Gentamicin release from biodegradable poly-l-lactide based composites for novel intramedullary nails

An osteoinductive and biodegradable intramedullary implant accelerates bone healing and mitigates complications of bone transport in male rats

Bone transport is a surgery-driven procedure for the treatment of large bone defects. However, challenging complications include prolonged consolidation, docking site nonunion and pin tract infection. Here, we develop an osteoinductive and biodegradable intramedullary implant by a hybrid tissue engineering construct technique to enable sustained delivery of bone morphogenetic protein-2 as an adjunctive therapy. In a male rat bone transport model, the eluting bone morphogenetic protein-2 from the implants accelerates bone formation and remodeling, leading to early bony fusion as shown by imaging, mechanical testing, histological analysis, and microarray assays. Moreover, no pin tract infection but tight osseointegration are observed. In contrast, conventional treatments show higher proportion of docking site nonunion and pin tract infection. The findings of this study demonstrate that the novel intramedullary implant holds great promise for advancing bone transport techniques by promoting bone regeneration and reducing complications in the treatment of bone defects.

Functionalized Halloysite Nanotubes as Potential Drug Carriers

The aim of the work was to examine the possibility of using modified halloysite nanotubes as a gentamicin carrier and to determine the usefulness of the modification in terms of the effect on the amount of the drug attached, its release time, but also on the biocidal properties of the carriers. In order to fully examine the halloysite in terms of the possibility of gentamicin incorporating, a number of modifications of the native halloysite were carried out prior to gentamicin intercalation with the use of sodium alkali, sulfuric and phosphoric acids, curcumin and the process of delamination of nanotubes (expanded halloysite) with ammonium persulfate in sulfuric acid. Gentamicin was added to unmodified and modified halloysite in an amount corresponding to the cation exchange capacity of pure halloysite from the Polish Dunino deposit, which was the reference sample for all modified carriers. The obtained materials were tested to determine the effect of surface modification and their interaction with the introduced antibiotic on the biological activity of the carrier, kinetics of drug release, as well as on the antibacterial activity against Escherichia coli Gram-negative bacteria (reference strain). For all materials, structural changes were examined using infrared spectroscopy (FTIR) and X-ray diffraction (XRD); thermal differential scanning calorimetry with thermogravimetric analysis (DSC/TG) was performed as well. The samples were also observed for morphological changes after modification and drug activation by transmission electron microscopy (TEM). The conducted tests clearly show that all samples of halloysite intercalated with gentamicin showed high antibacterial activity, with the highest antibacterial activity for the sample modified with sodium hydroxide and intercalated with the drug. It was found that the type of halloysite surface modification has a significant effect on the amount of gentamicin intercalated and then released into the surrounding environment but does not significantly affect its ability to further influence drug release over time. The highest amount of drug released among all intercalated samples was recorded for halloysite modified with ammonium persulfate (real loading efficiency above 11%), for which high antibacterial activity was found after surface modification, before drug intercalation. It is also worth noting that intrinsic antibacterial activity was found for non-drug-intercalated materials after surface functionalization with phosphoric acid (V) and ammonium persulfate in the presence of sulfuric acid (V).

Review on Surface Treatment for Implant Infection via Gentamicin and Antibiotic Releasing Coatings

Surface treatment of metallic implants plays a crucial role in orthopedics and orthodontics. Metallic implants produce side-effects such as physical, chemical/electro-chemical irritations, oligodynamic/catalytic and carcinogenic effects. These effects cause bacterial infections and account for huge medical expenses. Treatment for these infections comprises repeated radical debridement, replacement of the implant device and intravenous or oral injection antibiotics. Infection is due to the presence of bacteria in the patient or the surrounding environment. The antibiotic-based medication prevents prophylaxis against bacterial colonization, which is an emphatic method that may otherwise be catastrophic to a patient. Therefore, preventive measures are essential. A coating process was developed with its drug infusion and effect opposing biofilms. Modification in the medical implant surface reduces the adhesion of bacterial and biofilms, the reason behind bacterial attachment. Other polymer-based and nanoparticle-based carriers are used to resolve implant infections. Therefore, using an implant coating is a better approach to prevent infection due to biofilm.

Antibacterial Poly(ε-CL)/Hydroxyapatite Electrospun Fibers Reinforced by Poly(ε-CL)-b-poly(ethylene phosphoric acid)

In bone surgery and orthopedics, bioresorbable materials can be helpful in bone repair and countering post-op infections. Explicit antibacterial activity, osteoinductive and osteoconductive effects are essential to achieving this objective. Nonwoven electrospun (ES) fibers are receiving the close attention of physicians as promising materials for wound dressing and tissue engineering; potentially, in high contrast with dense materials, ES mats hamper regeneration of the bone extracellular matrix to a lesser extent. The use of the compositions of inherently biodegradable polyesters (poly(ε-caprolactone) PCL, poly(lactoglycolide), etc.), calcium phosphates and antibiotics is highly prospective, but the task of forming ES fibers from such compositions is complicated by the incompatibility of the main organic and inorganic ingredients, polyesters and calcium phosphates. In the present research we report the synthesis of hydroxyapatite (HAp) nanoparticles with uniform morphology, and demonstrate high efficiency of the block copolymer of PCL and poly(ethylene phosphoric acid) (PEPA) as an efficient compatibilizer for PCL/HAp mixtures that are able to form ES fibers with improved mechanical characteristics. The materials obtained in the presence of vancomycin exhibited incremental drug release against Staphylococcus aureus (St. aureus).

Biodegradable intramedullary nail (BIN) with high-strength bioceramics for bone fracture

About 10 million fractures occur worldwide each year, of which more than 60% are long bone fractures. It is generally agreed that intramedullary nails have significant advantages in rigid fracture fixation. Metal intramedullary nails (INs) can provide strong support but a stress shielding effect can occur that results in nonunion healing in clinic. Nondegradable metals also need to be removed by a second operation. Could INs be biodegradable and used to overcome this issue? As current degradable biomaterials always suffer from low strength and cannot be used in Ins, herein, we report a novel device consisting of biodegradable IN (BIN) made for the first time with bioceramics. These BINs have an extremely high bending strength and stable internal and external structure. Experiments show that the BINs could not only fix and support the tibial fracture model, but also promote osteogenesis and affect the microenvironment of the bone marrow cavity. Therefore, they could be expected to replace traditional metal IN and become a more effective treatment option for tibial fractures.

Material modifications enhancing the antibacterial properties of two biodegradable poly(3-hydroxybutyrate) implants

The aim of this study was to evaluate the antimicrobial efficacy of adding a gentamicin palmitate (GP) coating and zirconium dioxide (ZrO₂) to biodegradable poly(3-hydroxybutyrate) (PHB) to reduce biofilm formation. Cylindrical pins with and without a coating were incubated in Müller-Hinton broth inoculated with 2 × 10⁵ colony-forming units (CFU) ml-1 of Staphylococcus aureus for 2 d or 7 d, then sonicated to disrupt biofilms. Pure PHB (PHB + GP) and PHB pins with ZrO₂ added (PHBzr + GP) were coated with GP and compared with PHB pins lacking a coating (PHB). Cells (CFU) were counted to quantify the number of bacteria in the biofilm and a cell proliferation assay was employed to evaluate metabolic activity, and scanning electron microscopy (SEM) was performed to visualize the structure of the biofilm. After 2 d of incubation there were significantly more cells in biofilms on PHB pins than PHB + GP and PHBzr + GP pins (p < 0.0001), and cells in the sonication fluid obtained from GP-coated pins exhibited significantly lower metabolic activity than cells from uncoated PHB pins (p < 0.0001). After 7 d of incubation metabolic activity was lowest for PHBzr + GP, with significant differences between PHB and PHBzr + GP (p = 0.001). SEM revealed more cells attached to the surface, and more structured biofilms, on pins without a coating. Coating pins with GP significantly reduced early biofilm formation on PHB implants. This could lower the potential risk of surgical site infections when using PHB implants. Addition of ZrO₂ might further enhance the antibacterial properties. Such modification of the implant material should therefore be considered when developing new biodegradable PHB implants.

Increased Staphylococcus aureus Biofilm Formation on Biodegradable Poly(3-Hydroxybutyrate)-Implants Compared with Conventional Orthopedic Implants: An In Vitro Analysis

OBJECTIVE

To compare the biofilm formation on a biodegradable material, poly(3-hydroxybutyrate) (PHB), with that on conventional titanium (Ti) and steel (St) implant material.

METHODS

Pins made of the different materials were incubated in Müller-Hinton broth inoculated with 2 × 10 colony-forming units (CFU)·mL of Staphylococcus aureus for 2 and 7 days and then sonicated for the disruption of the biofilms. CFU were counted to quantify the number of bacteria in the biofilm, and the cell proliferation assay 2,3-Bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H- tetrazolium-5-carboxanilid salt was used to evaluate their metabolic activity. Scanning electron microscopy visualized the structure of the biofilm.

RESULTS

We found a significantly higher metabolic activity and CFU count in the biofilm of PHB pins compared with St and Ti pins (analysis of variance, P < 0.0001). Scanning electron microscopy revealed structured biofilms on PHB pins already after 2 days of incubation, which was not observed on the other tested implants.

CONCLUSION

PHB implants seem to provide an environment that advantages the formation of biofilms of S. aureus, a common pathogen in implant-related infections. The amount of biofilm is higher on PHB implant compared with conventionally used orthopedic titanium and steel implants. To overcome the potential risk of surgical site infections linked to the clinical use of PHB implants, possible modifications of the material, increasing its antibacterial properties, need to be further investigated.

Burst Release of Antibiotics Combined with Long-Term Release of Silver Targeting Implant-Associated Infections: Design, Characterization and in vitro Evaluation of Novel Implant Hybrid Surface

Implant-associated infections represent a serious risk in human medicine and can lead to complications, revisions and in worst cases, amputations. To target these risks, the objective was to design a hybrid implant surface that allows a local burst release of antibiotics combined with long-term antimicrobial activity based on silver. The efficacy should be generated with simultaneous in vitro cytocompatibility. The investigations were performed on titanium K-wires and plates and gentamicin was selected as an illustrative antibiotic. A gentamicin depot (max 553 µg/cm2) was created on the surface using laser structuring. The antibiotic was released within 15 min in phosphate buffered saline (PBS) or agar medium. Metallic silver particles (4 µg/cm2) in a titanium dioxide layer were deposited using plasma vapor deposition (PVD). About 16% of the silver was released within 28 days in the agar medium. The local efficacy of the incorporated silver was demonstrated in a direct contact assay with a reduction of more than 99.99% (Escherichia coli). The local efficacy of the hybrid surface was confirmed in a zone of inhibition (ZOI) assay using Staphylococcus cohnii. The biocompatibility of the hybrid surface was proven using fibroblasts and osteoblasts as cell systems. The hybrid surface design seems to be promising as treatment of implant-associated infections, considering the achieved amount and release behavior of the active ingredients (gentamicin, silver). The generated in vitro results (efficacy, biocompatibility) proofed the concept. Further in vivo studies will be necessary translate the hybrid surface towards clinical applied research.

Formulation and characterization of a novel PHBV nanocomposite for bone defect filling and infection treatment

Biodegradable materials that combine bioactivity with sustained drug release have been proved promising for the treatment and prophylaxis of bone infection. In this work, injection-molded nanocomposites were formulated from poly(3-hydroxybutyrate-co-3-6%hydroxyvalerate) (PHBV), nanodiamond (nD) and nanohydroxyapatite (nHA) loaded with vancomycin (VC). The components were compounded using a rotary evaporator (PHBV/nHA/VC/nD-R) or a spray-dryer (PHBV/nHA/VC/nD-SD). The nanoparticles acted as a nucleating agent, increasing PHBV crystallinity from 57.1% to up to 73.3% (PHBV/nHA/VC/nD-SD). The nHA particles were found to be well distributed on the formulations fracture surface observed by SEM-EDS micrographs. PHBV/nHA/VC/nD-SD presented higher glass transition temperature (18.1 vs 14.8 °C) and stronger interface than PHBV/nHA/VC/nD-R, as determined by dynamic mechanical analysis (DMA). Furthermore, the incorporation of nanoparticles increased PHBV flexural elastic modulus by 34% and match the reported for human bone. Both systems were able to present a sustained release of VC for 22 days, reaching 7.1 ± 1.3%(PHBV/nHA/VC/nD-R) and 4.8 ± 0.6% (PHBV/nHA/VC/nD-SD). VC presented antibacterial activity even after being processed at 178 °C in an injection molding machine. Moreover, in vitro assays showed a good adhesion and growth of cells on the specimens and suggested a non-cytotoxic and non-cytostatic behavior. These findings indicate that these systems can be further explored as bone defect filling material.

Drug Delivery From Polymer-Based Nanopharmaceuticals-An Experimental Study Complemented by Simulations of Selected Diffusion Processes

The success of medical therapy depends on the correct amount and the appropriate delivery of the required drugs for treatment. By using biodegradable polymers a drug delivery over a time span of weeks or even months is made possible. This opens up a variety of strategies for better medication. The drug is embedded in a biodegradable polymer (the "carrier") and injected in a particular position of the human body. As a consequence of the interplay between the diffusion process and the degrading polymer the drug is released in a controlled manner. In this work we study the controlled release of medication experimentally by measuring the delivered amount of drug within a cylindrical shell over a long time interval into the body fluid. Moreover, a simple continuum model of the Fickean type is initially proposed and solved in closed-form. It is used for simulating some of the observed release processes for this type of carrier and takes the geometry of the drug container explicitly into account. By comparing the measurement data and the model predictions diffusion coefficients are obtained. It turns out that within this simple model the coefficients change over time. This contradicts the idea that diffusion coefficients are constants independent of the considered geometry. The model is therefore extended by taking an additional absorption term into account leading to a concentration dependent diffusion coefficient. This could now be used for further predictions of drug release in carriers of different shape. For a better understanding of the complex diffusion and degradation phenomena the underlying physics is discussed in detail and even more sophisticated models involving different degradation and mass transport phenomena are proposed for future work and study.

Biodegradable intramedullary nails reinforced with carbon and alginate fibers: In vitro and in vivo biocompatibility

BACKGROUND

Commonly, intramedullary nails are made of nondegradable materials, and hence they need to be removed once the bone fracture is healed. We propose a novel composite material consisting of poly-L-lactide matrix modified with carbon and alginate fibers to be used for biodegradable intramedullary fixation. The aim of this study was to make in vitro and in vivo biocompatibility assessments.

METHODS

In the in vitro conditions, biocompatibility of biomaterials was compared using normal human osteoblasts. After 3 and 7 days, cytotoxicity, viability and proliferation tests were performed, as well as cell morphology and adhesion observations. In the in vivo experiments, Californian rabbits (approx. 9 months old) were used. The composite nails and controls (Kirschner wires) were used for fixation of distal femoral osteotomy. The evaluation was made on the basis of clinical observations, radiographs taken after 2, 4, 6 and 8 weeks post implantation, and macroscopic and histological observations.

RESULTS

Cell tests indicated that both modifiers had a positive influence on cell viability. Biodegradable composite nails led to bony union when used for fixation of distal diaphysis osteotomy in rabbits. Histological analysis showed that the initial focal necrosis should be fully compensated for by the osteoblast proliferation and trabeculae formation.

CONCLUSIONS

Both in vitro and in vivo tests confirmed biocompatibility and potential applicability of novel biodegradable intramedullary nails modified with long carbon and alginate fibers for osteosynthesis of bone epiphysis.

Bi-directional controlled release of ibuprofen and Mg(2+) from magnesium alloys coated by multifunctional composite

Two major problems for magnesium alloy implant are the high degradation rate and easy infection associated with implantation. Herein, a surface drug delivery system (Mg/Epoxy resin-ZnO/PCL-Ibuprofen) which can realize bi-directional controlled release of ibuprofen and Mg(2+) was designed via a dip coating process followed by spraying. The in vitro test demonstrated that the ibuprofen in drug-eluting compound material showed sustained release profiles for 22days, which can effectively solve the local cellular rejection and inflammation during the early stage of implantation. Besides, the drug carrier also exhibited improved corrosion resistance duel to the high combining strength between Epoxy resin-ZnO coating and magnesium alloy, so Mg(2+) can release slowly at first and then speeded up later. This approach may be suitable for coating other implant materials such as stainless steel, titanium alloy etc.