Vehicle For Local Delivery Research Articles

Modulation of protein release from photocrosslinked networks by gelatin microparticles

Injectable delivery systems are attractive as vehicles for localized delivery of therapeutics especially in the context of regenerative medicine. In this study, photocrosslinked polyanhydride (PA) networks were modified by incorporation of microparticles to modulate long-term delivery of macromolecules. The in vitro release of two model proteins (horseradish peroxidase (HRP) and bovine serum albumin labeled with fluorescein isothiocyanate (FITC-BSA)) were evaluated from networks composed of sebacic acid dimethacrylate (MSA), 1,6-bis-carboxyphenoxyhexane dimethacrylate (MCPH), poly(ethylene glycol) diacrylate (PEGDA), and calcium carbonate (CaCO 3), supplemented with gelatin microparticles or sodium chloride crystals. Prior to incorporation into the networks, proteins were formulated into granules by dilution with a cyclodextrin excipient and gelatin-based wet-granulation. Protein release was modulated by incorporation of microparticles into photocrosslinked PA networks, presumably by enabling aqueous channels through the matrix. Furthermore, a dual release system has been demonstrated by incorporation of protein in both the PA matrix and the gelatin microparticles. These results suggest that microparticle incorporation into the photocrosslinked PA system may be a useful strategy to modulate protein release in injectable delivery systems for the long-term delivery of macromolecules. These composites present an interesting class of materials for bone regeneration applications.

Daptomycin Eluted From Calcium Sulfate Appears Effective Against Staphylococcus

The emergence of resistant strains of Gram-positive organisms in osteomyelitis creates treatment challenges. Daptomycin is an antibiotic that shows promise for treating some resistant strains of Gram-positive infections; however, it has not been widely used clinically for the treatment of osteomyelitis. We determined whether daptomycin eluted from calcium sulfate-a local delivery vehicle used for the treatment of osteomyelitis-retained activity against Gram-positive bacteria. Daptomycin was mixed with calcium sulfate hemihydrate, with both laboratory powder and a commercial kit, to form a hardened pellet. Daptomycin was eluted from calcium sulfate and retained its ability to inhibit bacterial growth of Staphylococcus aureus and Staphylococcus epidermidis for eluates gathered up to 28 days. Our preliminary data demonstrates sterilized pellets with daptomycin retained their ability to inhibit bacterial growth of certain strains of Gram-positive organisms.

Photocrosslinked anhydride systems for long-term protein release

Injectable delivery systems are attractive as vehicles for localized delivery of therapeutics especially in the context of regenerative medicine. In this study, the potential of photocrosslinked polyanhydride (PA) networks as an encapsulation matrix for long-term delivery of macromolecules was studied. The in vitro release of two model proteins (horseradish peroxidase (HRP) and bovine serum albumin labeled with fluorescein isothiocyanate (FITC-BSA)) was evaluated from crosslinked networks composed of sebacic acid dimethacrylate (MSA), 1,6-bis-carboxyphenoxyhexane dimethacrylate (MCPH), and poly(ethylene glycol) diacrylate (PEGDA), supplemented with calcium carbonate. Prior to incorporation into the networks, proteins were formulated by dilution in a cyclodextrin excipient followed by gelatin-based wet granulation. Protein release was quantified by activity assay (HRP) or fluorescence (FITC-BSA). Each protein was readily released from the networks with a unique release behavior. Most importantly, release of protein with retention of activity was achieved for durations ranging from 1 week to 4 months. The released HRP was additionally visualized using SDS-PAGE. In general, a more hydrophobic network resulted in slower rates of protein release. Incorporation of PEGDA into the matrices was critical for maintenance of integrity during degradation. These results suggest that this system may be useful as an injectable delivery system for long-term delivery of macromolecules.

A Motion Maintaining Antibiotic Delivery System

Two-stage radical debridement with implant removal, antibiotic therapy, and delayed reimplantation remains the treatment of choice for deep infection in total joint arthroplasty. Studies have shown that articulating vs static spacers better improve functional results, increase patient satisfaction, prevent bone loss, and facilitate reimplantation without increasing risk of infection. Articulating spacers fabricated from cement provide a vehicle for prolonged local delivery of antibiotics. We currently use a mold system for creating antibiotic-laden articulating cement spacers. Disposable femoral and tibial molds are injection-filled with low-viscosity cement vacuum mixed with 3.6 to 4.8 g of tobramycin or gentamicin and 3.0 to 4.0 g of vancomycin per 40-g unit and massaged to fill any voids. After curing, the temporary spacers are removed from the molds, trimmed smooth, and cemented loosely into the joint space.

Use of Tobramycin-Impregnated Calcium Sulphate Pellets in Addition to Oral Antibiotics

To supplement surgical debridement, pellets of calcium sulfate (CS) were used as vehicles for local antibiotic delivery in treating osteomyelitis (1). We are aware of one case series in which diabetic pedal osteomyelitis was resolved with postoperatively implanted polymethylmethacrylate antibiotic beads and intravenous antibiotics (2). We now present a case of radiologically successful, nonsurgical management of diabetic foot osteomyelitis with tobramycin-impregnated CS pellets, in addition to oral antibiotic …

New routes for delivery of anti-epileptic medications.

Use of novel drug delivery methods might enhance efficacy and reduce toxicity, in comparison with currently existing oral anti-epileptic drugs (AEDs). Novel methods aim to deliver optimal drug concentration more specifically to the seizure focus or foci. In this review, we first consider unconventional routes of drug delivery to the peripheral system, then potential new methods of targeted CNS drug delivery. Intrathecal or intraventricular AEDs might circumvent systemic toxicity. Drug-eluting wafers could be surgically positioned over an epileptogenic region of brain. Drug can be delivered to a seizure focus by an implanted catheter and subcutaneous pump. Inactive prodrugs, given systemically, can be made active only at the seizure focus, by interaction with locally-released substances. Liposomes and polysomes are engineered slow-release storage vehicles for drugs. Targeting components can hold liposomes near a region of interest, provided that they can penetrate the blood brain barrier. Lastly, we discuss future prospects for the use of transplanted cells and genes as potential vehicles for local delivery of renewable anti-epileptic regimen.

Tethering Functional Ligands onto Shell of Ultrasound Active Polymeric Microbubbles

Hollow (air-filled) microparticles, i.e., microbubbles, provide a promising novel vehicle for both local delivery of therapeutic agents and simultaneous diagnostic ultrasound echo investigations. In this paper, we describe the synthetic routes for decorating the polymeric shell of a poly(vinyl alcohol)-based microbubble with low and high molecular weight ligands with pharmacological relevance. Investigations on physical properties of microbubbles and surface chemical coupling with different cargo molecules such as L-cysteine, L-lysine, poly(L-lysine), chitosan, and beta-cyclodextrin were carried out by CD and NMR spectroscopies, confocal laser scanning microscopy, and microcalorimetry. The in vitro cytotoxicity and biocompatibility of the polymer microbubbles have been also determined toward different cell lines. The results are discussed in terms of the features shown by this device, i.e., injectability, long shelf life, ease of preparation, biocompatibility, loading and cargo capacities, and functional properties.

In situ gelling hydrogels for conformal repair of spinal cord defects, and local delivery of BDNF after spinal cord injury

Permanent functional loss usually occurs after injury to the spinal cord. Currently, a clinical strategy to promote regeneration in the injured spinal cord does not exist. It has become evident that in order to promote regeneration, a growth permissive substrate at the injury site is critical. In this study, we report the utilization of an agarose scaffold that gels in situ, conformally filling an irregular, dorsal over-hemisection spinal cord defect in adult rats. Besides being growth permissive, the scaffolds also serve as carriers of trophic factors when embedded with BDNF releasing microtubules. We report that our thermo-reversible scaffolds are capable of supporting 3D neurite extension in vivo and are effective carriers of drug delivery vehicles for sustained local delivery of trophic factors. We demonstrate that BDNF encourages neurite growth into the scaffolds, and reduces further the minimal inflammatory response agarose gels generate in vivo as evidenced by quantitative analysis of the extent of NF-160 kDA positive neurons and axons, GFAP positive reactive astrocytes, and CS-56 positive chondroitin sulfate proteoglycan at the interface of the scaffold and host spinal cord. We suggest that these thermo-reversible scaffolds have great potential to serve as growth permissive 3D scaffolds, and to present neurotrophic factors and potentially anti-scar agents to the injury site and enhance regeneration after spinal cord injury.

Local Antibiotic Delivery Systems

Local Antibiotic Delivery Systems

Local Antibiotic Delivery Vehicles in the Treatment of Musculoskeletal Infection

The primary benefit achieved with local antibiotic delivery vehicles is the ability to obtain extremely high levels of local antibiotics without increasing systemic toxicity. Antibiotic-loaded bone cement represents the current standard as an antibiotic delivery vehicle in orthopaedic surgery. Biodegradable alternatives to antibiotic-loaded bone cement also are being used clinically and there are many new products in the active stages of development. These alternatives can be categorized as bone graft, bone graft substitutes or extenders, natural polymers (protein-based products), and synthetic polymers. Composite biomaterials that simultaneously provide the functions of variable antibiotic delivery patterns and also contribute to the process of bone regeneration represent the most ideal class of local antibiotic delivery vehicles. High concentrations of certain antibiotics have been shown to affect the process of normal bone regeneration adversely in a dose dependent response. Considerable investigation still is required to determine the proper use of locally administered antibiotics to negotiate the balance between eradicating infection without excessively inhibiting the processes of bone regeneration.

Biological evaluation of calcium alginate microspheres as a vehicle for the localized delivery of a therapeutic enzyme

Gaucher disease (GD) is caused by the decreased activity and/or stability of the lysosomal enzyme glucocerebrosidase (GCR). The available treatment consists in the intravenous administration of exogenous GCR, and is effective in reverting most of the symptoms. However, in terms of bone pathology, which is among the most disabling manifestations, a slow and incomplete response is observed, indicating that adjuvant therapies are necessary to consistently restore GCR activity in bone and accelerate regeneration. In this study, calcium alginate microspheres were analyzed as a vehicle for localized GCR delivery to bone. Results demonstrated that the entrapped enzyme retained full activity and exhibited a broader pH-dependent activity profile, compared to that of free-GCR, with improved stability at physiological pH. GCR release profile was established, and it was demonstrated that GCR could be released in a sustained manner. The biological behavior of the system was evaluated by analyzing the uptake of released GCR by GCR-deficient cells from GD patients, using different techniques: GCR activity measurements, radiolabeling, and cellulose acetate electrophoresis. Results demonstrated that GCR was internalized by cells significantly enhancing the residual enzymatic activity. To achieve an activity reconstitution level comparable to that obtained using free-GCR, only half of the dose was required with entrapped-GCR.

Heparin functionalized PEG gels that modulate protein adsorption for hMSC adhesion and differentiation

Heparin was modified with methacrylate groups, copolymerized with dimethacrylated poly(ethylene glycol), and analyzed as a localized delivery vehicle for bFGF and synthetic extracellular matrix for the differentiation of hMSCs. By deriving cues from molecules normally present in the extracellular matrix (ECM), a complex network of collagens, laminin, fibronectin, glycosaminoglycans, and growth factors, synthetic cell scaffolds can be designed that actively sequester important bioactive signals. Among the glycosaminoglycans, heparin binds reversibly with many proteins, therefore, poly(ethylene glycol) based biomaterials, normally resistant to cell adhesion, functionalized with heparin in order to sequester important proteins, can actively and selectively stimulate desired cell functions. Results demonstrate that methacrylate-modified heparin retained its ability to bind heparin-binding proteins both in solution and when copolymerized with dimethacrylated PEG in a hydrogel. In addition, the heparin functionalized gels can deliver biologically active bFGF for up to 5 weeks. Finally, the gels were examined as a potential scaffold for hMSC culture and were found to promote adhesion, proliferation, and osteogenic differentiation.

Cortical allograft as a vehicle for antibiotic delivery

Background Infection can be a devastating complication after implantation of a cortical bone allograft. The allograft could act as a vehicle for local antibiotic prophylaxis.Material and methods We studied the release of antibiotics in vitro from cortical bone allografts impregnated with antibiotics for different periods of time. We also studied whether cortical allografts impregnated with antibiotics could eradicate Staphylococcus aureus from an experimentally infected graft in vivo. In the in vitro study, pieces of cortical bone were impregnated with netilmicin, vancomycin, ciprofloxacin and rifampicin for 1 h, 10 h and 100 h. The antibiotics were eluted into phosphate-buffered saline (PBS) for 7 days, with daily transfer of the bone into fresh PBS. In the in vivo study, cortical allografts impregnated with antibiotics were placed in rats intramuscularly. 10 μL of an S. aureus suspension (0.6 × 105 CFU) was placed in the intramedullary cavity. After 15 days, the allografts were removed and examined for bacterial growth.Results The amount of antibiotics released in vitro was influenced by the time used for antibiotic impregnation of the bone. Allografts impregnated with netilmicin, vancomycin and rifampicin effectively eradicated perioperative contamination with S. aureus in vivo.Interpretation This study shows that a cortical bone allograft would be an effective vehicle for local antibiotic delivery.

Engineered fibrin matrices for functional display of cell membrane-bound growth factor-like activities: Study of angiogenic signaling by ephrin-B2

With the rapid increase in approaches to pro- or anti-angiogenic therapy, new and effective methodologies for administration of cell-bound growth factors will be required. We sought to develop the natural hydrogel matrix fibrin as platform for extensive interactions and continuous signaling by the vascular morphogen ephrin-B2 that normally resides in the plasma membrane and requires multivalent presentation for ligation and activation of Eph receptors on apposing endothelial cell surfaces. Using fibrin and protein engineering technology to induce multivalent ligand presentation, a recombinant mutant ephrin-B2 receptor binding domain was covalently coupled to fibrin networks at variably high densities. The ability of fibrin-bound ephrin-B2 to act as ligand for endothelial cells was preserved, as demonstrated by a concomitant, dose-dependent increase of endothelial cell binding to engineered ephrin-B2–fibrin substrates in vitro. The therapeutic relevance of ephrin-B2–fibrin implant matrices was demonstrated by a local angiogenic response in the chick embryo chorioallontoic membrane evoked by the local and prolonged presentation of matrix-bound ephrin-B2 to tissue adjacing the implant. This new knowledge on biomimetic fibrin vehicles for precise local delivery of membrane-bound growth factor signals may help to elucidate specific biological growth factor function, and serve as starting point for development of new treatment strategies.

Comparison of vascular endothelial growth factor and basic fibroblast growth factor on angiogenesis in SCID mice

Therapeutic angiogenesis is a promising approach to treat patients with cardiovascular disease, and will likely be critical to engineering large tissues. Many growth factors have been found to play significant roles in angiogenesis, and vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are the most extensively investigated angiogenic factors to date. However, the appropriate dose to obtain a desired response and the effectiveness of each factor, relative to the other, in promoting angiogenesis at a specific site in the body remains unclear. We have used alginate hydrogels as localized delivery vehicles for VEGF and bFGF, and compared the ability of these factors to promote new blood vessel formation in the subcutaneous tissue of severe combined immunodeficient (SCID) mice. We have found that the thickness of a granulation tissue layer formed around the gel and the number of blood vessels in the layer increased with the dose of VEGF in the gel, but the density of new blood vessels remained relatively constant. Sustained and localized delivery of bFGF from the gels, while similarly leading to an increase in the density of blood vessels in the granulation tissue, did not lead to as high of a blood vessel density as VEGF. The results of this study support previous studies demonstrating the utility of both VEGF and bFGF in promoting angiogenesis, and suggest VEGF is more appropriate for creating a dense bed of new blood vessels in this model.

Adenoviral mediated interleukin-2 gene transfer to human long-term bone marrow stromal cultures.

Human long-term bone marrow stromal cultures (LTBMC) have been transduced to express the immunostimulatory cytokine interleukin-2 (IL-2). LTBMC were established from normal bone marrow and characterized by gross morphology, immunohistochemistry, immunophenotyping, and immunofluorescent staining. A stromal marrow cell (SMC) population expressing the markers CD68, CD29, CD13, and CD54 was identified. These cells were successfully transduced with an adenoviral vector containing the human IL-2 gene. Production of IL-2 was demonstrated for at least 13 days post-transduction and was maximal on day 10 at 19,350 pg (or 38 IU) of IL-2/10(6) cells/24 h. IL-2 expressed by the transduced SMC was demonstrated to be biologically active, resulting in the proliferation of autologous T lymphocytes in a mixed lymphocyte reaction. Autologous human LTBMC can be obtained and manipulated with relative ease and may be a useful vehicle for sustained local cytokine delivery.

Elution characteristics of tobramycin from polycaprolactone in a rabbit model.

This study investigated the elution characteristics of tobramycin from polycaprolactone, a bioabsorbable polymer, in a rabbit model. Sixty rabbits were divided into two groups. Group 1 had polycaprolactone rods impregnated with 6% tobramycin surgically implanted into the proximal femoral intramedullary canal. Group 2 received polymethylmethacrylate rods of like size, shape, and antibiotic concentration. Serum and urine samples were obtained, and tobramycin levels were determined via fluorescent immunosorbent assay. Rabbits were sacrificed as long as 56 days after surgery. Local bone tobramycin concentration was determined using the agar diffusion method. Polycaprolactone delivered a significantly higher peak bone concentration of tobramycin (22.4 microg/mL) than did polymethylmethacrylate (13.59 microg/mL). Polycaprolactone also had a more gradual decrease in local tobramycin concentration than did polymethylmethacrylate. Neither polycaprolactone nor polymethylmethacrylate yielded consistently detectable (> 0.1 microg/mL) serum tobramycin levels. Urine concentrations mirrored those seen in bone, with polycaprolactone achieving significantly higher tobramycin concentrations than did polymethylmethacrylate. Polycaprolactone had superior elution characteristics compared with polymethylmethacrylate in this lapine model, suggesting that polycaprolactone might be a promising local antibiotic delivery vehicle for the treatment of osteomyelitis.

Dentin regeneration in vital pulp therapy: design principles.

The nature and specificity of the mechanisms by which the amputated dentin-pulp interface is therapeutically healed determine the properties of the barrier at this site and play a critical role in the outcome of vital pulp therapy. Healing of the dentin-pulp complex proceeds either by natural repair-which results in defensive hard-tissue formation, or therapeutically regulated dentin regeneration, which aims to reconstitute the normal tissue architecture at the pulp periphery. Progress in biomedical research opens new directions for the design of biologically effective pulp therapies. Application of biocompatible and biodegradable carrier vehicles for local delivery of signaling molecules in pulp-capping situations showed induction of fibrodentin/reparative dentin formation, but often at the expense of underlying pulp tissue. An alternative pre-clinical model aiming to reconstitute normal tissue architecture directly at the dentin-pulp interface should be designed on the basis of the direct induction of odontoblast-like cell differentiation and reparative dentin formation at the pulp-capping material interface. Experimental data clearly showed that pulpal cells can differentiate directly into odontoblast-like cells in association with specific extracellular matrices (dentinal or fibrodentinal matrix) or TGF beta 1-containing artificial substrates. Dentin-induced dentinogenesis can be used as a master plan for the achievement of new therapeutic opportunities. In the present study, several short-term experimental studies on dog teeth for potential direct induction of odontoblast-like cell differentiation at the surface of rhTGF beta 1-containing artificial substrates (Millipore filters, hydroxyapatite granules, calcium hydroxide, pure titanium) failed to induce any specific reparative dentinogenic effects.

Potential applications and delivery strategies for bone morphogenetic proteins

Bone morphogenetic proteins (BMPs) are multifunctional cytokines which are members of the Transforming Growth Factor-β superfamily. They are the only signaling molecules which can singly induce de novo bone formation at orthotopic and heterotopic sites and their osteoinductive potency makes them clinically valuable as alternatives to bone graft. Several means of delivering BMPs to patients are undergoing evaluation including systemic administration, gene transfer and local matrix delivery vehicle implantation. The latter methodology is in advanced stages of development for application in humans in the treatment of selected spinal fusions, fracture repairs, craniomaxillofacial surgery and periodontal injury and disease. The BMPs are also widely distributed in non-skeletal tissues such as nerve, gastrointestinal tract, kidney, heart and lungs and they have a central role in vertebrate and non-vertebrate organogenesis. Initial studies indicate that the BMPs have neuro, cardio and reno-protective actions and it is likely that therapeutic indications for their use will extend well beyond skeletal disease and injury.

Scattering properties of encapsulated gas bubbles at high ultrasound pressures

Encapsulated types of contrast agents possess a specific acoustical signature. When the applied acoustic pressure exceeds a specific threshold, the scattering level increases abruptly for a short time. A “dualistic” character of the encapsulated gas bubbles explains this signature, observed for Quantison™ (air bubbles encapsulated by a shell of human albumin). For acoustic pressures below a threshold, the bubbles act as encapsulated gas bubbles and are stable linear or nonlinear scatterers, depending on the applied acoustic pressure. For acoustic pressures above the threshold, the bubbles rupture and release the contained gas, subsequently acting as free-gas bubbles. The effect is transient and lasts until the released free-gas bubbles are dissolved in the surrounding liquid. This explanation was investigated experimentally and evaluated by theoretical models. A 15–20-dB increase in scattering, the appearance of higher harmonics, and a finite duration of the effect could be measured and agreed with corresponding theory. Therefore, ultrasound in combination with this dualistic character suggests that encapsulated gas bubbles can be construed as a robust vehicle for localized delivery of free-gas bubbles, the ultimate ultrasound contrast agent.