Vancomycin release from bioresorbable calcium phosphate–polymer composites with high ceramic volume fractions

Bioresorbable calcium phosphate–polymer composite implants are a desirable alternative to the traditional metal bone-healing devices. Incorporation of antimicrobial drugs into the composite material and their sustained delivery may dramatically reduce the risk of implant infections. The paper reports the fabrication of drug-incorporated bioresorbable CaP–polymer nanocomposites that can be used for fracture fixation devices and at the same time function as local delivery systems. Vancomycin was incorporated into β-tricalcium phosphate (β-TCP)- and biphasic CaP (BCP)-based composites containing ≤30 vol.% polycaprolactone (PCL) or polylactic acid (PLA), during their high pressure consolidation at 2.5 GPa and room temperature. The antibiotic release was studied in Tris buffer solution at 37 °C. Up to 5 wt% vancomycin could be included without compromising material’s integrity upon immersion into Tris solution. Vancomycin release profile was found to depend on the specific surface area of the test specimens and on the composite porosity. β-TCP–30 vol.% PLA composites were found to have the best combination of compression strength and drug release pattern. Complete drug release was accompanied by only negligible material dissolution suggesting a diffusion mechanism of release. In the context of bone-healing applications, such a release-dissolution pattern will allow local prophylaxis against implant-related infection at the early stages after implantation followed by a much more slow dissolution of the load-carrying device.     

Prolonged release from PLGA/HAp scaffolds containing drug-loaded PLGA/gelatin composite microspheres

Porous scaffolds that can prolong the release of bioactive factors are urgently required in bone tissue engineering. In this study, PLGA/gelatin composite microspheres (PGMs) were carefully designed and prepared by entrapping poly(l-lactide-co-glycolide) (PLGA) microspheres (PMs) in gelatin matrix. By mixing PGMs with PLGA solution directly, drug-loaded PLGA/carbonated hydroxyapatite (HAp)/PGMs composite scaffolds were successfully fabricated. In vitro release of fluorescein isothiocyanate-dextran (FD70S) as a model drug from the scaffolds as well as PMs and PGMs was studied by immersing samples in phosphate buffered saline (pH = 7.4) at 37°C for 32 days. Compared with PMs, PGMs and PLGA/HAp/PGMs scaffolds exhibited slow and steady release behavior with constant release rate and insignificantly original burst release. The swelling of PGMs, diffusion of drugs, and degradation of polymer dominated the release behaviors synergistically. The PLGA/HAp/PGMs scaffold offers a novel option for sequential or simultaneous release of several drugs in terms of bone regeneration.     

Novel Polylactide‐Based Release Systems for Local Antibiotic Therapies

Antibiotic delivery systems based on biodegradable polymers have found considerable interest for the local therapy of bone infections. In this study polylactide based polymer and composite delivery systems for the release of gentamicin have been fabricated from poly‐L‐lactides and a poly(L‐lactide‐co‐D,L‐lactide) as well as biodegradable inorganic fillers (calcium hydrogen phosphate, calcium sulfate dihydrate). The in vitro release profiles of the polymer delivery systems were characterized by an initial burst release followed by a sustained release of small gentamicin amounts up to 3 weeks. In the composite delivery systems a loss of retardation was observed with an increasing content of inorganic filler material. It was found that the in situ complex formation of gentamicin by adding defined amounts of sodium dodecyl sulfate represents a valuable tool to overcome this problem and to modulate the release profile of the delivery systems in a wide range. Under in vitro conditions, calcium sulfate dihydrate containing delivery systems are rapidly degraded in aqueous medium within several months. Based on these results, the developed composite delivery systems are promising candidates for the efficient treatment of bone infections.     

5-Fluorouracil encapsulated HA/PLGA composite microspheres for cancer therapy

5-Fluorouracil (5FU) was successfully entrapped within poly(lactide-co-glycolide) (PLGA) and hydroyapatite (HA) composite microspheres using the emulsification/solvent extraction technique. The effects of HA to PLGA ratio, solvent ratio as well as polymer inherent viscosity (IV) on encapsulation efficiency were investigated. The degradation and drug release rates of the microspheres were studied for 5?weeks in vitro in phosphate buffered solution of pH 7.4 at 37?°C. The drug release profile followed a biphasic pattern with a small initial burst followed by a zero-order release for up to 35?days. The initial burst release decreased with increasing HA content. The potential of HA in limiting the initial burst release makes the incorporation of HA into PLGA microspheres advantageous since it reduces the risk of drug overdose from high initial bursts. The linear sustained drug release profile over the course of 5?weeks makes these 5-FU-loaded HA/PLGA composite microparticles a promising delivery system for the controlled release of chemotherapy drugs in the treatment of cancer.     

In situ synthesized ceramic–polymer composites for bone tissue engineering: bioactivity and degradation studies

As an alternative to current bone grafting strategies, a poly-lactide-co-glycolide/calcium phosphate composite microsphere-based scaffold has been synthesized by the direct formation of calcium phosphate within forming microspheres. It was hypothesized that the synthesis of low crystalline calcium phosphate within forming microspheres would provide a site-specific delivery of calcium ions to enhance calcium phosphate reprecipitation onto the scaffold. Both polymeric and composite scaffolds were incubated in simulated body fluid (SBF) for 8 weeks, during which time polymer molecular weight, scaffold mass, calcium ion concentration of SBF, pH of SBF, and calcium phosphate reprecipitation was monitored. Results showed a 20% decrease in polymeric scaffold molecular weight compared to 11–14% decrease for composite scaffolds over 8 weeks. Composite scaffold mass and SBF pH decreased for the first 2 weeks but began increasing after 2 weeks and continued to do so up to 8 weeks, suggesting interplay between pH changes and calcium phosphate dissolution/reprecipitation. Free calcium ion concentration of SBF containing composite scaffolds increased 20–40% over control values within 4 h of incubation but then dropped as low as 40% below control values, suggesting an initial burst release of calcium ions followed by a reprecipitation onto the scaffold surface. Scanning electron micrographs confirm calcium phosphate reprecipitation on the scaffold surface after only 3 days of incubation. Results suggest the composite scaffold is capable of initiating calcium phosphate reprecipitation which may aid in bone/implant integration.     

Bioresorbable and bioactive polymer/Bioglass® composites with tailored pore structure for tissue engineering applications

An overview about the development of porous bioresorbable composite materials for applications as scaffolds in tissue engineering is presented. A thermally induced phase separation method was developed to fabricate porous foam-like structures of poly(lactide-co-glycolide) (PLGA) containing bioactive glass particle additions (up to 50 wt.%) and exhibiting well-defined, oriented and interconnected porosity. The in vitro bioactivity and the degradability of the composite foams were investigated in contact with phosphate buffer saline (PBS). Weight loss, water absorption and molecular weight measurements were used to monitor the polymer degradation after incubation periods of up to 7 weeks in PBS. It was found that the presence of bioactive glass retards the polymer degradation rate for the time period investigated. The present results show a way of controlling the in vitro degradation behaviour of PLGA porous composite scaffolds by tailoring the concentration of bioactive glass.     

A dynamic mechanical thermal analysis study of the viscoelastic properties and glass transition temperature behaviour of bioresorbable polymer matrix nanocomposites

The application of bioresorbable polymer nanocomposites in orthopaedics offer the potential to address several of the limitations associated with the use of metallic implants. Their enhanced biological performance has been demonstrated recently, but until now relatively little work has been reported on their mechanical properties. To this end, the viscoelastic properties and T_g of bioresorbable polylactide-co-glycolide/α-tricalcium phosphate nanocomposites were investigated by dynamic mechanical thermal analysis. At room temperature of approximately 20°C, the storage moduli of the nanocomposites were generally higher than the storage modulus of the unfilled polymer due to the stiffening effect of the nano-particles. However at physiological temperature of approximately 37°C, the storage moduli of the nanocomposites decreased from 6.2 to 15.4% v/v nano-particle loadings. Similarly the T_g of the nanocomposites also decreased from 6.2 to 15.4% v/v nano-particle loadings. These effects were thought to be due to weak interfacial bonding between the nano-particles and polymer matrix. The storage moduli at 37°C and T_g increased from the minimum value when the particle loading was raised to 25.7 and 34.2% v/v loadings. SEM and particle size distribution histograms showed that at these loadings, there was a broad particle size distribution consisting of nano-particles and micro-particles and that some particle agglomeration was present. The consequent reduction in the interfacial area and the number of weak interfaces presumably accounts for the rise in the storage modulus at 37°C and the T_g.     

Effect of filler level and particle size on dental caries-inhibiting Ca–PO4 composite

Secondary caries and restoration fracture are common problems in restorative dentistry. The aim of this study was to develop Ca–PO₄ nanocomposite having improved stress-bearing properties and Ca and PO₄ ion release to inhibit caries, and to determine the effects of filler level. Nanoparticles of dicalcium phosphate anhydrous (DCPA), two larger DCPA powders, and reinforcing whiskers were incorporated into a resin. A 6 × 3 design was tested with six filler mass fractions (0, 30, 50, 65, 70, and 75%) and three DCPA particle sizes (112 nm, 0.88 μm, 12.0 μm). The DCPA nanocomposite at 75% fillers had a flexural strength (mean ± SD; n = 6) of 114 ± 23 MPa, matching the 112 ± 22 MPa of a commercial non-releasing, hybrid composite (P > 0.1). This was 2-fold of the 60 ± 6 MPa of a commercial releasing control. Decreasing the particle size increased the ion release. Increasing the filler level increased the ion release at a rate faster than being linear. The amount of ion release from the nanocomposite matched or exceeded those of previous composites that released supersaturating levels of Ca and PO₄ and remineralized tooth lesions. This suggests that the much stronger nanocomposite may also be effective in remineralizing tooth lesion and inhibiting caries. In summary, combining calcium phosphate nanoparticles with reinforcing co-fillers in the composite provided a way to achieving both caries-inhibiting and stress-bearing capabilities. Filler level and particle size can be tailored to achieve optimal composite properties. Disclaimer: Certain commercial materials and equipment are identified to specify the experimental procedure. This does not imply recommendation or endorsement by NIST or ADAF.     

Effect of enzymatic degradation of chitosan in polyhydroxybutyrate/chitosan/calcium phosphate composites on in vitro osteoblast response

Polyhydroxybutyrate/chitosan/calcium phosphate composites are interesting biomaterials for utilization in regenerative medicine and they may by applied in reconstruction of deeper subchondral defects. Insufficient informations were found in recent papers about the influence of lysozyme degradation of chitosan in calcium phosphate/chitosan based composites on in vitro cytotoxicity and proliferation activity of osteoblasts. The effect of enzymatic chitosan degradation on osteoblasts proliferation was studied on composite films in which the porosity of origin 3D scaffolds was eliminated and the surface texture was modified. The significantly enhanced proliferation activity with faster population growth of osteoblasts were found on enzymatically degraded biopolymer composite films with α-tricalcium phosphate and nanohydroxyapatite. No cytotoxicity of composite films prepared from lysozyme degraded scaffolds containing a large fraction of low molecular weight chitosans (LMWC), was revealed after 10 days of cultivation. Contrary to above in the higher cytotoxicity origin untreated nanohydroxyapatite films and porous composite scaffolds. The results showed that the synergistic effect of surface distribution, morphology of nanohydroxyapatite particles, microtopography and the presence of LMWC due to chitosan degradation in composite films were responsible for compensation of the cytotoxicity of nanohydroxyapatite composite films or porous composite scaffolds.     

In situ synthesis of calcium phosphate-polycaprolactone nanocomposites with high ceramic volume fractions

Biodegradable calcium phosphate-PCL nanocomposite powders with unusually high ceramic volume fractions (80–95%) and uniform PCL distribution were synthesized by a non-aqueous chemical reaction in the presence of the dissolved polymer. No visible polymer separation occurred during processing. Depending on the reagents combination, either dicalcium phosphate (DCP) or Ca-deficient HA (CDHA) was obtained. CDHA-PCL composite powders were high pressure consolidated at room temperature yielding dense materials with high compressive strengths. Such densification route provides the possibility of incorporating drug and proteins without damaging their biological activity. The CDHA-PCL composites were tested in osteoblastic and endothelial cell line cultures and were found to support the attachment and proliferation of both cell types.     

Biocompatibility of Surface-Modified Biphasic Calcium Phosphate/Poly-L-Lactide Biocomposite in vitro and in vivo

The biocompatibility of surface-modified biphasic calcium phosphate (mBCP)/poly-L-Lactide (PLLA) biocomposite was investigated through a series of experiments in vitro and in vivo. Acute toxicity and short term systemic toxicity experiments revealed no toxicity of the materials. Hemolysis assay indicated the good blood compatibility of the composite. In cytotoxicity assay, L929 mouse fibroblasts could well differentiate and proliferate. Animal experiments in vivo were performed by implanting the materials i...     

Evaluation of hydroxylapatite/poly(l-lactide) composites: physico-chemical properties

The aim of this in vitro study was to examine the physico-chemical behaviour of hydroxylapatite/poly(l-lactide) (HA/PLLA) composites in solution tests. The polymer PLLA, the composites 30 wt% HA/PLLA (C30) and 50 wt% HA/PLLA (C50) and a one-side HA-coated PLLA (HAcP) were evaluated. Rectangular specimens were incubated in various acellular aqueous buffer solutions [citrate, Gomori's and phosphate-buffered saline (PBS)] up to 24 weeks. Data for cumulative release of calcium, phosphate and l-lactate release in solutions containing C30 or C50 showed linear patterns. Release data for solutions containing HAcP combined with scanning micrographs, X-ray microanalysis and X-ray diffraction patterns of the specimens in time showed that the plasma-sprayed HA coating on PLLA dissolves significantly, progressively in the first weeks and almost completely within the tested period of 24 weeks in vitro. A precipitate of scaly crystallites (calcium phosphates) was observed at the HA coating-PBS interface. After 24 weeks incubation all materials were still above their initial weight, indicating that swelling still exceeded dissolution. Application of C30, C50 and HAcP as implant materials seems interesting where initial stabilization through bone bonding is needed or where the linear release of constituents is a requirement. HAcP has the advantage that the HA coating acts as a hydrolysis barrier and consequently delays the degradation of PLLA in vitro.     

Poly (<Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactide)/nano-hydroxyapatite composite scaffolds for bone tissue engineering and biocompatibility evaluation

Biodegradable polymer/bioceramic composite scaffolds can overcome the limitations of conventional ceramic bone substitutes such as brittleness and difficulty in shaping. However, conventional methods for fabricating polymer/bioceramic composite scaffolds often use organic solvents (e.g., the solvent casting and particulate leaching (SC/PL) method), which might be harmful to cells or tissues. In this study, Poly (d,l-lactide)/nano-hydroxyapatite (PDLLA/NHA) composites were prepared by in-situ polymerization, and highly porous scaffolds were fabricated using a novel method, supercritical CO₂/salt-leaching method (SC CO₂/SL). The materials and scaffolds were investigated by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and gel permeation chromatography (GPC). GPC showed that the molecular weight of composites decreased with increase of NHA content. However, the water absorption and compressive strength increased dramatically. The SEM micrographs showed that the scaffolds with pore size about 250 μm were obtained by controlling parameters of SC CO₂/SL. The biocompatibility of PDLLA/NHA porous scaffolds were evaluated in vitro and in vivo. The evaluation on the cytotoxicity were carried out by cell relative growth rate (RGR) method and cell direct contact method. The cytotoxicity of these scaffolds was in grade I according to ISO 10993-1. There was no toxicosis and death cases observed in acute systemic toxicity test. And histological observation of the tissue response (1 and 9 weeks after the implantation) showed that there are still some slight inflammation responses.     

New biocomposite [biphasic calcium phosphate/ poly-DL-lactide-co-glycolide/biostimulative agent] filler for reconstruction of bone tissue changed by osteoporosis

Biphasic calcium phosphate-poly-DL-lactide-co-glycolide composite biomaterial with and without biostimulative agents (protein-rich plasma or fibrin) was synthesised in the form suitable for reconstruction of bone defects. The composite used as filler was obtained by precipitation in solvent-non-solvent systems. The material, calcium phosphate granules covered by polymer, was characterised by wide-angle X-ray structural analysis, scanning electron microscopy, infrared spectroscopy and differential scanning calorimetry. Reparation of bone tissue damaged by osteoporosis was investigated in vivo on rats. The method applied enabled production of granules of calcium phosphate-poly-DL-lactide-co- glycolide composite biomaterial of average diameter 150–200 μm. Histological analysis confirmed recuperation of the alveolar bone, which osteoporosis-induced defects were repaired using composite biomaterial. By addition of biostimulative agents, intensity of osteogenesis increases accompanied by the formation of regular, new bone structure.     

A platelet derived growth factor delivery system for bone regeneration

platelet derived growth factor (PDGF) was formulated in a calcium phosphate/biodegradable polymer system for local and controlled delivery to enhance bone regeneration. Implants with a porosity of 67 %, composed of hydroxyapatite, PLGA microspheres and Pluronic(?), were obtained by compression. An increase in porosity with time was expected due to Pluronic(?) dissolution and PLGA microsphere degradation. In vivo PDGF release and tissue distribution were monitored after system implantation into femurs of rabbits using (125)I-PDGF. Most of the PDGF was released within approximately 5 days and remained located around the implantation site with negligible systemic exposure. Compared with the reference groups, an important enhancement of bone regeneration was found with doses of 600 and 1,200 ng of PDGF, although no histological differences were observed between the two doses. In conclusion, the elaborated system exhibited good biocompatibility and offered a physiologically relevant PDGF profile that enhances bone formation compared to the non-treated bone defect.     

Processing of homogeneous ceramic/polymer blends for bioresorbable composites

Three methods to mix ceramic fillers, hydroxyapatite or β-tricalcium phosphate, with a polymer matrix, a poly l-lactic acid, are investigated as a first step prior to supercritical foaming to prepare porous composite structures for biomedical applications. First the dry process consists in mixing ceramic powder and polymer pellets before a compression molding step. The second technique is based on the dispersion of ceramic fillers into a polymer–solvent solution. The third method is a melt extrusion of a ceramic/polymer powder mixture. Each technique is first optimized by defining the processing parameters suitable for the bioresorbable materials considered. Then comparison of the three methods shows that solvent or melt processing results in a more homogeneous filler distribution than the dry technique. Extrusion leads to composites with a higher modulus than solvent prepared compounds and is a solvent-free approach. The former technique is therefore selected to prepare ceramic/polymer blends before supercritical CO₂ foaming.     

Fabrication,characterization and long-term in vitro release of hydrophilic drug using PHBV/HA composite microspheres

In this paper, we fabricated polyhydroxybutyrate-co-hydroxyvalerate (PHBV)/Hydroxyapatite (HA) composite microspheres as a long-term drug delivery system. The characterization and in vitro release properties of the system were investigated. It was observed that the PHBV/HA composite microspheres showed very low initial burst that could be neglected, owing to the high affinity and absorbability of nano-HA particles, and the sustained release lasted more than 10 weeks. The in vitro release rate was controlled by diffusion rate of drugs from polymer matrices, and the release profile can be expressed by the Higuchi equation. From our work, it indicated that PHBV/HA composite microsphere could be a promising long-term drug release system.     

原位自发泡制备磷酸钙/聚氨酯复合骨修复支架

磷酸钙/聚氨酯(CaP/PU)复合骨修复支架制备过程中随着材料体系粘度逐渐增大, 后期加入的发泡剂难于均匀分散, 影响支架孔隙率及孔结构均匀性。本研究在CaP/PU材料合成过程中将发泡剂水以磷酸氢钙结晶水合物(DCPD)的形式均匀复合在材料中, 在一定条件下释放结晶水与聚氨酯(PU)中的异氰酸根反应生成CO₂, 实现自发泡成型。实验结果显示, 90 ℃条件下自发泡制备的CaP/PU支架孔隙率高、孔结构均匀、贯通性好。将90 ℃发泡成型的CaP/PU多孔支架在110 ℃再熟化处理, 可提高支架的力学性能高达1倍以上。该方法简便易行, 为聚氨酯基多孔支架的制备提供了新思路。     

明胶微球/磷酸镁基骨水泥复合药物缓释体系的构建

采用乳化交联法制备出粒径主要分布在100~300 μm的载药明胶微球, 分析了交联剂含量、药物含量和转速对载药率和包封率的影响及药物含量和转速对微球粒径的影响。对载药明胶微球与磷酸镁基骨水泥进行复合, 探讨微球降解过程中复合体系孔隙率的变化及其在体外药物释放的规律, 以期获得一种具有药物缓释性能的多孔磷酸镁基复合骨水泥。结果表明, 随着葡萄糖浓度增加, 载药率和包封率先上升再下降; 随着药物含量的增加, 载药率保持上升, 包封率先上升后下降; 随着转速增加, 载药率和包封率均下降。综合分析, 在转速为400 r/min、葡萄糖浓度为0.5 g/mL、药物与明胶质量比为1:2的条件下制备的载药明胶微球载药量较高, 且粒径合适。将复合不同比例该载药微球的磷酸镁基骨水泥浸泡在Tris-HCl缓冲溶液中进行体外药物释放研究, 结果表明: 在释放前期(0~10 h)药物释放速率较快, 之后药物释放明显减缓。7 d后, 微球几乎降解完全, 药物释放率达到60%~89%, 达到了一定的药物缓释效果。     

Role of nanoparticle in PNN-PZT/Ag nanocomposite

In the present work, we studied the role of nanoparticles in ferroelectric/silver composites, in which silver is the secondary particle. The ferroelectric system that we adapted was PNN-PZT. To make the PNN-PZT/silver nanocomposite, we hot-pressed the composite at 850 °C/2 h. A nanocomposite could be obtained with <0.5 vol.% of silver. We found that silver nanoparticles more effectively relieved the internal stresses than microparticles, which affected lattice parameter and transition temperature of the nanocomposites.