Antimicrobial biocompatible bioscaffolds for orthopaedic implants

A Sr@Ag-based spatiotemporal and step-release scaffold against chronic osteomyelitis, fabricated by coaxial 3D-printing

Chronic osteomyelitis (OM) represents a severe and persistent infectious bone disease. Effective treatment requires controlled anti-inflammatory releases and bone regeneration across disease phases. A Sr@Ag-based scaffold was successfully printed, featuring micron-scale coaxial fibers containing Ag-doped hydroxyapatite (HA) in the outer layer of PLLA and Sr-doped HA in the inner layer of PLLA, facilitating the spatiotemporal and sequential release of Ag and Sr ions during OM treatment. Most antibacterial agent (Ag) was released during the first 20 days, followed by a slow-release plateau over the next 40 days in phosphate-buffered saline solution (PBS). Meanwhile, the pro-angiogenic agent (Sr) was released in minimal amounts during the initial 20 days, followed by a rapid and considerable release in the following 40 days. The coaxial design effectively inhibited the growth of Staphylococcus aureus and Escherichia coli while preserving the viability of bone cells. The ion-based scaffold exhibited broad-spectrum antibacterial effects and enhanced bone-regenerating gene expression in a complex air-bacteria environment. The Sr@Ag-based coaxial scaffold demonstrated effective antibacterial activity during the early stage and exhibited excellent non-toxic bone regeneration results during the middle and late stages in vivo. This work offered a promising treatment strategy through sequential anti-inflammatory and pro-osteogenic effects for infectious bone-defect diseases.

Assessing Antimicrobial Efficacy on Plastics and Other Non-Porous Surfaces: A Closer Look at Studies Using the ISO 22196:2011 Standard

The survival and spread of foodborne and nosocomial-associated bacteria through high-touch surfaces or contamination-prone sites, in either healthcare, domestic or food industry settings, are not always prevented by the employment of sanitary hygiene protocols. Antimicrobial surface coatings have emerged as a solution to eradicate pathogenic bacteria and prevent future infections and even outbreaks. Standardised antimicrobial testing methods play a crucial role in validating the effectiveness of these materials and enabling their application in real-life settings, providing reliable results that allow for comparison between antimicrobial surfaces while assuring end-use product safety. This review provides an insight into the studies using ISO 22196, which is considered the gold standard for antimicrobial surface coatings and examines the current state of the art in antimicrobial testing methods. It primarily focuses on identifying pitfalls and how even small variations in methods can lead to different results, affecting the assessment of the antimicrobial activity of a particular product.

Novel dalbavancin-PLLA implant coating prevents hematogenous Staphylococcus aureus infection in a minimally invasive mouse tail vein model

Infective/bacterial endocarditis is a rare but life-threatening disease with a hospital mortality rate of 22.7% and a 1-year mortality rate of 40%. Therefore, continued research efforts to develop efficient anti-infective implant materials are of the utmost importance. Equally important is the development of test systems that allow the performance of new materials to be comprehensively evaluated. In this study, a novel antibacterial coating based on dalbavancin was tested in comparison to rifampicin/minocycline, and the suitability of a recently developed mouse tail vein model for testing the implant coatings was validated. Small polymeric stent grafts coated with a poly-L-lactic acid (PLLA) layer and incorporated antibiotics were colonized with Staphylococcus (S.) aureus before implantation into the tail vein of mice. The main assessment criteria were the hematogenous spread of the bacteria and the local tissue reaction to the contaminated implant. For this purpose, colony-forming units (CFU) in the blood, spleen and kidneys were determined. Tail cross sections were prepared for histological analysis, and plasma cytokine levels and expression values of inflammation-associated genes were examined. Both antibiotic coatings performed excellently, preventing the onset of infection. The present study expands the range of available methods for testing the anti-infectivity of cardiovascular implants, and the spectrum of agents for effective surface coating.

Unprecedented Biodegradable Cellulose-Derived Polyesters with Pendant Citronellol Moieties: From Monomer Synthesis to Enzymatic Degradation

Levoglucosenone (LGO) is a cellulose-derived molecule that is present commercially on a multi-ton/year scale. Taking advantage of the α,β-conjugated ketone of LGO, a new citronellol-containing 5-membered lactone (HBO-citro) was synthesized through a one-pot two-step pathway involving oxa-Michael addition and Baeyer-Villiger oxidation. The solvent-free treatment of HBO-citro with NaBH4 at room temperature led to the full reduction of the lactone moiety which gave a novel fully renewable triol monomer having a citronellol side chain (Triol-citro). Noticeably, by simply changing the reducing agent, temperature and reaction duration, the partial reduction of HBO-citro can be achieved to yield a mixture of 5- and 6-membered Lactol-citro molecules. Triol-citro was chosen to prepare functional renewable polyesters having citronellol pendant chains via polycondensation reactions with diacyl chlorides having different chain lengths. Good thermal stability (Td5% up to 170 °C) and low glass transition temperatures (as low as -42 °C) were registered for the polyesters obtained. The polymers were then hydrolyzed using a commercial lipase from Thermomyces lanuginosus (Lipopan® 50 BG) to assess their biodegradability. A higher degradation profile was found for the polyesters prepared using co-monomers (acyl chlorides) having longer chain lengths. This is likely due to the decreased steric hindrance around the ester bonds which allowed enhanced accessibility of the enzyme.

Current standards and ethical landscape of engineered tissues-3D bioprinting perspective

Tissue engineering is an evolving multi-disciplinary field with cutting-edge technologies and innovative scientific perceptions that promise functional regeneration of damaged tissues/organs. Tissue engineered medical products (TEMPs) are biomaterial-cell products or a cell-drug combination which is injected, implanted or topically applied in the course of a therapeutic or diagnostic procedure. Current tissue engineering strategies aim at 3D printing/bioprinting that uses cells and polymers to construct living tissues/organs in a layer-by-layer fashion with high 3D precision. However, unlike conventional drugs or therapeutics, TEMPs and 3D bioprinted tissues are novel therapeutics and need different regulatory protocols for clinical trials and commercialization processes. Therefore, it is essential to understand the complexity of raw materials, cellular components, and manufacturing procedures to establish standards that can help to translate these products from bench to bedside. These complexities are reflected in the regulations and standards that are globally in practice to prevent any compromise or undue risks to patients. This review comprehensively describes the current legislations, standards for TEMPs with a special emphasis on 3D bioprinted tissues. Based on these overviews, challenges in the clinical translation of TEMPs & 3D bioprinted tissues/organs along with their ethical concerns and future perspectives are discussed.

Chitosan-calcium phosphate composite scaffolds for control of post-operative osteomyelitis: Fabrication, characterization, and in vitro-in vivo evaluation

Osteomyelitis is a progressive inflammatory disease requiring prolonged systemic treatment with high antibiotic doses, and is very challenging to be treated. The use of locally applied antibiotics loaded on a biodegradable carrier at surgery sites is hypothesized to prevent post-operative osteomyelitis, while providing site-specific drug release. In this work, chitosan-based calcium phosphate composites were prepared and loaded with moxifloxacin hydrochloride. The in-situ formation of calcium phosphates within the composite was experimentally confirmed by Fourier transform infra-red spectroscopy, X-ray powder diffraction, and scanning electron microscopy. Results showed that the composites provided complete drug release over three days, and the selected composite formulation induced differentiation and proliferation of osteoblasts, while reducing bacterial count, inflammation and intra-medullary fibrosis in bone tissue specimens of osteomyelitis-induced animal model. Hence, we can conclude that the in situ prepared antibiotic-loaded calcium phosphate chitosan composite is promising in preventing post-operative osteomyelitis, and is worthy of clinical experimentation.

Gentamicin-loaded silk/nanosilver composite scaffolds for MRSA-induced chronic osteomyelitis

Methicillin-resistant Staphylococcus aureus (MRSA) often induces chronic osteomyelitis and then bone defects. Here, gentamicin-loaded silk/nanosilver composite scaffolds were developed to treat MRSA-induced chronic osteomyelitis. AgNO3 was reduced with silk as a reducing agent in formic acid, forming silver nanoparticles in situ that were distributed uniformly in the composite scaffolds. Superior antibacterial properties against MRSA were achieved for the composite scaffolds, without the compromise of osteogenesis capacity. Then gentamicin was loaded on the scaffolds for better treatment of osteomyelitis. In vivo results showed effective inhibition of the growth of MRSA bacteria, confirming the promising future in the treatment of chronic osteomyelitis.

Clinical Applications of Bone Tissue Engineering in Orthopedic Trauma

Purpose of Review

Orthopaedic trauma is a major cause of morbidity and mortality worldwide. Although many fractures tend to heal if treated appropriately either by nonoperative or operative methods, delayed or failed healing, as well as infections, can lead to devastating complications. Tissue engineering is an exciting, emerging field with much scientific and clinical relevance in potentially overcoming the current limitations in the treatment of orthopaedic injuries.

Recent Findings

While direct translation of bone tissue engineering technologies to clinical use remains challenging, considerable research has been done in studying how cells, scaffolds, and signals may be used to enhance acute fracture healing and to address the problematic scenarios of nonunion and critical-sized bone defects. Taken together, the research findings suggest that tissue engineering may be considered to stimulate angiogenesis and osteogenesis, to modulate the immune response to fractures, to improve the biocompatibility of implants, to prevent or combat infection, and to fill large gaps created by traumatic bone loss. The abundance of preclinical data supports the high potential of bone tissue engineering for clinical application, although a number of barriers to translation must first be overcome.

Summary

This review focuses on the current and potential applications of bone tissue engineering approaches in orthopaedic trauma with specific attention paid to acute fracture healing, nonunion, and critical-sized bone defects.

Critical physiological factors influencing the outcome of antimicrobial testing according to ISO 22196 / JIS Z 2801

Bactericidal materials gained interest in the health care sector as they are capable of preventing material surfaces from microbial colonization and subsequent spread of infections. However, commercialization of antimicrobial materials requires proof of their efficacy, which is usually done using in vitro methods. The ISO 22196 standard (Japanese test method JIS Z 2801) is a method for measuring the antibacterial activity of daily goods. As it was found reliable for testing the biocidal activity of antimicrobially active materials and surface coatings most of the laboratories participating in this study used this protocol. Therefore, a round robin test for evaluating antimicrobially active biomaterials had to be established. To our knowledge, this is the first report on inaugurating a round robin test for the ISO 22196 / JIS Z 2801. The first round of testing showed that analyses in the different laboratories yielded different results, especially for materials with intermediate antibacterial effects distinctly different efficacies were noted. Scrutinizing the protocols used by the different participants and identifying the factors influencing the test outcomes the approach was unified. Four critical factors influencing the outcome of antibacterial testing were identified in a series of experiments: (1) incubation time, (2) bacteria starting concentration, (3) physiological state of bacteria (stationary or exponential phase of growth), and (4) nutrient concentration. To our knowledge, this is the first time these parameters have been analyzed for their effect on the outcome of testing according to ISO 22196 / JIS Z 2801. In conclusion, to enable assessment of the results obtained it is necessary to evaluate these single parameters in the test protocol carefully. Furthermore, uniform and robust definitions of the terms antibacterial efficacy / activity, bacteriostatic effects, and bactericidal action need to be agreed upon to simplify communication of results and also regulate expectations regarding antimicrobial tests, outcomes, and materials.

Recent coating developments for combination devices in orthopedic and dental applications: A literature review

Orthopedic and dental implants have been used successfully for decades to replace or repair missing or damaged bones, joints, and teeth, thereby restoring patient function subsequent to disease or injury. However, although device success rates are generally high, patient outcomes are sometimes compromised due to device-related problems such as insufficient integration, local tissue inflammation, and infection. Many different types of surface coatings have been developed to address these shortcomings, including those that incorporate therapeutic agents to provide localized delivery to the surgical site. While these coatings hold enormous potential for improving device function, the list of requirements that an ideal combination coating must fulfill is extensive, and no single coating system today simultaneously addresses all of the criteria. Some of the primary challenges related to current coatings are non-optimal release kinetics, which most often are too rapid, the potential for inducing antibiotic resistance in target organisms, high susceptibility to mechanical abrasion and delamination, toxicity, difficult and expensive regulatory approval pathways, and high manufacturing costs. This review provides a survey of the most recent developments in the field, i.e., those published in the last 2-3years, with a particular focus on technologies that have potential for overcoming the most significant challenges facing therapeutically-loaded coatings. It is concluded that the ideal coating remains an unrealized target, but that advances in the field and emerging technologies are bringing it closer to reality. The significant amount of research currently being conducted in the field provides a level of optimism that many functional combination coatings will ultimately transition into clinical practice, significantly improving patient outcomes.

An effective treatment of experimental osteomyelitis using the antimicrobial titanium/silver-containing nHP66 (nano-hydroxyapatite/polyamide-66) nanoscaffold biomaterials

Effective treatment of osteomyelitis remains a formidable clinical challenge. The rapid emergence of multidrug-resistant bacteria has renewed interest in developing antimicrobial biomaterials using antiseptic silver ions to treat osteomyelitis. However, inadequate local retention and severe cytotoxic effects have limited the clinical use of ionic silver for bone grafts. We recently developed novel porous nano-hydroxyapatite/polyamide 66 (nHP66)-based nanoscaffold materials containing varied concentrations of silver ions (Ag⁺) (TA-nHAPA66) and oxidized titanium (TiO₂), which was added as a second binary element to enhance antibacterial activity and biocompatibility. In this study, we establish a large cohort of rabbit model of experimental osteomyelitis and investigate the in vivo antimicrobial and therapeutic effects of TA-nHP66 biomaterials and their in vivo silver release kinetics. We find the TA-nHP66 scaffolds exhibit potent antibacterial activities against E. coli and S. aureus, support cell adhesion and cell proliferation of pre-osteoblasts, and stimulate osteogenic regulator/marker expression. Moreover, the TA2-nHP66 scaffold exerts potent antibacterial/anti-inflammation effects in vivo and promotes bone formation at the lesion site of osteomyelitis. We further demonstrate that TA2-nHP66 exhibits excellent biosafety profile without apparent systemic toxicities. Therefore, the TA-nHP66 scaffold biomaterials may be further explored as an effective adjuvant therapy for infected bone defects and/or osteomyelitis debridement.

Plasmon-Enhanced Photocleaving Dynamics in Colloidal MicroRNA-Functionalized Silver Nanoparticles Monitored with Second Harmonic Generation

The photocleaving dynamics of colloidal microRNA-functionalized nanoparticles are studied using time-dependent second harmonic generation (SHG) measurements. Model drug-delivery systems composed of oligonucleotides attached to either silver nanoparticles or polystyrene nanoparticles using a nitrobenzyl photocleavable linker are prepared and characterized. The photoactivated controlled release is observed to be most efficient on resonance at 365 nm irradiation, with pseudo-first-order rate constants that are linearly proportional to irradiation powers. Additionally, silver nanoparticles show a 6-fold plasmon enhancement in photocleaving efficiency over corresponding polystyrene nanoparticle rates, while our previous measurements on gold nanoparticles show a 2-fold plasmon enhancement compared to polystyrene nanoparticles. Characterizations including extinction spectroscopy, electrophoretic mobility, and fluorimetry measurements confirm the analysis from the SHG results. The real-time SHG measurements are shown to be a highly sensitive method for investigating plasmon-enhanced photocleaving dynamics in model drug delivery systems.

Titania nanotubes for orchestrating osteogenesis at the bone-implant interface

Titanium implants can fail due to inappropriate biomechanics at the bone-implant interface that leads to suboptimal osseointegration. Titania nanotubes (TNTs) fabricated on Ti implants by the electrochemical process have emerged as a promising modification strategy to facilitate osseointegration. TNTs enable augmentation of bone cell functions at the bone-implant interface and can be tailored to incorporate multiple functionalities including the loading of active biomolecules into the nanotubes to target anabolic processes in bone conditions such as osteoporotic fractures. Advanced functions can be introduced, including biopolymers, nanoparticles and electrical stimulation to release growth factors in a desired manner. This review describes the application of TNTs for enhancing osteogenesis at the bone-implant interface, as an alternative approach to systemic delivery of therapeutic agents.

Nanostructured platforms for the sustained and local delivery of antibiotics in the treatment of osteomyelitis

This article provides a critical view of the current state of the development of nanoparticulate and other solid-state carriers for the local delivery of antibiotics in the treatment of osteomyelitis. Mentioned are the downsides of traditional means for treating bone infection, which involve systemic administration of antibiotics and surgical debridement, along with the rather imperfect local delivery options currently available in the clinic. Envisaged are more sophisticated carriers for the local and sustained delivery of antimicrobials, including bioresorbable polymeric, collagenous, liquid crystalline, and bioglass- and nanotube-based carriers, as well as those composed of calcium phosphate, the mineral component of bone and teeth. A special emphasis is placed on composite multifunctional antibiotic carriers of a nanoparticulate nature and on their ability to induce osteogenesis of hard tissues demineralized due to disease. An ideal carrier of this type would prevent the long-term, repetitive, and systemic administration of antibiotics and either minimize or completely eliminate the need for surgical debridement of necrotic tissue. Potential problems faced by even hypothetically "perfect" antibiotic delivery vehicles are mentioned too, including (i) intracellular bacterial colonies involved in recurrent, chronic osteomyelitis; (ii) the need for mechanical and release properties to be adjusted to the area of surgical placement; (iii) different environments in which in vitro and in vivo testings are carried out; (iv) unpredictable synergies between drug delivery system components; and (v) experimental sensitivity issues entailing the increasing subtlety of the design of nanoplatforms for the controlled delivery of therapeutics.

Photoactivated miR-148b-nanoparticle conjugates improve closure of critical size mouse calvarial defects

Inducible systems providing temporal control of differentiation have the potential to improve outcomes in surgical reconstruction and regenerative medicine by precise modulation of wound healing and tissue repair processes. The aim of this study was to demonstrate that nanoformulated microRNA (miRNA) conjugates activated via photo exposure can lead to the induced osteogenic differentiation of human adipose-derived stromal/stem cells (hASCs) in vivo. The conjugate PC-miR-148b-SNP, a mimic of miRNA-148b tethered to silver nanoparticles (SNPs) via a photolabile linker, was used to modulate gene expression for improved closure of a critical size defect drilled on the right parietal bone of male CD-1 nude homozygous mice. The PC-miR-148b-SNP conjugates added to hASCs and loaded to either Matrigel or polycaprolactone (PCL) scaffolds resulted in different levels of healing of the defect. After 4 and 12weeks, 3-D micro-computed tomography reconstructed images indicate statistically significant defect closure from 3.83±1.19% to 5.46±2.01% and 6.54±4.28% to 32.53±8.3% for non-photoactivated and photoactivated conjugates, respectively, in the PCL scaffolds. The results were confirmed with H&E and Masson's Trichrome stains in the transverse sections of photoactivated conjugates. Collagen fiber staining was greatest at 12weeks when it reached approximately the same density and thickness as the native calvarium. This technology provides a platform that can be used with other miRNAs that actively govern the pathways responsible for regenerative and wound healing processes.

In vitro and in vivo characterization of pentaerythritol triacrylate-co-trimethylolpropane nanocomposite scaffolds as potential bone augments and grafts

A thiol-acrylate-based copolymer synthesized via an amine-catalyzed Michael addition was studied in vitro and in vivo to assess its potential as an in situ polymerizing graft or augment in bone defect repair. The blends of hydroxyapatite (HA) with pentaerythritol triacrylate-co-trimethylolpropane (PETA), cast as solids or gas foamed as porous scaffolds, were evaluated in an effort to create a biodegradable osteogenic material for use as a bone-void-filling augment. Osteogenesis experiments were conducted with human adipose-derived mesenchymal stromal cells (hASCs) to determine the ability of the material to serve as an osteoinductive substrate. Poly(ɛ-caprolactone) (PCL) composites PCL:HA (80:20) (wt/wt%) served as the control scaffold, while the experimental scaffolds included PETA:HA (100:0), (85:15), (80:20), and (75:25) composites (wt/wt%). The results indicate that PETA:HA (80:20) foam composites had higher mechanical strength than the corresponding porous PCL:HA (80:20) scaffolds made by thermo-precipitation method, and in the case of foamed composites, increasing HA content directly correlated with increased yield strength. For cytotoxicity and osteogenesis experiments, hASCs cultured for 21 days on PETA:HA scaffolds in stromal medium displayed the greatest number of live cells compared with PCL:HA composites. Moreover, hASCs cultured on foamed PETA:HA (80:20) scaffolds resulted in the greatest mineralization, increased alkaline phosphatase (ALP) expression, and the highest osteocalcin (OCN) expression after 21 days. Overall, the PETA:HA (80:20) and PETA:HA (85:15) scaffolds, with 66.38% and 72.02% porosity, respectively, had higher mechanical strength and cytocompatibility compared with the PCL:HA control. The results of the 6-week in vivo biocompatibility study using a posterior lumbar spinal fusion model demonstrate that PETA:HA can be foamed in vivo without serious adverse effects at the surgical site. Additionally, it was demonstrated that cells migrate into the interconnected pore volume and are found within centers of ossification.

Simultaneous bactericidal and osteogenic effect of nanoparticulate calcium phosphate powders loaded with clindamycin on osteoblasts infected with Staphylococcus aureus

Staphylococcus aureus internalized by bone cells and shielded from the immune system provides a reservoir of bacteria in recurring osteomyelitis. Its targeting by the antibiotic therapy may thus be more relevant for treating chronic bone infection than eliminating only the pathogens colonizing the bone matrix. Assessed was the combined osteogenic and antibacterial effect of clindamycin-loaded calcium phosphate nanoparticles of different monophasic compositions on co-cultures comprising osteoblasts infected with S. aureus. Antibiotic-carrying particles were internalized by osteoblasts and minimized the concentration of intracellular bacteria. In vitro treatments of the infected cells, however, could not prevent cell necrosis due to the formation of toxic byproducts of the degradation of the bacterium. Antibiotic-loaded particles had a positive morphological effect on osteoblasts per se, without reducing their viability, alongside stimulating the upregulation of expression of different bone growth markers in infected osteoblasts to a higher degree than achieved during the treatment with antibiotic only.

Silver nanoscale antisense drug delivery system for photoactivated gene silencing

The unique photophysical properties of noble metal nanoparticles contribute to their potential as photoactivated drug delivery vectors. Here we demonstrate the synthesis and characterization of 60-80 nm silver nanoparticles (SNPs) decorated with thiol-terminated photolabile DNA oligonucleotides. In vitro assays and fluorescent confocal microscopy of treated cell cultures show efficient UV-wavelength photoactivation of surface-tethered caged ISIS2302 antisense oligonucleotides possessing internal photocleavable linkers. As a demonstration of the advantages of these novel nanocarriers, we investigate properties including: enhanced stability to nucleases, increased hybridization activity upon photorelease, and efficient cellular uptake as compared to commercial transfection vectors. Their potential as multicomponent delivery agents for oligonucleotide therapeutics is shown through regulation of ICAM-1 (Intracellular Adhesion Molecule-1) silencing. Our results suggest a means to achieve light-triggered, spatiotemporally controlled gene silencing via nontoxic silver nanocarriers, which hold promise as tailorable platforms for nanomedicine, gene expression studies, and genetic therapies.