Low-Loss Dielectric Ink for Printed Radio Frequency and Microwave Devices

Direct write printing is restricted by the lack of dielectric materials that can be printed with high resolution and offer dissipation factors at radio frequency (RF) within the range of commercial RF laminates. Herein, we outline the development of dielectric materials with dielectric loss below 0.006 in X and Ku frequency bands (8.2-18 GHz), the range required for radio frequency and microwave applications. The described materials were designed for printability and processability, specifically a prolonged viscosity below 1000 cps and a robust cure procedure, which requires minimal heat treatment. In the first stage of this work, nonpolar ring-opening metathesis polymerization (ROMP) is demonstrated at room temperature in an open-air environment with a low-viscosity monomer, 5-vinyl-2-norbornene, using the second-generation Grubbs catalyst (G-II). Differential scanning calorimetry (DSC) was used to study how the catalyst activity is increased with heating at various stages in the reaction, which is then used as a strategy to cure the material after printing. The resulting cured poly(5-vinyl-2-norbornene) material is then characterized for dielectric and mechanical performance before and after a secondary heat treatment, which mimics processing procedures to incorporate subsequent printed conductor layers for multilayer applications. After the secondary heat treatment, the material exhibits a 55.0% reduction in the coefficient of thermal expansion (CTE), an increase in glass-transition temperature (T_g) from 32.4 to 46.1 °C, and an increased 25 °C storage modulus from 428 to 1031 MPa while demonstrating a minimal change in dielectric loss. Lastly, samples of the developed dielectric material are printed with silver overtop to demonstrate how the material can be effectively incorporated into fully printed, multilayer RF applications.

Asymmetric Polymerization-Induced Crystallization-Driven Self-Assembly of Helical, Rod-Coil Poly(aryl isocyanide) Block Copolymers

Polymerization-induced crystallization-driven self-assembly (PI-CDSA) is combined, for the first time, with helical, rod-coil block copolymer (BCP) self-assembly to enable scalable and controllable in situ synthesis of chiral nanostructures of variable shape, size, and dimensionality. Herein, we report newly developed asymmetric PI-CDSA (A-PI-CDSA) methodologies in the synthesis and in situ self-assembly of chiral, rod-coil BCPs composed of poly(aryl isocyanide) (PAIC) rigid-rod and poly(ethylene glycol) (PEG) random-coil components. Using PEG-based nickel(II) macroinitiators, the construction of PAIC-BCP nanostructures with variable chiral morphologies is accomplished at solids contents ranging 5.0-10 wt %. At low core-to-corona ratios for PAIC-BCPs, we demonstrate the scalable formation of chiral one-dimensional (1D) nanofibers via "living" A-PI-CDSA whose contour lengths can be tuned through alterations to unimer-to-1D seed particle ratio. At high core-to-corona ratios, A-PI-CDSA was implemented for the rapid fabrication of molecularly thin, uniform hexagonal nanosheets via spontaneous nucleation and growth aided by vortex agitation. Investigations into 2D seeded, living A-PI-CDSA revealed a brand-new paradigm in the context of CDSA where hierarchically chiral, M helical spirangle morphologies (i.e., hexagonal helicoids) are size-tuned in three dimensions (i.e., heights and areas) via alterations to unimer-to-seed ratio. These unique nanostructures are formed in situ at scalable solids contents up to 10 wt % via rapid crystallization about screw dislocation defect sites in an enantioselective fashion. The liquid crystalline nature of PAIC blocks dictates the hierarchical assembly of these BCPs, with chirality translated across length scales and in multiple dimensions affording large amplifications in chiroptical activity with g-factors reaching -0.030 for spirangle nanostructures.

Trehalose-Grafted Glycopolymer: Synthesis via the Staudinger Reaction and Capture of Mycobacteria

A new trehalose-grafted poly(2-hydroxyethyl methacrylate) (HEMA) glycopolymer was synthesized via the perfluorophenyl azide (PFPA)-mediated Staudinger reaction between poly(HEMA-co-HEMA-PFPA) and a diphenylphosphine-derivatized trehalose. The reaction occurred rapidly at room temperature without the use of any catalyst, giving the trehalose glycopolymers over 68% yield after 1 h. The grafting density of trehalose can be controlled by the copolymer composition in poly(HEMA-co-HEMA-PFPA), resulting in 6.1% (TP1) or 37% (TP2) at 10:1 and 1:1 HEMA/HEMA-PFPA feed ratio, respectively. The trehalose glycopolymer was covalently attached on glass slides or silicon wafers using a thin film of poly(HEMA-co-HEMA-PFPA) as the adhesion layer, achieved through the C-H insertion reaction of the photogenerated singlet perfluorophenyl nitrene. To demonstrate the ability of the trehalose glycopolymer to capture mycobacteria, arrays of the trehalose glycopolymer were fabricated and treated with Mycobacterium smegmatis. Results from the optical, fluorescence, and scanning electron microscopy showed that mycobacteria were indeed captured on the trehalose glycopolymer. The amount of mycobacteria captured increased with the percent trehalose in the trehalose glycopolymer and also with the concentration of the trehalose glycopolymer. In addition, the captured bacteria could be visualized by the naked eye under the illumination of a hand-held UV lamp.

Molecular Encryption and Steganography Using Mixtures of Simultaneously Sequenced, Sequence-Defined Oligourethanes

Molecular encoding in abiotic sequence-defined polymers (SDPs) has recently emerged as a versatile platform for information and data storage. However, the storage capacity of these sequence-defined polymers remains underwhelming compared to that of the information storing biopolymer DNA. In an effort to increase their information storage capacity, herein we describe the synthesis and simultaneous sequencing of eight sequence-defined 10-mer oligourethanes. Importantly, we demonstrate the use of different isotope labels, such as halogen tags, as a tool to deconvolute the complex sequence information found within a heterogeneous mixture of at least 96 unique molecules, with as little as four micromoles of total material. In doing so, relatively high-capacity data storage was achieved: 256 bits in this example, the most information stored in a single sample of abiotic SDPs without the use of long strands. Within the sequence information, a 256-bit cipher key was stored and retrieved. The key was used to encrypt and decrypt a plain text document containing The Wonderful Wizard of Oz. To validate this platform as a medium of molecular steganography and cryptography, the cipher key was hidden in the ink of a personal letter, mailed to a third party, extracted, sequenced, and deciphered successfully in the first try, thereby revealing the encrypted document.

Electrostatic and Covalent Assemblies of Anionic Hydrogel-Coated Gold Nanoshells for Detection of Dry Eye Biomarkers in Human Tears

Although dry eye is highly prevalent, many challenges exist in diagnosing the symptom and related diseases. For this reason, anionic hydrogel-coated gold nanoshells (AuNSs) were used in the development of a label-free biosensor for detection of high isoelectric point tear biomarkers associated with dry eye. A custom, aldehyde-functionalized oligo(ethylene glycol)acrylate (Al-OEGA) was included in the hydrogel coating to enhance protein recognition through the formation of dynamic covalent (DC) imine bonds with solvent-accessible lysine residues present on the surface of select tear proteins. Our results demonstrated that hydrogel-coated AuNSs, composed of monomers that form ionic and DC bonds with select tear proteins, greatly enhance protein recognition due to changes in the maximum localized surface plasmon resonance wavelength exhibited by AuNSs in noncompetitive and competitive environments. Validation of the developed biosensor in commercially available pooled human tears revealed the potential for clinical translation to establish a method for dry eye diagnosis.

Thermal Regeneration of Spent Granular Activated Carbon Presents an Opportunity to Break the Forever PFAS Cycle

Extensive use of per- and polyfluoroalkyl substances (PFAS) has caused their ubiquitous presence in natural waters. One of the standard practices for PFAS removal from water is adsorption onto granular activated carbon (GAC); however, this approach generates a new waste stream, i.e., PFAS-laden GAC. Considering the recalcitrance of PFAS molecules in the environment, inadequate disposal (e.g., landfill or incineration) of PFAS-laden GAC may let PFAS back into the aquatic cycle. Therefore, developing approaches for PFAS-laden GAC management present unique opportunities to break its forever circulation within the aqueous environment. This comprehensive review evaluates the past two decades of research on conventional thermal regeneration of GAC and critically analyzes and summarizes the literature on regeneration of PFAS-laden GACs. Optimized thermal regeneration of PFAS-laden GACs may provide an opportunity to employ existing regeneration infrastructure to mineralize the adsorbed PFAS and recover the spent GAC. The specific objectives of this review are (i) to investigate the role of physicochemical properties of PFAS on thermal regeneration, (ii) to assess the changes in regeneration yield as well as GAC physical and chemical structure upon thermal regeneration, and (iii) to critically discuss regeneration parameters controlling the process. This literature review on the engineered regeneration process illustrates the significant promise of this approach that can break the endless environmental cycle of these forever chemicals, while preserving the desired physicochemical properties of the valuable GAC adsorbent.

Helical polymer self-assembly and chiral nanostructure formation

This review surveys recent progress towards robust chiral nanostructure fabrication techniques using synthetic helical polymers, the unique inferred properties that these materials possess, and their intricate connection to natural, biological chirality.

Condition-Dependent Coordination and Peroxidase Activity of Hemin-Aβ Complexes

The peroxidase activity of hemin-peptide complexes remains a potential factor in oxidative damage relevant to neurodegeneration. Here, we present the effect of temperature, ionic strength, and pH relevant to pathophysiological conditions on the dynamic equilibrium between high-spin and low-spin hemin-Aβ₄₀ constructs. This influence on peroxidase activity was also demonstrated using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and dopamine (DA) oxidation rate analyses with increasing ratios of Aβ₁₆ and Aβ₄₀ (up to 100 equivalents). Interaction and reactivity studies of aggregated Aβ₄₀-hemin revealed enhanced peroxidase activity versus hemin alone. Comparison of the results obtained using Aβ₁₆ and Aβ₄₀ amyloid beta peptides revealed marked differences and provide insight into the potential effects of hemin-Aβ on neurological disease progression.

Nanogel receptors for high isoelectric point protein detection: influence of electrostatic and covalent polymer-protein interactions

An aldehyde acrylate-based functional monomer was incorporated into poly(N-isopropylacrylamide-co-methacrylic acid) nanogels for use as protein receptors. The aldehyde component forms dynamic imines with surface exposed lysine residues, while carboxylic acid/carboxylate moieties form electrostatic interactions with high isoelectric point proteins. Together, these interactions effect protein adsorption and recognition.

Metallotexaphyrins as MRI-Active Catalytic Antioxidants for Neurodegenerative Disease: A Study on Alzheimer's Disease

The complex etiology of neurodegeneration continues to stifle efforts to develop effective therapeutics. New agents elucidating key pathways causing neurodegeneration might serve to increase our understanding and potentially lead to improved treatments. Here, we demonstrate that a water-soluble manganese(II) texaphyrin (MMn) is a suitable magnetic resonance imaging (MRI) contrast agent for detecting larger amyloid beta constructs. The imaging potential of MMn was inferred on the basis of in vitro studies and in vivo detection in Alzheimer's disease C. elegans models via MRI and ICP-MS. In vitro antioxidant- and cellular-based assays provide support for the notion that this porphyrin analog shows promise as a therapeutic agent able to mitigate the oxidative and nitrative toxic effects considered causal in neurodegeneration. The present report marks the first elaboration of an MRI-active metalloantioxidant that confers diagnostic and therapeutic benefit in Alzheimer's disease models without conjugation of a radioisotope, targeting moiety, or therapeutic payload.

Chemically Triggered Synthesis, Remodeling, and Degradation of Soft Materials

Polymer topology dictates dynamic and mechanical properties of materials. For most polymers, topology is a static characteristic. In this article, we present a strategy to chemically trigger dynamic topology changes in polymers in response to a specific chemical stimulus. Starting with a dimerized PEG and hydrophobic linear materials, a lightly cross-linked polymer, and a cross-linked hydrogel, transformations into an amphiphilic linear polymer, lightly cross-linked and linear random copolymers, a cross-linked polymer, and three different hydrogel matrices were achieved via two controllable cross-linking reactions: reversible conjugate additions and thiol-disulfide exchange. Significantly, all the polymers, before or after topological changes, can be triggered to degrade into thiol- or amine-terminated small molecules. The controllable transformations of polymeric morphologies and their degradation herald a new generation of smart materials.

Tunable Orthogonal Reversible Covalent (TORC) Bonds: Dynamic Chemical Control over Molecular Assembly

Dynamic assembly of macromolecules in biological systems is one of the fundamental processes that facilitates life. Although such assembly most commonly uses noncovalent interactions, a set of dynamic reactions involving reversible covalent bonding is actively being exploited for the design of functional materials, bottom-up assembly, and molecular machines. This Minireview highlights recent implementations and advancements in the area of tunable orthogonal reversible covalent (TORC) bonds for these purposes, and provides an outlook for their expansion, including the development of synthetically encoded polynucleotide mimics.

2,2'-Bipyridine and hydrazide containing peptides for cyclization and complex quaternary structural control

A synthetic peptide containing two N_ε-methyl lysines (Ac-K(N_ε-Me)GYTGYTGK(N_ε-Me)D-OH) was alkylated with bipyridine (bipy) ligands substituted at the fifth (MP-5) and sixth (MP-6) positions, thereby creating Ac-K(N_ε-Me, N_ε-Bipy)GYTGYTGK(N_ε-Me, N_ε-Bipy)D-OH. Peptides with 6-position bipyridine did not bind to Fe²⁺ and Zn²⁺. Peptides with 5-position bipyridine bound these metals, and in the presence of one equivalent of a free bipy derivative folded into a macrocycle. Further, the free bipy derivative could also contain a cyclized peptide derived from hydrazone formation, resulting in complex but controlled quaternary peptide structure.

A Versatile Approach to Noncanonical, Dynamic Covalent Single- and Multi-Loop Peptide Macrocycles for Enhancing Antimicrobial Activity

Peptide oligomers offer versatile scaffolds for the formation of potent antimicrobial agents due to their high sequence versatility, inherent biocompatibility, and chemical tunability. Though many methods exist for the formation of peptide-based macrocycles (MCs), increasingly pervasive in commercial antimicrobial therapeutics, the introduction of multiple looped structures into a single peptide oligomer remains a significant challenge. Herein, we report the utilization of dynamic hydrazone condensation for the versatile formation of single-, double-, and triple-loop peptide MCs using simple dialdehyde or dihydrazide small-molecule cross-linkers, as confirmed by MALDI-TOF MS, HPLC, and SDS-PAGE. Furthermore, incorporation of aldehyde-containing side chains onto peptides synthesized from hydrazide C-terminal resins resulted in tunable peptide MC assemblies formed directly upon resin cleavage post solid-phase peptide synthesis. Both of these types of dynamic covalent assemblies produced significant enhancements to overall antimicrobial properties when introduced into a known antimicrobial peptide, buforin II, when compared to the original unassembled sequence.

An efficient methodology to introduce o-(aminomethyl)phenyl-boronic acids into peptides: alkylation of secondary amines

Current approaches for incorporating boronic acids into peptides require one of the following: the synthesis of commercially unavailable pinacol-protected boronate ester amino acid building blocks, amidation of small-molecule amine-containing boronic acids, or reductive amination of amine residues with 2-formylphenyl boronic acid. These methods have drawbacks, such as the use of excess starting materials, the lack of reactive-site specificity, or the inability to add multiple boronic acids in solution. In addition, several of these approaches do not allow for incorporation of the critical o-aminomethyl functionality that allows for binding of sacharrides under physiological conditions. In this work, we report three methods to functionalize synthetic peptides with boronic acids using solid-phase and solution-phase chemistries by alkylating a secondary amine with o-(bromomethyl)phenylboronic acid. Solution-phase chemistries afforded the highest yields, and were used to synthesize seven complex biotinylated multi-boronic acid peptides.

[Rapid prototyping in planning reconstructive surgery of the head and neck. Review and evaluation of indications in clinical use]

PURPOSE

The aim was to define the indications for use of rapid prototyping models based on data of patients treated with this technique.

PATIENTS AND METHODS

Since 1987 our department has been developing methods of rapid prototyping in surgery planning. During the study, first the statistical and reproducible anatomical precision of rapid prototyping models was determined on pig skull measurements depending on CT parameters and method of rapid prototyping.

RESULTS

Measurements on stereolithography models and on selective laser sintered models confirmed an accuracy of +/-0.88 mm or 2.7% (maximum deviation: -3.0 mm to +3.2 mm) independently from CT parameters or method of rapid prototyping, respectively. With the same precision of models multilayer helical CT with a higher rate is the preferable method of data acquisition compared to conventional helical CT. From 1990 to 2002 in atotal of 122 patients, 127 rapid prototyping models were manufactured: in 112 patients stereolithography models, in 2 patients an additional stereolithography model, in 2 patients an additional selective laser sinter model, in 1 patient an additional milled model, and in 10 patients just a selective laser sinter model.

CONCLUSION

Reconstructive surgery, distraction osteogenesis including midface distraction, and dental implantology are proven to be the major indications for rapid prototyping as confirmed in a review of the literature. Surgery planning on rapid prototyping models should only be used in individual cases due to radiation dose and high costs. Routine use of this technique only seems to be indicated in skull reconstruction and distraction osteogenesis.

Evaluation der osteoinduktiven Potenz von gentechnisch modifizierten BMP-2-Varianten

BACKGROUND

The alteration of the N-terminal amino acid sequence of BMP-2 allows modification of heparin binding of the new protein. This leads to a change in the local retention time at the site of implantation. Mutants with increased (T3, T4) and with no binding (EHBMP-2) to heparin were assessed for their osteoinductivity in vivo and compared with the wild type BMP-2.

METHODS

Cylindrical collagenous carriers (diameter = 5 mm, height = 10) were loaded with different concentrations (0.25-4 micro g) of the proteins. Following intramuscular implantation into the hind legs, the bone formation was measured in radiographic follow-ups. After 28 days the newly formed bone was characterized histologically.

RESULTS

Elimination of the heparin binding leads to massive reduction in osteoinductivity. On the other hand, an increase in the heparin binding leads to enhancement in the osteoinductive properties, resulting in faster bone formation with a higher yield.

CONCLUSION

It could be shown for the first time that modifications of BMP-2 by gene technology can lead to proteins with enhanced binding to components of the extracellular matrix. The resulting prolonged retention time at the implantation site results in an increased osteoinductivity compared with the wild type.

Unterkieferrekonstruktion mit autologem Knochen und einem induktiven Implantat beim G�ttinger Minischwein

BACKGROUND

Direct mandibular reconstruction with an autologous bone transplant was compared with an osteoinductive implant following an extensive continuity resection of the lower jaw in Göttinger mini-pigs.

METHOD

In nine full-grown mini-pigs a one-sided continuity defect (5 cm) was created in the lower jaw. In four animals it was filled with a 50 x 25 x 15 mm(3) collagenous carrier enhanced by rhBMP-2 (400 micro g/cm(3) rhBMP-2). In two animals only the carrier was implanted as a control. Three animals received the resected autologous bone as a free transplant. Bone regeneration and consolidation of the defects was analyzed radiographically and histologically.

RESULTS

Following implantation of the osteoinductive implant, complete osseous consolidation of the continuity defect in the lower jaw was observed in all animals. The defects were completely filled with a biomechanically stable bone which showed signs of functional adaptation. The replantation of the orthotopic autologous bone did not lead to functional stability quickly enough. In the periphery only an incomplete bony bridge was formed which was interrupted by large pseudarthrosis. No consolidation of the defects was found in the control group (carrier alone).

CONCLUSION

Direct reconstruction of an extensive, biomechanically loaded defect with an osteoinductive implant proved to be the superior method. The osseous regeneration observed shows an immediate functional orientation. The necessity for extensive adaptive remodeling is thus minimized.

Die bimaxilläre Osteotomie mit und ohne Kondylenpositionierung—eine Langzeitstudie 1981–2002

PURPOSE

The introduction of the four-splint technique in our hospital in 1997 made possible the reproducible centric condyle positioning in bimaxillary osteotomies, while taking the auto rotation of the mandible into consideration and avoiding steps in the mandibular osteotomy line.

PATIENTS AND METHODS

From 1981 to 2002 a total of 622 patients underwent bimaxillary osteotomy surgery. During 1981-1997 a total of 395 patients (63.5%) underwent surgery without or only with centric condyle positioning in sagittal ramus osteotomy of the mandible. During 1997-2002 a total of 227 patients (36.5%) underwent surgery with continuous centric condyle positioning with the four-splint technique.

RESULTS

In patients with preoperative functional disorders, surgery with continuous centric condyle positioning resulted in statistically significant (p<0.05) improvement compared to those who underwent surgery without continuous centric condyle positioning.

CONCLUSION

The results confirm the indication for continuous centric condyle positioning in bimaxillary osteotomies.

[Effect of periosteum on induced bone formation by autolyzed, antigen-extracted, allogeneic bone. Determination of the extent of bone formation using quantitative computerized tomography]

Autolyzed, antigen-extracted, allogenic (AAA) bone is an osteoinductive preparation of completely demineralized bone matrix. It has been clinically applied for years. In an experimental study in rabbits, we evaluated the influence of cortical bone and periosteum on the amount of bone formation following augmentation with AAA bone. Two implants of standardized size were placed on the femoral bone of rabbits. A cell-excluding PTFE membrane was wrapped circularly around the femur as well as the anterior implant shielding the implant from the surrounding periosteum. The posterior implant was exposed directly to the periosteum while being shielded from the cortical bone by the membrane. Thus, two compartments were created selectively, preventing contact between the periosteum or cortical bone and the implants. For each compartment the area and volume of the induced new bone were evaluated by computerized radiograph analysis and quantitative CT (pQCT) scans. Implantation of AAA bone led to new bone formation in both compartments. Contact of the periosteum and the implant led to an almost four-fold increase in bone volume. Although bone formation showed interindividual variations, the difference of both compartments was highly significant using the Student's t-test for paired samples (P < 0.0001). The data show that periosteum is the primary source of new bone formation in augmentations with osteoinductive materials as it is rich in inducible progenitor cells and is well vascularized. In osseous augmentations with AAA bone, the periosteum should be preserved in order to achieve a close contact of the osteoinductive implant. Shielding from the periosteum, e.g., by cell-excluding membranes, leads to significantly less bone formation following implantation of AAA bone and should therefore be avoided.

[Effect of different factors on the bone forming properties of recombinant BMPs]

The extent of BMP-induced new bone formation is mainly determined by the number of mesenchymal target cells in the recipient bed as well as by the biological half-life of the BMP molecules within the tissue. While the number of inducible cells is determined by the age and vascularization of the tissue, the retention time of the BMP molecules can be influenced. One possibility is the coupling of BMPs to suitable carriers, which significantly increases the osteoinductive effect. The reason for this is the physical binding of BMPs to the carrier material, which delays the resorption of the proteins. Other factors are the composition of the carrier materials, their structural stability, and possible dislocations of carrier particles. The local tissue concentration of BMPs can also be increased by an enhanced binding of the proteins to the extracellular matrix. A BMP-2 mutant (BMP-2xa) was produced by the specific modification of the amino acid sequence using recombinant technologies. BMP-2xa induces heterotopic bone formation at significantly lower concentrations than natural BMP-2. Furthermore, BMP-2xa-induced bone tissue possesses a higher bone density.

[EHBMP-2. Initial BMP analog with osteoinductive properties]

For the first time a non natural BMP-variant (EHBMP-2) with osteoinductive properties was produced by expression in E. coli through specific mutation of the amino acid sequence. The substitution of 12 N-terminal amino acids by a nonsense sequence results in a neglectible affinity of EHBMP-2 to the extracellular matrix. In vitro EHBMP-2 induces dose-dependent cartilage formation in neonatal muscle tissue. Single intramuscular implantation in mice results in the formation of an ossicle with functional active bone marrow. The size of the ossicle depends on the amount of implanted EHBMP-2 and can significantly be increased by the combination with a collagen carrier. The largest bone formation is observed after injection of EHBMP-2 containing collagen suspensions. In rats a stronger osteoinductive activity can be achieved by coupling of EHBMP-2 to collagen discs than by coupling natural BMP-2 to the same collagen carrier. Critical size defects in rats' mandibular angels can be restored by the combination of granular collagenous bone matrix (ICBM) with EHBMP-2. Further investigations have to show whether the altered pharmacokinetics of EHBMP-2 has advantages regarding its therapeutical use and tissue-engineering.

[Comparative studies of sinus floor elevation with autologous or allogeneic bone tissue]

In 63 patients, 82 elevations of the maxillary sinus were performed. As augmentation, materials autografts from the iliac crest (combined with alveolar ridge augmentations in 16 sinus lifts) were transplanted in 39 cases and osteoinductive, allogeneic bone powder (AAA bone (autolyzed, antigen-extracted, allogeneic bone): n = 8, DFDBA (demineralized freeze-dried bone allograft) and/or Grafton (demineralized bone matrix gel): n = 35) were used in 43 cases. Some 4-6 months after implantation, osteoinductive, allogeneic (demineralized) bone implants showed radio-opaque areas as an equivalent of bone formation. Histological examinations revealed that osteoinductive implants were completely transformed into patients' own bone tissue. The average augmentation height after autograft transplantations was 14 (+/- 3) mm in comparison with 9 (+/- 3) mm after allograft implantations. Histologically as well as radiologically no differences of the bone quality could be determined between the two augmentation materials. Endoscopic controls showed, in both groups, nonirritated mucous membranes. On an average 2 endosseous implants (Bone Lock or ITI-screw implants) were inserted into the augmentated maxillary sinus floors in both groups. No osseointegration was achieved in 4 out of 67 dental implants when bone autografts were used and in 2 out of 74 dental implants of the allogeneic bone group. Patients with bone autografts suffered from postoperative complaints on an average of 19 (+/- 9) days (without consideration of 2 patients with postoperative complaints persisting for more than 90 days). The average postoperative complaints of recipients of allogeneic bone implants continued for 3 (+/- 5) days. The 13 patients who underwent an ambulant sinus lift procedure with allogeneic bone powder were already symptom-free several hours after the operation. Under critical consideration of all investigated parameters, osteoinductive bone implants are preferable to iliac bone autografts for maxillary sinus augmentations in those cases in which no additional alveolar ridge augmentation is required.

Inductive properties of recombinant human BMP-2 produced in a bacterial expression system

Recombinant human BMP-2, produced in E. coli, refolded and concentrated to a purity of more than 98%, has been demonstrated to be biologically active. In vitro, amounts of 0.4 microg BMP-2 or more induced new cartilage formation in 27 out of 47 samples of a neonatal muscle tissue assay, with chondroneogenesis occurring 14 days after a four-hour contact between BMP-2 and the muscle tissue. In vivo, BMP-2 was implanted in the thigh muscle of ICR mice for a period of three weeks. Amounts of 4 microg BMP-2 and more showed heterotopic bone formation in 15 out of 17 samples. When BMP-2 was combined with a collagen carrier, amounts of 0.4 microg protein or more induced heterotopic bone formation in 30 out of 33 samples four weeks after the implantation in the abdominal wall of Sprague-Dawley rats. The results show that the E. coli-derived BMP-2 was active in different assay systems in concentrations equal to those required with mammalian cell-expressed BMP-2. It could also be demonstrated that a single morphogen (BMP-2) is enough to initiate the differentiation process associated with bone induction. The presented bacterial expression system also offers the opportunity to produce large quantities of recombinant BMP-2 for clinical applications.

[Clinical application of osteoinductive implants in craniofacial surgery]

Autolyzed, antigen-extracted, allogeneic bone (AAA bone) is prepared from cortical bones of human organ donors. AAA bone possesses osteoinductive properties as it delivers BMPs from its bone matrix. Within a prospective study, 37 cranial defects were reconstructed using AAA bone implants over a period of more than 7 years. The patients were followed-up at standardized intervals. Roentgenographic assessments and bone scintigraphies revealed osseous integration and remodelling of the AAA bone implants. In one quarter of the cases re-entry was performed 10 to 18 months after the cranioplasty (removal of osteosynthesis material, recurrence of tumor). All nine AAA bone reconstructions showed bleeding surfaces and bony integrations. A bone biopsy was taken from the center of one of these AAA bone implants and this showed new bone formation originating from the surface of the implant. In one case an AAA bone implant was lost due to infection. This is noteworthy as in approximately one third of the cases the bone implants were in direct contact with the frontal sinus. The clinical results clearly emphasize the therapeutical benefit of AAA bone for cranioplasties. Large AAA bone chips from human skull bones facilitate the reconstruction of the skull's convexity, especially when sterolithography-based operation planning is performed.

[Biological activity of E. coli expressed BMP-4]

BMP-4 is physiologically present in low concentrations in human bone matrix. So far the protein has only been produced in small quantities by expression in mammalian cell cultures. In this study we investigated the biological activity of E. coli-expressed BMP-4. In vitro neonatal rat muscle tissue was incubated together with BMP-4 during 4 h, followed by an incubation period of 14 days on cellulose acetate membranes in BMP-free medium. The addition of 0.4 microgram BMP-4 induced cartilage formation in 1/8 samples while 4 micrograms BMP-4 showed chondroneogenesis in 2/10 samples. When the BMP-4 concentration was increased to 40 micrograms, new cartilage formation was seen in 5/7 samples. In vivo BMP-4 was implanted intramuscularly for 3 weeks in ICR mice. Amounts of 10 micrograms rhBMP-4 and more (up to 100 micrograms) constantly induced heterotopic ossicle formation. BMP-4 was also combined with a collagen carrier and implanted for 2 and 4 weeks in the abdominal muscle of SD rats. While 0.4 microgram BMP-4 showed no bone or cartilage formation, the amount of 40 micrograms BMP-4 showed new heterotopic cartilage formation, followed by endochondral ossification in almost all samples. The results prove that E. coli-expressed BMP-4 possesses the same inductive properties as mammalian-cell-expressed BMP-4.

Long-term maintenance of alveolar bone gain after implantation of autolyzed, antigen-extracted, allogenic bone in periodontal intraosseous defects

This randomized controlled trial assessed the long-term maintenance of alveolar bone gain after implantation of autolyzed, antigen-extracted, allogenic (AAA) bone. AAA bone is a demineralized freeze-dried bone allograft processed after previously described methods. In each of 14 patients, AAA bone was implanted into the intraosseous defect of 1 tooth (test); a second tooth with an intraosseous defect was treated by modified Widman flap surgery alone (control). All patients were offered supportive periodontal therapy at 3- to 6-month intervals following treatment. Clinical measurements were taken prior to surgery, 6 months, and 3 years following surgery. Of the 14 patients enrolled, 11 patients completed the 6-month and 8 patients the 3-year examination. In test teeth, bone gain was significantly greater compared to control teeth at 6 months (2.2+/-0.5 mm and 1.2+/-0.5 mm, respectively) and 3 years (2.3+/-0.7 mm and 1.1+/-0.8 mm, respectively) (P < 0.05). Also, more probing attachment was gained in test compared to control teeth at 3 years (2.0+/-0.7 mm and 0.8+/-0.5 mm, respectively; P < 0.05). At 3 years, Porphyromonas gingivalis was detected in 3 test and 2 control teeth by polymerase chain reaction, whereas no Actinobacillus actinomycetemcomitans was found. Due to the low detection frequency, there was no clear correlation between the maintenance of alveolar bone during supportive periodontal therapy and subgingival infection with P. gingivalis. The data indicated that alveolar bone gain after implantation of AAA bone may be maintained over a minimum of 3 years in patients receiving periodontal supportive therapy.

[Osteosynthesis after sagittal division of the mandible. Biomechanical stability of various methods in a pig mandibular model]

Forty years after the introduction of sagittal split osteotomy for transposition of the mandible according to Obwegeser, very different procedures for osteosynthesis are still discussed and practised. In a simple biomechanical model in the porcine mandible, five different methods for osteosynthesis using metallic screws (titanium, cobalt-chromium-molybdenum alloy) and one using a polymer screw (polylactic acid-copolymer blend), as well as the use of miniplates, were studied with regard to the stability of the compound. The Kruskal-Wallis H-test (variance analysis by ranks) showed statistically highly significant differences (P = 0.00017) regarding maximum stability. Osteosynthesis by miniplates was very stable with regard to the maximum load (Fmax = 234 N +/- 47), but not so in terms of three-dimensional stability of the osteosynthesis itself. The highest stability of osteosynthesis with screws only (Fmax = 183 N +/- 65) was found for a 2.7-mm titanium screw in triangular geometry. The use of 2.7-mm cobalt-chromium-molybdenum screws (Fmax = 173 N +/- 42) and 3.5-mm titanium screws (Fmax = 160 N +/- 76) did not make an statistical difference (P = 0.37). The mechanical values of 2.0-mm titanium screws in linear (Fmax = 113 N +/- 37) or triangular (Fmax = 136 N +/- 62) geometry and of 3.5-mm polylactic acid-copolymer blend screws (Fmax = 121 N +/- 33) did not differ statistically from each other (P = 0.75) but they did from the previous group (P = 0.019). In consideration of the low biting forces following sagittal split osteotomy, all tested procedures of osteosynthesis meet the mechanical requirements for clinical practice.

[Interventions for improving the facial profile with osteoinductive bone implants]

Osteoinductive bone allografts (autolyzed, antigen-extracted, allogeneic bone; AAA bone) were implanted in 207 cases. The patients had plastic surgery procedures to improve their profiles and were followed up for a maximum of 72 months. Twenty-two patients had an asymmetric mandible corrected with AAA bone chips. In 14 cases AAA bone implants were used for genioplasties. Forehead defects were reconstructed in 20 patients using AAA bone. Hypoplasia of the midface was corrected in 88 cases by augmentations with AAA bone chips or powder. A total of 63 patients underwent rhinoplasties in which AAA bone chips were used to shape or erect the dorsum nasi. Patient follow-up and reoperations to remove the osteosynthesis material revealed that the AAA bone implants were remodeled in the patients' own bone within several months. Less than 3% of the AAA bone implants were lost due to local infections. Except for rhinoplasties, secondary resorption of the bone allografts was extremely low. However, in cases in which strong tension resulted from scar formation or from lack of soft tissue, considerable resorption was observed, especially when AAA bone was implanted in the nose (25% of the rhinoplasties). On the other hand, this biodynamic behavior protected the implants from soft tissue perforation. In summary, AAA bone implants represent a convenient alternative to bone autografts in recipient beds with strong regenerative capacity. Since they are remodeled into the patient's bone none of the late complications found with alloplastic implants need to be expected.

[Therapeutic concept in comminuted and defect fractures of the mandible]

Immediate live-saving emergency treatment of patients with heavily communited and partially defective mandibles by airway intubation, control of haemorhage and primary treatment of wounds necessarily must be followed by a staged concept of treatment for the functional and aesthetic rehabilitation of hard and soft tissue in order to enable the patient to survive not only biologically but also socially. Out of 384 patients with surgically treated mandibular fractures, 120 had multiple fractures, 24 heavily comminuted fractures and 6 sustained vast defects. All multiple and communited fractures could be treated successfully by an intraoral approach using function-orientated miniplate-osteosynthesis and in 30 cases functionally stable plates. In patients having sustained vast avulsions of soft and hard tissue, immediate emergency-revascularisation was well to the fore. In cases of tissue destruction, primarily the position of the jaw stumps was secured by plates and reconstruction was done in the early secondary stage using composed microvascularly transferred scapular flaps.

Stereolithography in oral and maxillofacial operation planning

Stereolithography (STL) is a method of organ-model-production based on computed tomography scans which enables the representation of complex 3-dimensional anatomical structures. Surfaces and internal structures of organs can be produced by polymerization of UV-sensitive liquid resin using a laserbeam. In oral and maxillofacial surgery this technique is advantageous for reconstruction of severe skull defects because a more accurate preoperative planning is possible. Using recently developed software we are able to reconstruct unilateral bony defects by virtual mirror imaging of the contralateral side and production of a STL mirror model as well as the reconstruction of non-mirrorable defects by superposition. Advantages of STL are the representation of complex anatomical structures, high precision and accuracy, and the option to sterilize the models for intraoperative use. More accurate planning using this method improves postoperative results, decreases risks and shortens treatment time.

Poly(L-lactide): a long-term degradation study in vivo. Part III. Analytical characterization

Three poly(L-lactides) with different molecular weights were synthesized as solid blocks from the melt. Two batches were ground and small specimens were produced by injection moulding. The third block was processed by machining, yielding crystalline parts. All were implanted as small rods into the dorsal muscle of rats. The implants were recovered, weight loss was determined, and the samples analysed. The samples degraded very fast, reaching the same molecular weight level after 20 wk, then degraded simultaneously. Analysis showed differences depending on the solid state of the polymer. The differences in the degradation behaviour of the amorphous and crystalline samples can be explained by assuming a simple hydrolysis as the main degradation mechanism, affecting the whole polymer, if in an amorphous state, but only the amorphous domains in a crystalline polymer.