Internal Fixation Of Bone Fractures Research Articles

On Possibility of Application of COMSOL Multiphysics Software for Topological Optimization of Osteosynthesis Plates

Тhe paper describes a technique of topological optimization of osteosynthesis plates used for internal fixation of bone fractures. The proposed technique is based on the application of the density method and the commercially available COMSOL Multiphysics software intended for finite element modeling. A comparative analysis of the characteristics (axial stiffness, volume and maximum von Mises stress) is presented for initial design of the plate and two optimized variants of the design. It has been established that the optimized variants provide a reduction in the plate volume by 49–54 %. In this case, the axial stiffness decreases by 43–53 %, which is a positive effect in terms of minimizing the effect of stress shielding. The optimized variants of the design possess close values of axial stiffness and maximum von Mises stress, however, in one of them, deflection of the axial segments occurs, resulting in an increase in the total strain energy, which is used as an objective function during optimization. In the variant 2 of the design, the deflection of the longitudinal segments of the plate is eliminated due to the presence of a transverse bridge between them, and the total strain energy takes on a lower value. The variant of the design without a bridge should be additionally studied, since shear stresses resulting from the contact interaction of the longitudinal segments of the plate with the bone can have a positive effect on regeneration of the bone tissue.

Are Absorbable Plates More Resistant to Infection Than Titanium Implants? An Experimental Pre-Clinical Trial in Rabbits.

Background: Infection of orthopaedic implants after internal fixation of bone fractures remains a major complication with occasionally devastating consequences. Recent studies have reported that the use of absorbable materials, instead of metallic ones, may lead to a lower incidence of postoperative infection. In this experimental pre-clinical animal study, we compared the infection rate between absorbable implants consisting of copolymers composed from trimethylene carbonate, L-polylactic acid, and D, L-polylactic acid monomers, and titanium implants after the inoculation of a pathogenic microorganism. Material and Methods: We used an experimental implant-related infection model in rabbits. Sixty animals were randomly and equally divided into two groups. In all animals, the right femur was exposed via a lateral approach and a 2.5 mm two-hole titanium plate with screws (Group A), or a two-hole absorbable plate and screws (Group B), were applied in the femoral shaft. Afterwards, the implant surface was inoculated with Pseudomonas Aeruginosa at a concentration of 2 × 108 CFU/mL. The primary outcome was the comparison of the incidence of developed infection between the two groups. The wound condition was monitored on a daily basis and radiographies were obtained at 12 weeks postoperatively. Infection-related laboratory markers (white blood cell count, erythrocyte sedimentation rate, and C-reactive protein values) were assessed at 3, 6, and 16 weeks postoperatively. Histologic analysis and cultures of tissue samples were also performed to evaluate the presence of infection. Results: Clinical and laboratory signs of infection were evident in 11 rabbits in Group A (36.7%), and 4 in Group B (13.3%). The difference between the groups was statistically significant (p = 0.04). Five animals in Group B (16.7%) had clinical and histologic signs of a foreign-body reaction with significantly elevated CRP and ESR values but no simultaneous presence of infection was identified (p = 0.04). Bone remodelling with thickening of the periosteum and surrounding sclerosis was demonstrated radiologically in animals developing infection or foreign-body reactions. Conclusions: Absorbable plates and screws show lower susceptibility to infection compared to titanium ones. However, their application is associated with foreign-body reaction and the potential need for a second surgical intervention.

Laser additive manufacturing of biodegradable Mg-based alloys for biomedical applications: A review

Metallic implants are widely used in internal fixation of bone fracture in surgical treatment. They are mainly used for providing mechanical support and stability during bone reunion, which usually takes a few months to complete. Conventional implants made of stainless steels, Ti-based alloys and CoCrMo alloys have been widely used for orthopedic reconstruction due to their high strength and high corrosion resistance. Such metallic implants will remain permanently inside the body after implantation, and a second surgery after bone healing is needed because the long-term presence of implant will lead to various problems. An implant removal surgery not only incurs expenditure, but also risk and psychological burden. As a consequence, studies on the development of biodegradable implants, which would degrade and disappear in vivo after bone reunion is completed, have drawn researchers’ attention. In this connection, Mg-based alloys have shown great potentials as promising implant materials mainly due to their low density, inherent biocompatibility, biodegradability and mechanical properties close to those of bone. However, the high degradation rate of Mg-based implants in vivo is the biggest hurdle to overcome. Apart from materials selection, a fixation implant is ideally tailor-made in size and shape for an individual case, for best surgical outcomes. Therefore, laser additive manufacturing (LAM), with the advent of sophisticated laser systems and software, is an ideal process to solve these problems. In this paper, we reviewed the progress in LAM of biodegradable Mg-based alloys for biomedical applications. The effect of powder properties and laser processing parameter on the formability and quality was thoroughly discussed. The microstructure, phase constituents and metallurgical defects formed in the LAMed samples were delineated. The mechanical properties, corrosion resistance, biocompatibility and antibacterial properties of the LAMed samples were summarized and compared with samples fabricated by traditional processes. In addition, we have made some suggestions for advancing the knowledge in the LAM of Mg-based alloys for biomedical implants.

Bone tissue engineering potentials of 3D printed magnesium-hydroxyapatite in polylactic acid composite scaffolds.

The primary role of bone tissue engineering is to reconcile the damaged bones and facilitate the speedy recovery of the injured bones. However, some of the investigated metallic implants suffer from stress-shielding, palpability, biocompatibility, etc. Consequently, the biodegradable scaffolds fabricated from polymers have gathered much attention from researchers and thus helped the tissue engineering sector by providing many alternative materials whose functionality is similar to that of natural bones. Herein, we present the fabrication and testing of a novel composite, magnesium (Mg)-doped hydroxyapatite (HAp) glazed onto polylactic acid (PLA) scaffolds where polyvinyl alcohol (PVA) used as a binder. For the composite formation, Creality Ender-3 pro High Precision 3D Printer with Shape tool 3D Technology on an FSD machine operated by Catia design software was employed. The composite has been characterized for the crystallinity (XRD), surface functionality (FTIR), morphology (FESEM), biocompatibility (hemolytic and protein absorption), and mechanical properties (stress-strain and maximum compressive strength). The powder XRD analysis confirmed the semicrystalline nature and intact structure of HAp even after doping with Mg, while FTIR studies for the successful formation of Mg-HAp/PVA@PLA composite. The FESEM provided analysis indicated for the 3D porous architecture and well-defined morphology to efficiently transport the nutrients, and the biocompatibility studies are supporting that the composite for blood compatible with the surface being suitable enough for the protein absorption. Finally, the composite's antibacterial activity (against Staphylococcus aureus and Escherichia coli) and the test of mechanical properties supported for the enhanced inhibition of active growth of microorganisms and maximum compressive strength, respectively. Based on the research outcomes of biocompatibility, antibacterial activity, and mechanical resistance, the fabricated Mg-HAp/PVA@PLA composite suits well as a promising biomaterial platform for orthopedic applications by functioning towards the open reduction internal fixation of bone fractures and internal repairs.

Usability evaluation of 3D user interface for virtual planning of bone fixation plate placement

Abstract Universal pre-contoured plates are commonly used for internal fixation of bone fracture. Optimal plate placement can be determined through visual inspection of the relative position between the plate and the fractured bone as displayed on x-rays. While computer-assisted approaches have been developed to enable the manipulation of 3D models of the bone and the plate in virtual environments, as the 3D models are usually maneuvered using a 2D mouse with the virtual trackball paradigm, the process is counter-intuitive and could hamper system usability. An intuitive 3D haptic device was therefore employed to develop a virtual training system for fixation plate placement. A four-session study over two weeks were conducted with 15 subjects to evaluate the usability of the system, with 2D mouse and 3D haptic device employed as user interface. The effect of force feedback was also studied. A questionnaire was administered at the end of the study to assess user satisfaction towards the usability of the two input devices. User performance of virtual plate placement using a 3D haptic device was found to be superior to that using a 2D mouse, in terms of completion time and accuracy. The performance with and without force feedback was not significantly different. Preference toward 3D haptic device was reflected from the responses to the usability questionnaire. In conclusion, employing a 3D input device as user interface can potentially facilitate virtual planning of bone fixation plate placement.

Efficiently reduced heat rise in TiO2 coating Ti-based metallic implants using anodic oxidation method

Microwave diathermy treatment has been successfully applied to such patients as for it can induce clinical hyperthermia to healing muscle skeletal injuries. However, as a contraindication, patients implanted with metallic implants for internal fixation of bone fracture could not take the microwave diathermy treatment. This is mainly due to microwave induced sudden temperature rise in metal implants, which will lead to heat damages in local tissues. The aim of this study is to improve the heat-resisting effect of titanium implants by modifying its surface. A uniform TiO2 coating has been designed and fabricated on the surface of Ti (TA3) substrate by the method of anodic oxidation to inhibit the excessive heat generation of metallic implants. In vitro microwave irradiation experiment, the temperature of Ti substrate increased 2.5 °C, TiO2 coated substrate increased only 1.4 °C, decreasing almost 50% under the same testing condition. The results indicate that the anodized TiO2 coating may be an effective method to reducing the temperature rise of the metal implants during microwave diathermy treatment, which will provide a potential rehabilitation solution to internal fixation of bone fracture.

On the Use of a Continuum Manipulator and a Bendable Medical Screw for Minimally Invasive Interventions in Orthopedic Surgery.

Accurate placement and stable fixation are the main goals of internal fixation of bone fractures using the traditional medical screws. These goals are necessary to expedite and avoid improper fracture healing due to misalignment of the bone fragments. However, the rigidity of the screw, geometry of the fractured anatomy (e.g., femur and pelvis), and osteoporosis may cause an array of complications. To address these challenges, we propose the use of a continuum manipulator and a bendable medical screw (BMS) to drill curved tunnels and fixate the bone fragments. This novel approach provides the clinicians with a degree of freedom in selecting the drilling entry point as well as the navigation of drill in complex anatomical and osteoporotic bones. This technique can also facilitate the treatment of osteonecrosis and augmentation of the hip to prevent osteoporotic fractures. In this paper: 1) we evaluated the performance of the curved drilling technique on human cadaveric specimens by making several curved tunnels with different curvatures and 2) we also demonstrated the feasibility of internal fixation using the BMS versus a rigid straight screw by performing finite element simulation of fracture fixation in an osteoporotic femur.

Inroads Toward Robot-Assisted Internal Fixation of Bone Fractures Using a Bendable Medical Screw and the Curved Drilling Technique.

Internal fixation is a common orthopedic procedure in which a rigid screw is used to fix fragments of a fractured bone together and expedite the healing process. However, the rigidity of the screw, geometry of the fractured anatomy (e.g. femur and pelvis), and patient's age can cause an array of complications during screw placement, such as improper fracture healing due to misalignment of the bone fragments, lengthy procedure time and subsequently high radiation exposure. To address these issues, we propose a minimally invasive robot-assisted procedure comprising of a continuum robot, called ortho-snake, together with a novel bendable medical screw (BMS) for fixating the fractures. We describe the implementation of a curved drilling technique and focus on the design, manufacturing, and evaluation of a novel BMS, which can passively morph into the drilled curved tunnels with various curvatures. We evaluate the performance and efficacy of the proposed BMS using both finite element simulations as well as experiments conducted on synthetic bone samples.

Evolution of fracture treatment with bone plates

Internal fixation of bone fractures by plate osteosynthesis has continuously evolved for more than 100 years. The aim of internal fracture fixation has always been to restore the functional capacity of the broken bone. The principal requirements of operative fracture management, those being anatomical fracture reduction, durable fixation, preservation of biology, promotion of fracture healing and early patient mobilization, have always been crucial but were accomplished to different extents depending on the focus of the specific fracture fixation principle employed. The first successful approach for internal fracture fixation was anatomic open reduction and interfragmentary compression. This secured the fracture fragments, maintained alignment and enabled direct healing of the fracture fragments. However, the highly invasive approach inflicted an immense amount of biologic stress to the area surrounding the fracture site. Modern preferably anatomically pre-contoured locking plates with relative stability of the bone-implant construct enable durable fixation while allowing a less invasive approach that preserves the biology at the fracture site. In contrast to conventional plating, locked plating provides a certain amount of flexibility, which is required to induce the formation of periosteal callus through interfragmentary motion. Most recently the concept of dynamic plating was introduced, which aims to induce more controlled interfragmentary motion and active stimulation of periosteal callus formation. This review article describes the historic development of plating from conventional plating to locked and dynamic plating.

New concept of 3D printed bone clip (polylactic acid/hydroxyapatite/silk composite) for internal fixation of bone fractures

Open reduction with internal fixation is commonly used for the treatment of bone fractures. However, postoperative infection associated with internal fixation devices (intramedullary nails, plates, and screws) remains a significant complication, and it is technically difficult to fix multiple fragmented bony fractures using internal fixation devices. In addition, drilling in the bone to install devices can lead to secondary fracture, bone necrosis associated with postoperative infection. In this study, we developed bone clip type internal fixation device using three- dimensional (3D) printing technology. Standard 3D model of the bone clip was generated based on computed tomography (CT) scan of the femur in the rat. Polylacticacid (PLA), hydroxyapatite (HA), and silk were used for bone clip material. The purpose of this study was to characterize 3D printed PLA, PLA/HA, and PLA/HA/Silk composite bone clip and evaluate the feasibility of these bone clips as an internal fixation device. Based on the results, PLA/HA/Silk composite bone clip showed similar mechanical property, and superior biocompatibility compared to other types of the bone clip. PLA/HA/Silk composite bone clip demonstrated excellent alignment of the bony segments across the femur fracture site with well-positioned bone clip in an animal study. Our 3D printed bone clips have several advantages: (1) relatively noninvasive (drilling in the bone is not necessary), (2) patient-specific design (3) mechanically stable device, and (4) it provides high biocompatibility. Therefore, we suggest that our 3D printed PLA/HA/Silk composite bone clip is a possible internal fixation device.

Finite Element-Derived Surrogate Models of Locked Plate Fracture Fixation Biomechanics.

Internal fixation of bone fractures using plates and screws involves many choices-implant type, material, sizes, and geometric configuration-made by the surgeon. These decisions can be important for providing adequate stability to promote healing and prevent implant mechanical failure. The purpose of this study was to develop mathematical models of the relationships between fracture fixation construct parameters and resulting 3D biomechanics, based on parametric computer simulations. Finite element models of hundreds of different locked plate fixation constructs for midshaft diaphyseal fractures were systematically assembled using custom algorithms, and axial, torsional, and bending loadings were simulated. Multivariate regression was used to fit response surface polynomial equations relating fixation design parameters to outputs including maximum implant stresses, axial and shear strain at the fracture site, and construct stiffness. Surrogate models with as little as three regressors showed good fitting (R 2=0.62-0.97). Inner working length was the strongest predictor of maximum plate and screw stresses, and a variety of quadratic and interaction terms influenced resulting biomechanics. The framework presented in this study can be applied to additional types of bone fractures to provide clinicians and implant designers with clinical insight, surgical optimization, and a comprehensive mathematical description of biomechanics.

A perspective on molybdenum biocompatibility and antimicrobial activity for applications in implants

The use of biomaterials has become routine in dentistry, reconstructive surgery of the locomotor system, treatment of congenital, traumatic and tumor situations, and knee or hip arthroplasty. The main issue related to metal biomaterials is the systemic release of metal ions and the related biological risks. When placed in contact with a living organism, they must meet a set of criteria: they must be biocompatible and biofunctional, as well as have the ability to produce a specific biological response at the surface, leading to the formation of a bond between the material and the receiving tissue and a surface texture which allows cell adhesion and bone growth; they must also provide adequate structure and mechanical strength, without causing adverse reactions in the surrounding physiological environment; they must not cause oncogenic effects; they must be easy to manipulate during surgery; and they must be amenable to visible imaging and sterilization. The ability to use biomaterials is linked to the degree of biocompatibility and biofunctionality which in turn, are dependent on their physicochemical and mechanical properties, macroscopic and microscopic configuration, and the biological environment where they are deployed. Metal alloys, particularly stainless steel, cobalt, molybdenum, chromium alloys, and titanium-based alloys find wide application in orthopedics for making joint replacement prostheses, systems for external or internal fixation of bone fractures, surgical correction of degenerative conditions, or in the composition of staples, screws, and wires. Any synthetic biomaterial can replace or restore the function of body tissues while maintaining a continuous or intermittent contact with the fluid. When in contact with the fluid, it is essential that materials be biocompatible, so they do not produce adverse biological responses or induce systemic effects. Thus, they must not be toxic, carcinogenic, mutagenic, or antigenic. Bioactive materials with antibacterial properties are also of significant medical interest. Materials exhibiting good antimicrobial activity that minimize the formation of biofilm without the risk of promoting the development of resistant microorganisms are desirable. In this respect, this review briefly summarizes the recent successes of this metal as a biocompatible material with antibacterial activity for biomedical applications.

An in vivo evaluation of PLLA/PLLA-gHA nano-composite for internal fixation of mandibular bone fractures

Internal fixation of bone fractures using biodegradable poly(L-lactic-acid) (PLLA)-based materials has attracted the attention of many researchers. In the present study, 36 male beagle dogs were randomly assigned to two groups: PLLA/PLLA-gHA (PLLA-grafted hydroxyapatite) group and PLLA group. PLLA/PLLA-gHA and PLLA plates were embedded in the muscular bags of the erector spinae and also implanted to fix mandibular bone fractures in respective groups. At 1, 2, 3, 6, 9, and 12 months postoperatively, the PLLA/PLLA-gHA and PLLA plates were evaluated by adsorption and degradation tests, and the mandibles were examined through radiographic analysis, biomechanical testing, and histological analysis. The PLLA/PLLA-gHA plates were non-transparent and showed a creamy white color, and the PLLA plates were transparent and faint yellow in color. At all time points following surgery, adsorption and degradation of the PLLA/PLLA-gHA plates were significantly less than those of the PLLA plates, and the lateral and longitudinal bending strengths of the surgically treated mandibles of the beagle dogs in the PLLA/PLLA-gHA group were significantly greater than those of the PLLA group and reached almost the value of intact mandibles at 12 months postoperatively. Additionally, relatively rapid bone healing was observed in the PLLA/PLLA-gHA group with the formation of new lamellar bone tissues at 12 months after the surgery. The PLLA/PLLA-gHA nano-composite can be employed as a biodegradable material for internal fixation of mandibular bone fractures.

Effect of l-lysine-assisted surface grafting for nano-hydroxyapatite on mechanical properties and invitro bioactivity of poly(lactic acid-co-glycolic acid).

It is promising and challenging to study surface modification for nano-hydroxyapatite to improve the dispersion and enhance the mechanical properties and bioactivity of poly(lactic acid-co-glycolic acid). In this paper, we designed an effective new surface grafting with the assist of l-lysine for nano-hydroxyapatite, and the nano-hydroxyapatite surface grafted with the assist of l-lysine (g-nano-hydroxyapatite) was incorporated into poly(lactic acid-co-glycolic acid) to develop a series of g-nano-hydroxyapatite/poly(lactic acid-co-glycolic acid) nano-composites. The surface modification reaction for nano-hydroxyapatite, the mechanical properties, and invitro human osteoblast-like cell (MG-63) response were characterized and investigated by Fourier transformation infrared, thermal gravimetric analysis, dispersion test, electromechanical universal tester, differential scanning calorimeter measurements, and invitro cells culture experiment. The results showed that the grafting amount on the surface of nano-hydroxyapatite was enhanced with the increase of l-lysine, and the dispersion of nano-hydroxyapatite was improved more, so that it brought about better promotion crystallization and more excellent mechanical enhancement effect for poly(lactic acid-co-glycolic acid), comparing with the unmodified nano-hydroxyapatite. Moreover, the cells' attachment and proliferation results confirmed that the incorporation of the g-nano-hydroxyapatite into poly(lactic acid-co-glycolic acid) exhibited better biocompatibility than poly(lactic acid-co-glycolic acid). The above results indicated that the new surface grafting with the assist of l-lysine for nano-hydroxyapatite was an ideal novel surface modification method, which brought about better mechanical enhancement effect and invitro bioactivity for poly(lactic acid-co-glycolic acid) with adding higher g-nano-hydroxyapatite content, suggesting it had a great potential to be used as bone fracture internal fixation materials in future.

High strength chitosan rod prepared via LiOH/urea solvent through centrifugation induced orientation processing

High strength chitosan rod prepared via LiOH/urea solvent utilizing the unique centrifugation induced orientation method.

Bone plate composed of a ternary nano-hydroxyapatite/polyamide 66/glass fiber composite: biomechanical properties and biocompatibility

An ideal bone plate for internal fixation of bone fractures should have good biomechanical properties and biocompatibility. In this study, we prepared a new nondegradable bone plate composed of a ternary nano-hydroxyapatite/polyamide 66/glass fiber (n-HA/PA66/GF) composite. A breakage area on the n-HA/PA66/GF plate surface was characterized by scanning electron microscopy. Its mechanical properties were investigated using bone-plate constructs and biocompatibility was evaluated in vitro using bone marrow-derived mesenchymal stem cells. The results confirmed that adhesion between the n-HA/PA66 matrix and the glass fibers was strong, with only a few fibers pulled out at the site of breakage. Fractures fixed by the n-HA/PA66/GF plate showed lower stiffness and had satisfactory strength compared with rigid fixation using a titanium plate. Moreover, the results with regard to mesenchymal stem cell morphology, MTT assay, Alizarin Red S staining, enzyme-linked immunosorbent assay, and reverse transcription polymerase chain reaction for alkaline phosphatase and osteocalcin showed that the n-HA/PA66/GF composite was suitable for attachment and proliferation of mesenchymal stem cells, and did not have a negative influence on matrix mineralization or osteogenic differentiation of mesenchymal stem cells. These observations indicate that the n-HA/PA66/GF plate has good biomechanical properties and biocompatibility, and may be considered a new option for internal fixation in orthopedic surgery.

Effect of hydroxyapatite with different morphology on the crystallization behavior, mechanical property and in vitro degradation of hydroxyapatite/poly(lactic-co-glycolic) composite

This work describes the effect of hydroxyapatite with different morphology of nano-particle (n-HA) and whisker (w-HA) on the properties of hydroxyapatite/poly-lactic-co-glycolic acid (HA/PLGA) composite. The crystallization behavior, mechanical property and in vitro degradation of HA/PLGA composite were studied by scanning electron microscope, differential scanning calorimeter, polarized optical microscopy, electromechanical universal tester and soaking in simulated body fluid (SBF) at 37 °C for 2, 4, 8, 12 and 16 weeks, comparing with pure PLGA. The results showed that n-HA had better mechanical increment effect for PLGA than w-HA, because of the more uniformly dispersion in PLGA matrix without any cavities and the better promotion crystallization effectiveness in HA/PLGA composite than w-HA. However, the in vitro degradation showed that w-HA could keep denser microstructure so that the w-HA/PLGA composite had lower bending strength reduction percent than the n-HA/PLGA composite, owing to the higher crystallinity of w-HA and the more perfectly microcrystalline of PLGA (PLGA/w-HA) than n-HA. The study would be of guidance to select the suitable filler for poly(lactic acid) (PLA) or PLGA polymers in manufacturing bone fracture internal fixation material in future.

Effect of a new surface-grafting method for nano-hydroxyapatite on the dispersion and the mechanical enhancement for poly(lactide-co-glycolide)

In this paper, a new surface-grafting D, L-lactide (DLLA) for nano-hydroxyapatite (n-HA) with the assist of cit- ric acid was designed. The dispersion of new surface modified n-HA was characterized by Fourier transformation infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and dispersion test, and the mechanical enhancement effect for poly(lactide-co-glycolide (PLGA) was evaluated by scanning electron microscopy (SEM), differential scanning calorimeter measurements (DSC) and electro- mechanical universal tester. The results showed that citric acid played a critical role in surface-grafting, which could greatly increase grafting amount and improve dispersion of n-HA, so that it resulted in better interfacial adhesion throughout PLGA matrix, higher crystallinity and better mechanical enhancement for PLGA than the surface-grafting method for n-HA with- out citric acid, whose bending strength and tensile strength were both over 20% higher than those of pure PLGA when 3 wt% n-HA was added, and it still enhanced 8 and 6% higher than those of pure PLGA even the introduction of 15 wt% n-HA, respectively. The above results suggested that the surface-grafting for n-HA with the aid of citric acid was an ideal novel surface modification method, which could greatly improve the dispersion of n-HA and exhibit excellent mechanical enhancement effect for PLGA, suggesting it has a great potential in the bone fracture internal fixation application in future.

Degradation behavior of hydroxyapatite/poly(lactic-co-glycolic) acid nanocomposite in simulated body fluid

To investigate the effect of hydroxyapatite(HA) on the degradation behavior of hydroxyapatite/poly(lactic-co-glycolic) acid (HA/PLGA) nanocomposite, the degradation experiment of n-HA/PLGA composite and pure PLGA were carried out by soaking in simulated body fluid(SBF) at 37°C for 1, 2, 4 and 6 months. The change of intrinsic viscosity, thermal properties, inner structure, bending strength reduction, surface morphology and the surface deposit of n-HA/PLGA composite and pure PLGA with respect to the soaking time were investigated by means of UbbeloHde Viscometer, differential scanning calorimeter (DSC), scanning electron microscope(SEM), electromechanical universal tester, a conventional camera and X-ray diffraction (XRD). The results showed that n-HA played an important role in improving the degradation behavior of n-HA/PLGA composite, which can accelerate the degradation PLGA and endow it with bioactivity, after n-HA was detached from PLGA during the degradation, so that n-HA/PLGA composite may have a more promising prospect of the clinical application than pure PLGA as bone fracture internal fixation materials.

In situ forming chitosan/hydroxyapatite rods reinforced via genipin crosslinking

Chitosan/hydroxyapatite composite rods are good candidates as temporary mechanical supports in bone regeneration; however the mechanical properties of this kind of materials should be improved. In this work, chitosan/hydroxyapatite composite rods with multilayer structure were reinforced using a bio-crosslinker to improve their mechanical properties and anti-degradation ability. The SEM results revealed that the composite rods had a tree-ring structure. The bending strength and bending modulus of the crosslinked rods could arrive at 161MPa and 7.2GPa, respectively, increased by 59.4% and 26.3% compared with uncrosslinked ones (p<0.05). The enzymatic degradation studies indicated that genipin crosslinking could effectively enhance the biostability of the composite rods. Consequently, genipin-crosslinked chitosan/hydroxyapatite composite rods with excellent mechanical properties would be a novel device used for internal fixation of bone fracture.