Biomedical subjects

Michael J Yaszemski

Publications and source records attributed to Michael J Yaszemski.

At least 19 recordsLinked to original sources

PubMed2007

Double-stranded RNA-dependent protein kinase is involved in 2-methoxyestradiol-mediated cell death of osteosarcoma cells.

UNLABELLED: We studied the involvement of interferon-regulated, PKR on 2-ME-mediated actions in human osteosarcoma cells. Our results show that PKR is activated by 2-ME treatment and is necessary for 2-ME-mediated induction of osteosarcoma cell death. INTRODUCTION: Osteosarcoma is the most common primary bone tumor and most frequently develops during adolescence. 2-Methoxyestradiol (2-ME), a metabolite of 17beta-estradiol, induces interferon gene expression and apoptosis in human osteosarcoma cells. In this report, we studied the role of interferon-regulated double-stranded (ds)RNA-dependent protein kinase (PKR) protein on 2-ME-mediated cell death in human osteosarcoma cells. MATERIALS AND METHODS: Western blot analyses were used to measure PKR protein and phosphorylation levels. Cell survival and apoptosis assays were measured using trypan blue exclusion and Hoechst dye methods, respectively. A transient transfection protocol was used to express the dominant negative PKR mutants. RESULTS AND CONCLUSIONS: PKR was increased in 2-ME-treated MG63 cells, whereas 17beta-estradiol, 4-hydroxyestradiol, and 16alpha-hydroxyestradiol, which do not induce cell death, had no effect on PKR protein levels. Also, 2-ME treatment induced PKR kinase activity as indicated by increased autophosphorylation and phosphorylation of the endogenous substrate, eukaryotic initiation factor (eIF)-2alpha. dsRNA poly (I).poly (C), an activator of PKR protein, increased cell death when osteosarcoma cells were treated with a submaximal concentration of 2-ME. In contrast, a serine-threonine kinase inhibitor SB203580 and a specific PKR inhibitor 2-aminopurine (2-AP) blocked the 2-ME-induced cell death in MG63 cells. A dominant negative PKR mutant protein conferred resistance to 2-ME-induced cell death to MG63 osteosarcoma and 2-ME-mediated PKR regulation did not require interferon gene expression. PKR protein is activated in cell free extracts by 2-ME treatment, resulting in autophosphorylation and in the phosphorylation of the substrate eIF-2alpha. We conclude from these results that PKR is regulated by 2-ME independently of interferon and is essential for 2-ME-mediated cell death in MG63 osteosarcoma cells.

2-Methoxyestradiol↗

PubMed2006

Optimizing conditions and avoiding pitfalls for prolonged axonal tracing with carbocyanine dyes in fixed rat spinal cords.

We have characterized a method of labeling of axons in the post-mortem spinal cord using a silastic disc holding pins coated with DiI and DiO at the rostral and caudal ends of the cord. We optimized the DiI and DiO tracing techniques under different conditions of fixative concentration (1% versus 4% paraformaldehyde, PF), at room temperature (RT) versus 37 degrees C for up to 24 weeks. Crystal coated pins embedded in a silastic disc provided a novel method of dye application. Confocal microscopy of longitudinal sections showed DiI and DiO labeled both the axonal membrane and myelin sheath. DiI diffused significantly longer distances than DiO. Both dyes migrated greater distances at 37 degrees C compared with RT. No significant difference of dye labeling was found between 1% and 4% PF fixation. After prolonged incubation there was evidence that dye diffused through the aqueous medium and produced circumferential labeling of the cord. Placing a wax seal around the labeling site prevented this non-contiguous labeling. Labeling of myelin sheaths at extended distances into the cord suggested that dye could migrate between cells with prolonged incubation periods. Our data suggested that higher temperature facilitated dye diffusion along the axons, and demonstrated that with caution DiI and DiO could be used as specific tracers in the same spinal cords.

Animals↗

PubMed2006

Controlled drug release from a novel injectable biodegradable microsphere/scaffold composite based on poly(propylene fumarate).

The ideal biomaterial for the repair of bone defects is expected to have good mechanical properties, be fabricated easily into a desired shape, support cell attachment, allow controlled release of bioactive factors to induce bone formation, and biodegrade into nontoxic products to permit natural bone formation and remodeling. The synthetic polymer poly(propylene fumarate) (PPF) holds great promise as such a biomaterial. In previous work we developed poly(DL-lactic-co-glycolic acid) (PLGA) and PPF microspheres for the controlled delivery of bioactive molecules. This study presents an approach to incorporate these microspheres into an injectable, porous PPF scaffold. Model drug Texas red dextran (TRD) was encapsulated into biodegradable PLGA and PPF microspheres at 2 microg/mg microsphere. Five porous composite formulations were fabricated via a gas foaming technique by combining the injectable PPF paste with the PLGA or PPF microspheres at 100 or 250 mg microsphere per composite formulation, or a control aqueous TRD solution (200 microg per composite). All scaffolds had an interconnected pore network with an average porosity of 64.8 +/- 3.6%. The presence of microspheres in the composite scaffolds was confirmed by scanning electron microscopy and confocal microscopy. The composite scaffolds exhibited a sustained release of the model drug for at least 28 days and had minimal burst release during the initial phase of release, as compared to drug release from microspheres alone. The compressive moduli of the scaffolds were between 2.4 and 26.2 MPa after fabrication, and between 14.9 and 62.8 MPa after 28 days in PBS. The scaffolds containing PPF microspheres exhibited a significantly higher initial compressive modulus than those containing PLGA microspheres. Increasing the amount of microspheres in the composites was found to significantly decrease the initial compressive modulus. The novel injectable PPF-based microsphere/scaffold composites developed in this study are promising to serve as vehicles for controlled drug delivery for bone tissue engineering.

Bone Cements↗

PubMed2006

Sacral osteomyelitis after ileal pouch-anal anastomosis: report of four cases.

PURPOSE: This study describes an institutional experience with sacral osteomyelitis after proctocolectomy and ileal pouch-anal anastomosis. METHODS: A total of 2,375 patients underwent ileal pouch-anal anastomosis at the Mayo Clinic between January 1981 and January 2002. In addition, we have served as a tertiary referral base for patients with complications after ileal pouch-anal anastomosis performed at other institutions. Review of our ileal pouch-anal anastomosis prospective database and directed search of the central pathology, microbiology, radiology, and surgical records at the Mayo Clinic was performed using these keywords: osteomyelitis, ileal pouch-anal anastomosis, inflammatory bowel disease, chronic ulcerative colitis, and Crohn's disease. RESULTS: Two of 2,375 patients (0.08 percent) with ileal pouch-anal anastomosis performed at our institution have had sacral osteomyelitis. In addition, two patients have been referred for continuing care after construction of an ileal pouch-anal anastomosis and diagnosis of sacral osteomyelitis at another institution. Two of the four patients maintained normal pouch function after sacral debridement and a period of fecal stream diversion. One patient remains diverted with resolved sacral osteomyelitis after debridement. The last patient died from squamous-cell cancer involving the sacrum. CONCLUSIONS: Sacral osteomyelitis is a rare and heretofore unreported complication of ileal pouch-anal anastomosis. Conservative measures using antibiotics alone proved unsuccessful, and delaying definitive management may have contributed to the degeneration of a chronic sacral abscess into squamous-cell cancer. With more aggressive treatment comprising sacral debridement, long-term antibiotics, and fecal diversion, pouch function can potentially be preserved.

Adenomatous Polyposis Coli↗

PubMed2006

Bone-tissue-engineering material poly(propylene fumarate): correlation between molecular weight, chain dimensions, and physical properties.

Poly(propylene fumarate) (PPF) is an important biodegradable and cross-linkable polymer designed for bone-tissue-engineering applications. For the first time we report the extensive characterization of this biomaterial including molecular weight dependences of physical properties such as glass transition temperature Tg, thermal degradation temperature Td, density rho, melt viscosity eta0, hydrodynamic radius RH, and intrinsic viscosity [eta]. The temperature dependence of eta0 changes progressively with molecular weight, whereas it can be unified when the temperature is normalized to Tg. The plateau modulus and entanglement molecular weight Me have been obtained from the rheological master curves. A variety of chain microstructure parameters such as the Mark-Houwink-Sakurada constants K and alpha, characteristic ratio Cinfinity, unperturbed chain dimension r0(2)/M, packing lengthp, Kuhn length b, and tube diameter a have been deduced. Further correlation between the microstructure and macroscopic physical properties has been discussed in light of recent progress in polymer dynamics to supply a better understanding about this unsaturated polyester to advance its biomedical uses. The molecular weight dependence of Tg for six polymer species including PPF has been summarized to support that Me is irrelevant for the finite length effect on the glass transition, whereas surprisingly these polymers can be divided into two groups when their normalized Tg is plotted simply against Mw to indicate the deciding roles of inherent chain properties such as chain fragility, intermolecular cooperativity, and chain end mobility.

Bone Substitutes↗

PubMed2006

Local antibiotic delivery with OsteoSet, DBX, and Collagraft.

Biodegradable local antibiotic delivery systems have gained interest for prophylaxis and treatment of musculoskeletal infections. We studied the biodegradable materials Osteo- Set, DBX and Collagraft for local delivery of vancomycin and gentamicin in vitro. We determined the antimicrobial activity of vancomycin and gentamicin after mixing with each biodegradable material and determined the release of each antimicrobial from each material in an intermittent flow chamber. Antimicrobial activity was expressed as percent of antimicrobial loaded into each sample that was detected; antimicrobial release was expressed as concentration (microg/mL) after timed intervals of chamber flow, peak concentration, area under the curve and percent antimicrobial recovered. Activity of vancomycin after mixing with Osteo- Set, DBX and Collagraft was > 73%. Activity of gentamicin after mixing with DBX was 100%; after mixing with OsteoSet and Collagraft it was reduced to < 61%. AUC0-48hrs of vancomycin was 469, 426 and 432 microg x hr/mL, and the AUC0-48hrs of gentamicin was 368, 306 and 301 microg x hr/mL after release from OsteoSet, DBX, and Collagraft, respectively. Recovered percentages of vancomycin were 39%, 11% and 25%, and recovered percentages of gentamicin were 39%, 9% and 23% after release from OsteoSet, DBX, and Collagraft, respectively. OsteoSet, DBX and Collagraft may be suitable for local delivery of vancomycin and gentamicin.

Absorbable Implants↗

PubMed2006

Mechanical effects of partial sacrectomy: when is reconstruction necessary?

We examined the mechanical consequences of high partial transverse sacrectomy. Ten human cadaveric pelves were randomly assigned to three groups. In the Control Group, the sacrum was left entirely intact. In Group I, transverse partial sacrectomy was performed just caudal to the S1 neural foramina. In Group II, transverse partial sacrectomy was performed just cephalad to the S1 neural foramina. Each pelvis was mounted on a testing apparatus and loaded vertically at the L4/L5 disk space until failure occurred. The average resection of the sacroiliac joints was 16% in Group I, and 25% in Group II. The average load to failure was 3014 N in the Control Group, 2166 N in Group I, and 1045 N in Group II. The average stiffness was 353 N/mm in the Control Group, 222 N/mm in Group I, and 100 N/mm in Group II. All specimens failed because of fractures through the sacrum (mostly Denis Zone II) in the sagittal plane. Using the literature to predict normal forces at the lumbosacral junction, we suggest Group I pelves could withstand postoperative mobilization without fracture, whereas Group II would probably not. Reconstruction should therefore be considered when performing transverse partial sacrectomy above the S1 nerve root.

Aged↗

PubMed2005

Optimal segmentation of microcomputed tomographic images of porous tissue-engineering scaffolds.

The morphometric properties of the porous tissue-engineering scaffolds play a dominant role in the initial cell attachment and subsequent tissue regeneration. These properties can be derived nondestructively with the use of quantitative analysis of high-resolution microcomputed tomography (microCT) imaging of scaffolds. Accurate segmentation of these acquired images into solid and porous subspaces is critical to the integrity of morphometric analysis. The absence of a single image-processing technique to provide such accurate separability immune to all the intricacies of the acquired data makes this seemingly simple task significantly error prone. Consequently, an optimal segmentation has to be selected by ranking the segmentations produced by a multiplicity of methods. This article proposes a robust, easy-to-implement, unambiguous, signal-processing-based, ground-truth-free, segmentation rating metric that correlates with visual acuity. With the use of this metric it is possible, for the first time, to threshold the data with a wide range of techniques and select automatically the technique that best delineates the acquired image. The proposed solution has been extensively tested on microCT images of scaffolds fabricated with biodegradable poly (propylene fumarate) (PPF) with the use of a solvent casting particulate leaching process. The approaches proposed and the results obtained may have profound implications for accurate image-based characterization of tissue-engineering scaffolds.

Biocompatible Materials↗

PubMed2005

Multiple-channel scaffolds to promote spinal cord axon regeneration.

As molecular, cellular, and tissue-level treatments for spinal cord injury are discovered, it is likely that combinations of such treatments will be necessary to elicit functional recovery in animal models or patients. We describe multiple-channel, biodegradable scaffolds that serve as the basis for a model to investigate simultaneously the effects on axon regeneration of scaffold architecture, transplanted cells, and locally delivered molecular agents. Poly(lactic-co-glycolic acid) (PLGA) with copolymer ratio 85:15 was used for these initial experiments. Injection molding with rapid solvent evaporation resulted in scaffolds with a plurality of distinct channels running parallel along the length of the scaffolds. The feasibility of creating scaffolds with various channel sizes and geometries was demonstrated. Walls separating open channels were found to possess void fractions as high as 89%, with accessible void fractions as high as 90% through connections 220 microm or larger. Scaffolds degraded in vitro over a period of 30 weeks, over which time-sustained delivery of a surrogate drug was observed for 12 weeks. Primary neonatal Schwann cells were distributed in the channels of the scaffold and remained viable in tissue culture for at least 48 h. Schwann-cell containing scaffolds implanted into transected adult rat spinal cords contained regenerating axons at one month post-operation. Axon regeneration was demonstrated by three-dimensional reconstruction of serial histological sections.

Absorbable Implants↗

PubMed2005

Synthesis and characterizations of biodegradable and crosslinkable poly(epsilon-caprolactone fumarate), poly(ethylene glycol fumarate), and their amphiphilic copolymer.

A series of self-crosslinkable and biodegradable polymers, poly(caprolactone fumarate) (PCLF), poly(ethylene glycol fumarate) (PEGF), and their copolymer PEGF-co-PCLF, has been developed for tissue engineering applications using a novel synthesis method. The current method employs potassium carbonate (K2CO3), other than the previously reported triethylamine, as the proton scavenger. The new synthetic route is more convenient and less time-consuming to carry out, and the synthesized polymers have a much lighter color, which renders them more suitable for self-crosslinking via photo-initiation. This group of polymers are essentially copolymers of fumaryl chloride, which contains double bonds for in situ crosslinking, with poly(epsilon-caprolactone) (PCL) or/and poly(ethylene glycol) (PEG) that has a flexible chain to facilitate self-crosslinking. Both PCLF and PEGF, and their amphiphilic copolymer PEGF-co-PCLF could be self-crosslinked or photocrosslinked to produce scaffolds without the use of a crosslinking agent. Our results suggest that these polymers are potentially useful as injectable, self-crosslinkable, and photo-crosslinkable materials for diverse tissue engineering applications.

Biocompatible Materials↗

PubMed2005

Chondroconductive potential of tantalum trabecular metal.

Mesenchymal stem cells or chondrocytes have been implanted into joints in biodegradable matrices in order to improve the quality of healing cartilage defects; however, insufficient biomechanical strength of the construct at implantation is a limiting factor for clinical application. Logically, a construct with better biomechanical characteristics would provide better results. Tantalum trabecular metal (TTM) is osteoconductive and mechanically similar to subchondral bone. The objective of this pilot study was to determine if TTM is also chondroconductive. Small sections of TTM were cultured with emu and canine chondrocytes in static and dynamic culture environments. The sections cultured in dynamic bioreactors were diffusely covered with a cartilaginous matrix. Sections cultured in static conditions had no growth. Histologic evaluation from emu and canine dynamic cultures showed tissue that was heavily populated with mesenchymal cells that resembled chondrocytes, and glycosaminoglycan staining that was distributed throughout the matrix. Type II collagen content in the canine dynamic culture was 84% by SDS-PAGE. Tantalum trabecular metal is chondroconductive in vitro in a dynamic environment when cultured with adult canine or emu chondrocytes. This technology could be expanded to determine if cartilaginous-metallic constructs may be used for joint resurfacing of osteoarthritic joints.

Animals↗

PubMed2005

Osteogenic differentiation of rat bone marrow stromal cells cultured on Arg-Gly-Asp modified hydrogels without dexamethasone and beta-glycerol phosphate.

In this study, we investigated the effect of signaling peptides incorporated into oligo(poly(ethylene glycol) fumarate) (OPF) hydrogels on in vitro differentiation and mineralization of marrow stromal cells (MSCs) cultured in media without soluble osteogenic supplements (dexamethasone and beta-glycerol phosphate). When MSCs were cultured for 16 days on OPF hydrogels modified with Arg-Gly-Asp (RGD) containing peptides, the normalized cell number was dependent on the peptide concentration between days 0 and 5 and reached comparable values at day 10 regardless of the concentration. The alkaline phosphatase (ALP) activity of MSCs on the peptide-modified OPF hydrogels was also concentration-dependent: ALP activity showed peaks on day 10 or day 13 on OPF hydrogels modified with 2.0 and 1.0 micromol peptide/g, which were significantly greater than those on the OPF hydrogels modified with 0.1 micromol peptides/g or no peptide. A characteristic marker of osteoblastic differentiation, osteopontin (OPN), was detected for all the test groups. However, OPN secretion between days 0 and 10 was significantly higher on the peptide modified hydrogels compared to that on tissue culture-treated polystyrene. Taken together, the results indicate that the presence of signaling peptide allows for a favorable microenvironment for MSCs to differentiate into osteoblasts and produce mineralized matrix, although the soluble factors may further enhance calcium deposition. These findings further support the usefulness of OPF hydrogels as scaffolds for guided bone regeneration, and represent an initial step in exploring the complex relationship between soluble and insoluble factors in osteogenic differentiation on biodegradable materials.

Absorbable Implants↗

PubMed2005

Reconstruction after total sacrectomy: early experience with a new surgical technique.

UNLABELLED: Nine patients had sacrectomy with ilio-lumbar arthrodesis for treatment of sacral malignancies at our institution between 2000 and 2004. Five patients had total sacrectomy, three had a sagittal hemisacrectomy, and one had an extended internal hemipelvectomy Type I-S. The average patient age was 39 years. Tumors were Stage IIB in seven patients and Stage IB in two patients. A combined anteroposterior approach was used and a wide surgical margin was attained in all seven patients. A new form of reconstruction using structural fibular grafts and pedicle screw-rod instrumentation was used to create a triangular construct along the anatomic force transmission vectors from the femoral heads to the lumbar spine. The average followup was 18 months. At latest followup, seven patients were alive with no evidence of disease, and two had died from disease. One patient suffered postoperative infection. Independent ambulation was noted in seven patients at last followup. Eight patients had stable reconstructions at latest followup (one patient, who died in December 2004, had a stable reconstruction and was walking with braces and a walker before her death). One patient had instrumentation failure twice and had additional revision instrumentation and bone grafting procedures. She eventually obtained a solid lumbopelvic fusion and walks with Canadian crutches and ankle-foot orthoses. The technique of reconstruction reported here offers promise in dealing with the challenges of reestablishing spinopelvic stability in this difficult anatomic location. LEVEL OF EVIDENCE: Therapeutic study, Level IV-1 (case series). See the Guidelines for Authors for a complete description of levels of evidence.

Adult↗

PubMed2005

Operative management of sacral chordoma.

BACKGROUND: Sacrococcygeal chordoma presents a difficult diagnostic and therapeutic problem, with a high rate of local recurrence. The purpose of this report is to define the importance of adequate surgical treatment for optimum outcome and survival. METHODS: Fifty-two patients underwent surgical treatment for sacrococcygeal chordoma between 1980 and 2001. The series included eighteen female patients and thirty-four male patients, with an average age of fifty-six years (range, thirteen to seventy-six years) at the time of the diagnosis. The surgical approach depended on the level and extent of the lesion, with a posterior approach performed in twenty-two patients and a combined anteroposterior approach used in thirty. A wide surgical margin was achieved in twenty-one patients. RESULTS: At an average of 7.8 years (range, 2.1 to twenty-three years) postoperatively, twenty-three patients were alive with no evidence of disease. Twenty-three patients (44%) had local recurrence. The rate of recurrence-free survival was 59% at five years and 46% at ten years. The overall survival rates were 74%, 52%, and 47% at five years, ten years, and fifteen years, respectively. The most important predictor of survival was a wide margin. All patients with a wide margin survived, and this survival rate was significantly different from that for patients who had had either marginal or intralesional excision (p = 0.0001). Of the twenty-one patients with a wide margin, seventeen (81%) had undergone a combined anteroposterior approach and only four had been treated with a posterior approach. CONCLUSIONS: A wide surgical margin is the most important predictor of survival and of local recurrence in patients with sacrococcygeal chordoma. Use of a combined anteroposterior approach increases the likelihood of obtaining a wide margin. LEVEL OF EVIDENCE: Therapeutic Level IV.

Adolescent↗

PubMed2004

Quantitative analysis of interconnectivity of porous biodegradable scaffolds with micro-computed tomography.

Pore interconnectivity within scaffolds is an important parameter influencing cell migration and tissue ingrowth needed to promote tissue regeneration. Methods for assessment of interconnectivity are usually qualitative, restricted to two-dimensional images, or are destructive. Microcomputed tomography nondestructively provides three-dimensional (3D) images of intact specimens at high spatial resolutions. We describe an image analysis technique for quantitative assessment of scaffold interconnectivity. Scaffolds were made via a particulate leaching process with 75%, 80%, 85%, and 88% volumetric porogen fractions. Specimens were scanned and resulting 3D, digital images were analyzed with a custom algorithm. A series of virtual, idealized scaffolds were also created for illustration of the algorithm's analysis approach and for its validation. The program calculated accessible void fractions over a range of minimum connection sizes. In real specimens, nearly 100% of the porous volume was connected with outside air for connections greater than or equal to 20 microm in their smallest dimension. In scaffolds made with 75% porogen, the accessible void fraction decreased to 78% if only those connections greater than or equal to 260 microm were considered. The relationship between accessible void fraction and connection size varied as a function of porogen content. The interconnectivity parameter described here may have implications for cell migration and tissue growth into scaffolds.

Algorithms↗

PubMed2004

Development of biodegradable poly(propylene fumarate)/poly(lactic-co-glycolic acid) blend microspheres. I. Preparation and characterization.

We developed poly(propylene fumarate)/poly(lactic-co-glycolic acid) (PPF/PLGA) blend microspheres and investigated the effects of various processing parameters on the characteristics of these microspheres. The advantage of these blend microspheres is that the carbon-carbon double bonds along the PPF backbone could be used for their immobilization in a PPF scaffold. Microspheres containing the model drug Texas red dextran were fabricated using a double emulsion-solvent extraction technique. The effects of the following six processing parameters on the microsphere characteristics were investigated: PPF/PLGA ratio, polymer viscosity, vortex speed during emulsification, amount of internal aqueous phase, use of poly(vinyl alcohol) (PVA) in the internal aqueous phase, and PVA concentration in the external aqueous phase. Our results showed that the microsphere surface morphology was affected most by the viscosity of the polymer solution. Microspheres fabricated with a kinematic viscosity of 39 centistokes had a smooth, nonporous surface. In most microsphere formulations, the model drug was dispersed uniformly in the polymer matrix. For all fabricated formulations, the average microsphere diameter ranged between 19.0 and 76.9 microm. The external PVA concentration and vortex speed had most effect on the size distribution. Entrapment efficiencies varied from 60 to 98% and were most affected by the amount of internal aqueous phase, vortex speed, and polymer viscosity. Overall, we demonstrated the ability to fabricate PPF/PLGA blend microspheres with similar surface morphology, entrapment efficiency, and size distribution as conventional PLGA microspheres.

Biocompatible Materials↗

PubMed2004

Development of biodegradable poly(propylene fumarate)/poly(lactic-co-glycolic acid) blend microspheres. II. Controlled drug release and microsphere degradation.

This article describes the effects of six processing parameters on the release kinetics of a model drug Texas red dextran (TRD) from poly(propylene fumarate)/poly(lactic-co-glycolic acid) (PPF/PLGA) blend microspheres as well as the degradation of these microspheres. The microspheres were fabricated using a double emulsion-solvent extraction technique in which the following six parameters were varied: PPF/PLGA ratio, polymer viscosity, vortex speed during emulsification, amount of internal aqueous phase, use of poly(vinyl alcohol) in the internal aqueous phase, and poly(vinyl alcohol) concentration in the external aqueous phase. We have previously characterized these microspheres in terms of microsphere morphology, size distribution, and TRD entrapment efficiency. In this work, the TRD release profiles in phosphate-buffered saline were determined and all formulations showed an initial burst release in the first 2 days followed by a decreased sustained release over a 38-day period. The initial burst release varied from 5.1 (+/-1.1) to 67.7 (+/-3.4)% of the entrapped TRD, and was affected most by the viscosity of the polymer solution used for microsphere fabrication. The sustained release between day 2 and day 38 ranged from 7.9 (+/-0.8) to 27.2 (+/-3.1)% of the entrapped TRD. During 11 weeks of in vitro degradation, the mass of the microspheres remained relatively constant for the first 3 weeks after which it decreased dramatically, whereas the molecular weight of the polymers decreased immediately upon placement in phosphate-buffered saline. Increasing the PPF content in the PPF/PLGA blend resulted in slower microsphere degradation. Overall, this study provides further understanding of the effects of various processing parameters on the release kinetics from PPF/PLGA blend microspheres thus allowing modulation of drug release to achieve a wide spectrum of release profiles.

Biocompatible Materials↗

PubMed2004

Modulation of differentiation and mineralization of marrow stromal cells cultured on biomimetic hydrogels modified with Arg-Gly-Asp containing peptides.

We synthesized biomimetic hydrogels modified with an osteopontin-derived peptide (ODP) and used them as a substrate for in vitro culture of marrow stromal cells (MSCs) to investigate the effect of the biomimetic surface on differentiation of MSCs into osteoblasts. Proliferation and biological assays for 16 days proved that MSCs became differentiated into osteoblasts secreting osteogenic phenotypic markers such as alkaline phosphatase (ALP), osteopontin, and mineralized calcium. In addition, there was an additive effect of the cell-binding peptide on differentiation and mineralization of MSCs cultured in the presence of soluble osteogenic supplements in cell culture media. For example, calcium content at day 16 on peptide-modified hydrogels was significantly higher than on tissue culture polystyrene. Two general trends were observed: (1) proliferation of MSCs decreased as the amount of differentiation markers increased, and (2) higher peptide concentrations accelerated the differentiation of MSCs. On the hydrogel modified with ODP, ALP activity exhibited a maximum value of 36.7 +/- 4.2 pmol/cell/h at day 10 for the concentration of 2 micromol/g while the culture time needed for maximum ALP activity occurred on day 13 for the lower concentrations. On the same hydrogel, the calcium content at day 10 was 21.4 +/- 2.3 ng/cell for the peptide concentration of 2 micromol/g and 1.0 +/- 0.3 ng/cell for 1.0 micromol/g. We used Gly-Arg-Gly-Asp-Ser (GRGDS) for modification of the hydrogel as a comparison to the results with ODP. However, osteoblast development was not significantly affected by the nature of the binding peptide sequences. These results suggest that MSC function can be modulated by variation of the peptide concentration in biomimetic hydrogels used for scaffold-based bone tissue engineering.

Alkaline Phosphatase↗