fabricate regenerative bone scaffolds, their processing into 3D devices with suitable cell-instructing features is still prevented by insurmountable drawbacks. With respect to biomaterials science, new approaches maybe conceived to gain ground and promise for a substantial leap forward in this field. The present review provides an overview of physicochemical and structural features of bone tissue that are responsible for its biologic behavior. Moreover, relevant and recent technological approaches, also inspired by natural processes and structures, are described, which can be considered as a leverage for future development of next generation bioactive medical devices.

Synthesis and application of nanometer hydroxyapatite in biomedicine

Nano-hydroxyapatite (nano-HA) has been widely studied as a promising biomaterial because of its potential mechanical and biological properties. In this article, different synthesis methods for nano-HA were summarized. Key factors for the synthesis of nano-HA, including reactant concentration, effects of temperature, PH, additives, aging time, and sintering, were separately investigated. The biological performances of the nano-HA depend strongly on its structures, morphology, and crystallite sizes. Nano-HA with different morphologies may cause different biological effects, such as protein adsorption, cell viability and proliferation, angiogenesis, and vascularization. Recent research progress with respect to the biological functions of the nano-HA in some specific biological applications are summarized and the future development of nano-sized hydroxyapatite is prospected.