3D Printing-Enabled Nanoparticle Alignment: A Review of Mechanisms and Applications

3D printing (additive manufacturing (AM)) has enormous potential for rapid tooling and mass production due to its design flexibility and significant reduction of the timeline from design to manufacturing. The current state-of-the-art in 3D printing focuses on material manufacturability and engineering applications. However, there still exists the bottleneck of low printing resolution and processing rates, especially when nanomaterials need tailorable orders at different scales. An interesting phenomenon is the preferential alignment of nanoparticles that enhance material properties. Therefore, this review emphasizes the landscape of nanoparticle alignment in the context of 3D printing. Herein, a brief overview of 3D printing is provided, followed by a comprehensive summary of the 3D printing-enabled nanoparticle alignment in well-established and in-house customized 3D printing mechanisms that can lead to selective deposition and preferential orientation of nanoparticles. Subsequently, it is listed that typical applications that utilized the properties of ordered nanoparticles (e.g., structural composites, heat conductors, chemo-resistive sensors, engineered surfaces, tissue scaffolds, and actuators based on structural and functional property improvement). This review's emphasis is on the particle alignment methodology and the performance of composites incorporating aligned nanoparticles. In the end, significant limitations of current 3D printing techniques are identified together with future perspectives.

Synthesis, characterization and application of biodegradable polymer grafted novel bioprosthetic tissue

Animal tissue has an extended history of clinical use in applications like heart valve bioprosthesis devices, cardiovascular surgical applications etc. but often does not last long after implantation in the body due to rapid unwanted degradation. The goal of this work is to develop novel composite biomaterials by grafting biological tissue with synthetic, biodegradable polymers. In the current research phase, porcine submucosa, ureter and bovine pericardial tissue are grafted with poly DL-lactide (PLA), poly glycolide (PGA) and poly DL-lactide glycolide (PLGA) copolymers. The grafted and control tissues are characterized by FTIR and SEM. The biodegradability of the tissue-graft composite materials is determined by pepsin and collagenase digestion assays, showing it can be tailored by varying the grafted polymer type and amount. The grafted tissues can be tuned for a particular clinical or tissue engineering applications including drug delivery with little or no burst release and sustained/controlled delivery.

Oncolytic virus delivery: from nano-pharmacodynamics to enhanced oncolytic effect

With the advancement of a growing number of oncolytic viruses (OVs) to clinical development, drug delivery is becoming an important barrier to overcome for optimal therapeutic benefits. Host immunity, tumor microenvironment and abnormal vascularity contribute to inefficient vector delivery. A number of novel approaches for enhanced OV delivery are under evaluation, including use of nanoparticles, immunomodulatory agents and complex viral–particle ligands along with manipulations of the tumor microenvironment. This field of OV delivery has quickly evolved to bioengineering of complex nanoparticles that could be deposited within the tumor using minimal invasive image-guided delivery. Some of the strategies include ultrasound (US)-mediated cavitation-enhanced extravasation, magnetic viral complexes delivery, image-guided infusions with focused US and targeting photodynamic virotherapy. In addition, strategies that modulate tumor microenvironment to decrease extracellular matrix deposition and increase viral propagation are being used to improve tumor penetration by OVs. Some involve modification of the viral genome to enhance their tumoral penetration potential. Here, we highlight the barriers to oncolytic viral delivery, and discuss the challenges to improving it and the perspectives of establishing new modes of active delivery to achieve enhanced oncolytic effects.

PNIPAAm-based biohybrid injectable hydrogel for cardiac tissue engineering

Injectable biomaterials offer a non-invasive approach to deliver cells into the myocardial infarct region to maintain a high level of cell retention and viability and initiate the regeneration process. However, previously developed injectable matrices often suffer from low bioactivity or poor mechanical properties. To address this need, we introduced a biohybrid temperature-responsive poly(N-isopropylacrylamide) PNIPAAm-Gelatin-based injectable hydrogel with excellent bioactivity as well as mechanical robustness for cardiac tissue engineering. A unique feature of our work was that we performed extensive in vitro biological analyses to assess the functionalities of cardiomyocytes (CMs) alone and in co-culture with cardiac fibroblasts (CFs) (2:1 ratio) within the hydrogel matrix. The synthesized hydrogel exhibited viscoelastic behavior (storage modulus: 1260 Pa) and necessary water content (75%) to properly accommodate the cardiac cells. The encapsulated cells demonstrated a high level of cell survival (90% for co-culture condition, day 7) and spreading throughout the hydrogel matrix in both culture conditions. A dense network of stained F-actin fibers (∼ 6 × 10(4) μm(2) area coverage, co-culture condition) illustrated the formation of an intact and three dimensional (3D) cell-embedded matrix. Furthermore, immunostaining and gene expression analyses revealed mature phenotypic characteristics of cardiac cells. Notably, the co-culture group exhibited superior structural organization and cell-cell coupling, as well as beating behavior (average ∼ 45 beats per min, co-culture condition, day 7). The outcome of this study is envisioned to open a new avenue for extensive in vitro characterization of injectable matrices embedded with 3D mono- and co-culture of cardiac cells prior to in vivo experiments.

STATEMENT OF SIGNIFICANCE

In this work, we synthesized a new class of biohybrid temperature-responsive poly(N-isopropylacrylamide) PNIPAAm-Gelatin-based injectable hydrogel with suitable bioactivity and mechanical properties for cardiac tissue engineering. A significant aspect of our work was that we performed extensive in vitro biological analyses to assess the functionality of cardiomyocytes alone and in co-culture with cardiac fibroblasts encapsulated within the 3D hydrogel matrix.

Local gentamicin delivery from resorbable viscous hydrogels is therapeutically effective

BACKGROUND

Local delivery can achieve the high antimicrobial concentrations necessary to kill biofilm-related microbes. Degradation times for resorbable carriers are too long. Hydrogels (gels of hydrophilic polymer in water) can degrade faster but release antimicrobials too quickly. We previously developed hydrogels based on the copolymer poly(N-isopropylacrylamide-co-dimethyl-γ-butyrolactone acrylate-co-Jeffamine® M-1000 acrylamide) (PNDJ) with delivery times of several days with complete degradation in less than 6 weeks.

QUESTIONS/PURPOSES

We asked: (1) What is the elution profile of gentamicin from PNDJ hydrogels? (2) Is gentamicin released from gentamicin-loaded PNDJ (G-PNDJ) hydrogel effective for treatment of orthopaedic infection? (3) Does local gentamicin delivery from G-PNDJ hydrogel cause renal dysfunction?

METHODS

(1) Two formulations of G-PNDJ, lower dose (1.61 wt%) and higher dose (3.14 wt%), five samples each, were eluted in buffered saline under infinite sink conditions. (2) Infections were induced in 16 New Zealand White rabbits by inserting a Kirschner wire in a devascularized radius segment and inoculating with 7.5×10(6) colony-forming units Staphylococcus aureus. At 3 weeks, débridement was performed and a new Kirschner wire was placed in the dead space. Treatment was randomized to higher-dose G-PNDJ or no hydrogel. No systemic antimicrobials were used. Positive culture and acute inflammation on histology were used to determine the presence of infection 4 weeks postdébridement. (3) 3.14 wt% G-PNDJ, 0.75, 1.5, or 3.0 mL, was injected subcutaneously in nine Sprague-Dawley rats, three of each dose. Serum gentamicin, blood urea nitrogen, and creatinine were measured on Days 1, 3, 7, 14, and 28.

RESULTS

(1) Gentamicin release was sustained over 7 days with the higher-dose formulation release profile similar to release from high-dose antimicrobial-loaded bone cement. (2) Four weeks postdébridement, infection was present in eight of eight no-hydrogel rabbits but zero of eight rabbits treated with G-PNDJ hydrogel (p<0.001). (3) Blood urea nitrogen and creatinine were transiently elevated (p<0.05) only for the two of three rats receiving the 3.0-mL dose on Days 3 and 7.

CONCLUSIONS

Gentamicin is delivered from PNDJ hydrogel with low systemic exposure and decreased treatment failure for orthopaedic infection. Transient renal dysfunction occurs at high doses. Biodistribution and toxicity testing are needed for G-PNDJ to be clinically usable.

CLINICAL RELEVANCE

Resorbable viscous hydrogels for local antimicrobial delivery may improve outcomes for one-stage management of implant infections when uncemented reconstructions are performed.

Strength of antimicrobial bone cement decreases with increased poragen fraction

BACKGROUND

Adding soluble particulate poragens to antimicrobial-loaded bone cement increases the permeability of the bone cement and increases the antimicrobial release, but the mechanical effect of adding poragens is not well known.

QUESTIONS/PURPOSES

We therefore asked the following questions: (1) Does the poragen fraction in antimicrobial-loaded bone cement affect its antimicrobial release? (2) Does poragen fraction in antimicrobial-loaded bone cement affect its compressive strength; and (3) Does the effect on compressive strength change over time in elution?

METHODS

Antimicrobial-loaded bone cement made in the proportions of 40 g polymer powder, 20 mL monomer liquid, 1 g tobramycin powder and one of six different doses of poragen powder (0, 1, 2, 4, 8, or 16 g of particulate xylitol per batch) was formed into standardized test cylinders and eluted for 30 days. We determined the cumulative recovered tobramycin and the change in compressive strength over 30 days of elution.

RESULTS

Antimicrobial release progressively increased with increasing poragen fraction. Compressive strength progressively decreased with increasing poragen fraction and with increasing time in elution. Poragen fractions greater than 2 g per batch caused the compressive strength to decrease below 70 MPa over 30 days of elution.

CLINICAL RELEVANCE

The use of poragens can increase elution of antimicrobials from antimicrobial-loaded bone cement. However, for implant fixation, to avoid deleterious reduction of compressive strength, the amount of poragen that can be added in addition to 1 g of antimicrobial powder may be limited to 2 g per batch.

Corticosterone modulation of reproductive and immune systems trade-offs in female tree lizards: long-term corticosterone manipulations viainjectable gelling material

Physiological trade-offs arise because multiple processes compete for the same limiting resources. While competition for resources has been demonstrated between reproduction and immune function, the regulation of this competition remains unclear. Corticosterone (CORT) is a likely mediator due to its dual role in mobilizing energy stores throughout the body and regulating physiological responses to stressors. We manipulated CORT concentrations and resources in pre-reproductive and reproductive female tree lizards(Urosaurus ornatus) to test the hypothesis that CORT regulates the distribution of limiting resources between the reproductive and immune systems. To manipulate circulating concentrations of CORT we utilized a novel method of hormone implantation, in which a polymeric compound is mixed with hormone and injected in liquid form into the animal. After injection, the liquid quickly gels in situ forming a slow release hormone implant. This method of hormone delivery eliminated the need for substantial wounds to the animal or repeated handling required by other methods. In this study, the hormone-treated animals had plasma CORT concentrations comparable to high physiological concentrations. We found that CORT treatment suppressed immune function, but only when animals were energetically compromised. We assessed immune function by measuring the healing rate of a cutaneous biopsy. Healing was suppressed in all CORT-treated reproductive animals and in all CORT-treated animals (pre-reproductive and reproductive) undergoing food restriction, but CORT had no effect in ad libitum non-reproductive females. The context-dependent action of CORT renders its response adjustable to changing environmental conditions and may allow for the suppression of specific functions depending on resource availability.

Islet encapsulation: strategies to enhance islet cell functions

Diabetes is one of the most prevalent, costly, and debilitating diseases in the world. Although traditional insulin therapy has alleviated the short-term effects, long-term complications are ubiquitous and harmful. For these reasons, alternative treatment options are being developed. This review investigates one appealing area: cell replacement using encapsulated islets. Encapsulation materials, encapsulation methods, and cell sources are presented and discussed. In addition, the major factors that currently limit cell viability and functionality are reviewed, and strategies to overcome these limitations are examined. This review is designed to introduce the reader to cell replacement therapy and cell and tissue encapsulation, especially as it applies to diabetes.

Control of gel swelling and phase separation of weakly charged thermoreversible gels by salt addition

Doping of thermoreversible polymer gels with charged monomers provides a way to control phase separation and gelation conditions by coupling the properties of the gel with a tunable ionic environment. We analyze the dependence of the gelation and phase separation conditions on the amount of salt present using a mean field model of weakly charged associative polymers. The ions and co-ions present are explicitly considered at the mean field level, and we determine their concentrations in the different equilibrium phases when the system undergoes phase separation. For weak polymer charge, the entropic contributions of the ions to the free energy of the system play a central role in the determination of the location of phase equilibrium. In the simplest case, when the associative interaction responsible for gel formation is independent of the electrostatic interaction, the addition of salt changes the polymer equilibrium concentrations and indirectly changes the measurable swelling of the gel. We construct phase diagrams of these systems showing the location of the coexistence region, the gel-sol boundary and the location of the tie-lines. We determine the swelling of the gel within the co-existence region. Our main result is that the description of the effect of the salt on the properties of the weakly charged gel can be described through an extra contribution to the effective immiscibility parameter χ proportional to the square of the doping degree f(2) and to the inverse square of the added salt concentration s(-2).

Gel strength and solution viscosity of temperature-sensitive, in-situ-gelling polymers for endovascular embolization

The goal of this work was to investigate the relationship of the gel strength and stiffness (at 37 degrees C) to solution viscosity (at 25 degrees C) in poly(N-isopropylacrylamide-co-acrylic acid) solutions with regard to acid content, molecular weight and solution concentration. It was hypothesized that the gel strength could be maximized while minimizing the increase in solution viscosity. If so, there would be motivation to investigate these materials for arteriovenous malformation embolization. The co-polymers were synthesized with 0-2 mol% content of acrylic acid (AAc) in benzene, dioxane, THF, 50:50 benzene/dioxane, or 50:50 dioxane/THF to obtain polymers of different molecular weight. The polymers were characterized for molecular weight by GPC/light scattering, for acrylic acid content by acid titration, for lower critical solution temperature by differential scanning calorimetry, and for solution viscosity (at 25 degrees C) and gel strength (at 37 degrees C) by rheometry. Solutions of lower-molecular-weight polymers were shown to have lower viscosities while possessing higher strengths as gels than the highest manageable concentrations of higher-molecular-weight polymers. This work demonstrates that the mechanical properties of poly(N-isopropylacrylamide-co-acrylic acid) can be increased while minimizing the increase in solution viscosity.

In situ-gelling, erodible N-isopropylacrylamide copolymers

Copolymers of N-isopropylacrylamide, 2-hydroxyethyl methacryl lactate [(HEMA)-lactate] and acrylic acid (AAc) were prepared with varying mole ratios of monomers to develop copolymers with gelation properties above a certain concentration for a bioerodible, in-situ gelling material. The copolymers formed gels in situ under physiological condition. The gelation temperature of the copolymers decreased as the HEMA-lactate content of the copolymers increased due to the hydrophobicity of HEMA-lactate, and increased as the AAc content increased due to the hydrophilicity of AAc. The gels redissolve at 37 degrees C as their LCSTs increase above 37 degrees C due to the hydrolysis of the HEMA-lactate pendant groups.

Mechanical Optimization of an Arteriovenous Malformation Embolization Material: A Predictive Model Analysis

Arteriovenous malformations (AVMs) pose a constant danger of hemorrhages, seizures, and headaches to patients; they also disrupt oxygen-rich blood flow entering capillaries of the brain. We have utilized a linear model to mechanically characterize and optimize a water-borne, reverse emulsion, self-reactive, in situ cross-linking material, which we propose clinical use as an embolization material. The material is formed by cross-linking various acrylate and thiol multifunctional precursors with NaOH supplemented PBS. We compared theoretical elastic modulus values to modulus values observed during compression testing to determine the cross-linking efficiency of the material. Empirically determined elastic moduli for various material compositions ranged from 0.76 to 2.26 MPa, with corresponding cross-link efficiencies averaging 55+/-4%. We predict a reduction in theoretical circumferential stress exerted on AVM vasculature from 4933 to 10.9 Pa after embolization with the optimal material configuration. Theoretical risk of AVM rupture, as defined by Hademenos et al., was reduced below 1.0% for extreme variations of vessel modulus, thickness, and blood pressure after embolization with the optimized material. We will be using this material configuration to embolize swine rete mirabile AVM models and further assess the clinical viability of this potential embolization material.

Water-borne, in situ crosslinked biomaterials from phase-segregated precursors

A novel process for the preparation of water-borne biomaterials for hard tissue repair from injectable precursors is described, where the precursors form crosslinked materials in situ under physiological conditions. The precursors react by means of a Michael-type addition reaction that makes use of addition donors such as pentaerythritol tetrakis 3'-mercaptopropionate (QT) and addition acceptors such as poly(ethylene glycol) diacrylate 570 MW (PEGDA), pentaerythritol triacrylate (TA), and poly(propylene glycol) diacrylate 900 MW (PPODA). These crosslinked materials (at 75 wt% solid), prepared from water dispersions or reverse emulsions, showed ultimate strengths in compression of 1.8 +/- 0.2 and 6.7 +/- 0.5 MPa and ultimate deformations of 35 +/- 2+/- and 37 +/- 2%, respectively. Scanning electron microscopy (SEM) shows that the morphology of the precursors templated the morphology of the final materials. The current study indicates that it is possible to obtain injectable high-modulus materials that have appropriate mechanical properties and gelation kinetics for tissue augmentation and stabilization applications such as mechanical stabilization of the intervertebral disc annulus.

Thermoreversible copolymer gels for extracellular matrix

To improve the properties of a reversible synthetic extracellular matrix based on a thermally reversible polymer, copolymers of N-isopropylacrylamide and acrylic acid were prepared in benzene with varying contents of acrylic acid (0 to 3%) and the thermal properties were evaluated. The poly(N-isopropylacrylamide) and copolymers made with acrylic acid had molecular weights from 0.8 to 1.7 x10(6) D. Differential scanning calorimetry (DSC) showed the high-molecular-weight acrylic acid copolymers had similar onset temperatures to the homopolymers, but the peak width was considerably increased with increasing acrylic acid content. DSC and cloud point measurements showed that polymers with 0 to 3% acrylic acid exhibit a lower critical solution temperature (LCST) transition between 30 degrees and 37 degrees C. In swelling studies, the homopolymer showed significant syneresis at temperatures above 31 degrees C. Copolymers with 1 and 1.5% showed syneresis beginning at 32 degrees and 37 degrees C, respectively. At 37 degrees C the copolymers with 1.5-3% acrylic acid showed little or no syneresis. Due to the high water content and a transition near physiologic conditions (below 37 degrees C), the polymers with 1.5-2.0% acrylic acid exhibited properties that would be useful in the development of a refillable synthetic extracellular matrix. Such a matrix could be applied to several cell types, including islets of Langerhans, for a biohybrid artificial pancreas.

Exposure to suggestion and creation of false auditory memories

The experiment investigated the possibility of creating false auditory memory through exposure to suggestion. Research by Loftus and others has indicated that, through suggestion, false memories can be created. Participants viewed a short film and were given a 9-item questionnaire. Eight questions were used as filler while one question asked respondents to recall a phrase one character had said. Although the character actually said nothing, 23 of 30 respondents recalled having heard him speak and specifically recalled his words. This statistically significant result shows that auditory memories can also be created.

Insulin release from islets of Langerhans entrapped in a poly(N-isopropylacrylamide-co-acrylic acid) polymer gel

A copolymer of N-isopropylacrylamide (98 mol% in feed) and acrylic acid, poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAAm-co-AAc)), was prepared by free radical polymerization for development of a thermally reversible polymer to entrap islets of Langerhans for a refillable biohybrid artificial pancreas. A 5 wt% solution of the polymer in Hanks' balanced salt solution forms a gel at 37 degrees C that exhibits no syneresis. Diffusion of fluorescein isothiocyanate (FITC) dextrans having molecular weights of 4400 and 70000 were used to evaluate mass transport in the gel at 37 degrees C. Insulin secretion from islets in the polymer gel was also investigated in both static and dynamic systems. The polymer gel exhibited excellent diffusion of FITC dextran 4400 and FITC dextran 70000 with diffusion ratios, D/D0 (ratio of diffusion in the gel to diffusion in water), of 0.20+/-0.04 and 0.35+/-0.17, respectively. Human islets entrapped in the polymer gel showed prolonged insulin secretion in response to basal (5.5 mM) glucose concentration compared to free human islets. Rat islets showed prolonged insulin secretion in response to high (16.5 mM) glucose concentrations compared to free rat islets. Rat islets in the polymer gel maintained insulin secretion in response to the higher glucose concentration for over 26 days. Rat islets entrapped by the polymer also released higher quantities of insulin more rapidly in response to changes in concentrations of glucose and other stimulants than rat islets entrapped in an alginate control. These results suggest that this material would provide adequate diffusion for rapid insulin release in an application as a synthetic extracellular matrix for a biohybrid artificial pancreas.

Extracellular matrix for a rechargeable cell delivery system

Above a critical concentration, aqueous polymer solutions of N-isopropylacrylamide copolymers with small amounts of acrylic acid, synthesized in benzene by radical polymerization, exhibited four distinct phases as the temperature increased; clear solution, opaque solution, gel and shrunken gel. The transition between the opaque solution phase and the gel phase was in the range of 30-34 degrees C and was reversible without syneresis and noticeable hysteresis under the experimental conditions used in this study. Islets of Langerhans, isolated from Sprague-Dawley rat pancreata and entrapped in the gel matrix, remained viable, with no significant decrease in insulin secretion function in vitro for one month. When islets were encapsulated with the gel matrix in hollow fibers [molecular weight cut-off (MWCO)= approximately 400000] and were exposed to dynamic changes in glucose and theophylline concentrations, their insulin secretion patterns demonstrated a smaller lag time and higher amplitude in insulin release than islets entrapped in a conventional alginate matrix under the same experimental conditions. From these two observations, i.e. gel reversibility and islet functionality in the matrix observed in in vitro experiments, the N-isopropylacrylamide copolymers with acrylic acid synthesized in this study are optimum candidates for the extracellular matrix in a diffusion chamber-type cell delivery system in order to recharge the entrapped cells when cell functionality in the system decreases.

The vexed question of authorship: views of researchers in a British medical faculty

OBJECTIVE

To assess knowledge, views, and behaviour of researchers on criteria for authorship and causes and control of gift authorship.

DESIGN

Interview survey of stratified sample of researchers.

SETTING

University medical faculty.

SUBJECTS

66 staff (94% response rate) comprising several levels of university academic and research appointments.

MAIN OUTCOME MEASURES

Awareness and use of criteria for authorship, views on which contributions to research merit authorship, perceptions about gift authorship and strategies for reducing it, and experiences of authorship problems.

RESULTS

50 (76%) respondents supported criteria for authorship, but few knew about or used available criteria. Of the five people who could specify all three criteria of the International Committee of Medical Journal Editors, only one knew that all criteria had to be met. Forty one respondents (62%) disagreed with this stipulation. A range of practical and academic contributions were seen as sufficient for authorship. Gift authorship was perceived as common, promoted by pressure to publish, to motivate research teams, and to maintain working relationships. A signed statement justifying authorship and a published statement of the contribution of each author were perceived as practical ways of tackling gift authorship. Most researchers had experienced problems with authorship, most commonly the perception that authorship had been deserved but not awarded (49%).

CONCLUSION

There seems to be a gap between editors' criteria for authorship and researchers' practice. Lack of awareness of criteria is only a partial explanation. Researchers give more weight than editors to practical research contributions. Future criteria should be agreed by researchers and not be imposed by editors.

Ethics, funding and alcohol research

The field of alcohol research is a multidisciplinary area of inquiry. Moreover the debate about alcohol issues is highly politicized, involving not only researchers but also 'advocates' and those with strong ideological orientations or who represent powerful vested interests. Researchers may easily be caught in the crossfire in polemics involving such people. From time to time ethical malpractice is evident, yet there are often neither clear guidelines to delineate which behaviours are unacceptable nor how ethical violations are to be handled. This paper considers a number of key issues currently topical in the field. These are specifically concerned with the relationships between funders or sponsors and policy makers and researchers. Such issues include the ownership of data, sponsor control and the divergent cultures and outlooks of researchers and sponsors/funders. It is concluded that the field of alcohol research requires a code of ethics to regulate the relationship between researchers and funders. This should provide protection for subjects, patients, clients, researchers and those who pay for research. Some tentative suggestions are put forward for discussion.

Intestinal pseudo-obstruction related to using verapamil

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Complications in surgical patients. A comparison of methods for identifying occurrence

Because reporting of complications by physicians is not reliable, monitoring of the hospital course of surgical patients by nurses can improve effectiveness of identifying complications. Monitoring the course of only those patients who remain in the hospital more than four postoperative days will disclose 90 per cent of complications expected in all patients undergoing operation. Twenty hours per week of a nurse's time is sufficient to monitor 1,300 such patients annually. Identification of patients with large hospital bills will include most patients with complicated hospital courses but does not discriminate them from the large number of uncomplicated courses which also generate large hospital charges.