Biomaterials for bone regeneration: an orthopedic and dentistry overview

Delivery vehicles for light-mediated drug delivery: microspheres, microbots, and nanoparticles: a review

This review delves into the evolving landscape of mediated drug delivery, focusing on the versatility of a variety of drug delivery vehicles such as microspheres, microbots, and nanoparticles (NPs). The review also expounds on the critical components and mechanisms for light-mediated drug delivery, including photosensitizers and light sources such as visible light detectable by the human eye, ultraviolet (UV) light, shorter wavelengths than visible light, and near-infra-red (NIR) light, which has longer wavelength than visible light. This longer wavelength has been implemented in drug delivery for its ability to penetrate deeper tissues and highlighted for its role in precise and controlled drug release. Furthermore, this review discusses the significance of these drug delivery vehicles towards a spectrum of diverse applications spanning gene therapy, cancer treatment, diagnostics, and microsurgery, and the materials used in the fabrication of these vehicles encompassing polymers, ceramics, and lipids. Moreover, the review analyses the challenges and limitations of such drug delivery vehicles as areas of improvement to provide researchers with valuable insights for addressing current obstacles in the progression of drug delivery. Overall, this review underscores the potential of light-mediated drug delivery to revolutionise healthcare and personalised medicine, providing precise, targeted, and effective therapeutic interventions.

Evolution in Bone Tissue Regeneration: From Grafts to Innovative Biomaterials

Bone defects caused by various traumas and diseases such as osteoporosis, which affects bone density, and osteosarcoma, which affects the integrity of bone structure, are now well known. Given this situation, several innovative research projects have been reported to improve orthopedic methods and technologies that positively contribute to the regeneration of affected bone tissue, representing a significant advance in regenerative medicine. This review article comprehensively analyzes the transition from existing methods and technologies for implants and bone tissue regeneration to innovative biomaterials. These biomaterials have been of great interest in the last decade due to their physicochemical characteristics, which allow them to overcome the most common limitations of traditional grafting methods, such as the availability of biomaterials and the risk of rejection after their application in regenerative medicine. This could be achieved through an exhaustive study of the applications and properties of various materials with potential applications in regenerative medicine, such as using magnetic nanoparticles and hydrogels sensitive to external stimuli, including pH and temperature. In this regard, this review article describes the most relevant compounds used in bone tissue regeneration, promoting the integration of these biomaterials with the affected area's bone structure, thereby allowing for regeneration and preventing amputation. Additionally, the types of interactions between biomaterials and mesenchymal stem cells and their effects on bone tissue are discussed, which is critical for developing biomaterials with optimal regenerative properties. Furthermore, the mechanisms of action of the various biomaterials that enhance osteoconduction and osteoinduction, ensuring the success of orthopedic therapies, are analyzed. This enables the treatment of bone defects tailored to each patient's condition, thereby avoiding limb amputation. Consequently, a promising future for regenerative medicine is emerging, with various therapies that could revolutionize the management of bone defects, offering more efficient and safer solutions.

Application of Hydroxyapatite Composites in Bone Tissue Engineering: A Review

The treatment of bone defects is complicated by clinical conditions, such as trauma, tumor resection, and infection, which result in defects and impair the bone's regenerative capacity. Hydroxyapatite (HAp), the primary inorganic component of bone, possesses good biocompatibility and osteoconductivity. However, it has poor mechanical properties, a slow degradation rate, and limited functionality, necessitating combination with other materials to broaden its application scope. This paper summarizes the importance and properties of HAp composites and provides a categorized review of current research on HAp composites in bone tissue engineering. These composite scaffolds not only offer excellent mechanical support for cell growth and tissue regeneration but also facilitate new bone formation and vascularization. Additionally, the challenges faced by HAp composites, such as material property optimization and improvement of preparation techniques, are discussed. The paper also summarizes the applications of HAp composites in bone defect repair, dental implants, spinal fusion, and other fields.

Versatile application of magnesium-related bone implants in the treatment of bone defects

Magnesium-related bone implants have garnered significant attention in the treatment of bone defects. The applications of magnesium in promoting bone repair mainly include degradable magnesium-based scaffolds owing to its special physical properties and composite materials modified by magnesium ions because of its biological activity. Although numerous studies have confirmed the unique application advantages and efficacy of magnesium in promoting bone repair, some obvious shortcomings persist, including the rapid degradation of magnesium-based scaffolds. In this review, the deficiencies of magnesium and its alloys in the construction of orthopedic implants and their key influencing factors were summarized; furthermore, some advanced improvement schemes were summarized and analyzed. Additionally, the application strategies of magnesium-modified bone implants are summarized and discussed. Lastly, this review incorporates the latest research and discoveries on magnesium in orthopedic science, comprehensively exploring the mechanism of magnesium's role in the complex microenvironment of bone defects from multiple dimensions. This paper provides a comprehensive summary and analysis of cutting-edge concepts in the design and development of magnesium-based bone implants, considering various perspectives such as the physical properties and biological functions of magnesium.

Innovation in Osteogenesis Activation: Role of Marine-Derived Materials in Bone Regeneration

Marine-derived biomaterials are emerging as promising candidates for tissue regeneration due to their sustainability, biocompatibility, bioactivity, and unique chemical structure. This review provides an overview of different marine-derived inorganic and organic materials, such as calcium carbonate, magnesium salts, silica, polysaccharides, bioactive peptides, and lipid-based compounds, and their effects in promoting osteogenesis. Specifically, the osteoinductive, osteoconductive, and osteointegrative activities of traditional and innovative materials that influence key molecular pathways such as BMP/Smad and Wnt/β-catenin signaling underlying bone formation will be evaluated. This review also prospects innovative approaches, i.e., phage display technology, to optimize marine-derived peptides for targeted bone regeneration. In the context of innovative and sustainable materials, this review suggests some interesting applications of unusual materials able to overcome the limitations of conventional ones and stimulate cellular regeneration of bone tissue by activating specific molecular pathways.

Transforming orthodontic retention: potential of 3D printing and biocompatible material characteristics

This review article delves into the cutting-edge realm of 3D printing and its impact on the fabrication of customised orthodontic retainers, which is an essential utility in the prevention of relapse post orthodontic treatment. This review evaluates the use of biocompatible materials and provides insight into future perspectives and improvements in this field. It highlights the potential of data collecting method and 3D printing to improve orthodontic retainers' fabrication and emphasises the importance of using biocompatible materials for patient safety and efficacy. It also explains cytotoxic qualities of retainer fabrication materials, which are vital for safeguarding the oral health of the patient. The evaluation procedure enables the early diagnosis and correction of any potential difficulties, such as maladjustment or inappropriate fit, allowing for a more effective treatment. It illustrates the breakthroughs and innovations in the field of orthodontics, the advantages of 3D printing over conventional methods, as well as the advantages and disadvantages of various fabrication method. Incorporating 3D printing and review into the production of orthodontic retainers enhances the overall effectiveness and efficiency of patient treatment.

Tailoring membrane technology with galactomannan for enhanced biocompatibility and antibacterial action

In this study, we elaborated advanced asymmetric membranes using polyvinyl alcohol (PVA) and a galactomannan (GA) derived from Delonix regia seeds, a blend known for its biocompatibility properties. These membranes, crosslinked with sulfosuccinic acid (SSA), exhibited remarkable enhancements in various crucial aspects for biomedical applications, in particular provides antibacterial properties. The incorporation of GA leads to the formation of globular regions, enhancing crosslinking and swelling properties. Increasing GA content results in membranes with enhanced biodegradation, reduced mechanical resistance, and increased elongation at break. The chemical composition of these membranes actively stimulates the metabolism of fibroblasts, osteoblasts, and to a lesser extent, monocytes, promoting cell proliferation particularly at GA contents between 10 and 20 %. Notably, the membrane containing 20 wt% GA demonstrates anti-inflammatory effects by reducing MCP-1 cytokine secretion without compromising tissue repair capacity, as TGF-ß secretion remains unaffected in human monocytes. This multifaceted approach underscores the potential of these membranes in biomedical applications, particularly in wound healing and tissue engineering.

A 3D in vitro model of biphasic calcium phosphate (BCP) scaffold combined with human osteoblasts, osteoclasts, and endothelial cells as a platform to mimic the oral microenvironment for tissue regeneration

OBJECTIVES

This study aimed to develop an innovative 3D in vitro model based on the biphasic calcium phosphate (BCP) scaffold combined with human osteoblasts (hOBs), osteoclasts (hOCs), and endothelial cells to evaluate its effects on bone and vascular cells behavior.

METHODS

To this end, an optimized mixture of hydroxyapatite (HA) and β-tricalcium phosphate (TCP) with a weight ratio of 30/70 was employed to develop a BCP scaffold using the computer-aided design (CAD) approach. The BCP scaffold was combined with primary cultures of hOBs, hOCs and human umbilical vein endothelial cells (HUVECs).

RESULTS

Morphometric analyses using scanning electron microscopy (SEM) and X-ray micro-computed tomography, along with biomechanical testing, revealed that BCP scaffold exhibited a regular 3D structure with large interconnected internal pores (700 µm) and high mechanical strength. In terms of biological behavior, after 14 days of tri-culture with hOBs, hMCs and HUVECs, SEM, immunofluorescence, and histological analyses showed that all cell types were viable and adhered well to the entire surface of the scaffold. Interestingly, SEM and energy-dispersive X-ray spectroscopy analyses also revealed on the BCP scaffold the presence of mineralized matrix crystals of Ca, P, O and C within a tissue-like cell layer produced by the interaction of the three cell types.

CONCLUSIONS

Data confirmed the high performance of the BCP scaffold through biomechanical studies. Notably, for the first time, this study demonstrated the feasibility of combining BCP scaffold with hOBs, hOCs, and HUVEC, which remained viable and maintained their native phenotypes, creating also tissue-like cell layer.

CLINICAL SIGNIFICANCE

Although further investigation is needed, these results underscore the potential to develop a 3D in vitro model that mimics the oral microenvironment, which could be valuable for BTE approaches in vivo studies.

A sugary solution: Harnessing polysaccharide-based materials for osteoporosis treatment

Osteoporosis, a prevalent skeletal disorder characterized by diminished bone density, compromised microstructure, and heightened fracture susceptibility, poses a growing public health concern exacerbated by aging demographics. Polysaccharides-based materials, derived from a diverse range of sources, exhibit exceptional biocompatibility. They possess a structure similar to the extracellular matrix, which can enhance cell adhesion in vivo, and demonstrate superior biological activity compared to artificial materials. This study delved into an in-depth examination of the various biomaterials and polysaccharide families associated with the treatment of osteoporosis. This article elucidates the benefits and attributes of polysaccharide-based materials in contrast to current clinical treatment modalities, delineating how these materials address prevalent challenges in the clinical management of osteoporosis. An overview of the prospective applications of polysaccharide-based materials in the future is also provided, as well as outlines the challenges that should be addressed prior to the clinical implementation of such materials.

Management of pediatric ankle fractures: comparison of biodegradable PLGA implants with traditional metal screws

Introduction

The relevance of biodegradable implants has gained more importance in modern clinical practice. The study aimed to evaluate the effects and outcomes of ankle fracture treatment with absorbable implants compared to metal screws. These implants are made from poly l-lactic-co-glycolic acid (PLGA), however, there are several other materials available on the market.

Methods

In a retrospective review, a total of 128 patients were under observation, with distal tibial fracture types ranging from Salter-Harris II-IV. In the absorbable group, patients were treated with the implants (n = 76). The metal group included patients treated with titanium or steel screws (n = 52). The extremities were placed in a cast for six weeks after surgery and were utilized for another 6-8 weeks. Patients were followed up for 12-30 months and were evaluated accordingly. The authors examined several aspects such as age, gender, open or closed repair, mechanism of injury, length of hospitalization, type of fracture, time of recovery, and complications.

Results

There were no statistically significant differences between the groups regarding demographic qualities, such as age, type of fracture, side of injury, and length of cast application (p > 0.05 in all cases). Out of 76 patients in the PLGA group, only two presented with complications, so reoperation took place. The rest healed without complications or refractures. Two of those treated with metal screws (n = 52) had minor, and four had major complications with reoperation.

Discussion

In pediatric cases, PLGA implants may present excellent results for treating ankle fractures. They do not disturb the growth plate and do not require reoperation. For this reason, they reduce the burden on the patient and the healthcare provider while simultaneously decreasing the risk of complications, such as infections or problems due to general anesthesia.

Long-term effectiveness of UV functionalised short (≤ 6 mm) dental implants placed in the posterior segments of the atrophied maxilla: controlled case series

This study evaluated long-term effectiveness UV functionalised short implants (≤ 6 mm) placed in the posterior segments of the atrophied maxilla. The study included 47 patients from 2018 to 2023 (aged 27 to 56 years, 24 women and 23 men) without any systemic diseases, with unilateral/bilateral missing teeth and vertical atrophy of the posterior maxillary area. Total installed were 64 short UV-functionalized implants and 62 standard implants over 10 mm in length in segments maxilla with sufficient bone parameters. Clinical, laboratory and cone beam computed tomography (CBCT) methods were used to plan implant therapy. The clinical indices included the following parameters: ISQ, MBL, OHIP-G scale. For short implants, the median ISQ at placement was 62.2 for primary stability and the median ISQ at 5 months was 69.6 ISQ. For standard implant, the mean ISQ at placement was 64.3 ISQ, and ISQ after 5 months was 71.6 ISQ. After 6 months mean MBL short implants 0.87 mm, after 1 year 1.13 mm, after 5 years was 1.48 mm. After 6 months mean MBL standard implants 0.84 mm, after 1 year 1.24 mm, after 5 years was 1.58 mm. Mean OHIP-G scores-patients satisfaction with the implant at 4.8 ± 0.3, satisfaction with the operation 4.6 ± 0.4; satisfaction with prosthetics 4.7 ± 0.5. Cumulative success rate 5 years short implants was 96.7%, standard implants was 97.4%, and prosthesis cumulative survival rate was 97.2%. Short ultraviolet functionalized implants used in the posterior resorbed segment of maxilla have been shown to be a reliable alternative to sinus lift, demonstrating fewer complications, reduction in the number of additional surgical interventions and showed satisfactory long-term survival.

Biocomposite Scaffolds Based on Chitosan Extraction from Shrimp Shell Waste for Cartilage Tissue Engineering Application

Chitosan-based scaffolding possesses unique properties that make it highly suitable for tissue engineering applications. Chitosan is derived from deacetylating chitin, which is particularly abundant in the shells of crustaceans. This study aimed to extract chitosan from shrimp shell waste (Macrobrachium rosenbergii) and produce biocomposite scaffolds using the extracted chitosan for cartilage tissue engineering applications. Chitinous material from shrimp shell waste was deproteinized and deacetylated. The extracted chitosan was characterized and compared to commercial chitosan through various physicochemical analyses. The findings revealed that the extracted chitosan shares similar trends in the Fourier transform infrared spectroscopy spectrum, energy dispersive X-ray mapping, and X-ray diffraction pattern to commercial chitosan. Despite differences in the degree of deacetylation, these results underscore its comparable quality. The extracted chitosan was mixed with agarose, collagen, and gelatin to produce the blending biocomposite AG-CH-COL-GEL scaffold by freeze-drying method. Results showed AG-CH-COL-GEL scaffolds have a 3D interconnected porous structure with pore size 88-278 μm, high water uptake capacity (>90%), and degradation percentages in 21 days between 5.08% and 30.29%. Mechanical compression testing revealed that the elastic modulus of AG-CH-COL-GEL scaffolds ranged from 44.91 to 201.77 KPa. Moreover, AG-CH-COL-GEL scaffolds have shown significant potential in effectively inducing human chondrocyte proliferation and enhancing aggrecan gene expression. In conclusion, AG-CH-COL-GEL scaffolds emerge as promising candidates for cartilage tissue engineering with their optimal physical properties and excellent biocompatibility. This study highlights the potential of using waste-derived chitosan and opens new avenues for sustainable and effective tissue engineering solutions.

Unleashing innovation: 3D-printed biomaterials in bone tissue engineering for repairing femur and tibial defects in animal models - a systematic review and meta-analysis

Introduction

3D-printed scaffolds have emerged as an alternative for addressing the current limitations encountered in bone reconstruction. This study aimed to systematically review the feasibility of using 3D bio-printed scaffolds as a material for bone grafting in animal models, focusing on femoral and tibial defects. The primary objective of this study was to evaluate the efficacy, safety, and overall impact of these scaffolds on bone regeneration.

Methods

Electronic databases were searched using specific search terms from January 2013 to October 2023, and 37 relevant studies were finally included and reviewed. We documented the type of scaffold generated using the 3D printed techniques, detailing its characterization and rheological properties including porosity, compressive strength, shrinkage, elastic modulus, and other relevant factors. Before incorporating them into the meta-analysis, an additional inclusion criterion was applied where the regenerated bone area (BA), bone volume (BV), bone volume per total volume (BV/TV), trabecular thickness (Tb. Th.), trabecular number (Tb. N.), and trabecular separation (Tb. S.) were collected and analyzed statistically.

Results

3D bio-printed ceramic-based composite scaffolds exhibited the highest capacity for bone tissue regeneration (BTR) regarding BV/TV of femoral and tibial defects of animal models. The ideal structure of the printed scaffolds displayed optimal results with a total porosity >50% with a pore size ranging between 300- and 400 µM. Moreover, integrating additional features and engineered macro-channels within these scaffolds notably enhanced BTR capacity, especially observed at extended time points.

Discussion

In conclusion, 3D-printed composite scaffolds have shown promise as an alternative for addressing bone defects.

Hydroxyapatite-Based Natural Biopolymer Composite for Tissue Regeneration

Hydroxyapatite (HAp) polymer composites have gained significant attention due to their applications in bone regeneration and tooth implants. This review examines the synthesis, properties, and applications of Hap, highlighting various manufacturing methods, including wet, dry, hydrothermal, and sol-gel processes. The properties of HAp are influenced by precursor materials and are commonly obtained from natural calcium-rich sources like eggshells, seashells, and fish scales. Composite materials, such as cellulose-hydroxyapatite and gelatin-hydroxyapatite, exhibit promising strength and biocompatibility for bone and tissue replacement. Metallic implants and scaffolds enhance stability, including well-known titanium-based and stainless steel-based implants and ceramic body implants. Biopolymers, like chitosan and alginate, combined with Hap, offer chemical stability and strength for tissue engineering. Collagen, fibrin, and gelatin play crucial roles in mimicking natural bone composition. Various synthesis methods like sol-gel, hydrothermal, and solution casting produce HAp crystals, with potential applications in bone repair and regeneration. Additionally, the use of biowaste materials, like eggshells and snails or seashells, not only supports sustainable HAp production but also reduces environmental impact. This review emphasizes the significance of understanding the properties of calcium-phosphate (Ca-P) compounds and processing methods for scaffold generation, highlighting novel characteristics and mechanisms of biomaterials in bone healing. Comparative studies of these methods in specific applications underscore the versatility and potential of HAp composites in biomedical engineering. Overall, HAp composites offer promising solutions for improving patient outcomes in bone replacement and tissue engineering and advancing medical practices.

Tissue scaffolds mimicking hierarchical bone morphology as biomaterials for oral maxillofacial surgery with augmentation: structure, properties, and performance evaluation forin vitrotesting

In this study, tissue scaffolds mimicking hierarchical morphology are constructed and proposed for bone augmentation. The scaffolds are fabricated using lyophilization, before coating them with collagen (Col). Subsequently, the Col-coated scaffolds undergo a second lyophilization, followed by silk fibroin (SF) coating, and a third lyophilization. Thereafter, the scaffolds are divided into six groups with varying ratios of Col to SF: Col/SF = 7:3, 5:5, 3:7, 10:0, and 0:10, with an SF scaffold serving as the control group. The scaffold morphology is examined using a scanning electron microscope, while molecular and structural formations are characterized by Fourier transform infrared spectrometer and differential scanning calorimeter, respectively. Physical and mechanical properties including swelling and compression are tested. Biological functions are assessed throughin vitroosteoblast cell culturing. Biomarkers indicative of bone formation-cell viability and proliferation, alkaline phosphatase activity, and calcium content-are analyzed. Results demonstrate that scaffolds coated with Col and SF exhibit sub-porous formations within the main pore. The molecular formation reveals interactions between the hydrophilic groups of Col and SF. The scaffold structure contains bound water and SF formation gets disrupted by Col. Physical and mechanical properties are influenced by the Col/SF ratio and morphology due to coating. The biological functions of scaffolds with Col and SF coating show enhanced potential for promoting bone tissue formation, particularly the Col/SF (7:3) ratio, which is most suitable for bone augmentation in small defect areas.

Conventional Manufacturing by Pouring Versus Additive Manufacturing Technology of β-Tricalcium Phosphate Bone Substitute Implants

The aim of the study was to compare conventional sintering with additive manufacturing techniques for β-TCP bioceramics, focusing on mechanical properties and biocompatibility. A "critical" bone defect requires surgical intervention beyond simple stabilization. Autologous bone grafting is the gold standard treatment for such defects, but it has its limitations. Alloplastic bone grafting with synthetic materials is becoming increasingly popular. The use of bone graft substitutes has increased significantly, and current research has focused on optimizing these substitutes, whereas this study compares two existing manufacturing techniques and the resulting β-TCP implants. The 3D printed β-TCP hybrid structure implant was fabricated from two components, a column structure and a freeze foam, which were sintered together. The conventionally fabricated ceramics were fabricated by casting. Both scaffolds were characterized for porosity, mechanical properties, and biocompatibility. The hybrid structure had an overall porosity of 74.4 ± 0.5%. The microporous β-TCP implants had a porosity of 43.5 ± 2.4%, while the macroporous β-TCP implants had a porosity of 61.81%. Mechanical testing revealed that the hybrid structure had a compressive strength of 10.4 ± 6 MPa, which was significantly lower than the microporous β-TCP implants with 32.9 ± 8.7 MPa. Biocompatibility evaluations showed a steady increase in cell proliferation over time for all the β-TCP implants, with minimal cytotoxicity. This study provides a valuable insight into the potential of additive manufacturing for β-TCP bioceramics in the treatment of bone defects.

Study of biphasic calcium phosphate (BCP) ceramics of tilapia fish bones by age

Biphasic calcium phosphate (BCP), consisting of bioceramics such as HAp + β-TCP and Ca10(PO4)6(OH)2 + Ca3(PO4)2, is a popular choice for optimizing performance due to its superior biological reabsorption and osseointegration. In this study, BCP was produced by calcining the bones of tilapia fish (Oreochromis niloticus) reared in net cages and slaughtered at an age ranging from 15 to 420 days. The bones were cleaned and dried, calcined at 900 °C for 8 h, and then subjected to high-energy grinding for 3 h to produce BCP powders. After the calcination process, the crystalline phase's hydroxyapatite (HAp) and/or beta-tricalcium phosphate (β-TCP) were present in the composition of the bioceramic. The age-dependent variation in phase composition was confirmed by complementary vibrational spectroscopy techniques, revealing characteristic peaks and bands of the bioceramic. This variation was marked by an increase in HAp phase and a decrease in β-TCP phase. Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) from 25 to 1400 °C showed the characteristic mass losses of the material, with a greater loss observed for younger fish, indicating the complete removal of organic components at temperatures above 600 °C. Comparison of the results obtained by X-Ray Diffraction (XRD) and Rietveld refinement with Raman spectroscopy showed excellent agreement. These results showed that with temperature and environment control and adequate fish feeding, it is possible to achieve the desired amounts of each phase by choosing the ideal age of the fish. This bioceramic enables precise measurement of HAp and β-TCP concentrations and Ca/P molar ratio, suitable for medical orthopedics and dentistry.

Comparison of stress distribution in fully porous and dense-core porous scaffolds in dental implantation

The aim of this study is to compare the stress distribution in porous scaffolds with different structures with similar geometric parameters to study a new approach in dental implantation. Three-dimensional finite element models of the fully porous and dense-core porous scaffolds with defined porosity parameters including space diameter and thickness with two porosity patterns were embedded in the jaw bone model with cortical and cancellous bone. The cylindrical shape was considered as the main shape of the scaffolds. To evaluate the mechanical performance, the Von Mises stress was compared in the models under static and dynamic masticatory loading. Incidentally, to validate the modeling results, experimental strain gauge tests were performed on four specimens fabricated from Ti6Al4V. Finally, the stress distribution in the models was compared with the results of previous studies on commercial implants. The results of the finite element analysis show that there are considerable differences in the magnitude of the equivalent stress in the models in static and dynamic phases. Also, changes in the defined geometric parameters have significant effects on the stress distribution in terms of Von Mises stress in the overall models. The experimental results indicated good agreement with those of the modeling. It can be concluded that some porous structures with optimal geometries can be proposed as a new structure for dental implants. However, considering the physiology of bone when confronted with porous structures, further studies such as in vivo experiments are needed in this field.

Synthetic composites versus calcium phosphate cements in bone regeneration: A narrative review

BACKGROUND

When the natural process of bone remodeling is disturbed, the need arises for a stimulant material in order to enhance the formation of a new healthy and strong osseous tissue to replace the damaged one. Recent studies have reported synthetic biomaterials to be a very good option for supporting bone regeneration.

STUDY DESIGN

Narrative review.

OBJECTIVE

This review aims to provide a brief presentation of two of the most recently developed synthetic biomaterials, i.e. calcium phosphate cements and synthetic composites, that are currently being used in bone regeneration with promising results.

METHODS

Literature searches using broad terms such as "bone regeneration," "biomaterials," "synthetic composites" and "calcium phosphate cements" were performed using PubMed. The osteal cells state of the art was explored by searching topic-specific full text keywords using Google Scholar.

CONCLUSIONS

Synthetic polymers such as PCL (poly-ε-caprolactone) and PLGA (poly lactic-co-glycolic acid) can improve the effectiveness of biomaterials like HA (hydroxyapatite) and BG (bioglass). Calcium phosphate, although being a suitable material for stimulating bone regeneration, needs an adjuvant in order to be effective in larger bone defects.

Stem Cell and Regenerative Therapies for the Treatment of Osteoporotic Vertebral Compression Fractures

Osteoporotic vertebral compression fractures (OVCFs) significantly increase morbidity and mortality, presenting a formidable challenge in healthcare. Traditional interventions such as vertebroplasty and kyphoplasty, despite their widespread use, are limited in addressing the secondary effects of vertebral fractures in adjacent areas and do not facilitate bone regeneration. This review paper explores the emerging domain of regenerative therapies, spotlighting stem cell therapy's transformative potential in OVCF treatment. It thoroughly describes the therapeutic possibilities and mechanisms of action of mesenchymal stem cells against OVCFs, relying on recent clinical trials and preclinical studies for efficacy assessment. Our findings reveal that stem cell therapy, particularly in combination with scaffolding materials, holds substantial promise for bone regeneration, spinal stability improvement, and pain mitigation. This integration of stem cell-based methods with conventional treatments may herald a new era in OVCF management, potentially improving patient outcomes. This review advocates for accelerated research and collaborative efforts to translate laboratory breakthroughs into clinical practice, emphasizing the revolutionary impact of regenerative therapies on OVCF management. In summary, this paper positions stem cell therapy at the forefront of innovation for OVCF treatment, stressing the importance of ongoing research and cross-disciplinary collaboration to unlock its full clinical potential.

Bone Regeneration with Mesenchymal Stem Cells in Scaffolds: Systematic Review of Human Clinical Trials

The aim of the study is to determine the effectiveness of stem cells in scaffolds in the treatment of bone deficits, in regard of bone regeneration, safety, rehabilitation and quality of life in humans. The systematic review was conducted in accordance with PRISMA 2020. A systematic search was conducted in three search engines and two registries lastly in 29-9-2022.for studies of the last 15 years. The risk of bias was assessed with RoB-2, ROBINS- I and NIH Quality of Before-After (Pre-Post) Studies with no Control group. The certainty of the results was assessed with the GRADE assessment tool. Due to heterogeneity, the results were reported in tables, graphs and narratively. The study protocol was published in PROSPERO with registration number CRD42022359049. Of the 10,091 studies retrieved, 14 were meeting the inclusion criteria, and were qualitatively analyzed. 138 patients were treated with mesenchymal stem cells in scaffolds, showing bone healing in all cases, and even with better results than the standard care. The adverse events were mild in most cases and in accordance with the surgery received. When assessed, there was a rehabilitation of the deficit and a gain in quality of life was detected. Although the heterogeneity between the studies and the small number of patients, the administration of mesenchymal stem cells in scaffolds seems safe and effective in the regeneration of bone defects. These results pave the way for the conduction of more clinical trials, with greater number of participants, with more standardized procedures.

Construction of a PEGDA/chitosan hydrogel incorporating mineralized copper-doped mesoporous silica nanospheres for accelerated bone regeneration

Hydrogels, integrating diverse biocompatible materials, have emerged as promising candidates for bone repair applications. This study presents a double network hydrogel designed for bone tissue engineering, combining poly(ethylene glycol) diacrylate (PEGDA) and chitosan (CS) crosslinked through UV polymerization and ionic crosslinking. Concurrently, copper-doped mesoporous silica nanospheres (Cu-MSNs) were synthesized using a one-pot method. Cu-MSNs underwent additional modification through in-situ biomineralization, resulting in the formation of an apatite layer. Polydopamine was employed to facilitate the deposition of Calcium (Ca) and Phosphate (P) ions on the surface of Cu-MSNs (Cu-MSNs/PDA@CaP). Composite hydrogels were created by integrating varied concentrations of Cu-MSNs/PDA@CaP (25, 50, 100, 150, 200 μg/mL). Characterization unveiled distinctive interconnected porous structures within the composite hydrogel, showcasing a notable 169.6 % enhancement in compressive stress (elevating from 89.01 to 240.19 kPa) compared to pure PEGDA. In vitro biocompatibility experiments illustrated that the composite hydrogel maintained elevated cell viability (up to 106.6 %) and facilitated rapid cell proliferation over 7 days. The hydrogel demonstrated a substantial 57.58 % rise in ALP expression and a surprising 235.27 % increase in ARS staining. Moreover, it significantly enhanced the expression of crucial osteogenic genes, such as run-related transcription factors 2 (RUNX2), collagen 1a1 (Col1a1), and secreted phosphoprotein 1 (Spp1), establishing it as a promising scaffold for bone regeneration. This study shows how Cu-MSNs/PDA@CaP were successfully integrated into a double network hydrogel, resulting in a composite material with good biological responses. Due to its improved characteristics, this composite hydrogel holds the potential for advancing bone regeneration procedures.

Autophagy-modulating biomaterials: multifunctional weapons to promote tissue regeneration

Autophagy is a self-renewal mechanism that maintains homeostasis and can promote tissue regeneration by regulating inflammation, reducing oxidative stress and promoting cell differentiation. The interaction between biomaterials and tissue cells significantly affects biomaterial-tissue integration and tissue regeneration. In recent years, it has been found that biomaterials can affect various processes related to tissue regeneration by regulating autophagy. The utilization of biomaterials in a controlled environment has become a prominent approach for enhancing the tissue regeneration capabilities. This involves the regulation of autophagy in diverse cell types implicated in tissue regeneration, encompassing the modulation of inflammatory responses, oxidative stress, cell differentiation, proliferation, migration, apoptosis, and extracellular matrix formation. In addition, biomaterials possess the potential to serve as carriers for drug delivery, enabling the regulation of autophagy by either activating or inhibiting its processes. This review summarizes the relationship between autophagy and tissue regeneration and discusses the role of biomaterial-based autophagy in tissue regeneration. In addition, recent advanced technologies used to design autophagy-modulating biomaterials are summarized, and rational design of biomaterials for providing controlled autophagy regulation via modification of the chemistry and surface of biomaterials and incorporation of cells and molecules is discussed. A better understanding of biomaterial-based autophagy and tissue regeneration, as well as the underlying molecular mechanisms, may lead to new possibilities for promoting tissue regeneration. Video Abstract.

Influence of the addition of nanohydroxyapatite to scaffolds on proliferation and differentiation of human mesenchymal stem cells: a systematic review of in vitro studies

One of the main challenges of tissue engineering in dentistry is to replace bone and dental tissues with strategies or techniques that simulate physiological tissue repair conditions. This systematic review of in vitro studies aimed to evaluate the influence of the addition of nanohydroxyapatite (NHap) to scaffolds on cell proliferation and osteogenic and odontogenic differentiation of human mesenchymal stem cells. In vitro studies on human stem cells that proliferated and differentiated into odontogenic and osteogenic cells in scaffolds containing NHap were included in this study. Searches in PubMed/MEDLINE, Scopus, Web of Science, OpenGrey, ProQuest, and Cochrane Library electronic databases were performed. The total of 333 articles was found across all databases. After reading and analyzing titles and abstracts, 8 articles were selected for full reading and extraction of qualitative data. Results showed that despite the large variability in scaffold composition, NHap-containing scaffolds promoted high rates of cell proliferation, increased alkaline phosphatase (ALP) activity during short culture periods, and induced differentiation, as evidenced by the high expression of genes involved in osteogenesis and odontogenesis. However, further studies with greater standardization regarding NHap concentration, type of scaffolds, and evaluation period are needed to observe possible interference of these criteria in the action of NHap on the proliferation and differentiation of human stem cells.

Management of Juvenile Osteochondral Fractures Utilising Absorbable PLGA Implants

The incidence of articular injury, particularly osteochondral fractures (OCFs), has seen a cinnotable increase in recent years. Regardless of their location, fragments can be overlooked by plain radiographs, which might lead to osteoarthritis in the long run. Diagnostic imaging has a pivotal role in the assessment and classification of the fracture severity, as well as the presence of any associated dislocations. These fractures require surgical intervention for the restoration of joint function and the reduction of long-term complications. This paper aims to present the surgical correction and post-operative treatment of osteochondral fractures with absorbable implants in four children. The following affected areas are discussed: lateral condyle of the femur, patella and radial head. Utilising absorbable implants for the management of OCFs provides numerous advantages, including the elimination of the need for re-anaesthesia and reoperation, reduction of complications and facilitation of early rehabilitation. This approach also minimises the period of hospitalisation and proves effective in pediatric OCF treatment.

Comparative In Vitro Dissolution Assessment of Calcined and Uncalcined Hydroxyapatite Using Differences in Bioresorbability and Biomineralization

This study reports the effect of the not-calcining process on the bioresorption and biomineralization of hydroxyapatite through in vitro dissolution assessment. The prepared calcined hydroxyapatite (c-HAp) and uncalcined hydroxyapatite (unc-HAp) have a particle size of 2 μm and 13 μm, surface areas of 4.47 m2/g and 108.08 m2/g, and a Ca/P ratio of 1.66 and 1.52, respectively. In vitro dissolution assessments of c-HAp and unc-HAp were performed for 20 days at 37 °C in a citric acid buffer according to ISO 10993-14. During the dissolution, the c-HAp and unc-HAp confirmed an increase in weight, and the calcium and phosphorous ions were rapidly released. The calcium ions released from c-HAp formed rod-shaped particles with a longer and thinner morphology, while in unc-HAp, they appeared thicker and shorter. In the ICP-OES results, the concentrations of calcium elements were initially increased and then decreased by this formation. The rod-shaped particles identified as calcium citrate (Ca-citrate) through the XRD pattern. The calcium content of Ca-citrate particles from unc-HAp was higher than that from c-HAp. The unc-HAp demonstrated non-toxic properties in a cytotoxicity evaluation. Therefore, due to its higher bioresorption and biomineralization, unc-HAp exhibits enhanced biocompatibility compared to c-HAp.

Biocomposite-based strategies for dental bone regeneration

OBJECTIVE

Because of the anatomical complexity of the oral and maxillofacial sites, repairing bone defects in these regions is very difficult. This review article aims to consider the application of biocomposites-based strategies for dental bone regeneration.

STUDY DESIGN

Research papers related to the topic, published over the last 20 years, were selected using the Web of Science, Pubmed, Scopus, and Google Scholar databases.

RESULTS

The strategies of monophasic, biphasic/multiphasic scaffolds, and biopolymer-based nanocomposite scaffolds containing nanomaterials compared with traditional methods used for bone regeneration, such as autografts, allografts, xenografts, and alloplasts are found to be superior because of their ability to overcome the issues (e.g., limited bone sources, pain, immune responses, high cost) related to the applications of the traditional methods.

CONCLUSIONS

In addition, additive manufacturing technologies were found to be highly advantageous for improving the efficacy of biocomposite scaffolds for treating dental bone defects.

The effect of green synthesis of TiO2 nanoparticles/collagen/HA scaffold in bone regeneration: As an animal study

BACKGROUND

The bone defects cannot heal by themselves when their range exceeds the critical size defect (CSD). In clinical treatment, significant bone defects are often caused by trauma, developmental deformity, tumour resection and infection.

OBJECTIVES

The purpose of this study was to investigate the effect of green synthesis of TiO2 from propolis extract/collagen/HA (Hydroxyapatite) scaffolds on bone regeneration in rats.

METHODS

Water uptake, biodegradability, porosity and biodegradation of the scaffolds were evaluated after they were synthesised using freeze-dry method. Cell viability by MTT assay was then evaluated. During the 4, 8 and 12 weeks following the scaffold implantation, the bone regeneration was evaluated using macroscopic and microscopic tests to determine the effectiveness of green synthesis of TiO2 from propolis extract/collagen/HA scaffolds.

RESULTS

Compared to the HA/Coll scaffold, ProTiO2 /HA/Coll scaffold was reduced porosity, water absorption and degradability porosity. Based on in vitro tests, both synthetic scaffolds induced cell growth and were less toxic and stimulated cell growth. Based on histopathological testing, the ProTiO2 /HA/Coll scaffolds formed high levels of bone during 12 weeks in comparison with HA/Coll and control group.

CONCLUSIONS

ProTiO2 /HA/Coll composite can be used in regenerative medicine, bone fillers and scaffolds. As a result, this research suggests that ProTiO2 /HA/Coll composites could be promising candidates for bone regeneration.

Evaluation of the time-dependent osteogenic activity of glycerol incorporated magnesium oxide nanoparticles in induced calvarial defects

Introduction

Magnesium-based biomaterials have been explored for their potential as bone healing materials, as a result of their outstanding biodegradability and biocompatibility. These characteristics make magnesium oxide nanoparticles (MgO NPs) a promising material for treating bone disorders. The purpose of this investigation is to assess the osteogenic activity of newly-developed locally administered glycerol-incorporated MgO NPs (GIMgO NPs) in rabbits' calvarial defects.

Materials and methods

Characterization of GIMgO was done by X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Bilateral calvarial defects were created in eighteen New Zealand Rabbits, of which they were divided into 3 groups with time points corresponding to 2, 4, and 6 weeks postoperatively (n = 6). One defect was implanted with absorbable gel foam impregnated with GIMgO NPs while the other was implanted with gel foam soaked with glycerol (the control). The defects were assessed using histological, Micro-Computed Tomography (Micro-CT), and histometric evaluation.

Results

The characterization of the GIMgO nanogel revealed the presence of MgO NPs and glycerol as well as the formation of the crystalline phase of the MgO NPs within the nanogel sample. The histological and micro-CT analysis showed time-dependent improvement of healing activity in the calvarial defects implanted with GIMgO NPs when compared to the control. Furthermore, the histometric analysis demonstrated a marked increase in the total area of new bone, connective tissue, new bone area and volume in the GIMgO NPs implanted site. Statistically, the amount of new bone formation was more significant at 6 weeks than at 2 and 4 weeks postoperatively in the calvarial defects implanted with GIMgO NPs as compared to the control.

Conclusion

The locally applied GIMgO NPs demonstrated efficacy in promoting bone formation, with more significant effects observed over an extended period. These findings suggest its suitability for clinical use as a therapeutic alternative to enhance bone healing.

3D printed strontium-zinc-phosphate bioceramic scaffolds with multiple biological functions for bone tissue regeneration

Calcium phosphate (CaP) bioceramics are broadly employed for bone regeneration due to their excellent biocompatibility and osteoconductivity. However, they are not capable of repairing healing-impaired bone defects such as defects with conditions of ischemia or infection due to restricted bioactivities. In this study, we synthesized single-phased strontium-zinc-phosphate (SZP, SrZn2(PO4)2) bioceramics via a solution combustion method and further fabricated SZP scaffolds using a three-dimensional (3D) printing technique. Compared to 3D printed β-tricalcium phosphate (β-TCP) scaffolds, the 3D printed SZP scaffolds presented comparable porosity, compressive strength, and Young's modulus, but increased ability of osteogenesis, angiogenesis, immunomodulation and anti-bacterial activity. Specifically, 3D printed SZP scaffolds not only led to significantly higher osteogenic differentiation of MC3T3-E1 cells and pro-angiogenesis of human umbilical vein endothelial cells (HUVECs) directly or through macrophage-mediated immunomodulation, but also inhibited the growth of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The in vivo study of the rat cranial bone defect model further confirmed better vascularized bone regeneration in 3D-printed SZP scaffolds. These findings indicate that the proposed 3D-printed SZP scaffolds might be a versatile candidate for bone tissue engineering.

Comparison of Osteoconductive Ability of Two Types of Cholesterol-Bearing Pullulan (CHP) Nanogel-Hydrogels Impregnated with BMP-2 and RANKL-Binding Peptide: Bone Histomorphometric Study in a Murine Calvarial Defect Model

The receptor activator of NF-κB ligand (RANKL)-binding peptide is known to accelerate bone morphogenetic protein (BMP)-2-induced bone formation. Cholesterol-bearing pullulan (CHP)-OA nanogel-crosslinked PEG gel (CHP-OA nanogel-hydrogel) was shown to release the RANKL-binding peptide sustainably; however, an appropriate scaffold for peptide-accelerated bone formation is not determined yet. This study compares the osteoconductivity of CHP-OA hydrogel and another CHP nanogel, CHP-A nanogel-crosslinked PEG gel (CHP-A nanogel-hydrogel), in the bone formation induced by BMP-2 and the peptide. A calvarial defect model was performed in 5-week-old male mice, and scaffolds were placed in the defect. In vivo μCT was performed every week. Radiological and histological analyses after 4 weeks of scaffold placement revealed that the calcified bone area and the bone formation activity at the defect site in the CHP-OA hydrogel were significantly lower than those in the CHP-A hydrogel when the scaffolds were impregnated with both BMP-2 and the RANKL-binding peptide. The amount of induced bone was similar in both CHP-A and CHP-OA hydrogels when impregnated with BMP-2 alone. In conclusion, CHP-A hydrogel could be an appropriate scaffold compared to the CHP-OA hydrogel when the local bone formation was induced by the combination of RANKL-binding peptide and BMP-2, but not by BMP-2 alone.

Phytochemical Compounds Involved in the Bone Regeneration Process and Their Innovative Administration: A Systematic Review

Bone metabolism is a complex process which is influenced by the activity of bone cells (e.g., osteocytes, osteoblasts, osteoclasts); the effect of some specific biomarkers (e.g., parathyroid hormone, vitamin D, alkaline phosphatase, osteocalcin, osteopontin, osteoprotegerin, osterix, RANKL, Runx2); and the characteristic signaling pathways (e.g., RANKL/RANK, Wnt/β, Notch, BMP, SMAD). Some phytochemical compounds-such as flavonoids, tannins, polyphenols, anthocyanins, terpenoids, polysaccharides, alkaloids and others-presented a beneficial and stimulating effect in the bone regeneration process due to the pro-estrogenic activity, the antioxidant and the anti-inflammatory effect and modulation of bone signaling pathways. Lately, nanomedicine has emerged as an innovative concept for new treatments in bone-related pathologies envisaged through the incorporation of medicinal substances in nanometric systems for oral or local administration, as well as in nanostructured scaffolds with huge potential in bone tissue engineering.

Wood as Possible Renewable Material for Bone Implants-Literature Review

Bone fractures and bone defects affect millions of people every year. Metal implants for bone fracture fixation and autologous bone for defect reconstruction are used extensively in treatment of these pathologies. Simultaneously, alternative, sustainable, and biocompatible materials are being researched to improve existing practice. Wood as a biomaterial for bone repair has not been considered until the last 50 years. Even nowadays there is not much research on solid wood as a biomaterial in bone implants. A few species of wood have been investigated. Different techniques of wood preparation have been proposed. Simple pre-treatments such as boiling in water or preheating of ash, birch and juniper woods have been used initially. Later researchers have tried using carbonized wood and wood derived cellulose scaffold. Manufacturing implants from carbonized wood and cellulose requires more extensive wood processing-heat above 800 °C and chemicals to extract cellulose. Carbonized wood and cellulose scaffolds can be combined with other materials, such as silicon carbide, hydroxyapatite, and bioactive glass to improve biocompatibility and mechanical durability. Throughout the publications wood implants have provided good biocompatibility and osteoconductivity thanks to wood's porous structure.

Long-Term Fate and Efficacy of a Biomimetic (Sr)-Apatite-Coated Carbon Patch Used for Bone Reconstruction

Critical bone defect repair remains a major medical challenge. Developing biocompatible materials with bone-healing ability is a key field of research, and calcium-deficient apatites (CDA) are appealing bioactive candidates. We previously described a method to cover activated carbon cloths (ACC) with CDA or strontium-doped CDA coatings to generate bone patches. Our previous study in rats revealed that apposition of ACC or ACC/CDA patches on cortical bone defects accelerated bone repair in the short term. This study aimed to analyze in the medium term the reconstruction of cortical bone in the presence of ACC/CDA or ACC/10Sr-CDA patches corresponding to 6 at.% of strontium substitution. It also aimed to examine the behavior of these cloths in the medium and long term, in situ and at distance. Our results at day 26 confirm the particular efficacy of strontium-doped patches on bone reconstruction, leading to new thick bone with high bone quality as quantified by Raman microspectroscopy. At 6 months the biocompatibility and complete osteointegration of these carbon cloths and the absence of micrometric carbon debris, either out of the implantation site or within peripheral organs, was confirmed. These results demonstrate that these composite carbon patches are promising biomaterials to accelerate bone reconstruction.

The bioelectrical properties of bone tissue

Understanding the bioelectrical properties of bone tissue is key to developing new treatment strategies for bone diseases and injuries, as well as improving the design and fabrication of scaffold implants for bone tissue engineering. The bioelectrical properties of bone tissue can be attributed to the interaction of its various cell lineages (osteocyte, osteoblast and osteoclast) with the surrounding extracellular matrix, in the presence of various biomechanical stimuli arising from routine physical activities; and is best described as a combination and overlap of dielectric, piezoelectric, pyroelectric and ferroelectric properties, together with streaming potential and electro-osmosis. There is close interdependence and interaction of the various electroactive and electrosensitive components of bone tissue, including cell membrane potential, voltage-gated ion channels, intracellular signaling pathways, and cell surface receptors, together with various matrix components such as collagen, hydroxyapatite, proteoglycans and glycosaminoglycans. It is the remarkably complex web of interactive cross-talk between the organic and non-organic components of bone that define its electrophysiological properties, which in turn exerts a profound influence on its metabolism, homeostasis and regeneration in health and disease. This has spurred increasing interest in application of electroactive scaffolds in bone tissue engineering, to recapitulate the natural electrophysiological microenvironment of healthy bone tissue to facilitate bone defect repair.

Interactions between Dental MSCs and Biomimetic Composite Scaffold during Bone Remodeling Followed by In Vivo Real-Time Bioimaging

Oral-maxillofacial tumor removal can generate critical bone defects and major problems for patients, causing dysfunctionalities and affecting oral competencies such as mastication, swallowing, and breathing. The association of novel biomaterials and cell therapies in tissue engineering strategies could offer new strategies to promote osteomucosa healing. This study focused on the development of a bioengineered construct loaded with human dental follicle cells (MSCs). To increase the bioconstruct integration to the surrounding tissue, a novel and comprehensive approach was designed combining an injectable biomimetic hydrogel and dental stem cells (hDFMSCs) expressing luminescence/fluorescence for semi-quantitative tissue imaging in live animals. This in vivo model with human MSCs was based on an intramembranous bone regeneration process (IMO). Biologically, the biocomposite based on collagen/nanohydroxyapatite filled with cell-loaded osteopontin-fibrin hydrogel (Coll/nanoHA OPN-Fb) exhibited a high cellular proliferation rate, increased bone extracellular matrix deposition (osteopontin) and high ALP activity, indicating an early osteogenic differentiation. Thus, the presence of human OPN enhanced hDFMSC adhesion, migration, and spatial distribution within the 3D matrix. The developed 3D bioconstruct provided the necessary pro-regenerative effect to modulate the biological response, precisely fitting the bone defect with fine-tuned adjustment to the surrounding original structure and promoting oral osteomucosa tissue regeneration. We were also able to track the cells in vivo and evaluate their behavior (migration, proliferation, and differentiation), providing a glimpse into bone regeneration and helping in the optimization of patient-specific therapies.

Review of Physical, Mechanical, and Biological Characteristics of 3D-Printed Bioceramic Scaffolds for Bone Tissue Engineering Applications

This review focuses on the advancements in additive manufacturing techniques that are utilized for fabricating bioceramic scaffolds and their characterizations leading to bone tissue regeneration. Bioscaffolds are made by mimicking the human bone structure, material composition, and properties. Calcium phosphate apatite materials are the most commonly used scaffold materials as they closely resemble live bone in their inorganic composition. The functionally graded scaffolds are fabricated by utilizing the right choice of the 3D printing method and material combinations to achieve the requirement of the bioscaffold. To tailor the physical, mechanical, and biological properties of the scaffold, certain materials are reinforced, doped, or coated to incorporate the functionality. The biomechanical loading conditions that involve flexion, torsion, and tension exerted on the implanted scaffold are discussed. The finite element analysis (FEA) technique is used to investigate the mechanical property of the scaffold before fabrication. This helps in reducing the actual number of samples used for testing. The FEA simulated results and the experimental result are compared. This review also highlights some of the challenges associated while processing the scaffold such as shrinkage, mechanical instability, cytotoxicity, and printability. In the end, the new materials that are evolved for tissue engineering applications are compiled and discussed.

The Preliminary Assessment of New Biomaterials Necessitates a Comparison of Direct and Indirect Cytotoxicity Methodological Approaches

BACKGROUND

Cytotoxicity testing is a primary method to establish the safety of biomaterials, e.g., biocomposites. Biomaterials involve a wide range of medical materials, which are usually solid materials and are used in bone regeneration, cardiology, or dermatology. Current advancements in science and technology provide several standard cytotoxicity testing methods that are sufficiently sensitive to detect various levels of cellular toxicity, i.e., from low to high. The aim was to compare the direct and indirect methodology described in the ISO guidelines UNE-EN ISO 10993-5:2009 Part 5.

METHODS

Cell proliferation was measured using WST-1 assay, and cytotoxicity was measured using LDH test kit.

RESULTS

The results indicate that the molecular surface of biomaterials have impact on the cytotoxicity and proliferation profile. Based on these results, we confirm that the indirect method does not provide a clear picture of the cell condition after the exposure to the surface, and moreover, cannot provide complete results about the effects of the material.

CONCLUSIONS

Comparison of both methods shows that it is pivotal to investigate biomaterials at the very early stages using both indirect and direct methods to access the influence of the released toxins and surface of the material on the cell condition.

Bio-Activation of HA/β-TCP Porous Scaffolds by High-Pressure CO2 Surface Remodeling: A Novel "Coating-from" Approach

Biphasic macroporous Hydroxyapatite/β-Tricalcium Phosphate (HA/β-TCP) scaffolds (BCPs) are widely used for bone repair. However, the high-temperature HA and β-TCP phases exhibit limited bioactivity (low solubility of HA, restricted surface area, low ion release). Strategies were developed to coat such BCPs with biomimetic apatite to enhance bioactivity. However, this can be associated with poor adhesion, and metastable solutions may prove difficult to handle at the industrial scale. Alternative strategies are thus desirable to generate a highly bioactive surface on commercial BCPs. In this work, we developed an innovative "coating from" approach for BCP surface remodeling via hydrothermal treatment under supercritical CO2, used as a reversible pH modifier and with industrial scalability. Based on a set of complementary tools including FEG-SEM, solid state NMR and ion exchange tests, we demonstrate the remodeling of macroporous BCP surface with the occurrence of dissolution-reprecipitation phenomena involving biomimetic CaP phases. The newly precipitated compounds are identified as bone-like nanocrystalline apatite and octacalcium phosphate (OCP), both known for their high bioactivity character, favoring bone healing. We also explored the effects of key process parameters, and showed the possibility to dope the remodeled BCPs with antibacterial Cu2+ ions to convey additional functionality to the scaffolds, which was confirmed by in vitro tests. This new process could enhance the bioactivity of commercial BCP scaffolds via a simple and biocompatible approach.

Could Curdlan/Whey Protein Isolate/Hydroxyapatite Biomaterials Be Considered as Promising Bone Scaffolds?-Fabrication, Characterization, and Evaluation of Cytocompatibility towards Osteoblast Cells In Vitro

The number of bone fractures and cracks requiring surgical interventions increases every year; hence, there is a huge need to develop new potential bone scaffolds for bone regeneration. The goal of this study was to gain knowledge about the basic properties of novel curdlan/whey protein isolate/hydroxyapatite biomaterials in the context of their use in bone tissue engineering. The purpose of this research was also to determine whether the concentration of whey protein isolate in scaffolds has an influence on their properties. Thus, two biomaterials differing in the concentration of whey protein isolate (i.e., 25 wt.% and 35 wt.%; hereafter called Cur_WPI25_HAp and Cur_WPI35_HAp, respectively) were fabricated and subjected to evaluation of porosity, mechanical properties, swelling ability, protein release capacity, enzymatic biodegradability, bioactivity, and cytocompatibility towards osteoblasts in vitro. It was found that both biomaterials fulfilled a number of requirements for bone scaffolds, as they demonstrated limited swelling and the ability to undergo controllable enzymatic biodegradation, to form apatite layers on their surfaces and to support the viability, growth, proliferation, and differentiation of osteoblasts. On the other hand, the biomaterials were characterized by low open porosity, which may hinder the penetration of cells though their structure. Moreover, they had low mechanical properties compared to natural bone, which limits their use to filling of bone defects in non-load bearing implantation areas, e.g., in the craniofacial area, but then they will be additionally supported by application of mechanically strong materials such as titanium plates. Thus, this preliminary in vitro research indicates that biomaterials composed of curdlan, whey protein isolate, and hydroxyapatite seem promising for bone tissue engineering applications, but their porosity and mechanical properties should be improved. This will be the subject of our further work.

Strontium Functionalization of Biomaterials for Bone Tissue Engineering Purposes: A Biological Point of View

Strontium (Sr) is a trace element taken with nutrition and found in bone in close connection to native hydroxyapatite. Sr is involved in a dual mechanism of coupling the stimulation of bone formation with the inhibition of bone resorption, as reported in the literature. Interest in studying Sr has increased in the last decades due to the development of strontium ranelate (SrRan), an orally active agent acting as an anti-osteoporosis drug. However, the use of SrRan was subjected to some limitations starting from 2014 due to its negative side effects on the cardiac safety of patients. In this scenario, an interesting perspective for the administration of Sr is the introduction of Sr ions in biomaterials for bone tissue engineering (BTE) applications. This strategy has attracted attention thanks to its positive effects on bone formation, alongside the reduction of osteoclast activity, proven by in vitro and in vivo studies. The purpose of this review is to go through the classes of biomaterials most commonly used in BTE and functionalized with Sr, i.e., calcium phosphate ceramics, bioactive glasses, metal-based materials, and polymers. The works discussed in this review were selected as representative for each type of the above-mentioned categories, and the biological evaluation in vitro and/or in vivo was the main criterion for selection. The encouraging results collected from the in vitro and in vivo biological evaluations are outlined to highlight the potential applications of materials’ functionalization with Sr as an osteopromoting dopant in BTE.

Clinical Applications of Cell-Scaffold Constructs for Bone Regeneration Therapy

Bone tissue engineering (BTE) is a process of combining live osteoblast progenitors with a biocompatible scaffold to produce a biological substitute that can integrate into host bone tissue and recover its function. Mesenchymal stem cells (MSCs) are the most researched post-natal stem cells because they have self-renewal properties and a multi-differentiation capacity that can give rise to various cell lineages, including osteoblasts. BTE technology utilizes a combination of MSCs and biodegradable scaffold material, which provides a suitable environment for functional bone recovery and has been developed as a therapeutic approach to bone regeneration. Although prior clinical trials of BTE approaches have shown promising results, the regeneration of large bone defects is still an unmet medical need in patients that have suffered a significant loss of bone function. In this present review, we discuss the osteogenic potential of MSCs in bone tissue engineering and propose the use of immature osteoblasts, which can differentiate into osteoblasts upon transplantation, as an alternative cell source for regeneration in large bone defects.