Bioabsorbable implants: review of clinical experience in orthopedic surgery

Self-dissolving microneedles for the percutaneous absorption of EPO in mice

Erythropoietin (EPO) loaded microneedles were prepared using thread-forming polymer as a base for the percutaneous administration of EPO. The used polymers were dextrin, chondroitin sulfate and albumin. Under room temperature, EPO solution was added to high concentration of polymer solution and microneedles were prepared by forming thread with polypropylene tips. The mean weight of microneedle was 0.59 +/- 0.01 mg and length and basal diameter were 3.24 +/- 0.16 and 0.55 +/- 0.03 mm, respectively. Four microneedles were percutaneously (pc) administered to mice at the EPO dose levels of 100 IU/kg. After administration, blood samples were collected for 24 h and serum EPO levels were measured. Dextrin EPO microneedles were administered both pc and subcutaneously (sc) to mice. Serum EPO levels vs. time profiles showed Cmax of 138.6 +/- 16.1 and 146.5 +/- 8.0 mIU/ml, respectively. Tmax were 7.5 h. The values of bioavailability (BA) of EPO were 82.1 and 99.4%, respectively. By decreasing the dose from 100 to 50 and 25 IU/kg, dose-dependent serum EPO levels vs. time profiles were not clearly obtained. When chondroitin sulfate and albumin were used as the microneedle base, the serum EPO levels vs. time profiles showed almost the same pattern. Cmax of chondroitin sulfate and albumin microneedles were 96.3 +/- 8.8 and 132.2 +/- 18.9 mIU/ml, respectively. AUCs were 835.1 and 1098.7 mIU h/ml. Tmax were 8 and 6.8 h. These results suggest the usefulness of microneedles for the percutaneous administration of EPO.

Biodegradation of Inion fast-absorbing biodegradable plates and screws

Biodegradable plates and screws are recommended for use in surgery of the craniofacial skeleton of children. To be effective and not interfere with growth of the child's skull, the plates must biodegrade sufficiently to release the holding power of the plate and screw within 1 year. It is also essential that excessive foreign body reaction and cyst formation does not occur when the plates and screws biodegrade. The purpose of this experimental study was to evaluate the rate of biodegradation of Inion CPS Baby biodegradable plates and screws under different clinical circumstances in the rabbit craniofacial skeleton and evaluate their efficacy for use in pediatric craniofacial surgery. Foreign body reaction would be evaluated. Inion baby plates and screws were tested in a rabbit model. Plates were applied to the frontal bone, over a bony defect of the parietal bone, to a nasal bone fracture, and inserted in the subcutaneous space over the occipital bone in thirty 6-week-old rabbits. Six rabbits were euthanized at 9, 12, 15, and 18 months' postoperative time point and examined for residual plates and screws. Bone from each surgical site was excised, fixed by immersion in 10% neutral-buffered formalin, decalcified in Immunocal solution, and examined by 7-microm paraffin sections stained with hematoxylin and eosin. At 9 months, the plates and screws had effectively biodegraded and no longer had holding power on the bones. Fragmentation of the implant material was noted. Residual implant material was still present on gross and histologic examination in rabbits at 9, 12, 15, and 18 months. Residue of a screw was still palpable in 1 rabbit at 18 months. There was no evidence of cyst formation in any of the examined specimens. Macrophages and giant cells were present in most of the specimens at 9, 12, 15, and 18 months. Findings from the current study revealed a relative short resorption time (9 mo) and normal inflammatory sequelae in an adult rabbit model. These findings suggest that these plates may be used safely in fixing the pediatric craniofacial skeleton.

Evaluation of self-dissolving needles containing low molecular weight heparin (LMWH) in rats

Feasibility study of self-dissolving needles containing polysaccharide was performed. Low molecular weight heparin (LMWH) was used as a representative polysaccharide. Using chondroitin, dextran and dextrin as the base, self-dissolving needles (SDN) were prepared. The obtained SDNs were evaluated in rat absorption experiment, where pharmacological availability (PA) was calculated by comparing the plasma anti-Xa activity vs. time curves between SDNs and i.v. solution. After the insertion of SDNs to rats skin where the doses of LMWH were 25, 50 and 100 IU/kg, plasma samples were collected for 6h and anti-Xa activity was measured as the pharmacological index of LMWH. The anti-Xa level was maintained above 0.2 IU/ml, the therapeutic level, for about 2h at a dose of 100 IU/kg. Almost the same PAs of LMWH were obtained with dextran and dextrin SDNs, 97.7% and 102.3%, though lower PA was obtained with chondroitin SDN, 81.5%. In vitro dissolution experiment showed that LMWH was released from dextran, dextrin and chondroitin SDNs within 10 min. The T(50%)s were 0.84+/-0.06 min for dextran SDN, 1.07+/-0.12 min for chondroitin SDN and 2.11+/-0.31 min for dextrin SDN, respectively. Plasma anti-Xa activity vs. time profiles showed good dose-dependency in the 25-100 IU/kg range and high PAs were obtained, 90.0% for 25 IU/kg, 95.4% for 50 IU/kg and 97.7% for 100 IU/kg from dextran SDNs. Stability experiment was performed with dextran SDNs for 3 months. Above 97% of LMWH were remained in SDNs under three different conditions, -80, 4 and 40 degrees C. These results suggest the usefulness of SDN to polysaccharide drug.

Biodegradable polymer microneedles: fabrication, mechanics and transdermal drug delivery

To overcome skin's barrier properties that block transdermal delivery of most drugs, we and others have microfabricated arrays of microscopic needles, primarily out of silicon or metal. This study addresses microneedles made of biocompatible and biodegradable polymers, which are expected to improve safety and manufacturability. To make biodegradable polymer microneedles with sharp tips, we adapted microelectromechanical masking and etching to produce beveled-tip and chisel tip microneedles and developed a new fabrication method to produce tapered-cone microneedles using an in-situ lens-based lithographic approach. To replicate microfabricated master structures, PDMS micromolds were generated and a novel vacuum-based method was developed to fill the molds with polylactic acid, polyglycolic acid and their copolymers. Mechanical testing of the resulting needles measured the force at which needles broke during axial loading and found that this failure force increased with Young's modulus of the material and needle base diameter and decreased with needle length. Failure forces were generally much larger than the forces needed to insert microneedles into skin, indicating that biodegradable polymers can have satisfactory mechanical properties for microneedles. Finally, arrays of polymer microneedles were shown to increase permeability of human cadaver skin to a low-molecular weight tracer, calcein, and a macromolecular protein, bovine serum albumin, by up to three orders of magnitude. Altogether, these results indicate that biodegradable polymer microneedles can be fabricated with an appropriate geometry and sufficient strength to insert into skin, and thereby dramatically increase transdermal transport of molecules.

Bioabsorbable implants

Absorbable implants have become the hottest implant material, overtaking titanium as the future. Absorbable devices have moved beyond orthopedics and maxillofacial surgery to spine, vascular, plastics and general surgery. This chapter outlines the experiences of many specialties.

Feasibility of microneedles for percutaneous absorption of insulin

Insulin loaded microneedles were prepared using dextrin as the base for the percutaneous administration of insulin. Under room temperature, insulin solution was added to high concentration of dextrin solution, glue, and microneedles were prepared by forming thread with polypropylene tips. The mean weight of the microneedles was 0.59+/-0.01 (S.E.) mg. The mean length and basal diameter were 3.24+/-0.16 and 0.55+/-0.03 mm, respectively. Five microneedles were percutaneously administered to mice at the insulin dose levels of 0.5, 1.0 and 2.5IU/kg. After administration, blood samples were collected for 5 h and plasma glucose levels were measured. Lowest plasma glucose level appeared at 1 h after the administration of microneedles and dose-dependent hypoglycemic effect of insulin was clearly observed in those dose range. By comparing the mean area above the plasma glucose level versus time curve (AAC) between microneedle preparation and i.v. solution, the pharmacological availabilities were calculated to be 97.7% (0.5IU/kg), 93.3% (1.0IU/kg) and 91.3% (2.5IU/kg), respectively. When highly loaded insulin loaded microneedle was administered to mice with one microneedle, there was not a significant difference on the plasma glucose level versus time curves between 5 and 1 microneedle experiments. In vitro release study showed that almost all of the formulated insulin was released within 1 h. The T50% was estimated to be 15.4+/-1.1 min. Stability of insulin in the microneedle preparations showed that the remaining insulin after 1 month of the storage were 98.2% (-80 degrees C), 98.9% (20 degrees C) and 99.0% (40 degrees C). Evans blue (EB) loaded microneedles were also prepared and histological study was performed with HWY-Slc hairless rats. The diffusion of EB from the microneedle to the environmental skin reached to the maximum at 3 h after administration. The scab was formed at 24 h after administration. The wound formed by the administration of microneedle was cured at 72 h after administration. Those results suggest the usefulness of a self-dissolving microneedle for the percutaneous delivery of peptide/protein drugs like insulin.

Degradação acelerada de suportes de poli(épsilon-caprolactona) e poli(D,L-ácido láctico-co-ácido glicólico) em meio alcalino

O estudo da degradação in vitro de polímeros bioreabsorvíveis em soluções alcalinas vem sendo proposto nos últimos anos como alternativa aos estudos tradicionais feitos em tampão fosfato. Este trabalho descreve a degradação acelerada de poli(épsilon-caprolactona) (PCL) e poli(D,L-ácido láctico-co-ácido glicólico) (50/50) (PLGA50), polímeros biodegradáveis e bioreabsorvíveis, amplamente estudados em aplicações biomédicas. Amostras foram preparadas pelo método de fusão seguido de injeção em molde cilíndrico (2 mm diâmetro), a 160 ºC, e submetidas à degradação em soluções de NaOH em pH 12, 13 e 13,7 a 37 ºC. Por meio da caracterização da variação da massa, morfologia e propriedades térmicas, por calorimetria exploratória diferencial, os resultados mostraram que as amostras de PCL são mais estáveis quando comparadas às de PLGA50. Pela taxa de variação das propriedades térmicas foi possível extrapolá-las em função do tempo em pH fisiológico, 7,4. Validado, o estudo da degradação acelerada em meio alcalino mostrou-se como uma técnica útil e de baixo custo para avaliar o comportamento em curtos períodos de degradação.

Proliferation and osteogenic differentiation of mesenchymal stem cells cultured onto three different polymers in vitro

In this study, the osteoinductive and cell-binding properties of three different resorbable polymers were evaluated by human mesenchymal stem cells (MSCs). MSCs were isolated, expanded, and cultivated onto resorbable D,D,L,L-polylactide (PLLA), collagen I/III, and polygalactin-910/polydioxanone (PGPD) scaffolds in vitro. To evaluate the influence of dexamethasone, ascorbic acid, and beta-glycerolphosphate (DAG) on osteoblast differentiation, MSCs were incubated in a DAG-enriched medium. After a 28-day period in vitro, the cellular loaded polymers were digested enzymatically by papain and HCl. The Ca(2+) content of the biomembranes was evaluated by an o-kresolphthalein-complexon reaction via photometer. A PicoGreen assay was performed for dsDNA quantification. Significant differences between the number of adherent MSCs were documented (collagen > PLLA > PGPD). Compared to the initial number of adherent cells, all biomaterials induced a significant decrease in cellular adherence after 28 days in vitro. The presence of DAG-enriched culture medium stimulated the cellular proliferation for PLLA and slightly for PGPD, whereas cell proliferation was inhibited when MSCs were cultivated onto collagen I/III. In comparison with the control groups, all biomaterials (PLLA, PGPD, and collagen I/III) showed a significant increase in local Ca(2+) accumulation under DAG stimulation after 28 days in vitro. Furthermore, collagen I/III and PLLA scaffolds showed osteoinductive properties without DAG stimulation. These results were verified by immunocytochemical stainings against osteoblast-typical markers (osteopontin and alkaline phosphatase) and completed by calcified matrix detection (von Kossa staining). MSCs were identified by CD105 and CD13 antigen expression. Corresponding to an absence of CD34, CD45, and collagen II expression, we found no chondrogenic or hematopoietic cell differentiation. The results indicate significant differences for the proliferation, differentiation, adherence, and Ca(2+) accumulation between the tested polymers in a MSC culture.

Bone challenges for the hand surgeon: from basic bone biology to future clinical applications

Bone is a complex tissue composed of a calcified extracellular matrix with specialized cells that produce, maintain, and resorb the bone. Bone also has a rich vascular and neural supply. Bone has a great capability of regeneration, healing, and remodelling that is influenced by external factors, such as stress forces, and internal regulators that include hormones, vitamins, and growth factors. These factors dictate bone biology, and variations result in pathophysiologic conditions that have clinical implications in hand surgery. Solutions to the challenges in hand surgery rely on a thorough understanding of the biology of bone.

Long-term evaluation of porous poly(epsilon-caprolactone-co-L-lactide) as a bone-filling material

Porous poly(epsilon-caprolactone-co-L-lactide) (P(CL-co-LA, wt % ca. 5/95) sponges were prepared, coated biomimetically with CaP/apatite, and implanted with noncoated control sponges into rat femur cortical defects and dorsal subcutaneous space. The implants were inspected histologically at 2, 4, and 33 weeks after the operation. All implants were filled with fibrovascular tissue within 4 weeks. The femur implants were partially ossified with compact bone, which in the CaP-coated sponges was less mature and more fragmented. Approximately equal amounts of bone were observed in both types of implants. The polymer induced a mild inflammatory reaction with foreign body giant cells but no accumulation of fluid. Degradation of the polymer was slow; most of it was found intact at 33 weeks in histological samples. Nondegraded polymer seems to prevent complete ossification. Cultured osteoblasts proliferated well on apatite-coated material, whereas only a few cells were seen on noncoated material. Thus CaP/apatite coating helped the attachment of osteoblasts in cell cultures but did not offer any advantage in bone formation over noncoated material in vivo. We conclude that a shorter degradation time of P(CL-co-LA) is needed to create an optimal implant. Furthermore, in vivo experiments seem to be necessary for the estimation of osteopromotive properties of a biomaterial.

A comparative radiological assessment of polylactide pins over 3 years in vivo

Biodegradable polylactide implants allow secure fixation of osteochondral fractures with minimal adverse effects. The goal of this prospective, randomized animal study was to show whether osteoconductive effects can be achieved through the development of poly-L/DL(70/30)lactide composite implants with 10% beta-tricalcium phosphate, and whether degradation can be positively influenced and adverse effects minimized using such implants. An additional goal was to clarify which radiological procedure is most suitable to observe the course of follow-up. Thirtysix medial femoral condyle osteotomies of sheep were fixed with either 3 poly-L/DL-lactide pins or 3 composite pins, and the pin canal widths were measured with conventional radiographs, with CT, MRI, and histologically after 3, 18, and 36 months. All fractures healed completely without displacement or clinically relevant complications. The pin canals dilated secondary to pin degradation at the 12th month, and then decreased in size later. At 36 months, the pins had microscopically disappeared, and the canals were filled with bone or scar tissue. There were no statistically significant differences between the pin-types. Poly-L/DL-lactide pins and composite C-pins are suitable for secure fixation of small osteochondral fractures. Osteoconductive effects of biocompatibility or osseous integration relating to composite development were not evident. Conventional radiography and computer tomography were suitable techniques for observation of pin canals. Due to frequently observed artifact, MRI was not suitable to observe the course of the implants.

Biodegradable polymer microneedles: fabrication, mechanics and transdermal drug delivery

To overcome the skin's barrier properties that block transdermal delivery of most drugs, arrays of microscopic needles have been microfabricated primarily out of silicon or metal. This study addresses microneedles made of biocompatible and biodegradable polymers, which are expected to improve safety and manufacturability. To make biodegradable polymer microneedles with sharp tips, micro-electromechanical masking and etching were adapted to produce beveled- and chisel-tip microneedles and a new fabrication method was developed to produce tapered-cone microneedles using an in situ lens-based lithographic approach. To replicate microfabricated master structures, PDMS micromolds were generated and a novel vacuum-based method was developed to fill the molds with polylactic acid, polyglycolic acid, and their co-polymers. Mechanical testing of the resulting needles measured the force at which needles broke during axial loading and found that this failure force increased with Young's modulus of the material and needle base diameter and decreased with needle length. Failure forces were generally much larger than the forces needed to insert microneedles into skin, indicating that biodegradable polymers can have satisfactory mechanical properties for microneedles. Finally, arrays of polymer microneedles were shown to increase permeability of human cadaver skin to a low-molecular weight tracer, calcein, and a macromolecular protein, bovine serum albumin, by up to three orders of magnitude. Altogether, these results indicate that biodegradable polymer microneedles can be fabricated with an appropriate geometry and sufficient strength to insert into skin, and thereby dramatically increase transdermal transport of molecules.

Polímeros bioreabsorvíveis na engenharia de tecidos

A Engenharia de Tecidos consiste em um conjunto de conhecimentos e técnicas para a reconstrução de novos órgãos e tecidos. Baseada em conhecimentos das áreas de ciência e engenharia de materiais, biológica e médica, a técnica envolve a expansão in vitro de células viáveis do paciente doador sobre suportes de polímeros bioreabsorvíveis. O suporte degrada enquanto um novo órgão ou tecido é formado. Os poli(alfa-hidróxi ácidos) representam a principal classe de polímeros sintéticos bioreabsorvíveis e biodegradáveis utilizados na engenharia de tecidos. No desenvolvimento e na seleção desses materiais, o tempo de degradação é fundamental para o sucesso do implante. Os estudos e os desafios atuais são normalmente direcionados ao entendimento das relações entre composição química, cristalinidade, morfologia do suporte, e o processamento desses materiais. Este artigo faz uma revisão dos trabalhos recentes sobre a utilização dos polímeros sintéticos bioreabsorvíveis como suportes na engenharia de tecidos.

Biocompatibility and functionality of the degradable polymer alkylene bis(dilactoyl)-methacrylate for screw augmentationin vivo

Recently, a new degradable polymer has been developed on the basis of alkylene bis(dilactoyl)-methacrylate as an alternative material for screw augmentation. The polymer has been investigated in vitro and in a short-term experiment in rabbits exhibiting promising results. The aim of the present study was to investigate its long-term biocompatibility and mechanical functionality in a large animal model. The polymer was used for screw augmentation in the cancellous bone of the femoral condyle and tibia epiphysis of 12 sheep and was compared to polymethylmethacrylate (PMMA) augmented and nonaugmented screws. After an implantation period of 6 months, bone, regional lymph nodes, and several organs were histologically evaluated. The mechanical efficacy was investigated by a biomechanical pullout test. A lot of mononuclear macrophages and multinuclear foreign body giant cells with incorporated polymer particles indicate strong inflammatory reactions. Large osteolysis zones with osteoclasts were found in the surrounding polymer. The polymer was fragmented but not substantially degraded. Polymer particles were also found in the regional lymph nodes. Lung, liver, kidney, and spleen did not show any pathological signs. The pullout force of screws augmented with the new polymer was significantly reduced in comparison to PMMA augmented and nonaugmented screws, respectively. It was concluded that the material has poor biocompatibility and cannot be recommended for clinical application as screw augmentation material.

Degradation of poly-L/DL-lactide versus TCP composite pins: A three-year animal study

Biodegradable polylactide implants allow secure fixation of osteochondral fractures. This quasirandomized parallel-group animal study investigates whether a composite implant of poly-L/DL-lactide (PLDLLA) with additional 10% beta-tricalcium phosphate produces an osteoconductive effect, whether the admixture positively influences implant degradation (assessed by comparing time to implant degradation), and whether the pin sites of degraded implants are replaced with bone tissue. On 36 medial femoral condyles of sheep, osteotomies were fixed with either three PLDLLA pins or three composite pins. At 3, 18, and 36 months, the pin sites were measured histologically and the state of degradation assessed according to Pistner's classification. All fractures healed without clinically relevant complications and without displacement. Both pin types led to asymptomatic pin-site enlargement at 18 months, which disappeared by 36 months. At 18 months, 14 of 18 PLDLLA pins were no longer evident, whereas 16 of 18 composite pins showed only peripheral degradation. By 36 months, all implants from both groups were completely degraded and replaced with scar (2/18) or bone tissue (16/18). At 36 months there was no evidence for significant improvement of either degradation performance or osseointegration through use of the 10% TCP composite mixture.