Polylactide (LTS) causes less inflammation response than polydioxanone (PDS): a meniscus repair model in sheep

[Current regulations in the Animal Welfare Act and the significance for animal research]

Due to the legal implantation of the 3R principle, the number of laboratory animals decreased significantly over the past 10 years. In this article, the historical development of animal experiments over the last decade will be presented in the context of the current regulations of the Animal Welfare Act. It points out bureaucratic obstacles to the approval of animal experiments, which jeopardize Germany as a research location for both academia and industry. The article presents constructive proposals for solutions. This should be done in accordance with the DFG recommendation to ensure efficient biomedical research while maintaining the highest animal welfare standards.

Preparation of Medicated Polylactide Micropieces by Means of Ultrasonic Technology

A technology based on the application of ultrasound as an energy source was applied to get polylactide (PLA) micropieces with minimum degradation and processing time. This requirement could be even shorter than 1.5 s. The ultrasound technology was also demonstrated to be efficient for the incorporation of drugs with a pharmacological activity. Thus, the loading of two representative bactericide agents (i.e., triclosan (TCS), and chlorhexidine (CHX)), having differentiated chemical properties was evaluated. Typical physicochemical characterization included mechanical and thermal properties together with the evaluation of molecular degradation during processing for both unloaded and loaded specimens. Results pointed out that the thermally stable TCS could be loaded into the specimens without any problem, but cautions should be taken into account for CHX. Nevertheless, degradation could in this case be avoided when the drug load was lower than 3 wt-%, a result that contrasts with the significant decomposition attained by using conventional melting processes, which required long processing times at high temperatures. Morphologic analyses of loaded specimens did not reveal significant defects, while spectroscopic analyses showed that a good dispersion of drugs inside pieces could be attained. Drugs were slowly released from micropieces with a rate that was dependent on their hydrophilic character. Thus, release in a phosphate buffered saline (PBS)-ethanol medium (70% of PBS) followed a first order kinetics with constants of 0.0356 h−1 and 0.027 h−1 for CHX and TCS, respectively. A clear bactericide effect against both Gram-positive and Gram-negative bacteria was achieved at the beginning of exposure to the corresponding culture media, while a bacteriostatic effect was interestingly still detected after long exposure times. In fact, bacterial growth could be reduced to near 20% when micropieces were loaded with only 3 wt-% of any of the selected CHX and TCS drugs.

Influence of Sutures on Cartilage Integrity: Do Meniscus Sutures Harm Cartilage? An Experimental Animal Study

PURPOSE

To evaluate whether different suture materials in meniscal repair may harm cartilage.

METHODS

A preloaded linear friction testing setup including porcine knees with porcine cartilage, porcine meniscus, and different suture materials (braided nonabsorbable, absorbable monofilament) was used. Five groups with different tribological pairs were tested: cartilage on meniscus (control), cartilage on cartilage (control No. 2), and cartilage on different meniscus sutures (3 groups). Cartilage integrity was analyzed macroscopically by the India ink method and histologically using Giemsa-eosin-stained undecalcified methyl methacrylate sections. Cartilage lesions were classified by using a quantitative scoring system.

RESULTS

The control groups did not show cartilage damage, either macroscopically or histologically. Loading cartilage with sutured menisci led to significant damage of the superficial radial and transitional zones with braided nonabsorbable (P = .03) and absorbable monofilament (P = .02) sutures at final examination. Menisci sutured with braided nonabsorbable material resulted in deeper damage to the cartilage. However, there were no significant differences between the suture materials. Sutures oriented perpendicular to surface motion led to a larger defect than parallel-oriented sutures.

CONCLUSIONS

Braided nonabsorbable and absorbable monofilament suture materials cause significant damage to cartilage during long-term cyclic loading in vitro. The extent of damage depends on suture orientation.

CLINICAL RELEVANCE

This study provides data on the extent to which different suture materials in meniscus repair may harm cartilage.

Microsurgical tunica albuginea transplantation in an animal model

Several andrological diseases require surgical repair or reconstruction of tunica albuginea, which envelops the corpora cavernosa penis. Despite intense research efforts involving a variety of biological materials, such as skin, muscle aponeurosis, human dura mater, tunica vaginalis, and pericardium, engineered tunica albuginea suitable for graft use is yet to be obtained. The study investigates microsurgical tunica albuginea allotransplantation in an animal model with the purpose of creation of an organ-specific tissue bank to store penile tissue, from cadaveric donors and male-to-female trans-sexual surgery, for allogeneic transplantation. Materials were tunica albuginea tissue explanted from 15 donor rats, cryopreserved at −80°C, gamma-irradiated, and implanted in 15 recipient rats, of which three rats were used as controls. Penile grafts were explanted at different time intervals; after macroscopic evaluation of the organ, the grafts were processed to morphological, histochemical, and immunohistochemical examinations by light microscopy. Detection of pro-inflammatory cytokines was also performed. Examination of the tunica albuginea allografts collected 1, 3, or 6 months after surgery and of control tunica albuginea fragments showed that tunica albuginea implants achieved biointegration with adjacent tissue at all-time points. The integration of cryopreserved rat tunica albuginea allografts, documented by our study, encourages the exploration of tunica albuginea allotransplantation in humans. In conclusion, the effectiveness and reliability of the tunica albuginea conditioning protocol described here suggest the feasibility of setting up a tunica albuginea bank as a further tissue bank.

Biodegradable vascular stents with high tensile and compressive strength: a novel strategy for applying monofilaments via solid-state drawing and shaped-annealing processes

Monofilaments such as those consisting of polyamide (PA), polydioxanone (PDS), and poly(vinylidene fluoride) (PVDF), have been commonly used in various industries. However, most are non-biodegradable, which is unfavorable for many biomedical applications. Although biodegradable polymers offer significant benefits, they are still limited by their weak mechanical properties, which is an obstacle for use as a biomaterial that requires high strength. To overcome the current limitations of biodegradable monofilaments, a novel solid-state drawing (SSD) process was designed to significantly improve the mechanical properties of both PA and poly(l-lactic acid) (PLLA) monofilaments in this study. Both PA and PLLA monofilaments exhibited more than two-fold increased tensile strength and a highly reduced thickness using SSD. In X-ray diffraction and scanning electron microscopy analyses, it was determined that SSD could not only promote the α-crystal phase, but also smoothen the surface of PLLA monofilaments. To apply SSD-monofilaments with superior properties to cardiovascular stents, a shaped-annealing (SA) process was designed as the follow-up process after SSD. Using this process, three types of vascular stents could be fabricated, composed of SSD-monofilaments: double-helix, single-spring and double-spring shaped stents. The annealing temperature was optimized at 80 °C to minimize the loss of mechanical and physical properties of SSD-monofilaments for secondary processing. All three types of vascular stents were tested according to ISO 25539-2. Consequently, it was confirmed that spring-shaped stents had good recovery rate values and a high compressive modulus. In conclusion, this study showed significantly improved mechanical properties of both tensile and compressive strength simultaneously and extended the potential for biomedical applications of monofilaments.

Biodegradable polymeric microcapsules for sustained release of riboflavin

In the current study, a series of polylactic acid and polylactic-co-glycolic acid were prepared in an easy, simple, safe and economically feasible way with yield% greater than 90%. Studying the effect of a catalyst on polymerization process was performed. Riboflavin (RF) was chosen as a model drug and microencapsulated in different (drug: polymer) ratios to modify its performance via o/w emulsion solvent evaporation technique and characterized in terms of the morphology and entrapment efficiency (E.E.) and evaluated via in vitro RF release studies. It has been found that, the release rate consists a burst release at the first 12h, followed by a gradual release over 3days. The cumulative riboflavin release from these microcapsules formulations at the end of 3days was 70% and 80% for PDLA and PDLAGA respectively. The kinetics of release profiles were zero order. The highest (E.E.) of RF obtained among all formulations was 85%.

Micro-molding with ultrasonic vibration energy: new method to disperse nanoclays in polymer matrices

Ultrasound technology was proved as an efficient processing technique to obtain micro-molded specimens of polylactide (PLA) and polybutylene succinate (PBS), which were selected as examples of biodegradable polyesters widely employed in commodity and specialty applications. Operational parameters such as amplitude, molding force and processing time were successfully optimized to prepare samples with a decrease in the number average molecular weight lower than 6%. Ultrasonic waves also seemed an ideal energy source to provide effective disaggregation of clay silicate layers, and therefore exfoliated nanocomposites. X-ray diffraction patterns of nanocomposites prepared by direct micro-molding of PLA or PBS powder mixtures with natural montmorillonite or different organo-modified clays showed the disappearance of the 001 silicate reflection for specimens having up to 6 wt.% clay content. All electron micrographs revealed relatively homogeneous dispersion and sheet nanostructures oriented in the direction of the melt flow. Incorporation of clay particles during processing had practically no influence on PLA characteristics but enhanced PBS degradation when an organo-modifier was employed. This was in agreement with thermal stability data deduced from thermogravimetric analysis. Cold crystallization experiments directly performed on micro-molded PLA specimens pointed to a complex influence of clay particles reflected by the increase or decrease of the overall non-isothermal crystallization rate when compared to the neat polymer. In all cases, the addition of clay led to a clear decrease in the Avrami exponent.

Forces charging the orbital floor after fractures

The objective of this study was first to establish a method to measure forces and displacement of the orbital content in defects of the orbital floor in truncated fresh and unfixed heads and second to characterize reconstruction materials with regard to punctuation strength and compression.Orbital floor defects (10 × 20 mm and 15 × 20 mm; 3 mm behind the orbital rim) were prepared after Le Fort I osteotomy. The values of force and displacement were recorded in 6 freshly frozen human heads. In addition, the punctuation strength of 2 reconstruction materials (polydioxanone [PDS] foil and collagen membrane) was evaluated using a Zwick Z010 TN1 universal testing machine. The forces of the orbital content (28.41 [SD, 1.6] g) applied to the defects of 10 × 20 mm and 15 × 20 mm with an intact periorbita were 0.04 (SD, 0.003) N (0.0002 MPa) and 0.07 (SD, 0.02) N (0.0002 MPa), respectively, and with a split periorbita were 0.06 (SD, 0.03) N (0.0003 MPa) and 0.08 (SD, 0.06) N (0.00026 MPa), respectively. The displacement values without reconstruction materials of the 10 × 20-mm and 15 × 20-mm defects were 0.94 (SD, 0.7) mm and 1.2 (SD, 0.5) mm, respectively. The PDS foil could withstand forces of 118.9 (SD, 14.1) N (0.375 MPa), and the collagen membrane could withstand forces of 44.5 (SD, 5.3) N (0.14 MPa). This is the first study to report forces charging the orbital floor. The presented results support the use of PDS foils and collagen membranes as reconstruction materials for orbital floor defects, at least in smaller and medium-sized fractures.

Local treatment of meniscal lesions with vascular endothelial growth factor

BACKGROUND

The healing potential in the avascular regions of the meniscus is very limited, and improving the vascularity might be a reasonable way to improve healing. Vascular endothelial growth factor (VEGF) is one of the most potent proangiogenetic factors. We hypothesized that the local application of VEGF(165) would (1) improve the healing of a lesion in the avascular region of the meniscus, (2) induce angiogenesis in both the avascular and vascular regions, and (3) increase the amounts of VEGF mRNA and VEGF.

METHODS

In eighteen sheep, the medial menisci were cut longitudinally in the avascular region and were sutured. Three groups were established depending on the suture material: (1) uncoated Ethibond, (2) Ethibond coated with VEGF(165) and its carrier Poly(D,L-Lactide) (PDLLA), and (3) Ethibond coated with PDLLA. The contralateral medial menisci served as a control group. Each of the three suture type groups included six animals. After eight weeks, the sheep were killed, and the menisci were examined macroscopically. Immunohistochemistry of Factor VIII and VEGF and real-time reverse-transcription polymerase chain reaction (RT-PCR) of VEGF mRNA were performed. Additionally, the VEGF release kinetics from the VEGF/PDLLA-coated suture were evaluated in vitro.

RESULTS

In this model, VEGF did not improve meniscal healing. It did not increase angiogenesis in the avascular or vascular region, the VEGF concentration, or the amount of VEGF mRNA. VEGF release from the coated suture peaked on Day 3 and was nearly zero on Day 9.

CONCLUSIONS

The local application of VEGF(165) as eluted from suture did not increase meniscal angiogenesis or improve meniscal healing. In addition, there was no effect on the amount of VEGF mRNA and VEGF. The VEGF carrier (PDLLA) may have been inadequate because of the short duration of VEGF supply.

A rabbit model for efficacy evaluation of endovascular coil materials

BACKGROUND

To investigate biomaterials seeking for their possible use for aneurysm treatment, in vivo screening tests using a number of potential materials are required. However, there is no established animal model that is suitable for such purpose. Some models require special preparation of tested materials for transcatheter delivery and others are inappropriate in view of their cost-effectiveness. The purpose of this study is to establish an animal model that overcomes these limitations and help us select potential materials before the preclinical evaluation.

METHODS

Bilateral CCAs in a rabbit were surgically ligated, and a 2-cm segment of either a bare platinum coil or a polymeric coil (a platinum coil coated with PLGA 10/90) was implanted into each blind-ended arterial segment (n = 26). They were harvested at day 1, 7, 10, 14, or 30, respectively. Angiographic and histologic evaluations as well as quantitative analysis on the development of the organized thrombus were performed.

RESULTS

One day after the implantation, both platinum and PLGA coils were surrounded by immature thrombus that was induced by blood flow stagnation in the arterial segment. At day 7, minimal thrombus organization was observed around both types of materials. At postimplantation days 10 and 14, fibrocellular responses, the early findings of the thrombus organization process, were observed in both material groups. Such histologic findings were more prominent in the PLGA coil group as compared to the platinum coil group (day 10, P = .051; day 14, P = .011). Well-organized thrombus was observed in both material groups at day 30 without showing statistical difference (P = .12).

CONCLUSION

Given the cost-effectiveness, the simple material preparation process, and its feasible histologic evaluation methods, this new animal model can be useful in screening other potential biomaterials for the development of new coil devices.