Unveiling the potential of biomaterials and their synergistic fusion in tissue engineering.

Inspired by nature, tissue engineering aims to employ intricate mechanisms for advanced clinical interventions, unlocking inherent biological potential and propelling medical breakthroughs. Therefore, medical, and pharmaceutical fields are growing interest in tissue and organ replacement, repair, and regeneration by this technology. Three primary mechanisms are currently used in tissue engineering: transplantation of cells (I), injection of growth factors (II) and cellular seeding in scaffolds (III). However, to develop scaffolds presenting highest potential, reinforcement with polymeric materials is growing interest. For instance, natural and synthetic polymers can be used. Regardless, chitosan and keratin are two biopolymers presenting great biocompatibility, biodegradability and non-antigenic properties for tissue engineering purposes offering restoration and revitalization. Therefore, combination of chitosan and keratin has been studied and results exhibit highly porous scaffolds providing optimal environment for tissue cultivation. This review aims to give an historical as well as current overview of tissue engineering, presenting mechanisms used and polymers involved in the field.

Phosphatase-degradable nanoparticles providing sustained drug release.

AIM: The study aimed to develop enzyme-degradable nanoparticles comprising polyphosphates and metal cations providing sustained release of the antibacterial drug ethacridine (ETH). METHODS: Calcium polyphosphate (Ca-PP), zinc polyphosphate (Zn-PP) and iron polyphosphate nanoparticles (Fe-PP NPs) were prepared by co-precipitation of sodium polyphosphate with cations and ETH. Developed nanocarriers were characterized regarding particle size, PDI, zeta potential, encapsulation efficiency and drug loading. Toxicological profile of nanocarriers was assessed via hemolysis assay and cell viability on human blood erythrocytes and HEK-293 cells, respectively. The enzymatic degradation of NPs was evaluated in presence of alkaline phosphatase (ALP) monitoring the release of monophosphate, shift in zeta potential and particle size as well as drug release. The antibacterial efficacy against Escherichia coli was determined via microdilution assay. RESULTS: NPs were obtained in a size range between 300 - 480 nm displaying negative zeta potential values. Encapsulation efficiency was in the range of 83.73 %- 95.99 %. Hemolysis assay underlined sufficient compatibility of NPs with blood cells, whereas drug and NPs showed a concentration dependent effect on HEK-293 cells viability. Ca- and Zn-PP NPs exhibited remarkable changes in zeta potential, particle size, monophosphate and drug release upon incubation with ALP, compared to Fe-PP NPs showing only minor differences. The released ETH from Ca- and Zn-PP nanocarriers retained the antibacterial activity against E. coli, whereas no antibacterial effect was observed with Fe-PP NPs. CONCLUSION: Polyphosphate nanoparticles cross-linked with divalent cations and ETH hold promise for sustained drug delivery triggered by ALP for parental administration.

Preparation and Evaluation of Charge Reversal Solid Lipid Nanoparticles.

The aim of this study was to design and investigate solid lipid nanoparticles (SLN) providing an intestinal alkaline phosphatase (IAP) triggered charge reversion. SLN containing the monophosphate ester bearing surfactant P-PEG-9-lauryl ether and the cationic surfactant benzalkonium chloride were prepared via step-wise hot microemulsion method enabling P-PEG-9-lauryl ether to accumulate the phosphate moiety on the surface of the particles accessible for IAP. Charge reversal SLN were characterized in vitro and ex vivo. SLN containing 10% of P-PEG-9-lauryl ether and 1% of cationic surfactant displayed a z-average of 92 nm and a PDI of 0.33 remaining stable over one year stored at 2-8 °C. An enzyme induced charge reversion from -18.4 mV to +16.5 mV correlated with the cleavage of 82% of the incorporated phosphate. SLN maintained their size during charge reversion, as no significant difference in z-average was observed. Mucin interaction studies revealed a higher interaction between SLN and mucins in the presence of IAP causing an increase in z-average from 190 nm to 2500 nm as well as a decrease in zeta potential from -26 mV to -17 mV. No significant change in z-average and zeta potential was observed when IAP was absent indicating lower mucin interaction of negatively charged particles. In contrast, higher interaction with cell membrane was evidenced by 85% hemolysis when SLN were pretreated with IAP, whereas control SLN without IAP resulted in 16% hemolysis. To investigate the phosphate cleavage by membrane bound IAP, SLN were incubated on excised rat intestinal mucosa and a significant higher release of phosphate was observed in comparison to samples treated with an enzyme inhibitor. Charge reversal SLN might be promising drug delivery systems for alkaline phosphatase bearing membranes that are covered by a mucus gel layer such as the intestine.

Spray-dried mucoadhesive microparticles based on S-protected thiolated hydroxypropyl-ß-cyclodextrin for budesonide nasal delivery.

Budesonide (BUD) is used as first choice therapy for the treatment of allergic rhinitis, a chronic allergic-immune condition with an increased incidence in the pediatric population. The main problem of BUD nasal formulations is related to its poor aqueous solubility (S0 = 5.03·10-5 M), sometimes compensated by the administration of high doses of the drug. The ability of thiolated hydroxypropyl-ß-cyclodextrin (HP- ß -CD-SH, 100 mM) to increase the water solubility of BUD (SHP- ß-CD-SH = 10.9·10-3 M) more than pristine hydroxypropyl- ß -cyclodextrin (HP- ß-CD, SHP- ß-CD = 4.3·10-3 M) has been previously demonstrated. Considering that S-protected thiomers have the advantage of increasing the stability of thiols over a wide pH range prolonging their residence time at the target site, 2-mercapto-nicotinic acid (MNA) was used in this study to protect the free thiol groups on HP- ß -CD-SH generating the corresponding S-protected cyclodextrin (HP-ß-CD-MNA). Besides, given the increased stability and processability of HP-ß-CD-MNA, mucoadhesive microparticles (MPs) were prepared via spray-drying of aqueous solutions of the inclusion complex HP-ß-CD-MNA/BUD. MPs were morphologically and dimensionally homogeneous exhibiting an average diameter of 3.24 ± 0.57 µm. Over time these MPs formed larger aggregates with an average diameter of 10-50 µm, suitable for the design of intranasal delivery systems. Differential scanning calorimetry analyses revealed the absence of crystalline BUD from spray-dried complexes. Dissolution studies shown that spray-dried MPs dissolved quickly and the complexed drug was completely solubilized within the first 20 min of the dissolution process. Cell viability assay indicated that spray-dried complexes are safe. In vitro mucoadhesion studies on freshly excised porcine nasal mucosa showed a 1.4- and 2.3-fold prolonged mucosal residence time of HP- ß -CD-SH/BUD and HP-ß-CD-MNA/BUD in comparison to the unmodified cyclodextrin (CD), respectively. Rheological behaviour of spray-dried MPs complexes/mucus mixtures confirmed the results of the mucoadhesion studies, as the dynamic viscosity of the spray-dried inclusion complexes HP-ß-CD-SH/BUD and HP-ß-CD-MNA/BUD was 1.1-fold and 2.4 fold increased in comparison to the unmodified HP-ß-CD/BUD complex. According to these results, MPs comprising HP- ß -CD-MNA/BUD might be a promising tool for nasal delivery of poorly water-soluble corticosteroids such as BUD.

Thiolated polymeric hydrogels for biomedical application: Cross-linking mechanisms.

This review focuses on the synthesis of hydrogel networks using thiomers such as thiolated hyaluronic acid, chitosan, cyclodextrin, poly(ethylene glycol) and dextran that are cross-linked via their thiol substructures. Thiomers have been widely investigated as matrix of hydrogels due to the high reactivity of these sulfhydryl moieties. They are well known for their in situ gelling properties due to the formation of inter- and intra-chain disulfide bonds. Furthermore, as thiol groups on the polymeric backbone of thiomers cannot only react with each other but also with different other functional groups, several "click" methods such as thiol-ene/yne, Michael type addition and thiol-epoxy reactions have been developed within the last decades to fabricate thiomer hydrogels. These hydrogels are meanwhile used as scaffolds for tissue engineering, regenerative medicine, diagnostics and as matrix for drug and protein delivery.