Electrospun Polyhydroxybutyrate/Poly(ε-caprolactone)/58S Sol-Gel Bioactive Glass Hybrid Scaffolds with Highly Improved Osteogenic Potential for Bone Tissue Engineering

Effect of nanodiamonds surface deposition on hydrophilicity, bulk degradation andin-vitrocell adhesion of 3D-printed polycaprolactone scaffolds for bone tissue engineering

This study was designed to deposit nanodiamonds (NDs) on 3D-printed poly-ϵ-caprolactone (PCL) scaffolds and evaluate their effect on the surface topography, hydrophilicity, degradation, andin-vitrocell adhesion compared to untreated PCL scaffolds. The PCL scaffold specimens were 3D-printed by fused deposition modeling (FDM) technique with specific porosity parameters. The 3D-printed specimens' surfaces were modified by NDs deposition followed by oxygen plasma post-treatment using a plasma focus device and a non-thermal atmospheric plasma jet, respectively. Specimens were evaluated through morphological characterization by field emission scanning electron microscope (FESEM), microstructure characterization by Raman spectroscopy, chemical characterization by Fourier transform infrared (FTIR) spectroscopy, hydrophilicity degree by contact angle and water uptake measurements, andin-vitrodegradation measurements (n= 6). In addition,in-vitrobone marrow mesenchymal stem cells adhesion was evaluated quantitatively by confocal microscopy and qualitatively by FESEM at different time intervals after cell seeding (n= 6). The statistical significance level was set atp⩽ 0.05. The FESEM micrographs, the Raman, and FTIR spectra confirmed the successful surface deposition of NDs on scaffold specimens. The NDs treated specimens showed nano-scale features distributed homogeneously across the surface compared to the untreated ones. Also, the NDs treated specimens revealed a statistically significant smaller contact angle (17.45 ± 1.34 degrees), higher water uptake percentage after 24 h immersion in phosphate buffer saline (PBS) (21.56% ± 1.73), and higher degradation rate after six months of immersion in PBS (43.92 ± 0.77%). Moreover, enhanced cell adhesion at all different time intervals was observed in NDs treated specimens with higher nuclei area fraction percentage (69.87 ± 3.97%) compared to the untreated specimens (11.46 ± 1.34%). Surface deposition of NDs with oxygen-containing functional groups on 3D-printed PCL scaffolds increased their hydrophilicity and degradation rate with significant enhancement of thein-vitrocell adhesion compared to untreated PCL scaffolds.

Development and physiochemical assessment of graphene-bioactive glass-P(3HB-co-4HB) composite scaffold as prospect biomaterial for wound healing

The clinical management of wounds presents a considerable challenge because dressing selection must prioritise the provision of appropriate barrier and the healing properties, consider patient's compliance factors such as comfort, functionality and practicality. This study primarily aimed to develop a composite scaffold patch for potential application in wound healing. Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] is a biopolymer that originated from bacteria. It is well-recognised owing to its distinctive mechanical and physical characteristics suitable for biomedical applications. Graphene (G) and bioactive glass (BG) are biocompatible towards humans, and enhanced properties are achievable by adding biopolymer. In this study, composite scaffolds were developed by combining P(3HB-co-4HB) at a distinct proportion of 4HB monomer reinforced with G (3.0 wt.%) and BG (2.5 wt.%) by using solvent casting, resulting in two types of composite scaffolds: P(3HB-co-25%4HB)/G/BG and P(3HB-co-37%4HB)/G/BG. A successful composite scaffold as a unified structure was achieved based on chemical assessments of organic and inorganic elements within the composites. The pure polymer displayed a smooth surface, and the BG and G addition into the composite scaffolds increased surface roughness, forming irregular pores and protuberances. The wettability and hydrophilicity of the composites significantly improved up to 40% in terms of water uptake. An increment in crystallisation temperature diminished the flexibility of the composite's scaffolds. Evaluation of Presto Blue biocompatibility demonstrated nontoxic behaviour with a dosage of less than 25.00 mg ml-1of composite scaffold-conditioned media. The L929 fibroblast cells displayed excellent adhesion to both types of composite scaffolds, as evidenced by the increased percentage of cell viability observed throughout 14 d of exposure. These findings demonstrate the importance of optimising each component within the composite scaffolds and their interrelation, paving the way for excellent material properties and enhancing the potential for wound healing applications.

Revealing an important role of piezoelectric polymers in nervous-tissue regeneration: A review

Nerve injuries pose a drastic threat to nerve mobility and sensitivity and lead to permanent dysfunction due to low regenerative capacity of mature neurons. The electrical stimuli that can be provided by electroactive materials are some of the most effective tools for the formation of soft tissues, including nerves. Electric output can provide a distinctly favorable bioelectrical microenvironment, which is especially relevant for the nervous system. Piezoelectric biomaterials have attracted attention in the field of neural tissue engineering owing to their biocompatibility and ability to generate piezoelectric surface charges. In this review, an outlook of the most recent achievements in the field of piezoelectric biomaterials is described with an emphasis on piezoelectric polymers for neural tissue engineering. First, general recommendations for the design of an optimal nerve scaffold are discussed. Then, specific mechanisms determining nerve regeneration via piezoelectric stimulation are considered. Activation of piezoelectric responses via natural body movements, ultrasound, and magnetic fillers is also examined. The use of magnetoelectric materials in combination with alternating magnetic fields is thought to be the most promising due to controllable reproducible cyclic deformations and deep tissue permeation by magnetic fields without tissue heating. In vitro and in vivo applications of nerve guidance scaffolds and conduits made of various piezopolymers are reviewed too. Finally, challenges and prospective research directions regarding piezoelectric biomaterials promoting nerve regeneration are discussed. Thus, the most relevant scientific findings and strategies in neural tissue engineering are described here, and this review may serve as a guideline both for researchers and clinicians.

Chitosan/MWCNTs nanocomposite coating on 3D printed scaffold of poly 3-hydroxybutyrate/magnetic mesoporous bioactive glass: A new approach for bone regeneration

The utilization of 3D printing has become increasingly common in the construction of composite scaffolds. In this study, magnetic mesoporous bioactive glass (MMBG) was incorporated into polyhydroxybutyrate (PHB) to construct extrusion-based 3D printed scaffold. After fabrication of the PHB/MMBG composite scaffolds, they were coated with chitosan (Cs) and chitosan/multi-walled carbon nanotubes (Cs/MWCNTs) solutions utilizing deep coating method. FTIR was conducted to confirm the presence of Cs and MWCNTs on the scaffolds' surface. The findings of mechanical analysis illustrated that presence of Cs/MWCNTs on the composite scaffolds increases compressive young modulus significantly, from 16.5 to 42.2 MPa. According to hydrophilicity evaluation, not only MMBG led to decrease the contact angle of pure PHB but also scaffolds surface modification utilization of Cs and MWCNTs, the contact angle decreased significantly from 82.34° to 54.15°. Furthermore, investigation of cell viability, cell metabolism and inflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) and interleukin-10 (IL-10) and transforming growth factor-beta (TGF-β) proved that the scaffolds not only do not stimulate the immune system, but also polarize macrophage cells from M1 phase to M2 phase. The present study highlights the suitability of 3D printed scaffold PHB/MMBG with Cs/MWCNTs coating for bone tissue engineering.

Magnetoactive Composite Conduits Based on Poly(3-hydroxybutyrate) and Magnetite Nanoparticles for Repair of Peripheral Nerve Injury

Peripheral nerve injury poses a threat to the mobility and sensitivity of a nerve, thereby leading to permanent function loss due to the low regenerative capacity of mature neurons. To date, the most widely clinically applied approach to bridging nerve injuries is autologous nerve grafting, which faces challenges such as donor site morbidity, donor shortages, and the necessity of a second surgery. An effective therapeutic strategy is urgently needed worldwide to overcome the current limitations. Herein, a magnetic nerve guidance conduit (NGC) based on biocompatible biodegradable poly(3-hydroxybutyrate) (PHB) and 8 wt % of magnetite nanoparticles modified by citric acid (Fe3O4-CA) was fabricated by electrospinning. The crystalline structure of NGCs was studied by X-ray diffraction, which indicated an enlarged β-phase of PHB in the composite conduit compared to a pure PHB conduit. Tensile tests revealed greater ductility of PHB/Fe3O4-CA: the composite conduit has Young's modulus of 221 ± 52 MPa and an elongation at break of 28.6 ± 2.9%, comparable to clinical materials. Saturation magnetization (σs) of Fe3O4-CA and PHB/Fe3O4-CA is 61.88 ± 0.29 and 7.44 ± 0.07 emu/g, respectively. The water contact angle of the PHB/Fe3O4-CA conduit is lower as compared to pure PHB, while surface free energy (σ) is significantly higher, which was attributed to higher surface roughness and an amorphous phase as well as possible PHB/Fe3O4-CA interface interactions. In vitro, the conduits supported the proliferation of rat mesenchymal stem cells (rMSCs) and SH-SY5Y cells in a low-frequency magnetic field (0.67 Hz, 68 mT). In vivo, the conduits were used to bridge damaged sciatic nerves in rats; pure PHB and composite PHB/Fe3O4-CA conduits did not cause acute inflammation and performed a barrier function, which promotes nerve regeneration. Thus, these conduits are promising as implants for the regeneration of peripheral nerves.

In Vitro Modulation of Spontaneous Activity in Embryonic Cardiomyocytes Cultured on Poly(vinyl alcohol)/Bioglass Type 58S Electrospun Scaffolds

Because of the physiological and cardiac changes associated with cardiovascular disease, tissue engineering can potentially restore the biological functions of cardiac tissue through the fabrication of scaffolds. In the present study, hybrid nanofiber scaffolds of poly (vinyl alcohol) (PVA) and bioglass type 58S (58SiO2-33CaO-9P2O5, Bg) were fabricated, and their effect on the spontaneous activity of chick embryonic cardiomyocytes in vitro was determined. PVA/Bg nanofibers were produced by electrospinning and stabilized by chemical crosslinking with glutaraldehyde. The electrospun scaffolds were analyzed to determine their chemical structure, morphology, and thermal transitions. The crosslinked scaffolds were more stable to degradation in water. A Bg concentration of 25% in the hybrid scaffolds improved thermal stability and decreased degradation in water after PVA crosslinking. Cardiomyocytes showed increased adhesion and contractility in cells seeded on hybrid scaffolds with higher Bg concentrations. In addition, the effect of Ca2+ ions released from the bioglass on the contraction patterns of cultured cardiomyocytes was investigated. The results suggest that the scaffolds with 25% Bg led to a uniform beating frequency that resulted in synchronous contraction patterns.

The Development and Characterisation of a P(3HB-co-4HB)-Bioactive Glass-Graphene Hydrogel as a Potential Formulation for Biomedical and Therapeutical Translation

The clinical management of wounds is known to be a significant challenge: not only does the dressing need to ensure and provide the appropriate barrier and healing characteristics, but consideration of patient compliance concerning comfort, functionality, and practicality also needs to be included. The poly(3-hydroxybutyrate-co-4-hydroxubutyrate) (P(3HB-co-4HB)) copolymer, isolated from Cupriavidus malaysiensis USM1020 (C. malaysiensis USM1020), was produced in the presence of excess carbon sources (1,4-butanediol and 1,6-hexanediol) using either a shake flask cultivation process or a bioreactor fermentation system. P(3HB-co-4HB) is widely known to be biodegradable and highly biocompatible and contains a tuneable 4HB monomer molar fraction, which is known to affect the final physicochemical properties of the intracellular copolymer. In this paper, we describe not only the fabrication of the polymeric gel but also its optimised profiling using a range of physical and mechanical techniques, i.e., SEM, FTIR, DMA, DSC, and WCA. The further enhancement of the gel through additional functionalisation with sol-gel-derived bioactive glass and liquid-exfoliated graphene was also investigated. The biocompatibility and biological characterisation of the substrates was assessed using murine osteoblasts (MC3T3), human primary dermal fibroblasts (HDFs), human fibroblast (BJ) cells, and standard cell culture assays (i.e., metabolic activity, LDH release, and live/dead staining). In short, P(3HB-co-4HB) was successfully isolated from the bacteria, with the defined physico-chemical profiles dependent on the culture substrate and culturing platform used. The additional enhancement of the copolymer with bioactive glass and/or graphene was also demonstrated by varying the combination loading of the materials, i.e., graphene resulted in an increase in tensile strength (~11 MPa) and the wettability increased following the incorporation of bioactive glass and 0.01 wt% graphene (WCA ~46.3°). No detrimental effects in terms of biocompatibility were noticed during the 7 days of culture in the primary and established cell lines. This study demonstrates the importance of optimising each of the individual components within the biocomposite and their relationship concerning the fine-tuning of the material's properties, thus targeting and impacting the endpoint application.

Novel PVAMA/GelMA aerogels prepared by liquid-phase collection of photoinitiated polymerisation: injectable and flowable low-density 3D scaffolds for bone regeneration

Nanofibrous scaffolds, which are morphologically/structurally similar to native extracellular matrix, are ideal biomaterials for tissue engineering and regenerative medicine. However, the use of traditional electrospinning techniques to produce three-dimensional (3D) nanofibrous scaffolds with desired structural properties presents difficulty. To address this challenge, we prepared a novel liquid-phase-collected photoinitiated polymerised aerogel 3D scaffold (LPPI-AG) using the thermally induced (nanofiber) self-aggregation method after liquid-phase electrospinning of the hydroxyapatite-doped methacrylated polyvinyl alcohol/methacrylated gelatine solution obtained by photoinitiated polymerisation. The fabricated aerogel scaffolds had a high porosity of approximately 99.01% ± 0.40% and an interconnected network structure with pore sizes ranging from submicron to ∼300 μm. The new aerogel rapidly became flowable when exposed to a solution, and it can fill gaps and repair gap edges effectively and be loaded with nutrients and growth factors that promote bone growth for bone tissue engineering. LPPI-AG scaffolds can considerably promote osteogenic differentiation of bone marrow mesenchymal stem cells in vitro. Furthermore, in vivo studies showed that the LPPI-AG scaffold significantly promoted bone formation in a mouse model of critical-size calvarial defects.

Multi-leveled Nanosilicate Implants Can Facilitate Near-Perfect Bone Healing

Several studies have shown that nanosilicate-reinforced scaffolds are suitable for bone regeneration. However, hydrogels are inherently too soft for load-bearing bone defects of critical sizes, and hard scaffolds typically do not provide a suitable three-dimensional (3D) microenvironment for cells to thrive, grow, and differentiate naturally. In this study, we bypass these long-standing challenges by fabricating a cell-free multi-level implant consisting of a porous and hard bone-like framework capable of providing load-bearing support and a softer native-like phase that has been reinforced with nanosilicates. The system was tested with rat bone marrow mesenchymal stem cells in vitro and as a cell-free system in a critical-sized rat bone defect. Overall, our combinatorial and multi-level implant design displayed remarkable osteoconductivity in vitro without differentiation factors, expressing significant levels of osteogenic markers compared to unmodified groups. Moreover, after 8 weeks of implantation, histological and immunohistochemical assays indicated that the cell-free scaffolds enhanced bone repair up to approximately 84% following a near-complete defect healing. Overall, our results suggest that the proposed nanosilicate bioceramic implant could herald a new age in the field of orthopedics.

Preparation of superhydrophobic, green, and eco-friendly modified polylactic acid foams for separation oil from water

Developing a facile and green strategy to fabricate polymer foams with super hydrophobicity and eco-friendliness for large-scale oil-water separation remains a challenge. In this study, biocompatible polylactic acid polymer foam modified by nanochitosan and stearic acid was used to remove petroleum and organic contaminants in water. All three materials used to prepare and modify this foam are green and inexpensive. F₄d foam (prepared by solvent displacement method) and F₈d foam (prepared by freeze dryer) can selectively remove oil pollutants in water with a contact angle of 164.01° and 168.51°, respectively. The maximum absorption capacity of oil pollutants by F₄d and F₈d are related to chloroform with values of 32.7 g/g and 48.51 g/g, respectively. Also, the minimum absorption capacity is related to n-hexane with values of 24.83 g/g and 32.06 g/g. The absorption percentage range of F₄d and F₈d foams after 15 cycles of absorption-desorption for chloroform is 82.56 % and 87.81 %, respectively, and for n-hexane, is 77.28 % and 85.99 %, respectively. During the continuous water-oil pumping test, the efficiency of foam can be maintained for >15 h, which shows promising hope for large-scale oil pollution cleaning.

Bioactive glass-based organic/inorganic hybrids: an analysis of the current trends in polymer design and selection

Bioactive glass-based organic/inorganic hybrids are a family of materials holding great promise in the biomedical field. Developed from bioactive glasses following recent advances in sol-gel and polymer chemistry, they can overcome many limitations of traditional composites typically used in bone repair and orthopedics. Thanks to their unique molecular structure, hybrids are often characterized by synergistic properties that go beyond a mere combination of their two components; it is possible to synthesize materials with a wide variety of mechanical and biological properties. The polymeric component, in particular, can be tailored to prepare tough, load-bearing materials, or rubber-like elastomers. It can also be a key factor in the determination of a wide range of interesting biological properties. In addition, polymers can also be used within hybrids as carriers for therapeutic ions (although this is normally the role of silica). This review offers a brief look into the history of hybrids, from the discovery of bioactive glasses to the latest developments, with a particular emphasis on polymer design and chemistry. First the benefits and limitations of hybrids will be discussed and compared with those of alternative approaches (for instance, nanocomposites). Then, key advances in the field will be presented focusing on the polymeric component: its chemistry, its physicochemical and biological advantages, its drawbacks, and selected applications. Comprehensive tables summarizing all the polymers used to date to fabricate sol-gel hybrids for biomedical applications are also provided, to offer a handbook of all the available candidates for hybrid synthesis. In addition to the current trends, open challenges and possible avenues of future development are proposed.

Fabrication and characterization of novel polyhydroxybutyrate-keratin/nanohydroxyapatite electrospun fibers for bone tissue engineering applications

The role of scaffolds in bone regeneration is of great importance. Here, the electrospun scaffolds of poly (3-hydroxybutyrate)-keratin (PHB-K)/nanohydroxyapatite (nHA) with different morphologies (long nanorods (HAR) and very short nanorods (HAP)) and weight percentages (up to 10 w/w%) of nHA were fabricated and characterized. The fibers integrity, the porosity of above 80%, and increase in pore size up to 16 μm were observed by adding nHA. The nanofibers crystallinity increased by 13.5 and 22.8% after the addition of HAR and HAP, respectively. The scaffolds contact angle decreased by almost 20° and 40° after adding 2.5 w/w% HAR and HAP, respectively. The tensile strength of the scaffolds increased from 2.99 ± 0.3 MPa for PHB-K to 6.44 ± 0.16 and 9.27 ± 0.04 MPa for the scaffolds containing 2.5 w/w% HAR and HAP, respectively. After immersing the scaffolds into simulated body fluid (SBF), the Ca concentration decreased by 55% for HAR- and 73% for HAP-containing scaffolds, showing the bioactivity of nHA-containing scaffolds. The results of cell attachment, proliferation, and viability of MG-63 cells cultured on the nanocomposites showed the positive effects of nHA. The results indicate that the nanocomposite scaffolds, especially HAP-containing ones, can be suitable for bone tissue engineering applications.

Fabrication, morphological, mechanical and biological performance of 3D printed poly(ε-caprolactone)/bioglass composite scaffolds for bone tissue engineering applications

Several techniques, such as additive manufacturing, have been used for the manufacture of polymer-ceramic composite scaffolds for bone tissue engineering. A new extruder head recently developed for improving the manufacturing process is an experimental 3D printer Fab@CTI that enables the use of ceramic powders in the processing of composite materials or polymer blends. Still, the manufacturing process needs improvement to promotes the dispersion of ceramic particles in the polymer matrix. This article addresses the manufacture of scaffolds by 3D printing from mixtures of poly(ε-caprolactone) (PCL) and a glass powder of same composition of 45S5Bioglass®, labeled as synthesized bioglass (SBG), according to two different methods that investigated the efficiency of the new extruder head. The first one is a single extrusion process in a Fab@CTI 3D printer, and the other consists in the pre-processing of the PCL-SBG mixture in a mono-screw extruder with a Maddock^®element, followed by direct extrusion in the experimental Fab@CTI 3D printer. The morphological characterization of the extruded samples by SEM showed an architecture of 0o/90o interconnected struts and suitable porosity for bone tissue engineering applications. Scaffolds fabricated by two methods shows compressive modulus ranging from 54.4 ± 14.2 MPa to 155.9 ± 20.4 MPa, results that are compatible to use in bone tissue engineering. Cytotoxicity assays showed non-toxic effects and viability for in vitro MG-63 cell proliferation. Alizarin Red staining test showed calcium deposition in all scaffolds, which suggests PCL/SBG composites promising candidates for use in bone tissue engineering. Results of cell morphology suggest more cell growth and adhesion for scaffolds fabricated using the pre-processing in a mono-screw extruder.

Electrospun nanofibers containing chitosan-stabilized bovine serum albumin nanoparticles for bone regeneration

Bone tissue engineering is becoming a key approach in bone repair and regeneration. In the present study, we fabricated a nanofiber scaffold containing chitosan-stabilized bovine serum albumin (BSA) nanoparticles for the delivery of abaloparatide and aspirin (ASA). The chitosan-stabilized BSA nanoparticles acted as a release barrier for the encapsulated abaloparatide. Polymeric nanofibers were produced by electrospinning from a mixture of abaloparatide-loaded nanoparticles, ASA, poly(ε-caprolactone) (PCL), and nanohydroxyapatite (n-HA). The nanoparticle and nanofiber scaffolds were characterized in terms of their morphology, construction, surface hydrophilicity, degradation, and drug release efficiency. In vitro osteogenesis as well as in vitro cell adhesion, viability, and proliferation were determined to assess their osteoinductive activity. The results showed that the drugs were successfully encapsulated in the scaffolds. Most of the ASA was released within seven days, whereas abaloparatide was released for more than 30 days. The dual-drug-loaded nanofiber scaffolds enhanced the proliferation and osteogenic differentiation of osteoblasts. These findings indicate that electrospun nanofibers containing chitosan-stabilized BSA nanoparticles may be useful in bone tissue engineering.

Biomedical Applications of Polyhydroxyalkanoate in Tissue Engineering

Tissue engineering technology aids in the regeneration of new tissue to replace damaged or wounded tissue. Three-dimensional biodegradable and porous scaffolds are often utilized in this area to mimic the structure and function of the extracellular matrix. Scaffold material and design are significant areas of biomaterial research and the most favorable material for seeding of in vitro and in vivo cells. Polyhydroxyalkanoates (PHAs) are biopolyesters (thermoplastic) that are appropriate for this application due to their biodegradability, thermo-processability, enhanced biocompatibility, mechanical properties, non-toxicity, and environmental origin. Additionally, they offer enormous potential for modification through biological, chemical and physical alteration, including blending with various other materials. PHAs are produced by bacterial fermentation under nutrient-limiting circumstances and have been reported to offer new perspectives for devices in biological applications. The present review discusses PHAs in the applications of conventional medical devices, especially for soft tissue (sutures, wound dressings, cardiac patches and blood vessels) and hard tissue (bone and cartilage scaffolds) regeneration applications. The paper also addresses a recent advance highlighting the usage of PHAs in implantable devices, such as heart valves, stents, nerve guidance conduits and nanoparticles, including drug delivery. This review summarizes the in vivo and in vitro biodegradability of PHAs and conducts an overview of current scientific research and achievements in the development of PHAs in the biomedical sector. In the future, PHAs may replace synthetic plastics as the material of choice for medical researchers and practitioners.

Scaffolds the backbone of tissue engineering: Advancements in use of polyhydroxyalkanoates (PHA)

Our body is built to heal from inside out naturally but wide-ranging medical conditions necessitate the need for artificial assistance, and therefore, something that can assist the body to heal wounds and damaged tissues quickly and efficiently is of utmost importance. Tissue engineering technology helps to regenerate new tissue to replace the diseased or injured one. The technology uses biodegradable porous three-dimensional scaffolds for mimicking the structure and functions of the natural extracellular matrix. The material and design of scaffolds are critical areas of biomaterial research. Biomaterial-based three-dimensional structures have been the most promising material to serve as scaffolds for seeding cells, both in vivo and in vitro. One such material is polyhydroxyalkanoates (PHAs) which are thermoplastic biopolyesters that are highly suitable for this purpose due to their enhanced biocompatibility, biodegradability, thermo-processability, diverse mechanical properties, non-toxicity and natural origin. Moreover, they have tremendous possibilities of customization through biological physical and chemical modification as well as blending with other materials. They are being used for several tissue engineering applications such as bone graft substitute, cardiovascular patches, stents, for nerve repair and in implantology as valves and sutures. The present review overviews usage of a multitude of PHA-based biomaterials for a wide range of tissue engineering applications, based on their properties suitable for the specific applications.

3D gel-printed porous magnesium scaffold coated with dibasic calcium phosphate dihydrate for bone repair in vivo

Background

/Objective: The treatment of bone defect has always been a difficult problem in orthopedic clinic. The search for alternative biodegradable implants is a hot topic. The development of biodegradable magnesium scaffolds for the treatment of bone defects has long been a goal of the public.

Methods

In this study, we proposed a porous magnesium scaffold prepared by 3D gel printing and surface modification with an additional calcium phosphate coating and use of its strength, degradability and slow degradation rate in a bone graft substitute material. The porous magnesium granular scaffold was prepared by 3D gel printing technology and modified by DCPD (Dibasic Calcium Phosphate Dihydrate) coating. The biocompatibility, degradation rate, and osteogenic ability of the scaffold were evaluated in vitro and in vivo.

Results

The biocompatibility, in vivo degradation and bone defect healing response of the implants were investigated. Porous magnesium scaffolds were successfully prepared, and the strength of sintered scaffolds reached 5.38 ​MPa. The degradation rates of scaffolds were significantly reduced after coating with DCPD. The cell compatibility evaluation showed that DCPD-coated Mg scaffold was suitable for cell proliferation. In vivo biosafety monitoring showed that scaffold implantation did not cause an increase in Mg ion concentration in vivo, and no toxic damage was detected in the liver or kidney. Micro-CT and pathological results showed that a large amount of new bone was formed at 6 weeks. At 12 weeks, approximately 52% of the scaffold volume remained. At 24 weeks, osteogenesis, which was stimulated by some residual scaffold, still can be observed. In summary, this study suggests that 3D gel-printed DCPD-coated porous magnesium scaffolds have great potential as bone graft alternatives.

Conclusion

In summary, this study suggests that 3D gel-printed DCPD-coated porous magnesium scaffolds have great potential as bone graft alternatives.

The Translational potential of this article

The translational potential of this article is to make use of the advantages of 3D gel printing technology with higher efficiency and lower cost compared with SLM and SLS technologies, and use pure magnesium powder as raw material to prepare degradable porous magnesium metal scaffolds, opening up a new technical route for the preparation of degradable porous magnesium scaffolds which are made for bone defect regeneration in the future.

Metronidazole Topically Immobilized Electrospun Nanofibrous Scaffold: Novel Secondary Intention Wound Healing Accelerator

The process of secondary intention wound healing includes long repair and healing time. Electrospun nanofibrous scaffolds have shown potential for wound dressing. Biopolymers have gained much attention due to their remarkable characteristics such as biodegradability, biocompatibility, non-immunogenicity and nontoxicity. This study anticipated to develop a new composite metronidazole (MTZ) immobilized nanofibrous scaffold based on poly (3-hydroxy butyrate) (PHB) and Gelatin (Gel) to be utilized as a novel secondary intention wound healing accelerator. Herein, PHB and Gel were mixed together at different weight ratios to prepare polymer solutions with final concentration of (7%), loaded with two different concentrations 5% (Z₁) and 10% (Z₂) of MTZ. Nanofibrous scaffolds were obtained by manipulating electrospinning technique. The properties of MTZ immobilized PHB/Gel nanofibrous scaffold were evaluated (SEM, FTIR, TGA, water uptake, contact angle, porosity, mechanical properties and antibacterial activity). Additionally, in vitro cytocompatibility of the obtained nanofibrous scaffolds were assessed by using the cell counting kit-8 (CCK-8 assay). Moreover, in vivo wound healing experiments revealed that the prepared nanofibrous scaffold highly augmented the transforming growth factor (TGF-β) signaling pathway, moderately suppressed the pro-inflammatory cytokine (IL-6). These results indicate that MTZ immobilized PHB/Gel nanofibrous scaffold significantly boost accelerating secondary intention wound healing.

Microbial-Derived Polyhydroxyalkanoate-Based Scaffolds for Bone Tissue Engineering: Biosynthesis, Properties, and Perspectives

Polyhydroxyalkanoates (PHAs) are a class of structurally diverse natural biopolyesters, synthesized by various microbes under unbalanced culture conditions. PHAs as biomedical materials have been fabricated in various forms to apply to tissue engineering for the past years due to their excellent biodegradability, inherent biocompatibility, modifiable mechanical properties, and thermo-processability. However, there remain some bottlenecks in terms of PHA production on a large scale, the purification process, mechanical properties, and biodegradability of PHA, which need to be further resolved. Therefore, scientists are making great efforts via synthetic biology and metabolic engineering tools to improve the properties and the product yields of PHA at a lower cost for the development of various PHA-based scaffold fabrication technologies to widen biomedical applications, especially in bone tissue engineering. This review aims to outline the biosynthesis, structures, properties, and the bone tissue engineering applications of PHA scaffolds with different manufacturing technologies. The latest advances will provide an insight into future outlooks in PHA-based scaffolds for bone tissue engineering.

Bone Scaffolds: An Incorporation of Biomaterials, Cells, and Biofactors

Large injuries to bones are still one of the most challenging musculoskeletal problems. Tissue engineering can combine stem cells, scaffold biomaterials, and biofactors to aid in resolving this complication. Therefore, this review aims to provide information on the recent advances made to utilize the potential of biomaterials for making bone scaffolds and the assisted stem cell therapy and use of biofactors for bone tissue engineering. The requirements and different types of biomaterials used for making scaffolds are reviewed. Furthermore, the importance of stem cells and biofactors (growth factors and extracellular vesicles) in bone regeneration and their use in bone scaffolds and the key findings are discussed. Lastly, some of the main obstacles in bone tissue engineering and future trends are highlighted.

Multifunctional polyethylene imine hybrids decorated by silica bioactive glass with enhanced mechanical properties, antibacterial, and osteogenesis for bone repair

Inorganic/organic hybrids and bioactive glasses demonstrate promising potential as bone substitute biomaterials. A sol-gel hybrid consisting of silica bioactive glass and biodegradable polymer can combine the high bioactivity of a glass with the toughness of a polymer. In this study, multifunctional hybrids with a combination of organic-inorganic hybrid structure class II consisting of polyethyleneimine (PEI) generation 4 (G4) and bioactive glass with enhanced mechanical properties, mineralization, antibacterial, and osteogenesis activities were synthesized by the sol-gel method. Glycidoxypropyl) trimethoxysilane (GPTMS) with different concentrations was used as a covalent bonding agent between PEI polymer and bioactive glass. The effect of GPTMS content was assessed in the presence and absence of calcium in the hybrid structures in terms of morphology, wettability, mechanical properties, antibacterial activity, cell viability, and in vitro osteogenic differentiation properties. By increasing the amount of GPTMS, the compressive strength increased from 1.95 MPa to 2.34 MPa, which was comparable to human trabecular bone. All the hybrids presented antibacterial activity against Staphylococcus aureus, forming an inhibition zone of 13-16 mm. An increase in cell viability of 82.22% in PSCaG90 was obtained after 1 day of MG-63 cell culture. Alkaline phosphatase expression and mineralization of MG-63 cells increased in the PSCaG90 hybrid in the absence of an osteogenic medium compared to PSG60 and PSG90. The PSCaG90 hybrid indicated considerable in vitro osteogenic capacity in the absence of a differentiation medium, expressing high levels of bone-specific proteins including collagen I (COL1A1), Runt-related transcription factor 2 (RUNX2), osteopontin (OPN), and osteocalcin (OCN), compared to calcium-free hybrids. Overall, our results suggest that the presence of calcium in the PSCaG90 leads to a significant increase in osteogenic differentiation of MG-63 cells even in the absence of differentiation medium, which suggests these hybrid structures with multifunctional properties as promising candidates for bone repair.

Evaluation of the effects of starch on polyhydroxybutyrate electrospun scaffolds for bone tissue engineering applications

Efficient design for bone tissue engineering requires an understanding of the appropriate selection of biomimetic natural or synthetic materials and scalable fabrication technologies. In this research, poly (3-hydroxybutyrate) (PHB) and starch (5-15 wt%) as biological macromolecules were used to fabricate novel biomimetic scaffolds by electrospinning method. SEM results of electrospun scaffolds revealed bead-free nanofibers and three-dimensional homogenous structures with highly interconnected pores. Results of FTIR and Raman demonstrated that there were hydrogen bonds between the two polymers. The tensile strength of scaffolds was significantly improved by adding starch up to 10 wt%, from 3.05 to 15.54 MPa. In vitro degradation and hydrophilicity of the scaffolds were improved with the presence of starch. The viability and proliferation of MG-63 cells and alkaline phosphatase (ALP) activity were remarkably increased in the PHB-starch scaffolds compared to the PHB and control samples. The mineralization and calcium deposition of MG-63 cells were confirmed by alizarin red staining. It is concluded that PHB/starch electrospun scaffold could be a good candidate for bone tissue engineering applications.

Hierarchical Nanostructured Electrospun Membrane with Periosteum-Mimic Microenvironment for Enhanced Bone Regeneration

An ideal periosteum substitute should be able to mimic the periosteum microenvironment that continuously provides growth factors, recruits osteoblasts, and subsequent extracellular matrix (ECM) mineralization to accelerate bone regeneration. Here, a calcium-binding peptide-loaded poly(ε-caprolactone) (PCL) electrospun membrane modified by the shish-kebab structure that can mimic the periosteum microenvironment was developed as a bionic periosteum. The calcium-binding peptide formed by the negatively charged heptaglutamate domain (E7) in the E7-BMP-2 with calcium ion in the tricalcium phosphate sol (TCP sol) through electrostatic chelation not only extended the release cycle of E7-BMP-2 but also promoted the biomineralization of the bionic periosteum. Cell experiments showed that the bionic periosteum could significantly improve the osteogenic differentiation of the rat-bone marrow-derived mesenchymal stem cells (rBMSCs) through both chemical composition and physical structure. The in vivo evaluation of the bionic periosteum confirmed the inherent osteogenesis of this periosteum microenvironment, which could promote the regeneration of vascularized bone tissue. Therefore, the hierarchical nanostructured electrospun membrane with periosteum-mimic microenvironment is a promising periosteum substitute for the treatment of bone defects.

Microbial production and recovery of hybrid biopolymers from wastes for industrial applications- a review

Agro-industrial wastes to be a global concern since agriculture and industrial processes are growing exponentially with the fast increase of the world population. Biopolymers are complex molecules produced by living organisms, but also found in many wastes or derived from wastes. The main drawbacks for the use of polymers are the high costs of the polymer purification processes from waste and the scale-up in the case of biopolymer production by microorganisms. However, the use of biopolymers at industrial scale for the development of products with high added value, such as food or biomedical products, not only can compensate the primary costs of biopolymer production, but also improve local economies and environmental sustainability. The present review describes some of the most relevant aspects related to the synthesis of hybrid materials and nanocomposites based on biopolymers for the development of products with high-added value.

Development and Advantages of Biodegradable PHA Polymers Based on Electrospun PHBV Fibers for Tissue Engineering and Other Biomedical Applications

Biodegradable polymeric biomaterials offer a significant advantage in disposable or fast-consuming products in medical applications. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is an example of a polyhydroxyalkanoate (PHA), i.e., one group of natural polyesters that are byproducts of reactions taking place in microorganisms in conditions with an excess carbon source. PHA polymers are a promising material for the production of everyday materials and biomedical applications. Due to the high number of monomers in the group, PHAs permit modifications enabling the production of copolymers of different compositions and with different proportions of individual monomers. In order to change and improve the properties of polymer fibers, PHAs are combined with either other natural and synthetic polymers or additives of inorganic phases. Importantly, electrospun PHBV fibers and mats showed an enormous potential in both the medical field (tissue engineering scaffolds, plasters, wound healing, drug delivery systems) and industrial applications (filter systems, food packaging). This Review summarizes the current state of the art in processing PHBV, especially by electrospinning, its degradation processes, and biocompatibility studies, starting from a general introduction to the PHA group of polymers.

Polyhydroxyalkanoates biopolymers toward decarbonizing economy and sustainable future

Polymers are synonymous with the modern way of living. However, polymers with a large carbon footprint, especially those derived from nonrenewable petrochemical sources, are increasingly perceived as detrimental to the environment and a sustainable future. Polyhydroxyalkanoate (PHA) is a microbial biopolymer and a plausible alternative for renewable sources. However, PHA in its monomeric forms has very limited applications due to its limited flexibility, tensile strength, and moldability. Herein, the life cycle of PHA molecules, from biosynthesis to commercial utilization for diverse applications is discussed. For clarity, the applications of this bioplastic biocomposite material are further segregated into two domains, namely, the industrial sector and the medical sector. The industry sectors reviewed here include food packaging, textiles, agriculture, automotive, and electronics. High-value addition of PHA for a sustainable future can be foreseen in the medical domain. Properties such as biodegradability and biocompatibility make PHA a suitable candidate for decarbonizing biomaterials during tissue repair, organ reconstruction, drug delivery, bone tissue engineering, and chemotherapeutics.

Biomedical applications of environmental friendly poly-hydroxyalkanoates

Biological polyesters of hydroxyacids are known as polyhydroxyalkanoates (PHA). They have proved to be an alternative, environmentally friendly and attractive candidate for the replacement of petroleum-based plastics in many applications. Many bacteria synthesize these compounds as an intracellular carbon and energy compound usually under unbalanced growth conditions. Biodegradability and biocompatibility of different PHA has been studied in cell culture systems or in an animal host during the last few decades. Such investigations have proposed that PHA can be used as biomaterials for applications in conventional medical devices such as sutures, patches, meshes, implants, and tissue engineering scaffolds as well. Moreover, findings related to encapsulation capability and degradation kinetics of some PHA polymers has paved their way for development of controlled drug delivery systems. The present review discusses about bio-plastics, their characteristics, examines the key findings and recent advances highlighting the usage of bio-plastics in different medical devices. The patents concerning to PHA application in biomedical field have been also enlisted that will provide a brief overview of the status of research in bio-plastic. This would help medical researchers and practitioners to replace the synthetic plastics aids that are currently being used. Simultaneously, it could also prove to be a strong step in reducing the plastic pollution that surged abruptly due to the COVID-19 medical waste.

An organic-inorganic hybrid scaffold with honeycomb-like structures enabled by one-step self-assembly-driven electrospinning

Electrospun organic/inorganic hybrid scaffolds have been appealing in tissue regeneration owing to the integrated physicochemical and biological performances. However, the conventional electrospun scaffolds with non-woven structures usually failed to enable deep cell infiltration due to the densely stacked layers among the fibers. Herein, through self-assembly-driven electrospinning, a polyhydroxybutyrate/poly(ε-caprolactone)/58S sol-gel bioactive glass (PHB/PCL/58S) hybrid scaffold with honeycomb-like structures was prepared by manipulating the solution composition and concentration during a one-step electrospinning process. The mechanisms enabling the formation of self-assembled honeycomb-like structures were investigated through comparative studies using Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) between PHB/PCL/58S and PHB/PCL/sol-gel silica systems. The obtained honeycomb-like structure was built up from nanofibers with an average diameter of 370 nm and showed a bimodal distribution of pores: large polygonal pores up to hundreds of micrometers within the honeycomb-cells and irregular pores among the nanofibers ranging around few micrometers. The cell-materials interactions were further studied by culturing MG-63 osteoblast-like cells for 7 days. Cell viability, cell morphology and cell infiltration were comparatively investigated as well. While cells merely proliferated on the surface of non-woven structures, MG-63 cells showed extensive proliferation and deep infiltration up to 100-200 μm into the honeycomb-like structure. Moreover, the cellular spatial organization was readily regulated by the honeycomb-like pattern as well. Overall, the newly obtained hybrid scaffold may integrate the enhanced osteogenicity originating from the bioactive components, and the improved cell-material interactions brought by the honeycomb-like structure, making the new scaffold a promising candidate for tissue regeneration.

Electrospinning of in situ synthesized silica-based and calcium phosphate bioceramics for applications in bone tissue engineering: A review

The field of bone tissue engineering (BTE) focuses on the repair of bone defects that are too large to be restored by the natural healing process. To that purpose, synthetic materials mimicking the natural bone extracellular matrix (ECM) are widely studied and many combinations of compositions and architectures are possible. In particular, the electrospinning process can reproduce the fibrillar structure of bone ECM by stretching a viscoelastic solution under an electrical field. With this method, nano/micrometer-sized fibres can be produced, with an adjustable chemical composition. Therefore, by shaping bioactive ceramics such as silica, bioactive glasses and calcium phosphates through electrospinning, promising properties for their use in BTE can be obtained. This review focuses on the in situ synthesis and simultaneous electrospinning of bioceramic-based fibres while the reasons for using each material are correlated with its bioactivity. Theoretical and practical considerations for the synthesis and electrospinning of these materials are developed. Finally, investigations into the in vitro and in vivo bioactivity of different systems using such inorganic fibres are exposed.

In Vitro Evaluation of Desensitizing Agents Containing Bioactive Scaffolds of Nanofibers on Dentin Remineralization

This study evaluated the effect of the incorporation of bioactive nanofibers in desensitizing agents on dentin permeability. Sixty disks of dentin were randomly distributed in four groups (n = 15). Distribution was based on the desensitizing agents, fluoride varnish and self-etching adhesive, and the presence of nanofibers: C (self-etching adhesive Clearfil SE Bond), CN (Clearfil SE Bond with 1% nanofiber), D (Duraphat varnish), and DN (Duraphat varnish with 1% nanofiber). Dentin permeability was determined using hydraulic conductivity. For a qualitative analysis, confocal laser microscopy and scanning electron microscopy were performed. The C group showed the lowest hydraulic conductance (Lp%) (89.33), while the DN group showed the highest Lp% (116.06). No statistical significance was observed in the Lp% values in all groups after the treatment and 6% citric acid challenge (p > 0.239). In the images, the CN group presented a higher superficial and intratubular deposition. In addition, this group presented a more homogeneous dentin surface and wide occlusion of dentinal tubules than the other treatments. Despite there being no statistical differences among the treatments employed, the images showed that the CN group presented a higher surface and intratubular deposition compared to the other treatments, even after the acid challenge.

A nano approach towards the creation of a biointerface as stimulator of osteogenic differentiation

There is a great need for tissue engineering constructs with the ability to modulate stem cell behavior. The initial adhesion, growth and differentiation of stem cell are a key strategy in bone tissue engineering and it can be controlled through biomaterial-cell interface. Here we engineered a polycaprolactone/gelatin/bioactive glass (PCL/GT/BG) nanocomposite scaffold coated with Fibronectin (FN) as a potential candidate to aid the bone regeneration process by giving cells a temporary template to grow into. For this purpose, initially BG nanoparticles (nBG) of 70 ± 15 nm were synthesized, characterized and then impregnated into PCL/GT matrix to create a nanocomposite fibrous mesh. An optimized structure was selected based on fiber uniformity, diameter, and the mechanical properties. Cell adhesion, growth, and the expression of osteogenic-related genes as a result of FN tethering, through specific surface interactions, was evaluated. Furthermore, the potential of optimized nanofiberous structure as a drug delivery vehicle for the local release of therapeutic agents was studied by using amoxicillin as a model drug. The release profile revealed that around 70% of drug was released in an hour for non-crosslinked fibers (burst release) followed by a gradual release up to 72 h. The release profile was steadier for crosslinked fibers. The scaffold also showed an antibacterial effect against ubiquitous gram-positive Staphylococcus aureus. The current study provides an insight for future researchers who aim to create nanocomposite materials as multifunctional scaffolds for bone tissue engineering applications.

Using Humidity to Control the Morphology and Properties of Electrospun BioPEGylated Polyhydroxybutyrate Scaffolds

Electrospinning produces nanofibrous scaffolds with potential for tissue engineering and wound repair. Spinning parameters control scaffold morphology and properties. BioPEGylation of polyhydroxybutyrate (PHB) introduces terminal hydrophilic groups into the hydrophobic chain, making this natural-synthetic hybrid copolymer more susceptible to humidity. Varying the humidity from 10 to 50% RH during electrospinning had a relatively little effect on polyhydroxybutyrate (PHB) average fiber and pore diameters, which remained around 3.0 and 8.7 μm, respectively. In contrast, fiber and pore diameters for electrospun bioPEGylated PHB scaffolds varied significantly with humidity, peaking at 30% RH (5.5 and 14.1 μm, respectively). While scaffolds showed little change, hydrophobicity decreased linearly with humidity during electrospinning. Compared to solvent-cast films, electrospun scaffolds showed significantly greater average cell spread. A 108% increase for olfactory ensheathing cells (OECs) cultivated on bioPEGylated PHB scaffolds was proportionally greater than their counterparts on electrospun PHB scaffolds, (70%). OECS grown on BioPEGylated PHB scaffolds were over twice the size, 260 ± 20 μm diameter, than those on PHB electrospun scaffolds, 110 ± 18 μm diameter. Electrospun scaffolds also promoted cell health compared to their solvent-cast counterparts, with increases in the mitochondrial activity of 165 ± 13 and 196 ± 13% for PHB and bioPEGylated PHB, respectively. OECS cultivated on electrospun scaffolds of bioPEGylated PHB had significantly better membrane integrities compared to their counterparts on solvent-cast films, 47 ± 5% reducing to 17 ± 6%. The combination of bioPEGylation and humidity during electrospinning permitted significant controllable changes to scaffold morphology and properties. These changes resulted in the significantly greater promotion of cell growth on electrospun bioPEGylated PHB scaffolds compared to their solvent-cast counterparts and electrospun PHB.

Electrospun PCL Fiber Mats Incorporating Multi-Targeted B and Co Co-Doped Bioactive Glass Nanoparticles for Angiogenesis

Vascularization is necessary in tissue engineering to keep adequate blood supply in order to maintain the survival and growth of new tissue. The synergy of biologically active ions with multi-target activity may lead to superior angiogenesis promotion in comparison to single-target approaches but it has been rarely investigated. In this study, polycaprolactone (PCL) fiber mats embedded with B and Co co-doped bioactive glass nanoparticles (BCo.BGNs) were fabricated as a tissue regeneration scaffold designed for promoting angiogenesis. BCo.NBGs were successfully prepared with well-defined spherical shape using a sol-gel method. The PCL fiber mats embedding co-doped bioactive glass nanoparticles were fabricated by electrospinning using benign solvents. The Young’s moduli of the nanoparticle containing PCL fiber mats were similar to those of the neat fiber mats and suitable for scaffolds utilized in soft tissue repair approaches. The mats also showed non-cytotoxicity to ST-2 cells. PCL fiber mats containing BCo.BGNs with a relatively high content of B and Co promoted the secretion of vascular endothelial growth factor to a greater extent than PCL fiber mats with a relatively low B and Co contents, which demonstrates the potential of dual ion release (B and Co) from bioactive glasses to enhance angiogenesis in soft tissue engineering.

Effect of zirconia-mullite incorporated biphasic calcium phosphate/biopolymer composite scaffolds for bone tissue engineering

New bioactive scaffolds with improved mechanical properties, biocompatibility and providing structural support for bone tissue are being developed for use in the treatment of bone defects. In this study, we have synthesized bioactive scaffolds consisting of biphasic calcium phosphate (BCP) and zirconia-Mullite (2ZrO₂·[3Al₂O₃ ·2 SiO₂] (ZAS)) (BCPZAS) combined with polymers matrix of polycaprolactone (PCL)-alginate (Alg)-chitosan (Chi) (Chi/Alg-PCL) (BCPZAS@Chi/Alg-PCL). The composite material scaffolds were prepared by a blending technique. The microstructure, mechanical, bioactivity and in vitro biological properties with different ratios of BCP to ZAS of 1:0, 3:1, 1:1, 1:3 and 0:1 wt% in polymer matrix were analyzed. Microstructure analysis showed a successful incorporation of the BCPZAS particles with an even distribution of them within the polymer matrix. The mechanical properties were found to gradually decrease with increasing the ratio of ZAS particles in the scaffolds. The highest compressive strength was 42.96 ± 1.01MPa for the 3:1 wt% BCP to ZAS mixing. Bioactivity test, the BCPZAS@Chi/Alg-PCL composite could induce apatite formation in simulate body fluid (SBF). In-vitro experiment using UMR-106 osteoblast-like cells on BCPZAS@Chi/Alg-PCL composite scaffold showed that there is cell attachment to the scaffolds with proliferation. These experimental results demonstrate that the BCPZAS@Chi/Alg-PCL composite especially for the BCP:ZAS at 3:1 wt% could be utilized as a scaffold for bone tissue engineering applications.

Poly(3-hydroxybutyrate): Promising biomaterial for bone tissue engineering

Poly(3-hydroxybutyrate) is a natural polymer, produced by different bacteria, with good biocompatibility and biodegradability. Cardiovascular patches, scaffolds in tissue engineering and drug carriers are some of the possible biomedical applications of poly(3-hydroxybutyrate). In the past decade, many researchers examined the different physico-chemical modifications of poly(3-hydroxybutyrate) in order to improve its properties for use in the field of bone tissue engineering. Poly(3-hydroxybutyrate) composites with hydroxyapatite and bioglass are intensively tested with animal and human osteoblasts in vitro to provide information about their biocompatibility, biodegradability and osteoinductivity. Good bone regeneration was proven when poly(3-hydroxy-butyrate) patches were implanted in vivo in bone tissue of cats, minipigs and rats. This review summarizes the recent reports of in vitro and in vivo studies of pure poly(3-hydroxy-butyrate) and poly(3-hydroxybutyrate) composites with the emphasis on their bioactivity and biocompatibility with bone cells.

Cell Interactions with Size-Controlled Colloidal Monolayers: Toward Improved Coatings in Bone Tissue Engineering

The surface structure of biomaterials is of key importance to control its interactions with biological environments. Industrial fabrication and coating processes often introduce particulate nanostructures at implant surfaces. Understanding the cellular interaction with particle-based surface topologies and feature sizes in the colloidal length scale therefore offers the possibility to improve the biological response of synthetic biomaterials. Here, surfaces with controlled topography and regular feature sizes covering the relevant length scale of particulate coatings (100-1000 nm) are fabricated by colloidal templating. Using fluorescent microscopy, WST assay, and morphology analysis, results show that adhesion and attachment of bone-marrow derived murine stromal cells (ST2) are strongly influenced by the surface feature size while geometric details play an insignificant role. Quantitative analysis shows enhanced cell adhesion, spreading, viability, and activity when surface feature size decreases below 200 nm compared to flat surfaces, while larger feature sizes are detrimental to cell adhesion. Kinetic studies reveal that most cells on surfaces with larger features lose contact with the substrate over time. This study identifies colloidal templating as a simple method for creating highly defined model systems to investigate complex cell functions and provides design criteria for the choice of particulate coatings on commercial implant materials.

Current Applications of Biopolymer-based Scaffolds and Nanofibers as Drug Delivery Systems

BACKGROUND

The high surface-to-volume ratio of polymeric nanofibers makes them an effective vehicle for the release of bioactive molecules and compounds such as growth factors, drugs, herbal extracts and gene sequences. Synthetic polymers are commonly used as sensors, reinforcements and energy storage, whereas natural polymers are more prone to mimicking an extracellular matrix. Natural polymers are a renewable resource and classified as an environmentally friendly material, which might be used in different techniques to produce nanofibers for biomedical applications such as tissue engineering, implantable medical devices, antimicrobial barriers and wound dressings, among others. This review sheds some light on the advantages of natural over synthetic polymeric materials for nanofiber production. Also, the most important techniques employed to produce natural nanofibers are presented. Moreover, some pieces of evidence regarding toxicology and cell-interactions using natural nanofibers are discussed. Clearly, the potential extrapolation of such laboratory results into human health application should be addressed cautiously.

Recent Advances in the Use of Polyhydroyalkanoates in Biomedicine

Polyhydroxyalkanoates (PHAs), a family of natural biopolyesters, are widely used in many applications, especially in biomedicine. Since they are produced by a variety of microorganisms, they possess special properties that synthetic polyesters do not have. Their biocompatibility, biodegradability, and non-toxicity are the crucial properties that make these biologically produced thermoplastics and elastomers suitable for their applications as biomaterials. Bacterial or archaeal fermentation by the combination of different carbohydrates or by the addition of specific inductors allows the bioproduction of a great variety of members from the PHAs family with diverse material properties. Poly(3-hydroxybutyrate) (PHB) and its copolymers, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHVB) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (PHB4HB), are the most frequently used PHAs in the field of biomedicine. PHAs have been used in implantology as sutures and valves, in tissue engineering as bone graft substitutes, cartilage, stents for nerve repair, and cardiovascular patches. Due to their good biodegradability in the body and their breakdown products being unhazardous, they have also been remarkably applied as drug carriers for delivery systems. As lately there has been considerable and growing interest in the use of PHAs as biomaterials and their application in the field of medicine, this review provides an insight into the most recent scientific studies and advances in PHAs exploitation in biomedicine.

Bone Repair and Regenerative Biomaterials: Towards Recapitulating the Microenvironment

Biomaterials and tissue engineering scaffolds play a central role to repair bone defects. Although ceramic derivatives have been historically used to repair bone, hybrid materials have emerged as viable alternatives. The rationale for hybrid bone biomaterials is to recapitulate the native bone composition to which these materials are intended to replace. In addition to the mechanical and dimensional stability, bone repair scaffolds are needed to provide suitable microenvironments for cells. Therefore, scaffolds serve more than a mere structural template suggesting a need for better and interactive biomaterials. In this review article, we aim to provide a summary of the current materials used in bone tissue engineering. Due to the ever-increasing scientific publications on this topic, this review cannot be exhaustive; however, we attempted to provide readers with the latest advance without being redundant. Furthermore, every attempt is made to ensure that seminal works and significant research findings are included, with minimal bias. After a concise review of crystalline calcium phosphates and non-crystalline bioactive glasses, the remaining sections of the manuscript are focused on organic-inorganic hybrid materials.

Multi-Functional Electrospun Nanofibers from Polymer Blends for Scaffold Tissue Engineering

Electrospinning and polymer blending have been the focus of research and the industry for their versatility, scalability, and potential applications across many different fields. In tissue engineering, nanofiber scaffolds composed of natural fibers, synthetic fibers, or a mixture of both have been reported. This review reports recent advances in polymer blended scaffolds for tissue engineering and the fabrication of functional scaffolds by electrospinning. A brief theory of electrospinning and the general setup as well as modifications used are presented. Polymer blends, including blends with natural polymers, synthetic polymers, mixture of natural and synthetic polymers, and nanofiller systems, are discussed in detail and reviewed.