Bone Mineral Affinity of Polyphosphodiesters

Progress in synthesis, modification, characterization and applications of hyperbranched polyphosphate polyesters

Hyperbranched polyphosphate polyesters (HPPs) as a special class of hyperbranched polymers have attracted increased interest and have been intensively studied, because of peculiar structures, excellent biocompatibility, flexibility in physicochemical properties, biodegradability, water soluble, thermal stability, and mechanical properties. HPPs can be divided into phosphates as monomers and phosphates as end groups. In this article, the classification, general synthesis, modifications, and applications of HPP are reviewed. In addition, recent developments in the application of HPP are described, such as modified or functionalized by end capping and hypergrafting to improve the performances in polymer blends, coatings, flame retardant, leather. Furthermore, the modifications and application of HPPs in biomedical materials, such as drug delivery and bone regeneration were discussed. In summary, the hyperbranched polymer enlarges its application range and improves its application performance compared with conventional polymer. In the future, more new HPPs composite materials will be developed through hyperbranched technique. This review of HPPs will provide useful theoretical basis and technical support for the development of new hyperbranched polymer material.

Effect of phosphodiester composition in polyphosphoesters on the inhibition of osteoclastic differentiation of murine bone marrow mononuclear cells

Osteoporosis is a common bone disorder characterized by reduced bone density and increased risk of fractures. The modulation of bone cell functions, particularly the inhibition of osteoclastic differentiation, plays a crucial role in osteoporosis treatment. Polyphosphoesters (PPEs) have shown the potential in reducing the function of osteoclast cells, but the effect of their chemical structure on osteoclastic differentiation remains largely unexplored. In this study, we evaluated the effect of PPE's chemical structure on the inhibition of osteoclastic differentiation of murine bone marrow mononuclear cells (BMNCs). PPEs containing phosphotriester and phosphodiester units at varying compositions were synthesized. Cytotoxicity testing confirmed the biocompatibility of the copolymers at concentrations below 0.5 mg/mL. Isolated from long bones, BMNCs were cultured in a differentiation medium supplemented with different PPE concentrations. Osteoclast formation was assessed through tartrate-resistant acid phosphatase and phalloidin staining. A significant decrease in the size of osteoclast cells formed upon BMNC contact with PPEs was observed, with a more pronounced effect observed at higher PPE concentrations. In addition, an increased composition of phosphodiester units in the PPEs yielded a decreased density of differentiated osteoclasts. Furthermore, real-time PCR analysis of major osteoclastic markers provided gene expression data that correlated with microscopic observations, confirming the effect of phosphodiester units in suppressing osteoclast differentiation of BMNCs from the early stages. These findings highlight the potential of PPEs as polymers are capable of modulating bone cell functions through their chemical structures.

Crystalline Micro-Sized Carbonated Apatites: Chemical Anisotropy of the Crystallite Surfaces, Biocompatibility, Osteoconductivity, and Osteoinductive Effect Enhanced by Poly(ethylene phosphoric acid)

Carbonated hydroxyapatites (CAp) are very close to natural bone apatite in chemical composition and are regarded as a prospective bone mineral substitute for bone surgery and orthopedics. However, until now, the studies and applications of CAp were limited because of the amorphous nature of the synthetic CAp. In the present work, microsized highly crystalline carbonated apatites with uniform hexagonal (hCAp) or platelike (pCAp) morphology have been studied for the first time in vitro and in vivo, comparing against commercial hydroxyapatite (HAp) and β-tricalcuim phosphate (βTCP). In vitro experiments on dissolution of those calcium phosphate ceramics (CPCs) in acetate (pH 5.5) and Tris (pH 7.3) buffer solutions showed the following rank order of the dissolution rates: βTCP > hCAp > pCAp > HAp. The higher dissolution rate of hCAp in comparison with pCAp is explained by chemical anisotropy of the crystallite surfaces, which was proven by SEM studies of the changes in the morphology of hCAp and pCAp crystallites during hydrolysis. A 5-week experiment on subcutaneous implantation of CPC species showed the following rank order of bioresorption rates: βTCP > pCAp > hCAp > HAp. pCAp matrixes exhibited the highest biocompatibility, confirmed by histomorphological analysis. Three-month bone regeneration experiments involving a rat tibial defect model were conducted with 250-500 μm granules of pCAp and pCAp-PEPA [pCAp, pretreated with 2 wt % poly(ethylene phosphoric acid)]. Notably, pCAp-PEPA implants were resorbed at higher rates and induced the formation of more mature osseous tissue, a compact bone with Haversian systems.

Dispersant and Protective Roles of Amphiphilic Poly(ethylene phosphate) Block Copolymers in Polyester/Bone Mineral Composites

Composites of synthetic bone mineral substitutes (BMS) and biodegradable polyesters are of particular interest for bone surgery and orthopedics. Manufacturing of composite scaffolds commonly uses mixing of the BMS with polymer melts. Melt processing requires a high homogeneity of the mixing, and is complicated by BMS-promoted thermal degradation of polymers. In our work, poly(L-lactide) (PLLA) and poly(ε-caprolactone) (PCL) composites reinforced by commercial β-tricalcium phosphate (βTCP) or synthesized carbonated hydroxyapatite with hexagonal and plate-like crystallite shapes (hCAp and pCAp, respectively) were fabricated using injection molding. pCAp-based composites showed advanced mechanical and thermal characteristics, and the best set of mechanical characteristics was observed for the PLLA-based composite containing 25 wt% of pCAp. To achieve compatibility of polyesters and pCAp, reactive block copolymers of PLLA or PCL with poly(tert-butyl ethylene phosphate) (C1 and C2, respectively) were introduced to the composite. The formation of a polyester-b-poly(ethylene phosphoric acid) (PEPA) compatibilizer during composite preparation, followed by chemical binding of PEPA with pCAp, have been proved experimentally. The presence of 5 wt% of the compatibilizer provided deeper homogenization of the composite, resulting in a marked increase in strength and moduli as well as a more pronounced nucleation effect during isothermal crystallization. The use of C1 increased the thermal stability of the PLLA-based composite, containing 25 wt% of pCAp. In view of positive impacts of polyester-b-PEPA on composite homogeneity, mechanical characteristics, and thermal stability, polyester-b-PEPA will find application in the further development of composite materials for bone surgery and orthopedics.

Bone-targeting polyphosphodiesters that promote osteoblastic differentiation

Polymers for pharmaceutical use have been attractive in medical treatments because of the conjugation of multifunctional components and their long circulation time in the blood stream. Bone-targeted drug delivery systems are also no exceptional, and several polymers have been proposed for the treatment of bone diseases, such as cancer metastasis and osteoporosis. Herein, we report that polyphosphodiesters (PPDEs) have a potential to enhance osteoblastic differentiation, and they have a targeting ability to bone tissues in vivo. Two types of PPDEs, poly (ethylene sodium phosphate) (PEP•Na) and poly (propylene sodium phosphate) (PPP•Na), have been synthesized. Regardless of the alkylene structure in the main chain of PPDEs, the gene expression of osteoblast-specific transcription factors and differentiation markers of mouse osteoblastic-like cells (MC3T3-E1 cells) cultured in a differentiation medium was significantly upregulated by the addition of PPDEs. Moreover, it was also clarified that the signaling pathway related to cytoplasmic calcium ions was activated by PPDEs. The mineralization of MC3T3-E1 cells has a similar trend with its gene expression and is synergistically enhanced by PPDEs with β-glycerophosphate. The biodistribution of fluorescence-labeled PPDEs was also determined after intravenous injection in mice. PPDEs accumulated well in the bone through the blood stream, whereas polyphosphotriesters (PPTEs) tended to be excreted from the kidneys. Hydrophilic PEP•Na showed a superior bone affinity as compared with PPP•Na. PPDEs could be candidate polymers for the restoration of bone remodeling and bone-targeting drug delivery platforms.

Dexamethasone-loaded zeolitic imidazolate frameworks nanocomposite hydrogel with antibacterial and anti-inflammatory effects for periodontitis treatment

Periodontitis is a bacterial-induced, chronic inflammatory disease characterized by progressive destruction of tooth-supporting structures. Pathogenic bacteria residing in deep periodontal pockets after traditional manual debridement can still lead to local inflammatory microenvironment, which remains a challenging problem and an urgent need for better therapeutic strategies. Here, we integrated the advantages of metal-organic frameworks (MOFs) and hydrogels to prepare an injectable nanocomposite hydrogel by incorporating dexamethasone-loaded zeolitic imidazolate frameworks-8 (DZIF) nanoparticles into the photocrosslinking matrix of methacrylic polyphosphoester (PPEMA) and methacrylic gelatin (GelMA). The injectable hydrogel could be easily injected into deep periodontal pockets, achieving high local concentrations without leading to antibiotic resistance. The nanocomposite hydrogel had high antibacterial activity and constructs with stable microenvironments maintain cell viability, proliferation, spreading, as well as osteogenesis, and down-regulated inflammatory genes expression in vitro. When evaluated on an experimental periodontitis rat model, micro-computed tomography and histological analyses showed that the nanocomposite hydrogel effectively reduced periodontal inflammation and attenuated inflammation-induced bone loss in a rat model of periodontitis. These findings suggest that the nanocomposite hydrogel might be a promising therapeutic candidate for treating periodontal disease.

Design, Synthesis and Actual Applications of the Polymers Containing Acidic P-OH Fragments: Part 1. Polyphosphodiesters

Among natural and synthetic polymers, main-chain phosphorus-containing polyacids (PCPAs) (polyphosphodiesters), stand in a unique position at the intersection of chemistry, physics, biology and medicine. The structural similarity of polyphosphodiesters PCPAs to natural nucleic and teichoic acids, their biocompatibility, mimicking to biomolecules providing the 'stealth effect', high bone mineral affinity of polyphosphodiesters resulting in biomineralization at physiological conditions, and adjustable hydrolytic stability of polyphosphodiesters are the basis for various biomedical, industrial and household applications of this type of polymers. In the present review, we discuss the synthesis, properties and actual applications of polyphosphodiesters.

Pharmaceutical electrospinning and 3D printing scaffold design for bone regeneration

Bone regenerative engineering provides a great platform for bone tissue regeneration covering cells, growth factors and other dynamic forces for fabricating scaffolds. Diversified biomaterials and their fabrication methods have emerged for fabricating patient specific bioactive scaffolds with controlled microstructures for bridging complex bone defects. The goal of this review is to summarize the points of scaffold design as well as applications for bone regeneration based on both electrospinning and 3D bioprinting. It first briefly introduces biological characteristics of bone regeneration and summarizes the applications of different types of material and the considerations for bone regeneration including polymers, ceramics, metals and composites. We then discuss electrospinning nanofibrous scaffold applied for the bone regenerative engineering with various properties, components and structures. Meanwhile, diverse design in the 3D bioprinting scaffolds for osteogenesis especially in the role of drug and bioactive factors delivery are assembled. Finally, we discuss challenges and future prospects in the development of electrospinning and 3D bioprinting for osteogenesis and prominent strategies and directions in future.

Controlled biointerfaces with biomimetic phosphorus-containing polymers

Phosphorus is a ubiquitous and one of the most common elements found in living organisms. Almost all molecules containing phosphorus in our body exist as analogs of phosphate salts or phosphoesters. Their functions are versatile and important, being responsible for forming the genetic code, cell membrane, and mineral components of hard tissue. Several materials inspired from these phosphorus-containing biomolecules have been recently developed. These materials have shown unique properties at the biointerface, such as nonfouling ability, blood compatibility, lubricity, mineralization induction capability, and bone affinity. Several unfavorable events occur at the interface of materials and living organisms because most of these materials have not been designed while taking host responses into account. These unfavorable events are directly linked to reducing functions and shorten the usable periods of medical devices. Biomimetic phosphorus-containing polymers can improve the reliability of materials in biological systems. In addition, phosphorus-containing biomimetic polymers are useful not only for improving the biocompatibility of material surfaces but also for adding new functions due to the flexibility in molecular design. In this review, we describe the recent advances in the control of biointerfacial phenomena with phosphorus-containing polymers. We especially focus on zwitterioninc phosphorylcholine polymers and polyphosphoesters.

Bioinspired zwitterionic polyphosphoester modified porous silicon nanoparticles for efficient oral insulin delivery

The intestinal epithelial and mucus barriers on the gastrointestinal tract limit the bioavailability of oral protein or peptide drugs. Therefore, efficient mucus permeability and cellular internalization are required properties for oral delivery systems. To overcome these two obstacles, porous silicon nanoparticles were modified with poly (pyridyl disulfide ethylene phosphate/sulfobetaine) polymers to make P(PyEP-g-SBm)n-AmPSiNPs (m = 0.1, 0.2, 0.3 and n = 10, 20, 30) nanoparticles (NPs). The insulin-loaded P(PyEP-g-SB)-AmPSiNPs showed favorable stability and good biocompatibility in vitro. The zwitterionic dodecyl sulfobetaine (SB) coated nanoparticles improved the mucus permeability. P(PyEP-g-SBm)20 with the optimal conjugated ratio (m = 0.3) of SB units was determined by evaluating the mucus diffusion rate of NPs. The cellular uptake of P(PyEP-g-SB0.3)n-AmPSiNPs (n = 10, 20, 30) was much higher than AmPSiNPs in the presence of inhibitors (N-acetylcysteine solution and sodium chlorate) (p < 0.01) due to the enhanced charge shielding effect of P(PyEP-g-SB) modification. The P(PyEP-g-SB0.3)20-AmPSiNPs showed about 1.4-1.7 fold increase in the apparent permeability of insulin across Caco-2/HT-29-MTX cell monolayers, compared to AmPSiNPs (p < 0.01). Finally, the in vivo study showed that insulin-loaded P(PyEP-g-SB0.3)20-AmPSiNPs generated 20% reduction of the blood glucose level with an 2-fold increase in oral bioavailability. These suggested that zwitterionic polyphosphoester modified porous silicon nanoparticles, which were of enhanced mucus permeability and cellular internalization, represent a promising carrier for oral delivery of peptide and protein.

Cyclic ethylene phosphates with (CH2)nCOOR and CH2CONMe2 substituents: synthesis and mechanistic insights of diverse reactivity in aryloxy-Mg complex-catalyzed (co)polymerization

Herein we present a comparative study of the reactivity of ethylene phosphates with –O(CH2)nCOOMe (n = 1–3, 5), –CH2COOtBu, –OCHMeCOOMe, and –OCH2CONMe2 substituents in BHT-Mg catalyzed ROP.

A New Approach to Developing Long-Acting Injectable Formulations of Anti-HIV Drugs: Poly(Ethylene Phosphoric Acid) Block Copolymers Increase the Efficiency of Tenofovir against HIV-1 in MT-4 Cells

Despite the world’s combined efforts, human immunodeficiency virus (HIV), the causative agent of AIDS, remains one of the world’s most serious public health challenges. High genetic variability of HIV complicates the development of anti-HIV vaccine, and there is an actual clinical need for increasing the efficiency of anti-HIV drugs in terms of targeted delivery and controlled release. Tenofovir (TFV), a nucleotide-analog reverse transcriptase inhibitor, has gained wide acceptance as a drug for pre-exposure prophylaxis or treatment of HIV infection. In our study, we explored the potential of tenofovir disoproxil (TFD) adducts with block copolymers of poly(ethylene glycol) monomethyl ether and poly(ethylene phosphoric acid) (mPEG-b-PEPA) as candidates for developing a long-acting/controlled-release formulation of TFV. Two types of mPEG-b-PEPA with numbers of ethylene phosphoric acid (EPA) fragments of 13 and 49 were synthesized by catalytic ring-opening polymerization, and used for preparing four types of adducts with TFD. Antiviral activity of [mPEG-b-PEPA]TFD or tenofovir disoproxil fumarate (TDF) was evaluated using the model of experimental HIV infection in vitro (MT-4/HIV-1_IIIB). Judging by the values of the selectivity index (SI), TFD exhibited an up to 14-fold higher anti-HIV activity in the form of mPEG-b-PEPA adducts, thus demonstrating significant promise for further development of long-acting/controlled-release injectable TFV formulations.

Particle-stabilized oil-in-water emulsions as a platform for topical lipophilic drug delivery

Low-environmental-impact emulsion systems for transdermal drug delivery in topical treatment have gained increasing interest. However, low stability and adverse systemic side effects severely decrease their efficiency. This study proposed a stable oil-in-water (O/W) emulsion loaded with bifonazole (BFZ) as a lipophilic drug stabilized by poly(2-isopropoxy-2-oxo-1,3,2-dioxaphospholane)-modified cellulose nanocrystals (CNC-g-PIPP) as vehicles for topical delivery of lipophilic drugs. We fully characterized stability, BFZ-loaded particle-stabilized emulsions (PEs) for morphology, droplet size, and its distribution. In addition, we evaluated the in vitro drug-releasing capacity and in vitro skin permeation of BFZ in a porcine skin animal model using a side-bi-side® diffusion cell. An O/W BFZ-loaded emulsion stabilized with CNC-g-PIPP particles (BFZ-loaded CP-PE) with a small mean droplet size of 2.54 ± 1.39 μm was developed and was stable for > = 15 days without a significant change in droplet size. The BFZ-loading efficiency in PEs was 83.1 %. BFZ was slowly released over an extended period, and the releasing ratio from BFZ-loaded CP-PE was only 17 % after 48 h. The BFZ-loaded CP-PE showed a ∼4.4-fold increase in BFZ permeation and penetration compared to a conventional surfactant-stabilized emulsion and BFZ control solution. Fluorescence-labeling studies showed that BFZ-loaded CP-PE could well penetrate skin layers from the stratum corneum (SC) to the dermis. In addition, histopathology studies of porcine skin treated with the PE formulation showed an intact SC with unaltered adjacent structures and no observed signs of inflammation. Therefore, the proposed CP-PE shows great potential as a transdermal drug carrier for enhancing lipophilic drug permeation.

Main-Chain Phosphorus-Containing Polymers for Therapeutic Applications

Polymers in which phosphorus is an integral part of the main chain, including polyphosphazenes and polyphosphoesters, have been widely investigated in recent years for their potential in a number of therapeutic applications. Phosphorus, as the central feature of these polymers, endears the chemical functionalization, and in some cases (bio)degradability, to facilitate their use in such therapeutic formulations. Recent advances in the synthetic polymer chemistry have allowed for controlled synthesis methods in order to prepare the complex macromolecular structures required, alongside the control and reproducibility desired for such medical applications. While the main polymer families described herein, polyphosphazenes and polyphosphoesters and their analogues, as well as phosphorus-based dendrimers, have hitherto predominantly been investigated in isolation from one another, this review aims to highlight and bring together some of this research. In doing so, the focus is placed on the essential, and often mutual, design features and structure-property relationships that allow the preparation of such functional materials. The first part of the review details the relevant features of phosphorus-containing polymers in respect to their use in therapeutic applications, while the second part highlights some recent and innovative applications, offering insights into the most state-of-the-art research on phosphorus-based polymers in a therapeutic context.