A high-strength biodegradable thermoset polymer for internal fixation bone screws: Preparation, in vitro and in vivo evaluation

Synthesis and Solvent Free DLP 3D Printing of Degradable Poly(Allyl Glycidyl Ether Succinate)

Digital light processing (DLP) printing forms solid constructs from fluidic resins by photochemically crosslinking polymeric resins with reactive functional groups. DLP is used widely due to its efficient, high-resolution printing, but its use and translational potential has been limited in some applications as state-of-the-art resins experience unpredictable and anisotropic part shrinkage due to the use of solvent needed to reduce resin viscosity and layer dependent crosslinking. Herein, poly(allyl glycidyl ether succinate) (PAGES), a low viscosity, degradable polyester, was synthesized by ring opening copolymerization and used in combination with degradable thiol crosslinkers to afford a solvent free resin that can be utilized in DLP printing. Varying resin formulations of PAGES polymer are shown to decrease part shrinkage from 14 % to 0.3 %. Photochemically printed parts fabricated from PAGES possess tensile moduli between 0.43 and 6.18 MPa and degradation profiles are shown to vary between 12 and 40 days under accelerated conditions based on degree of polymerization and crosslink ratio.

Review on Biodegradable Aliphatic Polyesters: Development and Challenges

Biodegradable polymers are gaining attention as alternatives to non-biodegradable plastics to address environmental issues. With the rising global demand for plastic products, the development of non-toxic, biodegradable plastics is a significant topic of research. Aliphatic polyester, the most common biodegradable polyester, is notable for its semi-crystalline structure and can be synthesized from fossil fuels, microbial fermentation, and plants. Due to great properties like being lightweight, biodegradable, biocompatible, and non-toxic, aliphatic polyesters are used in packaging, medical, agricultural, wearable devices, sensors, and textile applications. The biodegradation rate, crucial for biodegradable polymers, is discussed in this review as it is influenced by their structural properties and environmental conditions. This review discusses currently available biodegradable polyesters, their emerging applications, and the challenges in their commercialization. As research in this area grows, this review emphasizes the innovation in biodegradable aliphatic polyesters and their role in advancing environmental sustainability.

A biodegradable, osteo-regenerative and biomechanically robust polylactide bone screw for clinical orthopedic surgery

Poly (L-lactic acid) (PLLA) has emerged as a promising orthopedic implant material due to its favorable strength and biodegradability. However, challenges such as low toughness and limited osteoinductivity hinder its widespread use in bone fixation. This study focuses on enhancing the toughness and osteogenic activity of PLLA-based orthopedic implants. Inspired by reinforcement techniques in the construction industry, we designed a structure comprising flexible fibers enveloped by PLLA/hydroxyapatite (HA) crystalline phases. Initially, PLLA/poly (butylene succinate-co-adipate) (PBSA)/HA composites with "sea-island" morphology were prepared through melt-compounding. Subsequently, the highly oriented PBSA fibers were in situ formed during microinjection molding for bone screw fabrication. Comprehensive investigation into the structural-mechanical property relationship revealed a significant increase in elongation at break (from 5.4 % to 59.4 % with an optimal PBSA/HA ratio), while maintaining a high stiffness and a slight decrease in tensile strength (from 62.0 MPa to 56.0 MPa). The flexural tests of the resulting composite bone screws demonstrated a significant increase in toughness. Additionally, the in vivo studies corroborated the osteogenic potential of the microinjection molded bone screws by using hematoxylin and eosin (HE) and Masson staining. The methodology presented in this study offers a promising approach for advancing PLLA-based fixation devices in bone repair applications.

A functional analysis of a resorbable citrate-based composite tendon anchor

Rapid and efficient tendon fixation to a bone following trauma or in response to degenerative processes can be facilitated using a tendon anchoring device. Osteomimetic biomaterials, and in particular, bio-resorbable polymer composites designed to match the mineral phase content of native bone, have been shown to exhibit osteoinductive and osteoconductive properties in vivo and have been used in bone fixation for the past 2 decades. In this study, a resorbable, bioactive, and mechanically robust citrate-based composite formulated from poly(octamethylene citrate) (POC) and hydroxyapatite (HA) (POC-HA) was investigated as a potential tendon-fixation biomaterial. In vitro analysis with human Mesenchymal Stem Cells (hMSCs) indicated that POC-HA composite materials supported cell adhesion, growth, and proliferation and increased calcium deposition, alkaline phosphatase production, the expression of osteogenic specific genes, and activation of canonical pathways leading to osteoinduction and osteoconduction. Further, in vivo evaluation of a POC-HA tendon fixation device in a sheep metaphyseal model indicates the regenerative and remodeling potential of this citrate-based composite material. Together, this study presents a comprehensive in vitro and in vivo analysis of the functional response to a citrate-derived composite tendon anchor and indicates that citrate-based HA composites offer improved mechanical and osteogenic properties relative to commonly used resorbable tendon anchor devices formulated from poly(L-co-D, l-lactic acid) and tricalcium phosphate PLDLA-TCP.

Harnessing the power of polyol-based polyesters for biomedical innovations: synthesis, properties, and biodegradation

Polyesters based on polyols have emerged as promising biomaterials for various biomedical applications, such as tissue engineering, drug delivery systems, and regenerative medicine, due to their biocompatibility, biodegradability, and versatile physicochemical properties. This review article provides an overview of the synthesis methods, performance, and biodegradation mechanisms of polyol-based polyesters, highlighting their potential for use in a wide range of biomedical applications. The synthesis techniques, such as simple polycondensation and enzymatic polymerization, allow for the fine-tuning of polyester structure and molecular weight, thereby enabling the tailoring of material properties to specific application requirements. The physicochemical properties of polyol-based polyesters, such as hydrophilicity, crystallinity, and mechanical properties, can be altered by incorporating different polyols. The article highlights the influence of various factors, such as molecular weight, crosslinking density, and degradation medium, on the biodegradation behavior of these materials, and the importance of understanding these factors for controlling degradation rates. Future research directions include the development of novel polyesters with improved properties, optimization of degradation rates, and exploration of advanced processing techniques for fabricating scaffolds and drug delivery systems. Overall, polyol-based polyesters hold significant potential in the field of biomedical applications, paving the way for groundbreaking advancements and innovative solutions that could revolutionize patient care and treatment outcomes.

A Review on Polymers for Biomedical Applications on Hard and Soft Tissues and Prosthetic Limbs

In the past decades, there has been a significant increase in the use of polymers for biomedical applications. The global medical polymer market size was valued at USD 19.92 billion in 2022 and is expected to grow at a CAGR of 8.0% from 2023 to 2030 despite some limitations, such as cost (financial limitation), strength compared to metal plates for bone fracture, design optimization and incorporation of reinforcement. Recently, this increase has been more pronounced due to important advances in synthesis and modification techniques for the design of novel biomaterials and their behavior in vitro and in vivo. Also, modern medicine allows the use of less invasive surgeries and faster surgical sutures. Besides their use in the human body, polymer biomedical materials must have desired physical, chemical, biological, biomechanical, and degradation properties. This review summarizes the use of polymers for biomedical applications, mainly focusing on hard and soft tissues, prosthetic limbs, dental applications, and bone fracture repair. The main properties, gaps, and trends are discussed.

Synthesis of Prepolymers of Poly(glycerol-co-diacids) Based on Sebacic and Succinic Acid Mixtures

In this study, poly(glycerol-co-diacids) prepolymers were produced using different ratios of glycerol (G), sebacic acid (S), and succinic acid (Su) (molar ratios: GS 1:1, GSSu 1:0.9:0.1, GSSu 1:0.8:0.2, GSSu 1:0.5:0.5, GSSu 1:0.2:0.8, GSSu 1:0.1:0.9, GSu 1:1). All polycondensation reactions were performed at 150 °C until reaching a degree of polymerization of ≈55%, inferred by the water volume collected from a reactor. We concluded that the reaction time is correlated with the ratio of diacids used, that is, the increase in succinic acid is proportional to a decrease in the duration of the reaction. In fact, the reaction of poly(glycerol sebacate) (PGS 1:1) is twice as slow as the reaction of poly(glycerol succinate) (PGSu 1:1). The obtained prepolymers were analyzed by electrospray ionization mass spectrometry (ESI-MS) and ¹H and ¹³C nuclear magnetic resonance (NMR). Besides its catalytic influence in poly(glycerol)/ether bond formation, the presence of succinic acid also contributes to a mass growth of ester oligomers, the formation of cyclic structures, a greater number of oligomers detected, and a difference in mass distribution. When compared with PGS (1:1), and even at lower ratios, the prepolymers produced with succinic acid presented mass peak characteristics of oligomer species with a glycerol unit as its end group in higher abundance. Generally, the most abundant oligomers have molecular weights between 400 and 800 g/mol.

Synthesis of Poly(glycerol butenedioate)-PGB-Unsaturated Polyester toward Biomedical Applications

A new polyester poly(glycerol butenedioate) (PGB) was obtained in the bulk polycondensation of glycerin and maleic anhydride. Glycerol polyesters are new biomaterials commonly used in tissue engineering. PGB, containing the α,β-unsaturated moiety, could be very interesting due to potential modifications such as additions or oxidation. Such modifications are not possible on the heretofore known glycerol polyesters due to their structure without α,β-unsaturated moieties. In this work, the developed process was optimized by applying the design of experiments. The optimization criterium was the minimization of the E/Z isomer ratio. Applying the two-stage process, the E/Z isomer ratio was reduced from 5.5 to 0.5 compared to the one-stage process. The degree of branching was also reduced from 17 to 9%, as well as the degree of esterification from 0.89 to 0.72. The obtained structure can be used in modifying or cross-linking via Michael additions.

Optimisation of Glycerol and Itaconic Anhydride Polycondensation

Glycerol polyesters have recently become objects of interest in tissue engineering. Barely known so far is poly(glycerol itaconate) (PGItc), a biocompatible, biodegradable polyester. Due to the presence of a C=C electron-acceptor moiety, it is possible to post-modify the product by Michael additions to change the properties of PGItc. Thus, using PGItc as one of the elements of cellular scaffold crosslinked in situ for bone tissue regeneration seems to be a very attractive yet unexplored solution. This work aims to optimize the synthesis of PGItc to obtain derivatives with a double bond in the side chain with the highest conversion rates. The experiments were performed with itaconic anhydride and glycerol using mathematical planning of experiments according to the Box-Behnken plan without solvent and catalyst. The input variables of the process were the ratio of the OH/COOH, temperature, and reaction time. The optimised output variables were: the degree of esterification (EDtitr), the degree of esterification calculated from the analysis of 1H NMR spectra (EDNMR), and the degree of itaconic anhydride conversion-calculation based on 13C NMR spectra (%X13CNMR). In each of statistical models, the significance of the changed synthesis parameters was determined. Optimal conditions are when OH/COOH ratio is equal to 1.5, temperature is 140 °C and time of reaction is 5 h. The higher OH/COOH ratio, temperature and longer the experiment time, the higher the value of the degree of esterification and the degree of anhydride conversion.

Chitosan-based biomaterials for the treatment of bone disorders

Bone is an alive and dynamic organ that is well-differentiated and originated from mesenchymal tissues. Bone undergoes continuous remodeling during the lifetime of an individual. Although knowledge regarding bones and their disorders has been constantly growing, much attention has been devoted to effective treatments that can be used, both from materials and medical performance points of view. Polymers derived from natural sources, for example polysaccharides, are generally biocompatible and are therefore considered excellent candidates for various biomedical applications. This review outlines the development of chitosan-based biomaterials for the treatment of bone disorders including bone fracture, osteoporosis, osteoarthritis, arthritis rheumatoid, and osteosarcoma. Different examples of chitosan-based formulations in the form of gels, micro/nanoparticles, and films are discussed herein. The work also reviews recent patents and important developments related to the use of chitosan in the treatment of bone disorders. Although most of the cited research was accomplished before reaching the clinical application level, this manuscript summarizes the latest achievements within chitosan-based biomaterials used for the treatment of bone disorders and provides perspectives for future scientific activities.

Synthesis of bio-based polyester elastomers and evaluation of the in vivo biocompatibility and biodegradability as biomedical materials

Biodegradable polyester elastomers have found wide applications in the tissue engineering field. In this study, all bio-based polyester elastomer (BPE) is synthesized from five bio-based monomers; and the in vivo...

Effect of Dioxane and N-Methyl-2-pyrrolidone as a Solvent on Biocompatibility and Degradation Performance of PLGA/nHA Scaffolds

Background

Solvent casting/particulate leaching is one of the most conventional methods for fabricating polymer/ceramic composite scaffolds. In this method, the solvent generally affects resulting scaffold properties, including porosity and degradation rate.

Methods

Herein, composite scaffolds of PLGA (poly(lactide-co-glycolide))/ nano-hydroxyapatite (nHA) with different percentages of nHA (25, 35, and 45 wt. %) were prepared by the solvent casting/particle leaching combined with freeze drying. The effects of two different solvents, 1,4-dioxane (DIO) and N-methyl-2-pyrrolidone (NMP), on morphology, porosity, bioactivity, degradation rate, and biocompatibility of the resulting scaffolds were investigated.

Results

The results revealed that increasing the nano-hydroxyapatite (nHA) percentages had no significant effect on the porosity and interconectivity of scaffolds (p > 0.05), whereas altering the solvent from DIO into NMP decreased the porosity from about 87% into 71%, respectively. Moreover, scaffolds of DIO illustrated the high results of cell proliferation compared to those of NMP; the cell viability of GD25 decreased from 85% to 65% for GN25. The findings also indicated that scaffolds prepared by NMP had a higher rate of losing weight in comparison to DIO. Adding nHA to PLGA had a significant effect on the bioactivity of scaffolds (p < 0.05), composite scaffolds with 45 wt % nHA had at least 30% more weight gain compared to the neat polymer scaffolds.

Conclusion

The DIO scaffolds have higher rates of porosity, interconnectivity, bioactivity, and biocompatibility than NMP scaffolds due to its high evaporation rate.