Biomaterials and biomedical engineering

The Influence of Iron Particles and Polyethylene Glycol on Selected Properties of Polylactide-Based Composites

This article presents the characteristics of composites comprising polylactide combined with iron powder, from 1 to 10 wt.%, and nanoiron powders with a mass fraction from 0.1 to 1.0 wt.%, along with polyethylene glycol. A total of nine composites were prepared, with three variations each: polylactide with iron powder, polylactide with nanoiron powder, and polylactide with micro- and nanoiron powder combined with polyethylene glycol. The samples underwent mixing, extrusion, and pressing processes. To assess the properties of the resultant composite samples, ultimate tensile tests, Shore hardness tests, fracture surface observations, degradation tests in 0.9% saline solution, and DSC analyses were conducted. The findings revealed that nanoiron powder incorporated into the polylactide matrix demonstrates better tensile properties, both strength and elongation, compared to those incorporating micrometric-iron powder only. However, both iron powder additions led to a decrease in the total elongation of neat polylactide acid except for the composite with 1% nanoiron. Furthermore, all samples with polyethylene glycol addition show a lower Young's modulus compared to neat PLA. In general, the microiron powder decreases the Young's modulus of PLA composites, whereas the nanoiron powder slightly increases the Young's modulus of these samples. Polyethylene glycol, a biocompatible substance, emerged as a suitable candidate for enhancing the adhesion of iron particles and improving the strength and elongation properties of the tested composites. Also, fracture surface analysis of the tensile samples suggests using fine nanoiron particles instead of coarse ones to improve the mechanical properties due to the stronger bonding of nanoiron particles to the PLA matrix.

Unraveling and Harnessing the Immune Response at the Cell-Biomaterial Interface for Tissue Engineering Purposes

Biomaterials are defined as "engineered materials" and include a range of natural and synthetic products, designed for their introduction into and interaction with living tissues. Biomaterials are considered prominent tools in regenerative medicine that support the restoration of tissue defects and retain physiologic functionality. Although commonly used in the medical field, these constructs are inherently foreign toward the host and induce an immune response at the material-tissue interface, defined as the foreign body response (FBR). A strong connection between the foreign body response and tissue regeneration is suggested, in which an appropriate amount of immune response and macrophage polarization is necessary to trigger autologous tissue formation. Recent developments in this field have led to the characterization of immunomodulatory traits that optimizes bioactivity, the integration of biomaterials and determines the fate of tissue regeneration. This review addresses a variety of aspects that are involved in steering the inflammatory response, including immune cell interactions, physical characteristics, biochemical cues, and metabolomics. Harnessing the advancing knowledge of the FBR allows for the optimization of biomaterial-based implants, aiming to prevent damage of the implant, improve natural regeneration, and provide the tools for an efficient and successful in vivo implantation.

Piezoelectric Hydrogels: Hybrid Material Design, Properties, and Biomedical Applications

Hydrogels show great potential in biomedical applications due to their inherent biocompatibility, high water content, and resemblance to the extracellular matrix. However, they lack self-powering capabilities and often necessitate external stimulation to initiate cell regenerative processes. In contrast, piezoelectric materials offer self-powering potential but tend to compromise flexibility. To address this, creating a novel hybrid biomaterial of piezoelectric hydrogels (PHs), which combines the advantageous properties of both materials, offers a systematic solution to the challenges faced by these materials when employed separately. Such innovative material system is expected to broaden the horizons of biomedical applications, such as piezocatalytic medicinal and health monitoring applications, showcasing its adaptability by endowing hydrogels with piezoelectric properties. Unique functionalities, like enabling self-powered capabilities and inducing electrical stimulation that mimics endogenous bioelectricity, can be achieved while retaining hydrogel matrix advantages. Given the limited reported literature on PHs, here recent strategies concerning material design and fabrication, essential properties, and distinctive applications are systematically discussed. The review is concluded by providing perspectives on the remaining challenges and the future outlook for PHs in the biomedical field. As PHs emerge as a rising star, a comprehensive exploration of their potential offers insights into the new hybrid biomaterials.

Imaging moiety-directed co-assembly for biodegradation control with synchronous four-modal biotracking

The complexity of existing methods for biodegradation control limits the multi-functionality of biomedical materials. It is urgent to develop simple and straightforward strategies to control the biodegradation rate with precise tracking of various parameters in real-time. Here, we show an imaging moiety-directed co-assembly strategy, in which different imaging moieties bearing non-covalent interaction sites are covalently introduced into the poly (D,l-lactic acid) (PDLLA) chain as end groups, followed by alternate non-covalent interactions with polymer chains upon compression molding. This strategy takes advantage of a variety of bonding types (including CH-π, CH-F, etc.) to firmly integrate the PDLLA chains and strongly control the biodegradation rate, making the amorphous prototype degraded much slower than higher-molecular-weight counterparts, and the local inflammatory response is insignificant. On this basis, a synchronous four-modal (X-ray computed tomography + fluorescence + photoacoustics + ultrasound) imaging was achieved on the single entity in vivo, even within a millimeter-scale thick-skin tissue. These imaging signals can precisely correlate the multi parameter variation trend of material mass, volume and molecular weight, signifying that co-assembly can be utilized to develop advanced theranostic systems. SINGLE SENTENCE SUMMARY: We developed an imaging moiety-directed co-assembly strategy to control the biodegradation rate and achieve the synchronization of real-time four-modal imaging in vivo. These imaging signals can precisely correlate the multi-parameter variation trend of material mass, volume and molecular weight, which provided comprehensive biomedical information accessing both qualitatively and quantitatively.

Antibacterial Hydrogels Derived from Poly(γ-glutamic acid) Nanofibers

Biocompatible hydrogels with antibacterial properties derived from γ-polyglutamic acid (γ-PGA) were prepared from bulk and electrospun nanofibers. The antibacterial drugs loaded in these hydrogels were triclosan (TCS), chlorhexidine (CHX) and polyhexamethylene biguanide (PHMB); furthermore, bacteriophages were loaded as an alternative antibacterial agent. Continuous and regular γ-PGA nanofibers were successfully obtained by the electrospinning of trifluoroacetic acid solutions in a narrow polymer concentration range and restricted parameter values of flow rate, voltage and needle-collector distance. Hydrogels were successfully obtained by using cystamine as a crosslinking agent following previous published procedures. A closed pore structure was characteristic of bulk hydrogels, whereas an open but structurally consistent structure was found in the electrospun hydrogels. In this case, the morphology of the electrospun nanofibers was drastically modified after the crosslinking reaction, increasing their diameter and surface roughness according to the amount of the added crosslinker. The release of TCS, CHX, PHMB and bacteriophages was evaluated for the different samples, being results dependent on the hydrophobicity of the selected medium and the percentage of the added cystamine. A high efficiency of hydrogels to load bacteriophages and preserve their bactericide activity was demonstrated too.

Customized Fading Scaffolds: Strong Polyorthoester Networks via Thiol-Ene Cross-linking for Cytocompatible Surface-Eroding Materials in 3D Printing

Polyorthoesters are a highly desirable class of cytocompatible materials that are able to rapidly surface-erode. Despite their promise, their mechanical weakness and complex synthesis have limited their processability and application in advanced technologies. Herein, we report a readily accessible family of cross-linked poly(orthoester-thioether) (POETE) materials that are suitable for processing via photopolymerization. Polymer networks are accessed through bifunctional orthoester precursors using simple thiol-ene addition chemistry. The mobility of the polymer chains and the cross-linking density within the polymer structure can be tuned through the choice of the monomer, which in turn presents customizable thermal and mechanical properties in the resulting materials. The photopolymerizability of these POETE materials also allows for processing via additive manufacturing, which is demonstrated on a commercial 3D printer. Post-processing conditions and architecture are crucial to material degradability and are exploited for programmed bulk-release applications with degradation rate and release time linearly dependent on the specimen dimensions, such as strand or shell thickness. Analogous to acid-releasing polylactide materials, degradation products of the POETE materials show cytocompatibility below a certain concentration/acidity threshold. This research highlights the simplicity, versatility, and applicability of POETE networks as cytocompatible, surface-eroding materials that can be processed by additive manufacturing for advanced applications.

Cardiovascular stents: overview, evolution, and next generation

Compared to bare-metal stents (BMSs), drug-eluting stents (DESs) have been regarded as a revolutionary change in coronary artery diseases (CADs). Releasing pharmaceutical agents from the stent surface was a promising progress in the realm of cardiovascular stents. Despite supreme advantages over BMSs, in-stent restenosis (ISR) and long-term safety of DESs are still deemed ongoing concerns over clinically application of DESs. The failure of DESs for long-term clinical use is associated with following factors including permanent polymeric coating materials, metallic stent platforms, non-optimal drug releasing condition, and factors that have recently been supposed as contributory factors such as degradation products of polymers, metal ions due to erosion and degradation of metals and their alloys utilizing in some stents as metal frameworks. Discovering the direct relation between stent materials and associating adverse effects is a complicated process, and yet it has not been resolved. For clinical success it is of significant importance to optimize DES design and explore novel strategies to overcome all problems including inflammatory response, delay endothelialization, and sub-acute stent thrombosis (ST) simultaneously. In this work, scientific reports are reviewed particularly focusing on recent advancements in DES design which covers both potential improvements of existing and recently novel prototype stent fabrications. Covering a wide range of information from the BMSs to recent advancement, this study mostly sheds light on DES's concepts, namely stent composition, drug release mechanism, and coating techniques. This review further reports different forms of DES including fully biodegradable DESs, shape-memory ones, and polymer-free DESs.

Two surface gradients of polyethylene glycol for a reduction in protein adsorption

Polyethylene glycol (PEG) coatings have been commonly used in reducing protein adsorption with the intent of improving a biomaterial's biocompatibility. To elucidate the role of PEG surface density in reducing protein adsorption, two types of grafted PEG surface density gradients were evaluated for the adsorption and desorption of albumin and fibrinogen, two blood proteins. PEG density gradients were characterized using contact angle measurements and X-ray photoelectron spectroscopy. Total internal reflection fluorescence was used to measure protein adsorption kinetics and adsorption profiles on the two types of PEG gradients. The PEG gradient generated by the flow method decreased adsorption of both proteins in proportion to the PEG surface density; however, their desorption by buffer solution from the grafted PEG layer was not complete. In contrast, desorption of two proteins from the grafted PEG layer generated by a UV oxidation method resulted in near-zero adsorbed amount. The difference between the two types of gradients might have originated from counter-diffusion of PEG and water molecules occurring during the flow method procedure.

Balanced electrostatic blending approach--an alternative to chemical crosslinking of Thai silk fibroin/gelatin scaffold

In tissue engineering, chemical crosslinking is widely used for conjugating two or more biomaterials to mainly control biodegradability and strength. For example, Thai silk fibroin/gelatin scaffold will offer mechanical strength from Thai silk fibroin and cell attraction from gelatin. However, chemical crosslinking requires crosslinking agent which could potentially pose negative impact from remaining trace amount of chemicals especially in medical application. Here we present an alternative approach to chemical crosslinking-a balance electrostatic blending approach. In this approach, two opposite charge biomaterials were selected for blending, with different ratios. Both materials were bound together with electrostatic force. The maximum binding was achieved when mixture electric potential approaches zero. In this work, we compared this approach with traditionally chemical crosslinking in terms of physical appearance, binding effectiveness, mechanical strength (in dry/wet conditions), in vitro biodegradation, and cell proliferation. We found that 50/50 weight ratio of Thai silk fibroin/gelatin scaffold had almost comparable properties to chemical crosslinked scaffold. It has similar appearance, binding effectiveness, and affinity for cell proliferation. For mechanical properties, even this approach yields lower dry compressive modulus compared with chemical crosslinking. But in wet condition, the compressive modulus from both methods is similar. However, the biodegradation time of non-crosslinked scaffolds is slightly faster than that of chemical crosslinked ones. These results demonstrate that a balance electrostatic approach is an alternative approach to chemical crosslinking when there is a concern of remaining trace amount of crosslinking agent in medical application.

Decreased material-activation of the complement system using low-energy plasma polymerized poly(vinyl pyrrolidone) coatings

In the current study we investigate the activation of blood complement on medical device silicone rubber and present a plasma polymerized vinyl pyrrolidone (ppVP) coating which strongly decreases surface-activation of the blood complement system. We show that uncoated silicone and polystyrene are both potent activators of the complement system, measured both as activated, deposited C3b and quantifying fluid-phase release of the cleavage fragment C3c. The ppVP coated silicone exhibits approximately 90% reduced complement activation compared to untreated silicone. Quartz crystal microbalance with dissipation (QCM-D) measurements show relatively strong adsorption of blood proteins including native C3 to the ppVP surface, indicating that reduction of complement activation on ppVP is neither a result of low protein adsorption nor lower direct C3-binding, and is therefore possibly a consequence of differences in the adsorbed protein layer composition. The alternative and classical complement pathways are barely detectable on ppVP while the lectin pathway through MBL/ficolin-2 deposition remains active on ppVP suggesting this pathway is responsible for the remaining subtle activation on the ppVP coated surface. The ppVP surface is furthermore characterized physically and chemically using scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR), which indicates preservation of chemical functionality by the applied plasma process. Overall, the ppVP coating shows a potential for increasing complement-compatibility of blood-contacting devices.

DNA delivery in vitro via surface release from multilayer assemblies with poly(glycoamidoamine)s

Localized controlled release of nucleic acid therapeutics could be an effective way to reduce the extracellular barriers associated with systemic delivery. Herein, we have used the layer-by-layer film deposition approach to construct ultrathin multilayer assemblies for in vitro controlled release of plasmid DNA (pDNA). Layer-by-layer assemblies containing alternate layers of cationic poly(l-tartaramidopentaethylenetetramine) (T4), and anionic pDNA were fabricated. The film thickness and the absorbance at 260 nm for different T4/pDNA multilayer assemblies were characterized by ellipsometry and UV-vis spectrophotometry, respectively. The results indicated an increased loading capacity of pDNA with respect to an increase in the number of T4/pDNA bilayers deposited. For the controlled-release studies we incubated the bilayers coated on quartz slides in phosphate-buffered saline (PBS) at 37 degrees C and collected the media at different incubation time points. The collected PBS samples were characterized for pDNA release by complexing solutions containing the released pDNA with Lipofectamine 2000 and following cellular pDNA uptake via flow cytometry and GFP gene expression assays with HeLa cells. The study showed that the multilayer films started to release pDNA after 1 day of incubation and increased after 7 days of incubation. Assays monitoring green fluorescent protein (GFP) expression in HeLa cells indicated that about 20% of the cells were positive for GFP expression at all sample time points up to 11 days. Although an increase in cells positive for Cy5-pDNA was found as the incubation time increased, the number of cells positive for GFP expression remained constant over the same time frame.

Matrices and scaffolds for protein delivery in tissue engineering

The tissue engineering of functional tissues depends on the development of suitable scaffolds to support three dimensional cell growth. To improve the properties of the scaffolds, many cell carriers serve dual purposes; in addition to providing cell support, cutting-edge scaffolds biologically interact with adhering and invading cells and effectively guide cellular growth and development by releasing bioactive proteins like growth factors and cytokines. To design controlled release systems for certain applications, it is important to understand the basic principles of protein delivery as well as the stability of each applied biomolecule. To illustrate the enormous progress that has been achieved in the important field of controlled release, some of the recently developed cell carriers with controlled release capacity, including both solid scaffolds and hydrogel-derived scaffolds, are described and possible solutions for unresolved issues are illustrated.

Biomimetic polymers in pharmaceutical and biomedical sciences

This review describes recent developments in the emerging field of biomimetic polymeric biomaterials, which signal to cells via biologically active entities. The described biological effects are, in contrast to many other known interactions, receptor mediated and therefore very specific for certain cell types. As an introduction into this field, first some biological principles are illustrated such as cell attachment, cytokine signaling and endocytosis, which are some of the mechanisms used to control cells with biomimetic polymers. The next topics are then the basic design rules for the creation of biomimetic materials. Here, the major emphasis is on polymers that are assembled in separate building blocks, meaning that the biologically active entity is attached to the polymer in a separate chemical reaction. In that respect, first individual chemical standard reactions that may be used for this step are briefly reviewed. In the following chapter, the emphasis is on polymer types that have been used for the development of several biomimetic materials. There is, thereby, a delineation made between materials that are processed to devices exceeding cellular dimensions and materials predominantly used for the assembly of nanostructures. Finally, we give a few current examples for applications in which biomimetic polymers have been applied to achieve a better biomaterial performance.

In Vitro Assessment of the Enzymatic Degradation of Several Starch Based Biomaterials

The susceptibility of starch-based biomaterials to enzymatic degradation by amylolytic enzymes (glucoamylase and alpha-amylase) was investigated by means of incubating the materials with a buffer solution, containing enzymes at different concentrations and combinations, at 37 degrees C for 6 weeks. Two polymeric blends of corn starch with poly(ethylene-vinyl alcohol) copolymer and poly(epsilon-caprolactone), designated by SEVA-C and SPCL, respectively, were studied. The material degradation was characterized by gravimetry measurements, tensile mechanical testing, scanning electron microscopy (SEM), and Fourrier transform infrared-attenuated total reflectance (FTIR-ATR). The degradation liquors were analyzed for determination of reducing sugars, as a result of enzyme activity, and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was used to identify the degradation products. All of the analysis performed showed that starch polymeric blends are susceptible to enzymatic degradation, as detected by increased weight loss and reducing sugars in solution. alpha-Amylase caused significant changes on the overall mechanical properties of the materials, with a decrease of about 65% and 58% being observed in the moduli for SEVA-C and SPCL, respectively, when compared with the control (samples incubated in buffer only). SEM analysis detected the presence of fractures and pores at the material's surface as a result of starch degradation by amylolytic enzymes. FTIR spectra confirmed a decrease on the band corresponding to glycosidic linkage (-C-O-C-) of starch after incubation of the materials with alpha-amylase. In contrast, the incubation of the polymers in buffer only, did not cause significant changes on the material's properties and morphology. Comparing the two materials, SEVA-C exhibited a higher degradability, which is related to the physicochemical structure of the materials and also to the fact that the starch concentration is higher in SEVA-C. The identification of the degradation products by HPAEC-PAD revealed that glucose was the major product of the enzymatic degradation of starch-based polymers. alpha-Amylase, as expected, is the key enzyme involved in the starch degradation, contributing to major changes on the physicochemical properties of the materials. Nevertheless, it was also found that starch-based polymers can also be degraded by other amylolytic enzymes but in a smaller extent.

Clonazepam release from core-shell type nanoparticles of poly(epsilon-caprolactone)/poly(ethylene glycol)/poly(epsilon-caprolactone) triblock copolymers

The triblock copolymer based on poly(epsilon-caprolactone) (PCL) as hydrophobic part and poly(ethylene glycol) (PEG) as hydrophilic one was synthesized and characterized. Core-shell type nanoparticles of poly(epsilon-caprolactone)/poly(ethylene glycol)/poly(epsilon-caprolactone) (CEC) block copolymer were prepared by a dialysis technique. According to the amphiphilic characters, CEC block copolymer can self-associate at certain concentration and their critical association concentration (CAC) was determined by fluorescence probe technique. CAC value of the CEC-2 block copolymer was evaluated as 0.0030 g/l. CAC values of CEC block copolymer decreased with the increase of PCL chain length, i.e. the shorter the PCL chain length, the higher the CAC values. From the observation of transmission electron microscopy (TEM), the morphologies of CEC-2 core-shell type nanoparticles were spherical shapes. Particle size of CEC-2 nanoparticles was 32.3+/-17.3 nm as a monomodal and narrow distribution. Particle size, drug loading, and drug release rate of CEC-2 nanoparticles were changed by the initial solvents and the molecular weight of CEC. The degradation behavior of CEC-2 nanoparticles was observed by 1H NMR spectroscopy. It was suggested that clonazepam (CNZ) release kinetics were dominantly governed by diffusion mechanism.

On the structural preservation of recombinant human growth hormone in a dried film of a synthetic biodegradable polymer

In this work we describe the structural investigation of the model protein recombinant human growth hormone (rhGH) under conditions relevant to polymeric sustained-delivery depots, including the dried protein entrapped in a film of poly(DL-lactic-co-glycolic)acid. At each step of the procedure, dehydration of rhGH by lyophilization, suspension in methylene chloride, and drying from that suspension, the structure of rhGH was probed noninvasively using Fourier transform infrared (FTIR) spectroscopy. We found that the structure of rhGH was significantly changed by the dehydration process as indicated by a marked drop in the alpha-helix content and increase in the beta-sheet content. Subsequent suspension of this powder in methylene chloride, drying from that suspension, and drying from a methylene chloride/PLGA solution introduced only minor additional structural changes when using appropriate conditions. This result is likely due to the limited molecular mobility of proteins in nonprotein-dissolving organic solvents. Finally, when rhGH was co-lyophilized with the lyoprotectant trehalose, which preserves the secondary structure, the rhGH entrapped in the PLGA matrix also had a nativelike secondary structure.