Modeling vancomycin release kinetics from microporous calcium phosphate ceramics comparing static and dynamic immersion conditions

Effect of pH on hydroxyapatite coatings obtained by spray pyrolysis and their use as matrices for antibiotic adsorption by spin coating and release properties

Calcium phosphate materials, particularly hydroxyapatite (HA), are extensively used in biomedical applications because of their prominence as primary inorganic constituents of human hard tissues. This study investigates the synthesis of HA coatings via spray pyrolysis using various precursors, including HA derived from bovine bone. The effects of pH on the formation and properties of HA coatings were systematically examined. Samples exposed to acidic conditions or left without pH adjustment led to the formation of HA, contrasting with the outcomes observed through dissolution methods. Different characterization techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), were employed to evaluate the quality and crystallinity of the coatings. Among the samples, those exhibiting superior crystallinity and nanostructured features, including bovine HA, were selected for further surface functionalization with the antibiotic enrofloxacin using spin coating. As expected, the antibiotic loading on each material's surface depended on the amount of HA deposited on the substrate. However, the desorption results indicated that, in all cases, desorption persisted beyond 38 h, implying that HA-loaded matrices could be effective systems for controlled and prolonged drug release, which could be useful in dental or orthopedic implants for inhibiting the growth of bacterial biofilms.

Drug delivery strategies through 3D-printed calcium phosphate

3D printing has revolutionized bone tissue engineering (BTE) by enabling the fabrication of patient- or defect-specific scaffolds to enhance bone regeneration. The superior biocompatibility, customizable bioactivity, and biodegradability have enabled calcium phosphate (CaP) to gain significance as a bone graft material. 3D-printed (3DP) CaP scaffolds allow precise drug delivery due to their porous structure, adaptable structure-property relationship, dynamic chemistry, and controlled dissolution. The effectiveness of conventional scaffold-based drug delivery is hampered by initial burst release and drug loss. This review summarizes different multifunctional drug delivery approaches explored in controlling drug release, including polymer coatings, formulation integration, microporous scaffold design, chemical crosslinking, and direct extrusion printing for BTE applications. The review also outlines perspectives and future challenges in drug delivery research, paving the way for next-generation bone repair methodologies.

Targeted Clindamycin Delivery Systems: Promising Options for Preventing and Treating Bacterial Infections Using Biomaterials

Targeted therapy represents a real opportunity to improve the health and lives of patients. Developments in this field are confirmed by the fact that the global market for drug carriers was worth nearly $40 million in 2022. For this reason, materials engineering and the development of new drug carrier compositions for targeted therapy has become a key area of research in pharmaceutical drug delivery in recent years. Ceramics, polymers, and metals, as well as composites, are of great interest, as when they are appropriately processed or combined with each other, it is possible to obtain biomaterials for hard tissues, soft tissues, and skin applications. After appropriate modification, these materials can release the drug directly at the site requiring a therapeutic effect. This brief literature review characterizes routes of drug delivery into the body and discusses biomaterials from different groups, options for their modification with clindamycin, an antibiotic used for infections caused by aerobic and anaerobic Gram-positive bacteria, and different methods for the final processing of carriers. Examples of coating materials for skin wound healing, acne therapy, and bone tissue fillers are given. Furthermore, the reasons why the use of antibiotic therapy is crucial for a smooth and successful recovery and the risks of bacterial infections are explained. It was demonstrated that there is no single proven delivery scheme, and that the drug can be successfully released from different carriers depending on the destination.

Biofunctionalization with Cissus quadrangularis Phytobioactives Accentuates Nano-Hydroxyapatite Based Ceramic Nano-Cement for Neo-Bone Formation in Critical Sized Bone Defect

Developing biofunctionalized ceramic bone substitutes with phytobioactives for their sustained delivery is highly desired to enhance the osteo-active potential of ceramic bone substitutes, reduce the systemic toxicity of synthetic drugs, and increase the bioavailability of phytobioactives. The present work highlights the local delivery of phytobioactives of Cissus quadrangularis (CQ) through nano-hydroxyapatite (nHAP) based ceramic nano-cement. The phytoconstituent profiling represented the optimized CQ fraction to be rich in osteogenic polyphenols and flavonoids like quercetin, resveratrol, and their glucosides. Further, CQ phytobioactives-based formulation was biocompatible, increased bone formation, calcium deposition, proliferation, and migration of cells with simultaneous alleviation of cellular oxidative stress. In the in vivo critical-sized bone defect model, enhanced formation of highly mineralized tissue (BV mm³) in CQ phytobioactives functionalized nano-cement (10.5 ± 2 mm³) were observed compared to the control group (6.5 ± 1.2 mm³). Moreover, the addition of CQ phytobioactives to the bone nano-cement increased the fractional bone volume (BV/TV%) to 21 ± 4.2% compared to 13.1 ± 2.5% in non-functionalized nano-cement. The results demonstrated nHAP-based nano-cement as a carrier for phytobioactives which could be a promising approach for neo-bone formation in different bone defect conditions.

Clindamycin-Loaded Nanosized Calcium Phosphates Powders as a Carrier of Active Substances

Bioactive calcium phosphate ceramics (CaPs) are one of the building components of the inorganic part of bones. Synthetic CaPs are frequently used as materials for filling bone defects in the form of pastes or composites; however, their porous structure allows modification with active substances and, thus, subsequent use as a drug carrier for the controlled release of active substances. In this study, four different ceramic powders were compared: commercial hydroxyapatite (HA), TCP, brushite, as well as HA obtained by wet precipitation methods. The ceramic powders were subjected to physicochemical analysis, including FTIR, XRD, and determination of Ca/P molar ratio or porosity. These techniques confirmed that the materials were phase-pure, and the molar ratios of calcium and phosphorus elements were in accordance with the literature. This confirmed the validity of the selected synthesis methods. CaPs were then modified with the antibiotic clindamycin. Drug release was determined on HPLC, and antimicrobial properties were tested against Staphylococcus aureus. The specific surface area of the ceramic has been demonstrated to be a factor in drug release efficiency.

Dynamic investigation of zein-based degradable and hemocompatible coatings for drug-eluting stents: a microfluidic approach

Biodegradable stent coatings have shown great potential in terms of delivering drugs to a damaged vessel wall, and their release profiles are key elements governing the overall performance of drug-eluting stents (DESs). However, release and degradation kinetics are usually not tested under simulated physiological conditions or in dynamic environments, both essential aspects in the design of novel DESs. To bridge this gap, fused silica-based microfluidic systems, with either round or square channel cross-sections, were designed to mimic the microenvironment of a stented vessel. In particular, we fabricated and characterized microfluidic chips based on customizable channels, which were spray-coated with a naturally-derived, rutin-loaded zein solution, to perform a comprehensive study under flow conditions. Dynamic assays after 6 hours showed how the degradation of the zein matrix was affected by the cross-sectional conformation (∼69% vs. ∼61%, square and round channel, respectively) and the simulated blood fluid components (∼55%, round channel with a more viscous solution). The released amount of rutin was ∼81% vs. ∼77% and ∼78% vs. ∼74% from the square and round channels, using the less and more viscous blood-simulated fluids, respectively. Fitting the drug release data to Korsmeyer-Peppas and first-order mathematical models provided further insight into the mechanism of rutin release and coating behavior under flowing conditions. More importantly, whole blood tests with our newly developed microfluidic platforms confirmed the hemocompatibility of our zein-based coating. In detail, in-flow and static studies on the blood cell behavior showed a significant reduction of platelet adhesion (∼73%) and activation (∼93%) compared to the stainless-steel substrate, confirming the benefits of using such naturally-derived coatings to avoid clogging. Overall, our microfluidic designs can provide a key practical tool for assessing polymer degradation and drug release from degradable matrices under flowing conditions, thus aiding future studies on the development of hemocompatible, controlled-release coatings for DESs.

Calcium phosphate bone cements as local drug delivery systems for bone cancer treatment

Bone cancer is usually a metastatic disease, affecting people of all ages. Its effective therapy requires a targeted drug administration locally at the cancer site so that the surrounding healthy organs and tissues stay unharmed. Upon a thorough literature search, a tremendous number of published articles are reporting on development of calcium phosphate cements (CPCs) for the treatment of a variety of diseases, such as osteoporosis, osteoarthritis, osteomyelitis, and other musculoskeletal disorders. However, just a limited number of research employs CPCs specifically for bone cancer treatment. In this review article, we study the factors influencing the local drug release from CPCs and particularly focus on bone cancer therapy. Finally, we locate the deficiencies in the literature regarding this specific topic and propose which other perspectives should be considered and discussed in future articles.

Formulation and In Vitro Evaluation of Mucoadhesive Sustained Release Gels of Phytoestrogen Diarylheptanoids from Curcuma comosa for Vaginal Delivery

Diarylheptanoids (DAs) characterized by a 1,7-diphenylheptane structural skeleton are considered a novel class of phytoestrogens. The DAs available in Curcuma comosa Roxb. (C. comosa) extract demonstrated significant estrogenic activities both in vitro and in vivo. This study aimed to develop and comprehensively evaluate a mucoadhesive vaginal gel for the sustained release of DAs. Different mucoadhesive polymers as gelling agents were investigated. C. comosa ethanolic crude extract was used as a source of DAs. All C. comosa gels were light brown homogeneous with pH within 4.4-4.6. Their flow behaviors were pseudoplastic with a flow behavior index of 0.18-0.38. The viscosity at a low shear rate varied from 6.2 to 335.4 Pa·s. Their mechanical and extrudability properties were associated well with rheological properties. Polycarbophil (PCP):hydroxypropyl methylcellulose (HPMC) blends had a higher mucoadhesiveness to porcine vaginal mucosa than those of PCP-based or HPMC-based gels. All C. comosa gels exhibited a sustained, zero-order DA release pattern over 72 h. Korsmeyer and Peppas equation fitting indicated a non-Fickian, case II transport release mechanism. C. comosa gels had good physical and chemical stability under low-temperature storage for up to 12 months. PCP:HPMC-based mucoadhesive gels could be a proper delivery system for vaginal administration of DAs.

3D printing of bioactive materials for drug delivery applications

INTRODUCTION

Three-dimensional (3D) printing, also known as additive manufacturing (AM), is a modern technique/technology, which makes it possible to construct 3D objects from computer-aided design (CAD) digital models. This technology can be used in the progress of drug delivery systems, where porosity has played important role in attaining an acceptable level of biocompatibility and biodegradability with improved therapeutic effects. 3D printing may also provide the user possibility to control the dosage of each ingredient in order to a specific purpose, and makes it probable to improve the formulation of drug delivery systems.

AREAS COVERED

This article covers the 3D printing technologies, bioactive materials including natural and synthetic polymers as well as some ceramics and minerals and their roles in drug delivery systems.

EXPERT OPINION

This technology is feasible to fabricate drug products by incorporating multiple drugs in different parts in such a mode that these drugs can release from the section at a predetermined rate. Furthermore, this 3D printing technology has the possible to transform personalized therapy to various age-groups by design flexibility and precise dosing. In recent years, the potential use of this technology can be realized in a clinical situation where patients will acquire individualized medicine as per their require.

Macrophage-targeted mannose-decorated PLGA-vegetable oil hybrid nanoparticles loaded with anti-inflammatory agents

This work pledge to extend the therapeutic windows of hybrid nanoparticulate systems by engineering mannose-decorated hybrid nanoparticles based on poly lactic-co-glycolic acid (PLGA) and vegetable oil for efficient delivery of two lipophilic anti-inflammatory therapeutics (Celecoxib-CL and Indomethacin-IMC) to macrophages. The mannose surface modification of nanoparticles is achieved via O-palmitoyl-mannose spacer during the emulsification and nanoparticles assembly process. The impact of targeting motif on the hydrodynamic features (R_H, PdI), stability (ζ-potential), drug encapsulation efficiency (DEE) is thoroughly investigated. Besides, the in vitro biocompatibility (MTT, LDH) and susceptibility of mannose-decorated formulations to macrophage as well their immunomodulatory activity (ELISA) are also evaluated. The monomodal distributed mannose-decorated nanoparticles are in the range of nanometric size (R_H < 115 nm) with PdI < 0.20 and good encapsulation efficiency (DEE = 46.15% for CL and 76.20% for IMC). The quantitative investigation of macrophage uptake shows a 2-fold increase in fluorescence (RFU) of cells treated with mannose-decorated formulations as compared to non-decorated ones (p < 0.001) suggesting an enhanced cell uptake respectively improved macrophage targeting while the results of ELISA experiments suggest the potential immunomodulatory properties of the designed mannose-decorated hybrid formulations.

Effect of Solvents, Stabilizers and the Concentration of Stabilizers on the Physical Properties of Poly(d,l-lactide-co-glycolide) Nanoparticles: Encapsulation, In Vitro Release of Indomethacin and Cytotoxicity against HepG2-Cell

A biocompatible, biodegradable and FDA-approved polymer [Poly lactic-co-glycolic acid (PLGA)] was used to prepare the nanoparticles (NPs) to observe the effect of solvents, stabilizers and their concentrations on the physical properties of the PLGA-NPs, following the encapsulation and in vitro release of Indomethacin (IND). PLGA-NPs were prepared by the single-emulsion solvent evaporation technique using dichloromethane (DCM)/chloroform as the organic phase with Polyvinyl-alcohol (PVA)/Polyvinylpyrrolidone (PVP) as stabilizers to encapsulate IND. The effects of different proportions of PVA/PVP with DCM/chloroform on the physiochemical properties (particle size, the polydispersity index, the zeta potential by Malvern Zetasizer and morphology by SEM) of the NPs were investigated. DSC was used to check the physical state, the possible complexation of PLGA with stabilizer(s) and the crystallinity of the encapsulated drug. Stabilizers at all concentrations produced spherical, regular-shaped, smooth-surfaced discrete NPs. Average size of 273.2–563.9 nm was obtained when PVA (stabilizer) with DCM, whereas it ranged from 317.6 to 588.1 nm with chloroform. The particle size was 273.2–563.9 nm when PVP was the stabilizer with DCM, while it was 381.4–466.6 nm with chloroform. The zeta potentials of PVA-stabilized NPs were low and negative (−0.62 mV) while they were comparatively higher and positive for PVP-stabilized NPs (+17.73 mV). Finally, drug-loaded optimal NPs were composed of PLGA (40 mg) and IND (4 mg) in 1 mL DCM/chloroform with PVA/PVP (1–3%), which resulted in sufficient encapsulation (54.94–74.86%) and drug loading (4.99–6.81%). No endothermic peak of PVA/PVP appeared in the optimized formulation, which indicated the amorphous state of IND in the core of the PLGA-NPs. The in vitro release study indicated a sustained release of IND (32.83–52.16%) from the PLGA-NPs till 72 h and primarily followed the Higuchi matrix release kinetics followed by Korsmeyer–Peppas models. The cell proliferation assay clearly established that the organic solvents used to prepare PLGA-NPs had evaporated. The PLGA-NPs did not show any particular toxicity in the HepG2 cells within the dose range of IND (250–500 µg/mL) and at an equivalent concentration of PLGA-NPs (3571.4–7142.7 µg/mL). The cytotoxicity of the hepatotoxic drug (IND) was reduced by its encapsulation into PLGA-NPs. The outcomes of this investigation could be implemented to prepare PLGA-NPs of acceptable properties for the encapsulation of low/high molecular weight drugs. It would be useful for further in vitro and in vivo applications to use this delivery system.

Ginger and Garlic Extracts Enhance Osteogenesis in 3D Printed Calcium Phosphate Bone Scaffolds with Bimodal Pore Distribution

Natural medicines have long been used to treat physiological ailments where both ginger (gingerol) and garlic (allicin) are key players in immune system promotion, reduction in blood pressure, and lowering inflammation response. With their efficacy in bone healing, these compounds have great value as medicinal additives in bone scaffolds for localized treatment to support tissue formation, along with providing their natural therapeutic benefits. Utilization of 3D-printed (3DP) bone tissue engineering scaffolds as drug delivery vehicles for ginger and garlic extracts enables patient specificity in bone defect applications with enhanced osseointegration. Our objective is to understand their combined efficacy on osteogenesis when released from 3DP calcium phosphate bone scaffolds designed with a bimodal pore distribution. With a porous core and dense exterior, the resulting scaffolds have good mechanical integrity with 10 ± 1 MPa compressive strengths. Results show that ginger + garlic extracts released from bone scaffolds enhance their osteogenic potential through on site drug delivery. Both compounds exhibit exponential drug release profiles which fit Weibull distribution equations. The release of ginger extract also increases osteoblast proliferation by 59%. Both compounds show decreased osteoclast resorption activity, with a greater than 20% reduction in pit area on sample surfaces. Ginger + garlic extract induces a twofold increase in early osteoid tissue formation in vivo at week 4, in addition to a 30% increase in total bone area and a 90% increase in osteocytes with respect to control 3DP tricalcium phosphate scaffolds. Late-stage bone healing at week 10 reveals healthy angiogenic tissue, a twofold higher bone mineralization, and significant enhancement of type I collagen formation in the presence of ginger and garlic extracts. Naturally sourced ginger and garlic extracts provide osteogenic promotion and improved bone tissue in-growth in a patient-specific 3DP scaffold biomedical device for low load-bearing bone tissue engineering and dental applications.

Effects of Vitamin A (Retinol) Release from Calcium Phosphate Matrices and Porous 3D Printed Scaffolds on Bone Cell Proliferation and Maturation

Vitamin A is a fat-soluble compound widely known for vision health. Highly variable reports on its effects on bone health have necessitated further research to truly understand its role on bone cell proliferation. Retinol, one bioactive form of vitamin A, is incorporated into synthetic bone graft scaffolds for low load-bearing clinical bone treatment. The objective of this work is to understand the effects of retinol on osteoblast and osteoclast cells when embedded within calcium phosphate matrices, including interconnected porous 3D printed tricalcium phosphate scaffolds. Results show that hydrophobic retinol can be released from bone scaffolds when a combination of biodegradable polymers, polycaprolactone and polyethylene glycol, are employed as drug carriers. The release of retinol in vitro can support a 20 ± 1% increase in osteoblast (bone-forming) cell proliferation with proper cell adhesion and filopodial extensions. Osteoclast cell morphology is necrosed and torn with a reduction in proliferation at approximately 6 ± 1% when retinol is present. In addition, inhibition of osteoclastic resorption pit bays is noted using scanning electron microscopy. With the scaffolds' round pore interconnectivity facilitating retinol release, this system can provide an alternative to traditional bone grafts while additionally supporting bone healing through enhanced osteoblast cell proliferation and inhibition of osteoclast resorption activity.

Real-Time Monitoring of Doxorubicin Release from Hybrid Nanoporous Anodic Alumina Structures

This work demonstrates an advanced approach to fabricate Hybrid nanoporous anodic alumina gradient-index filters (Hy-NAA-GIFs) through a heterogeneous anodization process combining sinusoidal current-density anodization and constant potential anodization. As a result, the hybrid structure obtained reveals a single photonic stopband (PSB), which falls within the absorption region of the drug molecule and the intensity of the spectrum that are far from such absorption range. The prepared structures were loaded with the doxorubicin (DOX) drug through the drop-casting method, which allows for evaluating the maximum reflectance of the relative height of the PSB with the average reflectance of the spectrum intensity. Thereafter, this property has been applied in a flow cell setup connected to a reflectance spectrophotometer where different drug-loaded samples were placed to study the behavior and kinetics of the drug release in real-time by varying two parameters, i.e., different pore length and flow rates. As such, obtained results were analyzed with a model that includes a sum of two inverted exponential decay functions with two different characteristic time releases. Overall, this study opens up several possibilities for the Hy-NAA-GIFs to study the drug kinetics from nanoporous structures.

Biological analysis of an innovative biodegradable antibiotic eluting bioactive glass/gypsum composite bone cement for treating experimental chronic MRSA osteomyelitis

A multi-barrier antibiotics loaded biodegradable composite bone cement for resolving chronic osteomyelitis has been studied to understand the physico-mechanical properties, drug loading/eluting efficiency, and different merits and demerits prior to clinical application. After successful induction of bone infection in 28 rabbits using methicillin-resistant Staphylococcus aureus (MRSA) strains, calcium sulfate/bioactive glass based composite cement was implanted in 12 defects to assess its performance over parenteral therapy with microscopic and radiological examination for 90 days. The composite cement revealed acceptable physico-mechanical properties and controlled drug elution kinetics. Furthermore, the antibiotics concentrations in bone up to 42 days were sufficient to kill MRSA without eliciting adverse drug reactions. The striking feature of platelets aggregation by composite cement could assist bone healing. The controlled degradation with simultaneous entrapment of composite cement within the osteoid tissues and complete repair of infected cortical defects (holes) in rabbit tibia at 6 weeks indicated the excellent anti-infective and osteoconductive properties of composite cement. Thus, the animal study demonstrated the superiority of composite over injectable antibiotic therapy based on infection resolution and bone regeneration. We thereby conclude that the composite cement can be effectively applied in the treatment of resistant cases of chronic osteomyelitis.

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Described the preparation method of multi-barrier CS/BG composite bone cement.

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Made by coating the antibiotics loaded porous BG granules with PLGA and α-CSH.

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Introduced antibiotics elution study in ideal immersion medium.

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Beneficial role of PLGA on drug release and activation of platelets by cement was explored.

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New cement showed great potential to repair bone infection and to hasten osteosynthesis.

Ion release from hydroxyapatite and substituted hydroxyapatites in different immersion liquids: in vitro experiments and theoretical modelling study

Multi-substituted hydroxyapatites (ms-HAPs) are currently gaining more consideration owing to their multifunctional properties and biomimetic structure, owning thus an enhanced biological potential in orthopaedic and dental applications. In this study, nano-hydroxyapatite (HAP) substituted with multiple cations (Sr2+, Mg2+ and Zn2+) for Ca2+ and anion ( Si O 4 4 - ) for P O 4 3 - and OH-, specifically HAPc-5%Sr and HAPc-10%Sr (where HAPc is HAP-1.5%Mg-0.2%Zn-0.2%Si), both lyophilized non-calcined and lyophilized calcined, were evaluated for their in vitro ions release. These nanomaterials were characterized by scanning electron microscopy, field emission-scanning electron microscopy and energy-dispersive X-ray, as well as by atomic force microscope images and by surface specific areas and porosity. Further, the release of cations and of phosphate anions were assessed from nano-HAP and ms-HAPs, both in water and in simulated body fluid, in static and simulated dynamic conditions, using inductively coupled plasma optical emission spectrometry. The release profiles were analysed and the influence of experimental conditions was determined for each of the six nanomaterials and for various periods of time. The pH of the samples soaked in the immersion liquids was also measured. The ion release mechanism was theoretically investigated using the Korsmeyer-Peppas model. The results indicated a mechanism principally based on diffusion and dissolution, with possible contribution of ion exchange. The surface of ms-HAP nanoparticles is more susceptible to dissolution into immersion liquids owing to the lattice strain provoked by simultaneous multi-substitution in HAP structure. According to the findings, it is rational to suggest that both materials HAPc-5%Sr and HAPc-10%Sr are bioactive and can be potential candidates in bone tissue regeneration.

Oral nanoparticles based on gellan gum/pectin for colon-targeted delivery of resveratrol

Nanoparticles based on gellan gum/pectin blends were designed for colon-targeted release of resveratrol (RES). Their impact on drug release rates and permeability were evaluated using Caco-2 cell model and mucus secreting triple co-culture model. Polymeric nanoparticles (PNP) were successfully prepared by nebulization/ionotropic gelation, achieving high drug loading (>80%). PNP were spherical with a low positive charge density (+5mV) and exhibited diameters of around 330 nm. Developed PNP were able to promote effective modulation of drug release rates, so that only 3% of RES was released in acidic media over 2 h, and, in pH 6.8, the drug was released in a sustained manner, reaching 85% in 30 h. The permeability of RES-loaded PNP in the Caco-2 model was 0.15%, while in the triple co-culture model, in the presence of mucus, it reached 5.5%. The everted gut sac experiment corroborated the low permeability of RES-loaded PNP in the presence or absence of mucus and highlighted their high ability to interact with the intestinal tissue. Results indicate that the novel PNP developed in this work are safe and promising carriers for controlled delivery of RES at the colon.

Amorphous calcium organophosphate nanoshells as potential carriers for drug delivery to Ca2+-enriched surfaces

Our amorphous calcium organophosphate nanoshells are prone to agglomerate and disassemble when Ca²⁺ ions are present in the solution and on surfaces. This have great implications for targeting and drug release in Ca-rich environments, such as bone.

Silicon-calcium phosphate ceramics and silicon-calcium phosphate cements: Substrates to customize the release of antibiotics according to the idiosyncrasies of the patient

Bone substitutes based on calcium phosphates can be classified in two major groups: ceramics and cements. Both are biomaterials with excellent biocompatibility that have been studied as local delivery systems for drugs. This study aims to evaluate drug-release kinetics in silicon beta-tricalcium phosphate ceramics (Si-β-TCP) and in silicon calcium phosphate cements (Si-CPCs). We want to investigate if the differences in composition and in structure of the Si-β-TCP and the Si-CPC may influence for drug loading and in its release kinetics from the biomaterial. The results obtained indicate that all drug-loaded materials were efficient to tailor drug release kinetics and inhibited the growth of Staphylococcus aureus. The cements prepared with high concentrations of silicon (80% Si-CPC) present zero-order release kinetics, independent of the drug concentration loaded. Si-β-TCP and Si-CPC offer a simple technology that could serve to personalize the delivery of bioactive molecules according to each patient's needs in the treatment of bone conditions, not only limited to prophylaxis, but also for the treatment of bone infection.

A Novel Phytantriol-Based Lyotropic Liquid Crystalline Gel for Efficient Ophthalmic Delivery of Pilocarpine Nitrate

The purpose of this paper was to investigate the potential of liquid crystalline (LC) gels for ophthalmic delivery, so as to enhance the bioavailability of pilocarpine nitrate (PN). The gels were prepared by a vortex method using phytantriol and water (in the ratio of 73:27 w/w). Their inner structures were confirmed by crossed polarized light microscopy, small-angle X-ray scattering, attenuated total reflectance-Fourier transform infrared spectrum, and rheology. The in vitro release studies revealed that PN could keep sustained release from the gels over a period of 12 h. The ex vivo apparent permeability coefficient of the gels demonstrated a 3.83-folds (P < 0.05) increase compared with that of eye drops. The corneal hydration levels of the gel maintained in the normal range of 79.46 ± 2.82%, hinting that the gel could be considered non-damaging and safe to the eyes. Furthermore, in vivo residence time evaluation suggested that a better retention performance of LC gel was observed in rabbit's eyes compared to eye drops. In vivo ocular irritation study indicated that LC gel was nonirritant and might be suitable for various eye applications. In conclusion, LC gels might represent a potential ophthalmic delivery strategy to overcome the limitations of eye drops.

Mechanical loading, an important factor in the evaluation of ion release from bone augmentation materials

The controlled release of therapeutic inorganic ions from biomaterials is an emerging area of international research. One of the foci for this research is the development of materials, which spatially and temporally modulate therapeutic release, via controlled degradation in the intended physiological environment. Crucially however, our understanding of the release kinetics for such systems remains limited, particularly with respect to the influence of physiological loading. Consequently, this study was designed to investigate the effect of dynamic mechanical loading on a composite material intended to stabilize, reinforce and strengthen vertebral bodies. The composite material contains a borate glass engineered to release strontium as a therapeutic inorganic ion at clinically relevant levels over extended time periods. It was observed that both cyclic (6 MPa 2 Hz) and static (4.3 MPa) compressive loading significantly increased the release of strontium ions in comparison to the static unloaded case. The observed alterations in ion release kinetics suggest that the mechanical loading of the implantation environment should be considered when evaluating the ion release kinetics.

Novel PEG-Modified Hybrid PLGA-Vegetable Oils Nanostructured Carriers for Improving Performances of Indomethacin Delivery

The purpose of this work was to more exhaustively study the influence of nanocarrier matrix composition and also the polyethylene glycol (PEG)-modified surface on the performances of formulations as lipophilic drug delivery systems. Poly (d,l-lactide-co-glycolide), two vegetable oils (Nigella sativa oil and Echium oil) and indomethacin were employed to prepare novel PEG-coated nanocarriers through emulsion solvent evaporation method. The surface modification was achieved by physical PEG adsorption (in the post-production step). Transmission electron microscopy (TEM) nanographs highlighted the core-shell structure of hybrid formulations while scanning electron microscopy (SEM) images showed no obvious morphological changes after PEG adsorption. Drug loading (DL) and entrapment efficiency (EE) varied from 4.6% to 16.4% and 28.7% to 61.4%, solely depending on the type of polymeric matrix. The oil dispersion within hybrid matrix determined a more amorphous structure, as was emphasized by differential scanning calorimetry (DSC) investigations. The release studies highlighted the oil effect upon the ability of nanocarrier to discharge in a more sustained manner the encapsulated drug. Among the kinetic models employed, the Weibull and Korsmeyer-Peppas models showed the better fit (R² = 0.999 and 0.981) with n < 0.43 indicating a Fickian type release pattern. According to cytotoxic assessment the PEG presence on the surface increased the cellular viability with ~1.5 times as compared to uncoated formulations.

Drug transport mechanisms and in vitro release kinetics of vancomycin encapsulated chitosan-alginate polyelectrolyte microparticles as a controlled drug delivery system

In this study, chitosan-alginate polyelectrolyte microparticles containing the antibiotic, vancomycin chloride were prepared using the ionotropic gelation (coacervation) technique. In vitro release and drug transport mechanisms were studied concerning the chitosan only and alginate only microparticles as a control group. Further, the effect of porosity on the drug transport mechanism was also studied for chitosan-alginate mixed particles produced by lyophilizing in contrast to the air-dried non-porous particles. According to the in vitro release data, alginate only and chitosan only microparticles showed burst release and prolonged release respectively. Chitosan-alginate lyophilized microparticles showed the best-controlled release of vancomycin with the average release of 22μg per day for 14days. Also, when increasing alginate concentration there was no increase in the release rate of vancomycin. The release data of all the microparticles were treated with Ritger-Peppas, Higuchi, Peppas-Sahlin, zero-order, and first-order kinetic models. The best fit was observed with Peppas-Sahlin model, indicating the drug transport mechanism was controlled by both Fickian diffusion and case II relaxations. Also, Fickian diffusion dominates the drug transport mechanism of all air-dried samples during the study period. However, the Fickian contribution was gradually reducing with time. Porosity significantly effects the drug transport mechanism as case II relaxation dominates after day 10 of the lyophilized microparticles.

3D Printing of Calcium Phosphate Ceramics for Bone Tissue Engineering and Drug Delivery

Additive manufacturing, also known as 3D printing, has emerged over the past 3 decades as a disruptive technology for rapid prototyping and manufacturing. Vat polymerization, powder bed fusion, material extrusion, and binder jetting are distinct technologies of additive manufacturing, which have been used in a wide variety of fields, including biomedical research and tissue engineering. The ability to print biocompatible, patient-specific geometries with controlled macro- and micro-pores, and to incorporate cells, drugs and proteins has made 3D-printing ideal for orthopaedic applications, such as bone grafting. Herein, we performed a systematic review examining the fabrication of calcium phosphate (CaP) ceramics by 3D printing, their biocompatibility in vitro, and their bone regenerative potential in vivo, as well as their use in localized delivery of bioactive molecules or cells. Understanding the advantages and limitations of the different 3D printing approaches, CaP materials, and bioactive additives through critical evaluation of in vitro and in vivo evidence of efficacy is essential for developing new classes of bone graft substitutes that can perform as well as autografts and allografts or even surpass the performance of these clinical standards.

Superparamagnetic iron-doped nanocrystalline apatite as a delivery system for doxorubicin

Iron-doped superparamagnetic apatite nanoparticles are promising materials for magnetic drug delivery systems due to their ability to strongly bind the anticancer doxorubicin and provide an active control over the drug release by using a low-frequency pulsed electromagnetic field.

Physicochemical properties affect the synthesis, controlled delivery, degradation and pharmacokinetics of inorganic nanoporous materials

Controlling size, shape and uniformity of porous constructs remains a major focus of the development of porous materials. Over the past two decades, we have seen significant developments in the fabrication of new, porous-ordered structures using a wide range of materials, resulting in properties well beyond their traditional use. Porous materials have been considered appealing, due to attractive properties such as pore size length, morphology and surface chemistry. Furthermore, their utilization within the life sciences and medicine has resulted in significant developments in pharmaceutics and medical diagnosis. This article focuses on various classes of porous materials, providing an overview of principle concepts with regard to design and fabrication, surface chemistry and loading and release kinetics. Furthermore, predictions from a multiscale mathematical model revealed the role pore length and diameter could have on payload release kinetics.

Phase stability and biological property evaluation of plasma sprayed hydroxyapatite coatings for orthopedic and dental applications

In this work we have investigated the effects of strontium (Sr) dopant on in vitro protein release kinetics and in vivo osteogenic properties of plasma sprayed hydroxyapatite (HA) coatings, along with their dissolution behavior. Plasma sprayed HA coatings are widely used in load-bearing implants. Apart from osseointegration, the new generation of HA coating is expected to deliver biomolecules and/or drugs that can induce osteoinduction. This paper reports the preparation of crystalline and amorphous HA coatings on commercially pure titanium (Cp-Ti) using inductively coupled radio frequency (RF) plasma spray, and their stability at different solution pH. Coatings prepared at 110 mm working distance from the nozzle showed an average Ca ion release of 18 and 90 ppm in neutral and acidic environments, respectively. Decreasing the working distance to 90 mm resulted in the formation of a coating with less crystalline HA and phases with higher solubility products, and consequently higher dissolution over 32 days. A 92% release of a model protein bovine serum albumin (BSA) in phosphate buffer with pH of 7.4 was measured for Sr-doped HA (Sr-HA) coating, while only a 72% release could be measured for pure HA coating. Distortion of BSA during adsorption on coatings revealed a strong interaction between the protein and the coating, with an increase in α-helix content. Osteoid formation was found on Sr-HA implants as early as 7 weeks post implantation compared to HA coated and uncoated Ti implants. After 12 weeks post implantation, osteoid new bone was formed on HA implants; whereas, bone mineralization started on Sr-HA samples. While no osteoid was formed on bare Ti surfaces, bone was completely mineralized on HA and Sr-HA coatings after 16 weeks post implantation. Our results show that both phase stability and chemistry can have a significant influence toward in vitro and in vivo response of HA coatings on Ti implants.

STUDY OF THE DIFFERENT RELEASE CHARACTERISTICS OF ANTIBIOTICS FROM PATIENTS: A DYNAMIC ELUTING SYSTEM TO INVESTIGATE DRUG RELEASE FROM ANTIBIOTIC-IMPREGNATED CALCIUM SULFATE DELIVERY

Background: Antibiotic-impregnated calcium sulfate delivery systems (ACDS) are commonly used to treat chronic osteomyelitis. Our research is to investigate drug release in vitro over a longer period, as a cautious predictor of in vivo release. Methods: The local release behavior of antibiotic in vitro was simulated. The consecutive dynamic eluting experiment was performed based on the pro-operative characteristic of osteomyelitis patients and the determined results of drug concentration in the human drainage tissue fluid (DTF). The concentration of each drug in the receiving solution was detected by ultra-performance liquid chromatography-tandem quadrupole detector mass spectrometry. The ACDS was reviewed by scanning electronic microscopy (SEM) after 48 h, and prepared to be eluted for another examination after 33 days. The mechanism of antibiotic release was analyzed by using the Ritger–Peppas and Weibull equations. Results: The cumulative release rate of vancomycin in a vancomycin-calcium sulfate delivery system (VCDS) was 77.50 % (3.0 mm diameter) and 72.43 % (4.8 mm diameter), while that of the tobramycin in a tobramycin-calcium sulfate delivery system (TCDS) was 88.0 % (3.0 mm diameter) and 84.55 % (4.8 mm diameter). At the 15th day, approximately 27.92% of vancomycin was and 29.35% of tobramycin was released from the local implant in vivo. Using SEM, numerous vancomycin and tobramycin particles were found to be attached to the columnar calcium sulfate crystals at the start of the experiment. The release behavior of the two antibiotics followed a combination of Fickian diffusion and Case II transport mechanisms within the first 48 h, and a Fickian diffusion mechanism during the subsequent time period. The correlation coefficient of tobramycin and vancomycin in vivo and in vitro was 0.9704–0.9949 and 0.9549–0.9782, respectively. Conclusion: A good correlation of the in vivo and in vitro cumulative release rates was observed by comparing the cumulative release rate of drugs in vitro by means of the dynamic eluting model, and in the DTF. Therefore, our study has proved that it is possible to use the dynamic eluting model as a cautious predictor of in vivo release.

Dual-setting brushite-silica gel cements

The current study describes a dual-mechanism-setting cement that combines a brushite-forming cement paste with a second inorganic silica-based precursor. Materials were obtained by pre-hydrolyzing tetraethyl orthosilicate (TEOS) under acidic conditions following the addition of a calcium phosphate cement (CPC) powder mixed of β-tricalcium phosphate and monocalcium phosphate. Cement setting occurred by a dissolution-precipitation process, while changes in pH during setting simultaneously initiated the condensation reaction of the hydrolyzed TEOS. This resulted in an interpenetrating phase composite material in which the macropores of the CPC were infiltrated by the microporous silica gel, leading to a higher density and a compressive strength ∼5-10 times higher than the CPC reference. This also altered the release of vancomycin as a model drug, whereby in contrast to the quantitative release from the CPC reference, 25% of the immobilized drug remained in the composite matrix. By varying the TEOS content in the composite, the cement phase composition could be controlled to form either brushite, anhydrous monetite or a biphasic mixture of both. The composites with the highest silicate content showed a cell proliferation similar to a hydroxyapatite reference with a significantly higher activity per cell. Surprisingly, the biological response did not seem to be attributed to the released silicate ions, but to the release of phosphate and the adsorption of magnesium ions from the cell culture medium.

Scavenging effect of Trolox released from brushite cements

In this study a brushite cement was doped with the chain-breaking antioxidant Trolox. The effect of the antioxidant on the physical properties of the cement was evaluated and the release of Trolox was monitored by UV spectroscopy. The ability of the Trolox set free to scavenge reactive oxygen species (ROS) released by macrophages was determined in vitro using a luminol-amplified chemiluminescence assay. Trolox did not modify the crystalline phases of the set cement, which mainly formed crystalline brushite after 7 days in humid conditions. The setting time, compressive strength and morphology of the cement also remained unaltered after the addition of the antioxidant. Trolox was slowly released from the cement following a non-Fickian transport mechanism and nearly 64% of the total amount was released after 3 days. Moreover, the capacity of Trolox to scavenge the ROS released by macrophages increased in a dose-dependent manner. Trolox-loaded cements are expected to reduce some of the first harmful effects of acute inflammation and can thus potentially protect the surrounding tissue during implantation of these as well as other materials used in conjunction.

Vancomycin containing PLLA/β-TCP controls experimental osteomyelitis in vivo

Background

Implant-related osteomyelitis (IRO) is recently controlled with local antibiotic delivery systems to overcome conventional therapy disadvantages. In vivo evaluation of such systems is however too little.

Questions/purposes

We asked whether vancomycin (V)-containing poly-l-lactic acid/β-tricalcium phosphate (PLLA/β-TCP) composites control experimental IRO and promote bone healing in vivo.

Methods

Fifty-six rats were distributed to five groups in this longitudinal controlled study. Experimental IRO was established at tibiae by injecting methicillin-resistant Staphylococcus aureus (MRSA) suspensions with titanium particles in 32 rats. Vancomycin-free PLLA/β-TCP composites were implanted into the normal and infected tibiae, whereas V-PLLA/β-TCP composites and coated (C)-V-PLLA/β-TCP composites were implanted into IRO sites. Sham-operated tibiae established the control group. Radiological and histological scores were quantified with microbiological findings on weeks 1 and 6.

Results

IRO is resolved in the CV- and the V-PLLA/β-TCP groups but not in the PLLA/β-TCP group. MRSA was not isolated in the CV- and the V-PLLA/β-TCP groups at all times whereas the bacteria were present in the PLLA/β-TCP group. Radiological signs secondary to infection are improved from 10.9 ± 0.9 to 3.0 ± 0.3 in the V-PLLA/β-TCP group but remained constant in the PLLA/β-TCP group. Histology scores are improved from 24.7 ± 6.5 to 17.6 ± 4.8 and from 27.6 ± 7.9 to 32.4 ± 8.9 in the CV-PLLA/β-TCP and the V-PLLA/β-TCP groups, respectively. New bone was formed in all the PLLA/β-TCP group at weeks 1 and 6.

Conclusions

CV- and V-PLLA/β-TCP composites controlled experimental IRO and promoted bone healing.

Clinical relevance

CV- and V-PLLA/β-TCP composites have the potential of controlling experimental IRO and promoting bone healing.

Real-time and in situ drug release monitoring from nanoporous implants under dynamic flow conditions by reflectometric interference spectroscopy

Herein, we present an innovative approach to monitoring in situ drug release under dynamic flow conditions from aluminum implants featuring nanoporous anodic alumina (NAA) covers used as a model of drug-releasing implants. In this method, reflectometric interference spectroscopy (RIfS) is used to monitor in real-time the diffusion of drug from these nanoporous implants. The release process is carried out in a microfluidic device, which makes it possible to analyze drug release under dynamic flow conditions with constant refreshing of eluting medium. This setup mimics the physiological conditions of biological milieu at the implant site inside the host body. The release of a model drug, indomethacin, is established by measuring the optical thickness change with time under four different flow rates (i.e. 0, 10, 30, and 50 μL min(-1)). The obtained data are fitted by a modified Higuchi model, confirming the diffusion-controlled release mechanism. The obtained release rate constants demonstrate that the drug release depends on the flow rate and the faster the flow rate the higher the drug release from the nanoporous covers. In particular, the rate constants increase from 2.23 ± 0.02 to 12.47 ± 0.04 μg min(-1/2) when the flow rate is increased from 10 to 50 μL min(-1), respectively. Therefore, this method provides more reliable and relevant information than conventional in vitro drug release methods performed under static conditions.

Calcium phosphate cements as drug delivery materials

Calcium phosphate cements are used as synthetic bone grafts, with several advantages, such as their osteoconductivity and injectability. Moreover, their low-temperature setting reaction and intrinsic porosity allow for the incorporation of drugs and active principles in the material. It is the aim of the present work to: a) provide an overview of the different approaches taken in the application of calcium phosphate cements for drug delivery in the skeletal system, and b) identify the most significant achievements. The drugs or active principles associated to calcium phosphate cements are classified in three groups, i) low molecular weight drugs; ii) high molecular weight biomolecules; and iii) ions.

Calcium phosphate ceramic systems in growth factor and drug delivery for bone tissue engineering: a review

Calcium phosphates (CaPs) are the most widely used bone substitutes in bone tissue engineering due to their compositional similarities to bone mineral and excellent biocompatibility. In recent years, CaPs, especially hydroxyapatite and tricalcium phosphate, have attracted significant interest in simultaneous use as bone substitute and drug delivery vehicle, adding a new dimension to their application. CaPs are more biocompatible than many other ceramic and inorganic nanoparticles. Their biocompatibility and variable stoichiometry, thus surface charge density, functionality, and dissolution properties, make them suitable for both drug and growth factor delivery. CaP matrices and scaffolds have been reported to act as delivery vehicles for growth factors and drugs in bone tissue engineering. Local drug delivery in musculoskeletal disorder treatments can address some of the critical issues more effectively and efficiently than the systemic delivery. CaPs are used as coatings on metallic implants, CaP cements, and custom designed scaffolds to treat musculoskeletal disorders. This review highlights some of the current drug and growth factor delivery approaches and critical issues using CaP particles, coatings, cements, and scaffolds towards orthopedic and dental applications.

Vancomycin containing PLLA/β-TCP controls MRSA in vitro

BACKGROUND

Osteomyelitis caused by Methicillin-resistant Staphylococcus aureus (MRSA) often requires surgery and prolonged systemic antibiotic treatment. Local antibiotic delivery systems of bioceramics or polymers have been developed to treat osteomyelitis. A disadvantage of biodegradable polymers is the initial burst of antibiotics into the environment; one advantage of bioceramics is its osteoconductivity. We therefore developed a vancomycin-containing poly-l-lactic acid/β-tricalcium phosphate (PLLA/β-TCP) composite to control antibiotic release and stimulate bone formation.

QUESTIONS/PURPOSES

We (1) characterized these composites, (2) assessed vancomycin release in inhibitory doses, and (3) determined whether they would permit cell adhesion, proliferation, and mineralization in vitro.

METHODS

We molded 250 vancomycin-containing (VC) and 125 vancomycin-free (VUC) composites using PLLA, β-TCP, and chloroform. One hundred twenty-five VC composites were further dip-coated with PLLA (CVC) to delay antibiotic release. Composites were characterized according to their pore structure, size, volume, density, and surface area. Vancomycin release and bioactivity were determined. Adhesion, proliferation, and mineralization were assessed for two and three replicates on Days 3 and 7 with mesenchymal stem (MSC) and Saos type 2 cells.

RESULTS

Pore size, volume, apparent density, and surface area of the CVC were 3.5 ± 1.9 μm, 0.005 ± 0.002 cm(3)/g, 1.18 g/cm(3) and 3.68 m(2)/g, respectively. CVC released 1.71 ± 0.13 mg (63.1%) and 2.49 ± 0.64 mg (91.9%) of its vancomycin on Day 1 and Week 6, respectively. MSC and Saos type 2 cells attached and proliferated on composites on Days 3 and 7.

CONCLUSIONS

Vancomycin-containing PLLA/β-TCP composites release antibiotics in inhibitory doses after dip coating and appeared biocompatible based on adhesion, proliferation, and mineralization.

CLINICAL RELEVANCE

Vancomycin-containing PLLA/β-TCP composites may be useful for controlling MRSA but will require in vivo confirmation.

β-TCP porous pellets as an orthopaedic drug delivery system: ibuprofen/carrier physicochemical interactions

Calcium phosphate bone substitute materials can be loaded with active substances for in situ, targeted drug administration. In this study, porous β-TCP pellets were investigated as an anti-inflammatory drug carrier. Porous β-TCP pellets were impregnated with an ethanolic solution of ibuprofen. The effects of contact time and concentration of ibuprofen solution on drug adsorption were studied. The ibuprofen adsorption equilibrium time was found to be one hour. The adsorption isotherms fitted to the Freundlich model, suggesting that the interaction between ibuprofen and β-TCP is weak. The physicochemical characterizations of loaded pellets confirmed that the reversible physisorption of ibuprofen on β-TCP pellets is due to Van der Waals forces, and this property was associated with the 100% ibuprofen release.

Functionalized Bridged Silsesquioxane-based Nanostructured Microspheres: Performance as Novel Drug-delivery Devices in Bone Tissue-related Applications

Two kinds of functionalized nanostructured hybrid microspheres, based on the bridged silsesquioxane family, were synthesized by employing the sol–gel method via self-assembly of two different organic–inorganic bridged monomers. The architecture reached at molecular level allowed the incorporation of acetylsalicylic acid (ASA) as an anti-inflammatory model drug. The ASA-functionalized microspheres were characterized as delivery devices in simulated body fluid (SBF). The release behaviors of the synthesized microspheres (Fickian or anomalous diffusion mechanisms) were shown to be dependent on the chemical nature of the bridged monomers employed to synthesize the hybrid materials. The functionalized microspheres were proposed as delivery systems into calcium phosphate cements (CPCs), in order to slow down the characteristic drug-delivery kinetics of this kind of bone tissue-related materials. The incorporation of the new functionalized microparticles into the CPCs represented a viable methodology to modify the ASA-release kinetics in comparison to a conventional CPC containing the drug dispersed into the solid phase. The ASA-delivery profiles obtained from the microsphere-loaded CPCs showed that 40–60% of drug can be released after 2 weeks of testing in SBF. The inclusion of the microspheres into the CPC matrices allowed modification of the release profiles through a mechanism that involved two stages: (1) the diffusion of the drug through the organic–inorganic matrix of the microspheres (according to a Fickian or anomalous diffusion, depending on the nanostructuring) and (2) the subsequent diffusion of the drug through the ceramic matrix of the hardened cements. The release behavior of the composite cements was shown to be dependent on the nanostructuring of the hybrid microspheres, which can be selectively tailored by choosing the desired chemical structure of the bridged precursors employed in the sol–gel synthesis. The obtained results demonstrated the ability of this new class of functionalized hybrid microdevices as delivery systems into calcium phosphate materials with potential bone tissue-related drug-delivery applications.