Biocompatibility and bone formation with porous modified PMMA in normal and irradiated mandibular tissue

A composite of polymethylmethacrylate, hydroxyapatite, and β-tricalcium phosphate for bone regeneration in an osteoporotic rat model

The purpose of this study was to test several modifications of the polymethylmethacrylate (PMMA) bone cement by incorporating osteoconductive and biodegradable materials for enhancing bone regeneration capacity in an osteoporotic rat model. Three bio-composites (PHT-1 [80% PMMA, 16% HA, 4% β-TCP], PHT-2 [70% PMMA, 24% HA, 6% β-TCP], and PHT-3 [30% PMMA, 56% HA, 14% β-TCP]) were prepared using different concentrations of PMMA, hydroxyapatite (HA), and β-tricalcium phosphate (β-TCP). Their morphological structure was then examined using a scanning electron microscope (SEM) and mechanical properties were determined using a MTS 858 Bionics test machine (MTS, Minneapolis, MN, USA). For in vivo studies, 35 female Wister rats (250 g, 12 weeks of age) were prepared and divided into five groups including a sham group (control), an ovariectomy-induced osteoporosis group (OVX), an OVX with pure PMMA group (PMMA), an OVX with PHT-2 group (PHT-2), and an OVX with PHT-3 group (PHT-3). In vivo bone regeneration efficacy was assessed using micro-CT and histological analysis after injecting the prepared bone cement into the tibial defects of osteoporotic rats. SEM investigation showed that the PHT-3 sample had the highest porosity and roughness among all samples. In comparison to other samples, the PHT-3 exhibited favorable mechanical properties for use in vertebroplasty procedures. Micro-CT and histological analysis of OVX-induced osteoporotic rats revealed that PHT-3 was more effective in regenerating bone and restoring bone density than other samples. This study suggests that the PHT-3 bio-composite can be a promising candidate for treating osteoporosis-related vertebral fractures.

A Review of the Application of Natural and Synthetic Scaffolds in Bone Regeneration

The management of bone defects is complicated by the presence of clinical conditions, such as critical-sized defects created by high-energy trauma, tumour resection, infection, and skeletal abnormalities, whereby the bone regeneration capacity is compromised. A bone scaffold is a three-dimensional structure matrix serving as a template to be implanted into the defects to promote vascularisation, growth factor recruitment, osteogenesis, osteoconduction, and mechanical support. This review aims to summarise the types and applications of natural and synthetic scaffolds currently adopted in bone tissue engineering. The merits and caveats of natural and synthetic scaffolds will be discussed. A naturally derived bone scaffold offers a microenvironment closer to in vivo conditions after decellularisation and demineralisation, exhibiting excellent bioactivity, biocompatibility, and osteogenic properties. Meanwhile, an artificially produced bone scaffold allows for scalability and consistency with minimal risk of disease transmission. The combination of different materials to form scaffolds, along with bone cell seeding, biochemical cue incorporation, and bioactive molecule functionalisation, can provide additional or improved scaffold properties, allowing for a faster bone repair rate in bone injuries. This is the direction for future research in the field of bone growth and repair.

Bone Regeneration in Small and Large Segmental Bone Defect Models after Radiotherapy Using Injectable Polymer-Based Biodegradable Materials Containing Strontium-Doped Hydroxyapatite Particles

The reconstruction of bones following tumor excision and radiotherapy remains a challenge. Our previous study, performed using polysaccharide-based microbeads that contain hydroxyapatite, found that these have osteoconductivity and osteoinductive properties. New formulations of composite microbeads containing HA particles doped with strontium (Sr) at 8 or 50% were developed to improve their biological performance and were evaluated in ectopic sites. In the current research, we characterized the materials by phase-contrast microscopy, laser dynamic scattering particle size-measurements and phosphorus content, before their implantation into two different preclinical bone defect models in rats: the femoral condyle and the segmental bone. Eight weeks after the implantation in the femoral condyle, the histology and immunohistochemistry analyses showed that Sr-doped matrices at both 8% and 50% stimulate bone formation and vascularization. A more complex preclinical model of the irradiation procedure was then developed in rats within a critical-size bone segmental defect. In the non-irradiated sites, no significant differences between the non-doped and Sr-doped microbeads were observed in the bone regeneration. Interestingly, the Sr-doped microbeads at the 8% level of substitution outperformed the vascularization process by increasing new vessel formation in the irradiated sites. These results showed that the inclusion of strontium in the matrix-stimulated vascularization in a critical-size model of bone tissue regeneration after irradiation.

Direct 3D printed biocompatible microfluidics: assessment of human mesenchymal stem cell differentiation and cytotoxic drug screening in a dynamic culture system

BACKGROUND

In vivo-mimicking conditions are critical in in vitro cell analysis to obtain clinically relevant results. The required conditions, comparable to those prevalent in nature, can be provided by microfluidic dynamic cell cultures. Microfluidics can be used to fabricate and test the functionality and biocompatibility of newly developed nanosystems or to apply micro- and nanoelectromechanical systems embedded in a microfluidic system. However, the use of microfluidic systems is often hampered by their accessibility, acquisition cost, or customization, especially for scientists whose primary research focus is not microfluidics.

RESULTS

Here we present a method for 3D printing that can be applied without special prior knowledge and sophisticated equipment to produce various ready-to-use microfluidic components with a size of 100 µm. Compared to other available methods, 3D printing using fused deposition modeling (FDM) offers several advantages, such as time-reduction and avoidance of sophisticated equipment (e.g., photolithography), as well as excellent biocompatibility and avoidance of toxic, leaching chemicals or post-processing (e.g., stereolithography). We further demonstrate the ease of use of the method for two relevant applications: a cytotoxicity screening system and an osteoblastic differentiation assay. To our knowledge, this is the first time an application including treatment, long-term cell culture and analysis on one chip has been demonstrated in a directly 3D-printed microfluidic chip.

CONCLUSION

The direct 3D printing method is tested and validated for various microfluidic components that can be combined on a chip depending on the specific requirements of the experiment. The ease of use and production opens up the potential of microfluidics to a wide range of users, especially in biomedical research. Our demonstration of its use as a cytotoxicity screening system and as an assay for osteoblastic differentiation shows the methods potential in the development of novel biomedical applications. With the presented method, we aim to disseminate microfluidics as a standard method in biomedical research, thus improving the reproducibility and transferability of results to clinical applications.

Preparation and characterization of TiO 2 ‐coated polymerization of methyl methacrylate (PMMA) for biomedical applications: In vitro study

Low surface energy and hydrophobicity of polymethyl methactylate (PMMA) are the main disadvantages of this biomaterial. The aim of this study was to investigate the effects of a new coating process on the surface characteristics and properties of PMMA. A combination of temperature and pressure was used for deposition of titanium dioxide (TiO₂) on the surface of PMMA. The PMMA coated with TiO₂ thin films and prepared by sputtering and non-coated PMMA were considered as control groups. The surface wettability, functional group, and roughness were determined by contact angle measurement, Fourier transform Infrared spectroscopy (FTIR), and 3D laser scanning digital microscopy, respectively. The flexural strength of coated and non-coated samples was measured using three-point bending test. The cell proliferation, attachment, and viability were determined using 3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl tetrazolium bromide, live and dead assay, scanning electron microscope (SEM), and DAPI (4',6-diamidino-2-phenylindole) staining. The antifungal activity of TiO₂ was also determined by examining the biofilm attachment of Candida albicans. The obtained results showed that TiO₂ was successfully coated on PMMA. The contact angle measurement shows a significant increase of hydrophilicity in TiO₂-coated PMMA. FTIR and roughness analysis revealed no loss of TiO₂ from coated specimens following sonication. The cell viability after 7 days culturing on TiO2-coated specimens was more than the cell viability on the control groups. SEM images and DAPI staining showed that the total number of the cells increased after 7 days of seeding on TiO₂-coated group, whereas it decreased gradually in both control groups. C. albicans attachment also decreased by 63% to 77% on the coated PMMA surface. Overall, this research suggested a new way for developing surface energy of PMMAs for biomedical applications.

Fabrication and characterization of a bioactive polymethylmethacrylate-based porous cement loaded with strontium/calcium apatite nanoparticles

Polymethylmethacrylate (PMMA)-based cements are used for bone reparation due to their biocompatibility, suitable mechanical properties, and mouldability. However, these materials suffer from high exothermic polymerization and poor bioactivity, which can cause the formation of fibrous tissue around the implant and aseptic loosening. Herein, we tackled these problems by adding Sr²⁺ -substituted hydroxyapatite nanoparticles (NPs) and a porogenic compound to the formulations, thus creating a microenvironment suitable for the proliferation of osteoblasts. The NPs resembled the structure of the bone's apatite and enabled the controlled release of Sr²⁺ . Trends in the X-ray patterns and infrared spectra confirmed that Sr²⁺ replaced Ca²⁺ in the whole composition range of the NPs. The inclusion of an effervescent additive reduced the polymerization temperature and lead to the formation of highly porous cement exhibiting mechanical properties comparable to the trabecular bone. The formation of an opened and interconnected matrix allowed osteoblasts to penetrate the cement structure. Most importantly, the gas formation confined the NPs at the surface of the pores, guaranteeing the controlled delivery of Sr²⁺ within a concentration sufficient to maintain osteoblast viability. Additionally, the cement was able to form apatite when immersed into simulated body fluids, further increasing its bioactivity. Therefore, we offer a formulation of PMMA cement with improved in vitro performance supported by enhanced bioactivity, increased osteoblast viability and deposition of mineralized matrix assigned to the loading with Sr²⁺ -substituted hydroxyapatite NPs and the creation of an interconnected porous structure. Altogether, our results hold promise for enhanced bone reparation guided by PMMA cements.

An Ovine Model of In Vivo Bioreactor-Based Bone Generation

The generation of vascularized mineralized tissues of complex geometry without the use of extrinsic growth factors or exogenous cells requires a large animal model to recapitulate the challenges seen in the clinic. The proposed versatile ovine model can be utilized to investigate the use of a customized bioreactor to generate mineralized tissue, matching the size and shape of a defect before transfer to and integration within another site. The protocol results in bioreactors that can be harvested for investigation of the effects of different biomaterials for the generation of bone or to generate tissues appropriate for repair of bony defects; this protocol focuses on reconstruction of the mandible but could be modified for orthopedic applications. The bioreactor packing material can be altered, allowing for the study of various commercially available or novel graft materials. The surgical procedure requires ∼1.5 h to implant four bioreactors adjacent to rib periosteum. After 9 weeks, the harvest of the bioreactor tissue takes approximately 1 h. If creating a craniofacial defect, an additional 2 h should be taken for mandibular defect creation and 2 to 3 h for the reconstruction. Sheep that have undergone reconstruction are typically euthanized after 12 weeks to allow for evaluation of transferred tissues. In this protocol, we discuss the necessary steps to ensure the reproducibility and analytical techniques to assess bone regeneration such as microcomputed tomography, mechanical analysis, and histology. Impact statement Bone grafting is a frequent procedure in the fields of orthopedics, otolaryngology, and oral and maxillofacial surgery. Generating customized, vascularized, and mechanically robust bony tissues while eliminating common complications such as donor site morbidity with autograft harvest or lack of suitable mechanical properties with commercially available synthetic graft would greatly improve the lives of patients. A large animal model is necessary to generate tissues of clinically relevant geometries. In this article, a reproducible ovine model of in vivo bioreactor technology toward customized bone generation is presented with broad application to tissue engineering and regenerative medicine.

Surface degradation-enabled osseointegrative, angiogenic and antiinfective properties of magnesium-modified acrylic bone cement

Objective

This work focuses on tackling the inadequate bone/implant interface strength of acrylic bone cements, which is a formidable problem diminishing their clinical performance, especially in percutaneous kyphoplasty surgery.

Methods

A new strategy of incorporating magnesium particles into clinically used poly(methylmethacrylate) (PMMA) bone cement to prepare a surface-degradable bone cement (SdBC) is proposed and validated both in vitro and in vivo.

Results

This surface degradation characteristic enables osseointegrative, angiogenic and antiinfective properties. SdBC showed fast surface degradation and formed porous surfaces as designed, while the desirable high compressive strengths (≥70 MPa) of the cement were preserved. Besides, the SdBC with proper Mg content promoted osteoblast adhesion, spreading, proliferation and endothelial cell angiogenesis capacity compared with PMMA. Also, SdBC demonstrated clear inhibitory effect on Staphylococcus aureus and Escherichia coli. In vivo evaluation on SdBC by the rat femur defect model showed that the bone/implant interface strength was significantly enhanced in SdBC (push-out force of 11.8 ± 1.5 N for SdBC vs 7.0 ± 2.3N for PMMA), suggesting significantly improved osseointegration and bone growth induced by the surface degradation of the cement. The injectability, setting times and compressive strengths of SdBC with proper content of Mg particles (2.8 wt% and 5.4 wt%) were comparable with those of the clinical acrylic bone cement, while the heat release during polymerization was reduced (maximum temperature 78 ± 1 °C for PMMA vs 73.3 ± 1.5 °C for SdBC).

Conclusions

This work validates a new concept of designing bioactive bone/implant interface in PMMA bone cement. And this surface-degradable bone cement possesses great potential for minimally invasive orthopaedic surgeries such as percutaneous kyphoplasty.

The translational potential of this article

This work reports PMMA/Mg surface-degradable acrylic bone cements that possess enhanced osseointegrative, angiogenic and antiinfective properties that are lacking in the clinically used acrylic bone cements. This new kind of bone cements could improve the treatment outcome of many orthopaedic surgeries such as percutaneous kyphoplasty and arthroplasty.

Healing potentials of polymethylmethacrylate bone cement combined with platelet gel in the critical-sized radial bone defect of rats

Polymethylmethacrylate (PMMA) is the most commonly used filler material that lacks biological properties and osteoconductivity or osteoinductivity. Platelet gel (PG) is a typical source of growth factors, cytokines and molecules efficient for bone formation and remodeling. The aim of this study was to evaluate bone healing and regeneration of bone defect in rat model by combining PMMA with PG. A total of 50 defects were created in the diaphysis of the radii of 25 male Sprague-Dawley rats. These defects were randomly divided into five groups (n = 10 defects for each group) and treated by autograft, plain PMMA, PG and PMMA-PG or left untreated. The rats were examined clinically and radiologically during the experiment and also after euthanasia at the 8^th post-operative week, the healed defects were evaluated by gross morphology, histopathology, histomorphometry, computed tomography, scanning electron microscopy and biomechanical testing. PG could function as efficiently as autograft in promoting bone healing of the radial bones. Additionally, bone formation, and densities of cartilaginous and osseous tissues in the defects treated with autograft, PG and PMMA-PG were more satisfactory than the untreated and PMMA treated defects. Compared with the PMMA-PG implant, more PMMA residuals remained in the defect area and induced more intense inflammatory reaction. In conclusion, addition of PG could improve the bone regenerative properties of PMMA bone cement compared with PMMA alone in vivo. Therefore, the PG-PMMA can be proposed as a promising option to increase regenerative potential of PMMA, particularly when it is used as fixator, filler or adhesive in the dentistry, neurosurgery and bone tissue engineering applications.

Effects of polymethylmethacrylate on the stability of screw fixation in mandibular angle fractures: A study on sheep mandibles

Aim: Malfixed miniplates can impair fracture healing, and the screw pilot holes may widen during repeated fixation trials. This in vitro study explored the extent to which screw fixation of mandibular angle fractures could be improved by augmenting the drilling holes with polymethylmethacrylate (PMMA). Materials and Methods: We measured stabilization by recording specimen displacement under a vertical force of 50 N applied using a hydraulic tester. We included 20 hemimandibles from sheep (average weight 40 kg). The specimens were randomly divided into two groups of 10 and pilot holes were created in the angulus region using a drill 1.2 mm in diameter. Next, we performed osteotomies simulating angulus fracture repair. In group 1, the fracture site was fixed using non-compression miniplates and four screws were inserted to the maximal possible extent employing a mechanical screwdriver. In group 2, the pilot drill holes were filled with PMMA prior to miniplate fixation. Then vertical forces of 50 N were applied to the molar region and the displacements were measured. The Shapiro-Wilks test was used to compare the two groups. Result: The maximum average displacement in the experimental group was significantly lower than that in the control group (p=0.026). Thus, PMMA-augmented screws better stabilized bone, affording reliable fixation.

Influence of External Beam Radiotherapy on the Properties of Polymethyl Methacrylate-Versus Silicone-Induced Membranes in a Bilateral Segmental Bone Defect in Rats

INTRODUCTION

Standard care for malignant tumors arising next to a bone structure is surgical removal with safety margins, followed by external beam radiotherapy (EBRT). Complete tumor removal can result in large bone defects. A two-step bone reconstruction technique using the induced membrane (IM) technique has proven its efficacy to bridge gap nonunion. During the first step, a spacer is placed in the bone gap. The spacer then is removed and the IM around it is filled with autologous cancellous bone graft. However, the feasibility of this technique with the addition of adjuvant EBRT between the two reconstruction steps has not yet been studied. Polymethyl methacrylate (PMMA) used to be the standard spacer material for the first step. Silicone spacers could replace them owing to their good behavior when submitted to EBRT and their easier removal from the surgical site during the second step. The aim of this study was to evaluate the influence of EBRT on the histological and biochemical properties of IM induced using PMMA or silicone as spacer.

MATERIALS AND METHODS

The analyses were performed on PMMA- or silicone-IM with and without EBRT in a 6-mm bilateral femoral defect in 32 rats. Thickness and vessel content were measured in both groups. Bone morphogenetic protein 2 (BMP2) and vascular endothelial growth factor (VEGF) content in lysates of the crushed membranes were measured by enzyme immunoassay. Finally, alkaline phosphatase activity was analyzed in human bone marrow stromal cell cultures in contact with the same lysates.

RESULTS

EBRT did not change the histological structure of the cellular internal layer or the fibrous outer layer. The nature of the spacer only influenced IM thickness, PMMA-IM with external radiotherapy being significantly thicker. EBRT decreased the vascular density of IM but was less effective on VEGF/BMP2 production. In vitro, IM could have an osteoinductive potential on human bone marrow stem cells.

CONCLUSION

EBRT did not modify the histological properties of IMs but decreased their vascular density. VEGF and BMP2 production within IMs was not affected by EBRT. Silicone spacers are able to induce membranes with similar histological characteristics to PMMA-IM.

Bone Response to Porous Poly(methyl methacrylate) Cement Loaded with Hydroxyapatite Particles in a Rabbit Mandibular Model

The aim of the current study was to evaluate bone formation and tissue response to porous poly(methyl methacrylate) (PMMA) cement with or without hydroxyapatite (HA) in a rabbit mandibular model. Therefore, 14 New Zealand White rabbits were randomly divided into two groups of seven according to the designed study end points of 4 and 12 weeks. For each rabbit, two decorticated defects (6 mm in height and 10 mm in width for each) were prepared at both sides of the mandible. Subsequently, the defects were filled with, respectively, porous PMMA and porous PMMA-HA cement. After reaching the designated implantation period, the rabbits were euthanized and the mandibles were retrieved for histological analysis. Results showed that both porous PMMA and porous PMMA-HA supported bone repair. Neither of the bone cements caused significant inflammation to nerve or other surrounding tissues. After implantation of 12 weeks, majority of the porosity was filled with newly formed bone for both cements, which supports the concept that a porous structure within PMMA can enhance bone ingrowth. Histomorphometrical evaluation, using histological grading scales, demonstrated that, at both implantation times, the presence of HA in the PMMA enhanced bone formation. Bone was always in direct contact with the HA particles, while intervening fibrous tissue was present at the PMMA-bone interface. On the basis of results, it was concluded that injectable porous PMMA-HA cement might be a good candidate for craniofacial bone repair, which should be further evaluated in a more clinically relevant large animal model.

Novel potential scaffold for periodontal tissue engineering

OBJECTIVE

The objective of the study is characterization of novel calcium and zinc-loaded electrospun matrices to be used for periodontal regeneration.

MATERIALS AND METHODS

A polymethylmetacrylate-based membrane was calcium or zinc loaded. Matrices were characterized morphologically by atomic force and scanning electron microscopy and mechanically probed by a nanoindenter. Biomimetic calcium phosphate precipitation on polymeric tissues was assessed. Cell viability tests were performed using oral mucosa fibroblasts. Data were analyzed by Kruskal-Wallis and Mann-Whitney tests or by ANOVA and Student-Newman-Keuls multiple comparisons.

RESULTS

Zinc and calcium loading on matrices did not modify their morphology but increased nanomechanical properties and decreased nanoroughness. Precipitation of calcium and phosphate on the matrix surfaces was observed in zinc-loaded specimens. Matrices were found to be non-toxic to cells in all the assays. Calcium- and zinc-loaded scaffolds presented a very low cytotoxic effect.

CONCLUSIONS

Zinc-loaded membranes permit cell viability and promoted mineral precipitation in physiological conditions. Based on the tested nanomechanical properties and scaffold architecture, the proposed membranes may be suitable for cell proliferation.

CLINICAL RELEVANCE

The ability of zinc-loaded matrices to promote precipitation of calcium phosphate deposits, together with their observed non-toxicity and its surface chemistry allowing covalent binding of proteins, may offer new strategies for periodontal regeneration.

Synthesis and characterization of an injectable and self-curing poly(methyl methacrylate) cement functionalized with a biomimetic chitosan–poly(vinyl alcohol)/nano-sized hydroxyapatite/silver hydrogel

Preparation and characterizations of injectable p-PMMA/CS–PVA/Nano-HA/Ag⁺ cements.

Biomolecular functionalization for enhanced cell-material interactions of poly(methyl methacrylate) surfaces

The integration of implants or medical devices into the body tissues requires of good cell-material interactions. However, most polymeric materials used for these applications lack on biological cues, which enhanced mid- and long-term implant failure due to weak integration with the surrounding tissue. Commonly used strategies for tissue-material integration focus on functionalization of the material surface by means of natural proteins or short peptides. However, the use of these biomolecules involves major drawbacks such as immunogenic problems and oversimplification of the constructs. Here, designed elastin-like recombinamers (ELRs) are used to enhance poly(methyl methacrylate) surface properties and compared against the use of short peptides. In this study, cell response has been analysed for different functionalization conditions in the presence and absence of a competing protein, which interferes on surface-cell interaction by unspecific adsorption on the interface. The study has shown that ELRs can induce higher rates of cell attachment and stronger cell anchorages than short peptides, being a better choice for surface functionalization.

Beneficial effects of biomimetic nano-sized hydroxyapatite/antibiotic gentamicin enriched chitosan–glycerophosphate hydrogel on the performance of injectable polymethylmethacrylate

Preparation and characterization and injectable p-PMMA/CS-GP/nano-HA/GM cements.

The bone-to-cement interface improvement by Ca-phosphate ceramics

BACKGROUND

Polymethylmethacrylate used in surgery is one of the first biomaterials. Conventional histology dissolves the resin; one of the reasons that only few complete histology is published. OBJECTIVES AND PURPOSE: The question is, whether a complete histology changes the understanding, influences the application and opens approaches for improvements. The dos and don'ts of the processing technology are presented in reproducible manner.

MATERIAL AND METHODS

Ten femurs of giant rabbits were taken from running experiments of femur-canal filling with bone cement. Different stages were considered for high-resolution histology and electron microscopy: 4-weeks-stage (bone healing), 12-weeks-stage (remodelling) and one and two years. A human-cadaver specimen with a follow up of two years was processed. All animals were perfusion-fixated and the complete vasculature micro-casted. Serial cuts were performed with a stone saw, followed by a wet grinding processing. The fluorescence documentation in the High Intensity Incident Fluorescent Light (HIIFL) and Orthoplan Leitz Ploemopak(®) was applied and high resolution microradiography used the Siemens Kristalloflex(®) . The Scanning Electron Microscopy (SEM) was performed applying deep-freezing technology for the PSEM-500. The human specimen was embedded after sectioning using epoxy-resin.

RESULTS

All cement implants showed osseointegration and remodelling with a tangential adherence of bone onto the ceramic/PMMA surfaces. Intact cancellous structures after one and two years did not show any signs of heat necrosis. The human specimen confirmed the results from the animal experiments.

CONCLUSION

The complete bone-to-cement histology changed the understanding of the bone cements function, influenced its application and opened new ways for improvement.

Construction and accuracy assessment of patient-specific biocompatible drill template for cervical anterior transpedicular screw (ATPS) insertion: an in vitro study

Background

With the properties of three-column fixation and anterior-approach-only procedure, anterior transpedicular screw (ATPS) is ideal for severe multilevel traumatic cervical instabilities. However, the accurate insertion of ATPS remains challenging. Here we constructed a patient-specific biocompatible drill template and evaluated its accuracy in assisting ATPS insertion.

Methods

After ethical approval, 24 formalin-preserved cervical vertebrae (C2–C7) were CT scanned. 3D reconstruction models of cervical vertebra were obtained with 2-mm-diameter virtual pin tracts at the central pedicles. The 3D models were used for rapid prototyping (RP) printing. A 2-mm-diameter Kirschner wire was then inserted into the pin tract of the RP model before polymethylmethacrylate was used to construct the patient-specific biocompatible drill template. After removal of the anterior soft tissue, a 2-mm-diameter Kirschner wire was inserted into the cervical pedicle with the assistance of drill template. Cadaveric cervical spines with pin tracts were subsequently scanned using the same CT scanner. A 3D reconstruction was performed of the scanned spines to get 3D models of the vertebrae containing the actual pin tracts. The deviations were calculated between 3D models with virtual and actual pin tracts at the middle point of the cervical pedicle. 3D models of 3.5 mm-diameter screws were used in simulated insertion to grade the screw positions.

Findings

The patient-specific biocompatible drill template was constructed to assist ATPS insertion successfully. There were no significant differences between medial/lateral deviations (P = 0.797) or between superior/inferior deviations (P = 0.741). The absolute deviation values were 0.82±0.75 mm and 1.10±0.96 mm in axial and sagittal planes, respectively. In the simulated insertion, the screws in non-critical position were 44/48 (91.7%).

Conclusions

The patient-specific drill template is biocompatible, easy-to-apply and accurate in assisting ATPS insertion. Its clinical applications should be further researched.

Porous surface modified bioactive bone cement for enhanced bone bonding

BACKGROUND

Polymethylmethacrylate bone cement cannot provide an adhesive chemical bonding to form a stable cement-bone interface. Bioactive bone cements show bone bonding ability, but their clinical application is limited because bone resorption is observed after implantation. Porous polymethylmethacrylate can be achieved with the addition of carboxymethylcellulose, alginate and gelatin microparticles to promote bone ingrowth, but the mechanical properties are too low to be used in orthopedic applications. Bone ingrowth into cement could decrease the possibility of bone resorption and promote the formation of a stable interface. However, scarce literature is reported on bioactive bone cements that allow bone ingrowth. In this paper, we reported a porous surface modified bioactive bone cement with desired mechanical properties, which could allow for bone ingrowth.

MATERIALS AND METHODS

The porous surface modified bioactive bone cement was evaluated to determine its handling characteristics, mechanical properties and behavior in a simulated body fluid. The in vitro cellular responses of the samples were also investigated in terms of cell attachment, proliferation, and osteoblastic differentiation. Furthermore, bone ingrowth was examined in a rabbit femoral condyle defect model by using micro-CT imaging and histological analysis. The strength of the implant-bone interface was also investigated by push-out tests.

RESULTS

The modified bone cement with a low content of bioactive fillers resulted in proper handling characteristics and adequate mechanical properties, but slightly affected its bioactivity. Moreover, the degree of attachment, proliferation and osteogenic differentiation of preosteoblast cells was also increased. The results of the push-out test revealed that higher interfacial bonding strength was achieved with the modified bone cement because of the formation of the apatite layer and the osseointegration after implantation in the bony defect.

CONCLUSIONS

Our findings suggested a new bioactive bone cement for prosthetic fixation in total joint replacement.