Simultaneous monitoring of different vitrification solution components permeating into tissues.

Cryopreservation can be used for long-term preservation of tissues and organs. It relies on using complex mixtures of cryoprotective agents (CPAs) to reduce the damaging effects of freezing, but care should be taken to avoid toxic effects of CPAs themselves. In order to rationally design cryopreservation strategies for tissues, it is important to precisely determine permeation kinetics of the protectants that are used to ensure maximum permeation, while minimizing the exposure time and toxicity effects. This is particularly challenging with protectant solutions consisting of multiple components each with different physical properties and diffusing at a different rate. In this study, we show that an attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) setup can be used to simultaneously monitor diffusion of multiple components in a mixture into tissues in real time. Diffusion studies were done with decellularized heart valves using a sucrose-DMSO mixture as well as vitrification solution VS83. To assess diffusion kinetics of different solutes in mixtures, the increase in specific infrared absorbance bands was monitored during diffusion through the tissue. Solute specific wavenumber ranges were selected, and the calculated area was assumed to be proportional to the CPA concentration in the tissue. A diffusion equation based on Fick's second law of diffusion fitted the experimental data quite well, and clear differences in permeation rates were observed among the different mixture components dependent on molecular size and physical properties.

Spectral fingerprinting of decellularized heart valve scaffolds.

Decellularized heart valves hold promise for their use as bioscaffolds in cardiovascular surgery. Quality assessment of heart valves after decellularization processing and/or storage is time consuming and destructive. Fourier transform infrared spectroscopy (FTIR) allows rapid non-invasive assessment of biomolecular structures in tissues. In this study, IR-spectra taken from different layers of the pulmonary artery trunk and leaflet tissues of decellularized porcine heart valves were compared with those of pure collagen and elastin, the main protein components in these tissues. In addition, spectral changes associated with aging and oxidative damage were investigated. Infrared absorbance spectra of the arteria intima and media layer were found to be very similar, whereas distinct differences were observed when compared with spectra of the externa layer. In the latter, the shape of the CH-stretching vibration region (3050-2800 cm-1) resembled that of pure collagen. Also, pronounced νCOOH and amide-II bands and a relatively high content of α-helical structures in the externa layer indicated the presence of collagen in this layer. The externa layer of the artery appeared to be sensitive to collagenase treatment, whereas the media and intima layer were particularly affected by elastase and not by collagenase treatment. Protein conformational changes after treatment with collagenase were observed in all three layers. Collagenase treatment completely degraded the leaflet tissue sections. Spectra were also collected from scaffolds after 2 and 12 weeks storage at 37 °C, and after induced oxidative damage. Spectral changes related to aging and oxidative damage were particularly evident in the CH-stretching region, whereas the shape of the amide-I band, reflecting the overall protein secondary structure, remained unaltered.

Preservation strategies for decellularized pericardial scaffolds for off-the-shelf availability.

Decellularized biological scaffolds hold great promise in cardiovascular surgery. In order to ensure off-the-shelf availability, routine use of decellularized scaffolds requires tissue banking. In this study, the suitability of cryopreservation, vitrification and freeze-drying for the preservation of decellularized bovine pericardial (DBP) scaffolds was evaluated. Cryopreservation was conducted using 10% DMSO and slow-rate freezing. Vitrification was performed using vitrification solution (VS83) and rapid cooling. Freeze-drying was done using a programmable freeze-dryer and sucrose as lyoprotectant. The impact of the preservation methods on the DBP extracellular matrix structure, integrity and composition was assessed using histology, biomechanical testing, spectroscopic and thermal analysis, and biochemistry. In addition, the cytocompatibility of the preserved scaffolds was also assessed. All preservation methods were found to be suitable to preserve the extracellular matrix structure and its components, with no apparent signs of collagen deterioration or denaturation, or loss of elastin and glycosaminoglycans. Biomechanical testing, however, showed that the cryopreserved DBP displayed a loss of extensibility compared to vitrified or freeze-dried scaffolds, which both displayed similar biomechanical behavior compared to non-preserved control scaffolds. In conclusion, cryopreservation altered the biomechanical behavior of the DBP scaffolds, which might lead to graft dysfunction in vivo. In contrast to cryopreservation and vitrification, freeze-drying is performed with non-toxic protective agents and does not require storage at ultra-low temperatures, thus allowing for a cost-effective and easy storage and transport. Due to these advantages, freeze-drying is a preferable method for the preservation of decellularized pericardium. STATEMENT OF SIGNIFICANCE: Clinical use of DBP scaffolds for surgical reconstructions or substitutions requires development of a preservation technology that does not alter scaffold properties during long-term storage. Conclusive investigation on adverse impacts of the preservation methods on DBP matrix integrity is still missing. This work is aiming to close this gap by studying three potential preservation technologies, cryopreservation, vitrification and freeze-drying, in order to achieve the off-the-shelf availability of DBP patches for clinical application. Furthermore, it provides novel insights for dry-preservation of decellularized xenogeneic scaffolds that can be used in the routine clinical cardiovascular practice, allowing the surgeon the opportunity to choose an ideal implant matching with the needs of each patient.

Use of sucrose to diminish pore formation in freeze-dried heart valves.

Freeze-dried storage of decellularized heart valves provides easy storage and transport for clinical use. Freeze-drying without protectants, however, results in a disrupted histoarchitecture after rehydration. In this study, heart valves were incubated in solutions of various sucrose concentrations and subsequently freeze-dried. Porosity of rehydrated valves was determined from histological images. In the absence of sucrose, freeze-dried valves were shown to have pores after rehydration in the cusp, artery and muscle sections. Use of sucrose reduced pore formation in a dose-dependent manner, and pretreatment of the valves in a 40% (w/v) sucrose solution prior to freeze-drying was found to be sufficient to completely diminish pore formation. The presence of pores in freeze-dried valves was found to coincide with altered biomechanical characteristics, whereas biomechanical parameters of valves freeze-dried with enough sucrose were not significantly different from those of valves not exposed to freeze-drying. Multiphoton imaging, Fourier transform infrared spectroscopy, and differential scanning calorimetry studies revealed that matrix proteins (i.e. collagen and elastin) were not affected by freeze-drying.

In vivo performance of freeze-dried decellularized pulmonary heart valve allo- and xenografts orthotopically implanted into juvenile sheep.

The decellularization of biological tissues decreases immunogenicity, allows repopulation with cells, and may lead to improved long-term performance after implantation. Freeze drying these tissues would ensure off-the-shelf availability, save storage costs, and facilitates easy transport. This study evaluates the in vivo performance of freeze-dried decellularized heart valves in juvenile sheep. TritonX-100 and sodium dodecylsulfate decellularized ovine and porcine pulmonary valves (PV) were freeze-dried in a lyoprotectant sucrose solution. After rehydration for 24 h, valves were implanted into the PV position in sheep as allografts (fdOPV) and xenografts (fdPPV), while fresh dezellularized ovine grafts (frOPV) were implanted as controls. Functional assessment was performed by transesophageal echocardiography at implantation and at explantation six months later. Explanted grafts were analysed histologically to assess the matrix, and immunofluorescence stains were used to identify the repopulating cells. Although the graft diameters and orifice areas increased, good function was maintained, except for one insufficient, strongly deteriorated frOPV. Cells which were positive for either endothelial or interstitial markers were found in all grafts. In fdPPV, immune-reactive cells were also found. Our findings suggest that freeze-drying does not alter the early hemodynamic performance and repopulation potential of decellularized grafts in vivo, even in the challenging xenogeneic situation. Despite evidence of an immunological reaction for the xenogenic valves, good early functionalities were achieved. STATEMENT OF SIGNIFICANCE: Decellularized allogeneic heart valves show excellent results as evident from large animal experiments and clinical trials. However, a long-term storing method is needed for an optimal use of this limited resource in the clinical setting, where an optimized matching of graft and recipient is requested. As demonstrated in this study, freeze-dried and freshly decellularized grafts reveal equally good results after implantation in the juvenile sheep concerning function and repopulation with recipients' cells. Thus, freeze-drying arises as a promising method to extend the shelf-life of valvular grafts compared to those stored in antibiotic-solution as currently practised.

Production of Limonoids with Insect Antifeedant Activity in a Two-Stage Bioreactor Process with Cell Suspension Culture of Azadirachta indica.

Neem tree (Azadirachta indica) cell suspension culture is an alternative for the production of limonoids for insect control that overcomes limitations related to the supply of neem seeds. To establish conditions for cell growth and azadiracthin-related limonoid production, the effect of different sucrose concentrations, nitrate and phosphate in Murashige and Skoog (MS) medium, and the addition of one precursor and three elicitors was evaluated in shake flasks. The process was scaled up to a 3-l stirred tank bioreactor in one- and two-stage batch cultivation. In shake flasks, more than fivefold increase in the production of limonoids with the modified MS medium was observed (increase from 0.77 to 4.52 mg limonoids/g dry cell weight, DCW), while an increase of more than fourfold was achieved by adding the elicitors chitosan, salicylic acid, and jasmonic acid together (increase from 1.03 to 4.32 mg limonoids/g DCW). In the bioreactor, the volumetric production of limonoids was increased more than threefold with a two-stage culture in day 18 (13.82 mg limonoids/l in control single-stage process and 41.44 mg/l in two-stage process). The cultivation and operating mode of the bioreactor reported in this study may be adapted and used in optimization and process plant development for production of insect antifeedant limonoids with A. indica cell suspension cultures.