Bone defects are caused by trauma, injury, cancer, infection, and some other factors. Their repair is a major challenge in orthopaedic surgery. There have been and continue to be numerous efforts to find materials or medications for the improvement of bone repair (5). Among the various methods available for this purpose, bone autograft has been considered the gold standard because of its osteoinductive and osteoconductive properties, high biocompatibility, and lesser risk of transmission of pathogens. Although autografts have shown the best clinical results, the need to perform a separate operation to harvest bone tissue needed for transplantation can in some cases lead to problems such as nerve injury, difficulty in walking, numbness, and back pain. The application of tissue engineering makes it possible to safely repair bone defects without the need for other surgical procedures using bone replacement. Up to now, a variety of natural or synthetic materials such as metals, ceramics, and polymers have been used to stimulate and enhance the process of bone regeneration. Ceramics are widely employed in tissue engineering, especially in bone regeneration (8). They can have either natural origins such as hydroxyapatite (HA), or synthetic origins, such as synthetic hydroxyapatite or β-tricalcium phosphate. Calcium phosphate ceramics have excellent biocompatibility and biodegradability, can be properly attached to bone tissue, and facilitate the healing process. In comparison with others, tricalcium phosphate (TCP) ceramics effect better osteoconduction and are highly biodegradable, as well as rapidly replaceable by bone matrix due to good absorption. (6). In recent years, the use of modern technology and especially nanotechnology in tissue engineering and the production of bone scaffolds has led to major improvements in the production of nano-based bony scaffolds. The nanofibres can be constructed with different pore architectures that have a high surface to volume ratio. Polycaprolactone (PCL) is one of the synthetic polymers which are extensively used in scaffold development and application in orthopaedics. The biocompatibility, bioabsorbability, and mechanical strength of PCL make it a good choice to study in tissue engineering (25). This highly biocompatible polymer is degraded to innocuous byproducts which are metabolised
This investigation was approved by the Committee of Ethics in Research with animals at the Islamic Azad University. The study was designed to minimise the number of animals required for the experiments.
A daily checkup was made to monitor any sign of infection, inflammation, or dehiscence at the operating site. At 15, 30, and 45 days after surgery, five rabbits from each group were randomly euthanised by intravenous infusion of Euthasol (pentobarbital; 2 mL/4.5kg, Chemische Fabrik Berg, Germany). Finally, the right hind limb femur of each animal was removed and fixed in 10% formalin for histological analysis.
Statistical analysis of union index
Group Day | 15 | 30 | 45 |
---|---|---|---|
Control | 0.2 ± 0.447 | 1 ± 0.707 | 2 ± 0.707 |
Hydroxyapatite | 0.8 ± 0.836 | 2 ± 0.707 | 2.6 ± 0.894 |
β-tricalcium phosphate | 1 ± 0.707 | 2.6 ± 1.14 | 3.4 ± 0.894 |
Nanocomposite polycaprolactone | 1.8 ± 0.836 | 3.4 ± 0.547 | 3.8 ± 0.447 |
Average union indices
Group | number | Average score | Test statistics | df | Sig |
---|---|---|---|---|---|
5 | 4 | ||||
Control | 5 | 7.9 | 9.009 | 2 | 0.011 |
5 | 12.1 | ||||
5 | 4.1 | ||||
Hydroxyapatite | 5 | 8.6 | 7.138 | 2 | 0.028 |
5 | 11.3 | ||||
5 | 3.7 | ||||
β-tricalcium | |||||
5 | 8.8 | 8.258 | 2 | 0.016 | |
phosphate | |||||
5 | 11.5 | ||||
5 | 3.4 | ||||
Nanocomposite | |||||
9.508 | 2 | 0.009 | |||
polycaprolactone | 5 | 9.2 | |||
5 | 11.4 |
The spongiosa indices of all groups are shown in Table 3. According to these statistics, the highest score on day 15 was for the nanocomposite PCL (1.4 ± 0.5) group, and the lowest was for the control group (0.2 ± 0.44). The nanocomposite PCL group had the highest spongiosa index on day 30 (3 ± 1), and the control group had the lowest (0.8 ± 0.83). on day 45 the nanocomposite PCL and control groups also exhibited the respective highest and lowest values (Table 3). Comparison of the average spongiosa indices among the groups revealed a statistically significant difference between them (P < 0.05) (Table 4).
Statistical analysis of spongiosa index
Group Day | 15 | 30 | 45 |
---|---|---|---|
Control | 0.2 ± 0.447 | 0.8 ± 0.836 | 2 ± 0.707 |
Hydroxyapatite | 0.6 ± 0.547 | 1.2 ± 0.447 | 2.8 ± 0.836 |
β-tricalcium phosphate | 1 ± 0.707 | 2.2 ± 0.447 | 3.2 ± 0.447 |
Nanocomposite polycaprolactone | 1.4 ± 0.547 | 3 ± 1 | 3.8 ± 0.447 |
Average spongiosa indices
Group | number | Average score | Test statistics | df | Sig |
---|---|---|---|---|---|
5 | 4.5 | ||||
Control | 5 | 7.3 | 8.422 | 2 | 0.015 |
5 | 12.2 | ||||
5 | 4.2 | ||||
Hydroxyapatite | 5 | 7 | 10.818 | 2 | 0.004 |
5 | 12.8 | ||||
5 | 3.4 | ||||
β-tricalcium phosphate | 5 | 8 | 11.482 | 2 | 0.003 |
5 | 12.6 | ||||
5 | 3.4 | ||||
Nanocomposite | 5 | 8.9 | 9.789 | 2 | 0.007 |
polycaprolactone | 5 | 11.7 |
As shown in Table 5, the nanocomposite PCL group showed the highest cortex index on day 15 (1.8 ± 0.83) and the control group showed the lowest (0.2 ± 0.44). On day 30, the highest value was in the nanocomposite PCL group (2.8 ± 0.83), and the lowest was in the control group (1 ± 0.7). on day 45 the nanocomposite PCL and control groups also showed the respective highest and lowest values. Comparison of average cortex indices among the groups indicated that there was a statistically significant difference between them (P < 0.05) (Table 6).
Statistical analysis of cortex index
Group Day | 15 | 30 | 45 |
---|---|---|---|
Control | 0.2 ± 0.447 | 1 ± 0.707 | 1.8 ± 0.447 |
Hydroxyapatite | 0.6 ± 0.547 | 1.4 ± 0.547 | 2.2 ± 0.836 |
β-tricalcium phosphate | 1.4 ± 0.547 | 2 ± 0.707 | 3.2 ± 0.836 |
Nanocomposite polycaprolactone | 1.8 ± 0.836 | 2.8 ± 0.836 | 3.6 ± 0.547 |
Average cortex indices
Group | number | Average score | Test statistics | df | Sig |
---|---|---|---|---|---|
5 | 4 | ||||
Control | 5 | 8 | 8.96 | 2 | 0.011 |
5 | 12 | ||||
5 | 5 | ||||
Hydroxyapatite | 5 | 6.9 | 7.808 | 2 | 0.02 |
5 | 12.1 | ||||
5 | 4.2 | ||||
β-tricalcium phosphate | 5 | 8.2 | 8.076 | 2 | 0.018 |
5 | 11.6 | ||||
5 | 4.2 | ||||
Nanocomposite | 7.591 | 2 | 0.022 | ||
polycaprolactone | 5 | 8.1 | |||
5 | 11.7 |
As shown in table 7, the bone marrow index in the nanocomposite PCL group on day 15 was 1.6 ±0.54 and the highest, while the control group had the lowest index of 0.2 ±0.44. On day 30 as well the highest value was that of nanocomposite PCL group with an index of 2.4 ±0.54, and the lowest was the control group with an index of 1 ±0.7. on day 45 the nanocomposite PCL and control groups exhibited the respective highest and lowest values (Table 7). According to a comparison of average bone marrow indices, there was a statistically significant difference between them (p<0.05) except for (not exclusively) the β-tricalcium phosphate group (Table 8).
Statistical analysis of bone marrow index
Day | |||
---|---|---|---|
Group | 15 | 30 | 45 |
Control | 0.2 ± 0.447 | 1 ± 0.707 | 1.4 ± 0.547 |
Hydroxyapatite | 1 ± 0.707 | 1.4 ± 0.547 | 2.4 ± 0.547 |
β-tricalcium phosphate | 1.4 ± 0.547 | 1.8 ± 0.836 | 2.8 ± 0.447 |
Nanocomposite polycaprolactone | 1.6 ± 0.547 | 2.4 ± 0.547 | 3.4 ± 0.547 |
Average bone marrow indices
Groups | number | Average scores | Test statistics | df | Sig |
---|---|---|---|---|---|
5 | 4.20 | ||||
Control | 5 | 8.80 | 7.023 | 2 | 0.030 |
5 | 11 | ||||
5 | 5 | ||||
Hydroxyapatite | 5 | 6.90 | 7.736 | 2 | 0.021 |
5 | 12.10 | ||||
5 | 5 | ||||
β-tricalcium phosphate | 5 | 7 | 7.280 | 2 | 0.26 |
5 | 12 | ||||
5 | 3.90 | ||||
Nanocomposite | 5 | 7.70 | 10.092 | 2 | 0.006 |
polycaprolactone | |||||
5 | 12.40 |
Microscopic view of healing area in control group on day 15. It shows abundant capillary buds (arrows) in granulation tissue (H&E, 100×)
Microscopic view of healing area in tricalcium phosphate (TCP) group on day 15. It shows abundant calcified cartilage (arrow) (H&E, 100×)
Microscopic view of healing area in hydroxyapatite (HA) group on day 15.It shows fibrous tissue (arrow) (H&E, 100×)
Microscopic view of healing area in PCL group on day 15. It shows primary bone (arrows) formation (H&E, 100×)
Microscopic view of healing area in control group on day 30. It shows abundant fibrous tissue (arrows) filling marrow space (H&E, 100×)
Microscopic view of healing area in tricalcium phosphate (TCP) group on day 30. Primary bones (arrow) are being produced (H&E, 100×)
Microscopic view of healing area in hydroxyapatite group on day 30. Calcified cartilage (arrow) in the mature granulation tissue (H&E, 100×)
Microscopic view of healing area in PCL group on day 30. Woven bones (arrows) are being produced (H&E, 100×)
Microscopic view of healing area in control group on day 45. Bone deposition within cartilage (star) at healing site shows primary (arrows) ossification (H&E, 100×)
Microscopic view of healing area in tricalcium phosphate (TCP) group on day 45. Lamellar bone formation (arrows) in healing site is shown (H&E, 100×)
Microscopic view of healing area in hydroxyapatite group on day 45. The defect is filled with primary bone (arrows) and well-formed marrow (star) (H&E, 100×)
Microscopic view of healing area in PCL group on day 45. The defect is filled with lamellar (arrows) bone (H&E, 100×)
Although bone has the ability to regenerate itself, some pathological or non-pathological conditions can lead to loss of this inherent ability, a situation which requires the use of bone scaffolds. In cases where the magnitude of the defect is greater than usual, the use of a bone replacement is necessary, in which case bone grafting is the only option available (9). The purpose of this study was to evaluate new bone formation using PCL nanocomposites compared with its formation with the help of TCP and HA in the rabbit femur. It seems that there was evidence of an advanced phase of remodelling and consolidation developing the Haversian system in the PCL group. In addition, the quantity of newly formed lamellar bone was greater than in other groups after 45 days.
This result is consistent with the findings of Esteves
There are significant ongoing attempts to design composite materials such as polymers and ceramics, to imitate bone microstructure. TCP and HA have been the subject of most studies because they have structure similar to the inorganic structure of bone and have osteoconductive properties (15).
Mature compact bone is composed of about 70% inorganic salts and 30% organic matrix. The main mineral component of bone matrix is HA crystals consisting of calcium and phosphate. HA has good bioactivity and osteoconductivity (16), but is mechanically weak. Calcium phosphate as a bone replacement material is used for bone grafts, and several studies have demonstrated that calcium phosphate has excellent resorbability and osteoconduction when filling the bone defect (21). However, TCP and HA also show fragility, which is a poor match for the mechanical properties of the natural tissue.
PCL is used as raw material in the manufacture of bone scaffolds (11) and is also blended with osteoconductive ceramics such as forsterite (30), calcium alginate (29), HA (4, 7, 22, 28), magnesium phosphate (MP) (19), bioactive glass microspheres (BGMs) (2), and TCP (17, 24). In addition, polypropylene can be mixed with natural polymer to produce bone scaffolds such as silk fibroin (SF) (27). PCL is a multipurpose biodegradable polymer having extraordinary potential in tissue engineering. It is nontoxic in nature and has been found to be cyto-compatible with several body tissues, which makes it an ideal material for tissue engineering. Abedalwafa
Ciapetti
Eftekhari
In another study by Lee
Vikingsson
In a study conducted by Di Liddo
Rezaei
In conclusion, the results of this study indicate that nanocomposite PCL has great potential for forming scaffolds to be extensively used for the repair of bone defects. Overall, we believe, with ongoing advances in nanotechnology, nanostructured implant materials will have a bright future in bone repair. nanocomposite PCL has positive effects on the bone healing process, and it can therefore be used as scaffold material in orthopaedic surgery.