Comparison of the bond strength of selected adhesive dental systems to cortical bone under in vitro conditions

Bone adhesive materials: From bench to bedside

Biodegradable bone adhesives represent a highly sought-after type of biomaterial which would enable replacement of traditional metallic devices for fixation of bone. However, these biomaterials should fulfil an extremely large number of requirements. As a consequence, bone-adhesive biomaterials which meet all of these requirements are not yet commercially available. Therefore, this comprehensive review provides an extensive overview of the development of bone adhesives from a translational perspective. First, the definition, classification, and chemistry of various types of bone adhesives are highlighted to provide a detailed overview of this emerging class of biomaterials. In this review we particularly focused studies which describe the use of materials that are capable of gluing two pieces of bone together within a time frame of minutes to days. Second, this review critically reflects on i) the experimental conditions of commonly employed adhesion tests to assess bone adhesion and ii) the current state-of-the-art regarding their preclinical and clinical applicability.

Bond Strength and Adhesion Mechanisms of Novel Bone Adhesives

Bone adhesives offer distinct advantages over the use of screws to attached internal fixation plates (IFPs). As the chemical composition of bone is similar to dentine, it is possible that the types of monomers used to make dentine adhesives could be utilised to affix IFPs to bone. The ability to attach a bio-resorbable IFP to porcine bone was assessed for the monomer 10-methacryloyloxydecyl dihydrogen phosphate (MDP), used either as a homopolymer or a copolymer with urethane dimethacrylate (MDP + U). Additionally, the addition of a priming step (MDP + U + P) was evaluated. The chemical interactions of the monomers with bone were assessed using XRD and imaged using TEM, revealing the formation of nano-layered structures with the MDP primer, something we believe has not been reported on bone. In a 6-week artificial aging study both MDP + U and MDP + U + P demonstrated adequate shear bond strength to affix bio-resorbable IFPs. The cytotoxicity profiles of the adhesive formulations were determined using indirect and direct contact with MC3T3 cells, with indirect conditions suggesting the MDP + U + P is as cytocompatible as the resorbable IFP. The findings of this study suggest our newly developed adhesive has the potential to be used as a bone adhesive to affix bioresorbable IFPs.

Investigating the effect of germanium on the structure of SiO2-ZnO-CaO-SrO-P2O5 glasses and the subsequent influence on glass polyalkenoate cement formation, solubility and bioactivity

A series of germanium (Ge)-containing glasses were synthesized based on a starting glass composition of SiO₂-ZnO-CaO-SrO-P₂O₅. Additions of GeO₂ (6 and 12 mol%) were incorporated at the expense of SiO_2, which retained the amorphous character, and each glass was processed to present similar particle size and surface area. Glass characterization using x-ray photoelectron spectroscopy (XPS) and magic angle spinning nuclear magnetic resonance (MAS-NMR) determined that the addition of GeO₂ increased the fraction of lower Q-speciation and subsequently the concentration of non-bridging oxygens (NBO). Glass Polyalkenoate Cements (GPC) were formulated from each glass with 40, 50 and 60 wt% PAA, and presented time dependent solubility profiles (1, 10, 100, 1000 h) for the release of Si⁴⁺ (4-140 mg/l), Ca²⁺ (1-8 mg/l), Zn²⁺ (<6 mg/l), Sr²⁺ (2-37 mg/l), PO₄^3- (2-43 mg/l) and Ge⁴⁺ (20-911 mg/l) and attained pH values close to 7.5 after 1000 h. Ge-GPCs containing 40 wt% polyacrylic acid (PAA) presented appropriate working time (T_w) and setting times (T_s), and the corresponding compressive strengths ranged from (14-30 MPa). The Ge-GPCs (40, 50 wt%) presented a linear increase (R²-0.99) with respect to time. Simulated Body Fluid (SBF) testing resulted in the Ge-GPCs encouraging the precipitation of crystalline hydroxyapatite on the GPC surface, more evidently after 100 and 1000 h incubation.

Characterization of Soybean Protein Adhesives Modified by Xanthan Gum

The aim of this study was to provide a basis for the preparation of medical adhesives from soybean protein sources. Soybean protein (SP) adhesives mixed with different concentrations of xanthan gum (XG) were prepared. Their adhesive features were evaluated by physicochemical parameters and an in vitro bone adhesion assay. The results showed that the maximal adhesion strength was achieved in 5% SP adhesive with 0.5% XG addition, which was 2.6-fold higher than the SP alone. The addition of XG significantly increased the hydrogen bond and viscosity, as well as increased the β-sheet content but decreased the α-helix content in the second structure of protein. X-ray diffraction data showed significant interactions between SP molecules and XG. Scanning electron microscopy observations showed that the surface of SP adhesive modified by XG was more viscous and compact, which were favorable for the adhesion between the adhesive and bone. In summary, XG modification caused an increase in the hydrogen bonding and zero-shear viscosity of SP adhesives, leading to a significant increase in the bond strength of SP adhesives onto porcine bones.

Development of a methacrylate-terminated PLGA copolymer for potential use in craniomaxillofacial fracture plates

We synthesised methacrylate-terminated PLGA (HT-PLGA, 85:15 LA:GA, 169kDa), for potential use as an adhesively attached craniomaxillofacial fracture fixation plate. The in vitro degradation of molecular weight, pH and flexural modulus were measured over 6weeks storage in PBS at 37°C, with commercially available high (225kDa, H-PLGA) and low (116kDa, L-PLGA) molecular weight 85:15 PLGAs used as comparators. Molecular weights of the materials reduced over 6weeks, HT-PLGA by 48%, H-PLGA by 23% and L-PLGA by 81%. HT-PLGA and H-PLGA exhibited a near constant pH (7.35) and had average flexural moduli in excess of 6GPa when produced, similar to that of the mandible. After 1week storage both exhibited a significant reduction in average modulus, however, from weeks 1-6 no further significant changes were observed, the average modulus never dropped significantly below 5.5GPa. In contrast, the L-PLGA caused a pH drop to below 7.3 by week 6 and an average modulus drop to 0.6 from an initial 4.6GPa. Cell culture using rat bone marrow stromal cells, revealed all materials were cytocompatible and exhibited no osteogenic potential. We conclude that our functionalised PLGA retains mechanical properties which are suitable for use in craniofacial fixation plates.

Activated dopamine derivatives as primers for adhesive-patch fixation of bone fractures

Activated dopamine derivatives are synthesized and evaluated as primers between a TEC-crosslinked matrix and bone. Dopamine derivatives are shown to significantly increase the adhesive strength of fiber-reinforced adhesive bone patches.

A new adhesive technique for internal fixation in midfacial surgery

Background

The current surgical therapy of midfacial fractures involves internal fixation in which bone fragments are fixed in their anatomical positions with osteosynthesis plates and corresponding screws until bone healing is complete. This often causes new fractures to fragile bones while drilling pilot holes or trying to insert screws. The adhesive fixation of osteosynthesis plates using PMMA bone cement could offer a viable alternative for fixing the plates without screws. In order to achieve the adhesive bonding of bone cement to cortical bone in the viscerocranium, an amphiphilic bone bonding agent was created, analogous to the dentin bonding agents currently on the market.

Methods

The adhesive bonding strengths were measured using tension tests. For this, metal plates with 2.0 mm diameter screw holes were cemented with PMMA bone cement to cortical bovine bone samples from the femur diaphysis. The bone was conditioned with an amphiphilic bone bonding agent prior to cementing. The samples were stored for 1 to 42 days at 37 degrees C, either moist or completely submerged in an isotonic NaCl-solution, and then subjected to the tension tests.

Results

Without the bone bonding agent, the bonding strength was close to zero (0.2 MPa). Primary stability with bone bonding agent is considered to be at ca. 8 MPa. Moist storage over 42 days resulted in decreased adhesion forces of ca. 6 MPa. Wet storage resulted in relatively constant bonding strengths of ca. 8 MPa.

Conclusion

A new amphiphilic bone bonding agent was developed, which builds an optimizied interlayer between the hydrophilic bone surface and the hydrophobic PMMA bone cement and thus leads to adhesive bonding between them. Our in vitro investigations demonstrated the adhesive bonding of PMMA bone cement to cortical bone, which was also stable against hydrolysis. The newly developed adhesive fixing technique could be applied clinically when the fixation of osteosynthesis plates with screws is impossible. With the detected adhesion forces of ca. 6 to 8 MPa, it is assumed that the adhesive fixation system is able to secure bone fragments from the non-load bearing midfacial regions in their orthotopic positions until fracture consolidation is complete.

The implantation of non-cell-based materials to prevent the recurrent disc herniation: an in vivo porcine model using quantitative discomanometry examination

Recurrent disc herniation is frequently observed due to leakage of nucleus pulposus through injured anulus fibrosus. There is no effective treatment to prevent recurrent disc herniation yet. In this study, we proposed to implant non-cell-based materials into the porcine disc to stimulate the growth of fibrous tissue and thereby increase the disc functional integrity. The disc herniation was simulated by anular punctures using the spinal needles. Four clinically used implantation materials, i.e., gelfoam, platinum coil, bone cement and tissue glue, were delivered into the discs via percutaneous spinal needles. Two months after the surgery, the swine were killed. The degree of disc integrity of intact, naturally healed and implanted discs, was examined by quantitative discomanometry apparatus. We found the disc injury could not recover after 2 months of healing, and the disc implantation affected the degree of disc integrity. The disc integrity of gelfoam-implanted discs was better than that of coil-, bone cement-, and glue-implanted discs. The implantation of non-cell-based material was proved to be a potentially clinically applicable method to recover the integrity of injured discs and to prevent recurrent disc herniation.

Treatment of tripod fracture of zygomatic bone by N-2-butyl cyanoacrylate glue fixation, and its effects on the tissues

The standard treatment of zygomatic bone fractures is fixation by microplates or miniplates and screws today. It is very difficult to place plates and screws into thin bones or small bone fragments especially in the facial bones and bones adjacent to important structures. Cyanoacrylate is used as a hemostatic agent, an embolic agent, in retinal tears, in corneal ulcers, in fixation of mandibular osteotomies and in craniofacial surgery. N-2-Butyl cyanoacrylate is a form of cyanoacrylate which is bioabsorbable and biocompatible. It is easily applied to the tissues. We aimed to determine the effect of N-2-butyl cyanoacrylate in the fixation of displaced zygomatic bone fractures. We examined the histotoxicity and the effects on healing and foreign body reaction of N-2-butyl cyanoacrylate. Eight New Zealand white rabbits underwent zygomatic osteotomies bilaterally. The fractures on left sides of the rabbits were determined as study site and right sides as control site. Knight and North classification of zygomatic bone fractures were used and group 4 fractures were made bilaterally. Open reduction of fractures was performed bilaterally and N-2-butyl cyanoacrylate was applied only on left sides. No fixation was made on right sides representing the control group. Postoperatively in the first, second, third and fourth weeks, two rabbits were sacrificed and the fracture sites were examined macroscopically and histopathologically. In the glued study group, fixation was obtained in all cases whereas in the control group, all the fractures were seen to be displaced. Tissue reaction was similar in the study and the control groups.