A poly(lactide) stereocomplex structure with modified magnesium oxide and its effects in enhancing the mechanical properties and suppressing inflammation

Enhancing the Potential of PHAs in Tissue Engineering Applications: A Review of Chemical Modification Methods

Polyhydroxyalkanoates (PHAs) are a family of polyesters produced by many microbial species. These naturally occurring polymers are widely used in tissue engineering because of their in vivo degradability and excellent biocompatibility. The best studied among them is poly(3-hydroxybutyrate) (PHB) and its copolymer with 3-hydroxyvaleric acid (PHBV). Despite their superior properties, PHB and PHBV suffer from high crystallinity, poor mechanical properties, a slow resorption rate, and inherent hydrophobicity. Not only are PHB and PHBV hydrophobic, but almost all members of the PHA family struggle because of this characteristic. One can overcome the limitations of microbial polyesters by modifying their bulk or surface chemical composition. Therefore, researchers have put much effort into developing methods for the chemical modification of PHAs. This paper explores a rarely addressed topic in review articles-chemical methods for modifying the structure of PHB and PHBV to enhance their suitability as biomaterials for tissue engineering applications. Different chemical strategies for improving the wettability and mechanical properties of PHA scaffolds are discussed in this review. The properties of PHAs that are important for their applications in tissue engineering are also discussed.

In situ MgO nanoparticle-doped Janus electrospun dressing against bacterial invasion and immune imbalance for irregular wound healing

Owing to the unpredictable size of wounds and irregular edges formed by trauma, nanofibers' highly customizable and adherent in situ deposition can contribute to intervention in the healing process. However, electrospinning is limited by the constraints of conventional polymeric materials despite its potential for anti-inflammatory and antimicrobial properties. Here, inspired by the Janus structure and biochemistry of nanometal ions, we developed an in situ sprayed electrospinning method to overcome bacterial infections and immune imbalances during wound healing. The bilayer fiber scaffold has a hydrophobic outer layer composed of polycaprolactone (PCL) and a hydrophilic inner layer composed of gelatin, poly(L-lactic acid) (PLLA), and magnesium oxide nanoparticles, constituting the PCL/PLLA-gelatin-MgO (PPGM) electrospun scaffold. This electrospun scaffold blocked the colonization and growth of bacteria and remained stable on the wound for continuous anti-inflammatory properties to promote wound healing. Furthermore, PPGM electrospinning modulated collagen deposition and the inflammatory microenvironment in the full-thickness skin model, significantly accelerating vascularization and epithelialization progression. This personalized Janus electrospun scaffold has excellent potential as a new type of wound dressing for first aid and wound healthcare.

Magnesium-oxide-enhanced bone regeneration: 3D-printing of gelatin-coated composite scaffolds with sustained Rosuvastatin release

Critical-size bone defects are one of the main challenges in bone tissue regeneration that determines the need to use angiogenic and osteogenic agents. Rosuvastatin (RSV) is a class of cholesterol-lowering drugs with osteogenic potential. Magnesium oxide (MgO) is an angiogenesis component affecting apatite formation. This study aims to evaluate 3D-printed Polycaprolactone/β-tricalcium phosphate/nano-hydroxyapatite/ MgO (PCL/β-TCP/nHA/MgO) scaffolds as a carrier for MgO and RSV in bone regeneration. For this purpose, PCL/β-TCP/nHA/MgO scaffolds were fabricated with a 3D-printing method and coated with gelatin and RSV. The biocompatibility and osteogenicity of scaffolds were examined with MTT, ALP, and Alizarin red staining. Finally, the scaffolds were implanted in a bone defect of rat's calvaria, and tissue regeneration was investigated after 3 months. Our results showed that the simultaneous presence of RSV and MgO improved biocompatibility, wettability, degradation rate, and ALP activity but decreased mechanical strength. PCL/β-TCP/nHA/MgO/gelatin-RSV scaffolds produced sustained release of MgO and RSV within 30 days. CT images showed that PCL/β-TCP/nHA/MgO/gelatin-RSV scaffolds filled approximately 86.83 + 4.9 % of the defects within 3 months and improved angiogenesis, woven bone, and osteogenic genes expression. These results indicate the potential of PCL/β-TCP/nHA/MgO/gelatin-RSV scaffolds as a promising tool for bone regeneration and clinical trials.

Development of Stereocomplex Polylactide Nanocomposites as an Advanced Class of Biomaterials-A Review

This review paper analyzes the development of advanced class polylactide (PLA) materials through a combination of stereocomplexation and nanocomposites approaches. The similarities in these approaches provide the opportunity to generate an advanced stereocomplex PLA nanocomposite (stereo-nano PLA) material with various beneficial properties. As a potential "green" polymer with tunable characteristics (e.g., modifiable molecular structure and organic-inorganic miscibility), stereo-nano PLA could be used for various advanced applications. The molecular structure modification of PLA homopolymers and nanoparticles in stereo-nano PLA materials enables us to encounter stereocomplexation and nanocomposites constraints. The hydrogen bonding of D- and L-lactide fragments aids in the formation of stereococomplex crystallites, while the hetero-nucleation capabilities of nanofillers result in a synergism that improves the physical, thermal, and mechanical properties of materials, including stereocomplex memory (melt stability) and nanoparticle dispersion. The special properties of selected nanoparticles also allow the production of stereo-nano PLA materials with distinctive characteristics, such as electrical conductivity, anti-inflammatory, and anti-bacterial properties. The D- and L-lactide chains in PLA copolymers provide self-assembly capabilities to form stable nanocarrier micelles for encapsulating nanoparticles. This development of advanced stereo-nano PLA with biodegradability, biocompatibility, and tunability properties shows potential for use in wider and advanced applications as a high-performance material, in engineering field, electronic, medical device, biomedical, diagnosis, and therapeutic applications.

Angiogenesis coupled with osteogenesis in a bone tissue engineering scaffold enhances bone repair in osteoporotic bone defects

Increased life expectancy has resulted in an increase in osteoporosis incidence worldwide. The coupling of angiogenesis and osteogenesis is indispensable for bone repair. Although traditional Chinese medicine (TCM) exerts therapeutic effects on osteoporosis, TCM-related scaffolds, which focus on the coupling of angiogenesis and osteogenesis, have not yet been used for the treatment of osteoporotic bone defects.Panax notoginsengsaponin (PNS), the active ingredient ofPanax notoginseng, was added to a poly (_L-lactic acid) (PLLA) matrix. Osteopractic total flavone (OTF), the active ingredient ofRhizoma Drynariae, was encapsulated in nano-hydroxyapatite/collagen (nHAC) and added to the PLLA matrix. Magnesium (Mg) particles were added to the PLLA matrix to overcome the bioinert character of PLLA and neutralize the acidic byproducts generated by PLLA. In this OTF-PNS/nHAC/Mg/PLLA scaffold, PNS was released faster than OTF. The control group had an empty bone tunnel; scaffolds containing OTF:PNS = 100:0, 50:50, and 0:100 were used as the treatment groups. Scaffold groups promoted new vessel and bone formation, increased the osteoid tissue, and suppressed the osteoclast activity around osteoporotic bone defects. Scaffold groups upregulated the expression levels of angiogenic and osteogenic proteins. Among these scaffolds, the OTF-PNS (50:50) scaffold exhibited a better capacity for osteogenesis than the OTF-PNS (100:0 and 0:100) scaffolds. Activation of the bone morphogenic protein (BMP)-2/BMP receptor (BMPR)-1A/runt-related transcription factor (RUNX)-2signaling pathway may be a possible mechanism for the promotion of osteogenesis. Our study demonstrated that the OTF-PNS/nHAC/Mg/PLLA scaffold could promote osteogenesis via the coupling of angiogenesis and osteogenesis in osteoporotic rats with bone defects, and activating theBMP-2/BMPR1A/RUNX2signaling pathway may be an osteogenesis-related mechanism. However, further experiments are necessary to facilitate its practical application in the treatment of osteoporotic bone defects.

Stereocomplexation Reinforced High Strength Poly(L-lactide)/Nanohydroxyapatite Composites for Potential Bone Repair Applications

Composite materials composed of polylactide (PLA) and nano-hydroxyapatite (n-HA) have been recognized as excellent candidate material in bone repai The difference in hydrophilicity/hydrophobicity and poor interfacial compatibility between n-HA filler and PLA matrix leads to non-uniform dispersion of n-HA in PLA matrix and consequent poor reinforcement effect. In this study, an HA/PLA nanocomposite was designed based on the surface modification of n-HA with poly(D-lactide) (PDLA), which not only can improve the dispersion of n-HA in the poly(L-lactide) (PLLA) matrix but also could form a stereocomplex crystal with the matrix PLLA at the interface and ultimately lead to greatly enhanced mechanical performance The n-HA/PLA composites were characterized by means of scanning electron microscopy, Fourier transform infrared spectroscopy, X-Ray diffraction, thermal gravity analysis, differential scanning calorimetry, and a mechanical test; in vitro cytotoxicity of the composite material as well as its efficacy in inducing osteogenic differentiation of rat bone marrow stromal cells (rMSCs) were also evaluated. Compared with those of neat PLLA, the tensile strength, Young's modulus, interfacial shear strength, elongation at break and crystallinity of the composites increased by 34%, 53%, 26%, 70%, and 17%, respectively. The adhesion and proliferation as well as the osteogenic differentiation of rMSCs on HA/PLA composites were clearly evidenced. Therefore, the HA/PLA composites have great potential for bone repai.

Bioactive PCL microspheres with enhanced biocompatibility and collagen production for functional hyaluronic acid dermal fillers

Polymeric microspheres containing magnesium hydroxide (MH) and a bioactive agent (BA), such as apocynin (APO) and astaxanthin (ATX), have been prepared as functional dermal fillers with enhanced physicochemical and biological performance.

Antimicrobial Polymeric Composites with Embedded Nanotextured Magnesium Oxide

Nanotextured magnesium oxide (MgO) can exhibit both antibacterial and tissue regeneration activity, which makes it very useful for implant protection. To successfully combine these two properties, MgO needs to be processed within an appropriate carrier system that can keep MgO surface available for interactions with cells, slow down the conversion of MgO to the less active hydroxide and control MgO solubility. Here we present new composites with nanotextured MgO microrods embedded in different biodegradable polymer matrixes: poly-lactide-co-glycolide (PLGA), poly-lactide (PLA) and polycaprolactone (PCL). Relative to their hydrophilicity, polarity and degradability, the matrices were able to affect and control the structural and functional properties of the resulting composites in different manners. We found PLGA matrix the most effective in performing this task. The application of the nanotextured 1D morphology and the appropriate balancing of MgO/PLGA interphase interactions with optimal polymer degradation kinetics resulted in superior bactericidal activity of the composites against either planktonic E. coli or sessile S. epidermidis, S. aureus (multidrug resistant-MRSA) and three clinical strains isolated from implant-associated infections (S. aureus, E. coli and P. aeruginosa), while ensuring controllable release of magnesium ions and showing no harmful effects on red blood cells.

Impact of Lipid/Magnesium Hydroxide Hybrid Nanoparticles on the Stability of Vascular Endothelial Growth Factor-Loaded PLGA Microspheres

The purpose of the present study is to characterize poly(d,l-lactide-co-glycolide) (PLGA) composite microcarriers for vascular endothelial growth factor (VEGF) delivery. To reduce the initial burst release and protect the bioactivity, VEGF is encapsulated in soybean l-α-phosphatidylethanolamine (PE) and l-α-phosphatidylcholine (PC) anhydrous reverse micelle (VEGF-RM) nanoparticles. Also, mesoporous nano-hexagonal Mg(OH)₂ nanostructure (MNS)-loaded PE/PC anhydrous reverse micelle (MNS-RM) nanoparticles are synthesized to suppress the induced inflammation of PLGA acidic byproducts and regulate the release profile. The flow-focusing microfluidic geometry platforms are used to fabricate different combinations of PLGA composite microspheres (PLGA-CMPs) with MNSs, MNS-RM, VEGF-RM, and native VEGF. The essential parameters of each formulation, such as release profiles, encapsulation efficacy, bioactivity, inflammatory response, and cytotoxicity, are investigated by in vitro and in vivo studies. The results indicate that generated acidic byproducts during the hydrolytic degradation process of PLGA can be buffered, and pH values inside and outside microspheres can remain steady during degradation by MNSs. Furthermore, the significant improvement in the stability of the encapsulated VEGF is confirmed by the bioactivity assay. In vitro release study shows that the VEGF initial burst release is well minimized in the present microcarriers. The present monodisperse PLGA-CMPs can be widely used in various tissue engineering and therapeutic applications.

In Vivo Degradation Mechanisms of Aliphatic Polycarbonates and Functionalized Aliphatic Polycarbonates

Aliphatic polycarbonates (APCs) have been studied for decades but have not been as utilized as aliphatic polyesters in biomaterial applications such as drug delivery and tissue engineering. With the recognition that functionalized aliphatic polymers can be readily synthesized, increased attention is being paid to these materials. A frequently provided reason for utilizing these polymers is that they degrade to form diols and carbon dioxide. However, depending on the structure and molecular weight of the APC, degradation may not occur. In this review, the mechanisms by which APCs and functionalized APCs have been found to degrade in vivo are examined with the objective of providing guidance in the continued development of these polymers as biomaterials.

In Vivo Degradation Mechanism and Biocompatibility of a Biodegradable Aliphatic Polycarbonate: Poly(Trimethylene Carbonate-co-5-Hydroxy Trimethylene Carbonate)

A recently developed viscous liquid aliphatic polycarbonate, poly(trimethylene carbonate-co-5-hydroxy trimethylene carbonate), has advantageous properties for the delivery of acid-sensitive drugs such as proteins and peptides. This copolymer degrades in vitro via an alkaline-catalyzed intramolecular cyclization reaction yielding oligo (trimethylene carbonate), glycerol, and carbon dioxide, but its in vivo degradation mechanisms are presently unknown. The in vivo degradation mechanism and tissue response to this copolymer were investigated following subcutaneous implantation in Wistar rats. The molecular weight and composition of the copolymer varied in the same manner following subcutaneous implantation as observed in vitro. These findings suggest that the copolymer also degraded in vivo principally via intramolecular cyclization. The tissue response in terms of the inflammatory zone cell density, fibrous capsule thickness, and macrophage response was intermediate to that of two clinically used biodegradable sutures, Vicryl and Monocryl, indicating that the copolymer can be considered biotolerable. Collectively, the data show that further development of this copolymer as a drug delivery material is warranted.

In Vivo Cartilage Regeneration with Cell-Seeded Natural Biomaterial Scaffold Implants: 15-Year Study

Articular cartilage can be easily damaged from human's daily activities, leading to inflammation and to osteoarthritis, a situation that can diminish the patients' quality of life. For larger cartilage defects, scaffolds are employed to provide cells the appropriate three-dimensional environment to proliferate and differentiate into healthy cartilage tissue. Natural biomaterials used as scaffolds, attract researchers' interest because of their relative nontoxic nature, their abundance as natural products, their easy combination with other materials, and the relative easiness to establish Marketing Authorization. The last 15 years were chosen to review, document, and elucidate the developments on cell-seeded natural biomaterials for articular cartilage treatment in vivo. The parameters of the experimental designs and their results were all documented and presented. Considerations about the newly formed cartilage and the treatment of cartilage defects were discussed, along with difficulties arising when applying natural materials, research limitations, and tissue engineering approaches for hyaline cartilage regeneration.

Biocompatible and functional inorganic magnesium ceramic particles for biomedical applications

Magnesium ceramics hold promise for numerous biological applications. This review covers the synthesis of magnesium ceramic particles with specific morphologies and potential modification techniques. Magnesium ceramic particles possess multiple characteristics directly applicable to human biology; they are anti-inflammatory, antibacterial, antiviral, and offer anti-cancer effects. Based on these advantages, magnesium hydroxide nanoparticles have been extensively utilized across biomedical fields. In a vascular stent, the incorporation of magnesium ceramic nanoparticles enhances re-endothelialization. Additionally, tissue regeneration for bone, cartilage, and kidney can be promoted by magnesium ceramics. This review enables researchers to identify the optimum synthetic conditions to prepare magnesium ceramics with specific morphologies and sizes and select the appropriate modification protocols. It is also intended to elucidate the desirable physicochemical properties and biological benefits of magnesium ceramics.

Formulation parameters governing sustained protein delivery from degradable viscous liquid aliphatic polycarbonates

Viscous liquid degradable polymers have advantages as drug depots for sustained protein delivery. We have created a new aliphatic polycarbonate for this purpose, poly(trimethylene carbonate-co-5-hydroxy trimethylene carbonate), which upon degradation retains a near neutral micro-environmental pH. As such, this copolymer is highly suited to the delivery of acid sensitive proteins. We show that the mechanism of protein release from this liquid copolymer is consistent with the formation of super-hydrated regions as a result of the osmotic activity of the solution formed upon distributed protein particle dissolution. Protein release can be manipulated by controlling polymer hydrophobicity which can be adjusted by molecular weight and choice of initiator. Moreover, protein release is highly dependent on protein solubility which impacts the osmotic activity of the solution formed upon dissolution of the protein particles while protein molecular size and isoelectric point are not as influential. As demonstrated by the release of highly bioactive vascular endothelial growth factor, formulations of this copolymer are suitable for prolonged delivery of protein therapeutics.

Enhanced mechanical and biological characteristics of PLLA composites through surface grafting of oligolactide on magnesium hydroxide nanoparticles

Poly(l-lactic acid) (PLLA) is a biocompatible and biodegradable polymer that has received much attention as a biomedical material. However, PLLA also produces by-products that acidify the surrounding tissues during in vivo degradation, which induces inflammatory responses. To overcome these problems, magnesium hydroxide nanoparticles (nano-magnesium hydroxide; nMH) were added to the PLLA matrix as a bioactive filler that can suppress inflammatory responses by neutralizing the acidified environment caused by the degradation of PLLA. Despite the advantages of nMH, the strong cohesion of these nanoparticles toward each other makes it difficult to manufacture a polymer matrix containing homogeneous nanoparticles through thermal processing. Here, we prepared two types of surface-modified nMH with oligolactide (ODLLA) utilizing grafting to (GT) and grafting from (GF) strategies to improve the mechanical and biological characteristics of the organic-inorganic hybrid composite. The incorporation of surface-modified nMH not only enhanced mechanical properties, such as Young's modulus, but also improved homogeneity of magnesium hydroxide particles in the PLLA matrix due to the increase in interfacial interaction. Additionally, the PLLA composites with surface-modified nMH exhibited reduced bulk erosion during hydrolytic degradation with lower cytotoxicity and immunogenicity. Hemocompatibility tests on the PLLA composites with nMH showed a higher albumin to fibrinogen ratio (AFR) and a lower influence of platelet activation, when compared with unmodified control samples. Taken all together, the surface-modified nMH could be seen to successfully improve the physical and biological characteristics of polymer composites. We believe this technology has great potential for the development of hybrid nanocomposites for biomedical devices, including cardiovascular implants.

Effects of Magnesium Oxide (MgO) Shapes on In Vitro and In Vivo Degradation Behaviors of PLA/MgO Composites in Long Term

Biodegradable devices for medical applications should be with an appropriate degradation rate for satisfying the various requirements of bone healing. In this study, composite materials of polylactic acid (PLA)/stearic acid-modified magnesium oxide (MgO) with a 1 wt% were prepared through blending extrusion, and the effects of the MgO shapes on the composites’ properties in in vitro and in vivo degradation were investigated. The results showed that the long-term degradation behaviors of the composite samples depended significantly on the filler shape. The degradation of the composites is accelerated by the increase in the water uptake rate of the PLA matrix and the composite containing the MgO nanoparticles was influenced more severely by the enhanced hydrophilicity. Furthermore, the pH value of the phosphate buffer solution (PBS) was obviously regulated by the dissolution of MgO through the neutralization of the acidic product of the PLA degradation. In addition, the improvement of the in vivo degrading process of the composite illustrated that the PLA/MgO materials can effectively regulate the degradation of the PLA matrix as well as raise its bioactivity, indicating the composites for utilization as a biomedical material matching the different requirements for bone-related repair.

A biodegradable multifunctional nanofibrous membrane for periodontal tissue regeneration

Biomaterial-based membranes represent a promising therapeutic option for periodontal diseases. Although conventional periodontal membranes function greatly in preventing the ingrowth of both fibroblasts and epithelial cells as well as connective tissues, they are not capable of promoting periodontal tissue regeneration. Here, we report a multifunctional periodontal membrane prepared by electrospinning biodegradable polymers with magnesium oxide nanoparticles (nMgO). nMgO is a light metal-based nanoparticle with high antibacterial capacity and can be fully resorbed in the body. Our results showed that incorporating nMgO into poly(L-lactic acid) (PLA)/gelatin significantly improved the overall properties of membranes, including elevated tensile strength to maintain structural stability and adjusted degradation rate to fit the time window of periodontal regeneration. Acidic degradation products of PLA were neutralized by alkaline ions from nMgO hydrolysis, ameliorating pH microenvironment beneficial for cell proliferation. In vitro studies demonstrated considerable antibacterial and osteogenic properties of nMgO-incorporated membranes that are highly valuable for periodontal regeneration. Further investigations in a rat periodontal defect model revealed that nMgO-incorporated membranes effectively guided periodontal tissue regeneration. Taken together, our data indicate that nMgO-incorporated membranes might be a promising therapeutic option for periodontal regeneration. STATEMENT OF SIGNIFICANCE: Traditional clinical treatments of periodontal diseases largely focus on the management of the pathologic processes, which cannot effectively regenerate the lost periodontal tissue. GTR, a classic method for periodontal regeneration, has shown promise in clinical practice. However, the current membranes might not fully fulfill the criteria of ideal membranes. Here, we report bioabsorbable nMgO-incorporated nanofibrous membranes prepared by electrospinning to provide an alternative for the clinical practice of GTR. The membranes not only function greatly as physical barriers but also exhibit high antibacterial and osteoinductive properties. We therefore believe that this study will inspire more practice work on the development of effective GTR membranes for periodontal regeneration.

Scaffold-supported extracellular matrices preserved by magnesium hydroxide nanoparticles for renal tissue regeneration

Fibroblast-derived extracellular matrix-supported scaffolds made up of PLGA were prepared with the enhanced preservation of ECM components by composites with magnesium hydroxide nanoparticles, and were applied for renal tissue regeneration.

Magnesium hydroxide-incorporated PLGA composite attenuates inflammation and promotes BMP2-induced bone formation in spinal fusion

Spinal fusion has become a common surgical technique to join two or more vertebrae to stabilize a damaged spine; however, the rate of pseudarthrosis (failure of fusion) is still high. To minimize pseudarthrosis, bone morphogenetic protein-2 (BMP2) has been approved for use in humans. In this study, we developed a poly(lactide-co-glycolide) (PLGA) composite incorporated with magnesium hydroxide (MH) nanoparticles for the delivery of BMP2. This study aimed to evaluate the effects of released BMP2 from BMP2-immobilized PLGA/MH composite scaffold in an in vitro test and an in vivo mice spinal fusion model. The PLGA/MH composite films were fabricated via solvent casting technique. The surface of the PLGA/MH composite scaffold was modified with polydopamine (PDA) to effectively immobilize BMP2 on the PLGA/MH composite scaffold. Analyzes of the scaffold revealed that using PLGA/MH-PDA improved hydrophilicity, degradation performance, neutralization effects, and increased BMP2 loading efficiency. In addition, releasing BMP2 from the PLGA/MH scaffold significantly promoted the proliferation and osteogenic differentiation of MC3T3-E1 cells. Furthermore, the pH neutralization effect significantly increased in MC3T3-E1 cells cultured on the BMP2-immobilized PLGA/MH scaffold. In our animal study, the PLGA/MH scaffold as a BMP2 carrier attenuates inflammatory responses and promotes BMP2-induced bone formation in posterolateral spinal fusion model. These results collectively demonstrate that the BMP2-immobilized PLGA/MH scaffold offers great potential in effectively inducing bone formation in spinal fusion surgery.

Optical and biological properties of polymer-based nanocomposites with improved dispersion of ceramic nanoparticles

This article reports a new process for creating polymer-based nanocomposites with enhanced dispersion of ceramic nanoparticles without using any surfactants, and the resulted changes in their optical and biological properties. Specifically, dispersion of two different ceramic nanoparticles, that is, hydroxyapatite (nHA) and magnesium oxide (nMgO) nanoparticles, in a model biodegradable polymer, namely poly(lactic-co-glycolic acid) (PLGA), was studied. High-power sonication was integrated with dual asymmetric centrifugal (DAC) mixing to improve dispersion of nanoparticles during solvent casting. The polymer/solvent ratio was optimized to improve nanoparticle dispersion in the multistep processing, including enhancing the efficacy of sonication and DAC mixing and reducing nanoparticle sedimentation during solvent-casting. Microstructural characterization confirmed that this new process improved nanoparticle dispersion in nMgO/PLGA and nHA/PLGA nanocomposites. Improved nanoparticle dispersion increased the optical transparency visually and optical transmission quantitatively for both nHA/PLGA and nMgO/PLGA nanocomposites. Improved dispersion of nanoparticles improved the adhesion of bone marrow derived mesenchymal stem cells (BMSCs) on nHA/PLGA but decreased BMSC viability on nMgO/PLGA. This difference is likely because the chemistry of nHA and nMgO had different effects on BMSCs. This study provided a new process for enhancing dispersion of ceramic nanoparticles in a polymer matrix and revealed the effects of dispersion on optical properties and cell responses, which are valuable for engineering optimal ceramic/polymer nanocomposites for different biomedical applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2692-2707, 2018.

Biodegradable Magnesium-Incorporated Poly(l-lactic acid) Microspheres for Manipulation of Drug Release and Alleviation of Inflammatory Response

Poly(l-lactic acid) (PLLA) and magnesium (Mg) are widely concerned biodegradable materials, but during in vivo implantation, the former produces acidic degradation byproducts and can easily induce inflammation in surrounding tissues, whereas the latter is fast corroded and generates alkaline products. The purpose of this study is to develop Mg/PLLA composite microspheres as a novel delivery system, in which Mg particles are used to regulate the drug release profile and suppress PLLA-induced inflammatory response. Morphological observation shows that multiple Mg particles are dispersed both on the surface and in the interior of composite microspheres. In vitro release study indicates that by varying the Mg contents or its particle sizes, the internal connectivity of composite microspheres is changed during hydrolytic degradation, and drug delivery can be facilely manipulated with tunable release patterns. In vivo release study further confirms the feasibility of Mg/PLLA microspheres for tailoring drug release in a physiological environment. The animal experiment reveals that Mg particles can alleviate macrophage infiltration and inflammatory cytokine expression. These results demonstrate the availability of using biodegradable Mg particles to manipulate drug release as well as alleviate PLLA-induced inflammation. The present Mg/PLLA composite microspheres have potential applications in controlled delivery of various therapeutic agents, especially some growth factors, for bone regeneration.

Fabrication, Crystalline Behavior, Mechanical Property and In-Vivo Degradation of Poly(l-lactide) (PLLA)-Magnesium Oxide Whiskers (MgO) Nano Composites Prepared by In-Situ Polymerization

The present work focuses on the preparation of poly(l-lactide)-magnesium oxide whiskers (PLLA-MgO) composites by the in-situ polymerization method for bone repair and implant. PLLA-MgO composites were evaluated using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and solid-state 13C and 1H nuclear magnetic resonance spectroscopy (NMR). It was found that the whiskers were uniformly dispersed in the PLLA matrix through the interfacial interaction bonding between PLLA and MgO; thereby, the MgO whisker was found to be well-distributed in the PLLA matrix, and biocomposites with excellent interface bonding were produced. Notably, the MgO whisker has an effect on the crystallization behavior and mechanical properties; moreover, the in vivo degradation of PLLA-MgO composites could also be adjusted by MgO. These results show that the whisker content of 0.5 wt % and 1.0 wt % exhibited a prominent nucleation effect for the PLLA matrix, and specifically 1.0 wt % MgO was found to benefit the enhanced mechanical properties greatly. In addition, the improvement of the degrading process of the composite illustrated that the MgO whisker can effectively regulate the degradation of the PLLA matrix as well as raise its bioactivity. Hence, these results demonstrated the promising application of PLLA-MgO composite to serve as a biomedical material for bone-related repair.

One step bulk modification of poly(L-lactic acid) composites with functional additives to improve mechanical and biological properties for cardiovascular implant applications

Poly(L-lactic acid) (PLLA) has been widely used as a promising biomaterial in biomedical applications due to its biodegradability and high mechanical strength. However, because of the inherent brittleness, low impact resistance, and weak thermal stability of PLLA, the modification process is usually required to utilize it for biomedical devices. Furthermore, acidic byproducts resulting from the hydrolysis of PLLA after implantation reduce the pH of the surrounding environment and cause inflammatory responses in the implanted area, leading to the failure of their clinical applications. To this end, here, we demonstrate a novel modification process for the PLLA composite with various functional additives, such as cis-aconitic anhydride (AA), triacetin (TA), isosorbide derivative (ISB), and/or Pluronic® F127 (F). The modified PLLA composite with TA and F (PLLA/TF) showed significantly improved elongation at break and Young's modulus and retained tensile strength. Moreover, incorporating magnesium hydroxide (MH) nanoparticles (PLLA/TFMH) significantly reduced acid-induced inflammation responses caused by the acidic degradation products of PLLA. Reduced plasma protein adsorption was observed in the PLLA/TFMH. These results suggest that the one step bulk modification of biodegradable PLLA using TA, F, and MH will have great potential in cardiovascular implant applications.

Multi-Functional Drug Carrier Micelles With Anti-inflammatory Drug

The multi-functional micelles poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide-co-10 undecanoic acid)/CM-Dextran Fe3O4 (PNDU/CM-Dex Fe3O4) were poly (NIPAAm-co-DMAAm-co-UA) (PNDU) grafting hydrophilic CM-Dextran Fe3O4 which possess pH-dependent temperature response and magnetic response. In this research, anti-inflammation drug Hesperetin was encapsulated by micelles using membrane dialysis method to obtain the different ratio of Hesperetin-embedded P5DF10, P10DF10, and P20DF10. These micelles were characterized by Fourier transform infrared spectroscopy, 1H-NMR, thermogravimetric analyzer, and superconducting quantum interference device magnetometer. The morphology and particle size of micelles was observed by transmission electron microscopy and dynamic light scattering. The low critical solution temperature of the P10DF10 micelles is in pH 6.6 at about 37.76°C and in pH 7.4 at about 41.70°C. The biocompatibility of micelles was confirmed by cytotoxicity study. Inflammatory inhibition of hesperetin-embedded P10DF10 micelles also studied through RAW264.7. Hesperetin-embed P10DF10 micelles suppressed LPS-induced inflammatory response. Via immunofluorescence cell staining demonstrate that Hesperetin-embed P10DF10 micelles inhibited the activation of NF-κB p60 and markedly attenuated in a drug dose-dependent manner. At a concentration of 1,000 ug/ml, an inflammatory rate can be reduced to 36.9%. Based on these results, the hesperetin-embed P10DF10 micelles had successfully synthesized and enable to carry and release the anti-inflammatory drugs, which instrumental for biomedical therapy and applications.

The Degradation Properties of MgO Whiskers/PLLA Composite In Vitro

In this study, composite films of stearic acid⁻modified magnesium oxide whiskers (Sa⁻w-MgO)/poly-l-lactic acid (PLLA) were prepared through solution casting, and the in vitro degradation properties and cytocompatibility of the composites with different whisker contents were investigated. The results showed that the degradation behavior of the composite samples depended significantly on the whisker content, and the degradation rate increased with the addition of MgO content. Furthermore, the degradation of the composites with higher contents of whiskers was influenced more severely by the hydrophilicity and pH value, leading to more final weight loss, but the decomposition rate decreased gradually. Furthermore, the pH value of the phosphate buffer solution (PBS) was obviously regulated by the dissolution of MgO whiskers through neutralization of the acidic product of PLLA degradation. The cytocompatibility of the composites also increased remarkably, as determined from the cell viability results, and was higher than that of PLLA at the chosen whisker content. This was beneficial for the cell affinity of the material, as it notably led to an enhanced biocompatibility of the PLLA, in favor of promoting cell proliferation, which significantly improved its bioactivity, as well.

Modified Magnesium Hydroxide Nanoparticles Inhibit the Inflammatory Response to Biodegradable Poly(lactide- co-glycolide) Implants

Biodegradable polymers have been extensively used in biomedical applications, ranging from regenerative medicine to medical devices. However, the acidic byproducts resulting from degradation can generate vigorous inflammatory reactions, often leading to clinical failure. We present an approach to prevent acid-induced inflammatory responses associated with biodegradable polymers, here poly(lactide- co-glycolide), by using oligo(lactide)-grafted magnesium hydroxide (Mg(OH)₂) nanoparticles, which neutralize the acidic environment. In particular, we demonstrated that incorporating the modified Mg(OH)₂ nanoparticles within degradable coatings on drug-eluting arterial stents efficiently attenuates the inflammatory response and in-stent intimal thickening by more than 97 and 60%, respectively, in the porcine coronary artery, compared with that of drug-eluting stent control. We also observed that decreased inflammation allows better reconstruction of mouse renal glomeruli in a kidney tissue regeneration model. Such modified Mg(OH)₂ nanoparticles may be useful to extend the applicability and improve clinical success of biodegradable devices used in various biomedical fields.

Versatile effects of magnesium hydroxide nanoparticles in PLGA scaffold-mediated chondrogenesis

Artificial scaffolds made up of various synthetic biodegradable polymers have been reported to have many advantages including cheap manufacturing, easy scale up, high mechanical strength, convenient manipulation, and molding into an unlimited variety of shapes. However, the synthetic biodegradable polymers still have the insufficiency for cartilage regeneration owing to their acidic degradation products. To reduce acidification by degradation of synthetic polymers, we incorporated magnesium hydroxide (MH) nanoparticles into porous polymer scaffold not only to effectively neutralize the acidic hydrolysate but also to minimize the structural disturbance of scaffolds. The neutralization effect of poly(D,L-lactic-co-glycolic acid; PLGA)/MH scaffold was confirmed with the maintenance of neutral pH, contrary to a PLGA scaffold with low pH. Further, the scaffolds were applied to evaluate the chondrogenic differentiation of the human bone marrow mesenchymal stem cells. In in vitro study, the PLGA/MH scaffold enhanced the chondrogenesis markers and reduced the calcification, compared to the PLGA scaffold. Additionally, the PLGA/MH scaffold reduced the release of inflammatory cytokines, compared to the PLGA scaffold, as the cell death decreased. Moreover, the addition of MH reduced necrotic cell death at the early stage of chondrogenic differentiation. Further, the necrotic cell death by the PLGA scaffold was mediated by cleavage of caspase-1, the so-called interleukin 1-converting enzyme, and MH alleviated it as well as nuclear factor kappa B expression. Furthermore, the PLGA/MH scaffold highly supported chondrogenic healing of rat osteochondral defect sites in in vivo study. Therefore, it was suggested that a synthetic polymer scaffold containing MH could be a novel healing tool to support cartilage regeneration and further treatment of orthopedic patients.

STATEMENT OF SIGNIFICANCE

Synthetic polymer scaffolds have been widely utilized for tissue regeneration. However, they have a disadvantage of releasing acidic products through degradation. This paper demonstrated a novel type of synthetic polymer scaffold with pH-neutralizing ceramic nanoparticles composed of magnesium hydroxide for cartilage regeneration. This polymer showed pH-neutralization property during polymer degradation and significant enhancement of chondrogenic differentiation of mesenchymal stem cells. It reduced not only chondrogenic calcification but also release of proinflammatory cytokines. Moreover, it has an inhibitory effect on necrotic cell death, particularly caspase-1-mediated necrotic cell death (pyroptosis). In in vivo study, it showed higher healing rate of the damaged cartilage in a rat osteochondral defect model. We expected that this novel type of scaffold can be effectively applied to support cartilage regeneration and further treatment of orthopedic patients.

Macrophage infiltration of electrospun polyester fibers

Ibuprofen (IBU)-loaded fibrous PLA membranes can prevent peritendinous adhesion/granuloma formation and inflammation by reducing macrophage infiltration.

Poly(lactic acid) stereocomplexes: A decade of progress

Upon blending enantiomeric poly(l-lactide) [i.e., poly(l-lactic acid) (PLLA)] and poly(d-lactide) (PDLA) [i.e., poly(d-lactic acid) (PDLA)] or synthesis of stereo block poly(lactide) [i.e., poly(lactic acid) (PLA)], a stereocomplex (SC) is formed. PLA SC has a higher melting temperature (or heat resistance), mechanical performance, and hydrolysis-resistance compared to those of neat PLLA and PDLA. Because of such effects, PLA SC has been extensively studied in terms of biomedical and pharmaceutical applications as well as commodity, industrial, and environmental applications. Stereocomplexation stabilizes and strengthens PLA-based hydrogel or nanoparticles for biomedical applications. Stereocomplexation increases the barrier property of PLA-based materials and thereby prolongs drug release from PLA based materials. In addition, PLA SC is attracting significant attention because it can act as a nucleating agent for the widely used biobased polymer PLLA and thereby the heat resistance of PLLA-based materials can be enhanced. Interestingly, a wide variety of SCs other than PLA SC are found to have been formed in the enantiomeric substituted PLA blends and stereo block substituted PLA polymers. In the present review article, a decade of progress in investigation of PLA SCs is summarized.

Bi-directional controlled release of ibuprofen and Mg(2+) from magnesium alloys coated by multifunctional composite

Two major problems for magnesium alloy implant are the high degradation rate and easy infection associated with implantation. Herein, a surface drug delivery system (Mg/Epoxy resin-ZnO/PCL-Ibuprofen) which can realize bi-directional controlled release of ibuprofen and Mg(2+) was designed via a dip coating process followed by spraying. The in vitro test demonstrated that the ibuprofen in drug-eluting compound material showed sustained release profiles for 22days, which can effectively solve the local cellular rejection and inflammation during the early stage of implantation. Besides, the drug carrier also exhibited improved corrosion resistance duel to the high combining strength between Epoxy resin-ZnO coating and magnesium alloy, so Mg(2+) can release slowly at first and then speeded up later. This approach may be suitable for coating other implant materials such as stainless steel, titanium alloy etc.

Concentration-dependent behaviors of bone marrow derived mesenchymal stem cells and infectious bacteria toward magnesium oxide nanoparticles

This article reports the quantitative relationship between the concentration of magnesium oxide (MgO) nanoparticles and its distinct biological activities towards mammalian cells and infectious bacteria for the first time. The effects of MgO nanoparticles on the viability of bone marrow derived mesenchymal stem cells (BMSCs) and infectious bacteria (both gram-negative Escherichia coli and gram-positive Staphylococcus epidermidis) showed a concentration-dependent behavior in vitro. The critical concentrations of MgO nanoparticles identified in this study provided valuable guidelines for biomaterial design toward potential clinical translation. BMSCs density increased significantly when cultured in 200μg/mL of MgO in comparison to the Cells Only control without MgO. The density of BMSCs decreased significantly after culture in the media with 500μg/mL or more of MgO. Concentrations at or above 1000μg/mL of MgO resulted in complete BMSCs death. Quantification of colony forming units (CFU) revealed that the minimum bactericidal concentration (MBC) of MgO for E. coli and S. epidermidis was 1200μg/mL. The addition of MgO nanoparticles into the cultures increased the pH and Mg(2+) ion concentration in the respective culture media, which might have played a role in the observed cell responses but not the main factors. E. coli and S. epidermidis still proliferated significantly at alkaline pH up to 10 or with supplemental Mg(2+) dosages up to 50mM, indicating bactericidal properties of MgO are beyond the effects of increased media pH and Mg(2+) ion concentrations. MgO nanoparticles at a concentration of 200μg/mL provided dual benefits of promoting BMSC proliferation while reducing bacterial adhesion, which should be further studied for potential medical implant applications. The use of free MgO nanoparticles yielded detrimental effects to BMSCs in concentrations above 300μg/mL. We recommend further study into MgO nanoparticle as a coating material or as a part of a composite.

STATEMENT OF SIGNIFICANCE

This article reports the quantitative relationship between the concentration of magnesium oxide (MgO) nanoparticles and its distinct biological activities towards mammalian cells and infectious bacteria for the first time. The effects of MgO nanoparticles on the viability of bone marrow derived mesenchymal stem cells (BMSCs) and infectious bacteria (both gram-negative Escherichia coli and gram-positive Staphylococcus epidermidis) showed a concentration-dependent behavior in vitro. The critical concentrations of MgO nanoparticles identified in this study provided valuable guidelines for biomaterial design toward potential clinical translation.

WITHDRAWN: PLA Stereocomplexes: A Decade of Progress

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The crystallization behaviors and mechanical properties of poly(l-lactic acid)/magnesium oxide nanoparticle composites

Nanocomposites of biodegradable PLLA and magnesium oxide composite (PLLA/MgO-NPs) and surface modified magnesium oxide composite (PLLA/m-MgO-NPs) were prepared using a solution casting method.

Critical review on the physical and mechanical factors involved in tissue engineering of cartilage

Articular cartilage defects often progress to osteoarthritis, which negatively impacts quality of life for millions of people worldwide and leads to high healthcare expenditures. Tissue engineering approaches to osteoarthritis have concentrated on proliferation and differentiation of stem cells by activation and suppression of signaling pathways, and by using a variety of scaffolding techniques. Recent studies indicate a key role of environmental factors in the differentiation of mesenchymal stem cells to mature cartilage-producing chondrocytes. Therapeutic approaches that consider environmental regulation could optimize chondrogenesis protocols for regeneration of articular cartilage. This review focuses on the effect of scaffold structure and composition, mechanical stress and hypoxia in modulating mesenchymal stem cell fate and the current use of these environmental factors in tissue engineering research.