This review discusses and summarizes the recent developments and advances in the use of biodegradable materials for bone repair purposes. The choice between using degradable and non-degradable devices for orthopedic and maxillofacial applications must be carefully weighed. Traditional biodegradable devices for osteosynthesis have been successful in low or mild load bearing applications. However, continuing research and recent developments in the field of material science has resulted in development of biomaterials with improved strength and mechanical properties. For this purpose, biodegradable materials, including polymers, ceramics and magnesium alloys have attracted much attention for osteologic repair and applications. The next generation of biodegradable materials would benefit from recent knowledge gained regarding cell material interactions, with better control of interfacing between the material and the surrounding bone tissue. The next generations of biodegradable materials for bone repair and regeneration applications require better control of interfacing between the material and the surrounding bone tissue. Also, the mechanical properties and degradation/resorption profiles of these materials require further improvement to broaden their use and achieve better clinical results.

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Biodegradable Materials for Bone Repair and Tissue Engineering Applications

During the resorbable-polymer-boom of the 1970s and 1980s, polycaprolactone (PCL) was used in the biomaterials field and a number of drug-delivery devices. Its popularity was soon superseded by faster resorbable polymers which had fewer perceived disadvantages associated with long term degradation (up to 3-4 years) and intracellular resorption pathways; consequently, PCL was almost forgotten for most of two decades. Recently, a resurgence of interest has propelled PCL back into the biomaterials-arena. The superior rheological and viscoelastic properties over many of its aliphatic polyester counterparts renders PCL easy to manufacture and manipulate into a large range of implants and devices. Coupled with relatively inexpensive production routes and FDA approval, this provides a promising platform for the production of longer-term degradable implants which may be manipulated physically, chemically and biologically to possess tailorable degradation kinetics to suit a specific anatomical site. This review will discuss the application of PCL as a biomaterial over the last two decades focusing on the advantages which have propagated its return into the spotlight with a particular focus on medical devices, drug delivery and tissue engineering.

The return of a forgotten polymer : Polycaprolactone in the 21st century

Biodegradable Materials for Bone Repairs: A Review

Poly(lactic acid) (PLA) is regarded as one of the most promising bio-based and biodegradable polymers, due to its excellent biodegradability, biocompatibility, renewability, high strength, and easy processibility. However, disadvantages such as brittleness and relatively high cost have restricted its applications significantly. Polymer blending provides an economic and efficient way to modify the properties of PLA. Most shortcomings of PLA are theoretically surmountable by blending with abundant polymers with various properties. But, unfortunately, PLA is thermodynamically immiscible with most existing polymers. High-performance PLA-based blends are usually unanticipated by direct blending. In order to obtain PLA-based blends with excellent overall properties, compatibilization is required during polymer blending. Various strategies have been employed or developed to compatibilize PLA blends with different polymers, as reported in recent studies. This article aims to review the development in compatibilization strategies employed in PLA-based blends.

Compatibilization strategies in poly(lactic acid)-based blends

Compared with non-degradable materials, biodegradable biomaterials play an increasingly important role in the repairing of severe bone defects, and have attracted extensive attention from researchers. In the treatment of bone defects, scaffolds made of biodegradable materials can provide a crawling bridge for new bone tissue in the gap and a platform for cells and growth factors to play a physiological role, which will eventually be degraded and absorbed in the body and be replaced by the new bone tissue. Traditional biodegradable materials include polymers, ceramics and metals, which have been used in bone defect repairing for many years. Although these materials have more or fewer shortcomings, they are still the cornerstone of our development of a new generation of degradable materials. With the rapid development of modern science and technology, in the twenty-first century, more and more kinds of new biodegradable materials emerge in endlessly, such as new intelligent micro-nano materials and cell-based products. At the same time, there are many new fabrication technologies of improving biodegradable materials, such as modular fabrication, 3D and 4D printing, interface reinforcement and nanotechnology. This review will introduce various kinds of biodegradable materials commonly used in bone defect repairing, especially the newly emerging materials and their fabrication technology in recent years, and look forward to the future research direction, hoping to provide researchers in the field with some inspiration and reference.

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Biodegradable materials for bone defect repair

In vitro hydrolytic degradation of poly(para-dioxanone)/poly(d,l-lactide) blends

The in vitro hydrolytic degradation of high molecular weight poly (para-dioxanone) was studied by examining the changes of weight retention, water absorption, pH value, tensile strength, break elongation, thermal properties, and morphology of high molecular weight PPDO in phosphate buffered saline (PBS) (pH 7.44) at 37°C for 8 weeks. During the degradation, all samples’ weight retention decreased and water absorption increased significantly, whereas hydrolysis rate of PPDO bars varied with molecular weight. Compared with lower molecular weight samples, higher molecular weight PPDO samples exhibited higher hydrolysis rate. The samples’ glass transition temperature (Tg) decreased notably, while the degrees of crystallinity (Dc) increased. The samples almost totally lost their tensile strengths and breaking elongation after 4 weeks of degradation. The results suggested that the stability of PPDO in vitro hydrolytic degradation increased with the increase of molecular weight.

In vitro hydrolytic degradation of poly( para -dioxanone) with high molecular weight

BACKGROUND: Poly(para-dioxanone) (PPDO) is a biodegradable polyester with excellent biodegradability, bioabsorbability, biocompatibility and mechanical flexibility. However, its high cost and relatively fast degradation rate have hindered the development of commercial applications. Blending with other polymers is a simple and convenient way of modifying the properties of aliphatic polyesters. Poly(D,L-lactide) (PDLLA) is another polyester that has been extensively studied for biomedical applications due to its biocompatibility and suitable degradation rate. However, to our knowledge, blends of PPDO/PDLLA have not been reported in the literature.



RESULTS: A series of biodegradable polymers were blended by solution co-precipitation of PPDO and PDLLA in various blend ratios. The miscibility, morphology and thermal properties of the materials were investigated. DSC curves for all blends revealed two discrete glass transition temperatures which matched the values for pure PPDO and PDLLA. SEM images of fracture surfaces displayed evidence of phase separation consistent with the DSC results. The contact angles increased with the addition of PDLLA.



CONCLUSION: PPDO/PDLLA blends exhibit two distinct glass transition temperatures that remain nearly constant and correspond to the glass transition temperatures of the homopolymers for all blend compositions, indicating that blends of PPDO and PDLLA are immiscible. Images of the surface obtained using SEM were also suggestive of a two-phase material. The crystallinity of the PPDO phase in the blends was affected by the PDLLA content. The mechanical properties of the blends changed dramatically with composition. Adding PDLLA makes the blends less hydrophilic than PPDO. Copyright © 2008 Society of Chemical Industry

Miscibility, morphology and thermal properties of poly(para-dioxanone)/poly(D,L-lactide) blends

In this work, poly(para-dioxanone) (PPDO) was mixed with 1% (by weight) calcium carbonate (CaCO(3)), beta-tricalcium phosphate (beta-TCP), or calcium sulphate dihydrate (CSD) by solution co-precipitation. Samples were compression molded into bars using a platen-vulcanizing press. The morphology, thermal and mechanical properties, and crystalline structure of the composites were investigated using differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy, and X-ray diffraction. All results suggest that three types of inorganic particle in this system promote the crystallinity of PPDO and act as an effective nucleating agent: the relative degree of crystallinity of PPDO increased from 30.74% to 100%, and the crystallization temperature of PPDO was increased by 18 degrees C. On the other hand, the mechanical properties of PPDO were changed by the presence of inorganic particles: the tensile strength of PPDO/CSD increased by 11.46%.

Poly(para‐dioxanone)/inorganic particle composites as a novel biomaterial

A series of biodegradable polymers was prepared by solution co-precipitation of poly(para-dioxanone) (PPDO) and poly(lactic-co-glycolic acid) (PLGA) in various blend ratios. Samples were compression-molded into bars using a platen vulcanizing press. The miscibility, thermal and mechanical properties of the materials were investigated using differential scanning calorimetry (DSC), polarized optical microscopy, and scanning electron microscopy (SEM). Dynamic contact angle was used to characterize the water wettability of PLGA/PPDO blends. The mechanical properties of blends and pure polymers were measured by tensile tests. The position of the glass transition temperatures (T
 g
 ) was dependent upon composition. When 10 % PLGA was added into PPDO, the DSC curve revealed only one T
 g
 (−7.35 °C) which was located between the T
 g
 values of PPDO and PLGA. When 20 % PLGA was added into the blend, two independent T
 g
 values for PPDO/PLGA blends were observed, and such characteristics improved further upon addition of 30 % PLGA. SEM images of fractured surfaces displayed evidence of the morphology of PPDO/PLGA blends that were consistent with the DSC results. Hence, a relationship was found between homogeneity and the contents of PLGA in the blend. The compatibility of the blends increased with addition of small amounts of PLGA, followed by a leveling-off at higher content.

Qing Li

Papers

In vitro hydrolytic degradation of poly(para-dioxanone)/poly(d,l-lactide) blends

In vitro hydrolytic degradation of poly( para -dioxanone) with high molecular weight

Miscibility, morphology and thermal properties of poly(para-dioxanone)/poly(D,L-lactide) blends

Poly(para‐dioxanone)/inorganic particle composites as a novel biomaterial

Miscibility, Thermal and Mechanical Properties of Poly(para-dioxanone)/Poly(lactic-co-glycolic acid) Blends