Calibrated bioresorbable microspheres: a preliminary study on the level of occlusion and arterial distribution in a rabbit kidney model

PURPOSE

To assess the level of occlusion and arterial distribution of calibrated bioresorbable microspheres (BRMS-I and BRMS-II) compared with tris-acryl gelatin microspheres (TGMS) after renal embolization.

MATERIALS AND METHODS

Six rabbits underwent renal embolization with 100-300 µm BRMS-I and TGMS; three rabbits received partial occlusion (group 1, n = 3), and three rabbits received total occlusion (group 2, n = 3). Four other rabbits received 100-300 µm BRMS-II (with higher cross-linking density than BRMS-I) in the left kidneys reaching total occlusion (group 3, n = 4). Coronal sections of the kidneys were histologically analyzed. Ease of injection, microsphere deformation, vessel sizes, and arterial distribution were assessed.

RESULTS

The injection of BRMS-I, BRMS-II, and TGMS through microcatheters went smoothly without any clogging. In group 1, BRMS identification was easier than TGMS. In group 2, both BRMS-I and TGMS were observed in all three arterial levels (interlobar, arcuate, and interlobular arteries) without a significant difference (P = .84). BRMS-I were not significantly different from TGMS in the mean diameter of vessels occluded (197 µm ± 23 vs 158 µm ± 21, P = .25) or the microsphere deformation (8.85% ± 0.53% vs 11.80% ± 0.64%, P = .071). In group 3, the arterial distribution of BRMS-II was significantly different from BRMS-I and TGMS (P < .0001).

CONCLUSIONS

In occluding arteries, 100-300 µm BRMS-I were not significantly different from 100-300 µm TGMS. Arterial distribution of BRMS can be influenced by their cross-linking density.

Nano-ferrosponges for controlled drug release

Magnetic sponge-like hydrogels (ferrosponges) were fabricated by using an in-situ synthesis of magnetic nanoparticles (MNPs) in the presence of various concentrations of gelatin. The resulting ferrosponges show an interconnected nanopore structure which serves as a reservoir to accommodate therapeutic drugs and the nanoporous networks demonstrate magnetic sensitive behavior under the application of magnetic field. The ferrosponges showed high swelling ratios, together with excellent elasticity and hydrophilicity, allow them to response rapidly to an external magnetic stimulation for fast and repeatable swelling-deswelling (or expansion-contractile) operations. The ferrosponges with lower gelatin concentration exhibited good performance on magnetification. Furthermore, drug release from the ferrosponges is relatively magnetic-sensitive and is dominated by its magnetism and associated interaction between the magnetic nanoparticle and the gelatin matrix under an external magnetic field. Higher MNPs concentration in the ferrosponges exhibited higher degree of magnetic sensitive which is due to stronger interparticle forces. By taking these peculiar magnetic sensitive behaviors of the ferrosponges, a novel drug delivery system can be designed for medical uses.

Controlling bone morphogenetic protein diffusion and bone morphogenetic protein-stimulated bone growth using fibrin glue

STUDY DESIGN

An in vitro and in vivo study.

OBJECTIVE

To evaluate the ability of fibrin glue to limit diffusion of recombinant human bone morphogenetic protein (rhBMP)-2 and its ability to protect spinal nerves from rhBMP-2 stimulated bone growth.

SUMMARY OF BACKGROUND DATA

Studies have shown bone morphogenetic protein (rhBMP-2) stimulated bone growth can encroach on the spinal canal and nerves, causing neural compression. More recently, rhBMP-2 use in the cervical spine has been associated with life-threatening swelling. Fibrin glue has been used as a biologic carrier but has not been evaluated for its ability to limit rhBMP-2.

METHODS

In phase 1 of the study, rhBMP-2 soaked absorbable collagen sponges (ACS) were encapsulated in fibrin glue and immediately incubated in physiologic lactated ringers solution at 38 degrees C. Samples of solution were tested for rhBMP-2 concentration. In phase 2 of the study, rats were surgically treated with laminectomy and placement of rhBMP-2/ACS versus laminectomy and placement of fibrin glue before placement of rhBMP-2/ACS. After 8 weeks, animals were euthanized and imaged using micro-computerized tomography.

RESULTS

The diffusion study showed a significant limitation in rhBMP-2 diffusion when encapsulated in fibrin glue. The laminectomy study revealed blockage of bone formation by fibrin glue and protection of the spinal canal.

CONCLUSIONS

Fibrin glue can limit the diffusion of rhBMP-2, and, thus, it can be used to help protect the spinal canal and nerve roots from rhBMP-2 stimulated bone growth.

Bio-sorption of acidic gelatine hydro-gels implanted in the back tissues of Fisher's rats

Recent advance in tissue engineering therapy requires new scaffold materials. Acidic gelatine powders (10 wt%) were, thus, dissolved in water, were or were not cross-linked, and freeze-dried. After sterilization, prepared small sponges were implanted in 7-week-old Fisher's rats' subcutaneous tissues for up to 2 weeks. Sponges absorbed body fluid and changed into hydro-gels in vivo. Non-cross-linked hydro-gels were absorbed within 3 days, while cross-linked hydro-gels were eliminated after 7 days' implantation. Histological observations revealed that the common captivation process was mild while granulocytes and macrophages were encountered. Because acidic gelatine sponges can accommodate various basic growth factors, it can be speculated that prepared sponges might be used as short-time hydro-gel scaffolds and growth-factor carriers.

The preparation and characterisation of drug-loaded alginate and chitosan sponges

Sponges composed of sodium alginate and chitosan were prepared via a freeze drying process in order to assess the utility of mixed sponges as potential wound dressings or matrices for tissue engineering. Sponge preparation involved dissolving both polymers (either individually or mixed) in 1% acetic acid and freeze-drying the corresponding solutions. The mechanical properties of the sponges were assessed using texture analysis and the microstructure examined using scanning electron microscopy. The dissolution of a model drug (paracetamol) from the sponges was assessed as a function of polysaccharide composition. It was noted that the sponges had a flexible yet strong texture, as assessed macroscopically. Measurement of the resistance to compression ('hardness') indicated that the chitosan sponges were the 'hardest' while the alginate sponges showed the least resistance to compression, with all sponges showing a high degree of recovery. In contrast, the breaking force (tensile force) of the sponges were greatest for the single component systems, while the elongation prior to breaking was similar for each material. SEM studies indicated that the mixed systems had a less well-defined microstructure than the single component sponges. This was ascribed to the two polysaccharides interacting in aqueous solution via coulombic forces, leading to a more randomly ordered network being formed on freezing. Dissolution studies indicated that systems containing chitosan alone showed the slowest release profile, with the mixed systems showing a relatively rapid dissolution profile. The use of chitosan and alginates together, therefore, appears to allow the formulator to manipulate both the mechanical properties and the drug release properties of the sponges.

The effect on the middle-ear cavity of an absorbable gelatine sponge alone and with corticosteroids

The objectives of this study were to establish whether there is an obvious difference between intact mucosa and abraded mucosa of the middle-ear cavity in respect to the potential side effects from the application of absorbable gelatine sponge (Gelfoam) and to investigate if Gelfoam combined with corticosteroid ointment (cortimycine, sterile 1% hydrocortisone acetate) can reduce the occurrence of these effects. Twenty Albino rats were used in the study. These animals were divided into four groups, with ten ears in each group. In group A, the middle-ear mucosa was kept intact, and Gelfoam was inserted into the middle-ear cavity. In group B, the middle-ear mucosa was abraded, and Gelfoam was inserted. In group C, Gelfoam with corticosteroid was implanted over the intact mucosa, and in group D, the mucosa was abraded prior to the insertion of Gelfoam with corticosteroid. The changes were evaluated 8 weeks postoperatively. In group A, there was a minimal increase in fibroblastic activity, vascular proliferation with mild to moderate fibrosis and all but two tympanic membranes were perfectly normal. However, in group B, we encountered a significant increase in fibroblastic activity, vascular proliferation and fibrosis, and we observed that all tympanic membranes were moderately to severely thickened. These histopathologic changes related to Gelfoam were noted to be decreased in group C and especially in group D. As previously reported in the literature, Gelfoam was found to promote the formation of connective tissue in the middle-ear cavity regardless of the status of the mucosa. The unwanted effects of this material may be decreased if it is combined with corticosteroids in the middle-ear cavity.

Effect of composition on the physicochemical properties and active substance release from gelatin-alginate sponge

The aim the study was physicochemically characterize and develop ability of the active substance (cefradine) from the implantable porous carriers. The drug delivery systems consisting of the gelatine and alginic acid sodium salt and glycerol (GL) or peanut oil (AO). Gelatin-alginate sponge was prepared by foamed components and next freeze-dried this foam. The composition of the sponges affected on the sorption ability and on the stability to proteolytic enzymes. Owing to porous structure obtained specific profile of active substance release.

Tissue implantation test in rabbits with gelatine sponges

The purpose of this implantation study was to evaluate possible toxic effects and quality and quantity of resorption of two different resorbable gelatine sponges when implanted into the paravertebral muscle of the rabbit for a period of 7, 14 or 21 days and to evaluate bioequivalence of two types of test material. Test materials (Gelaspon) and a commercially available reference material were compared in three groups with 6 rabbits each. Tissue reaction to the implants and sponge degradation were scored on a graded scale and the sponges were compared for evaluation. No treatment-related mortality or body weight changes were observed. Clinical signs, indicative of local effects, were mainly seen for reference material. Tissue reaction after 7 days was comparable, after 14 and 21 days a significant increase in granulomatous reaction was seen for reference material. Sponge degradation was complete for test materials after 14 and 21 days without inflammatory tissue reaction, but small sponge rests of reference material were still present, accompanied by an increased inflammatory response. Results show test materials to fulfil the clinical requirements for implant material concerning fast resorption without inflammatory reactions and its superiority to reference material. Bioequivalence of used types of test material could be confirmed.