Collagen type I coating stimulates bone regeneration and osteointegration of titanium implants in the osteopenic rat

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.

Unlocking Osseointegration: Surface Engineering Strategies for Enhanced Dental Implant Integration

Tooth loss is a prevalent problem faced by individuals of all ages across the globe. Various biomaterials, such as metals, bioceramics, polymers, composites of ceramics and polymers, etc., have been used for the manufacturing of dental implants. The success of a dental implant primarily depends on its osseointegration rate. The current surface modification techniques fail to imbibe the basics of tooth development, which can impart better mineralization and osseointegration. This can be improved by developing an understanding of the developmental pathways of dental tissue. Stimulating the correct signaling pathways through inductive material systems can bring about a paradigm shift in dental implant materials. The current review focuses on the developmental pathway and mineralization process that happen during tooth formation and how surface modifications can help in biomimetic mineralization, thereby enhancing osseointegration. We further describe the effect of dental implant surface modifications on mineralization, osteoinduction, and osseointegration; both in vitro and in vivo. The review will help us to understand the natural process of teeth development and mineralization and how the surface properties of dental implants can be further improved to mimic teeth development, in turn increasing osseointegration.

Preliminary Evaluation of Bioactive Collagen-Polyphenol Surface Nanolayers on Titanium Implants: An X-ray Photoelectron Spectroscopy and Bone Implant Study

To endow an implant surface with enhanced properties to ensure an appropriate seal with the host tissue for inflammation/infection resistance, next-generation bone implant collagen-polyphenol nanolayers were built on conventional titanium surfaces through a multilayer approach. X-ray Photoelectron Spectroscopy (XPS) analysis was performed to investigate the chemical arrangement of molecules within the surface layer and to provide an estimate of their thickness. A short-term (2 and 4 weeks) in vivo test of bone implants in a healthy rabbit model was performed to check possible side effects of the soft surface layer on early phases of osteointegration, leading to secondary stability. Results show the building up of the different nanolayers on top of titanium, resulting in a final composite collagen-polyphenol surface and a layer thickness of about 10 nm. In vivo tests performed on machined and state-of-the-art microrough titanium implants do not show significant differences between coated and uncoated samples, as the surface microroughness remains the main driver of bone-to-implant contact. These results confirm that the surface nanolayer does not interfere with the onset and progression of implant osteointegration and prompt the green light for specific investigations of the potential merits of this bioactive coating as an enhancer of the device/tissue seal.

Evaluation of the effect of co-transplantation of collagen-hydroxyapatite bio-scaffold containing nanolycopene and human endometrial mesenchymal stem cell derived exosomes to regenerate bone in rat critical size calvarial defect

This study aimed to evaluate the effect of nanoparticles based on the PLGA and biomolecule of lycopene (i.e. NLcp) and exosomes loaded on hydroxyapatite/collagen-based scaffolds (HA/Coll), on human endometrial MSCs (hEnMSCs) differentiation into osteoblast cells. To this end, after synthesizing NLcp and isolating hEnMSC-derived exosomes, and studying their characterizations, HA/Coll scaffold with/without NLcp and exosome was fabricated. In following, the rat skull-defect model was created on 54 male Sprague-Dawley rats (12 weeks old) which were classified into 6 groups [control group (4 healthy rats), negative control group: bone defect without grafting (10 rats), and experimental groups including bone defect grafted with HA/Coll scaffold (10 rats), HA/Coll/NLcp scaffold (10 rats), HA/Coll scaffold + exosome (10 rats), and HA/Coll-NLcp scaffold + exosome (10 rats)]. Finally, the grafted membrane along with its surrounding tissues was removed at 90 days after surgery, to assess the amount of defect repair by Hematoxylin and eosin staining. Moreover, immunohistochemical and X-ray Micro-Computed Tomography (Micro-CT) analyses were performed to assess osteocalcin and mean bone volume fraction (BVF). Based on the results, although, the existence of the exosome in the scaffold network can significantly increase mean BVF compared to HA/Coll scaffold and HA/Coll-NLcp scaffold (2.25-fold and 1.5-fold, respectively). However, the combination of NLcp and exosome indicated more effect on mean BVF; so that the HA/Coll-NLcp scaffold + exosome led to a 15.95 % increase in mean BVF than the HA/Coll scaffold + exosome. Hence, synthesized NLcp in this study can act as a suitable bioactive to stimulate the osteogenic, promotion of cell proliferation and its differentiation when used in the polymer scaffold structure or loaded into polymeric carriers containing the exosome.

Biofabrication methods for reconstructing extracellular matrix mimetics

In the human body, almost all cells interact with extracellular matrices (ECMs), which have tissue and organ-specific compositions and architectures. These ECMs not only function as cellular scaffolds, providing structural support, but also play a crucial role in dynamically regulating various cellular functions. This comprehensive review delves into the examination of biofabrication strategies used to develop bioactive materials that accurately mimic one or more biophysical and biochemical properties of ECMs. We discuss the potential integration of these ECM-mimics into a range of physiological and pathological in vitro models, enhancing our understanding of cellular behavior and tissue organization. Lastly, we propose future research directions for ECM-mimics in the context of tissue engineering and organ-on-a-chip applications, offering potential advancements in therapeutic approaches and improved patient outcomes.

Construction of functional surfaces for dental implants to enhance osseointegration

Dental implants have been extensively used in patients with defects or loss of dentition. However, the loss or failure of dental implants is still a critical problem in clinic. Therefore, many methods have been designed to enhance the osseointegration between the implants and native bone. Herein, the challenge and healing process of dental implant operation will be briefly introduced. Then, various surface modification methods and emerging biomaterials used to tune the properties of dental implants will be summarized comprehensively.

Repair of critical-sized bone defects in rabbit femurs using graphitic carbon nitride (g-C3N4) and graphene oxide (GO) nanomaterials

Various biomaterials have been evaluated to enhance bone formation in critical-sized bone defects; however, the ideal scaffold is still missing. The objective of this study was to investigate the in vitro and in vivo regenerative capacity of graphitic carbon nitride (g-C₃N₄) and graphene oxide (GO) nanomaterials to stimulate critical-sized bone defect regeneration. The in vitro cytotoxicity and hemocompatibility of g-C₃N₄ and GO were evaluated, and their potential to induce the in vitro osteogenesis of human fetal osteoblast (hFOB) cells was assessed using qPCR. Then, bone defect in femoral condyles was created in rabbits and left empty as control or filled with either g-C₃N₄ or GO. The osteogenesis of the different implanted scaffolds was evaluated after 4, 8, and 12 weeks of surgery using X-ray, computed tomography (CT), macro/microscopic examinations, and qPCR analysis of osteocalcin (OC) and osteopontin (OP) expressions. Both materials displayed good cell viability and hemocompatibility with enhanced collagen type-I (Col-I), OC, and OP expressions of the hFOB cells. Compared to the control group, the bone healing process in g-C₃N₄ and GO groups was promoted in vivo. Moreover, complete healing of the bone defect was observed radiologically and grossly in g-C₃N₄ implanted group. Additionally, g-C₃N₄ implanted group showed higher percentages of osteoid tissue, mature collagen, biodegradation, and expressions of OC and OP. In conclusion, our results revealed that g-C₃N₄ and GO nanomaterials could induce osteogenesis in critical-sized bone defects.

Accelerated Bone Regeneration by an Astaxanthin-Modified Antioxidant Aerogel through Relieving Oxidative Stress via the NRF2 Signaling Pathway

Bone regeneration of critical-sized bone defects (CSBDs) with biomimetic collagen-based aerogels remains a significant challenge due to the oxidative stress on the microenvironment. The excessive oxidative stress could induce apoptosis and dysfunction of host-derived cells. Astaxanthin (ATX) exhibits excellent antioxidant ability to block free radical chain reactions. In the present study, hybrid antioxidant collagen-derived aerogels (ATX-Col aerogels) were fabricated by a simple one-step method through the covalent cross-linking of Col and ATX. The resulting ATX-Col aerogels show porous and interconnected structures due to freeze-drying strategies. The ATX-Col aerogels exhibited excellent biocompatibility and biosafety. Furthermore, ATX-Col aerogels demonstrated favorable antioxidant capacity by eliminating intracellular ROS by activating the NRF2 signaling pathway. Finally, excellent reparative effects in repairing rat cranial defects were observed in ATX-Col aerogels. Taken together, ATX-Col aerogels can accelerate bone regeneration by relieving oxidative stress via the NRF2 signaling pathway and act as a potential bone graft for CSBD. This study provides a simple method of developing antioxidant aerogels for bone regeneration.

Titanium Dental Implants: An Overview of Applied Nanobiotechnology to Improve Biocompatibility and Prevent Infections

This review addresses the different aspects of the use of titanium and its alloys in the production of dental implants, the most common causes of implant failures and the development of improved surfaces capable of stimulating osseointegration and guaranteeing the long-term success of dental implants. Titanium is the main material for the development of dental implants; despite this, different surface modifications are studied aiming to improve the osseointegration process. Nanoscale modifications and the bioactivation of surfaces with biological molecules can promote faster healing when compared to smooth surfaces. Recent studies have also pointed out that gradual changes in the implant, based on the microenvironment of insertion, are factors that may improve the integration of the implant with soft and bone tissues, preventing infections and osseointegration failures. In this context, the understanding that nanobiotechnological surface modifications in titanium dental implants improve the osseointegration process arouses interest in the development of new strategies, which is a highly relevant factor in the production of improved dental materials.

Advanced Surface Modification for 3D-Printed Titanium Alloy Implant Interface Functionalization

With the development of three-dimensional (3D) printed technology, 3D printed alloy implants, especially titanium alloy, play a critical role in biomedical fields such as orthopedics and dentistry. However, untreated titanium alloy implants always possess a bioinert surface that prevents the interface osseointegration, which is necessary to perform surface modification to enhance its biological functions. In this article, we discuss the principles and processes of chemical, physical, and biological surface modification technologies on 3D printed titanium alloy implants in detail. Furthermore, the challenges on antibacterial, osteogenesis, and mechanical properties of 3D-printed titanium alloy implants by surface modification are summarized. Future research studies, including the combination of multiple modification technologies or the coordination of the structure and composition of the composite coating are also present. This review provides leading-edge functionalization strategies of the 3D printed titanium alloy implants.

MiRNA-Nanofiber, the Next Generation of Bioactive Scaffolds for Bone Regeneration: A Review

Scaffold-based bone tissue engineering has been introduced as an alternative treatment option for bone grafting due to limitations in the allograft. Not only physical conditions but also biological conditions such as gene expression significantly impact bone regeneration. Scaffolds in composition with bioactive molecules such as miRNA mimics provide a platform to enhance migration, proliferation, and differentiation of osteoprogenitor cells for bone regeneration. Among scaffolds, fibrous structures showed significant advantages in promoting osteogenic differentiation and bone regeneration via delivering bioactive molecules over the past decade. Here, we reviewed the bone and bone fracture healing considerations for the impact of miRNAs on bone regeneration. We also examined the methods used to improve miRNA mimics uptake by cells, the fabrication of fibrous scaffolds, and the effective delivery of miRNA mimics using fibrous scaffold and their processes for bone development. Finally, we offer our view on the principal challenges of miRNA mimics delivery by nanofibers for bone tissue engineering.

Experimental study of the effects of hypoxia simulator on osteointegration of titanium prosthesis in osteoporotic rats

Background

Poor osseointegration is the key reason for implant failure after arthroplasty,whether under osteoporotic or normal bone conditions. To date, osseointegration remains a major challenge. Recent studies have shown that deferoxamine (DFO) can accelerate osteogenesis by activating the hypoxia signaling pathway. The purpose of this study was to test the following hypothesis: after knee replacement, intra-articular injection of DFO will promote osteogenesis and osseointegration with a 3D printed titanium prosthesis in the bones of osteoporotic rats.

Materials and methods

Ninety female Sprague–Dawley rats were used for the experiment. Ten rats were used to confirm the successful establishment of the osteoporosis model: five rats in the sham operation group and five rats in the ovariectomy group. After ovariectomy and knee arthroplasty were performed, the remaining 80 rats were randomly divided into DFO and control groups (n = 40 per group). The two groups were treated by intraarticular injection of DFO and saline respectively. After 2 weeks, polymerase chain reaction (PCR) and immunohistochemistry were used to evaluate the levels of HIF-1a, VEGF, and CD31. HIF-1a and VEGF have been shown to promote angiogenesis and bone regeneration, and CD31 is an important marker of angiogenesis. After 12 weeks, the specimens were examined by micro-computed tomography (micro-CT), biomechanics, and histopathology to evaluate osteogenesis and osseointegration.

Results

The results of PCR showed that the mRNA levels of VEGF and CD31 in the DFO group were significantly higher than those in the control group. The immunohistochemistry results indicated that positive cell expression of HIF-1a, VEGF, and CD31 in the DFO group was also higher. Compared with the control group, the micro-CT parameters of BMD, BV/TV, TB. N, and TB. Th were significantly higher. The maximal pull-out force and the bone-to-implant contact value were also higher.

Conclusions

The local administration of DFO, which is used to activate the HIF-1a signaling pathway, can promote osteogenesis and osseointegration with a prosthesis in osteoporotic bone.

Men who stare at bone: multimodal monitoring of bone healing

Knowledge of the physiological and pathological processes, taking place in bone during fracture healing or defect regeneration, is essential in order to develop strategies to enhance bone healing under normal and critical conditions. Preclinical testing allows a wide range of imaging modalities that may be applied both simultaneously and longitudinally, which will in turn lower the number of animals needed to allow a comprehensive assessment of the healing process. This work provides an up-to-date review on morphological, functional, optical, biochemical, and biophysical imaging techniques including their advantages, disadvantages and potential for combining them in a multimodal and multiscale manner. The focus lies on preclinical testing of biomaterials modified with artificial extracellular matrices in various animal models to enhance bone remodeling and regeneration.

Effects of Gamma Radiation-Induced Crosslinking of Collagen Type I Coated Dental Titanium Implants on Osseointegration and Bone Regeneration

This study aimed to compare two methods of crosslinking collagen type I on implanted titanium surfaces, that is, using glutaraldehyde (GA) or gamma-rays (GRs), in a beagle dog model. For in vivo experiments, implants were allocated to three groups and applied to mandibular bone defects in beagle dogs; Group SLA; non-treated Sandblasted, large grit, acid-etched (SLA) implants, Group GA; SLA implants coated with GA crosslinked collagen type I, Group GR; SLA surface implants coated with collagen type I and crosslinked using 25 kGy of ⁶⁰Co gamma radiation. New bone μCT volumes were obtained, and histologic and histometric analyses were performed in regions of interest. The GR group had significantly better new bone areas (NBAs) and bone to implant contact (BIC) results than the SLA group (p < 0.05), but the GA and GR groups were similar in this respect. New bone volumes and inter-thread bone densities (ITBD) were non-significantly different in the three groups (p > 0.05). Within the limits of this study, gamma-ray collagen crosslinking on titanium implants can be considered a substitute for glutaraldehyde crosslinking.

Multifunctional natural polymer-based metallic implant surface modifications

High energy traumas could cause critical damage to bone, which will require permanent implants to recover while functionally integrating with the host bone. Critical sized bone defects necessitate the use of bioactive metallic implants. Because of bioinertness, various methods involving surface modifications such as surface treatments, the development of novel alloys, bioceramic/bioglass coatings, and biofunctional molecule grafting have been utilized to effectively integrate metallic implants with a living bone. However, the applications of these methods demonstrated a need for an interphase layer improving bone-making to overcome two major risk factors: aseptic loosening and peri-implantitis. To accomplish a biologically functional bridge with the host to prevent loosening, regenerative cues, osteoimmunomodulatory modifications, and electrochemically resistant layers against corrosion appeared as imperative reinforcements. In addition, interphases carrying antibacterial cargo were proven to be successful against peri-implantitis. In the literature, metallic implant coatings employing natural polymers as the main matrix were presented as bioactive interphases, enabling rapid, robust, and functional osseointegration with the host bone. However, a comprehensive review of natural polymer coatings, bridging and grafting on metallic implants, and their activities has not been reported. In this review, state-of-the-art studies on multifunctional natural polymer-based implant coatings effectively utilized as a bone tissue engineering (BTE) modality are depicted. Protein-based, polysaccharide-based coatings and their combinations to achieve better osseointegration via the formation of an extracellular matrix-like (ECM-like) interphase with gap filling and corrosion resistance abilities are discussed in detail. The hypotheses and results of these studies are examined and criticized, and the potential future prospects of multifunctional coatings are also proposed as final remarks.

Transcript-Activated Coatings on Titanium Mediate Cellular Osteogenesis for Enhanced Osteointegration

Osteointegration is one of the most important factors for implant success. Several biomolecules have been used as part of drug delivery systems to improve implant integration into the surrounding bone tissue. Chemically modified mRNA (cmRNA) is a new form of therapeutic that has been used to induce bone healing. Combined with biomaterials, cmRNA can be used to develop transcript-activated matrices for local protein production with osteoinductive potential. In this study, we aimed to utilize this technology to create bone morphogenetic protein 2 (BMP2) transcript-activated coatings for titanium (Ti) implants. Therefore, different coating methodologies as well as cmRNA incorporation strategies were evaluated. Three different biocompatible biomaterials were used for the coating of Ti, namely, poly-d,l-lactic acid (PDLLA), fibrin, and fibrinogen. cmRNA-coated Ti disks were assayed for transfection efficiency, cmRNA release, cell viability and proliferation, and osteogenic activity in vitro. We found that cmRNA release was significantly delayed in Ti surfaces previously coated with biomaterials. Consequently, the transfection efficiency was greatly improved. PDLLA coating improved the transfection efficiency in a concentration-dependent manner. Lower PDLLA concentration used for the coating of Ti resulted in higher transfection efficiency. Fibrin and fibrinogen coatings showed even higher transfection efficiencies compared to all PDLLA concentrations. In those disks, not only the expression was up to 24-fold higher but also the peak of maximal expression was delayed from 24 h to 5 days, and the duration of expression was also extended until 7 days post-transfection. For fibrin, higher transfection efficiencies were obtained in the coatings with the lowest thrombin amounts. Accordingly, fibrinogen coatings gave the best results in terms of cmRNA transfection. All biomaterial-coated Ti surfaces showed improved cell viability and proliferation, though this was more noticeable in the fibrinogen-coated disks. The latter was also the only coating to support significant amounts of BMP2 produced by C2C12 cells in vitro. Osteogenesis was confirmed using BMP2 cmRNA fibrinogen-coated Ti disks, and it was dependent of the cmRNA amount present. Alkaline phosphatase (ALP) activity of C2C12 increased when using fibrinogen coatings containing 250 ng of cmRNA or more. Similarly, mineralization was also observed that increased with increasing cmRNA concentration. Overall, our results support fibrinogen as an optimal material to deliver cmRNA from titanium-coated surfaces.

Osseointegration of additive manufacturing Ti-6Al-4V and Co-Cr-Mo alloys, with and without surface functionalization with hydroxyapatite and type I collagen

The introduction of additive manufacturing (AM) technologies has profoundly revolutionized the implant manufacturing industry, with a particularly significant impact on the field of orthopedics. Electron Beam Melting (EBM) and Direct Metal Laser Sintering (DMLS) represents AM fabrication techniques with a pivotal role in the realization of complex and innovative structure starting from virtual 3D model data. In this study, Ti-6Al-4V and Co-Cr-Mo materials, developed by EBM (Ti-POR) and DMLS (Co-POR) techniques, respectively, with hydroxyapatite (Ti-POR + HA; Co-POR + HA) and type I collagen (Ti-POR-COLL; Co-POR-COLL) coatings, were implanted into lateral femoral condyles of rabbits. Osseointegration process was investigated by histological, histomorphometrical and microhardness evaluations at 4 and 12 weeks after implantation. Both Ti-6Al-4V and Co-Cr-Mo implants, with or without HA and COLL coatings, demonstrated good biocompatibility. As expected, HA coating hastened bone-to-implant contact (BIC) process, while collagen did not significantly improved the osseointegration process in comparison to controls. Regarding newly trabecular bone formation (B.Ar/T.Ar), Co-POR presented the highest values, significantly different from those of Co-POR-COLL. Over time, an increase of BIC parameter and a decrease of B.Ar/T.Ar were detected. Higher mineral apposition rate was observed for Ti-POR and Co-POR in comparison to Ti-POR-COLL and Co-POR-COLL, respectively, at 12 weeks. The same behavior was found for bone formation rate between Co-POR and Co-POR-COLL at 12 weeks. In conclusion, the AM materials guarantee a good osseointegration and provide a suitable environment for bone regeneration with the peculiarity of allowing personalized and patient-specific needs customization to further improve the long-term clinical outcomes.

Bone healing at collagenated bicortically installed implants: an experimental study in rabbits

PURPOSE

To study the healing at collagenated bicortically installed implants.

METHODS

Twenty albino New Zealand rabbits were used for implant installation. Two implants with a double acid etched surface, coated with a collagen type I or left uncoated, were installed bicortically in the metaphysis and in the diaphysis of each tibia. Ten rabbits were euthanized after 2 weeks and ten after 6 weeks after installation. Ground sections were prepared for histological analyses that were performed both in the cortical layers and in the marrow regions.

RESULTS

After 2 weeks of healing, highest amounts of new bone were found at the collagenated implants (43.2 ± 6.0%) compared to the standard implants (33.9 ± 6.1%; p = 0.022). After 6 weeks of healing, similar percentages of new bone were observed, being 51.8 ± 7.3% and 50.9 ± 9.6% (p = 0.678) for the standard and collagenated surfaces, respectively.

CONCLUSIONS

A coated surface with collagen type I promoted bone apposition in the earliest periods of healing. However, the effect vanished over time so that similar results were obtained after 6 weeks of healing.

Macrophages' contribution to ectopic osteogenesis in combination with blood clot and bone substitute: possibility for application in bone regeneration strategies

PURPOSE

Given the great potential of macrophages in the processes of tissue repair and regeneration, the aim of our study was to examine the contribution that macrophages will have in osteogenic process when combined and implanted with blood clot (BC) and mineral bone substitute (MBS) in mice subcutaneous implantation model.

METHODS

Three types of implants were constructed and implanted subcutaneously into BALB/c mice: (1) RMBM implants (made of resident tissue macrophages, BC and MBS), (2) BM implants (made of BC and MBS), and (3) M implants (made of MBS only) where the last two served as control implants. One, two, four and eight weeks after implantation implants were explanted, and histochemical, immunohistochemical, and histomorphometric analyses were performed.

RESULTS

Increased vascularization, particularly pronounced two and four weeks after implantation and pronounced tissue infiltration in eight week term in RMBM implants compared with both other types, likewise the presence of osteoblast-like cells, osteoid-like structures, and more prominent osteopontin and osteocalcin immunoexpression in RMBM implants indicated more pronounced osteogenic process within them.

CONCLUSION

Our results suggest that macrophages deserve to be considered as a cell component when constructing implants in bone regenerative medicine strategies to improve bone fracture healing process.

Phenolic-Enriched Collagen Fibrillar Coatings on Titanium Alloy to Promote Osteogenic Differentiation and Reduce Inflammation

The adsorption of biomolecules on biomaterial surfaces can promote their integration with surrounding tissue without changing their bulk properties. For biomaterials in bone reconstruction, the promotion of osteogenic differentiation and reduction of inflammation are desirable. Fibrillar coatings are interesting because of fibrils’ high surface area-volume ratio, aiding adsorption and adhesion. Fibrils also serve as a matrix for the immobilization of biomolecules with biological activity, such as the phenolic compound phloroglucinol (PG), the subunit of marine polyphenols. The aim of this work was to investigate the influence of PG coatings on fibroblast- and osteoblast-like cells to increase the osseointegration of titanium implants. Collagen fibril coatings, containing PG at low and high concentrations, were produced on titanium alloy (Ti6Al4V) scaffolds generated by additive manufacturing (AM). These coatings, especially PG-enriched coatings, reduced hydrophobicity and modulated the behavior of human osteosarcoma SaOS-2 and mouse embryonic fibroblast 3T3 cell lines. Both osteoblastic and fibroblastic cells spread and adhered well on PG-enriched coatings. Coatings significantly reduced the inflammatory response. Moreover, osteogenic differentiation was promoted by collagen coatings with a high PG concentration. Thus, the enrichment of collagen fibril coatings with PG is a promising strategy to improve Ti6Al4V implants for bone contact in orthopedics and dentistry and is worthy of further investigation.

The Bone Extracellular Matrix in Bone Formation and Regeneration

Bone regeneration repairs bone tissue lost due to trauma, fractures, and tumors, or absent due to congenital disorders. The extracellular matrix (ECM) is an intricate dynamic bio-environment with precisely regulated mechanical and biochemical properties. In bone, ECMs are involved in regulating cell adhesion, proliferation, and responses to growth factors, differentiation, and ultimately, the functional characteristics of the mature bone. Bone ECM can induce the production of new bone by osteoblast-lineage cells, such as MSCs, osteoblasts, and osteocytes and the absorption of bone by osteoclasts. With the rapid development of bone regenerative medicine, the osteoinductive, osteoconductive, and osteogenic potential of ECM-based scaffolds has attracted increasing attention. ECM-based scaffolds for bone tissue engineering can be divided into two types, that is, ECM-modified biomaterial scaffold and decellularized ECM scaffold. Tissue engineering strategies that utilize the functional ECM are superior at guiding the formation of specific tissues at the implantation site. In this review, we provide an overview of the function of various types of bone ECMs in bone tissue and their regulation roles in the behaviors of osteoblast-lineage cells and osteoclasts. We also summarize the application of bone ECM in bone repair and regeneration. A better understanding of the role of bone ECM in guiding cellular behavior and tissue function is essential for its future applications in bone repair and regenerative medicine.

Calcium Bioavailability of Opuntia ficus-indica Cladodes in an Ovariectomized Rat Model of Postmenopausal Bone Loss

Osteoporosis is a disease of the skeletal system characterized by low bone mass and bone weakening, which increase the risk of fracture. This disease is associated with menopause because hypoestrogenism induces the maturation and activation of osteoclasts. In addition, a low dietary intake of calcium leads to low bone mineral density and postmenopausal osteoporosis. The objectives of this work were to determine calcium bioavailability of Opuntia ficus-indica cladodes at a late maturity stage and to assess its contribution in improving bone health in an ovariectomized rat model. Two-month-old Wistar female rats (n = 35) were used and distributed in seven experimental groups: (i) control group (Crtl), (ii) sham group (SH), (iii) ovariectomized group (OVX), (iv) ovariectomized group supplemented with calcium citrate (CCa), (v) ovariectomized group supplemented with O. ficus-indica powder (NI), (vi) ovariectomized group supplemented with soluble fiber from O. ficus-indica (FS) and (vii) ovariectomized group supplemented with insoluble fiber from O. ficus-indica (FI). Our results showed that calcium in the soluble fiber of O. ficus-indica is bioavailable and contributes to improve the physical, densitometric, biomechanical and microstructural properties of bones in ovariectomized rats. These findings indicated that O. ficus-indica cladodes at a late maturity stage represent a good source of bioavailable calcium and consumption of these cladodes might be beneficial for the prevention of osteoporosis and other bone diseases.

Nano-scale modification of titanium implant surfaces to enhance osseointegration

The main aim of this review study was to report the state of art on the nano-scale technological advancements of titanium implant surfaces to enhance the osseointegration process. Several methods of surface modification are chronologically described bridging ordinary methods (e.g. grit blasting and etching) and advanced physicochemical approaches such as 3D-laser texturing and biomimetic modification. Functionalization procedures by using proteins, peptides, and bioactive ceramics have provided an enhancement in wettability and bioactivity of implant surfaces. Furthermore, recent findings have revealed a combined beneficial effect of micro- and nano-scale modification and biomimetic functionalization of titanium surfaces. However, some technological developments of implant surfaces are not commercially available yet due to costs and a lack of clinical validation for such recent surfaces. Further in vitro and in vivo studies are required to endorse the use of enhanced biomimetic implant surfaces. STATEMENT OF SIGNIFICANCE: Grit-blasting followed by acid-etching is currently used for titanium implant modifications, although recent technological biomimetic physicochemical methods have revealed enhanced osteoconductive and anti-microbial outcomes. An improvement in wettability and bioactivity of titanium implant surfaces has been accomplished by combining micro and nano-scale modification and functionalization with protein, peptides, and bioactive compounds. Such morphological and chemical modification of the titanium surfaces induce the migration and differentiation of osteogenic cells followed by an enhancement of the mineral matrix formation that accelerate the osseointegration process. Additionally, the incorporation of bioactive molecules into the nanostructured surfaces is a promising strategy to avoid early and late implant failures induced by the biofilm accumulation.

The effects of type I collagen on bone defects and gene expression changes for osteogenesis: In a rat model

The aim of this study is to investigate the effects of type I collagen on bone defects and on genes specifically for osteogenesis in a rat model. Two millimeter drill hole bone defect was created in the femur of rats. In the experimental group, type I collagen was applied in bone defects whereas in control group defects were left empty. Inflammation, development of connective tissue, osteogenesis, and foreign body reaction parameters evaluated with histologically and genes evaluated by blood samples. In the experimental group, the histopathologically significant change was found in favor of bone healing only at the first week. A significant increase was found in genetic expressions of BMP-1, 2, 3, 4, 5, 6, 7, TGF-βRII, Smad-1, IL-6, BMPR-IA, BMPR-IB, Eng, BMPR-II, c-fos, Cdkn1a, Chrd, Gdf-5, Id-1, PDGF-β, IGF-1, Serpine-1, and TGF-βRI at the first hour. At the first, third, and sixth week, no significant increase was found in any of the gene expressions. Type I collagen is found to be effective in favor of bone healing through increased inflammatory cytokines and expression of BMP genes in the early stages of fracture healing.

Enhanced Cell Response to Zirconia Surface Immobilized with Type I Collagen

Zirconia (ZrO₂) dental implants provide good biocompatibility, have good corrosion resistance, and have a color that is similar to that of natural teeth. Unfortunately, ZrO₂ is a bioinert material and therefore achieves osseointegration difficultly. In this study, we sought to enhance osseointegration by producing rough ZrO₂ surfaces that contain hydroxyl groups (designated ZSA) through the use of sandblasting in conjunction with alkaline treatment. We immobilized type I collagen on ZSA surfaces using the natural cross-linker, procyanidin. Our results further showed that surfaces produced in ZSA-P/C featured more and steadier type I collagen than surfaces produced in ZSA-C. The ZSA-P/C also presented superior cell responses in terms of adhesion, proliferation, and mineralization of human bone marrow mesenchymal stem cells. The enhanced cell responses in the ZSA-P/C were induced through the prolonged activation of focal adhesion kinase, AKT (the phosphoinositide 3-kinase pathway), and p38 (the mitogen-activated protein kinase pathway). The simple and novel approach to immobilize type I collagen on roughened ZrO₂ surfaces presented in this article can likely benefit dental implant applications.

Covalently-Linked Hyaluronan versus Acid Etched Titanium Dental Implants: A Crossover RCT in Humans

Biochemical modification of titanium surfaces (BMTiS) entails immobilization of biomolecules to implant surfaces in order to induce specific host responses. This crossover randomized clinical trial assesses clinical success and marginal bone resorption of dental implants bearing a surface molecular layer of covalently-linked hyaluronan in comparison with control implants up to 36 months after loading. Patients requiring bilateral implant rehabilitation received hyaluronan covered implants in one side of the mouth and traditional implants in the other side. Two months after the first surgery, a second surgery was undergone to uncover the screw and to place a healing abutment. After two weeks, the operator proceeded with prosthetic procedures. Implants were evaluated by periapical radiographs and the crestal bone level was recorded at mesial and distal sites—at baseline and up to 36 months. One hundred and six implants were positioned, 52 HY-coated, and 48 controls were followed up. No differences were observed in terms of insertion and stability, wound healing, implant success, and crestal bone resorption at any time considered. All interventions had an optimal healing, and no adverse events were recorded. This trial shows, for the first time, a successful use in humans of biochemical-modified implants in routine clinical practice and in healthy patients and tissues with satisfactory outcomes.

Effect of Titanium Implants Coated with Radiation-Crosslinked Collagen on Stability and Osseointegration in Rat Tibia

This study aimed to evaluate the titanium (Ti) implants coated with collagen type Ⅰ crosslinked using gamma-irrigation or glutaraldehyde (GA). The in vitro surface observations, quantification assay, and cell studies using human mesenchymal stem cells (hMSCs) were conducted. For in vivo experiments, the implants were divided into three groups and inserted into the rat tibias: control group (non-treated Ti implant), GA group (Ti implants coated with GA-crosslinked collagen) and 25 kGy group (Ti implants coated with gamma-radiation-crosslinked collagen at dose of 25 kGy). The animals were sacrificed at 4 weeks after implantation and the tissue sections were obtained. New bone volume (mm³) and bone-to-implant contact (BIC, %) within the region of interest (ROI) was measured. The in vitro results showed the highest osteogenic differentiation and levels of osteogenesis-related gene expressions in the 25 kGy group without cytotoxicity. The new bone volume of GA group was significantly higher than the control (p < 0.05). In the result of the BIC, the 25 kGy group was significantly higher than the control (p < 0.05). However, there was no significant difference between the experimental groups. Within the limitations of this study, Ti implant coated with gamma-radiation-crosslinked collagen has potential utility without side effects from chemical agents.

Bone physiology as inspiration for tissue regenerative therapies

The development, maintenance of healthy bone and regeneration of injured tissue in the human body comprise a set of intricate and finely coordinated processes. However, an analysis of current bone regeneration strategies shows that only a small fraction of well-reported bone biology aspects has been used as inspiration and transposed into the development of therapeutic products. Specific topics that include inter-scale bone structural organization, developmental aspects of bone morphogenesis, bone repair mechanisms, role of specific cells and heterotypic cell contact in the bone niche (including vascularization networks and immune system cells), cell-cell direct and soluble-mediated contact, extracellular matrix composition (with particular focus on the non-soluble fraction of proteins), as well as mechanical aspects of native bone will be the main reviewed topics. In this Review we suggest a systematic parallelization of (i) fundamental well-established biology of bone, (ii) updated and recent advances on the understanding of biological phenomena occurring in native and injured tissue, and (iii) critical discussion of how those individual aspects have been translated into tissue regeneration strategies using biomaterials and other tissue engineering approaches. We aim at presenting a perspective on unexplored aspects of bone physiology and how they could be translated into innovative regeneration-driven concepts.

Comparative analysis of osseointegration in various types of acetabular implant materials

BACKGROUND

There is a lack of comparative data on osseointegration (BIC) of acetabular cup surfaces in hip arthroplasty in both normal bone mineral density and in conditions of osteoporosis.

AIM

To compare osseointegration of acetabular implants with various types of surfaces in an animal model with normal and osteoporotic bone tissue.

MATERIAL AND METHODS

The study was performed on 60 rats. To simulate osteoporosis ovariectomy was performed in 30 animals. Thirty healthy rats served as controls. In standardised defects of the distal metadiaphysis of the femur we implanted: porous tantalum Trabecular Metal (A), Trabecular Titanium (B), Titanium with Gription coating (C), Stiktite (D), and Tritanum (E). Bone apposition (osseointegration) was defined as all areas of direct "bone-to-implant contact" (BIC).

RESULTS

No qualitative morphological differences in the evaluation of BIC around different implant types was seen in normal rats and rats with osteoporosis. Connective tissue areas around implants were larger in rats with osteoporosis. Morphometric studies showed that the highest BIC were seen in implants A and B, both in healthy animals ([72.00 ± 3.48]% and [67.46 ± 1.69]%) and ones with osteoporosis ([59.19 ± 2.10]% and [53.36 ± 2.57]%). BIC was (60.10 ± 2.05)%, (60.26 ± 2.36)%, and (61.78 ± 2.27)% around implants C, D and E in healthy rats, respectively. BIC in osteoporosis was (45.39 ± 2.37)%, (47.81 ± 2.41)% and (42.10 ± 1.44)%, respectively.

CONCLUSION

Our study showed that the evaluated implants have good BIC features. Furthermore, based on histomorthometry and histology, Porous tantalum Trabecular Metal (A) and Trabecular Titanium (B) implants exhibit higher BIC with bone tissue.

Collagen-Coated Poly(lactide-co-glycolide)/Hydroxyapatite Scaffold Incorporated with DGEA Peptide for Synergistic Repair of Skull Defect

The treatment of large-area bone defects remains a challenge; however, various strategies have been developed to improve the performances of scaffolds in bone tissue engineering. In this study, poly(lactide-co-glycolide)/hydroxyapatite (PLGA/HA) scaffold was coated with Asp-Gly-Glu-Ala (DGEA)-incorporated collagen for the repair of rat skull defect. Our results indicated that the mechanical strength and hydrophilicity of the PLGA/HA scaffold were clearly improved and conducive to cell adhesion and proliferation. The collagen-coated scaffold with DGEA significantly promoted the repair of skull defect. These findings indicated that a combination of collagen coating and DGEA improved scaffold properties for bone regeneration, thereby providing a new potential strategy for scaffold design.

A Xenogenic Bone Derivative as a Potential Adjuvant for Bone Regeneration and Implant Osseointegration: An In Vitro Study

Several clinical conditions may limit the success of bone regeneration and/or implant osseointegration. For this reason, many compounds have been tested for their ability to stimulate this biological process. Synthetic hydroxyapatite (HA), mimicking natural bone hydroxyapatite, and extra-cellular matrix proteins, such as type I collagen, are potential candidates. However, the synthetic origin of HA and the denaturing conditions required for extracting collagen from skin and derma are sources of potential drawbacks. This study examines the in vitro effects of a natural bone derivative (NBD) extracted from equine bone and containing both natural, non-synthetic bone hydroxyapatite and native, non-denatured, type I bone collagen as a possible active compound for stimulating bone regeneration and implant osseointegration. The activity of NBD was tested on bone marrow stromal cells (BMSCs), evaluating their growth/viability by the methylthiazol tetrazolium (MTT) assay and their migration potential by a scratch assay. Moreover, expression of the hyaluronic acid receptor (CD44) and the C-X-C chemokine receptor type 4 (CXCR4, CD184) on the surface of BMSCs was assessed by flow cytometry, and the release of Transforming Growth Factor (TGF)-β, Interleukin (IL)-1α and IL-6 was quantified using an enzyme-linked immunosorbent assay (ELISA). The effect of NBD-coated implants on human osteoblasts was tested by measuring alkaline phosphatase (ALP) activity with the p-nitrophenyl phosphate (pNPP) degradation test. NBD stimulated BMSC growth/viability, migration, CD184 surface expression and the release of TGF-β1. NBD-coated implants increased ALP activity of human osteoblasts. These results indicate that NBD may be an adjuvant to accelerate both bone regeneration and osseointegration.

Controlled release of BMP-2 from a collagen-mimetic peptide-modified silk fibroin–nanohydroxyapatite scaffold for bone regeneration

Controlled release of BMP-2 from a collagen-mimetic peptide-modified scaffold for bone regeneration.

The synergistic effect of type I collagen and hyaluronic acid on the biological properties of Col/HA-multilayer-modified titanium coatings: an in vitro and in vivo study

The synergistic effect on osseointegration is existed between Type I collagen (ColI) and hyaluronic acid (HA), and the early osseogenetic activity of ColI/HA multilayer modified titanium coatings (TC) is higher than that ColI modified TC and HA modified TC.

A comparative analysis of antibacterial properties and inflammatory responses for the KR-12 peptide on titanium and PEGylated titanium surfaces

Covalent KR-12 peptide immobilisation on the Ti surface with a grafted PEG spacer showed remarkable antibacterial properties and reduced macrophage inflammatory responses.

The effect of different collagen modifications for titanium and titanium nitrite surfaces on functions of gingival fibroblasts

OBJECTIVES

Targeted modifications of the bulk implant surfaces using bioactive agents provide a promising tool for improvement of the long-term bony and soft tissue integration of dental implants. In this study, we assessed the cellular responses of primary human gingival fibroblasts (HGF) to different surface modifications of titanium (Ti) and titanium nitride (TiN) alloys with type I collagen or cyclic-RGDfK-peptide in order to define a modification improving long-term implants in dental medicine.

MATERIALS AND METHODS

Employing Ti and TiN implants, we compared the performance of simple dip coating and anodic immobilization of type I collagen that provided collagen layers of two different thicknesses. HGF were seeded on the different coated implants, and adhesion, proliferation, and gene expression were analyzed.

RESULTS

Although there were no strong differences in initial cell adhesion between the groups at 2 and 4 hours, we found that all surface modifications induced higher proliferation rates as compared to the unmodified controls. Consistently, gene expression levels of cell adhesion markers (focal adhesion kinase (FAK), integrin beta1, and vinculin), cell differentiation markers (FGFR1, TGFb-R1), extracellular protein markers (type I collagen, vimentin), and cytoskeletal protein marker aktinin-1 were consistently higher in all surface modification groups at two different time points of investigation as compared to the unmodified controls.

CONCLUSION

Our results indicate that simple dip coating of Ti and TiN with collagen is sufficient to induce in vitro cellular responses that are comparable to those of more reliable coating methods like anodic adsorption, chemical cross-linking, or RGD coating. TiN alloys do not possess any positive or adverse effects on HGF.

CLINICAL RELEVANCE

Our results demonstrate a simple, yet effective, method for collagen coating on titanium implants to improve the long term integration and stability of dental implants.

New Ti-Alloys and Surface Modifications to Improve the Mechanical Properties and the Biological Response to Orthopedic and Dental Implants: A Review

Titanium implants are widely used in the orthopedic and dentistry fields for many decades, for joint arthroplasties, spinal and maxillofacial reconstructions, and dental prostheses. However, despite the quite satisfactory survival rates failures still exist. New Ti-alloys and surface treatments have been developed, in an attempt to overcome those failures. This review provides information about new Ti-alloys that provide better mechanical properties to the implants, such as superelasticity, mechanical strength, and corrosion resistance. Furthermore, in vitro and in vivo studies, which investigate the biocompatibility and cytotoxicity of these new biomaterials, are introduced. In addition, data regarding the bioactivity of new surface treatments and surface topographies on Ti-implants is provided. The aim of this paper is to discuss the current trends, advantages, and disadvantages of new titanium-based biomaterials, fabricated to enhance the quality of life of many patients around the world.