Drug delivery from internally implanted biomedical devices used in traumatology and in orthopedic surgery

Strategies to Mitigate and Treat Orthopaedic Device-Associated Infections

Orthopaedic device implants play a crucial role in restoring functionality to patients suffering from debilitating musculoskeletal diseases or to those who have experienced traumatic injury. However, the surgical implantation of these devices carries a risk of infection, which represents a significant burden for patients and healthcare providers. This review delineates the pathogenesis of orthopaedic implant infections and the challenges that arise due to biofilm formation and the implications for treatment. It focuses on research advancements in the development of next-generation orthopaedic medical devices to mitigate against implant-related infections. Key considerations impacting the development of devices, which must often perform multiple biological and mechanical roles, are delineated. We review technologies designed to exert spatial and temporal control over antimicrobial presentation and the use of antimicrobial surfaces with intrinsic antibacterial activity. A range of measures to control bio-interfacial interactions including approaches that modify implant surface chemistry or topography to reduce the capacity of bacteria to colonise the surface, form biofilms and cause infections at the device interface and surrounding tissues are also reviewed.

A two-stage cold isostatic pressing and gelling approach for fabricating a therapeutically loaded amorphous calcium polyphosphate local delivery system

Local delivery systems have taken on a greater clinical focus for osteomyelitis therapy owing to their ability to overcome many disadvantages of systemic delivery. This study reports for the first time the capacity to fabricate strontium- and vancomycin-doped calcium polyphosphate beads using a two-stage cold isostatic pressing and gelling approach. The fabricated beads were of uniform shape and diameter, and upon gelling exhibited reduced porosity. Of greatest significance in the subsequent in vitro study was the improvement of bead long-term structural stability upon vancomycin incorporation; a characteristic that further encourages the extended release of therapeutically relevant levels of antibiotic. Overall, this study provides support for the inclusion of a cold isostatic pressing step in the fabrication of a therapeutically loaded calcium polyphosphate bead-based local delivery system intended for osteomyelitis treatment.

Beyond conventional antibiotics - New directions for combination products to combat biofilm

Medical device related infections are a significant and growing source of morbidity and mortality. Biofilm formation is a common feature of medical device infections that is not effectively prevented or treated by systemic antibiotics. Antimicrobial medical device combination products provide a pathway for local delivery of antimicrobial therapeutics with the ability to achieve high local concentrations while minimizing systemic side effects. In this review, we present considerations for the design of local antimicrobial delivery systems, which can be facilitated by modeling local pharmacokinetics in the context of the target device application. In addition to the need for local delivery, a critical barrier to progress in the field is the need to incorporate agents effective against biofilm. This article aims to review key properties of antimicrobial peptides that make them well suited to meet the demands of the next generation of antimicrobial medical devices, including broad spectrum activity, rapid and biocidal mechanisms of action, and efficacy against biofilm.

NF-κB as a Therapeutic Target in Inflammatory-Associated Bone Diseases

Inflammation is a defensive mechanism for pathogen clearance and maintaining tissue homeostasis. In the skeletal system, inflammation is closely associated with many bone disorders including fractures, nonunions, periprosthetic osteolysis (bone loss around orthopedic implants), and osteoporosis. Acute inflammation is a critical step for proper bone-healing and bone-remodeling processes. On the other hand, chronic inflammation with excessive proinflammatory cytokines disrupts the balance of skeletal homeostasis involving osteoblastic (bone formation) and osteoclastic (bone resorption) activities. NF-κB is a transcriptional factor that regulates the inflammatory response and bone-remodeling processes in both bone-forming and bone-resorption cells. In vitro and in vivo evidences suggest that NF-κB is an important potential therapeutic target for inflammation-associated bone disorders by modulating inflammation and bone-remodeling process simultaneously. The challenges of NF-κB-targeting therapy in bone disorders include: (1) the complexity of canonical and noncanonical NF-κB pathways; (2) the fundamental roles of NF-κB-mediated signaling for bone regeneration at earlier phases of tissue damage and acute inflammation; and (3) the potential toxic effects on nontargeted cells such as lymphocytes. Recent developments of novel inhibitors with differential approaches to modulate NF-κB activity, and the controlled release (local) or bone-targeting drug delivery (systemic) strategies, have largely increased the translational application of NF-κB therapy in bone disorders. Taken together, temporal modulation of NF-κB pathways with the combination of recent advanced bone-targeting drug delivery techniques is a highly translational strategy to reestablish homeostasis in the skeletal system.

One-step grafting of temperature-and pH-sensitive (N-vinylcaprolactam-co-4-vinylpyridine) onto silicone rubber for drug delivery

A one-step method was implemented to graft N-vinylcaprolactam (NVCL) and 4-vinylpyridine (4VP) onto silicone rubber (SR) films using gamma radiation in order to endow the silicone surface with temperature- and pH-responsiveness, and give it the ability to host and release diclofenac in a controlled manner and thus prevent bacterial adhesion. The effects of radiation conditions (e.g., dose and monomers concentration) on the grafting percentage were evaluated, and the modified films were characterized by means of FTIR-ATR, Raman spectroscopy, calorimetry techniques (DSC and TGA) and contact angle measurements. The films responsiveness to stimuli was evaluated by recording the swelling degree of pristine and modified SR in buffer solutions (critical pH point) and as a function of changes in temperature (Upper Critical Solution Temperature, UCST). The graft copolymers of SR-g-(NVCL-co-4VP) showed good cytocompatibility against fibroblast cells for prolonged times, could host diclofenac and release it in a sustained manner for up to 24 h, and exhibited bacteriostatic activity when challenged against Escherichia coli.

Assessing the potential of mathematical modelling in designing drug-releasing orthopaedic implants

Orthopaedic implants have been the subject of intense research in recent years, with academics, clinicians and industrialists seeking to broaden our understanding of their function and potential consequences within the human body. Current research is focussed on ways to improve the integration of an orthopaedic device within the body, whether it be to encourage better osseointegration, combat possible infection or stem the foreign body response. A key emerging strategy is the controlled delivery of therapeutics from the device, which may take the form of, for example, antibiotics, analgesics, anti-inflammatories or growth factors. However, the optimal device design that gives rise to the desired controlled release has yet to be defined. There are many examples in the literature of experimental approaches which attempt to tackle this issue. However, the necessity of having to conduct multiple experiments to test different scenarios is a major drawback of this approach. So enter stage left: mathematical modelling. Using a mathematical modelling approach can provide much more than experiments in isolation. For instance, a mathematical model can help identify key drug release mechanisms and uncover the rate limiting processes; allow for the estimation of values of the parameters controlling the system; quantify the effect of the interaction with the biological environment; and aid with the design of optimisation strategies for controlled drug release. In this paper we review current experimental approaches and some relevant mathematical models and suggest the future direction of such approaches in this field.

A controlled antibiotic release system to prevent orthopedic-implant associated infections: An in vitro study

A new device for local delivery of antibiotics is presented, with potential use as a drug-eluting fixation pin for orthopedic applications. The implant consists of a stainless steel hollow tubular reservoir packed with the desired antibiotic. Release takes place through several orifices previously drilled in the reservoir wall, a process that does not compromise the mechanical properties required for the implant. Depending on the antibiotic chosen and the number of orifices, the release profile can be tailored from a rapid release of the load (ca. 20 h) to a combination of rapid initial release and slower, sustained release for a longer period of time (ca. 200 h). An excellent bactericidal action is obtained, with 4-log reductions achieved in as little as 2 h, and total bacterial eradication in 8 h using 6-pinholed implants filled with cefazolin.

Processing and sustained in vitro release of rifampicin containing composites to enhance the treatment of osteomyelitis

The objective in this study was to develop an osteoconductive, biodegradable and rifampicin releasing bone filling composite material for the treatment of osteomyelitis, a bacterial infection of bone that is very difficult and expensive to treat. The composite material will be used together with a ciprofloxacin releasing composite, because of the rapid development of resistant bacteria when rifampicin is used alone. Three composites were manufactured by twin-screw extrusion. The polymer matrix for the composites was poly(L-lactide-co-ε-caprolactone) 70/30 and all the composites contained 8 wt% (weight percent) of rifampicin antibiotic. The β-TCP contents of the composites were 0 wt%, 50 wt% and 60 wt%. The composites were sterilized by gamma irradiation before in vitro degradation and drug release tests. The hydrolytical degradation of the studied composites proceeded quickly and the molecular weight of the polymer component of the composites decreased rapidly. Rifampicin release occurred in four phases in which the high β-TCP content of the samples, polymer degradation and mass loss all played a role in determining the phases. The ceramic component was seen to have a positive effect on the drug release. The composite with 50 wt% of β-TCP showed the most promising rifampicin release profile and it also showed activity against a common osteomyelitis causing bacteria Pseudomonas aeruginosa. A clear inhibition zone was formed in 16 h incubation. Overall, the tested materials showed great potential to be developed into a bone filler material for the treatment of osteomyelitis or other bone related infections in combination with the ciprofloxacin releasing materials.

Drug delivery from structured porous inorganic materials

Structured porous inorganic materials show high chemical and mechanical stability under an array of physiological conditions. Their hydrophilic character and porous structure can in principle be tailored to control the diffusion rate of an adsorbed or encapsulated drug, gene, or protein. This organized porosity has been used to achieve a sustained, controlled, or pulsed release in drug delivery applications. Their large surface areas together with their large pore volumes have been used to improve the solubility of poorly soluble drugs. Their low density allows them to float in the gastrointestinal tract and prolong the gastric retention of oral drugs. In addition, their easy surface functionalization allows their grafting with bioadhesive and targeting moieties, and their interior pore volume protects biological payloads from physiological degradation. Some of those porous inorganic materials can be synthesized or microfabricated to form deposits thus acting as drug reservoirs. Finally, diffusion-controlling porous membranes or coatings of those materials can be tailored with specific pore sizes to control drug release in eluting devices. Current research is focused on designing on demand targeted drug delivery systems using those inorganic porous materials as reservoirs together with triggering systems on their pore entrances to be externally activated to release the encapsulated therapeutic moiety. All of the previous scenarios will be overviewed to demonstrate the numerous possibilities of structured porous inorganic materials in drug delivery applications.

Hollow porous implants filled with mesoporous silica particles as a two-stage antibiotic-eluting device

A new type of implantable drug eluting device is presented, consisting of a bed of mesoporous microparticles packed inside a reservoir with a porous wall. This provides two sets of variables for drug release control that can be tailored independently. The first is related to the microparticles (packing density, size and pore structure) and the second to the reservoir (pore diameter and thickness of the wall, permeation area). In this work the concept is developed into a working model, used to fight bacterial (Staphylococcus aureus) growth by releasing linezolid that had previously been adsorbed on silica microparticles. These particles were placed inside the hollow interior of a porous medical grade stainless steel pin mimicking those used in traumatology and in orthopedic surgery. The mechanical behavior of the porous drug-eluting pin was tested and found satisfactory.

Biofilm inhibition and drug-eluting properties of novel DMAEMA-modified polyethylene and silicone rubber surfaces

Poly(2-(dimethylaminoethyl) methacrylate) (pDMAEMA) was grafted to low density polyethylene (LDPE) and silicone rubber (SR) in order to make them less susceptible to microbial biofilm formation. The direct grafting of DMAEMA using γ-rays was an efficient and fast procedure for obtaining modified materials, which could be quaternized in a second step using methyl iodide. Raman spectroscopy showed that the grafting occurred only at the surface of the LDPE, but both at the surface and in the bulk of the SR. Consequently, the grafted chains caused changes in the surface-related features of the LDPE (water contact angle and viscoelastic behavior in the dry state) and in the bulk-related properties of the SR (swelling and viscoelasticity in the swollen state). The microbiological assays revealed that the grafted DMAEMA reduced Candida albicans biofilm formation (almost no biofilm on SR), while the quaternized surfaces inhibited C. albicans and Staphylococcus aureus biofilm by more than 99% compared to pristine materials. Modified LDPE and SR were capable of holding considerable amounts of nalidixic acid, an anionic antimicrobial drug, and sustained the release for several hours. In addition, the grafted materials were cytocompatible (fibroblast cell survival > 70%). In conclusion, these materials have the ability to inhibit microbial biofilm formation and at the same time act as drug-eluting systems, and for that reason may hold great promise for anti-biofouling applications.