The Merit of Sintered PDLLA/TCP Composites in Management of Bone Fracture Internal Fixation

Abstract

Polyesters based on lactic acid have been reported in terms of safety and biodegradation in human beings for 2 decades. The greatest advantage of such material is its degradation conducted only by hydrolysis, whereby the ester backbones are supposed to be unchained in the aqueous condition. The final degradable products are carbon dioxide and water which can be metabolized and digested in the physiological environment. The goal of this study was aimed at developing a composite sintered with poly-DL-lactide (PDLLA) and tricalcium phosphate (TCP) ceramic particles for orthopedic application. The TCP particles in a range of 30-60 wt% with 5 wt% increments were doped into the PDLLA matrix which was prepared by melting and hot pressing techniques for the reinforcement. The basic mechanical strength, biodegradable behavior, and biological response of the composites were investigated in the study. Various techniques such as pH meter, UV, Fourier-transform infrared, and x-ray diffractometer were used to examine and record the degradable process of the composites soaked in saline for 1-16 weeks. The rabbit femur condyle fracture fixation test was used to evaluate tissue compatibility and the effects of bone fracture fixation on the composites. Histological observation and x-ray photography were used for investigating assistance. The mechanical strength of the composites initially increased with TCP additions up to 50wt%, but thereafter they showed no significant difference (p < 0.05). The composite with 50 wt% TCP addition showed greater mechanical strength and had good agreement with cortical bone in terms of its elastic modulus of 30-40 GPa. The weight loss of the pure PDLLA soaked in the saline started at 4 weeks and reached 95% after 16 weeks. The composites compared with pure PDLLA, however, showed no apparent evidence of degradation after soaked for 12 weeks. The possible mechanisms for the delayed degradation of the composites in saline might have been solution penetration retardation by the ceramic particles and chemical bonds formed between the interface of the TCP particles and the PDLLA matrix. In the histological evaluation of the rabbit femur condyle fracture fixation test, the surface of the composite with 50 wt% TCP addition was attached by the newly generated bone without fibrous tissue around 8 weeks after implantation. The fractured bone was gradually healed and the composite firmly and properly fixed on the fracture area during the implanted period, which provided a breeding environment for normal bone remodeling. The developed composite was thought to be an alternative material for orthopedic application in the future, especially for bone screws and bone plates.

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

“…Composite materials thus seem more favorable for bone consolidation than do pure polymer materials, and have been shown in vitro to improve biological behavior. These results confirm hypotheses on PLA/ TCP 23,24,35,36, materials and, more generally, the absorbable polyester/calcium phosphate composites presented in the literature, 20 -22,25-28,37,38 where the presence of minerals in the polymer matrix promoted the proliferation and phenotype expression of osteogenous cells in vitro. These findings were also corroborated by the histological examinations, which indicated clearly that pure PLA implants were systematically surrounded by a layer of conjunctival tissue containing large numbers of macrophages, irrespective of the length of implantation, whereas bone tissue grew in direct contact with composite implants during the first few months and matured gradually until the end of the study period, with no marked macrophage activation.…”

“…We know that the acidification that accompanies the degradation of lactic acid polymers may also set off an inflammatory reaction. 1 In a systematic in vitro study, Lin et al 24 measured the pH of solutions containing a variety of PDLLA/TCP composite materials. The pH stabilized at 2.3 for a pure polymer material and 5 for all the materials containing mineral, which shows the effect of ␤-TCP on the acidity of the solution.…”

Simple Signaling Molecules for Inductive Bone Regenerative Engineering

“…Mononuclear cells were found in a band along von Kossa stained calcium phosphate (CaP) analogous to osteoblasts lining up along mineralizing fronts of remodeled bone tissue. This behavior was not seen with the PLGA scaffolds and is similar to results seen with other polymer/CaP constructs [25], [26] suggesting that the HA component in PLGA/HA scaffolds can induce new mineralized bone growth without the inclusion of exogenous growth factors or cells.…”

Spherical calcium phosphate nanoparticle fillers allow polymer processing of bone fixation devices with high bioactivity

“…Stabilization of pH around an implant is of particular interest [14] and has been demonstrated by the addition of alkaline compounds, for example calcium phosphates [16,21] or bioactive glasses [22,23]. Lin et al [24] have shown that microsized and crystalline tricalcium phosphate (TCP) with low surface area used as filler in poly(α-hydroxy acids) resulted in decelerated degradation of the polymer and induced adverse mechanical properties during degradation [16]. A possibility to overcome this limitation can be the reduction of the filler particle size [25] to achieve enhanced dispersion and improved mode of action of tricalcium phosphate filler.…”