Bonding behavior of ultrahigh strength unsintered hydroxyapatite particles/poly(L-lactide) composites to surface of tibial cortex in rabbits

Calcium Orthophosphate (CaPO4) Containing Composites for Biomedical Applications: Formulations, Properties, and Applications

The goal of this review is to present a wide range of hybrid formulations and composites containing calcium orthophosphates (abbreviated as CaPO4) that are suitable for use in biomedical applications and currently on the market. The bioactive, biocompatible, and osteoconductive properties of various CaPO4-based formulations make them valuable in the rapidly developing field of biomedical research, both in vitro and in vivo. Due to the brittleness of CaPO4, it is essential to combine the desired osteologic properties of ceramic CaPO4 with those of other compounds to create novel, multifunctional bone graft biomaterials. Consequently, this analysis offers a thorough overview of the hybrid formulations and CaPO4-based composites that are currently known. To do this, a comprehensive search of the literature on the subject was carried out in all significant databases to extract pertinent papers. There have been many formulations found with different material compositions, production methods, structural and bioactive features, and in vitro and in vivo properties. When these formulations contain additional biofunctional ingredients, such as drugs, proteins, enzymes, or antibacterial agents, they offer improved biomedical applications. Moreover, a lot of these formulations allow cell loading and promote the development of smart formulations based on CaPO4. This evaluation also discusses basic problems and scientific difficulties that call for more investigation and advancements. It also indicates perspectives for the future.

Clinical Outcomes and Return-to-Sport Rates following Fragment Fixation Using Hydroxyapatite/Poly-L-Lactate Acid Threaded Pins for Knee Osteochondritis Dissecans: A Case Series

Osteochondritis dissecans (OCD) of the knee is an uncommon injury in young active patients. There is currently a lack of knowledge regarding clinical outcomes and return-to-sport rates after fragment fixation surgery using hydroxy appetite poly-L-lactic acid (HA/PLLA) threaded pins for knee OCD among athletes. Our purpose was to investigate the clinical outcomes and return-to-sport rates following osteochondral fragment fixation using HA/PLLA pins for the treatment of knee OCD lesions among athletes. A total of 45 patients were retrospectively reviewed. In total, 31 patients were excluded, and 14 patients were included. Pre- and postoperative patient-reported outcome scores (PROSs), including the International Knee Documentation Committee (IKDC) score and Knee Injury and Osteoarthritis Outcome Scale (KOOS), were compared. In addition, patients were categorized into four groups according to postoperative sports status: higher, same, lower than preinjury, or unable to return to sports. The mean age was 14.4 years (SD 1.67). All patients were male. All PROSs significantly improved at 6, 12, and 24 months postsurgery compared to presurgery. 50% of the patients returned to sports at the same or higher level after surgery. Fragment fixation using HA/PLLA pins leads to favorable clinical outcome scores and high return-to-sport rates in the treatment of athletes with knee OCD.

Fixation devices made of poly-L-lactide composite for rib reconstruction after thoracotomy

GRAND FIX mesh-type plates and pins (Gunze, Kyoto, Japan) are thin, bioabsorbable fixation devices made of poly-L-lactide (PLLA) composite. These devices are new, and how best to use them in clinical practice remains to be determined. Thus, we describe our approach to rib fixation after thoracotomy in an aortic surgery using GRAND FIX mesh-type plates and pins. The advantage of our approach is that it is easy to perform, but careful attention should be paid to fix the ribs appropriately.

Bone healing and stability after advancement genioplasty using a pre-bent absorbable plate and screws

This study aimed to compare the bone healing and stability of the chin with a pre-bent absorbable plate and a manually bent absorbable plate after advancement genioplasty. Patients with class II malocclusion who underwent genioplasty with bimaxillary surgery were included. After genioplasty, two absorbable bicortical screws were fixed on both sides. Then, a pre-bent absorbable plate and screws were used in the center area to fix the segment in advancement genioplasty (PB group). A manually bent absorbable plate was used for the remaining patients (MB group). Computed tomography (CT) was performed before surgery and 1 week and 1 year after surgery. Changes in the pogonion (Pog) and menton (Me) points, soft tissue points, and the ratio of bone squares under the plate were evaluated using lateral cephalometric images reconstructed with 3-dimensional CT data. 32 patients were included in the study. There were no significant differences in the cephalometric measurements in the time interval from 1 week to 1 year. However, the bone square ratio in the PB group showed a significant increase after 1 year (P = 0.0021). Within the limitations of the study it seems that the use of a pre-bent absorbable plate is effective in promoting bone healing after advancement genioplasty.

Fixation of intra-articular calcaneal fractures: A comparative study of the postoperative outcome between HA/PPLA screws and locking plates

Background

Forged unsintered hydroxyapatite and poly l-lactic acid (F-u-HA/PLLA) screw is bioactivite, bioabsorbable, and radiopaque with high mechanical strength. Its efficacy has been previously demonstrated in the treatment of lateral humeral condylar, lateral tibial condylar, ankle, and patellar fractures. However, studies on its efficacy in treatment of calcaneal fractures is lacking. This study aimed to compare the postoperative results of F-u-HA/PLLA screw fixation and locking plate fixation for intra-articular calcaneal fractures.

Methods

From January 2013 to December 2019, 47 closed intra-articular fractures treated with either F-u-HA/PLLA screws (group S, 18 feet in 17 patients) or locking plates (group P, 29 feet in 28 patients) in a single trauma center were retrospectively reviewed. The sinus tarsi approach was used in both groups. The time to bone union, step-off, varus deformity, Bohler's angle, and width and height of the calcaneus were assessed after surgery. Ankle joint range of motion (ROM) and postoperative complications were also assessed.

Results

All fractures were successfully treated. The Kaplan-Meier curves of the two groups showed similar trends. The log-rank test showed no significant difference in the time to bone union between the two groups (p = 0.48). In the Cox proportional hazards model adjusted for preoperative width and Bohler's angle, the hazard ratio for bone union was not statistically significant (HR: 1.13, 95%CI: 0.50-2.56, p = 0.78). Other variables included step-off (group S: 2.0 vs group P: 2.2 mm, p = 0.84), varus deformity (2.0° vs. 3.0°, p = 0.7), Gissane's angle (103.5° vs 104.0°, p = 0.84), width (38.0 vs 34.8 mm, p = 0.12), height (42.1 vs 44.0 mm, p = 0.07), and ankle ROM degrees (dorsal flexion, 20.0° vs. 20.0°, p = 0.13; plantar flexion 40.0° vs 40.0°, p = 0.56), which were not significantly different between groups P and S. The Bohler's angle was smaller in group S than in group P (20.5° vs 27.0°, p < 0.01). No skin necrosis or infection was observed in either group.

Conclusion

Postoperative results of F-u-HA/PLLA screw fixation using the sinus tarsi approach for intra-articular calcaneal fractures were as good as those of locking plate fixation.

A Narrative Review of u-HA/PLLA, a Bioactive Resorbable Reconstruction Material: Applications in Oral and Maxillofacial Surgery

The advent of bioresorbable materials to overcome limitations and replace traditional bone-reconstruction titanium-plate systems for bone fixation, thus achieving greater efficiency and safety in medical and dental applications, has ushered in a new era in biomaterial development. Because of its bioactive osteoconductive ability and biocompatibility, the forged composite of uncalcined/unsintered hydroxyapatite and poly L-lactic acid (u-HA/PLLA) has attracted considerable interest from researchers in bone tissue engineering, as well as from clinicians, particularly for applications in maxillofacial reconstructive surgery. Thus, various in vitro studies, in vivo studies, and clinical trials have been conducted to investigate the feasibility and weaknesses of this biomaterial in oral and maxillofacial surgery. Various technical improvements have been proposed to optimize its advantages and limit its disadvantages. This narrative review presents an up-to-date, comprehensive review of u-HA/PLLA, a bioactive osteoconductive and bioresorbable bone-reconstruction and -fixation material, in the context of oral and maxillofacial surgery, notably maxillofacial trauma, orthognathic surgery, and maxillofacial reconstruction. It simultaneously introduces new trends in the development of bioresorbable materials that could used in this field. Various studies have shown the superiority of u-HA/PLLA, a third-generation bioresorbable biomaterial with high mechanical strength, biocompatibility, and bioactive osteoconductivity, compared to other bioresorbable materials. Future developments may focus on controlling its bioactivity and biodegradation rate and enhancing its mechanical strength.

Treatment of patellar fractures using bioresorbable forged composites of raw particulate unsintered hydroxyapatite/poly-L-lactide cannulated screws and nonabsorbable sutures

BACKGROUND

Forged composites of raw particulate unsintered hydroxyapatite/poly-L-lactide (F-u-HA/PLLA) implants are widely used in surgeries because they possess high mechanical strength, bioactivity, and radio-opacity. We previously reported that F-u-HA/PLLA implants were useful for treating lateral tibial condylar, lateral humeral condylar, and ankle fractures. The study aim was to investigate the efficacy of F-u-HA/PLLA cannulated screws and FiberLoop® for treating transverse patellar fractures.

METHODS

From April 2013 to February 2019, 15 patients with transverse patellar fractures were treated with F-u-HA/PLLA cannulated screws and FiberLoop® as follows: Open reduction and internal fixation (ORIF) were performed with two F-u-HA/PLLA cannulated screws and a temporary fixation Kirshner wire (K-wire). Three No. 2 FiberLoops® were inserted into these two screw holes and the K-wire hole for temporary fixation. All patients were allowed to full weight-bearing gaits using a knee brace. Knee range of motion exercise was initiated on postoperative day 1. Knee flexion was restricted to ≤90° for 1 month postoperatively. Radiograph was performed to evaluate fracture healing, screw breakage, reduction loss, and screw radio-opacity. Clinical outcomes and postoperative complications were assessed.

RESULTS

The average follow-up was 16.0 months. All fractures were successfully united. Screw breakage, reduction loss, osteolysis, and radiolucent zones around the screws were not observed at the final radiographic follow-up. All F-u-HA/PLLA screw shadows were observed during the follow-up. The average range of flexion and extension were 132.0° and -2.7°, respectively. No patients experienced deep infection episodes, late aseptic tissue reactions, or foreign body reactions postoperatively. No patients complained of pain at the final follow-up. All patients returned to their pre-injury work level and activities of daily living.

CONCLUSION

Our results strongly suggest that ORIF with F-u-HA/PLLA screws and FiberLoop® could be an alternative treatment option for transverse patellar fractures.

The Stability of Hydroxyapatite/Poly-L-Lactide Fixation for Unilateral Angle Fracture of the Mandible Assessed Using a Finite Element Analysis Model

Recently, a hydroxyapatite particle/poly-L-lactide (HA-PLLA) composite device was introduced as an alternative to previous fixation systems. In this study, we used finite element analysis to simulate peak von Mises stress (PVMS) and deformation of bone plates and screws with the following four materials-Ti, Mg alloy, PLLA, and HA-PLLA-at a unilateral mandibular fracture. A three-dimensional virtual mandibular model was constructed, and the fracture surface was designed to run from the left mandibular angle. Masticatory loading was applied on the right first molars. Stress was concentrated at the upper part and the neck of the screw. The largest PVMS was observed for Ti; that was followed by Mg alloy, HA-PLLA, and PLLA. The largest deformation was observed for PLLA; next was HA-PLLA, then Mg alloy, and finally Ti. We could rank relative superiority in terms of mechanical properties. The HA-PLLA screw and mini-plate deformed less than 0.15 mm until 300 N. Thus, we can expect good bone healing with usual masticatory loading six weeks postoperatively. HA-PLLA is more frequently indicated clinically than PLLA owing to less deformation. If the quality of HA-PLLA fixation is improved, it could be widely utilized in facial bone trauma or craniofacial surgery.

Feasible Advantage of Bioactive/Bioresorbable Devices Made of Forged Composites of Hydroxyapatite Particles and Poly-L-lactide in Alveolar Bone Augmentation: A Preliminary Study

Purpose: We aimed to document the clinical usefulness of uncalcined and unsintered hydroxyapatite (u-HA) particles and poly-L-lactide (PLLA) composite materials and their advantageous properties. Methods: Between April 2016 and March 2018, five patients required anterior maxillary alveolar ridge augmentation using fixation with u-HA/PLLA screws for an onlay block bone graft harvested from the mandibular ramus at our institute. Bone biopsies were obtained from the dental implantation site following bone healing for histomorphometric and immunohistochemical (IHC) measurements. Results: Many stromal cells were positive for Osterix, RUNX2, and SOX9 but were negative for CD68. On cell counting, based on IHC staining for Osterix, RUNX2, SOX9 and CD68 from peripheral u-HA/PLLA screw or bone areas, both areas consistently showed no significant difference in terms of Osterix, RUNX2, and SOX9. Hematoxylin-eosin staining revealed direct bone connection to the biomaterials, and no inflammatory cells infiltrated the areas surrounding the bone or artificial material. Area between the bone and u-HA/PLLA screw was seamless with no boundary. Round small cells and immature fibroblasts were noted. The new bone showed the presence of bone lamellae, normal osteocytes, and osteoblasts. Conclusion: The u-HA/PLLA materials showed excellent biodegradability and bioactive osteoconductivity. In addition, this material induced no apparent inflammatory or foreign body reactions following implantation, and it directly bonded to the human bone. Therefore, this u-HA/PLLA material seems ideal and most suitable for use as a substitute for osteosynthesis.

Implantable composite devices of unsintered hydroxyapatite and poly-l-lactide with dispersive marbling morphology to enhance in vivo bioactivity and bioresorbability

A bone fixation device made of unsintered hydroxyapatite (u-HA) particles uniformly dispersed in a poly-l-lactide matrix and reinforced by compressive forging (uniformly dispersed composite; UDC) has been clinically applied in several fields. However, it has reported some foreign body reactions over a long implantation period due to its slow bioresorbability. To further enhance its bioresorbability, we developed devices comprising a fibrous assembly of poly-l-lactide only three-dimensionally intertwined with particulate hydroxyapatite/poly-l-lactide composite. The biological behavior of the proposed material, provisionally referred to as complementarily reinforced composite (CRC), was compared with that of UDC in vivo. Cylindrical rods of UDC and CRC with 3.2-mm diameters were inserted bilaterally into the intramedullary distal femurs of 32 male Japanese white rabbits. Eight rabbits were euthanized at four, eight, 12, and 25 weeks after insertion. There were no significant differences between the mechanical properties of UDC and CRC over time. However, the results from histological analyses, surface characterization, radiological analyses, and push-out mechanical testing substantiated CRC's superior affinity to bone and enhanced bioactivity and bioresorbability in comparison with UDC. These characteristics were attributed to the dispersive marbling morphology produced by the CRC material's successive connectivity of u-HA particles throughout the PLLA matrix, which would accelerate PLLA hydrolysis degradation by H₂O intrusion and enhance the bioactivity of u-HA particles exposed on the interface soon after implantation.

Evaluation of Space-Maintaining Sinus Membrane Using the Absorbable Screws in Sinus Lifting Bone Augmentation

PURPOSE

We investigated whether it was possible to perform a sinus lift maintaining absorbable screw material with biological activity.

MATERIALS AND METHODS

Thirty rabbits were used. The screws used in this study were unsintered hydroxyapatite/poly-L-lactic acid (uHA/PLLA) (uHA/PLLA group) and titanium alloy (Ti group). Some uHA/PLLA screws were treated with ultraviolet light (UV-uHA/PLLA group). Each group consisted of 10 rabbits, and 2 screws were implanted for 1 rabbit. The screws were implanted into the frontal bone. Rabbits were euthanized at 3 days, 1, 2, 3, and 4 weeks postoperatively and prepared for histological examination, BMP-2 cell staining, and micro-computed tomography (micro-CT) assessment.

RESULTS

At 1, 2, and 3 weeks, the UV uHA/PLLA group had significantly more bone contact and new bone ratio on histological assessment than the other 2 groups. At 1, 2, 3, and 4 weeks, micro-CT assessment revealed significant differences between the UV uHA/PLLA group and the other 2 groups.

CONCLUSIONS

Sinus lift surgery using absorbable screw allowed bone formation. The UV-treated hydroxyapatite/poly-L-lactic acid (uHA/PLLA) was superior for sinus lift bone augmentation using a screw.

Guided bone regeneration using a hydrophilic membrane made of unsintered hydroxyapatite and poly(L-lactic acid) in a rat bone-defect model

The effectiveness of a previously developed unsintered hydroxyapatite (uHA) and poly(L-lactic acid) (PLLA) hydrophilic membrane as a resorbable barrier for guided bone regeneration (GBR) was evaluated. Critical-size 8-mm diameter bone defects were surgically generated in the parietal bones of 24 12-week-old male Wistar rats, which were then divided into three groups in which either a uHA/PLLA or a collagen membrane or no membrane (control) was placed onto the bone defect. Following sacrifice of the animals 2 or 4 weeks after surgery, bone defects were examined using microcomputed tomography and histological analysis. Bone mineral density, bone mineral content, and relative bone growth area values 2 or 4 weeks after surgery were highest in the uHA/PLLA group. Four weeks after surgery, the relative bone growth area in the uHA/PLLA group was larger than that in the collagen group. The resorbable uHA/PLLA membrane is thus potentially effective for GBR.

Unsintered Hydroxyapatite and Poly-L-Lactide Composite Screws/Plates for Stabilizing β-Tricalcium Phosphate Bone Implants

Unsintered hydroxyapatite (u-HA) and poly-L-lactide (PLLA) composites (u-HA/PLLA) are osteoconductive and biodegradable. Screw (Super-Fixsorb MX30) and plate (Super-Fixsorb MX40 Mesh) systems made of u-HA/PLLA are typically used in small bones in maxillofacial surgeries. After the resection of bone tumors in larger bones, reconstructions with β-tricalcium phosphate (β-TCP) implants of strong compression resistance have been reported. After a resection, when the cavity is hemispheric- or concave-shaped, stabilization of the implanted β-TCP block is necessary. In the current series, u-HA/PLLA were used to stabilize the mechanically strong implanted low-porous β-TCP blocks in six bone tumor cases, including three giant cell tumors of bone, and one case each of chondroblastoma, chondrosarcoma, and parosteal osteosarcoma. The mean age of patients at the time of surgery was 31.3 years (range, 19 to 48 years). The bones involved were two ilia (posterior), a femur (diaphysis to distal metaphysis), and three tibias (proximal epiphysis, proximal metaphysis to epiphysis, and distal metaphysis to epiphysis). Neither displacement of the implanted β-TCP block nor any u-HA/PLLA-related complications were observed. The radiolucent character of the u-HA/PLLA did not hinder radiological examinations for potential signs of tumor recurrence. The method of using u-HA/PLLA components for the stabilization of β-TCP blocks makes the procedure easy to perform and reliable. It can extend the application of β-TCP blocks in reconstruction surgery.

Immediate and long-term results of unsintered hydroxyapatite and poly L-lactide composite sheets for orbital wall fracture reconstruction

INTRODUCTION

Bone defect reconstruction in orbital wall fractures with absorbable alloplastic such as the unsintered hydroxyapatite and poly L-lactide composite (u-HA/PLLA) system is gaining popularity. The u-HA/PLLA material has osteoconductive and osteosynthetic properties. However, quantitative, long-term outcome data after the use of u-HA/PLLA for orbital wall fractures are lacking.

PATIENTS AND METHODS

We retrospectively analyzed 115 patients who underwent surgical repair of orbital wall fractures with a u-HA/PLLA sheet from 2011 to 2016. A chart review was performed, and the time-dependent changes at fracture sites were assessed by imaging. The immediate postoperative and the latest follow-up bony orbital volumes of the affected side were compared.

RESULTS

Seventy patients were eligible for this study (mean age, 44.6 ± 22.1 years; 48 men and 22 women; mean follow-up period, 29.7 ± 12.8 months). Except for one case of hematoma, there were no postoperative wound complications. Of the 70 patients, 10 had postoperative diplopia and 2 had enophthalmos; these conditions were presumably caused by the extension and severity of the fracture. Satisfactory reduction in the entire orbital wall, without pathological changes, was demonstrated. There were no significant differences in the mean bony orbital volumes of the affected side immediately after surgery (24.774 ± 3.092 cm³) and at the latest follow-up (24.749 ± 3.205 cm³) (p = 0.756).

CONCLUSION

The u-HA/PLLA sheet is useful for orbital wall fracture reconstruction because of its desirable handling characteristics, initial mechanical strength, long-term maintenance of structural stability, radiopacity, and few associated complications. Future randomized controlled trials need to be performed to compare u-HA/PLLA with other conventional materials.

Clinical Evaluation of an Unsintered Hydroxyapatite/Poly-L-Lactide Osteoconductive Composite Device for the Internal Fixation of Maxillofacial Fractures

Introduction:

OSTEOTRANS MX (Takiron Co, Ltd, Osaka, Japan) is a resorbable osteosynthetic material composed of an unsintered hydroxyapatite/poly-l-lactide composite, and its osteoconductive capacity has been documented. The authors here report their clinical experience using OSTEOTRANS MX.

Methods:

The authors treated 35 patients (19 men, 16 women; age, 14–88 years; mean ± standard deviation, 38.4 ± 19.9 years) with maxillofacial fractures. The authors used standard surgery to stabilize fractures in all patients, fitting resorbable plates (thickness, 1.0 or 1.4 mm) and screws (diameter, 2 mm) according to Arbeitsgemeinschaft für Osteosynthesefragen/Association (AO) for the Study of Internal Fixation guidelines.

Results:

All patients eventually achieved satisfactory healing with favorable restoration of form and function without foreign body reaction. Complications occurred in 3 patients—plate exposure in 2 and discomfort in 1. However, fracture sites healed in all patients. Scanning electron microscopy revealed that the devices bonded directly to the bone without interposition of nonmineralized tissue.

Conclusion:

OSTEOTRANS MX is a useful material with few complications. Its osteoconductive bioactivity is advantageous for the early functional improvement of maxillofacial fractures.

Bone regeneration enhancement by ultra-violet (UV) treatment for uHA/PLLA absorbable mesh

PURPOSE

The purpose of this study was to evaluate the effect of bone regeneration enhancement by ultra-violet (UV) treatment of an unsintered hydroxyapatite (u-HA)/poly-l-lactic acid (PLLA) mesh in rabbitnasal bone.

MATERIALS AND METHODS

Thirty adult male Japanese white rabbits (12-16 weeks, 2.5-3.0 kg) were used in this study. After incising along the nasal bone, 6 × 6 × depth 1 mm two bone defects were made on both sides. In the UV group (n = 30), the defects were covered with uHA/PLLA mesh, treated by UV (wavelength 172 nm, tube wall illumination 13 mW/cm², period 8 min, intensity 6.26 J/cm²) and screwed. In the control group (n = 30), untreated uHA/PLLA was applied in a similar manner. The rabbits were sacrificed at 1, 2, 3, 4 and 6 weeks postoperatively, and formalin-fixed specimens were frozen. The specimens were stained with haematoxylin and eosin. For immunohistochemical analysis, the specimens were treated with anti-alkaline phosphatase (ALP). Finally, bone ratio and ALP expression were evaluated microscopically.

RESULTS

The UV group had a significantly higher number of ALP stained cells than the control group after 1, 2, and 3 weeks (P < 0.05). The bone ratio was also significantly higher in the UV group than in the control group after 1, 2, 3, and 4 weeks (P < 0.05).

CONCLUSION

This study suggests that bone regeneration can be enhanced by UV treatment using an uHA/PLLA mesh.

Repair of Bone Tissue Affected by Osteoporosis with Hydroxyapatite-Poly-L-lactide (HAp-PLLA) With and Without Blood Plasma

The aim of this study is to examine the reparatory ability of the synthetic biomaterial hydroxyapatite-poly-L-lactide (HAp-PLLA), the replacement of alveolar ridge, and rehabilitation of bone defects caused by osteoporosis, in an experimental group of animals. The experiments are performed on syngeneic Sprague Dawley rats. Osteoporosis is induced by glucocorticoids in rats during a 12-week period. After this, the experimental group of animals is divided into five subgroups. An artificial defect is made in the alveolar bone on the left side of the mandible. In one group of animals, the defect is left to heal by itself, while in other groups, pure HAp-PLLA or one mixed with plasma is implanted. The best results are achieved by the implantation of the HAp-PLLA composite biomaterial mixed with autologous plasma. Formation of a new mandibular bone is seen, growing intensely, leading to rapid osteogenesis.

Polylactic Acid Based Nanocomposites: Promising Safe and Biodegradable Materials in Biomedical Field

Polylactic acid (PLA) is widely used in biological areas due to its excellent compatibility, bioabsorbability, and degradation behavior in human bodies. Pure polylactic acid has difficulty in meeting all the requirements that specific field may demand. Therefore, PLA based nanocomposites are extensively investigated over the past few decades. PLA based nanocomposites include PLA based copolymers in nanometer size and nanocomposites with PLA or PLA copolymers as matrix and nanofillers as annexing agent. The small scale effect and surface effect of nanomaterials help improve the properties of PLA and make PLA based nanocomposites more popular compared with pure PLA materials. This review mainly introduces different kinds of PLA based nanocomposites in recent researches that have great potential to be used in biomedical fields including bone substitute and repair, tissue engineering, and drug delivery system.

Medial Wall Orbital Reconstruction using Unsintered Hydroxyapatite Particles/Poly L-Lactide Composite Implants

Background

Poly-L-lactide materials combined with hydroxyapatite (u-HA /PLLA) have been developed to overcome the drawbacks of absorbable materials, such as radiolucency and comparably less implant strength. This study was designed to evaluate the usefulness of u-HA/PLLA material in the repair of orbital medial wall defects.

Methods

This study included 10 patients with pure medial wall blow-out fractures. The plain radiographs were taken preoperatively, immediately after, and 2 months after surgery. The computed tomography scans were performed preoperatively and 2 months after surgery. Patients were evaluated for ease of manipulation, implant immobility, rigidity and complications with radiologic studies.

Results

None of the patients had postoperative complications, such as infection or enophthalmos. The u-HA/PLLA implants had adequate rigidity, durability, and stable position on follow-up radiographic studies. On average, implants were thawed 3.4 times and required 14 minutes of handling time.

Conclusion

The u-HA/PLLA implants are safe and reliable for reconstruction of orbital medial wall in terms of rigidity, immobility, radiopacity, and cost-effectiveness. These thin yet rigid implants can be useful where wide periosteal dissection is difficult due to defect location or size. Since the u-HA/PLLA material is difficult to manipulate, these implants are not suitable for use in complex 3-dimensional defects.

Calcium Orthophosphate-Containing Biocomposites and Hybrid Biomaterials for Biomedical Applications

The state-of-the-art on calcium orthophosphate (CaPO4)-containing biocomposites and hybrid biomaterials suitable for biomedical applications is presented. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through the successful combinations of the desired properties of matrix materials with those of fillers (in such systems, CaPO4 might play either role), innovative bone graft biomaterials can be designed. Various types of CaPO4-based biocomposites and hybrid biomaterials those are either already in use or being investigated for biomedical applications are extensively discussed. Many different formulations in terms of the material constituents, fabrication technologies, structural and bioactive properties, as well as both in vitro and in vivo characteristics have been already proposed. Among the others, the nano-structurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin, as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using CaPO4-based biocomposites and hybrid biomaterials in the selected applications are highlighted. As the way from a laboratory to a hospital is a long one and the prospective biomedical candidates have to meet many different necessities, the critical issues and scientific challenges that require further research and development are also examined.

In vitro and in vivo evaluation of a polylactic acid-bioactive glass composite for bone fixation devices

Poly(lactic acid) is nowadays among the most used bioabsorbable materials for medical devices. To promote bone growth on the material surface and increase the degradation rate of the polymer, research is currently focused on organic-inorganic composites by adding a bioactive mineral to the polymer matrix. The purpose of this study was to investigate the ability of a poly(L,DL-lactide)-Bioglass® (P(L,DL)LA-Bioglass(®) 45S5) composite to be used as a bone fixation device. In vitro cell viability testing of P(l,dl)LA based composites containing different amounts of Bioglass(®) 45S5 particles was investigated. According to the degradation rate of the P(L,DL)LA matrix and the cytocompatibility experiments, the composite with 30 wt % of Bioglass® particles seemed to be the best candidate for further investigation. To study its behavior after immersion in simulated physiological conditions, the degradation of the composite was analyzed by measuring its weight loss and mechanical properties and by proceeding with X-ray tomography. We demonstrated that the presence of the bioactive glass significantly accelerated the in vitro degradation of the polymer. A preliminary in vivo investigation on rabbits shows that the addition of 30 wt % of Bioglass(®) in the P(L,DL)LA matrix seems to trigger bone osseointegration especially during the first month of implantation. This composite has thus strong potential interest for health applications.

Microgel-functionalised fibres with pH-optimised degradation behaviour – a promising approach for short-term medical applications

Resorbable polymers have been established for several decades in biomedical applications. The most frequently used resorbable polymers are still the aliphatic polyesters polylactides (PLA), polyglycolid (PGA) and polycaprolactone (PCL) homo- and copolymers. However, inherent pH dropping during degradation of some biomaterials may provoke inflammation and, thus, hamper the healing process. In this study we investigate the manufacturing method of microgel functionalised PLA Fibres in a dry-spinning process and the buffering effect of the poly(N-vinylcaprolactam-co-acetoacetoxyethyl methacrylate) vinylimidazole (VCL/AAEM/Vlm) microgels during the degradation of the fibres. Furthermore we examine the biocompatibility of the produced fibres and established a mathematical model to describe and analyse the pH level in the vicinity of the PLA fibre.

A giant periosteal chondroma of the distal femur successfully reconstructed with synthetic bone grafts and a bioresorbable plate: a case report

Periosteal chondromas are rare benign cartilaginous tumors that arise adjacent to the cortex beneath the periosteum. These lesions are usually slow-growing and rarely exceed 3 cm in the greatest dimension. Here, we describe a 17-year-old boy who had a giant periosteal chondroma of the right distal femur, which was treated with intralesional resection and intensive curettage. In addition, we report a novel application of a bioresorbable plate in the management of the large bone defect after resection of a benign bone tumor.

Skeletal stability after mandibular setback surgery: comparison between the hybrid technique for fixation and the conventional plate fixation using an absorbable plate and screws

PURPOSE

The purpose of this study was to compare the temporal changes in condylar long axis and skeletal stability after sagittal split ramus osteotomy (SSRO) with the hybrid fixation technique and the conventional plate fixation.

PATIENTS AND METHODS

Of 44 Japanese patients diagnosed with mandibular prognathism, 22 underwent SSRO with the conventional plate fixation (1 u-HA/PLLA plate and 4 monocortical screws in each side) and 22 underwent SSRO with a hybrid fixation technique (1 u-HA/PLLA plate and 4 monocortical screws and bicortical screw in each side). The temporal changes in condylar long axis and skeletal stability were assessed by axial, frontal, and lateral cephalograms. After surgery, breakage of the plate and screws was checked by 3-dimensional computed tomography (3DCT).

RESULTS

Although there was a significant difference between the groups regarding Me-Ag in T1 (P = 0.0138), there were no significant differences between the groups for the other measurements in lateral, frontal and axial cephalometric analysis in each time interval. In two cases, 4 sides in the conventional plate fixation group, failure of the absorbable plate was found by 3DCT. However, there was no breakage in the hybrid fixation group.

CONCLUSION

This study suggested that there were no significant differences in the postoperative temporal changes between the two groups in mandibular setback surgery.

Hydroxyapatite/poly-L-lactide acid screws have better biocompatibility and femoral burr hole closure than does poly-L-lactide acid alone

Hydroxyapatite (HA)/poly-l-lactide(PLLA) composite biomaterials are available for orthopedic applications, but bioresorption and cell-mediated inflammation in bone cortex are unknown. We conducted an 84-month follow-up study with Beagle dogs that were subjected to implants with either PLLA (left femur) or HA/PLLA (right femur). Histological and radiographic analysis showed that HA/PLLA screws induced significant increases in HA content from 36 months onward and complete burr hole closure at 60 months, whereas PLLA screws did not. Moreover, PLLA screws induced more severe fibrous tissue and histiocyte infiltration. HA/PLLA screws promote earlier burr hole replacement and have superior biocompatibility compared to PLLA screws.

Surgical treatment of facial fracture by using unsintered hydroxyapatite particles/poly l-lactide composite device (OSTEOTRANS MX(®)): a clinical study on 17 cases

BACKGROUND

In Japan we currently use absorption properties for facial fractures. OSTEOTRANS MX(®) (Takiron co., ltd, Japan) is an absorption device, which is called Super FIXSORB MX(®) in Japan. This absorbable osteosynthetic device constitutes unsintered hydroxyapatite particles/poly l-lactide (u-HA/PLLA) composites. This study focuses on reporting clinical cases of using OSTEOTRANS MX(®).

MATERIALS AND METHODS

Seventeen patients (16 men and 1 woman) aged 10-80 years (mean: 39.9 years, SD: ±20.7) with 86 fracture sites were treated. In all cases we used 1.0 mm plates and 5 mm or 7 mm screws. The postoperative observation period was 6-60 months (mean: 21.8 months, SD: ±14.5).

RESULTS

The fracture site recovered in all cases. Complications included one bone excess on the forehead and one foreign-body reaction on the frontozygomatic suture, but the fracture sites were recovered and had no problems. In the case with the longest observation time 60 months, the plate was almost fully absorbed. However, in other cases the plate was not fully absorbed because of a shorter observation time.

CONCLUSION

OSTEOTRANS MX(®) is a useful device because of its suitable intensity, thinness, radiopaque, and few complications. A longer observation time is required for a plate to be absorbed completely.

Maxillary stability after Le Fort I osteotomy with self-setting α-tricalcium phosphate and an absorbable plate

The purpose of this study was to compare retrospectively postoperative differences in maxillary stability after Le Fort I osteotomy and fixation with an unsintered hydroxyapatite (u-HA)/poly-l-lactic acid (PLLA) plate with or without self-setting α-tricalcium phosphate (Biopex(®)) as interpositional material. Subjects comprised 45 patients diagnosed with mandibular prognathism with maxillary retrognathism and mandibular prognathism with bimaxillary asymmetry. All patients underwent Le Fort I osteotomy and bilateral sagittal split ramus osteotomy with fixation by uHA/PLLA plates. Patients were divided into 4 groups consisting of 9 maxillary impaction cases with Biopex(®) (group 1) to fill the gap between the bone segments, 14 maxillary advancement cases with Biopex(®) (group 2), 8 maxillary impaction cases without Biopex(®) (group 3) and 14 maxillary advancement cases without Biopex(®) (group 4). Changes in cepahalometric parameters at time intervals (1, 3 and 12 months) between the groups were compared. Results showed that stability did not depend on the use or otherwise of Biopex(®).

Mechanical comparison of novel bioabsorbable plates with titanium plates and small-series clinical comparisons for metacarpal fractures

BACKGROUND

The use of bioabsorbable implants to negate the need for subsequent removal could offer major clinical advantages for the fixation of fractures. The aims of this study were to compare the mechanical properties of novel bioabsorbable plates with those of titanium plates in a fracture model and to demonstrate the clinical results of the use of these new plates for metacarpal fractures.

METHODS

The first set of experiments compared the mechanical properties of bioabsorbable and titanium plates. Two types of bioabsorbable plates (one-third tubular and semi-tubular in cross-section) made of hydroxyapatite/poly-L-lactide and two types of titanium plates (for 1.5 and 2.0-mm screws) were tested. Each plate was fixed on a polyether ether ketone (PEEK) rod, which was transversely cut at its midsection. The second part of the study compared the clinical results associated with the bioabsorbable and titanium plates that were used in sixteen nonrandomized consecutive patients with metacarpal fractures.

RESULTS

The bending strength and stiffness of one-third tubular bioabsorbable plate constructs were comparable with those of titanium plates for 1.5-mm screws, and those of one-half tubular bioabsorbable plates were comparable with those of titanium plates for 2.0-mm screws. The mean torsional strength (and standard deviation) of the semi-tubular bioabsorbable plates (79.0 ± 7.9 N.cm) was significantly greater than that of titanium plates for 2.0 mm screws (56.7 ± 4.0 N.cm) (p < 0.05). There were no significant differences in six-month postoperative clinical results between patients who received bioabsorbable plates and those who received titanium plates (total range of active motion, 267.0° ± 6.0° compared with 250.0° ± 28.3°; grip strength, 92.7% ± 19.7% compared with 86.4% ± 28.6% of that on the contralateral side).

CONCLUSIONS

The bending strength, stiffness, and torsional strength of novel one-third or semi-tubular bioabsorbable plates, when fixed on a PEEK rod, were comparable with those for titanium plates for 1.5 or 2.0-mm screws. There were no significant differences in clinical results between these two types of plates in a small group of patients after short-term follow-up.

Maxillary stability after Le Fort I osteotomy using three different plate systems

The purpose of this study was to compare postoperative changes in maxillary stability after Le Fort I osteotomy in three groups: with an unsintered hydroxyapatite (u-HA)/poly-L-lactic acid (PLLA) plate; a PLLA plate; and a titanium plate. Subjects comprised 60 Japanese patients diagnosed with mandibular prognathism. All patients underwent Le Fort I osteotomy and bilateral sagittal split ramus osteotomy. All patients were randomized in groups of 20 to a u-HA/PLLA group, a PLLA plate group and a titanium plate group. Changes in postoperative time intervals between the plate groups were compared using lateral and posteroanterior cephalography. The uHA/PLLA group had significantly larger values than the PLLA group regarding change of mx1-S perpendicular to SN between 3 and 12 months (T3) (P=0.0269). The uHA/PLLA group had a significantly larger value than the PLLA group regarding change of S-A perpendicular to SN between baseline and 1 month (T1) (P=0.0257). There was no significant difference in the other measurements. This study suggests that maxillary stability with satisfactory results could be obtained in the u-HA/PLLA, PLLA plate and titanium plate groups, although there was a slight difference between the u-HA/PLLA and PLLA plate systems in Le Fort I osteotomy.

Biocomposites and hybrid biomaterials based on calcium orthophosphates

The state-of-the-art of biocomposites and hybrid biomaterials based on calcium orthophosphates that are suitable for biomedical applications is presented in this review. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through successful combinations of the desired properties of matrix materials with those of fillers (in such systems, calcium orthophosphates might play either role), innovative bone graft biomaterials can be designed. Various types of biocomposites and hybrid biomaterials based on calcium orthophosphates, either those already in use or being investigated for biomedical applications, are extensively discussed. Many different formulations, in terms of the material constituents, fabrication technologies, structural and bioactive properties as well as both in vitro and in vivo characteristics, have already been proposed. Among the others, the nanostructurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using biocomposites and hybrid biomaterials based on calcium orthophosphates in the selected applications are highlighted. As the way from the laboratory to the hospital is a long one, and the prospective biomedical candidates have to meet many different necessities, this review also examines the critical issues and scientific challenges that require further research and development.

Skeletal stability after mandibular setback surgery: comparisons among unsintered hydroxyapatite/poly-L-lactic acid plate, poly-L-lactic acid plate, and titanium plate

PURPOSE

The purpose of this study is to compare the time-course changes in condylar long-axis and skeletal stability after sagittal split ramus osteotomy (SSRO) with an unsintered hydroxyapatite (u-HA)/poly-L-lactic acid (PLLA) plate, PLLA plate, or titanium plate.

PATIENTS AND METHODS

Of 60 Japanese patients diagnosed with mandibular prognathism, 20 underwent SSRO with a u-HA/PLLA plate system, 20 underwent SSRO with a PLLA plate system, and 20 underwent SSRO with a conventional titanium plate system. The time-course changes in condylar long-axis and skeletal stability were assessed by use of axial, frontal, and lateral cephalograms.

RESULTS

Compared with the u-HA/PLLA group, the titanium group showed a significantly greater change in the right condyle angle between initially and 1 month (P = .0105) and intercondylar axes angle between 1 and 3 months (P = .0013). The PLLA group showed a significantly greater change than the titanium group (P = .0043) and u-HA/PLLA group (P = .0002) in terms of ramus inclination between 1 and 3 months; however, there were no significant differences among the 3 groups in the other measurements for each time interval.

CONCLUSION

This study suggests that there are no significant differences in postoperative time-course changes among a u-HA/PLLA plate system, PLLA plate system, and conventional titanium plate system.

An experimental study of use of absorbable plate in combination with self-setting α-tricalcium phosphate for orthognathic surgery

OBJECTIVE

The purpose of this study was to histologically and immunohistochemically evaluate bone formation using both self-setting α-tricalcium phosphate (α-TCP; Biopex) and absorbable plate (Super Fixsorb-MX) in rabbit cranium bone.

STUDY DESIGN

Twelve adult male Japanese white rabbits (12-16 wk, 2.5-3.0 kg) were used. The surgical defects were made in the nasal bone of a rabbit, and Biopex was implanted in the left side and no material in the right side. Two-hole absorbable plate and 2 screws (Super Fixsorb-MX) were fixed across the defect in each side. The rabbits were killed at 1, 4, 12, and 24 weeks after surgery, and formalin-fixed specimens were embedded in acrylic resin. The specimens were stained with hematoxylin and eosin. For immunohistochemical analysis, the specimens were treated with bone morphogenetic protein 2 (BMP-2) antibodies. Finally, these were evaluated microscopically.

RESULTS

New bone formation was observed in the region of absorbable plate and nasal membrane after >4 weeks. The area of new bone with Biopex was significantly larger than that of the control side after 1, 4, and 12 weeks (P < .05). The number of BMP-2-stained cells in the experimental side was significantly larger than in the control side after 4 and 12 weeks (P < .05).

CONCLUSION

This study suggests that the use of absorbable plate (Super Fixsorb-MX) in combination with Biopex could be useful and that both of Super Fixsorb-MX and Biopex could provide adequate bone regeneration.

Preparation and mechanical properties of carbon fiber reinforced hydroxyapatite/polylactide biocomposites

A novel biocomposite of carbon fiber (CF) reinforced hydroxyapatite (HA)/polylactide (PLA) was prepared by hot pressing a prepreg which consisting of PLA, HA and CF. The prepreg was manufactured by solvent impregnation process. Polymer resin PLA dissolved with chloroform was mixed with HA. After reinforcement CF bundle was impregnated in the mixture, the solvent was dried completely and subsequently hot-pressed uniaxially under a pressure of 40 MPa at 170 degrees C for 20 min. A study was carried out to investigate change in mechanical properties of CF/HA/PLA composites before and after degradation in vitro. The composites have excellent mechanical properties. A peak showed in flexural strength, flexural modulus and shear strength aspects, reaching up 430 MPa, 22 GPa, 212 MPa, respectively, as the HA content increased. Degraded in vitro for 3 months, the flexural strength and flexural modulus of the CF/HA/PLA fell 13.2% and 5.4%, respectively, while the shear strength of the CF/HA/PLA composites remains at the 190 MPa level. The SEM photos showed that there were gaps between the PLA matrix and CF after degradation. Water uptake increased to 5%, but the mass loss rate was only 1.6%. The pH values of the PBS dropped less than 0.1. That's because the alkaline of HA neutralize the acid degrades from PLA, which can prevent the body from the acidity harm.

Treatment of cervical OPLL by cervical anterior fusion using autologous vertebral bone grafts

BACKGROUND

In anterior fusion, we use autologous bone grafts from cervical vertebral bodies and bioabsorptive screws to prevent graft extrusion (Williams-Isu method). We report the application of and indication for the Williams-Isu method for OPLL and present our clinical and radiological results.

METHODS

Using the Williams-Isu method, we treated 17 patients with cervical OPLL; 15 had segmental- and 2 had continuous-type OPLL. The median follow-up term was 24 months. The patients underwent anterior decompression and fusion at a single level (n = 8) or at two levels (n = 9). As a control, 17 patients with cervical spondylosis underwent anterior single-level decompression and fusion using the Williams-Isu method. Pre- and postoperative radiographs of the cervical spine were obtained in all patients, and the alignment of the whole cervical and fused segment and the height of the fused segment were compared.

RESULTS

All but one patient experienced alleviation of clinical symptoms without deterioration during the follow-up period. The recovery rate on the JOA score was 71.7%. The patient with continuous-type OPLL suffered postoperative neurological deterioration because of a remnant of the upper-level OPLL. Radiological studies confirmed the absence of bone graft dislocation and fracture, and of satisfactory bone fusion in all patients. There was no significant difference between the two patient groups with respect to whole spine alignment and the alignment and height of the fused segment.

CONCLUSIONS

The Williams-Isu method is useful for treating not only cervical spondylosis but also cervical segmental OPLL at one or two levels.

Utility of new bioabsorptive screws in cervical anterior fusion

BACKGROUND

The aim of this study is to report our use of new bioabsorbable screws in cervical anterior fusion. These screws need not be removed because they are completely absorbed by resolution in vivo. We describe our method and the new bioabsorbable screws.

METHODS

We used PLLA screws until September 2004 and uncalcined uHA-PLLA screws thereafter. They are completely absorbed by resolution to water and carbon dioxide upon in vivo hydrolysis. The uHA-PLLA screws are x-ray impenetrable, and their uHA content renders them osteoconductive. In cervical anterior fusion, the graft is inserted in the area of deletion resulting from decompression. The screws are inserted in the 4 corners of the vertebral body and graft. In long fusion, they are introduced in the 2 lateral wings of the bone graft on each vertebral body and in the 4 corners. Our method eliminates the need for plates or mesh.

RESULTS

We have used this method in 62 patients and encountered no complications. There were no screw or graft extrusions and no surgery-related infections. The patients were able to walk a few hours after the operation and wore a simple neck collar for a few days.

CONCLUSIONS

This safe and easy method shortens the hospital stay and reduces the risk of graft extrusion and complications associated with the use of nonabsorbable devices.

A citric acid-based hydroxyapatite composite for orthopedic implants

We describe a novel approach to process bioceramic microparticles and poly(diol citrates) into bioceramic-elastomer composites for potential use in orthopedic surgery. The composite consists of the biodegradable elastomer poly(1,8-octanediol-citrate) (POC) and the bioceramic hydroxyapatite (HA). The objective of this work was to characterize POC-HA composites and assess the feasibility of fabricating tissue fixation devices using machining and molding techniques. The mechanical properties of POC-HA composites with HA (40, 50, 60, 65wt.%) were within the range of values reported for tissue fixation devices (for POC-HA 65wt.%, S(b)=41.4+/-3.1, E(b)=501.7+/-40.3, S(c)=74.6+/-9.0, E(c)=448.8+/-27.0, S(t)=9.7+/-2.3, E(t)=334.8+/-73.5, S(s)=27.7+/-2.4, T(s)=27.3+/-4.9, all values in MPa). At 20 weeks, the weight loss of POC-HA composites ranged between 8 and 12wt.%, with 65wt.% HA composites degrading the slowest. Exposure of POC-HA to simulated body fluid resulted in extensive mineralization in the form of calcium phosphate with Ca/P of 1.5-1.7 similar to bone. POC-HA supported osteoblast adhesion in vitro and histology results from POC-HA samples that were implanted in rabbit knees for 6 weeks suggest that the composite is biocompatible. Synthesis of POC-HA is easy and inexpensive, does not involve harsh solvents or initiators, and the mechanical properties of POC-HA with 65wt.% HA are suitable for the fabrication of potentially osteoconductive bone screws.

Biological performance of a new β-TCP/PLLA composite material for applications in spine surgery:In vitro andin vivo studies

The objective of this research was to carry out an in vitro and in vivo study of the biological performance of PLLA/beta-TCP composite materials, to estimate the scope of their potential applications in bone surgery. Samples with increasing beta-TCP (0-60% w/w) contents were processed by injection molding. The in vitro study consisted of an evaluation of inflammatory potential by assaying the IL-1alpha secreted by monocytes, and then cell proliferation (counting) and phenotype expression (PAL and I collagen) in human osteogenous cells. The in vivo study was carried out using cylindrical implants of composite materials composed of composite materials containing 0 or 60% beta-TCP and pure beta-TCP, respectively. The implants were inserted in femoral sites in rabbits, using the Kathagen protocol. Each animal received a 60% implant, with either a 0 or a 100% implant in the contralateral femur, so that the materials could be compared with one another. Five animals were examined for each material and implantation period, giving a total of 30 animals. This study showed that adding increasing percentages of beta-TCP to a lactic acid polymer matrix stimulated the proliferation of human osteogenous cells and synthesis of the extracellular bone matrix in a dose-dependent manner. In vivo results indicate that, in comparison with pure PLA, tricalcium phosphate-containing composite materials had faster degradation kinetics, caused less inflammatory reaction, and promoted contact osteogenesis. The composite material containing 60% beta-TCP demonstrated a similar performance to pure tricalcium phosphate bone grafts in terms of osteogenesis, and is apparently compatible with the production of intra-osseous implants for situations representing high levels of mechanical strain.

Long-term study of high-strength hydroxyapatite/poly(L-lactide) composite rods for the internal fixation of bone fractures: a 2-4-year follow-up study in rabbits

Biodegradation of hydroxyapatite (HA)/poly(L-lactide)(PLLA) composite bone implant rods was studied with the use of two types of HA particles as reinforcing fillers: uncalcined HA (u-HA) or calcined HA (c-HA). Composite rods of u-HA/PLLA and c-HA/PLLA containing 30 or 40% (w/w) HA were implanted in the distal femur of 21 rabbits, and specimens were examined by light microscopy, scanning-electron microscopy (SEM), and transmission-electron microscopy (TEM) 2-4 years later. For u-HA/PLLA, trabecular bone bonding directly onto the rod was maintained for up to 2 years. By 3 years, surface collapse had begun, and the implants were shrinking. By 4 years, they had shrunk further, with complete bone encapsulation. The u-HA particles were small and needle shaped in the peripheries, and TEM confirmed their resorption. The cross-sectional area after 4 years decreased by 23.3+/-8.4%. The mean ratio of bony ingrowth to the initial cross-sectional area around the shrunken rods was 6.7+/-1.3 %. The viscosity molecular weight of PLLA reduced from 2 x 10(5) to less than 1 x 10(3). Thus, most of the PLLA had released from the rods. The c-HA/PLLA implants also showed good osteoconductivity, but shrinkage and infiltration of histiocytes were less. No osteolytic or osteoarthritic changes were found.

Mechanical evaluation of novel spinal interbody fusion cages made of bioactive, resorbable composites

Osteoconductive and totally bioresorbable spinal/cervical interbody fusion cages were fabricated from a forged composite of raw particulate hydroxyapatite/poly L-lactide (u-HA/PLLA) with an u-HA 40wt% fraction (F-u-HA 40). The mechanical strengths of three types of cages, designed for open-box, screw and cylinder constructs, were compared with those of existing metal and carbon-fiber/polymer cages. Compressive strengths of these composite cages surpassed those of existing metal and carbon-fiber cages. Fatigue resistance to alternate and static compressive loading persisted for longer than the minimum period (6 months) necessary for spinal devices in simulated body fluid (SBF) at 37 degrees C. These novel interbody fusion cages await clinical application in humans.

Comparative biomechanical analysis of a cervical cage made of an unsintered hydroxyapatite particle and poly-L-lactide composite in a cadaver model

STUDY DESIGN

A new cage made from a forged composite of unsintered hydroxyapatite particles and poly-L-lactide (F-u-HA/PLLA) is compared biomechanically with the Ray threaded fusion cage.

OBJECTIVES

To compare the stability imparted to the human cadaveric spine by two different threaded cervical cages and the effect of cyclic loading on construct stability.

SUMMARY OF BACKGROUND DATA

Threaded cages have been developed for use in anterior cervical interbody fusions to provide initial stability during the fusion process. However, metallic instrumentation has several limitations. Recently, totally bioresorbable bone fixation devices made of F-u-HA/PLLA have been developed, including a cage for spinal interbody fusion. However, no biomechanical study has compared the F-u-HA/poly-L-lactide (PLLA) cage with metallic cages.

METHODS

For this study, 12 fresh ligamentous human cervical spines (C4-C7) were used. After anterior discectomy across C5-C6, stabilization was achieved with the F-u-HA/PLLA cage in six spines and with the Ray threaded fusion cage in the remaining six spines. Biomechanical testing of the spines was performed with six degrees of freedom before and after stabilization, and after cyclic loading of the stabilized spines (5000 cycles of flexion-extension at 0.5 Nm).

RESULTS

The specimens stabilized with either the F-u-HA/PLLA cage or the Ray cage were significantly more stable than the discectomy case in all directions except in extension. In extension, both groups were stiffer, although not at a significant level (P > 0.05). After fatigue, the stiffness, as compared with that in the prefatigue case, decreased in both groups, although not at a significant level. The Ray cage group exhibited better stability than the F-u-HA/PLLA cage group in all directions, although a significant difference was found only in right axial rotation.

CONCLUSIONS

The F-u-HA/PLLA cage has the possibility to supplant the use of metallic devices in interbody fusions of the cervical spine.