2023 International Consensus Meeting on musculoskeletal infection: Summary from the treatment workgroup and consensus on treatment in preclinical models.

In vitro and in vivo studies are critical for the preclinical efficacy assessment of novel therapies targeting musculoskeletal infections (MSKI). Many preclinical models have been developed and applied as a prelude to evaluating safety and efficacy in human clinical trials. In performing these studies, there is both a requirement for a robust assessment of efficacy, as well as a parallel responsibility to consider the burden on experimental animals used in such studies. Since MSKI is a broad term encompassing infections varying in pathogen, anatomical location, and implants used, there are also a wide range of animal models described modeling these disparate infections. Although some of these variations are required to adequately evaluate specific interventions, there would be enormous value in creating a unified and standardized criteria to animal testing in the treatment of MSKI. The Treatment Workgroup of the 2023 International Consensus Meeting on Musculoskeletal Infection was responsible for questions related to preclinical models for treatment of MSKI. The main objective was to review the literature related to priority questions and estimate consensus opinion after voting. This document presents that process and results for preclinical models related to (1) animal model considerations, (2) outcome measurements, and (3) imaging.

Local, Controlled Delivery of Local Anesthetics In Vivo from Polymer - Xerogel Composites.

PURPOSE: Polymer-xerogel composite materials have been introduced to better optimize local anesthetics release kinetics for the pain management. In a previous study, it was shown that by adjusting various compositional and nano-structural properties of both inorganic xerogels and polymers, zero-order release kinetics over 7 days can be achieved in vitro. In this study, in vitro release properties are confirmed in vivo using a model that tests for actual functionality of the released local anesthetics. METHODS: Composite materials made with tyrosine-polyethylene glycol(PEG)-derived poly(ether carbonate) copolymers and silica-based sol-gel (xerogel) were synthesized. The in vivo release from the composite controlled release materials was demonstrated by local anesthetics delivery in a rat incisional pain model. RESULTS: The tactile allodynia resulting from incision was significantly attenuated in rats receiving drug-containing composites compared with the control and sham groups for the duration during which natural healing had not yet taken place. The concentration of drug (bupivacaine) in blood is dose dependent and maintained stable up to 120 h post-surgery, the longest time point measured. CONCLUSIONS: These in vivo studies show that polymer-xerogel composite materials with controlled release properties represent a promising class of controlled release materials for pain management.

Restoring Segmental Biomechanics Through Nucleus Augmentation: An In Vitro Study.

STUDY DESIGN: In vitro biomechanical laboratory study. OBJECTIVES: The purpose of this study is to evaluate a mechanical treatment to create a degenerative motion segment and the ability of nucleus augmentation to restore biomechanics. SUMMARY OF BACKGROUND: In cases with an intact annulus fibrosus, the replacement or augmentation of the nucleus pulposus alone may provide a less invasive option to restore normal biomechanics and disk height when compared with spinal fusion or total disk replacement. Laboratory testing allows these changes to be fully characterized. However, without preexisting pathology, nucleus augmentation therapies are difficult to evaluate in vitro. METHODS: The present study evaluated pure moment bending and compressive biomechanics in 3 states (n=6): (1) intact, (2) after creep loading and nucleus disruption to induce degenerative biomechanical changes, and (3) after nucleus augmentation through an injectable polymer (DiscCell). RESULTS: Neutral zone and ROM were increased in all modes of bending after the degenerative treatment. The most sensitive mode of bending was lateral bending, with intact ROM (20.0±2.9 degrees) increased to 22.3±2.6 degrees after degenerative treatment and reduced to 18.4±1.6 degrees after injection of the polymer. All bending ROM and NZ changes induced by the degenerative treatment were reversed by nucleus augmentation. CONCLUSIONS: This material was shown to be effective at altering motion segment biomechanics and restoring disk height during time zero tests. This technique may provide a model to examine the time zero performance of a nucleus augmentation device/material.

Silicon oxide based materials for controlled release in orthopedic procedures.

By virtue of excellent tissue responses in bone tissue, silicon oxide (silica) based materials have been used for bone tissue engineering. Creating nanoscale porosity within silica based materials expands their applications into the realm of controlled release area. This additional benefit of silica based materials widens their application in the orthopedic fields in a major way. This review discusses the various chemical and physical forms of silica based controlled release materials, the release mechanisms, the applications in orthopedic procedures and their overall biocompatibility.

Percutaneous external fixator pins with bactericidal micron-thin sol-gel films for the prevention of pin tract infection.

Risk of infection is considerable in open fractures, especially when fracture fixation devices are used to stabilize the fractured bones. Overall deep infection rates of 16.2% have been reported. The infection rate is even greater, up to 32.2%, with external fixation of femoral fractures. The use of percutaneous implants for certain clinical applications, such as percutaneous implants for external fracture fixation, still represents a challenge today. Currently, bone infections are very difficult to treat. Very potent antibiotics are needed, which creates the risk of irreversible damage to other organs, when the antibiotics are administered systemically. As such, controlled, local release is being pursued, but no such treatments are in clinical use. Herein, the use of bactericidal micron-thin sol-gel films on metallic fracture fixation pins is reported. The data demonstrates that triclosan (2,4,4'-trichloro-2'-hydroxydiphenylether), an antimicrobial agent, can be successfully incorporated into micron-thin sol-gel films deposited on percutaneous pins. The sol-gel films continuously release triclosan in vitro for durations exceeding 8 weeks (longest measured time point). The bactericidal effect of the micron-thin sol-gel films follows from both in vitro and in vivo studies. Inserting percutaneous pins in distal rabbit tibiae, there were no signs of infection around implants coated with a micron-thin sol-gel/triclosan film. Healing had progressed normally, bone tissue growth was normal and there was no epithelial downgrowth. This result was in contrast with the results in rabbits that received control, uncoated percutaneous pins, in which abundant signs of infection and epithelial downgrowth were observed. Thus, well-adherent, micron-thin sol-gel films laden with a bactericidal molecule successfully prevented pin tract infection.

The economic significance of orthopaedic infections.

Musculoskeletal infections are a leading cause of patient morbidity and rising healthcare expenditures. The incidence of musculoskeletal infections, including soft-tissue infections, periprosthetic joint infection, and osteomyelitis, is increasing. Cases involving both drug-resistant bacterial strains and periprosthetic joint infection in total hip and total knee arthroplasty are particularly costly and represent a growing economic burden for the American healthcare system. With the institution of the Affordable Care Act, there has been an increasing drive in the United States toward rewarding healthcare organizations for their quality of care, bundling episodes of care, and capitating approaches to managing populations. In current reimbursement models, complications following the index event, including infection, are not typically reimbursed, placing the burden of caring for infections on the physician, hospital, or accountable care organization. Without the ability to risk-stratify patient outcomes based on patient comorbidities that are associated with a higher incidence of musculoskeletal infection, healthcare organizations are disincentivized to care for moderate- to high-risk patients. Reducing the cost of treating musculoskeletal infection also depends on incentivizing innovations in infection prevention.

The design and synthesis of a soluble composite silica xerogel and the short-time release of proteins.

Conventional silica xerogels prepared through sol-gel processing are regarded as suitable materials for the long-term release of proteins due to the mild processing conditions. However, they fall short of short-time release of these large molecules because of their small pore size and a slow dissolution rate. With the goal of achieving controlled release of large molecules (such as proteins) in a very short time (several days), herein we focus on the co-hydrolysis and co-condensation of different precursors to synthesize composite xerogels (co-xerogels) with adjustable degradation rates. Tetraethoxysilane and 3-(triethoxysilyl) propylsuccinic anhydride were employed to prepare the co-xerogels. Succinic anhydride was chosen due to its potential to crosslink with Si-OH and to integrate into the silica network under acidic conditions. Using the trypsin inhibitor (TI) as a model drug to characterize the release properties of co-xerogels, we obtained tailored release behavior of TI (2-7 days). It is demonstrated that the co-hydrolysis and co-condensation of different precursors is an easy technique that further expands the applicability of sol-gel materials as excellent carriers for the controlled release of a variety of drugs.

Bactericidal micron-thin sol-gel films prevent pin tract and periprosthetic infection.

Orthopedic injuries constitute the majority of wounds sustained by U.S. soldiers in recent conflicts. The risk of infection is considerable with fracture fixation devices. In this pilot study, we examined the use of unique bactericidal micron-thin sol-gel films on fracture fixation devices and their ability to prevent and eradicate infections. External fixation was studied with micron-thin sol-gel coated percutaneous pins releasing triclosan and inserted medially into rabbit tibiae. A total of 11 rabbits received percutaneous pins that were either uncoated or sol-gel/triclosan coated. Internal fracture fixation was also studied using sol-gel coated intramedullary (IM) nails releasing vancomycin in the intramedullary tibiae. Six sheep received IM nails that were coated with a sol-gel film that either contained vancomycin or did not contain vancomycin. All animals were challenged with Staphylococcus aureus around the implant. Animals were euthanized at 1 month postoperative. Rabbits receiving triclosan/sol-gel coated percutaneous pins did not show signs of infection. Uncoated percutaneous pins had a significantly higher infection rate. In the sheep study, there were no radiographic signs of osteomyelitis with vancomycin/sol-gel coated IM nails, in contrast to the observations in the control cohort. Hence, the nanostructured sol-gel controlled release technology offers the promise of a reliable and continuous delivery system of bactericidals from orthopedic devices to prevent and treat infection.

Sol-gel silica controlled release thin films for the inhibition of methicillin-resistant Staphylococcus aureus.

The incidence of methicillin-resistant Staphylococcus aureus (MRSA) infection has significantly increased. Generally, the success of this bacterium as a pathogen is attributed to its ability to adhere to surfaces and remain there, under the protection of an extracellular matrix known as biofilm. To combat MRSA with regular doses of vancomycin, efforts are continuously underway to increase its effectiveness. A promising technique is to use combinational therapeutics. In vitro experiments showed that farnesol can be used as an adjuvant with conventional antibiotics. Farnesol is a natural sesquiterpenoid and quorum-sensing molecule. The biggest obstacle to using this concept is that farnesol is highly water insoluble. This compromises its bioavailability if it were to be used along with vancomycin at the site of infection when the treatment needs to be administered in vivo. Herein we designed an efficient therapeutic strategy for the simultaneous delivery of both antibiotic and adjuvant in order to treat MRSA infections. We demonstrate that sufficient quantities of both vancomycin and farnesol can be incorporated into sol-gel silica applied as thin films on an implant surface. The incorporation of the hydrophobic farnesol does not affect the stability of the thin films and neither does it affect the controlled release of vancomycin. The data demonstrate the potent adjuvant effect of farnesol on vancomycin in inhibiting MRSA infection. In vitro experiments show the complete inhibition (10(6) fold reduction in growth compared to control) of methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) when the ratio of vancomycin to farnesol in the sol-gel silica films is optimized. The local delivery of antibiotics minimizes the need for systemic antibiotics. The incorporation of vancomycin and farnesol into thin sol-gel films represents a new treatment paradigm for the topical delivery of antibiotics with adjuvant. The potential clinical benefits are significant and include avoiding the need for revision surgery, preventing surgical site infection and controlling healthcare costs.

Nanostructural control of the release of macromolecules from silica sol-gels.

The therapeutic use of biological molecules such as growth factors and monoclonal antibodies is challenging in view of their limited half-life in vivo. This has elicited the interest in delivery materials that can protect these molecules until released over extended periods of time. Although previous studies have shown controlled release of biologically functional BMP-2 and TGF-ß from silica sol-gels, more versatile release conditions are desirable. This study focuses on the relationship between room temperature processed silica sol-gel synthesis conditions and the nanopore size and size distribution of the sol-gels. Furthermore, the effect on release of large molecules with a size up to 70kDa is determined. Dextran, a hydrophilic polysaccharide, was selected as a large model molecule at molecular sizes of 10, 40 and 70kDa, as it enabled us to determine a size effect uniquely without possible confounding chemical effects arising from the various molecules used. Previously, acid catalysis was performed at a pH value of 1.8 below the isoelectric point of silica. Herein the silica synthesis was pursued using acid catalysis at either pH 1.8 or 3.05 first, followed by catalysis at higher values by adding base. This results in a mesoporous structure with an abundance of pores around 3.5nm. The data show that all molecular sizes can be released in a controlled manner. The data also reveal a unique in vivo approach to enable release of large biological molecules: the use more labile sol-gel structures by acid catalyzing above the pH value of the isoelectric point of silica; upon immersion in a physiological fluid the pores expand to reach an average size of 3.5nm, thereby facilitating molecular out-diffusion.

Controlled release of small molecules from silica xerogel with limited nanoporosity.

Conventional sol-gel processing requires several distinct steps involving hydrolysis, condensation and drying to obtain a highly porous, glassy solid material. With the goal of achieving controlled release of small molecules, herein we focus on the acceleration of the condensation and drying steps by casting the hydrolyzed sol on a large open surface to achieve a denser 100 % silica xerogel structure. Thus, cast xerogel with a more limited porosity was prepared. The effect of synthesis parameters during sol-gel synthesis on the release kinetics of bupivacaine, vancomycin and cephalexin was investigated. The release kinetics fitted well with the Higuchi model, suggesting a diffusional release mechanism. Combining the release and nanostructure data, the formation mechanism of cast xerogel is described. Without introducing additional precursors or additives into sol-gel systems, sol-gel casting is an easy technique that further expands the applicability of sol-gel materials as excellent carriers for the controlled release of a variety of drugs.

Polymer-coated mesoporous silica nanoparticles for the controlled release of macromolecules.

With the goal of achieving constant release of large biological molecules over an extended period of time we focused on hybrid inorganic/organic nanoparticles. We synthesized poly(ethylene glycol) (PEG)-coated mesoporous silica nanoparticles (MSNs) with incorporated trypsin inhibitor (TI), a model protein molecule for growth factors. Due to the goal of incorporating large protein molecules the pore size of the as-synthesized MSNs was expanded by a hydrothermal treatment prior to TI incorporation. In vitro release from the MSNs without the thin polymer film shows an initial burst followed by continuous release. In the case of polymer-coated MSNs the initial burst release was completely suppressed and approximate zero order release was achieved for 4 weeks.

Polymer-xerogel composites for controlled release wound dressings.

Many polymers and composites have been used to prepare active wound dressings. These materials have typically exhibited potentially toxic burst release of the drugs within the first few hours followed by a much slower, potentially ineffective drug release rate thereafter. Many of these materials also degraded to produce inflammatory and cytotoxic products. To overcome these limitations, composite active wound dressings were prepared here from two fully biodegradable and tissue compatible components, silicon oxide sol-gel (xerogel) microparticles that were embedded in tyrosine-poly(ethylene glycol)-derived poly(ether carbonate) copolymer matrices. Sustained, controlled release of drugs from these composites was demonstrated in vitro using bupivacaine and mepivacaine, two water-soluble local anesthetics commonly used in clinical applications. By systematically varying independent compositional parameters of the composites, including the hydrophilic:hydrophobic balance of the tyrosine-derived monomers and poly(ethylene glycol) in the copolymers and the porosity, weight ratio and drug content of the xerogels, drug release kinetics approaching zero-order were obtained. Composites with xerogel mass fractions up to 75% and drug payloads as high as 13% by weight in the final material were fabricated without compromising the physical integrity or the controlled release kinetics. The copolymer-xerogel composites thus provided a unique solution for the sustained delivery of therapeutic agents from tissue compatible wound dressings.

The controlled release of drugs from emulsified, sol gel processed silica microspheres.

Controlled release silica sol gels are room temperature processed, porous, resorbable materials with generally good compatibility. Many molecules including drugs, proteins and growth factors can be released from sol gels and the quantity and duration of the release can vary widely. Processing parameters render these release properties exquisitely versatile. The synthesis of controlled release sol gels typically includes acid catalyzed hydrolysis to form a sol with the molecules included. This is then followed by casting, aging and drying. Additional steps such as grinding and sieving are required to produce sol gel granules of a desirable size. In this study, we focus on the synthesis of sol gel microspheres by using a novel process with only two steps. The novelty is related to acid-base catalysis of the sol prior to emulsification. Sol gel microspheres containing either vancomycin (antibiotic) or bupivacaine (analgesic) were successfully synthesized using this method. Both drugs showed controlled, load dependent and time dependent release from the microspheres. The in vitro release properties of sol gel microspheres were remarkably different from those of sol gel granules produced by grinding and sieving. In contrast to a fast, short-term release from granules, the release from microspheres was slower and of longer duration. In addition, the degradation rate of microspheres was significantly slower than that of the granules. Using various mathematical models, the data reveal that the release from sol gel powder is governed by two distinct phases of release. In addition, the release from emulsified microspheres is delayed, a finding that can be attributed to differences in surface properties of the particles produced by emulsification and those produced by casting and grinding. The presented results represent an excellent data set for designing and implementing preclinical studies.

Controlled release of vancomycin from thin sol-gel films on implant surfaces successfully controls osteomyelitis.

Peri-prosthetic infection remains a serious complication of joint replacement surgery. Herein, we demonstrate that a vancomycin-containing sol-gel film on Ti alloy rods can successfully treat bacterial infections in an animal model. The vancomycin-containing sol-gel films exhibited predictable release kinetics, while significantly inhibiting S. aureus adhesion. When evaluated in a rat osteomyelitis model, microbiological analysis indicated that the vancomycin-containing sol-gel film caused a profound decrease in S. aureus number. Radiologically, while the control side showed extensive bone degradation, including abscesses and an extensive periosteal reaction, rods coated with the vancomycin-containing sol-gel film resulted in minimal signs of infection. MicroCT analysis confirmed the radiological results, while demonstrating that the vancomycin-containing sol-gel film significantly protected dense bone from resorption and minimized remodeling. These results clearly demonstrate that this novel thin sol-gel technology can be used for the targeted delivery of antibiotics for the treatment of periprosthetic as well as other bone infections.

The inhibition of Staphylococcus epidermidis biofilm formation by vancomycin-modified titanium alloy and implications for the treatment of periprosthetic infection.

Peri-prosthetic infections are notoriously difficult to treat as the biomaterial implant is ideal for bacterial adhesion and biofilm formation, resulting in decreased antibiotic sensitivity. Previously, we reported that vancomycin covalently attached to a Ti alloy surface (Vanc-Ti) could prevent bacterial colonization. Herein we examine the effect of this Vanc-Ti surface on Staphylococci epidermidis, a Gram-positive organism prevalent in orthopaedic infections. By direct colony counting and fluorescent visualization of live bacteria, S. epidermidis colonization was significantly inhibited on Vanc-Ti implants. In contrast, the gram-negative organism Escherichia coli readily colonized the Vanc-Ti rod, suggesting retention of antibiotic specificity. By histochemical and SEM analysis, Vanc-Ti prevented S. epidermidis biofilm formation, even in the presence of serum. Furthermore, when challenged multiple times with S. epidermidis, Vanc-Ti rods resisted bacterial colonization. Finally, when S. epidermidis was continuously cultured in the presence of Vanc-Ti, the bacteria maintained a Vanc sensitivity equivalent to the parent strain. These findings indicate that antibiotic derivatization of implants can result in a surface that can resist bacterial colonization. This technology holds great promise for the prevention and treatment of periprosthetic infections.