Effects of bone morphogenetic protein-2 and hyaluronic acid on the osseointegration of hydroxyapatite-coated implants: An experimental study in sheep

Effect of Hyaluronic Acid Gel on Healing of Simple Dental Extraction Sockets: A Pilot Study

BACKGROUND: Hyaluronic acid (HA) was explored as a powerful positive biocompatible material that participates in numerous biological processes related to morphogenesis and tissue healing. AIM: In this context, we elevated in this pilot study the effect of HA on soft tissue healing and bone repair of dental sockets (DS) as well as the postoperative pain. MATERIALS AND METHODS: Ten individuals of both genders (80% females and 20% males) with age range 18–44 years, were included who were diagnosed with two non-restorable teeth (total sockets n = 20). A split-mouth study design was performed where the DS of each patient were divided into Group A (study group): Topical oral HA gel (Gengigel®) was applied into sockets while Group B (control group): Sockets were left untreated. Study variables were evaluated including socket length, socket healing scores (healing index), and post-operative pain in both groups at day 1, 5, and 10 for each patient. RESULTS: There were no statistically significant differences between the control and study groups regarding the reduction of the socket length and postoperative complications but results revealed that HA enhances and fasten the healing capacity. CONCLUSION: HA can be used as adjunctive treatment to improve the wound healing process.

Hyaluronic-Acid-Based Organic-Inorganic Composites for Biomedical Applications

Applications of natural hyaluronic acid (HYH) for the fabrication of organic-inorganic composites for biomedical applications are described. Such composites combine unique functional properties of HYH with functional properties of hydroxyapatite, various bioceramics, bioglass, biocements, metal nanoparticles, and quantum dots. Functional properties of advanced composite gels, scaffold materials, cements, particles, films, and coatings are described. Benefiting from the synergy of properties of HYH and inorganic components, advanced composites provide a platform for the development of new drug delivery materials. Many advanced properties of composites are attributed to the ability of HYH to promote biomineralization. Properties of HYH are a key factor for the development of colloidal and electrochemical methods for the fabrication of films and protective coatings for surface modification of biomedical implants and the development of advanced biosensors. Overcoming limitations of traditional materials, HYH is used as a biocompatible capping, dispersing, and structure-directing agent for the synthesis of functional inorganic materials and composites. Gel-forming properties of HYH enable a facile and straightforward approach to the fabrication of antimicrobial materials in different forms. Of particular interest are applications of HYH for the fabrication of biosensors. This review summarizes manufacturing strategies and mechanisms and outlines future trends in the development of functional biocomposites.

The Body's Cellular and Molecular Response to Protein-Coated Medical Device Implants: A Review Focused on Fibronectin and BMP Proteins

Recent years have seen a marked rise in implantation into the body of a great variety of devices: hip, knee, and shoulder replacements, pacemakers, meshes, glucose sensors, and many others. Cochlear and retinal implants are being developed to restore hearing and sight. After surgery to implant a device, adjacent cells interact with the implant and release molecular signals that result in attraction, infiltration of the tissue, and attachment to the implant of various cell types including monocytes, macrophages, and platelets. These cells release additional signaling molecules (chemokines and cytokines) that recruit tissue repair cells to the device site. Some implants fail and require additional revision surgery that is traumatic for the patient and expensive for the payer. This review examines the literature for evidence to support the possibility that fibronectins and BMPs could be coated on the implants as part of the manufacturing process so that the proteins could be released into the tissue surrounding the implant and improve the rate of successful implantation.

Hyaluronic acid as a bioactive component for bone tissue regeneration: Fabrication, modification, properties, and biological functions

Hyaluronic acid (HA) is widely distributed in the human body, and it is heavily involved in many physiological functions such as tissue hydration, wound repair, and cell migration. In recent years, HA and its derivatives have been widely used as advanced bioactive polymers for bone regeneration. Many medical products containing HA have been developed because this natural polymer has been proven to be nontoxic, noninflammatory, biodegradable, and biocompatible. Moreover, HA-based composite scaffolds have shown good potential for promoting osteogenesis and mineralization. Recently, many HA-based biomaterials have been fabricated for bone regeneration by combining with electrospinning and 3D printing technology. In this review, the polymer structures, processing, properties, and applications in bone tissue engineering are summarized. The challenges and prospects of HA polymers are also discussed.

How faithfully does intramembranous bone regeneration recapitulate embryonic skeletal development?

Postnatal intramembranous bone regeneration plays an important role during a wide variety of musculoskeletal regeneration processes such as fracture healing, joint replacement and dental implant surgery, distraction osteogenesis, stress fracture healing, and repair of skeletal defects caused by trauma or resection of tumors. The molecular basis of intramembranous bone regeneration has been interrogated using rodent models of most of these conditions. These studies reveal that signaling pathways such as Wnt, TGFβ/BMP, FGF, VEGF, and Notch are invoked, reminiscent of embryonic development of membranous bone. Discoveries of several skeletal stem cell/progenitor populations using mouse genetic models also reveal the potential sources of postnatal intramembranous bone regeneration. The purpose of this review is to compare the underlying molecular signals and progenitor cells that characterize embryonic development of membranous bone and postnatal intramembranous bone regeneration.

Customized Therapeutic Surface Coatings for Dental Implants

Dental implants are frequently used to support fixed or removable dental prostheses to replace missing teeth. The clinical success of titanium dental implants is owed to the exceptional biocompatibility and osseointegration with the bone. Therefore, the enhanced therapeutic effectiveness of dental implants had always been preferred. Several concepts for implant coating and local drug delivery had been developed during the last decades. A drug is generally released by diffusion-controlled, solvent-controlled, and chemical controlled methods. Although a range of surface modifications and coatings (antimicrobial, bioactive, therapeutic drugs) have been explored for dental implants, it is still a long way from designing sophisticated therapeutic implant surfaces to achieve the specific needs of dental patients. The present article reviews various interdisciplinary aspects of surface coatings on dental implants from the perspectives of biomaterials, coatings, drug release, and related therapeutic effects. Additionally, the various types of implant coatings, localized drug release from coatings, and how released agents influence the bone–implant surface interface characteristics are discussed. This paper also highlights several strategies for local drug delivery and their limitations in dental implant coatings as some of these concepts are yet to be applied in clinical settings due to the specific requirements of individual patients.

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.

Mediating bone regeneration by means of drug eluting implants: From passive to smart strategies

In addition to excellent biocompatibility and mechanical performance, the new generation of bone and craniofacial implants are expected to proactively contribute to the regeneration process and dynamically interact with the host tissue. To this end, integration and sustained delivery of therapeutic agents has become a rapidly expanding area. The incorporated active molecules can offer supplementary features including promoting oteoconduction and angiogenesis, impeding bacterial infection and modulating host body reaction. Major limitations of the current practices consist of low drug stability overtime, poor control of release profile and kinetics as well as complexity of finding clinically appropriate drug dosage. In consideration of the multifaceted cascade of bone regeneration process, this research is moving towards dual/multiple drug delivery, where precise control on simultaneous or sequential delivery, considering the possible synergetic interaction of the incorporated bioactive factors is of utmost importance. Herein, recent advancements in fabrication of synthetic load bearing implants equipped with various drug delivery systems are reviewed. Smart drug delivery solutions, newly developed to provide higher tempo-spatial control on the delivery of the pharmaceutical agents for targeted and stimuli responsive delivery are highlighted. The future trend of implants with bone drug delivery mechanisms and the most common challenges hindering commercialization and the bench to bedside progress of the developed technologies are covered.

Effect of sustained release of rhBMP-2 from dried and wet hyaluronic acid hydrogel carriers compared with direct dip coating of rhBMP-2 on peri-implant osteogenesis of dental implants in canine mandibles

Hyaluronic acid (HA) hydrogel has been used as a carrier of recombinant human bone morphogenetic protein (rhBMP)-2 for sustained delivery. To enhance peri-implant osteogenesis, a dried coating of rhBMP-2 HA hydrogel (BMP-HAH) on dental implants was designed; this approach provides the advantage of omitting in situ preparation of wet HA hydrogel. Sustained release of rhBMP-2 was more efficient for dried hydrogel over wet hydrogel. For both types, the released rhBMP-2 consistently led to enhanced alkaline phosphatase activity and osterix expression in human mesenchymal stromal cells. Histomorphometric analysis 4 weeks after placement of a dental implant in canine mandibles showed that the dried coating of BMP-HAH (10 μg/ml, n = 6) resulted in a significantly greater bone area (BA) than the wet BMP-HAH (10 μg/ml, n = 6) (p = 0.006) and implants without any coating (n = 6) (p = 0.022), while simple dip coating with rhBMP-2 (10 μg/ml, n = 6) resulted in significantly greater BA than the other three groups (p < 0.0005). Bone-to-implant contact (BIC) was significantly different only between the dried and wet coating of BMP-HAH (p = 0.014). Our results suggest that a simple dip coating of rhBMP-2 is more effective for increased peri-implant osteogenesis compared to a coating of BMP-HAH with sustained release.

Bone Regeneration Using Bone Morphogenetic Proteins and Various Biomaterial Carriers

Trauma and disease frequently result in fractures or critical sized bone defects and their management at times necessitates bone grafting. The process of bone healing or regeneration involves intricate network of molecules including bone morphogenetic proteins (BMPs). BMPs belong to a larger superfamily of proteins and are very promising and intensively studied for in the enhancement of bone healing. More than 20 types of BMPs have been identified but only a subset of BMPs can induce de novo bone formation. Many research groups have shown that BMPs can induce differentiation of mesenchymal stem cells and stem cells into osteogenic cells which are capable of producing bone. This review introduces BMPs and discusses current advances in preclinical and clinical application of utilizing various biomaterial carriers for local delivery of BMPs to enhance bone regeneration.

Nanofibrous yet injectable polycaprolactone-collagen bone tissue scaffold with osteoprogenitor cells and controlled release of bone morphogenetic protein-2

In this work, we developed a nanofibrous, yet injectable orthobiologic tissue scaffold that is capable of hosting osteoprogenitor cells and controlling kinetic release profile of the encapsulated pro-osteogenic factor without diminishing its bioactivity over 21days. This innovative injectable scaffold was synthesized by incorporating electrospun and subsequently O2 plasma-functionalized polycaprolactone (PCL) nanofibers within the collagen type-I solution along with MC3T3-E1 cells (pre-osteoblasts) and bone morphogenetic protein-2 (BMP2). Through changing the PCL nanofiber concentration within the injectable scaffolds, we were able to tailor the mechanical strength, protein retention capacity, bioactivity preservation, and osteoinductive potential of the scaffolds. The nanofibrous internal structure of the scaffold allowed us to use a low dose of BMP2 (200ng/ml) to achieve osteoblastic differentiation in in vitro culture. The osteogenesis capacity of the injectable scaffolds were evaluated though measuring MC3T3-E1 cell proliferation, ALP activity, matrix mineralization, and early- and late-osteoblast specific gene expression profiles over 21days. The results demonstrated that the nanofibrous injectable scaffold provides not only an osteoinductive environment for osteoprogenitor cells to differentiate, but also a suitable biomechanical and biochemical environment to act as a reservoir for osteogenic factors with controlled release profile.

Electrodeposited silk coatings for bone implants

The aim of this study was to characterize the mechanical properties and drug elution features of silk protein-based electrodeposited dental implant coatings. Silk processing conditions were modified to obtain coatings with a range of mechanical properties on titanium studs. These coatings were assessed for adhesive strength and dissolution, with properties tuned using water vapor annealing or glycerol incorporation to modulate crystalline content. Coating reproducibility was demonstrated over a range of silk concentrations from 1% to 10%. Surface roughness of titanium substrates was altered using industry relevant acid etching and grit blasting, and the effect of surface topography on silk coating adhesion was assessed. Florescent compounds were incorporated into the silk coatings, which were modulated for crystalline content, to achieve four days of sustained release of the compounds. This silk electrogelation technique offers a safe and relatively simple approach to generate mechanically robust, biocompatible, and degradable implant coatings that can also be functionalized with bioactive compounds to modulate the local regenerative tissue environment.

Silk electrogel coatings for titanium dental implants

The aim of this study was to develop biocompatible, biodegradable dental implant coatings capable of withstanding the mechanical stresses imparted during implant placement. Two techniques were developed to deposit uniform silk fibroin protein coatings onto dental implants. Two novel coating techniques were implemented to coat titanium shims, studs, and implants. One technique involved electrodeposition of the silk directly onto the titanium substrates. The second technique consisted of melting electrogels and dispensing the melted gels onto the titanium to form the coatings. Both techniques were tested for coating reproducibility using a stylus profilometer and a dial thickness gauge. The mechanical strength of adhered titanium studs was assessed using a universal mechanical testing machine. Uniform, controllable coatings were obtained from both the electrodeposition and melted electrogel coating techniques, tunable from 35 to 1654 µm thick under the conditions studied, and able to withstand delamination during implantation into implant socket mimics. Mechanical testing revealed that the adhesive strength of electrogel coatings, 0.369 ± 0.09 MPa, rivaled other biologically derived coating systems such as collagen, hydroxyapatite, and chitosan (0.07-4.83 MPa). These novel silk-based techniques offer a unique approach to the deposition of safe, simple, mechanically robust, biocompatible, and degradable implant coatings.

Surface modification of implants in long bone

Coatings of orthopedic implants are investigated to improve the osteoinductive and osteoconductive properties of the implant surfaces and thus to enhance periimplant bone formation. By applying coatings that mimic the extracellular matrix a favorable environment for osteoblasts, osteoclasts and their progenitor cells is provided to promote early and strong fixation of implants. It is known that the early bone ongrowth increases primary implant fixation and reduces the risk of implant failure. This review presents an overview of coating titanium and hydroxyapatite implants with components of the extracellular matrix like collagen type I, chondroitin sulfate and RGD peptide in different small and large animal models. The influence of these components on cells, the inflammation process, new bone formation and bone/implant contact is summarized.

In vivo and in vitro investigations of a nanostructured coating material - a preclinical study

Immediate loading of dental implants is only possible if a firm bone-implant anchorage at early stages is developed. This implies early and high bone apposition onto the implant surface. A nanostructured coating material based on an osseoinductive bone grafting is investigated in relation to the osseointegration at early stages. The goal is to transmit the structure (silica matrix with embedded hydroxyapatite) and the properties of the bone grafting into a coating material. The bone grafting substitute offers an osseoinductive potential caused by an exchange of the silica matrix in vivo accompanied by vascularization. X-ray diffraction and transmission electron microscopy analysis show that the coating material consists of a high porous silica matrix with embedded nanocrystalline hydroxyapatite with the same morphology as human hydroxyapatite. An in vitro investigation shows the early interaction between coating and human blood. Energy-dispersive X-ray analysis showed that the silica matrix was replaced by an organic matrix within a few minutes. Uncoated and coated titanium implants were inserted into the femora of New Zealand White rabbits. The bone-to-implant contact (BIC) was measured after 2, 4, and 6 weeks. The BIC of the coated implants was increased significantly at 2 and 4 weeks. After 6 weeks, the BIC was decreased to the level of the control group. A histological analysis revealed high bone apposition on the coated implant surface after 2 and 4 weeks. Osteoblastic and osteoclastic activities on the coating material indicated that the coating participates in the bone-remodeling process. The nanostructure of the coating material led to an exchange of the silica matrix by an autologous, organic matrix without delamination of the coating. This is the key issue in understanding initial bone formation on a coated surface.

Experimental investigation of the effect of surface roughness on bone-cement-implant shear bond strength

Debonding of cemented bone implants is regarded as a major contributor to complications. The relationship between shear bond strength and surface roughness has been investigated, however there are inconsistencies in the trends reported in different studies. The shear strength between poly(methyl methacrylate) bone-cement and sand blasted cobalt-chromium and titanium alloy surfaces was measured to investigate the relationship between interfacial shear strength and surface topology. Surface roughness was quantified by a power law relationship fitted to Fourier spectra as well as three traditional parameters (arithmetical average roughness (Ra), volume of interdigitation (Rr), and RMS slope (Rdq)). We found that the interfacial shear strength is directly proportional to the exponent of the surfaces power spectra (P2) and Rdq, but not to Ra and Rr. However, Rdq is shown to be critically dependent on sampling frequency, making it sensitive to measurement settings. P2 was found to be a robust measure of the surface roughness being independent of sampling frequency.

Bone response to biomimetic implants delivering BMP-2 and VEGF: an immunohistochemical study

This animal study evaluated bone healing around titanium implant surfaces biomimetically coated with bone morphogenic protein-2 (BMP-2) and/or vascular endothelial growth factor (VEGF) by examining bone matrix proteins and mineralisation. Five different implant surfaces were established: acid-etched surface (AE), biomimetic calcium phosphate surface (CAP), BMP-2 loaded CAP surface, VEGF loaded CAP surface and dual BMP-2 + VEGF loaded CAP surface. The implants were inserted into calvariae of adult domestic pigs. For the comparison of osteoconductive capacity of each surface, bone mineral density and expression of bone matrix proteins (collagen I, BMP-2/4, osteocalcin and osteopontin) inside defined chambers around the implant were assessed using light microscopy and microradiography and immunohistochemical analysis at 1, 2 and 4 weeks. In the both groups delivering BMP-2, the bone mineral density was significantly enhanced after 2 weeks and the highest value was measured for the group BMP + VEGF. In the group VEGF, collagen I and BMP-2/4 expressions were significantly up-regulated at the first and second weeks. The percentage of BMP-2/4 positive cells in the group BMP + VEGF was significantly enhanced compared with the groups AE and CAP at the second week. Although the highest osteocalcin and osteopontin expression values were observed for the group BMP + VEGF after 2 weeks, no statistically significant difference in osteocalcin and osteopontin expressions was found between all groups at any time. It was concluded that combined delivery of BMP-2 and VEGF favoured bone mineralisation and expression of important bone matrix proteins that might explain synergistic interaction between both growth factors.

Intra-operatively customized implant coating strategies for local and controlled drug delivery to bone

Bone is one of the few tissues in the human body with high endogenous healing capacity. However, failure of the healing process presents a significant clinical challenge; it is a tremendous burden for the individual and has related health and economic consequences. To overcome such healing deficits, various concepts for a local drug delivery to bone have been developed during the last decades. However, in many cases these concepts do not meet the specific requirements of either surgeons who must use these strategies or individual patients who might benefit from them. We describe currently available methods for local drug delivery and their limitations in therapy. Various solutions for drug delivery to bone focusing on clinical applications and intra-operative constraints are discussed and drug delivery by implant coating is highlighted. Finally, a new set of design and performance requirements for intra-operatively customized implant coatings for controlled drug delivery is proposed. In the future, these requirements may improve approaches for local and intra-operative treatment of patients.

Osteogenic protein-1 delivered by hydroxyapatite-coated implants improves bone ingrowth in extracortical bone bridging

BACKGROUND

Extracortical bone bridging for treatment of massive bone loss can improve stability and longevity of massive endoprostheses. Osteogenic protein-1 (OP-1), when used with allograft bone, reportedly improves extracortical bone bridging and bone ingrowth.

QUESTIONS/PURPOSES

We asked whether OP-1 delivered by hydroxyapatite (HA) without bone grafting could improve bone ingrowth and bone formation in the context of extracortical bone bridging.

METHODS

We implanted unilateral segmental femoral diaphyseal replacement prostheses in 18 dogs (three groups of six dogs). The groups consisted of an HA-coated group augmented with OP-1, an HA-coated group, and a plain porous group. Bone grafting techniques were not used to augment bone formation. The implants were retrieved at 12 weeks for histologic assessment.

RESULTS

After removing one specimen owing to a complication, 17 femora were analyzed (six HA-coated augmented with OP-1, five HA-coated, and six plain). We observed better bone ingrowth in the HA-coated OP-1 group than in the plain porous and HA-coated groups, with no difference between the latter two groups. There also was better bone apposition and callus height in the HA-coated OP-1 group than in the plain group but no differences between the HA-coated OP-1 and HA-coated groups or between the HA-coated and plain groups.

CONCLUSIONS

OP-1 (2.9 mg) delivered by HA-coated segmental replacement prostheses in this canine extracortical bone bridging model revealed improved bone ingrowth over HA-coated implants without OP-1 or plain porous-coated prostheses.

Amino-modified silica surfaces efficiently immobilize bone morphogenetic protein 2 (BMP2) for medical purposes

Due to its ability to induce de novo bone formation the differentiation factor bone morphogenetic protein 2 (BMP2) is often used to enhance the integration of bone implants. With the aim of reducing possible high dose side-effects and to lower the costs, in order to produce affordable implants, we developed a simple and fast method for the immobilization of BMP2 on silica-based surfaces using silane linkers which carry amino or epoxy functions. We put an especial emphasis on the influence of the nanoscale surface topography of the silica layer. Therefore, we chose glass (for control experiments) and Bioverit® II (as a typical implant base material) as support materials and coated these substrates with unstructured or nanoporous amorphous silica layers for comparison. Immobilized BMP2 was quantified by two different methods: by ELISA and by a cell-based assay for active BMP2. These tests probe for immunologically and biologically active BMP2, respectively. The results show that the amino functionalization is better suited for immobilizing the protein. Strikingly, a considerably higher amount of BMP2 could be immobilized on coated Bioverit® II surfaces compared with coated glass substrates, which was presumably due to the macroscopic roughness of the Bioverit® II substrates. In addition, it was found that the nanoporous silica coatings on Bioverit® II substrates were able to bind more BMP2 than the unstructured ones.

Hydroxyapatite nanoparticles in poly-D,L-lactic acid coatings on porous titanium implants conducts bone formation

It is well established in the field of biomaterials that hydroxyapatite (HA) may provide interesting osteoconductive properties. In this study, we investigated the osseointegrational effect of a 50/50 vol % composite of HA nanoparticles and poly-D,L-lactic acid (PDLLA) coated on model titanium bone implants in an in vivo animal model. The aim is to evaluate how the addition of HA to PDLLA may improve the bone formation and initial fixation of the implant. Two titanium implants coated with the PDLLA/HA composite and pure PDLLA, respectively, were implanted bilaterally in proximal part of humeri with a 2-mm peri-implant gap in 10 sheep. After 12 weeks, the remains of the coatings were present on 20.3 and 19.8% of PDLLA/HA composite- and PDLLA-coated implants, respectively. It was observed that newly formed bone (39.3%) and fibrous tissue (58.3%) had replaced the PDLLA/HA composite, whereas pure PDLLA was replaced almost completely by fibrous tissue (96.2%). Consequently, the PDLLA/HA composite-coated implants were better fixated as confirmed by push-out tests. Using quantification of peri-implant tissue and implant fixation as parameters, the present findings, therefore, clearly reveal that the addition of nanoparticulate HA to a PDLLA coating on titanium implants increases osseointegration.

MC3T3-E1 cell differentiation and in vivo bone formation induced by phosphoserine

Bone formation induced by phosphoserine was investigated in vitro and in vivo using MC3T3-E1 cells and a rabbit calvarial osseous defect model. MC3T3-E1 cells supplemented by phosphoserine displayed two-fold higher alkaline phosphatase activity and mineralization nodule formation, and calvarial defects treated with phosphoserine showed statistically significant new bone formation compared with the control (P < 0.05).

Synchrotron X-ray bioimaging of bone regeneration by artificial bone substitute of MegaGen Synthetic Bone and hyaluronate hydrogels

Synchrotron X-ray bioimaging was successfully carried out to observe bone regeneration by a novel artificial bone substitute of bioactive MegaGen Synthetic Bone (MGSB) and hyaluronate (HA) hydrogels. A biphasic calcium phosphate of MGSB was prepared by chemical precipitation method, with a porous spherical morphology. On the basis of the fact that HA plays important roles in bone regeneration and promotes the differentiation, vascularization, and migration of stem cells, HA-cystamine (CYS) hydrogels with cleavable disulfide linkages were prepared to supply HA continuously for effective bone regeneration by their controlled degradation in vivo. Among seven different samples using Bio-OSS®, MGSB, and/or several kinds of HA hydrogels, MGSB/HA-CYS hydrogels resulted in the most significant bone regeneration in the calvarial critical bone defect of New Zealand white rabbits. Histological and histomorphometric analyses revealed that the bone regeneration by MGSB/HA-CYS hydrogels was as high as 43%, occupying 71% of the bone defect area with MGSB in the form of a calvarial bone plate in 4 weeks. After that, MGSB was bioabsorbed and replaced gradually with regenerated bones as observed in 8 weeks. Synchrotron X-ray imaging clearly confirmed the effective bone regeneration by MGSB/HA-CYS hydrogels, showing three-dimensional micron-scale morphologies of regenerated bones interconnected with MGSB. In addition, sequential nondestructive synchrotron X-ray tomographic analysis results from anterior to posterior of the samples were well matched with the histomorphometric analysis results. The clinically feasible artificial bone substitutes of MGSB/HA-CYS hydrogels will be investigated further for various bone tissue engineering applications using the synchrotron X-ray bioimaging systems.

Ceramic/polymer nanocomposites with tunable drug delivery capability at specific disease sites

Pharmaceutical agents are often used to stimulate new bone formation for the treatment of bone injuries or diseases (such as osteoporosis). However, there are several problems associated with current orthopedic drug delivery methods. First, conventional systemic administration of pharmaceutical agents may not effectively reach targeted sites and, thus, they can cause nonspecific bone formation in areas not affected by injury or disease. Second, even if intentionally delivered or implanted locally to the damaged bone tissue, these agents tend to rapidly diffuse into adjacent tissues due to weak physical bonding to their drug carriers, which limits their potential to promote prolonged bone formation in targeted areas of bone disease. Therefore, in this study, biodegradable ceramic/polymer nanocomposites were explored as novel drug carriers for orthopedic applications to prolong local drug release and, thus, improve drug effectiveness at bone disease sites. Specifically, a bone morphogenetic protein (BMP-7) derived peptide (DIF-7c) was used as a model drug in this study and was first loaded onto nanocrystalline hydroxyapatite (nano-HA) by either covalent chemical attachment or physical adsorption. These drug-carrying nano-HA particles were then dispersed into a degradable polymer (poly-lactide-co-glycolide or PLGA) matrix to create an implantable system capable of long-term drug release. The aminophase silane covalent chemical immobilization process was utilized in this study. These nanocomposite-based drug delivery systems were then characterized for drug loading efficiency and in vitro drug release. Results demonstrated that DIF-7c was successfully immobilized onto nano-HA placed in PLGA. Moreover, a greater prolonged two-phase release profile (of more than 3 months) was achieved when using aminophase silane chemical immobilization to nano-HA particles. Since previous studies have demonstrated greater in vivo bone growth on nano- compared with micron-HA particles placed in rat calvaria, this study continued to demonstrate that ceramic/polymer nanocomposites are promising candidates as novel orthopedic materials to promote bone regeneration.

Long-term cell-mediated protein release from calcium phosphate ceramics

Efficient delivery of growth factors from carrier biomaterials depends critically on the release kinetics of the proteins that constitute the carrier. Immobilizing growth factors to calcium phosphate ceramics has been attempted by direct adsorption and usually resulted in a rapid and passive release of the superficially adherent proteins. The insufficient retention of growth factors limited their bioavailability and their efficacy in the treatment of bone regeneration. In this study, a coprecipitation technique of proteins and calcium phosphate was employed to modify the delivery of proteins from biphasic calcium phosphate (BCP) ceramics. To this end, tritium-labeled bovine serum albumin ([(3)H]BSA) was utilized as a model protein to analyze the coprecipitation efficacy and the release kinetics of the protein from the carrier material. Conventional adsorption of [(3)H]BSA resulted in a rapid and passive release of the protein from BCP ceramics, whereas the coprecipitation technique effectively prevented the burst release of [(3)H]BSA. Further analysis of the in vitro kinetics demonstrated a sustained, cell-mediated release of coprecipitated [(3)H]BSA from BCP ceramics induced by resorbing osteoclasts. The coprecipitation technique described herein, achieved a physiologic-like protein release, by incorporating [(3)H]BSA into its respective carriers, rendering it a promising tool in growth factor delivery for bone healing.

Evaluation of a novel nanocrystalline hydroxyapatite paste Ostim in comparison to Alpha-BSM - more bone ingrowth inside the implanted material with Ostim compared to Alpha BSM

Background

The purpose of this study was to evaluate the performance a newly developed nanocrystalline hydroxyapatite, OSTIM^® following functional implantation in femoral sites in thirty-eight sheep for 1, 2 or 3 months. Ostim^® 35 was compared to an established calcium phosphate, Alpha BSM^®.

Methods

Biomechanical testing, μ-CT analysis, histological and histomorphological analyses were conducted to compare the treatments including evaluation of bone regeneration level, material degradation, implant biomechanical characteristics.

Results

The micro-computed tomography (μCT) analysis and macroscopic observations showed that Ostim^® seemed to diffuse easily particularly when the defects were created in a cancellous bone area. Alpha BSM^® remained in the defect.

The performance of Ostim was good in terms of mechanical properties that were similar to Alpha BSM^® and the histological analysis showed that the bone regeneration was better with Ostim^® than with Alpha BSM^®. The histomorphometric analysis confirmed the qualitative analysis and showed more bone ingrowth inside the implanted material with Ostim^® when compared to Alpha BSM ^® at all time points.

Conclusions

The successful bone healing with osseous consolidation verifies the importance of the nanocrystalline hydroxyapatite in the treatment of metaphyseal osseous volume defects in the metaphyseal spongiosa.

Multifunctional implant coatings providing possibilities for fast antibiotics loading with subsequent slow release

The possibility to fast-load biomimetic hydroxyapatite coatings on surgical implant with the antibiotics Amoxicillin, Gentamicin sulfate, Tobramycin and Cephalothin has been investigated in order to develop a multifunctional implant device offering sustained local anti-bacterial treatment and giving the surgeon the possibility to choose which antibiotics to incorporate in the implant at the site of surgery. Physical vapor deposition was used to coat titanium surfaces with an adhesion enhancing gradient layer of titanium oxide having an amorphous oxygen poor composition at the interface and a crystalline bioactive anatase TiO(2) composition at the surface. Hydroxyapatite (HA) was biomimetically grown on the bioactive TiO(2) to serve as a combined bone in-growth promoter and drug delivery vehicle. The coating was characterized using scanning and transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The antibiotics were loaded into the HA coatings via soaking and the subsequent release and antibacterial effect were analyzed using UV spectroscopy and examination of inhibition zones in a Staphylococcus aureus containing agar. It was found that a short drug loading time of 15 min ensured antibacterial effects after 24 h for all antibiotics under study. It was further found that the release processes of Cephalothin and Amoxicillin consisted of an initial rapid drug release that varied unpredictably in amount followed by a reproducible and sustained release process with a release rate independent of the drug loading times under study. Thus, implants that have been fast-loaded with drugs could be stored for ~10 min in a simulated body fluid after loading to ensure reproducibility in the subsequent release process. Calculated release rates and measurements of drug amounts remaining in the samples after 22 h of release indicated that a therapeutically relevant dose could be achieved close to the implant surface for about 2 days. Concluding, the present study provides an outline for the development of a fast-loading slow-release surgical implant kit where the implant and the drug are separated when delivered to the surgeon, thus constituting a flexible solution for the surgeon by offering the choice of quick addition of antibiotics to the implant coating based on the patient need.

Covalently-linked hyaluronan promotes bone formation around Ti implants in a rabbit model

The goal of this study was the in vivo evaluation of nanoporous titanium (Ti) implants bearing a covalently linked surface hyaluronan (HA) layer. Implant surface topography and surface chemistry were previously evaluated by scanning electron microscopy and X-ray photoelectron spectroscopy. Results showed that the surface modification process did not affect surface topography, yielding a homogeneously HA-coated nanotextured implant surface. In vivo evaluation of implants in both cortical and trabecular bone of rabbit femurs showed a significant improvement of both bone-to-implant contact and bone ingrowth at HA-bearing implant interfaces at 4 weeks. The improvement in osteointegration rate was particularly evident in the marrow-rich trabecular bone (bone-to-implant contact: control 22.5%; HA-coated 69.0%, p < 0.01). Mechanical testing (push-out test) and evaluation of interfacial bone microhardness confirmed a faster bone maturation around HA-coated implants (Bone Maturation Index: control 79.1%; HA-coated 90.6%, p < 0.05). Suggestions based on the biochemical role of HA are presented to account for the observed behavior.

Assessing surface area evolution during biomimetic growth of hydroxyapatite coatings

The surface area of biomimetically deposited hydroxyapatite (HA) coatings on metallic implants is important for the biological performance of the implant. Thus, a nondestructive method of assessing this quantity directly on the solid substrate would be highly valuable. The objective of this study was to develop such a method and for the first time assess the evolution of surface area of HA during biomimetic growth. The surface area of a TiO2-covered titanium substrate was measured prior to and following the biomimetic coating deposition using Ar gas adsorption at 77 K. The presence of HA on the surface was verified with scanning electron microscopy and X-ray diffraction. The specific surface area of the coating was found to increase linearly during 1 week of deposition at a rate of approximately 100 cm2 day-1 (g substrate)-1. The presented method may be used as a tool for studying the evolution in surface area of coatings on solid substrates during biomimetic deposition or other growth processes.

Lack of effect on bone healing of injectable BMP-2 augmented hyaluronic acid

INTRODUCTION

Autologous bone graft is the gold standard for the filling of large osseous defects. Because of its limited supply and complications such as pain, bleeding or infection, the development of alternative bone substitutes has been the subject of several studies. In clinical practice, the most commonly used bone substitutes are calcium phosphates like hydroxyapatite or tricalcium phosphate. With the aim to improve the osseointegration of these materials, growth factors such as bone morphogenetic protein-2 (BMP-2) have been added. Preferably, an injectable bone substitute should be made available. Hyaluronic acid is a component of the extracellular matrix of many tissues, including bone. We examined the bone regenerative effect of commercially available, injectable hyaluronic acid (Hyalart) with and without addition of bone morphogenetic protein-2 (BMP-2).

MATERIALS AND METHODS

Trepanation defects of 9.4 mm diameter in the intercondylar groove of sheep femora were filled with pure and augmented (200 microg BMP-2) hyaluronic acid. As controls, empty defects and defects treated with autologous bone graft harvested from the contralateral side were used. After 3 months, the defects were analysed by fluorescence microscopy after intravital fluorescence staining, contact microradiography, histology and histomorphometry.

RESULTS

Treatment of the defects with loaded and unloaded hyaluronic acid resulted in a significant lack of bone formation inside the defects. Untreated defects showed an amount of 5.1% newly formed bone, and defects treated with autologous bone graft revealed a bone content of 20%. The difference between both groups was statistically significant (P < 0.05). Furthermore, there was neither a remarkable effect in the periphery of the defects nor ectopic bone formation.

CONCLUSION

The application of the used injectable hyaluronic acid (Hyalart) with and without BMP-2 is not advantageous as sole bone substitute for the filling of osseous defects.

Implanting hydroxyapatite-coated porous titanium with bone morphogenetic protein-2 and hyaluronic acid into distal femoral metaphysis of rabbits

OBJECTIVE

To assess the osseointegration capability of hydroxyapatite-coated porous titanium with bone morphogenetic protein-2 (BMP-2) and hyaluronic acid to repair defects in the distal femur metaphysis in rabbits.

METHODS

Porous titanium implants were made by sintering titanium powder at high temperature, which were coated with hydroxyapatite by alkali and heat treatment and with BMP-2 combined with bone regeneration materials. And hyaluronic acid was further used as delivery system to prolong the effect of BMP-2. The implants were inserted into the metaphysis of the distal femur of rabbits. The animals were killed at 6, 12 and 24 weeks to accomplish histological and biomechanical analyses.

RESULTS

According to the result of histological analysis, the osseointegration in BMP-2 group was better than that of the HA-coated porous titanium group. In push-out test, all the samples had bigger shear stress as time passed by. There was statistical difference between the two groups in 6 and 12 weeks but not in 24 weeks.

CONCLUSION

Hydroxyapatite-coated porous titanium with BMP-2 and hyaluronic acid has a good effect in repairing defects of distal femur in rabbits, which is a fine biotechnology for future clinical application.

Optimized bone regeneration based on sustained release from three-dimensional fibrous PLGA/HAp composite scaffolds loaded with BMP-2

Contemporary treatment of critical bone defect remains a significant challenge in the field of orthopedic surgery. Engineered biomaterials combined with growth factors have emerged as a new treatment alternative in bone repair and regeneration. Our approach is to encapsulate bone morphogenetic protein-2 (BMP-2) into a polymeric matrix in different ways and characterize their individual performance in a nude mouse model. The main objective of this study is to examine whether the PLGA/HAp composite fibrous scaffolds loaded with BMP-2 through electrospinning can improve bone regeneration. The hypothesis is that different loading methods of BMP-2 and different HAp contents in scaffolds can alternate the release profiles of BMP-2 in vivo, therefore modify the performance of scaffolds in bone regeneration. Firstly, mechanical strength of scaffolds and HAp nanoparticles distribution in scaffolds were investigated. Secondly, nude mice experiments extended to 6 weeks were carried out to test the in vivo performance of these scaffolds, in which measurements, like serum BMP-2 concentration, ALP activity, X-ray qualification, and H&E/IHC tissue staining were utilized to monitor the growth of new bone and the changes of the corresponding biochemical parameters. The results showed that the PLGA/HAp composite scaffolds developed in this study exhibited good morphology/mechanical strength and HAp nanoparticles were homogeneously dispersed inside PLGA matrix. Results from the animal experiments indicate that the bioactivity of BMP-2 released from the fibrous PLGA/HAp composite scaffolds is well maintained, which further improves the formation of new bone and the healing of segmental defects in vivo. It is concluded that BMP-2 loaded PLGA/HAp composite scaffolds are promising for bone healing.

Heat treatment of BMP-2 depots on implant materials generates an immobilized layer of BMP-2 with pronounced bioactivity

Bone cells seeded directly on depots of bone morphogenetic protein-2 (BMP-2) increase alkaline phosphatase (ALP) expression. Heating of such BMP-2 depots to 100 degrees C augmented the intensity of this local ALP induction. To understand this unexpected finding, we investigated the effect of heat treatment on BMP-2 depots more closely. Using a novel bioassay based on ALP-induction of remote cells, we found that the amount of released bioactive BMP-2 from heat-treated depots decays within days and could be described by an exponential function. From this function, we expected that pre-incubation of BMP-2 depots in culture medium for 4 weeks renders them insufficient to induce ALP. However, preincubated, heat-treated depots still induced maximal ALP, unless treated with the selective BMP-2 inhibitor noggin. Furthermore, heat treatment of BMP-2 depots generated a layer of immunoreactive BMP-2 at the surface of the carrier. In contrast, BMP-2 was washed off completely if heat treatment of adsorbed protein was omitted. Results show that heat treatment generates both a soluble pool of BMP-2 and a material-bound layer of BMP-2 in which the protein is protected against degradation. Therefore, heat treatment appears useful to locally immobilize BMP-2 on various implant surfaces.

Three-dimensional fibrous PLGA/HAp composite scaffold for BMP-2 delivery

A protein loaded three-dimensional scaffold can be used for protein delivery and bone tissue regeneration. The main objective of this project was to develop recombinant human bone morphogenetic protein-2 (rhBMP-2) loaded poly(D,L-lactide-co-glycolide)/hydroxylapatite (PLGA/HAp) composite fibrous scaffolds through a promising fabrication technique, electrospinning. In vitro release of BMP-2 from these scaffolds, and the attachment ability and viability of marrow derived messenchymal stem cells (MSCs) in the presence of the scaffolds were investigated. The PLGA/HAp composite scaffolds developed in this study exhibit good morphology and it was observed that HAp nanoparticles were homogeneously dispersed inside PLGA matrix within the scaffold. The composite scaffolds allowed sustained (2-8 weeks) release of BMP-2 whose release rate was accelerated with increasing HAp content. It was also shown that BMP-2 protein successfully maintained its integrity and natural conformations after undergoing the process of electrospinning. Cell culture experiments showed that the encapsulation of HAp could enhance cell attachment to scaffolds and lower cytotoxicity.

Autologous human-derived bone marrow cells exposed to a novel TGF-β1 fusion protein for the treatment of critically sized tibial defect

We report the first clinical case of transplantation of autologous bone marrow-derived cells in vitro exposed to a novel recombinant human transforming growth factor (rhTGF)-β1 fusion protein bearing a collagen-binding domain (rhTGF-β1-F2), dexamethasone (DEX) and β-glycerophosphate (β-GP). When such culture-expanded cells were loaded into porous ceramic scaffolds and transplanted into the bone defect of a 69-year-old man, they differentiated into bone tissue. Marrow cells were obtained from the iliac crest and cultured in collagen gels impregnated with rhTGF-β1-F2. Cells were selected under serum-restricted conditions in rhTGF-β1-F2-containing medium for 10 days, expanded in 20% serum for 22 days and osteoinduced for 3 additional days in DEX/β-GP-supplemented medium. We found that the cell number harvested from rhTGF-β1-F2-treated cultures was significantly higher (2.3- to 3-fold) than that from untreated cultures. rhTGF-β1-F2 treatment also significantly increased alkaline phosphatase activity (2.2- to 5-fold) and osteocalcin synthesis, while calcium was only detected in rhTGF-β1-F2-treated cells. Eight weeks after transplantation, most of the scaffold pores were filled with bone and marrow tissue. When we tested the same human cells treated in vitro in a rat model using diffusion chambers, there was subsequent development of cartilage and bone following the subcutaneous transplantation of rhTGF-β1-F2-treated cells. This supports the suggestion that such cells were marrow-derived cells, with chondrogenic and osteogenic potential, whereas the untreated cells were not under the same conditions. The ability for differentiation into cartilage and bone tissues, combined with an extensive proliferation capacity, makes such a marrow-derived stem cell population valuable to induce bone regeneration at skeletal defect sites.