Improved Bone Regeneration in Rabbit Bone Defects Using 3D Printed Composite Scaffolds Functionalized with Osteoinductive Factors

Improved Bone Regeneration Using Biodegradable Polybutylene Succinate Artificial Scaffold with BMP-2 Protein in a Rabbit Model

Extensive bone loss represents a great challenge for orthopedic and reconstructive surgery. On an in vivo rabbit model, the healing of two bone defects on a long bone, tibia, was studied. A polybutylene succinate (PBS) microfibrillar scaffold was implemented with BMP-2 protein and hydroxyapatite (HA) as potential osteogenic factors. The present study was carried out on 6 male New Zealand white (4-6 months old) rabbits in vivo model. One bone defect was created in each subject on the tibia. The controls were left to heal spontaneously while the study samples were treated with the polybutylene succinate (PBS) microfibrillar scaffolds doped with BMP-2 and HA. Histological and immunohistochemical analyses were performed after euthanasia at 3 and 6 months. The bone defect treated with the BMP-2 PBS scaffold shows, from 3 months, a significantly increased presence of activated osteoblasts with mineralized bone tissue deposition. This study confirms the great potential of PBS scaffolds in the clinical treatment of bone defects.

3D-Printed Scaffolds for Cranial Bone Regeneration: A Systematic Review of Design, Materials, and Computational Optimization

Cranial bone defects from trauma, congenital conditions, or surgery are challenging to treat due to the skull's limited regeneration. Traditional methods like autografts and allografts have drawbacks, including donor site issues and poor integration. 3D-printed scaffolds provide a patient-specific alternative, improving bone regeneration and integration. This review evaluates advancements in 3D-printed scaffolds for cranial bone regeneration, focusing on fabrication techniques, material innovations, and structural optimization while assessing their preclinical and clinical potential. A systematic literature search (2014-2024) was conducted using PubMed and other databases. Studies addressing scaffold properties such as porosity, pore interconnectivity, and mechanical stability were included, while non-cranial scaffold studies were excluded. Advances in 3D printing have enabled patient-specific scaffolds with optimized architecture to enhance bone regeneration, mechanical support, and nutrient transport. Bioceramics, polymers, and composites mimic native bone properties, while bioactive coatings further improve osteogenesis. However, limited clinical translation and insufficient customization remain challenges. Further preclinical and clinical trials are crucial to overcoming barriers in mechanical optimization and patient-specific scaffold fabrication, bridging the gap between research and clinical applications.

Engineered 3D-Printable Nanohydroxyapatite Biocomposites with Cold Plasma-Tailored Surface Features to Boost Osseointegration

Medical implants, being biomaterials with increasing global use, continue to attract researchers focused on enhancing clinical performance. In situations requiring bone substitutes, there is a search for advancements in synthetic graft biomaterials, with polymer-based implants being one of the potential materials. Thus, this study aims to develop versatile nanohydroxyapatite (nHAP) biocomposites that can not only be generalized by resin composite systems but also be applicable for 3D printing, overcoming the limitations associated with traditional implants. Polymeric biocomposites are prepared by incorporating nHAPs and strontium-doped SiO2 glass particles (GPs) into a photocurable methacrylate monomer system, followed by 3 min of cold atmosphere plasma irradiation. In light of our findings, this medical implant possesses strong mechanical strength. Its surface hydrophilicity is enhanced through cold plasma treatment, which involves surface dry etching with nanoscale precision and exposing the embedded nanofillers to the outmost surface. This cold plasma treatment also induces osteogenic activity in vitro and bone integration in vivo. Furthermore, the 3D printability is demonstrated through the fabrication of a gyroid lattice structure. Collectively, this nHAP-biocomposite exhibits promising biomechanical and biological properties, providing potential for revolutionizing future implant applications in dental and maxillofacial reconstruction as well as orthopedic interbody fusion.

Customized Hydrogel System for the Spatiotemporal Sequential Treatment of Periodontitis Propelled by ZEB1

Advanced periodontitis initiates with Porphyromonas gingivalis (P. gingivalis) infection, which subsequently triggers chronic inflammation, immune imbalance, and ultimately causes alveolar bone resorption. Traditional periodontal treatment focuses on the elimination of triggering factors, but tend to ignore the improvement of the inflammatory microenvironment and the remodeling of the osteogenic mineralization space. Herein, zinc-aluminum layered double hydroxide nanosheets (LDHs) loaded with icariin (ICA) are encapsulated into a gallic acid (GA)-modified hydroxybutyl chitosan hydrogel (GA-HBC), giving rise to a customized hydrogel system named GA-HBC-LIC, which can sequentially actualize antibacterial, anti-inflammatory, and remineralization functions. A neutral chemical-humoral space is created for osteogenesis via means of sequential regulation by the smart hydrogel. Concomitantly, appropriate mechanical properties and degradation performance of the hydrogel provide a desirable physical space for remineralization. In the spatiotemporal modulation of the hydrogel, zinc finger E-box-binding homeobox 1 (ZEB1) target of released zinc ions (Zn2+) action promotes macrophage polarization from M1 to M2 phenotype, thereby remodeling the immune microenvironment and releasing cytokines conducive to tissue regeneration. In sum, this study highlights the critical role of sequential inflammation regulation and the maintenance of osteogenic space in the regeneration of periodontal tissues, offering new insights for the clinical management of periodontitis.

Enhancing Osteogenesis and Mechanical Properties through Scaffold Design in 3D Printed Bone Substitutes

In the context of regenerative medicine, the design of scaffolds to possess excellent osteogenesis and appropriate mechanical properties has gained significant attention in bone tissue engineering. In this review, we categorized materials into metallic, inorganic, nonmetallic, organic polymer, and composite materials. This review provides a more integrated and multidimensional analysis of scaffold design for bone tissue engineering. Unlike previous works that often focus on single aspects, such as material type or fabrication technique, our review takes a broader approach. It analyzes the interaction between scaffold materials, 3D printing techniques, scaffold structural designs, modification methods, porosities, and pore sizes, and the composition of materials (particularly composite materials). Meanwhile, it focuses on their impacts on scaffolds' osteogenic potential and mechanical performance. This review also provides suggested ranges for porosity and pore size for different materials and outlines recommended surface modification methods. This approach not only consolidates current knowledge but also highlights the interdependencies among various factors affecting scaffold efficacy, offering deeper insights into optimization strategies tailored for specific clinical conditions. Furthermore, we introduce recent advancements in innovative 3D printing techniques and novel composite materials, which are rarely addressed in previous reviews, thereby providing a forward-looking perspective that informs future research directions and clinical applications.

Collagen as a bio-ink for 3D printing: a critical review

The significance of three-dimensional (3D) bioprinting in the domain of regenerative medicine and tissue engineering is readily apparent. To create a multi-functional bioinspired structure, 3D bioprinting requires high-performance bioinks. Bio-inks refer to substances that encapsulate viable cells and are employed in the printing procedure to construct 3D objects progressive through successive layers. For a bio-ink to be considered high-performance, it must meet several critical criteria: printability, gelation kinetics, structural integrity, elasticity and strength, cell adhesion and differentiation, mimicking the native ECM, cell viability and proliferation. As an exemplar application, tissue grafting is used to repair and replace severely injured tissues. The primary considerations in this case include compatibility, availability, advanced surgical techniques, and potential complications after the operation. 3D printing has emerged as an advancement in 3D culture for its use as a regenerative medicine approach. Thus, additive technologies such as 3D bioprinting may offer safe, compatible, and fast-healing tissue engineering options. Multiple methods have been developed for hard and soft tissue engineering during the past few decades, however there are many limitations. Despite significant advances in 3D cell culture, 3D printing, and material creation, a gold standard strategy for designing and rebuilding bone, cartilage, skin, and other tissues has not yet been achieved. Owing to its abundance in the human body and its critical role in protecting and supporting human tissues, soft and hard collagen-based bioinks is an attractive proposition for 3D bioprinting. Collagen, offers a good combination of biocompatibility, controllability, and cell loading. Collagen made of triple helical collagen subunit is a protein-based organic polymer present in almost every extracellular matrix of tissues. Collagen-based bioinks, which create bioinspired scaffolds with multiple functionalities and uses them in various applications, is a represent a breakthrough in the regenerative medicine and biomedical engineering fields. This protein can be blended with a variety of polymers and inorganic fillers to improve the physical and biological performance of the scaffolds. To date, there has not been a comprehensive review appraising the existing literature surround the use of collagen-based bioink applications in 'soft' or 'hard' tissue applications. The uses of the target region in soft tissues include the skin, nerve, and cartilage, whereas in the hard tissues, it specifically refers to bone. For soft tissue healing, collagen-based bioinks must meet greater functional criteria, whereas hard tissue restoration requires superior mechanical qualities. Herein, we summarise collagen-based bioink's features and highlight the most essential ones for diverse healing situations. We conclude with the primary challenges and difficulties of using collagen-based bioinks and suggest future research objectives.

3D Bioprinting in Limb Salvage Surgery

With the development of 3D bioprinting and the creation of innovative biocompatible materials, several new approaches have brought advantages to patients and surgical teams. Increasingly more bone defects are now treated using 3D-bioprinted prostheses and implementing new solutions relies on the ability of engineers and medical teams to identify methods of anchoring 3D-printed prostheses and to reveal the potential influence of bioactive materials on surrounding tissues. In this paper, we described why limb salvage surgery based on 3D bioprinting is a reliable and effective alternative to amputations, and why this approach is considered the new standard in modern medicine. The preliminary results of 3D bioprinting in one of the most challenging fields in surgery are promising for the future of machine-based medicine, but also for the possibility of replacing various parts from the human body with bioactive-based constructs. In addition, besides the materials and constructs that are already tested and applied in the human body, we also reviewed bioactive materials undergoing in vitro or in vivo testing with great potential for human applications in the near future. Also, we explored the recent advancements in clinically available 3D-bioprinted constructs and their relevance in this field.

Strontium-Substituted Nanohydroxyapatite Containing Biodegradable 3D Printed Composite Scaffolds for Bone Regeneration

Treatment of large-size bone defects is difficult, and acquiring autografts may be challenging due to limited availability. A synthetic patient-specific bone substitute can be developed by using 3D printing technologies in such cases. In the present study, we have developed photocurable composite resins with poly(trimethylene carbonate) (PTMC) containing a high percentage of biodegradable bioactive strontium-substituted nanohydroxyapatite (SrHA, size 30-70 nm). These photocurable resins have then been employed to develop high-surface-area 3D-printed bone substitutes using the digital light processing (DLP) technique. To enhance the surface area of the 3D-printed substitute, cryogels alone and functionalized with bioactive components of bone morphogenetic protein (BMP) and zoledronic acid (ZA) were filled within the 3D-printed scaffold/substitute. The scaffolds were tested in vitro for biocompatibility and functionality in vivo in two therapeutically relevant rat models with large bone defects (4 mm). The porosities of 3D printed scaffolds were found to be 60.1 ± 0.9%, 72.9 ± 0.5%, and 74.3 ± 1.6% for PTMC, PTMC-HA, and PTMC-SrHA, respectively, which is in the range of cancellous bone (50-95%). The thermogravimetric analysis demonstrated the fabrication of 3D printed composites with HA and SrHA concentrations of 51.5 and 57.4 wt %, respectively, in the PTMC matrix. The tensile Young's modulus (E), compressive moduli, and wettability increased post incorporation of SrHA and HA in the PTMC matrix. In vitro and in vivo results revealed that SrHA integrated into the PTMC matrix exhibited good physicochemical and biological properties. Furthermore, the osteoactive molecule-functionalized 3D printed composite scaffolds were found to have an adequate osteoconductive and osteoinductive surface that has shown increased bone regeneration and defect repair in both tibial and cranial bone defects. Our findings thus support the use of PTMC-SrHA composites as next-generation patient-specific synthetic bioactive biodegradable bone substitutes.

Cryogels Composites: Recent Improvement in Bone Tissue Engineering

Autogenous bone grafts have long been considered the optimal choice for bone reconstruction due to their excellent biocompatibility and osteogenic properties. However, their limited availability and associated donor site morbidity have led to exploration of alternative bone substitutes. Cryogels, with their interconnected porosity, shape recovery, and enhanced mass transport capabilities, have emerged as a promising polymer-based solution. By incorporating bioactive glasses and nanofillers, cryogel composites offer bioactivity, cost-efficiency, and easy cell integration. This approach not only enhances bone regeneration but also underscores the broader role of nanotechnology in regenerative medicine. This mini-review discusses the advancement of organic-inorganic composites, focusing on biopolymeric cryogels and inorganic elements for reinforcement. We highlight how cryogels can be integrated into minimally invasive procedures, reducing patient distress and complications, and advanced 3D-printing techniques that enable further customization of these materials to mimic bone tissue architecture, offering potential for patient-specific treatments.

Utilization of Additive Manufacturing Techniques for the Development of a Novel Scaffolds with Magnetic Properties for Potential Application in Enhanced Bone Regeneration

This study focuses on designing and evaluating scaffolds with essential properties for bone regeneration, such as biocompatibility, macroporous geometry, mechanical strength, and magnetic responsiveness. The scaffolds are made using 3D printing with acrylic resin and iron oxides synthesized through solution combustion. Utilizing triply periodic minimal surfaces (TPMS) geometry and mask stereolithography (MSLA) printing, the scaffolds achieve precise geometrical features. The mechanical properties are enhanced through resin curing, and magnetite particles from synthesized nanoparticles and alluvial magnetite are added for magnetic properties. The scaffolds show a balance between stiffness, porosity, and magnetic responsiveness, with maximum compression strength between 4.8 and 9.2 MPa and Young's modulus between 58 and 174 MPa. Magnetic properties such as magnetic coercivity, remanence, and saturation are measured, with the best results from scaffolds containing synthetic iron oxides at 1% weight. The viscosity of the mixtures used for printing is between 350 and 380 mPas, and contact angles between 90° and 110° are achieved. Biocompatibility tests indicate the potential for clinical trials, though further research is needed to understand the impact of magnetic properties on cellular interactions and optimize scaffold design for specific applications. This integrated approach offers a promising avenue for the development of advanced materials capable of promoting enhanced bone regeneration.

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.

Research progress of gene therapy combined with tissue engineering to promote bone regeneration

Gene therapy has emerged as a highly promising strategy for the clinical treatment of large segmental bone defects and non-union fractures, which is a common clinical need. Meanwhile, many preclinical data have demonstrated that gene and cell therapies combined with optimal scaffold biomaterials could be used to solve these tough issues. Bone tissue engineering, an interdisciplinary field combining cells, biomaterials, and molecules with stimulatory capability, provides promising alternatives to enhance bone regeneration. To deliver and localize growth factors and associated intracellular signaling components into the defect site, gene therapy strategies combined with bioengineering could achieve a uniform distribution and sustained release to ensure mesenchymal stem cell osteogenesis. In this review, we will describe the process and cell molecular changes during normal fracture healing, followed by the advantages and disadvantages of various gene therapy vectors combined with bone tissue engineering. The growth factors and other bioactive peptides in bone regeneration will be particularly discussed. Finally, gene-activated biomaterials for bone regeneration will be illustrated through a description of characteristics and synthetic methods.

Significance and considerations of establishing standardized critical values for critical size defects in animal models of bone tissue regeneration

Establishing animal models with critical size defects (CSDs) is critical for conducting experimental investigations engineering of bone tissue regeneration. Currently, a standardised protocol for establishing an animal CSDs model has not been developed. Furthermore, a consensus has not been reached regarding the critical values of CSDs. Successful establishment of animal models for CSDs is a complex process that requires researchers to meticulously consider a variety of factors such as age, species, bone defect size and anatomic location. The specific numerical values for CSDs in small animal models vary, and a clear definition of the critical value for large animal CSDs models in the literature is still lacking. This review consolidates the advancements in critical bone defects animal models by outlining the research landscape across variables, including animal species, age groups, bone defect sites, and sizes, to offer valuable guidance and a theoretical framework for the establishment of pertinent experimental animal models.

Correlation between Ca Release and Osteoconduction by 3D-Printed Hydroxyapatite-Based Templates

The application of hydroxyapatite (HA)-based templates is quite often seen in bone tissue engineering since that HA is an osteoconductive bioceramic material, which mimics the inorganic component of mineralized tissues. However, the reported osteoconductivity varies in vitro and in vivo, and the levels of calcium (Ca) release most favorable to osteoconduction have yet to be determined. In this study, HA-based templates were fabricated by melt-extrusion 3D-printing and characterized in order to determine a possible correlation between Ca release and osteoconduction. The HA-based templates were blended with poly(lactide-co-trimethylene carbonate) (PLATMC) at three different HA ratios: 10, 30, and 50%. The printability and physical properties of the HA templates were compared with those of pristine PLATMC. In vitro, osteoconductivity was assessed using seeded human bone marrow-derived mesenchymal stem cells. A mild rate of Ca release was observed for HA10 templates, which exhibited higher mineralized extracellular matrix (ECM) secretion than PLATMC at 14 and 21 days. In contrast, the high rate of Ca release exhibited by HA30 and HA50 templates was associated with reduced osteoconduction and impeded mineralized ECM secretion in vitro. Similar results were observed in vivo. In the calvarial defect model in rabbit, PLATMC and HA10 templates exhibited the highest amount of new bone formation, with obvious contact osteogenesis on their surfaces. In contrast, HA30 and HA50 exhibited distant osteogenesis and reduced amounts of new bone ingrowth. It is concluded that HA-based templates are osteoconductive only at low rates of Ca release.

Enriched mesoporous bioactive glass scaffolds as bone substitutes in critical diaphyseal bone defects in rabbits

In the field of orthopedic surgery, there is an increasing need for the development of bone replacement materials for the treatment of bone defects. One of the main focuses of biomaterials engineering are advanced bioceramics like mesoporous bioactive glasses (MBG´s). The present study compared the new bone formation after 12 weeks of implantation of MBG scaffolds with composition 82,5SiO2-10CaO-5P2O5-x 2.5SrO alone (MBGA), enriched with osteostatin, an osteoinductive peptide, (MBGO) or enriched with bone marrow aspirate (MBGB) in a long bone critical defect in radius bone of adult New Zealand rabbits. New bone formation from the MBG scaffold groups was compared to the gold standard defect filled with iliac crest autograft and to the unfilled defect. Radiographic follow-up was performed at 2, 6, and 12 weeks, and microCT and histologic examination were performed at 12 weeks. X-Ray study showed the highest bone formation scores in the group with the defect filled with autograft, followed by the MBGB group, in addition, the microCT study showed that bone within defect scores (BV/TV) were higher in the MBGO group. This difference could be explained by the higher density of newly formed bone in the osteostatin enriched MBG scaffold group. Therefore, MBG scaffold alone and enriched with osteostatin or bone marrow aspirate increase bone formation compared to defect unfilled, being higher in the osteostatin group. The present results showed the potential to treat critical bone defects by combining MBGs with osteogenic peptides such as osteostatin, with good prospects for translation into clinical practice. STATEMENT OF SIGNIFICANCE: Treatment of bone defects without the capacity for self-repair is a global problem in the field of Orthopedic Surgery, as evidenced by the fact that in the U.S alone it affects approximately 100,000 patients per year. The gold standard of treatment in these cases is the autograft, but its use has limitations both in the amount of graft to be obtained and in the morbidity produced in the donor site. In the field of materials engineering, there is a growing interest in the development of a bone substitute equivalent. Mesoporous bioactive glass (MBG´s) scaffolds with three-dimensional architecture have shown great potential for use as a bone substitutes. The osteostatin-enriched Sr-MBG used in this long bone defect in rabbit radius bone in vivo study showed an increase in bone formation close to autograft, which makes us think that it may be an option to consider as bone substitute.

Immunomodulatory nanomedicine for osteoporosis: Current practices and emerging prospects

Osteoporosis results from the disruption of the balance between bone resorption and bone formation. However, classical anti-osteoporosis drugs exhibit several limitations in clinical applications, such as multiple adverse reactions and poor therapeutic effects. Therefore, there is an urgent need for alternative treatment strategies. With the evolution of immunomodulatory nanomedicine, a variety of nanomaterials have been designed for anti-osteoporosis treatment, offering prospects of minimal adverse reactions, enhanced bone induction, and high osteogenic activity. This review initially provides a brief overview of the fundamental principles of bone reconstruction, current osteogenic clinical methods in osteoporosis treatment, and the significance of osteogenic-angiogenic coupling, laying the groundwork for understanding the pathophysiology and therapeutics of osteoporosis. Subsequently, the article emphasizes the relationship between bone immunity and osteogenesis-angiogenesis coupling and provides a detailed analysis of the application of immunomodulatory nanomedicines in the treatment of osteoporosis, including various types of nanomaterials and their integration with carrier biomaterials. Importantly, we discuss the potential of some emerging strategies in immunomodulatory nanomedicine for osteoporosis treatment. This review introduces the innovative applications of immunomodulatory nanomedicine in the treatment of osteoporosis, aiming to serve as a reference for the application of immunomodulatory nanomedicine strategies in osteoporosis treatment. STATEMENT OF SIGNIFICANCE: Osteoporosis, as one of the most prevalent skeletal disorders, poses a significant threat to public health. To date, conventional anti-osteoporosis strategies have been limited in efficacy and plagued with numerous side effects. Fortunately, with the advancement of research in osteoimmunology and nanomedicine, strategies integrating these two fields show great promise in combating osteoporosis. Nanomedicine with immunomodulatory properties exhibits enhanced efficiency, prolonged effectiveness, and increased safety. However, as of now, there exists no comprehensive review amalgamating immunomodulation with nanomedicine to delineate the progress of immunomodulatory nanomedicine in osteoporosis treatment, as well as the future direction of this strategy.

Current application and future perspectives of antimicrobial degradable bone substitutes for chronic osteomyelitis

Chronic osteomyelitis remains a persistent challenge for the surgeons due to its refractory nature. Generally, treatment involves extensive debridement of necrotic bone, filling of dead space, adequate antimicrobial therapy, bone reconstruction, and rehabilitation. However, the optimal choice of bone substitute to manage the bone defect remains debatable. This paper reviewed the clinical evidence for antimicrobial biodegradable bone substitutes in the treatment of osteomyelitis in recent years. Indeed, this combination was proved to eradicate infection and facilitate bone reconstruction, which might reduce the cost and hospital stay. Handling was associated with increased risk of unwanted side effect to affect bone healing. The study provides some valuable insights into the clinical evaluation of treatment outcomes in the aspects of infection eradication, bone reconstruction, and complications caused by materials. However, achieving complete infection eradication and subsequently perfect bone reconstruction remains challenging in compromised conditions, hence advanced innovative bone substitutes are imperative. In this review, we mainly focus on the desired functional effects of advanced bone substitutes on infection eradication and bone reconstruction from the future perspective. Handling property was optimized to simplify surgery process. It is expected that this review will provide an important opportunity to enhance the understanding of the design and application of innovative biomaterials to synergistically eradicate infection and restore integrity and function of bone.

In Vitro and In Vivo Degradation of Photo-Crosslinked Poly(Trimethylene Carbonate-co-ε-Caprolactone) Networks

Three-armed poly(trimethylene carbonate) (PTMC) and poly(trimethylene carbonate-co-Ɛ-caprolactone) (P(TMC-co-ε-CL)) macromers with molecular weights of approximately 30 kg mol-1 are synthesized by ring-opening polymerization and subsequent functionalization with methacrylic anhydride. Networks are then prepared by photo-crosslinking. To investigate the in vitro and in vivo degradation properties of these photo-crosslinked networks and assess the effect of ε-caprolactone content on the degradation properties, PTMC networks, and copolymer networks with two different TMC:ε-CL ratios are prepared. PTMC networks degraded slowly, via an enzymatic surface erosion process, both in vitro and in vivo. Networks prepared from P(TMC-co-ε-CL) macromers with a 74:26 ratio are found to degrade slowly as well, via a surface erosion process, albeit at a higher rate compared to PTMC networks. Increasing the ε-CL content to a ratio of 52:48, resulted in a faster degradation. These networks lost their mechanical properties much sooner than the other networks. Thus, PTMC and P(TMC-co-ε-CL) networks are interesting networks for tissue engineering purposes and the exact degradation properties can be tuned by varying the TMC:ε-CL ratio, providing researchers with a tool to obtain copolymer networks with the desired degradation rate depending on the intended application.

Towards the Clinical Translation of 3D PLGA/β-TCP/Mg Composite Scaffold for Cranial Bone Regeneration

Recent years have witnessed the rapid development of 3D porous scaffolds with excellent biocompatibility, tunable porosity, and pore interconnectivity, sufficient mechanical strength, controlled biodegradability, and favorable osteogenesis for improved results in cranioplasty. However, clinical translation of these scaffolds has lagged far behind, mainly because of the absence of a series of biological evaluations. Herein, we designed and fabricated a composite 3D porous scaffold composed of poly (lactic-co-glycolic) acid (PLGA), β-tricalcium phosphate (β-TCP), and Mg using the low-temperature deposition manufacturing (LDM) technique. The LDM-engineered scaffolds possessed highly porous and interconnected microstructures with a porosity of 63%. Meanwhile, the scaffolds exhibited mechanical properties close to that of cancellous bone, as confirmed by the compression tests. It was also found that the original composition of scaffolds could be maintained throughout the fabrication process. Particularly, two important biologic evaluations designed for non-active medical devices, i.e., local effects after implantation and subchronic systemic toxicity tests, were conducted to evaluate the local and systemic toxicity of the scaffolds. Additionally, the scaffolds exhibited significant higher mRNA levels of osteogenic genes compared to control scaffolds, as confirmed by an in vitro osteogenic differentiation test of MC3T3-E1 cells. Finally, we demonstrated the improved cranial bone regeneration performance of the scaffolds in a rabbit model. We envision that our investigation could pave the way for translating the LDM-engineered composite scaffolds into clinical products for cranial bone regeneration.

Cryogel Scaffolds for Tissue-Engineering: Advances and Challenges for Effective Bone and Cartilage Regeneration

Critical-sized bone defects and articular cartilage injuries resulting from trauma, osteonecrosis, or age-related degeneration can be often non-healed by physiological repairing mechanisms, thus representing a relevant clinical issue due to a high epidemiological incidence rate. Novel tissue-engineering approaches have been proposed as an alternative to common clinical practices. This cutting-edge technology is based on the combination of three fundamental components, generally referred to as the tissue-engineering triad: autologous or allogenic cells, growth-stimulating factors, and a scaffold. Three-dimensional polymer networks are frequently used as scaffolds to allow cell proliferation and tissue regeneration. In particular, cryogels give promising results for this purpose, thanks to their peculiar properties. Cryogels are indeed characterized by an interconnected porous structure and a typical sponge-like behavior, which facilitate cellular infiltration and ingrowth. Their composition and the fabrication procedure can be appropriately tuned to obtain scaffolds that match the requirements of a specific tissue or organ to be regenerated. These features make cryogels interesting and promising scaffolds for the regeneration of different tissues, including those characterized by very complex mechanical and physical properties, such as bones and joints. In this review, state-of-the-art fabrication and employment of cryogels for supporting effective osteogenic or chondrogenic differentiation to allow for the regeneration of functional tissues is reported. Current progress and challenges for the implementation of this technology in clinical practice are also highlighted.

Enabling New Approaches: Recent Advances in Processing Aliphatic Polycarbonate-Based Materials

Aliphatic polycarbonates (aPCs) have become increasingly popular as functional materials due to their biocompatibility and capacity for on-demand degradation. Advances in polymerization techniques and the introduction of new functional monomers have expanded the library of aPCs available, offering a diverse range of chemical compositions and structures. To accommodate the emerging requirements of new applications in biomedical and energy-related fields, various manufacturing techniques have been adopted for processing aPC-based materials. However, a summary of these techniques has yet to be conducted. The aim of this paper is to enrich the toolbox available to researchers, enabling them to select the most suitable technique for their materials. In this paper, a concise review of the recent progress in processing techniques, including controlled self-assembly, electrospinning, additive manufacturing, and other techniques, is presented. We also highlight the specific challenges and opportunities for the sustainable growth of this research area and the successful integration of aPCs in industrial applications.

Delivery of Growth Factors to Enhance Bone Repair

The management of critical-sized bone defects caused by nonunion, trauma, infection, malignancy, pseudoarthrosis, and osteolysis poses complex reconstruction challenges for orthopedic surgeons. Current treatment modalities, including autograft, allograft, and distraction osteogenesis, are insufficient for the diverse range of pathology encountered in clinical practice, with significant complications associated with each. Therefore, there is significant interest in the development of delivery vehicles for growth factors to aid in bone repair in these settings. This article reviews innovative strategies for the management of critical-sized bone loss, including novel scaffolds designed for controlled release of rhBMP, bioengineered extracellular vesicles for delivery of intracellular signaling molecules, and advances in regional gene therapy for sustained signaling strategies. Improvement in the delivery of growth factors to areas of significant bone loss has the potential to revolutionize current treatment for this complex clinical challenge.

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.

Embedded 3D Printing of Cryogel-Based Scaffolds

Cryogel-based scaffolds have attracted great attention in tissue engineering due to their interconnected macroporous structures. However, three-dimensional (3D) printing of cryogels with a high degree of precision and complexity is a challenge, since the synthesis of cryogels occurs under cryogenic conditions. In this study, we demonstrated the fabrication of cryogel-based scaffolds for the first time by using an embedded printing technique. A photo-cross-linkable gelatin methacryloyl (GelMA)-based ink composition, including alginate and photoinitiator, was printed into a nanoclay-based support bath. The layer-by-layer extruded ink was held in complex and overhanging structures with the help of pre-cross-linking of alginate with Ca2+ present in the support bath. The printed 3D structures in the support bath were frozen, and then GelMA was cross-linked at a subzero temperature under UV light. The printed and cross-linked structures were successfully recovered from the support bath with an integrated shape complexity. SEM images showed the formation of a 3D printed scaffold where porous GelMA cryogel was integrated between the cross-linked alginate hydrogels. In addition, they showed excellent shape recovery under uniaxial compression cycles of up to 80% strain. In vitro studies showed that the human fibroblast cells attached to the 3D printed scaffold and displayed spread morphology with a high proliferation rate. The results revealed that the embedded 3D printing technique enables the fabrication of cytocompatible cryogel based scaffolds with desired morphology and mechanical behavior using photo-cross-linkable bioink composition. The properties of the cryogels can be modified by varying the GelMA concentration, whereby various shapes of scaffolds can be fabricated to meet the specific requirements of tissue engineering applications.

3D-printed porous functional composite scaffolds with polydopamine decoration for bone regeneration

Large size bone defects affect human health and remain a worldwide health problem that needs to be solved immediately. 3D printing technology has attracted substantial attention for preparing penetrable multifunctional scaffolds to promote bone reconditioning and regeneration. Inspired by the spongy structure of natural bone, novel porous degradable scaffolds have been printed using polymerization of lactide and caprolactone (PLCL) and bioactive glass 45S5 (BG), and polydopamine (PDA) was used to decorate the PLCL/BG scaffolds. The physicochemical properties of the PLCL/BG and PLCL/BG/PDA scaffolds were measured, and their osteogenic and angiogenic effects were characterized through a series of experiments both in vitro and in vivo. The results show that the PLCL/BG2/PDA scaffold possessed a good compression modulus and brilliant hydrophilicity. The proliferation, adhesion and osteogenesis of hBMSCs were improved in the PDA coating groups, which exhibited the best performance. The results of the SD rat cranium defect model indicate that PLCL/BG2/PDA obviously promoted osteointegration, which was further confirmed through immunohistochemical staining. Therefore, PDA decoration and the sustained release of bioactive ions (Ca, Si, P) from BG in the 3D-printed PLCL/BG2/PDA scaffold could improve surface bioactivity and promote better osteogenesis and angiogenesis, which may provide a valuable basis for customized implants in extensive bone defect repair applications.

3D Printing of Bone Substitutes Based on Vat Photopolymerization Processes: A Systematic Review

Treatment options for critically sized bone defects are currently limited to metal osteosynthesis, autologous bone grafting, or calcium-based implants to bridge the gap. Additive manufacturing techniques pose a possible alternative. The light-basedthree-dimensional printing process of vat photopolymerization (VP) is of particular interest since it enables the printing of complex scaffold architectures at high resolution. This review compares multiple vat photopolymerization processes as well as the employed resin components' interactions with musculoskeletal cells and tissue. The results show an outstanding printing capability, exceeding the potential of other printing methods. However, despite the availability of various biocompatible materials, neither the mechanical strength of bone nor the scale necessary for clinical application has been achieved so far when relying on single material constructs. One possible solution is the development of adaptive hybrid constructs produced with multimaterial VP.

Additive Manufacturing of Bioceramic Implants for Restoration Bone Engineering: Technologies, Advances, and Future Perspectives

Treating bone defects is highly challenging because they do not heal on their own inside the patients, so implants are needed to assist in the reconstruction of the bone. Bioceramic implants based on additive manufacturing (AM) are currently emerging as promising treatment options for restoration bone engineering. On the one hand, additively manufactured bioceramic implants have excellent mechanical properties and biocompatibility, which are suitable for bone regeneration. On the other hand, the designable structure and adjustable pores of additively manufactured bioceramic implants allow them to promote suitable cell growth and tissue climbing. Herein, this review unfolds to introduce several frequently employed AM technologies for bioceramic implants. After that, advances in commonly used additively manufactured bioceramic implants, including bioinert ceramic implants, bioactive ceramic implants, and bioceramic/organic composite implants, are categorized and summarized. Finally, the future perspectives of additively manufactured bioceramic implants, in terms of mechanical performance improvement, innovative structural design, biological property enhancement, and other functionalization approaches, are proposed and forecasted. This review is believed to provide some fundamental understanding and cutting-edge knowledge for the additive manufacturing of bioceramic implants for restoration bone engineering.

Improved Bone Regeneration Using Biodegradable Polybutylene Succinate Artificial Scaffold in a Rabbit Model

The treatment of extensive bone loss represents a great challenge for orthopaedic and reconstructive surgery. Most of the time, those treatments consist of multiple-stage surgeries over a prolonged period, pose significant infectious risks and carry the possibility of rejection. In this study, we investigated if the use of a polybutylene succinate (PBS) micro-fibrillar scaffold may improve bone regeneration in these procedures. In an in vivo rabbit model, the healing of two calvarial bone defects was studied. One defect was left to heal spontaneously while the other was treated with a PBS scaffold. Computed tomography (CT) scans, histological and immunohistochemical analyses were performed at 4, 12 and 24 weeks. CT examination showed a significantly larger area of mineralised tissue in the treated defect. Histological examination confirmed a greater presence of active osteoblasts and mineralised tissue in the scaffold-treated defect, with no evidence of inflammatory infiltrates around it. Immunohistochemical analysis was positive for CD56 at the transition point between healthy bone and the fracture zone. This study demonstrates that the use of a PBS microfibrillar scaffold in critical bone defects on a rabbit model is a potentially effective technique to improve bone regeneration.

Precisely Tuning the Pore-Wall Surface Composition of Bioceramic Scaffolds Facilitates Angiogenesis and Orbital Bone Defect Repair

Orbital bone damage (OBD) may result in severe post-traumatic enophthalmos, craniomaxillofacial deformities, vision loss, and intracranial infections. However, it is still a challenge to fabricate advanced biomaterials that can match the individual anatomical structure and enhance OBD repair in situ. Herein, we aimed to develop a selective surface modification strategy on bioceramic scaffolds and evaluated the effects of inorganic or organic functional coating on angiogenesis and osteogenesis, ectopically and orthotopically in OBD models. It was shown that the low thermal bioactive glass (BG) modification or layer-by-layer assembly of a biomimetic hydrogel (Biogel) could readily integrate into the pore wall of the bioceramic scaffolds. The BG and Biogel modification showed appreciable enhancement in the initial compressive strength (∼30-75%) or structural stability in vivo, respectively. BG modification could enhance by nearly 2-fold the vessel ingrowth, and the osteogenic capacity was also accelerated, accompanied with a mild scaffold biodegradation after 3 months. Meanwhile, the Biogel-modified scaffolds showed enhanced osteogenic differentiation and mineralization through calcium and phosphorus retention. The potential mechanism of the enhanced bone repair was elucidated via vascular and osteogenic cell responses in vitro, and the cell tests indicated that the Biogel and BG functional layers were both beneficial for in vitro osteoblastic differentiation and mineralization on bioceramics. Totally, these findings demonstrated that the bioactive ions or biomolecules could significantly improve the angiogenic and osteogenic capabilities of conventional bioceramics, and the integration of inorganic or organic functional coating in the pore wall is a highly flexible material toolbox that can be tailored directly to improve orbital bone defect repair.

3D printing of inorganic-biopolymer composites for bone regeneration

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

Regulating Macrophage Polarization in High Glucose Microenvironment Using Lithium-Modified Bioglass-Hydrogel for Diabetic Bone Regeneration

Diabetes mellitus is a chronic metabolic disease with a proinflammatory microenvironment, causing poor vascularization and bone regeneration. Due to the lack of effective therapy and one-sided focus on the direct angiogenic properties of biomaterials and osteogenesis stimulation, the treatment of diabetic bone defect remains challenging and complex. In this study, using gelatin methacryloyl (GelMA) as a template, a lithium (Li) -modified bioglass-hydrogel for diabetic bone regeneration is developed. It exhibits a sustained ion release for better bone regeneration under diabetic microenvironment. The hydrogel is shown to be mechanically adaptable to the complex shape of the defect. In vitro, Li-modified bioglass-hydrogel promoted cell proliferation, direct osteogenesis, and regulated macrophages in high glucose (HG) microenvironment, with the secretion of bone morphogenetic protein-2 and vascular endothelial growth factor to stimulate osteogenesis and neovascularization indirectly. In vivo, composite hydrogels containing GelMA and Li-MBG (GM/M-Li) release Li ions to relieve inflammation, providing an anti-inflammatory microenvironment for osteogenesis and angiogenesis. Applying Li-modified bioglass-hydrogel, significantly enhances bone regeneration in a diabetic rat bone defect. Together, both remarkable in vitro and in vivo outcomes in this study present an opportunity for diabetic bone regeneration on the basis of HG microenvironment.

Rational integration of defense and repair synergy on PEEK osteoimplants via biomimetic peptide clicking strategy

Polyetheretherketone (PEEK) has been widely used as orthopedic and dental materials due to excellent mechanical and physicochemical tolerance. However, its biological inertness, poor osteoinduction, and weak antibacterial activity make the clinical applications in a dilemma. Inspired by the mussel adhesion mechanism, here we reported a biomimetic surface strategy for rational integration and optimization of anti-infectivity and osteo-inductivity onto PEEK surfaces using a mussel foot proteins (Mfps)-mimic peptide with clickable azido terminal. The peptide enables mussel-like adhesion on PEEK biomaterial surfaces, leaving azido groups for the further steps of biofunctionalizations. In this study, antimicrobial peptide (AMP) and osteogenic growth peptide (OGP) were bioorthogonally clicked on the azido-modified PEEK biomaterials to obtain a dual-effect of host defense and tissue repair. Since bioorthogonal clicking allows precise collocation between AMP and OGP through changing their feeding molar ratios, an optimal PEEK surface was finally obtained in this research, which could long-term inhibit bacterial growth, stabilize bone homeostasis and facilitate interfacial bone regeneration. In a word, this upgraded mussel surface strategy proposed in this study is promising for the surface bioengineering of inert medical implants, in particular, achieving rational integration of multiple biofunctions to match clinical requirements.

Patient-Specific Bioimplants and Reconstruction Plates for Mandibular Defects: Production Workflow and In Vivo Large Animal Model Study

A major challenge with extensive craniomaxillofacial bone reconstruction is the limited donor-site availability to reconstruct defects predictably and accurately according to the anatomical shape of the patient. Here, patient-specific composite bioimplants, consisting of cross-linked poly(trimethylene carbonate) (PTMC) networks and β-tricalcium phosphate (β-TCP), were tested in vivo in twelve Göttingen minipigs in a large mandibular continuity defect model. The 25 mm defects were supported by patient-specific titanium reconstruction plates and received either osteoconductive composite bioimplants (PTMC+TCP), neat polymer network bioimplants (PTMC), autologous bone segments (positive control) or were left empty (negative control). Post-operatively, defects treated with bioimplants showed evident ossification at 24 weeks. Histopathologic evaluation revealed that neat PTMC bioimplant surfaces were largely covered with fibrous tissue, while in the PTMC+TCP bioimplants, bone attached directly to the implant surface showing good osteoconduction and histological signs of osteoinductivity. However, PTMC+TCP bioimplants were associated with high incidence of necrosis and infection, possibly due to rapid resorption and/or particle size of the used β-TCP. The study highlights the importance of testing bone regeneration implants in a clinically relevant large animal model and at the in situ reconstruction site, since results on small animal models and studies in non-loadbearing areas do not translate directly. This article is protected by copyright. All rights reserved.

Periosteum-Mimicking Tissue-Engineered Composite for Treating Periosteum Damage in Critical-Sized Bone Defects

The periosteum is an indispensable part of the bone that nourishes the cortical bone and acts as a repertoire of osteoprogenitor cells. Periosteal damage as a result of traumatic injuries, infections, or surgical assistance in bone surgeries is often associated with a high incidence of delayed bone healing (union or nonunion) compounded with severe pain and a risk of a secondary fracture. Developing bioengineered functional periosteal substitutes is an indispensable approach to augment bone healing. In this study, we have developed a biomimetic periosteum membrane consisting of electrospun oxygen-releasing antioxidant polyurethane on collagen membrane (polyurethane-ascorbic acid-calcium peroxide containing fibers on collagen (PUAOCC)). Further, to assist bone formation, we have developed a bioactive inorganic-organic composite cryogel (bioglass-collagen-gelatin-nanohydroxyapatite (BCGH)) as a bone substitute. In an in vitro simulated oxidative stress model, PUAOCC supported the primary periosteal cell survival. Moreover, in an in vivo, critical-sized (5.9 mm × 3.2 mm × 1.50 mm) unicortical rat tibial bone defect, implantation of PUAOCC along with the functionalized BCGH led to significant improvement in bone formation along with periosteal regeneration. The periosteal regeneration was confirmed by expression of periosteum-specific periostin and neuronal regulation-related protein markers. Our study demonstrates the development of a periosteum-mimicking membrane with promising applications to facilitate periosteal regeneration, thus assisting bone formation when used in combination with bone composites and mimicking the natural bone repair process.